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Preview: Advanced Materials for Optics and Electronics

Advanced Functional Materials

Wiley Online Library : Advanced Functional Materials

Published: 2018-02-01T00:00:00-05:00


Evidence that Crystal Facet Orientation Dictates Oxygen Evolution Intermediates on Rutile Manganese Oxide


Elucidating the mechanism that differentiates the oxygen-evolving center of photosystem II with its inorganic counterpart is crucial to develop efficient catalysts for the oxygen evolution reaction (OER). Previous studies have suggested that the larger overpotential for MnO2 catalysts under neutral conditions may result from the instability of the Mn3+ intermediate to charge disproportionation. Here, by monitoring the surface intermediates of electrochemical OER on rutile MnO2 with different facet orientations, a correlation between the stability of the intermediate species and crystal facets is confirmed explicitly for the first time. The coverage of the Mn3+ intermediate is found to be 11-fold higher on the metastable (101) surfaces compared to (110) surfaces, leading to the superior OER activity of (101) surfaces. The difference in OER activity may result from the difference in surface electronic states of Mn3+, where interlayer charge comproportionation of Mn2+ and Mn4+ to generate two Mn3+ species is favored on (101) facets. Considering the fact that the OER enzyme accommodates Mn3+ stably during the Kok cycle, the enhanced OER activity of the rutile MnO2 catalyst with a metastable surface highlights the importance of mimicking not only the crystal structure but also the electronic structure of the targeted natural enzyme. The oxygen evolution activity of MnO2 with different facet orientations is studied to gain insight into the role of Mn3+ and allow for the rational design of functional analogs of the biological oxygen evolution center. (101) surfaces display higher activity compared to (110) surfaces despite having the same bulk crystal structure, due to the increased stabilization of Mn3+ on (101).

Tuning the Electronic and Photonic Properties of Monolayer MoS2 via In Situ Rhenium Substitutional Doping


Doping is a fundamental requirement for tuning and improving the properties of conventional semiconductors. Recent doping studies including niobium (Nb) doping of molybdenum disulfide (MoS2) and tungsten (W) doping of molybdenum diselenide (MoSe2) have suggested that substitutional doping may provide an efficient route to tune the doping type and suppress deep trap levels of 2D materials. To date, the impact of the doping on the structural, electronic, and photonic properties of in situ-doped monolayers remains unanswered due to challenges including strong film substrate charge transfer, and difficulty achieving doping concentrations greater than 0.3 at%. Here, in situ rhenium (Re) doping of synthetic monolayer MoS2 with ≈1 at% Re is demonstrated. To limit substrate film charge transfer, r-plane sapphire is used. Electronic measurements demonstrate that 1 at% Re doping achieves nearly degenerate n-type doping, which agrees with density functional theory calculations. Moreover, low-temperature photoluminescence indicates a significant quench of the defect-bound emission when Re is introduced, which is attributed to the MoO bond and sulfur vacancies passivation and reduction in gap states due to the presence of Re. The work presented here demonstrates that Re doping of MoS2 is a promising route toward electronic and photonic engineering of 2D materials. This work demonstrates in situ rhenium (Re) doping of synthetic monolayer MoS2 with ≈1 at% Re on r-plane sapphire. Electronic measurements elucidate that 1 at% Re doping achieves nearly degenerate n-type doping, which agrees with density functional theory calculations. Low-temperature photoluminescence measurements reveal suppression of defect emission induced by Re doping, resulting from the passivation of defects due to the presence of Re.

Highly In-Plane Optical and Electrical Anisotropy of 2D Germanium Arsenide


Anisotropic 2D materials exhibit unique optical, electrical, and thermoelectric properties that open up possibilities for diverse angle-dependent devices. However, the explored anisotropic 2D materials are very limited and the methods to identify the crystal orientations and to study the in-plane anisotropy are in the initial stage. Here azimuth-dependent reflectance difference microscopy (ADRDM), angle-resolved Raman spectra, and electrical transport measurements are used to systematically characterize the influence of the anisotropic structure on in-plane optical and electrical anisotropy of 2D GeAs, a novel group IV–V semiconductor. It is proved that ADRDM offers a way to quickly identify the crystal orientations and also to directly characterize the in-plane optical anisotropy of layered GeAs. The anisotropic electrical transport behavior of few-layer GeAs field-effect transistors is further measured and the anisotropic ratio of the mobility is as high as 4.6, which is higher than the other 2D anisotropic materials such as black phosphorus. The dependence of the Raman intensity anisotropy on the sample thickness, excitation wavelength, and polarization configuration is investigated both experimentally and theoretically. These data will be useful for designing new high-performance devices and the results suggest a general methodology for characterizing the in-plane anisotropy of low-symmetry 2D materials. Here the in-plane anisotropic optical and electrical properties of low-symmetry 2D layered GeAs are reported by combining the polarized Raman spectra, azimuth-dependent reflectance difference microscopy, and angle-resolved electrical transport measurements with related theoretical calculations.

A General Metal-Organic Framework (MOF)-Derived Selenidation Strategy for In Situ Carbon-Encapsulated Metal Selenides as High-Rate Anodes for Na-Ion Batteries


On account of increasing demand for energy storage devices, sodium-ion batteries (SIBs) with abundant reserve, low cost, and similar electrochemical properties have the potential to partly replace the commercial lithium-ion batteries. In this study, a facile metal-organic framework (MOF)-derived selenidation strategy to synthesize in situ carbon-encapsulated selenides as superior anode for SIBs is rationally designed. These selenides with particular micro- and nanostructured features deliver ultrastable cycling performance at high charge–discharge rate and demonstrate ultraexcellent rate capability. For example, the uniform peapod-like Fe7Se8@C nanorods represent a high specific capacity of 218 mAh g−1 after 500 cycles at 3 A g−1 and the porous NiSe@C spheres display a high specific capacity of 160 mAh g−1 after 2000 cycles at 3 A g−1. The current simple MOF-derived method could be a promising strategy for boosting the development of new functional inorganic materials for energy storage, catalysis, and sensors. Carbon-encapsulated metal selenide electrodes with multiscale, multidimensional, and hierarchical architectures are successfully designed and synthesized via a general and facile metal-organic framework derived selenidation strategy. Due to the novel and unique architecture design, these nanohybrid electrodes display ultrastable cycling performance as well as excellent rate capability for Na-ion batteries.

Fast, Self-Driven, Air-Stable, and Broadband Photodetector Based on Vertically Aligned PtSe2/GaAs Heterojunction


Group-10 layered transitional metal dichalcogenides including PtS2, PtSe2, and PtTe2 are excellent potential candidates for optoelectronic devices due to their unique properties such as high carrier mobility, tunable bandgap, stability, and flexibility. Large-area platinum diselenide (PtSe2) with semiconducting characteristics is far scarcely investigated. Here, the development of a high-performance photodetector based on vertically aligned PtSe2-GaAs heterojunction which exhibits a broadband sensitivity from deep ultraviolet to near-infrared light, with peak sensitivity from 650 to 810 nm, is reported. The Ilight/Idark ratio and responsivity of photodetector are 3 × 104 and 262 mA W−1 measured at 808 nm under zero bias voltage. The response speed of τr/τf is 5.5/6.5 µs, which represents the best result achieved for Group-10 TMDs based optoelectronic device thus far. According to first-principle density functional theory, the broad photoresponse ranging from visible to near-infrared region is associated with the semiconducting characteristics of PtSe2 which has interstitial Se atoms within the PtSe2 layers. It is also revealed that the PtSe2/GaAs photodetector does not exhibit performance degradation after six weeks in air. The generality of the above good results suggests that the vertically aligned PtSe2 is an ideal material for high-performance optoelectronic systems in the future. This work shows the large-area growth of high-quality vertically aligned PtSe2, and its application to photodetectors based on PtSe2-GaAs heterojunctions which exhibit a broadband sensitivity to illumination ranging from deep ultraviolet to near-infrared light, with a peak sensitivity in the region from 650 to 810 nm. The high-performance broadband photodetector will develop the next-generation 2D Group-10 materials based optoelectronic devices.

CdS Nanoribbon-Based Resistive Switches with Ultrawidely Tunable Power by Surface Charge Transfer Doping


Traditional metal–insulator–metal (MIM)-based resistive switches (RS) possess a high operating current, which can be read directly without an amplifier yet will inevitably produce large power consumption. Rational control of the energy consumption of RS devices is surely desirable to achieve the energy-efficient purpose in a variety of practical applications. Here a surface charge transfer doping (SCTD) strategy is reported to manipulate the operating current as well as power consumption of the RS devices by using doped CdS nanoribbon (NR) as a rheostat. By controlling the concentration of surface dopant of MoO3, the conductivity of doped CdS NR can be tuned in a wide range of nine orders of magnitude, showing the transition from insulator to semiconductor and to conductor. On the basis of CdS NRs with controllable conductivity, the as-fabricated RS devices exhibit an ultrawidely tunable-power consumption from 1 nW, the lowest value reported so far, to 0.1 mW, which is close to the typical values of MIM-based RS devices. In view of the high controllability of the SCTD method, this work opens up unique opportunities for future energy-efficient, performance-tunable, and multifunctional RS devices based on semiconductor nanostructures. Ultrawidely power-tunable resistive switching (RS) devices based on CdS nanoribbons are constructed via a surface charge transfer doping method. The doped CdS nanoribbons can serve as a rheostat in RS devices to adjust the power consumption from 1 nW to 0.1 mW, thus opening up unique opportunities for future energy-efficient, performance-tunable, and multifunctional RS devices based on semiconductor nanostructures.

Cilia-Inspired Flexible Arrays for Intelligent Transport of Viscoelastic Microspheres


Anisotropic microstructures are widely used by being cleverly designed to achieve important functions. Mammals' respiratory tract is filled with dense cilia that rhythmically swing back and forth in a unidirectional wave to propel mucus and harmful substances out of the lung through larynx. Inspired by the ciliary structure and motion mechanism of the respiratory tract systems, a viscoelastic microsphere transporting strategy based on integration of airway cilium-like structure and magnetically responsive flexible conical arrays is demonstrated. Under external magnetic fields, the viscoelastic microspheres can be directionally and continuously transported alongside the swing of the cilia-like arrays that contain magnetic particles. This work provides a promising route for the design of advanced medical applications in directional transport of microspheres, drug delivery systems, ciliary dyskinesia treating, and self-cleaning without liquid. A magnetically induced viscoelastic microsphere transporting device is designed and fabricated through the integration of cilia-inspired magnetically responsive flexible arrays. Under external magnetic field, microparticles can be continuously and directionally transported through the periodic vibration of flexible arrays. This work opens a new avenue for directional transport of microspheres, drug delivery systems, treatment of ciliary dyskinesia, and self-cleaning without a liquid.

Reduced Graphene Oxide as a Catalyst Binder: Greatly Enhanced Photoelectrochemical Stability of Cu(In,Ga)Se2 Photocathode for Solar Water Splitting


The photoelectrochemical (PEC) properties of a Cu(In,Ga)Se2 (CIGS) photocathode covered with reduced graphene oxide (rGO) as a catalyst binder for solar-driven hydrogen evolution are reported. Chemically reduced rGO with various concentrations is deposited as an adhesive interlayer between CIGS/CdS and Pt. PEC characteristics of the CIGS/CdS/rGO/Pt are improved compared to the photocathode without rGO due to enhancement of charge transfer via efficient lateral distribution of photogenerated electrons by conductive rGO to the Pt. More importantly, the introduction of rGO to the CIGS photocathode significantly enhances the PEC stability; in the absence of rGO, a rapid loss of PEC stability is observed in 2.5 h, while the optimal rGO increases the PEC stability of the CIGS photocathode for more than 7 h. Chemical and structural characterizations show that the loss of the Pt catalyst is one of the main reasons for the lack of long-term PEC stability; the introduction of rGO, which acts as a binder to the Pt catalysts by providing anchoring sites in the rGO, results in complete conservation of the Pt and hence much enhanced stability. Multiple functionality of rGO as an adhesive interlayer, an efficient charge transport layer, a diffusion barrier, and protection layer is demonstrated. Photoelectrochemical (PEC) stability of a Cu(In,Ga)Se2 (CIGS) photocathode with reduced graphene oxide (rGO) as a catalyst binder is evaluated. The introduction of the rGO between the CIGS/CdS and the Pt catalyst improves the PEC stability more than three times by suppressing agglomeration of Pt electrocatalysts, desorption into an electrolyte, and in-diffusion to the CdS buffer layer.

Fast and Accurate Imaging of Lymph Node Metastasis with Multifunctional Near-Infrared Polymer Dots


Metastasis to regional lymph nodes is a significant prognostic indicator for cancer progression. There is a great demand for rapid and accurate diagnosis of metastasis to the lymph nodes. In this work, folate receptor-targeted trimodal polymer dots are designed for near-infrared (NIR)/photoacoustic (PA)/magnetic resonance (MR) imaging of lymph node metastasis. Confocal microscopic analyses and flow cytometry show that pulmonary mucosa epithelial cell carcinoma NCI-H292 with expression of the folate receptor is positive for folate-functional polymer dots. In vivo and ex vivo NIR imaging results verify that prepared polymer dots show rapid and high uptake in the metastatic lymph nodes, can effectively distinguish metastatic and normal lymph nodes for 1 h postinjection, and have great potential in real-time imaging-guided surgery. Furthermore, ten metastatic lymph nodes from the tumor-bearing mice are detected by NIR imaging via intratumoral injection of polymer dots. Moreover, in vivo PA and MR imaging confirm the enhanced PA and MR signals of polymer dots in the metastatic lymph nodes as well as enlarged lymph nodes in tumor-bearing mice. The results of this study provide a unique approach using trimodal polymer dots for the rapid and precise diagnosis of lymph node metastasis in vivo. Trimodal near-infrared/photoacoustic/magnetic resonance polymer dots are prepared by the one-pot reprecipitation method, and demonstrated to be capable of the fast and accurate imaging of lymph nodes metastasis in tumor-bearing mice and photodynamic therapy.

Thin Film Condensation on Nanostructured Surfaces


Water vapor condensation is a ubiquitous process in nature and industry. Over the past century, methods achieving dropwise condensation using a thin (<1 µm) hydrophobic “promoter” layer have been developed, which increases the condensation heat transfer by ten times compared to filmwise condensation. Unfortunately, implementations of dropwise condensation have been limited due to poor durability of the promoter coatings. Here, thin-film condensation which utilizes a promoter layer not as a condensation surface, but rather to confine the condensate within a porous biphilic nanostructure, nickel inverse opals (NIO) with a thin (<20 nm) hydrophobic top layer of decomposed polyimide is developed. Filmwise condensation confined to thicknesses <10 µm is demonstrated. To test the stability of thin-film condensation, condensation experiments are performed to show that at higher supersaturations droplets coalescing on top of the hydrophobic layer are absorbed into the superhydrophilic layer through coalescence-induced transitions. Through detailed thermal-hydrodynamic modeling, it is shown that thin-film condensation has the potential to achieve heat transfer coefficients approaching ≈100 kW m−2 while avoiding durability issues by significantly reducing nucleation on the hydrophobic surface. The work presented here develops an approach to potentially ensure durable and high-performance condensation comparable to dropwise condensation. Thin-film condensation on hydrophobic-coated nickel inverse opal structures enables heat transfer performance approaching that of dropwise condensation while achieving higher robustness by confining the condensate film and reducing nucleation on the hydrophobic layer.

Protoporphyrin IX (PpIX)-Coated Superparamagnetic Iron Oxide Nanoparticle (SPION) Nanoclusters for Magnetic Resonance Imaging and Photodynamic Therapy


The ability to produce nanotherapeutics at large-scale with high drug loading efficiency, high drug loading capacity, high stability, and high potency is critical for clinical translation. However, many nanoparticle-based therapeutics under investigation suffer from complicated synthesis, poor reproducibility, low stability, and high cost. In this work, a simple method for preparing multifunctional nanoparticles is utilized that act as both a contrast agent for magnetic resonance imaging and a photosensitizer for photodynamic therapy for the treatment of cancer. In particular, the photosensitizer protoporphyrin IX (PpIX) is used to solubilize small nanoclusters of superparamagnetic iron oxide nanoparticles (SPIONs) without the use of any additional carrier materials. These nanoclusters are characterized with a high PpIX loading efficiency; a high loading capacity, stable behavior; high potency; and a synthetic approach that is amenable to large-scale production. In vivo studies of photodynamic therapy (PDT) efficacy show that the PpIX-coated SPION nanoclusters lead to a significant reduction in the growth rate of tumors in a syngeneic murine tumor model compared to both free PpIX and PpIX-loaded poly(ethylene glycol)-polycaprolactone micelles, even when injected at 1/8th the dose. These results suggest that the nanoclusters developed in this work can be a promising nanotherapeutic for clinical translation. A simple method for preparing multifunctional nanoparticles that act as both a contrast agent for magnetic resonance imaging and a photosensitizer for photodynamic therapy is developed. These nanoparticles lead to a significant reduction in the growth rate of tumors compared to both free protoporphyrin IX (PpIX) and PpIX-loaded micelles, even when injected at 1/8th the dose.

Hydrodynamically Guided Hierarchical Self-Assembly of Peptide–Protein Bioinks


Effective integration of molecular self-assembly and additive manufacturing would provide a technological leap in bioprinting. This article reports on a biofabrication system based on the hydrodynamically guided co-assembly of peptide amphiphiles (PAs) with naturally occurring biomolecules and proteins to generate hierarchical constructs with tuneable molecular composition and structural control. The system takes advantage of droplet-on-demand inkjet printing to exploit interfacial fluid forces and guide molecular self-assembly into aligned or disordered nanofibers, hydrogel structures of different geometries and sizes, surface topographies, and higher-ordered constructs bound by molecular diffusion. PAs are designed to co-assemble during printing in cell diluent conditions with a range of extracellular matrix (ECM) proteins and biomolecules including fibronectin, collagen, keratin, elastin-like proteins, and hyaluronic acid. Using combinations of these molecules, NIH-3T3 and adipose derived stem cells are bioprinted within complex structures while exhibiting high cell viability (>88%). By integrating self-assembly with 3D-bioprinting, the study introduces a novel biofabrication platform capable of encapsulating and spatially distributing multiple cell types within tuneable pericellular environments. In this way, the work demonstrates the potential of the approach to generate complex bioactive scaffolds for applications such as tissue engineering, in vitro models, and drug screening. Bridging the gap between advanced biomaterials and biofabrication. A novel bioink whereby peptide amphiphiles are used as “chaperones” to organize extracellular matrix proteins and biomolecules into hierarchical structures. The method takes advantage of interfacial forces generated between solutions of the co-assembling molecules enabling the possibility to bioprint while controlling biomolecular and structural elements of the printed scaffold.

Nanoscale Zr-Based MOFs with Tailorable Size and Introduced Mesopore for Protein Delivery


Introduction of large pore in the primitive microporous metal–organic frameworks (MOFs) with tailorable particle size can endow them with desired properties for potential applications in the intracellular delivery of membrane-impermeable proteins. However, no research is found to focus on this topic until now. Herein, a monocarboxylic acid (MA) and organic base comodulation strategy is developed to synthesize the hierarchically porous UiO-66 nanoparticles. MA of dodecanoic acid is utilized to control the pore size while trimethylamine (TEA) plays a key role in modulating the nucleation of crystallization to regulate the particle size. In comparison with microporous UiO-66, a model protein of cytochrome c (Cyt c) could be efficiently loaded into the mesoporous MOFs (mesoMOFs). The size-dependent cellular uptake is also evaluated, and it is verified that mesoMOFs with particle size of 90 nm could be endocytosed into living cells with highest efficiency. These outstanding merits enable the current mesoMOFs not only to exhibit efficient encapsulation of Cyt c but also facilitate the protein delivery into the cytosol and subsequent endosomal escape. Given the exceptional chemical stability, hierarchically porous structure as well as tunable particle size, the elaborated mesoUiO-66 nanoparticles might offer a promising platform for a variety of biomedical applications. Size-controllable mesoporous Zr-based metal–organic frameworks (MOFs) are successfully achieved using a facile acid/base comodulator strategy. In virtue of their high efficiency of internalization by living cells in concert with their high biocompatibility as well as the exceptional chemical stability, the prepared large-pore MOFs might offer a new platform for the intracellular delivery of membrane-impermeable biomolecules.

Low-Cost Chitosan-Derived N-Doped Carbons Boost Electrocatalytic Activity of Multiwall Carbon Nanotubes


An effective strategy is proposed to enhance the oxygen reduction reaction (ORR) performance of multiwall carbon nanotubes (MWCNTs) in both acid and alkaline electrolytes by coating them with a layer of biomass derivative N-doped hydrothermal carbons. The N-doped amorphous carbon coating plays triple roles: it (i) promotes the assembly of MWCNTs into a 3D network therefore improving the mass transfer and thus increasing the catalytic activity; (ii) protects the Fe-containing active sites, present on the surface of the MWCNTs, from H2O2 poisoning; (iii) creates nitrogenated active sites and hence further enhances ORR activity and robustness. A simple and effective strategy is reported to enhance the oxygen reduction reaction (ORR) performance of multiwall carbon nanotubes (MWCNTs). This approach is based on using biomass-derived amorphous carbon to coat CNTs via a hydrothermal process. The approach of manipulating the interface between MWCNTs and the electrolyte is easy to scale up to fit either batch or continuous process.

2D Nanomaterial Arrays for Electronics and Optoelectronics


Two-dimensional (2D) materials, benefitting from their unique planar structure and various appealing electronic properties, have attracted much attention for novel electronic and optoelectronic applications. As a basis for practical devices, the study of micro/nano-2D material arrays based on coupling effects and synergistic effects is critical to the functionalization and integration of 2D materials. Moreover, micro/nano-2D material arrays are compatible with traditional complementary metal oxide semiconductor (CMOS) electronics, catering well to high-integration, high-sensitivity, and low-cost sensing and imaging systems. This review presents some recent studies on 2D material arrays in sequence from their novel preparations to high-integration applications as well as explorations on dimension tuning. A first focus is on various typical fabrication methods for 2D material arrays, including photolithography, 2D printing, seeded growth, van der Waals epitaxial growth, and self-assembly. Then, the applications of 2D material arrays, such as field effect transistors, photodetectors, pressure sensors, as well as flexible electronic devices of photodetectors and strain sensors, are elaborately introduced. Furthermore, the recent burgeoning exploration of mixed-dimensional heterostructure arrays including 0D/2D, 1D/2D, and 3D/2D is discussed. Ultimately, conclusions and an outlook based on the current developments in this promising field are presented. Novel fabrication methods have caused a boom in 2D nanomaterials array development toward high-performance and low-cost microelectronic systems compatible with complementary metal oxide semiconductor electronics. The device prototypes achieved include field-effect transistors, photodetectors, and press sensors. Explorations based on mixed-dimensional heterostructure (0D/2D, 1D/2D, and 3D/2D) arrays are systematically reviewed, and further expectations of 2D arrays are presented.

High Performance BiOCl Nanosheets/TiO2 Nanotube Arrays Heterojunction UV Photodetector: The Influences of Self-Induced Inner Electric Fields in the BiOCl Nanosheets


BiOCl nanosheets/TiO2 nanotube arrays heterojunction UV photodetector (PD) with high performance is fabricated by a facile anodization process and an impregnation method. The heterojunction at the interface and the internal electric fields in the BiOCl nanosheets faciliate the separation of photogenerated charge carriers and regulate the transportation of the electrons. Compared with the large dark current (≈10−5 A), low on/off ratio (8.5), and slow decay time (>60 s) of the TiO2 PD, the optimized heterojunction PD (6-BiOCl–TiO2) yields dramatically decreased dark current (≈1 nA), ultrahigh on/off ratio (up to 2.2 × 105), and fast decay speed (0.81 s) under 350 nm light illumination at −5 V. Moreover, it exhibits an increased responsivity of 41.94 A W−1, a remarkable detectivity (D*) of 1.41 × 1014 Jones, and a high linear dynamic range of 103.59 dB. The loading amount and growth orientations of the BiOCl nanosheets alter the roles of the self-induced internal electric field in regulating the behaviors of the charge carriers, thus affecting the photoelectric properties of the heterojunction PDs. These results demonstrate that rational construction of novel heterojunctions hold great potentials for fabricating photodetectors with high performance. A BiOCl–TiO2 heterojunction UV photodetector with high performance is fabricated. Heterojunctions formed between BiOCl nanosheets and TiO2 nanotube arrays improve the UV photoresponses and response speed of TiO2 film photodetectors. The loading amount and growth orientation of BiOCl nanosheets on the TiO2 film have great influences on the photoelectric performance of the heterojunction photodetector.

Photoinduced Proton Transfer between Photoacid and pH-Sensitive Dyes: Influence Factors and Application for Visible-Light-Responsive Rewritable Paper


Ink-free printing based on rewritable paper is an efficient and environmental friendly way to reuse paper, protect resources, and save energy for sustainable development of human society. Among various kinds of rewritable media, light responsive rewritable paper (LRP) is one of the most popular research areas due to its clean and favorable noncontact writing. Visible light is more suitable for LRP for its superior penetration and much less damages to organic molecules than UV light. However, visible-light-responsive rewritable paper (VLRP) has only limited successes so far. Herein, a VLRP is newly designed and fabricated based on photoinduced proton transfer (PPT) between photoacid and pH-sensitive dyes. Success of it is highly benefited from systematical investigation and in-depth understanding on the key influence factors, such as concentration-induced undesired isomerization, temperature, humidity, and light intensity, on the PPT and its inverse process. As-prepared VLRP shows long-awaited properties, such as, high color contrast and resolution, appropriate legible time of prints, excellent reversibility (>100 cycles), easiness to achieve multicolor prints, and agreeing well with environmental concept of green printing. In addition, study of influence factors on PPT in this work, to some extent, may also help people understand complex photocycle process in biosystem. A new kind of visible-light-responsive rewritable paper (VLRP) is designed and fabricated based on bioinspired photocycle from photoinduced proton transfer (PPT) between a photoacid and a proton receptor dye. Systematical investigation and in-depth understanding key influence factors on the PPT and its inverse process endow the VLRP with excellent performances.

Self-Assembled Quasi-3D Nanocomposite: A Novel p-Type Hole Transport Layer for High Performance Inverted Organic Solar Cells


Hole transport layer (HTL) plays a critical role for achieving high performance solution-processed optoelectronics including organic electronics. For organic solar cells (OSCs), the inverted structure has been widely adopted to achieve prolonged stability. However, there are limited studies of p-type effective HTL on top of the organic active layer (hereafter named as top HTL) for inverted OSCs. Currently, p-type top HTLs are mainly 2D materials, which have an intrinsic vertical conduction limitation and are too thin to function as practical HTL for large area optoelectronic applications. In the present study, a novel self-assembled quasi-3D nanocomposite is demonstrated as a p-type top HTL. Remarkably, the novel HTL achieves ≈15 times enhanced conductivity and ≈16 times extended thickness compared to the 2D counterpart. By applying this novel HTL in inverted OSCs covering fullerene and non-fullerene systems, device performance is significantly improved. The champion power conversion efficiency reaches 12.13%, which is the highest reported performance of solution processed HTL based inverted OSCs. Furthermore, the stability of OSCs is dramatically enhanced compared with conventional devices. The work contributes to not only evolving the highly stable and large scale OSCs for practical applications but also diversifying the strategies to improve device performance. A novel self-assembled quasi-3D nanocomposite is demonstrated to be an effective top hole transport layer (HTL) for both fullerene and non-fullerene inverted organic solar cells. Due to the better conductivity of this nanocomposite HTL, the thickness sensitivity issue of graphene oxide is addressed. Surface recombination is suppressed and the highest power conversion efficiency can reach 12.13%.

In Situ Growth of 2D Perovskite Capping Layer for Stable and Efficient Perovskite Solar Cells


2D halide perovskites have recently been recognized as a promising avenue in perovskite solar cells (PSCs) in terms of encouraging stability and defect passivation effect. However, the efficiency (less than 15%) of ultrastable 2D Ruddlesden–Popper PSCs still lag far behind their traditional 3D perovskite counterparts. Here, a rationally designed 2D-3D perovskite stacking-layered architecture by in situ growing 2D PEA2PbI4 capping layers on top of 3D perovskite film, which drastically improves the stability of PSCs without compromising their high performance, is reported. Such a 2D perovskite capping layer induces larger Fermi-level splitting in the 2D-3D perovskite film under light illumination, resulting in an enhanced open-circuit voltage (Voc) and thus a higher efficiency of 18.51% in the 2D-3D PSCs. Time-resolved photoluminescence decay measurements indicate the facilitated hole extraction in the 2D-3D stacking-layered perovskite films, which is ascribed to the optimized energy band alignment and reduced nonradiative recombination at the subgap states. Benefiting from the high moisture resistivity as well as suppressed ion migration of the 2D perovskite, the 2D-3D PSCs show significantly improved long-term stability, retaining nearly 90% of the initial power conversion efficiency after 1000 h exposure in the ambient conditions with a high relative humidity level of 60 ± 10%. 2D perovskite capping layers are grown in situ on top of the 3D perovskite film, leading to an enhanced efficiency of 18.5% in the stacking-layered 2D-3D perovskite solar cells (PSCs). Moreover, the unencapsulated 2D-3D PSCs show drastically improved long-term stability, retaining nearly 90% of the original efficiency after 1000 h exposure in a highly humid environment.

Room-Temperature Electrochemical Conversion of Metal–Organic Frameworks into Porous Amorphous Metal Sulfides with Tailored Composition and Hydrogen Evolution Activity


The conversion of metal–organic frameworks (MOFs) into inorganic nanomaterials is considered as an attractive means to produce highly efficient electrocatalysts for alternative-energy related applications. Yet, traditionally employed MOF-conversion conditions (e.g., pyrolysis) commonly involve multiple complex high-temperature reaction processes, which often make it challenging to control the composition, pore structure, and active-sites of the MOF-derived catalysts. Herein, a general, simple, room-temperature method is presented for a controlled electrochemical conversion of MOF (EC-MOF) films into porous, amorphous metal sulfides (a-MSx). Detailed X-ray photoelectron spectroscopy analysis and control over independent EC-MOF parameters (e.g., scan-rate and potential window) enable to gain insights on the MOF-conversion mechanisms, and in turn to fine-tune the porosity and composition of the obtained MSx. As a result, a highly active amorphous cobalt sulfide (a-CoSx) electrocatalyst can be designed for hydrogen evolution reaction in neutral pH. Furthermore, the adjustable nature of the EC-MOF method allows to draw conclusions about the correlation between the concentration of catalytically active species (S22− sites) and the hydrogen evolution properties of the a-CoSx. Given the method's generality and the diversity of available MOF structures, EC-MOF provides a compelling platform for a rational design of a wide variety of active electrocatalytic materials. Electrochemical conversion of metal–organic framework (EC-MOF) films is introduced as a versatile tool for constructing active H2-evolution metal sulfide electrocatalysts. EC-MOF enables fine-tuning of the metal sulfide's chemical structure and composition. Thus, given the large variety of available MOFs, the EC-MOF method provides a powerful platform for designing a wide variety of active electrocatalytic materials.

Low-Voltage, Optoelectronic CH3NH3PbI3−xClx Memory with Integrated Sensing and Logic Operations


Nonvolatile optoelectronic memories integrated with the functions of sensing, data storage, and data processing are promising for the potential Internet of things (IoT) applications. To meet the requirements of IoT devices, multifunctional memory devices with low power consumption and secure data storage are highly desirable. This study demonstrates an optoelectronic resistive switching memory integrated with sensing and logic operations by adopting organic–inorganic hybrid CH3NH3PbI3−xClx perovskites, which possess unusual defect physics and excellent light absorption. The CH3NH3PbI3−xClx cell exhibits low operation voltage of 0.1 V with the assistance of light illumination, long-term retention property, and multiple resistance states. Its unique optoelectronic characteristics enable to perform logic operation for inputting one electrical pulse and one optical signal, and detect the coincidence of electrical and optical signal as well. This design provides possibilities for smart sensor in IoT application. Optoelectronic CH3NH3PbI3−xClx perovskite resistive switching memory is designed and fabricated. The memory cell exhibits a low operation voltage of 0.1 V with the assistance of light illumination, long-term retention, and light sensing properties, and can perform logic operations by inputting electrical and optical signals. This device provides possibilities for reducing the complexity in smart sensor design for Internet of things applications.

DNA Origami-Guided Assembly of the Roundest 60–100 nm Gold Nanospheres into Plasmonic Metamolecules


DNA origami can provide programmed information to guide the self-assembly of gold nanospheres (Au NSs) into higher-order supracolloids. Molecularly precise and truly 2D/3D integration of Au NSs is possible using DNA origami-enabled assembly, and the resulting assemblies have potential applications in plasmonics and metamaterials. However, the relatively small size (<60 nm) and randomly faceted Au NSs that have been used thus far in DNA origami-enabled assembly have limited their nanophotonic applications. Here, the robust self-assembly of the 60–100 nm roundest Au NSs into metamolecular assemblies using 3D DNA origami is described. These Au NSs are successfully conjugated with DNA oligonucleotides and are therefore stable at high salt concentrations even without backfilling using organic ligands. The roundest Au NSs are successfully assembled into supracolloidal metamolecules and chains via 3D DNA origami. These plasmonic metamolecules and chains display strong electric and unnatural magnetic resonances that can be deterministically controlled. 3D DNA origami-enabled robust self-assembly of relatively large, roundest gold nanospheres into various plasmonic assemblies ranging from supracolloidal ring clusters to oligomeric chains is reported. The plasmonic assemblies generate strong electric and unnatural magnetic resonances due to their high structural fidelity.

All-Inorganic CsPbI3 Perovskite Phase-Stabilized by Poly(ethylene oxide) for Red-Light-Emitting Diodes


Despite the excellent photoelectronic properties of the all-inorganic cesium lead iodide (CsPbI3) perovskite, which does not contain volatile and hygroscopic organic components, only a few CsPbI3 devices are developed mainly owing to the frequent formation of an undesirable yellow δ-phase at room temperature. Herein, it is demonstrated that a small quantity of poly(ethylene oxide) (PEO) added to the precursor solution effectively inhibits the formation of the yellow δ-phase during film preparation, and promotes the development of a black α-phase at a low crystallization temperature. A systematic study reveals that a thin, dense, pinhole-free CsPbI3 film is produced in the α-phase and is stabilized with PEO that effectively reduces the grain size during crystallization. A thin α-phase CsPbI3 film with excellent photoluminescence is successfully employed in a light-emitting diode with an inverted configuration of glass substrate/indium tin oxide/zinc oxide/poly(ethyleneimine)/α-CsPbI3/poly(4-butylphenyl-diphenyl-amine)/WO3/Al, yielding the characteristic red emission of the perovskite film at 695 nm with brightness, external quantum efficiency, and emission band width of ≈101 cd m−2, 1.12%, and 32 nm, respectively. A small quantity of a poly(ethylene oxide) added in the precursor solution is beneficial for the development of all-inorganic CsPbI3 perovskite in black α-phase with significantly improved ambient stability. Dense, uniform, and pinhole-free CsPbI3 thin films consisting of tens of nanometers black α-phase crystals are successfully fabricated with excellent photophysical properties, leading to high performance light-emitting diodes.

Kinetics of Space Charge Storage in Composites


Composites of ion and electron conducting phases allow for interfacial storage of a neutral component via space charge effects. The present contribution considers the rate of transport-controlled incorporation and excorporation in such artificial mixed conductors. The upper limit of the relaxation time is determined by interfacial job-sharing diffusion which is analyzed in greater detail. In general cases bulk phases assist by migration processes (dual phase transport). For more complex morphological situations, the considerations are complemented by numerical calculations. Thus the treatment also offers a pertinent approach with respect to the kinetics of solid state supercapacitors. Selected experimental results are included in the discussion. Mass storage at contacts of ionic and electronic conductors enables decoupling of the roles of ions and electrons. A treatment of the kinetics is presented covering diffusion along and transport to the active interfaces. Finite element calculations help understand the situation in complex microstructures. The contribution thus also offers a pertinent account of the kinetics of solid-state supercapacitors.

Advances in Manganese-Based Oxides Cathodic Electrocatalysts for Li–Air Batteries


Li–air batteries, characteristic of superhigh theoretical specific energy density, cost-efficiency, and environment-friendly merits, have aroused ever-increasing attention. Nevertheless, relatively low Coulomb efficiency, severe potential hysteresis, and poor rate capability, which mainly result from sluggish oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) kinetics, as well as pitiful cycle stability caused by parasitic reactions, extremely limit their practical applications. Manganese (Mn)-based oxides and their composites can exhibit high ORR and OER activities, reduce charge/discharge overpotential, and improve the cycling stability when used as cathodic catalyst materials. Herein, energy storage mechanisms for Li–air batteries are summarized, followed by a systematic overview of the progress of manganese-based oxides (MnO2 with different crystal structures, MnO, MnOOH, Mn2O3, Mn3O4, MnOx, perovskite-type and spinel-type manganese oxides, etc.) cathodic materials for Li–air batteries in the recent years. The focus lies on the effects of crystal structure, design strategy, chemical composition, and microscopic physical parameters on ORR and OER activities of various Mn-based oxides, and even the overall performance of Li–air batteries. Finally, a prospect of the research for Mn-based oxides cathodic catalysts in the future is made, and some new insights for more reasonable design of Mn-based oxides electrocatalysts with higher catalytic efficiency are provided. Manganese-based oxides have been proven to be effective electrocatalysts for Li–O2 electrochemistry. Here, recent research progress about Mn-based oxides with various crystal structures and their composites for Li–air batteries is reviewed; the aim is to provide some constructive guidance to design more effective Mn-based oxides electrocatalysts in this field.

Tailoring the Surface Chemical Reactivity of Transition-Metal Dichalcogenide PtTe2 Crystals


PtTe2 is a novel transition-metal dichalcogenide hosting type-II Dirac fermions that displays application capabilities in optoelectronics and hydrogen evolution reaction. Here it is shown, by combining surface science experiments and density functional theory, that the pristine surface of PtTe2 is chemically inert toward the most common ambient gases (oxygen and water) and even in air. It is demonstrated that the creation of Te vacancies leads to the appearance of tellurium-oxide phases upon exposing defected PtTe2 surfaces to oxygen or ambient atmosphere, which is detrimental for the ambient stability of uncapped PtTe2-based devices. On the contrary, in PtTe2 surfaces modified by the joint presence of Te vacancies and substitutional carbon atoms, the stable adsorption of hydroxyl groups is observed, an essential step for water splitting and the water–gas shift reaction. These results thus pave the way toward the exploitation of this class of Dirac materials in catalysis. Herein, it is demonstrated how the inert surface of PtTe2 can be transformed into a catalyst by implanting Te vacancies and by surface functionalization with substitutional carbon atoms. The stable adsorption of hydroxyl groups represents an essential step for water splitting and the water–gas shift reaction. These results pave the way toward the exploitation of Dirac materials in catalysis.

Synergistic Effect of Graphene Oxide for Impeding the Dendritic Plating of Li


Dendritic growth of lithium (Li) has severely impeded the practical application of Li-metal batteries. Herein, a 3D conformal graphene oxide nanosheet (GOn) coating, confined into the woven structure of a glass fiber separator, is reported, which permits facile transport of Li-ions thought its structure, meanwhile regulating the Li deposition. Electrochemical measurements illustrate a remarkably enhanced cycle life and stability of the Li-metal anode, which is explained by various microscopy and modeling results. Utilizing scanning electron microscopy, focused ion beam, and optical imaging, the formation of an uniform Li film on the electrode surface in the case of GO-modified samples is revealed. Ab initio molecular dynamics (AIMD) simulations suggest that Li-ions initially get adsorbed to the lithiophilic GOn and then diffuse through defect sites. This delayed Li transfer eliminates the “tip effect” leading to a more homogeneous Li nucleation. Meanwhile, CC bonds rupture observed in the GO during AIMD simulations creates more pathways for faster Li-ions transport. In addition, phase-field modeling demonstrates that mechanically rigid GOn coating with proper defect size (smaller than 25 nm) can physically block the anisotropic growth of Li. This new understanding is a significant step toward the employment of 2D materials for regulating the Li deposition. A three-dimensional conformal graphene oxide coating is reported, which permits regulated transport of lithium ions through its structure while suppressing the dendritic deposition of lithium. The electrochemical measurements illustrate a remarkably enhanced stability of the Li-metal anode, which is explained by various microscopy (optical, scanning electron microscopy/focused ion beam) and modeling (ab initio molecular dynamics and phase-field modeling) results.

Synergistically Enhanced Oxygen Reduction Electrocatalysis by Subsurface Atoms in Ternary PdCuNi Alloy Catalysts


For Pd-based alloy catalysts, the selection of metallic alloying elements and the construction of composition-gradient surface and subsurface layers are critical in achieving superior electrocatalytic activities in, e.g., the oxygen reduction reaction (ORR). Based on the Pd-containing alloy, highly monodispersed PdCuNi ternary alloy nanocrystals are prepared through a wet-chemical approach, and a solution-based oxidative surface treatment protocol is utilized to activate the surface of the nanocrystals. A drastically enhanced ORR activity can be achieved by removing the surface Ni and Cu atoms through the surface treatment protocol. The treated catalyst demonstrates a mass activity of 0.45 A mgPd−1 in alkaline medium, 5 and 2.4 times those of commercial Pt/C and Pd/C, respectively. The first-principle calculation result suggests the critical roles of the coexistence of Ni and Cu atoms and their synergistic interaction beneath the outmost pure Pd layer in optimizing the oxygen binding energy for ORR. The calculation also suggests that the optimal binding energy of oxygen requires an appropriate Ni/Cu ratio in the subsurface layer. This work demonstrates a class of high-performance Pt-free ternary alloy ORR catalysts and may provide a general guideline for the structural design of Pd-based ternary alloy catalysts. A composition-gradient surface-treatment strategy is developed for the PdCuNi ternary alloy electrocatalyst toward the oxygen reduction reaction. Theoretical calculation reveals that the enhancement originates from the synergistic interaction between Cu and Ni atoms in the subsurface layer with appropriate ratios.

Organic Salt Semiconductor with High Photoconductivity and Long Carrier Lifetime


Intrinsic photogeneration of charge carriers in organic semiconductors is generally attributed to high energy ionization or exciton dissociation by a strong electric field. Here, high bulk photoconductivity is reported in pristine pentamethine cyanine films with photocurrent onset at the band-edge of the organic semiconductor. Single-layer cyanine diodes with selective hole and electron contacts show linear dependence of photocurrent with reverse voltage and light intensity. Numerical drift-diffusion simulations reveal that the linear resistor behavior stems from low and unbalanced carrier mobilities giving rise to negative space charge. Slow bimolecular recombination kinetics of photoinduced charges obtained by time delayed charge extraction measurements show strongly reduced Langevin recombination with long carrier lifetime of the order of a millisecond. Such reduced charge carrier recombination puts forward a materials concept to be exploited in photodiodes and more generally in optoelectronic devices. High photocurrent generation efficiency in the bulk of a pristine organic salt semiconductor in the absence of electric field and donor–acceptor heterointerface is reported. The long carrier lifetime puts forward a materials concept with reduced charge carrier recombination to be exploited in photodiodes and more generally in optoelectronic devices.

Hydrocarbons-Driven Crystallization of Polymer Semiconductors for Low-Temperature Fabrication of High-Performance Organic Field-Effect Transistors


While many high-performance polymer semiconductors are reported for organic field-effect transistors (OFETs), most require a high-temperature postdeposition annealing of channel semiconductors to achieve high performance. This negates the fundamental attribute of OFETs being a low-cost alternative to conventional high-cost silicon technologies. A facile solution process is developed through which high-performance OFETs can be fabricated without thermal annealing. The process involves incorporation of an incompatible hydrocarbon binder or wax into the channel semiconductor composition to drive rapid phase separation and instantaneous crystallization of polymer semiconductor at room temperature. The resulting composite channel semiconductor film manifests a nano/microporous surface morphology with a continuous semiconductor nanowire network. OFET mobility of up to about 5 cm2 V−1 s−1 and on/off ratio ≥ 106 are attained. These are hitherto benchmark performance characteristics for room-temperature, solution-processed polymer OFETs, which are functionally useful for many impactful applications. Incorporation of a hydrocarbon binder into a polar donor-acceptor semiconductor enables room-temperature fabrication of a highly ordered channel semiconductor for organic field-effect transistors (OFETs) under ambient conditions. The resulting OFETs have afforded excellent field-effect mobility to about 5 cm2 V−1 s−1 – a benchmark performance for polymer OFETs without postdeposition thermal annealing.

Mechanically Robust, Highly Ionic Conductive Gels Based on Random Copolymers for Bending Durable Electrochemical Devices


Mechanically robust, highly ionic conductive gels based on a random copolymer of poly[styrene-ran-1-(4-vinylbenzyl)-3-methylimidazolium hexafluorophosphate] (P[S-r-VBMI][PF6]) and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]) are successfully prepared. The gels with either homo P[VBMI][PF6] or conventional PS-block-poly(methyl methacrylate)-block-PS (SMS) show significant trade-off between ionic conductivity and mechanical resilience. In contrast, the P[S-r-VBMI][PF6]-based gels exhibit both large elastic modulus (≈0.105 MPa) and ionic conductivity (≈1.15 mS cm−1) at room temperature. To demonstrate that these materials can be used as solid-state electrolytes, the ion gels are functionalized by incorporating electrochromic (EC) chromophores (ethyl viologen, EV2+) and are applied to EC devices (ECDs). The devices show low-voltage operation, large optical transmittance variation, and good cyclic coloration/bleaching stability. In addition, flexible ECDs are fabricated to take advantage of the mechanical properties of the gels. The ECDs have excellent bending durability under both compressive and tensile strains. The versatile P[S-r-VBMI][PF6]-based gel is anticipated to be of advantage in flexible electrochemical applications, such as batteries and electrochemical displays. Mechanically robust, highly conductive ion gels are obtained based on newly designed random copolymers and room-temperature ionic liquids. The versatile ion gels are functionalized to include electrochromism and applied to electrochromic (EC) devices. By taking advantage of the good mechanical resilience of the gel, flexible electrochromic devices are successfully demonstrated exhibiting high bending durability under both tensile and compressive strains.

Solid-State Light Emission Controlled by Tuning the Hierarchical Superstructure of Self-Assembled Luminogens


Solid-state luminescence is an important strategy for color generation via molecular self-assembly. Here, a new luminogen (AT3EMIS) containing both a rigid chromophore and a flexible dendron is designed and synthesized for multicolor emission. The emission energy of the target material is precisely controlled by adjusting three different columnar arrays through thermal and mechanical stimulation. With well-defined supramolecular organizations in different length scales, the luminescent properties of the light switch can be tuned. Supramolecular luminogens consist of a rigid chromophore with a flexible dendron, and the self-assembled columnar superstructure described here can provide highly predictable guidelines for switching the multicolor luminescence.

Hierarchically Structured Self-Healing Sensors with Tunable Positive/Negative Piezoresistivity


It is a challenge to manufacture flexible sensors that possess easily distinguishable biomotion signals, strong response reliability, and excellent self-healing capability. Herein, a self-healing sensor with tunable positive/negative piezoresistivity is designed by the construction of hierarchical structure connected through supramolecular metal–ligand coordination bonds. The developed sensors can be integrated with the human body to detect multiple tiny signals, such as pronunciation, coughing, and deep breathing. Interestingly, the nanostructured elastomer sensor with and without a flexible yarn electrode shows negative and positive current signals, respectively, making it easy to be identify. Furthermore, it exhibits very fast (2 min), autonomous, and repeatable self-healing ability with high-healing efficiency (88.6% after the third healing process). The healed samples still possess flexibility, high sensitivity, and accurate detection capability, even after bending over 10 000 cycles. The excellent biomimetic self-healing performance combined with the tunable piezoresistivity make it promising for next-generation wearable electronics. Self-healing sensors with tunable positive/negative piezoresistivity are developed by the construction of hierarchical structure connected through supramolecular metal–ligand coordination bonds. The resultant strain sensor exhibits very fast, autonomous, and repeatable self-healing ability with high-healing efficiency. More interestingly, it presents tunable positive/negative piezoresistivity, making it easy to be identified and is highly desired for human–machine interface application.

Regulation of Breathing CuO Nanoarray Electrodes for Enhanced Electrochemical Sodium Storage


Cupric oxide (CuO) represents an attractive anode material for sodium-ion batteries owing to its large capacity (674 mAh g−1) associated with multiple electron transfer. However, the substantial volume swelling and shrinking (≈170%) upon Na uptake and release, which mimics an electrode breathing process, disturbs the structural integrity, leading to poor electrochemical durability and low Coulombic efficiency. Here, a structural strategy to regulate the breathing of CuO nanoarray electrodes during Na cycling using an atomic layer deposition of cohesive TiO2 thin films is presented. CuO nanoarrays are electrochemically grown on 3D Cu foam and directly used as anodes for sodium storage. The regulated CuO electrode arrays enable a large reversible capacity (592 mAh g−1), a high cycle efficiency (≈100%), and an excellent cycling stability (82% over 1000 cycles), which are some of the best sodium storage performance values reported for CuO systems. Electrochemical impedance and microscopic examination reveal that the enhanced performance is a direct outcome of the efficient regulation of the breathing of CuO nanowires by TiO2 layer. A structural regulating strategy is applied to cupric oxide (CuO) nanowire electrode arrays, which imparts electronic conductivity, electrochemical durability, and structural stability to the array material and efficiently addresses the breathing issue of the electrode on Na cycling. The regulated CuO nanowire arrays exhibit a high reversible Na capacity, outstanding cycling stability (82% over 1000 cycles), and good compatibility with full batteries.

Washable Multilayer Triboelectric Air Filter for Efficient Particulate Matter PM2.5 Removal


Efficient removal of particulate matter (PM) is the major goal for various air cleaning technologies due to its huge impact on human health. Here, a washable high-efficiency triboelectric air filter (TAF) that can be used multiple times is presented. The TAF consists of five layers of the polytetrafluoroethylene (PTFE) and nylon fabrics. Compared with traditional electrostatic precipitator, which requires a high-voltage power supply, the TAF can be charged by simply rubbing the PTFE and nylon fabrics against each other. The electrical properties of the TAF are evaluated through the periodic contacting–separating of the PTFE and nylon fabrics using a linear motor, and an open-circuit voltage of 190 V is achieved. After charging, the TAF has a removal efficiency of 84.7% for PM0.5, 96.0% for PM2.5, which are 3.22 and 1.39 times as large as the uncharged one. Most importantly, after washing several times, the removal efficiency of the TAF maintains almost the same, while the commercial face mask drops to 70% of its original efficiency. Furthermore, the removal efficiency of the PM2.5 is very stable under high relative humidity. Therefore, the TAF is promising for fabricating a reusable and high-efficiency face mask. A multilayer triboelectric air filter consists of five layers of polytetrafluoroethylene (PTFE) and nylon fabrics. A high removal efficiency is achieved by rubbing the fabrics against each other, and the removal efficiency maintains high under high humidity, in a durability test or after several washing cycles. Moreover, a face mask made of this air filter can be used in daily life.

Sodium-Ion Batteries: Building Effective Layered Cathode Materials with Long-Term Cycling by Modifying the Surface via Sodium Phosphate


Surface stabilization of cathode materials is urgent for guaranteeing long-term cyclability, and is important in Na cells where a corrosive Na-based electrolyte is used. The surface of P2-type layered Na2/3[Ni1/3Mn2/3]O2 is modified with ionic, conducting sodium phosphate (NaPO3) nanolayers, ≈10 nm in thickness, via melt-impregnation at 300 °C; the nanolayers are autogenously formed from the reaction of NH4H2PO4 with surface sodium residues. Although the material suffers from a large anisotropic change in the c-axis due to transformation from the P2 to O2 phase above 4 V versus Na+/Na, the NaPO3-coated Na2/3[Ni1/3Mn2/3]O2/hard carbon full cell exhibits excellent capacity retention for 300 cycles, with 73% retention. The surface NaPO3 nanolayers positively impact the cell performance by scavenging HF and H2O in the electrolyte, leading to less formation of byproducts on the surface of the cathodes, which lowers the cell resistance, as evidenced by X-ray photoelectron spectroscopy and time-of-flight secondary-ion mass spectroscopy. Time-resolved in situ high-temperature X-ray diffraction study reveals that the NaPO3 coating layer is delayed for decomposition to Mn3O4, thereby suppressing oxygen release in the highly desodiated state, enabling delay of exothermic decomposition. The findings presented herein are applicable to the development of high-voltage cathode materials for sodium batteries. A NaPO3 coating layer functions effectively as cathode for sodium-ion batteries. The presence of the NaPO3 coating layers scavenges HF and thus lowers the HF content and the amount of water molecules in the electrolyte, which can successfully suppress detachment of the active materials, ensuring better cycling performance and improved thermal stability.

MRI-Visible siRNA Nanomedicine Directing Neuronal Differentiation of Neural Stem Cells in Stroke


A major challenge in stroke treatment is the restoration of neural circuit in which neuron function plays a central role. Although transplantation of exogenous neural stem cells (NSCs) is admittedly a promising therapeutical means, the treatment outcome is greatly affected due to the poor NSCs differentiation into neurons caused by myelin associated inhibitory factors binding to Nogo-66 receptor (NgR). Herein, a nanoscale polymersome is developed to codeliver superparamagnetic iron oxide nanoparticles and siRNA targeting NgR gene (siNgR) into NSCs. This multifunctional nanomedicine directs neuronal differentiation of NSCs through silencing the NgR gene and meanwhile allows a noninvasive monitoring of NSC migration with magnetic resonance imaging. An improved recovery of neural function is achieved in rat ischemic stroke model. The results demonstrate the great potential of the multifunctional siRNA nanomedicine in stroke treatment based on stem cell transplantation. A magnetic resonance imaging (MRI)-visible nanocarrier based on a cationic polymersome is constructed. The nanocarrier complexes siRNA in its cationic membrane and transfects NSCs effectively, resulting in remarkably enhanced neuronal differentiation of exogenous neural stem cells (NSCs) by downregulating the Nogo-66 receptor expression to promote functional recovery in acute ischemic stroke. Moreover, the MRI-visible nanomedicine shows advantage of providing noninvasive imaging of NSC migration and homing.

Increasing the Efficiency of Organic Dye-Sensitized Solar Cells over 10.3% Using Locally Ordered Inverse Opal Nanostructures in the Photoelectrode


3D inverse opal (3D-IO) oxides are very appealing nanostructures to be integrated into the photoelectrodes of dye-sensitized solar cells (DSSCs). Due to their periodic interconnected pore network with a high pore volume fraction, they facilitate electrolyte infiltration and enhance light scattering. Nonetheless, preparing 3D-IO structures directly on nonflat DSSC electrodes is challenging. Herein, 3D-IO TiO2 structures are prepared by templating with self-assembled polymethyl methacrylate spheres on glass substrates, impregnation with a mixed TiO2:SiO2 precursor and calcination. The specific surface increases from 20.9 to 30.7 m2 g−1 after SiO2 removal via etching, which leads to the formation of mesopores. The obtained nanostructures are scraped from the substrate, processed as a paste, and deposited on photoelectrodes containing a mesoporous TiO2 layer. This procedure maintains locally the 3D-IO order. When sensitized with the novel benzothiadiazole dye YKP-88, DSSCs containing the modified photoelectrodes exhibit an efficiency of 10.35% versus 9.26% for the same devices with conventional photoelectrodes. Similarly, using the ruthenium dye N719 as sensitizer an efficiency increase from 5.31% to 6.23% is obtained. These improvements originate mainly from an increase in the photocurrent density, which is attributed to an enhanced dye loading obtained with the mesoporous 3D-IO structures due to SiO2 removal. A significant improvement of the photocurrent density and hence the power conversion efficiency of dye-sensitized solar cells (DSSCs) is achieved by integrating mesoporous 3D inverse opal TiO2 nanostructures into the photoelectrode. Using an organic dye for sensitization leads to efficiencies up to 10.35%, which is the highest value reported using inverse opal structures as photoactive component in the photoelectrode.

Polycationic Synergistic Antibacterial Agents with Multiple Functional Components for Efficient Anti-Infective Therapy


Multifunctional antibacterial photodynamic therapy is a promising method to combat regular and multidrug-resistant bacteria. In this work, eosin Y (EY)-based antibacterial polycations (EY-QEGEDR, R = CH3 or C6H13) with versatile types of functional components including quaternary ammonium, photosensitizer, primary amine, and hydroxyl species are readily synthesized based on simple ring-opening reactions. In the presence of light irradiation, such antibacterial polymers exhibit high antibacterial efficiency against both Escherichia coli and Staphylococcus aureus. In particular, EY-QEGEDR elicits a remarkable synergistic antibacterial activity owing to the combined photodynamic and quaternary ammonium antibacterial effects. Due to its rich primary amine groups, EY-QEGEDR also can be readily coated on different substrates, such as glass slides and nonwoven fabrics via an adhesive layer of polydopamine. The resultant surface coating of EY-QEGEDCH3 (s-EY-QEGEDCH3) produces excellent in vitro antibacterial efficacy. The plentiful hydroxyl groups impart s-EY-QEGEDCH3 with potential antifouling capability against dead bacteria. The antibacterial polymer coatings also demonstrate low cytotoxicity and good hemocompatibility. More importantly, s-EY-QEGEDCH3 significantly enhances in vivo therapeutic effects on an infected rat model. The present work provides an efficient strategy for the rational design of high-performance antibacterial materials to fight biomedical device-associated infections. Polycationic synergistic antibacterial agents with versatile functional components including quaternary ammonium, photosensitizer, primary amine, and hydroxyl species are proposed for effective biomedical applications.

Artificial Micro/Nanomachines for Bioapplications: Biochemical Delivery and Diagnostic Sensing


Recent progress in artificial nanomachines offers promising solutions to grand challenges in biochemical delivery and diagnostics. In this work, advances of micro/nanomachines made of synthesized micro/nanostructures for applications in delivery and detection of biomolecules are reviewed, along with a discussion of pros and cons of each type of machine. The review of micro/nanomachines is categorized according to their working mechanisms, including motion actuation realized by magnetic, electric, and acoustic fields and chemical reactions. The developments of micro/nanomachines are discussed in depth in the fabrication, propulsion, and motion control, loading and releasing of micro/nanosubstances, and biochemical sensing. The rapid development of man-made miniaturized machines paves the road toward future intelligent nanorobots and nanofactories that can revolutionize society. Recent advances in micro/nanomachines made of synthesized micro/nanostructures for applications in biosubstance delivery and diagnosis sensing are reviewed, including the fabrication, propulsion and motion control, loading and releasing of micro/nanosubstances, and innovative sensing mechanisms and devices. The development of man-made miniaturized machines paves the road toward intelligent nanorobots and nanofactories that can revolutionize society.

Photogenerated Aldehydes for Protein Patterns on Hydrogels and Guidance of Cell Behavior


The immobilization of proteins to hydrogels is important and plays a significant role to provide suitable biomimetic material as extracellular matrix for cell behavior mediation. This study describes a novel and universal strategy for photopatterning unmodified proteins on hydrogels. The methodology creates photogenerated aldehyde regions within a protein-resistant hydrogel and then conjugates unmodified proteins by mild imine ligation with spatial, temporal, and dosage control. The relatively stable aldehyde intermediate enables the facile and highly efficient covalent immobilization of proteins by a postfunctionalization methodology and the sequential protein patterns provide an easy access to control the identity and dynamic change of proteins presented to cells on demand, thus mediating cell behaviors. This approach provides important opportunities for understanding and controlling cell behavior mediated by proteins, and opens up new avenues for hydrogels in tissue engineering and biotechnology applications. By a photogenerated aldehyde reaction, proteins can be covalently immobilized on hydrogels without any premodification by a facile postfunctionalization methodology. The control of identity and dynamic changes of proteins mediates cell adhesion, proliferation, and migration on the hydrogel. The successful guidance of cell behavior opens up new avenues for tissue engineering and biotechnology applications of hydrogel biomaterials.

A Yolk–Shell Nanoplatform for Gene-Silencing-Enhanced Photolytic Ablation of Cancer


Noninvasive near-infrared (NIR) light responsive therapy is a promising cancer treatment modality; however, some inherent drawbacks of conventional phototherapy heavily restrict its application in clinic. Rather than producing heat or reactive oxygen species in conventional NIR treatment, here a multifunctional yolk–shell nanoplatform is proposed that is able to generate microbubbles to destruct cancer cells upon NIR laser irradiation. Besides, the therapeutic effect is highly improved through the coalition of small interfering RNA (siRNA), which is codelivered by the nanoplatform. In vitro experiments demonstrate that siRNA significantly inhibits expression of protective proteins and reduces the tolerance of cancer cells to bubble-induced environmental damage. In this way, higher cytotoxicity is achieved by utilizing the yolk–shell nanoparticles than treated with the same nanoparticles missing siRNA under NIR laser irradiation. After surface modification with polyethylene glycol and transferrin, the yolk–shell nanoparticles can target tumors selectively, as demonstrated from the photoacoustic and ultrasonic imaging in vivo. The yolk–shell nanoplatform shows outstanding tumor regression with minimal side effects under NIR laser irradiation. Therefore, the multifunctional nanoparticles that combining bubble-induced mechanical effect with RNA interference are expected to be an effective NIR light responsive oncotherapy. A multifunctional yolk–shell nanoplatform is constructed to codeliver energy and small interfering RNA (siRNA) for photoacoustic and ultrasonic imaging guided photolytic cancer treatment. Combining a photothermal agent with low a boiling point liquid facilitates effective near-infrared light absorption to generate microbubbles for inducing a mechanical effect, and the delivered siRNA further enhances the damage to cancer cells, achieving an excellent anticancer effect.

Copper (I) Selenocyanate (CuSeCN) as a Novel Hole-Transport Layer for Transistors, Organic Solar Cells, and Light-Emitting Diodes


The synthesis and characterization of copper (I) selenocyanate (CuSeCN) and its application as a solution-processable hole-transport layer (HTL) material in transistors, organic light-emitting diodes, and solar cells are reported. Density-functional theory calculations combined with X-ray photoelectron spectroscopy are used to elucidate the electronic band structure, density of states, and microstructure of CuSeCN. Solution-processed layers are found to be nanocrystalline and optically transparent (>94%), due to the large bandgap of ≥3.1 eV, with a valence band maximum located at −5.1 eV. Hole-transport analysis performed using field-effect measurements confirms the p-type character of CuSeCN yielding a hole mobility of 0.002 cm2 V−1 s−1. When CuSeCN is incorporated as the HTL material in organic light-emitting diodes and organic solar cells, the resulting devices exhibit comparable or improved performance to control devices based on commercially available poly(3,4-ethylenedioxythiophene):polystyrene sulfonate as the HTL. This is the first report on the semiconducting character of CuSeCN and it highlights the tremendous potential for further developments in the area of metal pseudohalides. Copper (I) selenocyanate is successfully synthesized, studied, and applied as a wide bandgap hole-transporting material in transistors, organic solar cells, and light-emitting diodes, for the first time. Resulting devices exhibit excellent operating characteristics highlighting the tremendous potential of metal pseudohalides as a new class of highly transparent p-type semiconductors.

Metal Doped Core–Shell Metal-Organic Frameworks@Covalent Organic Frameworks (MOFs@COFs) Hybrids as a Novel Photocatalytic Platform


Metal doped core–shell Metal-Organic Frameworks@Covalent Organic Frameworks (MOFs@COFs) are presented as a novel platform for photocatalysis. A palladium (Pd) doped MOFs@COFs in the form of Pd/TiATA@LZU1 shows excellent photocatalytic performance for tandem dehydrogenation and hydrogenation reactions in a continuous-flow microreactor and a batch system, indicating the great potential of the metal doped MOFs@COFs as a multifunctional platform for photocatalysis. Explanations for the performance enhancement are elucidated. An integrated dual-chamber microreactor coupled with the metal doped MOFs@COFs is introduced to demonstrate a concept of an intensified green photochemical process, which can be broadly extended to challenging liquid–gas tandem and cascade reactions. Pd doped core–shell TiATA@LZU1 is fabricated and shows excellent photocatalytic performance for hydrogenation and dehydrogenation reactions in batch and in a newly designed dual-chamber microreactor. This indicates a great promise of metal–organic frameworks@covalent organic frameworks (MOFs@COFs) hybrids as a novel platform for efficient photocatalysis.

Host Exciton Confinement for Enhanced Förster-Transfer-Blend Gain Media Yielding Highly Efficient Yellow-Green Lasers


This paper reports state-of-the-art fluorene-based yellow-green conjugated polymer blend gain media using Förster resonant-energy-transfer from novel blue-emitting hosts to yield low threshold (≤7 kW cm−2) lasers operating between 540 and 590 nm. For poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) (15 wt%) blended with the newly synthesized 3,6-bis(2,7-di([1,1′-biphenyl]-4-yl)-9-phenyl-9H-fluoren-9-yl)-9-octyl-9H–carbazole (DBPhFCz) a highly desirable more than four times increase (relative to F8BT) in net optical gain to 90 cm−1 and 34 times reduction in amplified spontaneous emission threshold to 3 µJ cm−2 is achieved. Detailed transient absorption studies confirm effective exciton confinement with consequent diffusion-limited polaron-pair generation for DBPhFCz. This delays formation of host photoinduced absorption long enough to enable build-up of the spectrally overlapped, guest optical gain, and resolves a longstanding issue for conjugated polymer photonics. The comprehensive study further establishes that limiting host conjugation length is a key factor therein, with 9,9-dialkylfluorene trimers also suitable hosts for F8BT but not pentamers, heptamers, or polymers. It is additionally demonstrated that the host highest occupied and lowest unoccupied molecular orbitals can be tuned independently from the guest gain properties. This provides the tantalizing prospect of enhanced electron and hole injection and transport without endangering efficient optical gain; a scenario of great interest for electrically pumped amplifiers and lasers. Rapid host polaron-pair formation may compete with stimulated emission from guest molecules in blend gain media. This is shown to be especially problematic for poly(9,9-dioctylfluorene-co-benzothiadiazole) F8BT dispersed in blue polyfluorene hosts. Using hosts with more confined excitons allows sufficient delay for efficient F8BT optical gain to occur and yields high performance yellow-green lasers.

Honeycomb-Like Spherical Cathode Host Constructed from Hollow Metallic and Polar Co9S8 Tubules for Advanced Lithium–Sulfur Batteries


The practical application of lithium-sulfur (Li-S) batteries remains remote because of rapid capacity fade caused by the low conductivity of sulfur, dissolution of intermediate lithium polysulfides, severe volumetric expansion, and slow redox kinetics of polysulfide intermediates. Here, to address these obstacles, a new sulfiphilic and highly conductive honeycomb-like spherical cathode host constructed from hollow metallic and polar Co9S8 tubes is designed. Co9S8 can effectively bind polar polysulfides for prolonged cycle life, due to the strong chemisorptive capability for immobilizing the polysulfide species. The hollow structure, as the sulfur host, can further prevent polysulfide dissolution and offer sufficient space to accommodate the necessary volume expansion. Well-aligned tubular arrays provide a conduit for rapid conduction of electrons and Li-ions. More importantly, the experimental results and theoretical calculations show that Co9S8 plays an important catalytic role in improving the electrochemical reaction kinetics. When used as cathode materials for Li–S batteries, the S@Co9S8 composite cathode exhibits high capacity and an exceptional stable cycling life demonstrated by tests of 600 cycles at 1 C with a very low capacity decay rate of only ≈0.026% per cycle. Highly conductive sulfiphilic honeycomb-like spheres constructed from hollow, metallic, and polar Co9S8 tubules are synthesized. Experiment and simulation show that Co9S8 is a polysulfide (PS) immobilizer and electrocatalyst in Li–S batteries. Benefiting from excellent conductivity, strong LiPSs adsorption capability, and high catalytic activity, the S@Co9S8 composite cathode delivers a stable cycle life with a high discharge capacity for Li–S batteries.

Effective and Selective Anti-Cancer Protein Delivery via All-Functions-in-One Nanocarriers Coupled with Visible Light-Responsive, Reversible Protein Engineering


Efficient intracellular delivery of protein drugs and tumor-specific activation of protein functions are critical toward anti-cancer protein therapy. However, an omnipotent protein delivery system that can harmonize the complicated systemic barriers as well as spatiotemporally manipulate protein function is lacking. Herein, an “all-functions-in-one” nanocarrier doped with photosensitizer (PS) is developed and coupled with reactive oxygen species (ROS)-responsive, reversible protein engineering to realize cancer-targeted protein delivery, and spatiotemporal manipulation of protein activities using long-wavelength visible light (635 nm) at low power density (5 mW cm−2). Particularly, RNase A is caged with H2O2-cleavable phenylboronic acid to form 4-nitrophenyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl carbonate (NBC)-modified RNase (RNBC), which is encapsulated in acid-degradable, ketal-crosslinked PEI (KPEI)-based nanocomplexes (NCs) coated with PS-modified hyaluronic acid (HA). Such NCs harmonize the critical processes for protein delivery, wherein HA coating renders NCs with long blood circulation and cancer cell targeting, and KPEI enables endosomal escape as well as acid-triggered intracellular RNBC release. Tumor-specific light irradiation generates H2O2 to kill cancer cells and restore the protein activity, thus achieving synergistic anti-cancer efficacy. It is the first time to photomanipulate protein functions by coupling ROS-cleavable protein caging with PS-mediated ROS generation, and the “all-functions-in-one” nanocarrier represents a promising example for the programmed anti-cancer protein delivery. An “all-functions-in-one” nanocarrier doped with photosensitizers is developed and coupled with reactive oxygen species-responsive, reversible protein engineering to realize cancer-targeted protein delivery and spatiotemporal manipulation of protein activities using long-wavelength visible light at low power density. As such, synergistic anti-cancer efficacy is achieved by combining light-controlled protein therapy and light-assisted photodynamic therapy.

Plasmonic Metasurfaces for Simultaneous Thermal Infrared Invisibility and Holographic Illusion


In 1860s, Gustav Kirchhoff proposed his famous law of thermal radiation, setting a fundamental contradiction between the infrared reflection and thermal radiation. Here, for the first time an ultrathin plasmonic metasurface is proposed to simultaneously produce ultralow specular reflection and infrared emission across a broad spectrum and wide incident angle range by combining the low emission nature of metal and the photonic spin–orbit interaction in spatially inhomogeneous structures. As a proof-of-concept, a phase gradient metasurface composed of sub-wavelength metal gratings is designed and experimentally characterized in the infrared atmosphere window of 8–14 µm, demonstrating an ultralow specular reflectivity and infrared emissivity below 0.1. Furthermore, it is demonstrated that infrared illusion could be generated by the metasurface, enabling not only invisibility for thermal and laser detection, but also multifunctionalities for potential applications. This technology is also scalable across a wide range of electromagnetic spectrum and provides a feasible alternative for surface coating. An all-metallic metasurface that breaks the fundamental limitation set by Gustav Kirchhoff is reported. Compared to previous phase-gradient metamaterials and metasurfaces based on metal-dielectric composites, this technique not only demonstrates for the first time the possibility to realize simultaneous low reflectivity and infrared emission, but also shows dramatic advantages such as high efficiency, broadband operation, easy-fabrication, and multifunction compatibility.

Integration of Phase-Change Materials with Electrospun Fibers for Promoting Neurite Outgrowth under Controlled Release


A temperature-regulated system for the controlled release of nerve growth factor (NGF) to promote neurite outgrowth is reported. The system is based upon microparticles fabricated using coaxial electrospray, with the outer solution containing a phase-change material (PCM) and the inner solution encompassing payload(s). When the temperature is kept below the melting point of the PCM, there is no release due to the extremely slow diffusion through a solid matrix. Upon increasing the temperature to slightly pass the melting point, the encapsulated payload(s) can be readily released from the melted PCM. By leveraging the reversibility of the phase transition, the payload(s) can be released in a pulsatile mode through on/off heating cycles. The controlled release system is evaluated for potential use in neural tissue engineering by sandwiching the microparticles, coloaded with NGF and a near-infrared dye, between two layers of electrospun fibers to form a trilayer construct. Upon photothermal heating with a near-infrared laser, the NGF is released with well-preserved bioactivity to promote neurite outgrowth. By choosing different combinations of PCM, biological effector, and scaffolding material, this controlled release system can be applied to a wide variety of biomedical applications. On-demand release for tissue engineering: Microparticles comprised of a phase-change material, a near-infrared dye, and payload(s) are fabricated using coaxial electrospray. When sandwiched between two layers of electrospun fibers, the payload (e.g., nerve growth factor) can be released upon photothermal heating to promote neurite outgrowth.

Nonlinear Absorption Applications of CH3NH3PbBr3 Perovskite Crystals


Researchers have recently revealed that hybrid lead halide perovskites exhibit ferroelectricity, which is often associated with other physical characteristics, such as a large nonlinear optical response. In this work, the nonlinear optical properties of single crystal inorganic–organic hybrid perovskite CH3NH3PbBr3 are studied. By exciting the material with a 1044 nm laser, strong two-photon absorption-induced photoluminescence in the green spectral region is observed. Using the transmission open-aperture Z-scan technique, the values of the two-photon absorption coefficient are observed to be 8.5 cm GW−1, which is much higher than that of standard two-photon absorbing materials that are industrially used in nonlinear optical applications, such as lithium niobate (LiNbO3), LiTaO3, KTiOPO4, and KH2PO4. Such a strong two-photon absorption effect in CH3NH3PbBr3 can be used to modulate the spectral and spatial profiles of laser pulses, as well as to reduce noise, and can be used to strongly control the intensity of incident light. In this study, the superior optical limiting, pulse reshaping, and stabilization properties of CH3NH3PbBr3 are demonstrated, opening new applications for perovskites in nonlinear optics. The two-photon absorption properties of CH3NH3PbBr3 are investigated by exciting the material with a 1044 nm laser. Such a strong two-photon absorption effect can be used to modulate the spectral and spatial profiles of laser pulses. In this study, the superior optical limiting, pulse reshaping, and stabilization properties of CH3NH3PbBr3 are demonstrated.

2D or Not 2D: Strain Tuning in Weakly Coupled Heterostructures


A route to realize strain engineering in weakly bonded heterostructures is presented. Such heterostructures, consisting of layered materials with a pronounced bond hierarchy of strong and weak bonds within and across their building blocks respectively, are anticipated to grow decoupled from each other. Hence, they are expected to be unsuitable for strain engineering as utilized for conventional materials which are strongly bonded isotropically. Here, it is shown for the first time that superlattices of layered chalcogenides (Sb2Te3/GeTe) behave neither as fully decoupled two-dimensional (2D) materials nor as covalently bonded three-dimensional (3D) materials. Instead, they form a novel class of 3D solids with an unparalleled atomic arrangement, featuring a distribution of lattice constants, which is tunable. A map to identify further material combinations with similar characteristic is given. It opens the way for the design of a novel class of artificial solids with unexplored properties. A strain engineering pathway in weakly bonded heterostructures consisting of layered chalcogenide materials is established. Such heterostructures behave neither as fully decoupled two-dimensional materials nor as covalently bonded materials. Thus, a novel class of three-dimensional solids featuring a tunable distribution of lattice constants is formed. A map to identify further material combinations with similar characteristic is given.

Bifunctional Heterostructure Assembly of NiFe LDH Nanosheets on NiCoP Nanowires for Highly Efficient and Stable Overall Water Splitting


3D hierarchical heterostructure NiFe LDH@NiCoP/NF electrodes are prepared successfully on nickel foam with special interface engineering and synergistic effects. This research finds that the as-prepared NiFe LDH@NiCoP/NF electrodes have a more sophisticated inner structure and intensive interface than a simple physical mixture. The NiFe LDH@NiCoP/NF electrodes require an overpotential as low as 120 and 220 mV to deliver 10 mA cm−2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 m KOH, respectively. Tafel and electrochemical impedance spectroscopy further reveal a favorable kinetic during electrolysis. Specifically, the NiFe LDH@NiCoP/NF electrodes are simultaneously used as cathode and anode for overall water splitting, which requires a cell voltage of 1.57 V at 10 mA cm−2. Furthermore, the synergistic effect of the heterostructure improves the structural stability and promotes the generation of active phases during HER and OER, resulting in excellent stability over 100 h of continuous operation. Moreover, the strategy and interface engineering of the introduced heterostructure can also be used to prepare other bifunctional and cost-efficient electrocatalysts for various applications. As-synthesized NiFe layered double hydroxide (LDH)@NiCoP/Nickel foam (NF) electrodes exhibit excellent activity and stability for both hydrogen evolution reaction and oxygen evolution reaction owing to special interface engineering and synergistic effects. It is further used for overall water splitting with a cell voltage of 1.57 V and an outstanding stability for 100 h.

2D Layered Material-Based van der Waals Heterostructures for Optoelectronics


Van der Waals heterostructures (vdWHs) based on 2D layered materials with selectable materials properties pave the way to integration at the atomic scale, which may give rise to fresh heterostructures exhibiting absolutely novel physics and versatility. This feature article reviews the state-of-the-art research activities that focus on the 2D vdWHs and their optoelectronic applications. First, the preparation methods such as mechanical transfer and chemical vapor deposition growth are comprehensively outlined. Then, unique energy band alignments generated in 2D vdWHs are introduced. Furthermore, this feature article focuses on the applications in light-emitting diodes, photodetectors, and optical modulators based on 2D vdWHs with novel constructions and mechanisms. The recently reported novel constructions of the devices are introduced in three primary aspects: light-emitting diodes (such as single defect light-emitting diodes, circularly polarized light emission arising from valley polarization), photodetectors (such as photo-thermionic, tunneling, electrolyte-gated, and broadband photodetectors), and optical modulators (such as graphene integrated with silicon technology and graphene/hexagonal boron nitride (hBN) heterostructure), which show promising applications in the next-generation optoelectronics. Finally, the article provides some conclusions and an outlook on the future development in the field. van der Waals heterostructures (VdWHs) have experienced a booming development in recent years. In this feature article, preparation methods, electronic and optical properties, and applications in optoelectronics of vdWHs are presented.

Photoresponsive Sponge-Like Coating for On-Demand Liquid Release


Many publications report on stimuli responsive coatings, but only a few on the controlled release of species in order to change the coating surface properties. A sponge-like coating that is able to release and absorb a liquid upon exposure to light has been developed. The morphology of the porous coating is controlled by the smectic liquid crystal properties of the monomer mixture prior to its polymerization, and homeotropic order is found to give the largest contraction. The fast release of the liquid can be induced by a macroscopic contraction of the coating caused by a trans to cis conversion of a copolymerized azobenzene moiety. The liquid secretion can be localized by local light exposure or by creating a surface relief. The uptake of liquid proceeds by stimulating the back reaction of the azo compound by exposure at higher wavelength or by thermal relaxation. The surface forces of the sponge-like coating in contact with an opposing surface can be controlled by light-induced capillary bridging revealing that the controlled release of liquid gives access to tunable adhesion. A photosponge consisting of a porous liquid crystal network with smectic molecular order, crosslinked with an azobenzene molecule is reported. The pores are filled with liquid cyanobiphenyl. UV light irradiation shrinks the network, resulting in liquid secretion by the coating, while visible-light irradiation triggers reabsorption of the liquid. The coating regulates by light-induced adhesion and friction at its surface.

Inch-Size Single Crystal of a Lead-Free Organic–Inorganic Hybrid Perovskite for High-Performance Photodetector


Large-size crystals of organic–inorganic hybrid perovskites (e.g., CH3NH3PbX3, X = Cl, Br, I) have gained wide attention since their spectacular progress on optoelectronic technologies. Although presenting brilliant semiconducting properties, a serious concern of the toxicity in these lead-based hybrids has become a stumbling block that limits their wide-scale applications. Exploring lead-free hybrid perovskite is thus highly urgent for high-performance optoelectronic devices. Here, a new lead-free perovskite hybrid (TMHD)BiBr5 (TMHD = N,N,N,N-tetramethyl-1,6-hexanediammonium) is prepared from facile solution process. Emphatically, inch-size high-quality single crystals are successfully grown, the dimensions of which reach up to 32 × 24 × 12 mm3. Furthermore, the planar arrays of photodetectors based on bulk lead-free (TMHD)BiBr5 single crystals are first fabricated, which shows sizeable on/off current ratios (≈103) and rapid response speed (τrise = 8.9 ms and τdecay = 10.2 ms). The prominent device performance of (TMHD)BiBr5 strongly underscores the lead-free hybrid perovskite single crystals as promising material candidates for optoelectronic applications. A new lead-free perovskite hybrid (TMHD)BiBr5 (TMHD = N,N,N,N-Tetramethyl-1,6-hexanediammonium) is prepared from solution and high-quality inch-size single crystals are successfully grown with dimensions up to 32 × 24 × 12 mm3. Moreover, planar arrays of photodetectors based on bulk (TMHD)BiBr5 single-crystal are first fabricated, which show prominent photodetection performance.

Functionalized Gold Nanoclusters Identify Highly Reactive Oxygen Species in Living Organisms


Surface engineering of nanomaterials allows fine tuning of their interactions with biological systems, and thus can benefit their applications in monitoring intracellular events. Herein, the facile synthesis of ligand-functionalized gold nanoclusters (AuNCs) as intracellular probes targeting highly reactive oxygen species (hROS, such as •OH, ClO−, and ONOO−) is demonstrated. Selected ligands such as quaternary ammonium and oligopeptides are utilized to modulate the surface chemistry of AuNCs. It is shown that AuNCs decorated with the cell-penetrating oligoarginine peptide facilitate cellular uptake and intracellular imaging of hROS in living cells and the zebrafish, with high stability and selectivity. A highly reactive oxygen species (hROS) assay in living organisms based on one-step synthesis of functionalized gold nanoclusters (AuNCs) is reported, allowing imaging-guided sensing of hROS including •OH, ClO−, and ONOO− with good biocompability, efficient internalization, and high optical stability. This strategy avoids the complex postmodification of AuNCs and can extend to other kinds of AuNCs for biological applications.

Synthesis of Predesigned Ferroelectric Liquid Crystals and Their Applications in Field-Sequential Color Displays


A series of low transition temperature and fast response chiral smectic C (SmC*) liquid crystals is designed and synthesized. The phase transition behaviors and electrooptical properties of the synthesized compounds are investigated and compared with reported values. The ferroelectric phase of the liquid crystals is characterized by means of differential scanning calorimetry, polarizing optical microscopy, wide-angle X-ray scattering (WAXS), and electrooptical measurements. The wide SmC* phase is achieved via the induction of achiral trisiloxane and a chiral methyl-lateral substituent onto the terminuses of the molecules. The optimized packing arrangement model is studied based on the exceptionally high apparent tilt angles (≈41°) and smectic layer spacing observed using WAXS. A fast response time of 0.3 ms in an electric field of 10 V µm−1 provides an opportunity to use the synthesized materials for field-sequential color liquid crystal displays (FSCLCDs). An FSCLCD sample cell is fabricated using the synthesized ferroelectric liquid crystals via a red (R), green (G), and blue (B) backlight. A color-frame frequency of more than 500 Hz (i.e., a frame frequency more than 166 Hz) is achieved. As a single material liquid crystal display cell, the synthesized ferroelectric liquid crystals show great performances at room temperature. Target image of National Cheng Kung University (NCKU) emblem is displayed using a newly fabricated field-sequential color cell. Each field image (red, green, and blue) is driving at 500 Hz (each color-frame frequency is 166 Hz).

Stable White Light-Emitting Biocomposite Films


The demonstration of reliable and stable white light-emitting diodes (LEDs) is one of the main technological challenges of the LED industry. This is usually accomplished by incorporation of light-emitting rare-earth elements (REEs) compounds within an external polymeric coating of a blue LED allowing the generation of white light. However, due to both environmental and cost issues, the development of low-cost REE-free coatings, which exhibit competitive performance compared to conventional white LED is of great importance. In this work, the formation of an REE-free white LED coating is demonstrated. This biocomposite material, composed of biological (crystalline nanocellulose and porcine gastric mucin) and organic (light-emitting dyes) compounds, exhibits excellent optical and mechanical properties as well as resistance to heat, humidity, and UV radiation. The coating is further used to demonstrate a working white LED by incorporating it within a commercial blue LED. Light-emitting films made out of biocomposite materials are demonstrated. These comprise of dyes incorporated in proteins, hosted in a crystalline nanocellulose matrix. The films do not contain rare-earth materials and exhibit excellent optical and mechanical properties as well as resistance to heat, humidity, and UV radiation. The biocomposite is utilized to form a stable working white light-emitting diode.

Hybrid Silver Nanowire and Graphene-Based Solution-Processed Transparent Electrode for Organic Optoelectronics


The research on transparent conductive electrodes is in rapid ascent in order to respond to the requests of novel optoelectronic devices. The synergic coupling of silver nanowires (AgNWs) and high-quality solution-processable exfoliated graphene (EG) enables an efficient transparent conductor with low-surface roughness of 4.6 nm, low sheet resistance of 13.7 Ω sq−1 at high transmittance, and superior mechanical and chemical stabilities. The developed AgNWs–EG films are versatile for a wide variety of optoelectronics. As an example, when used as a bottom electrode in organic solar cell and polymer light-emitting diode, the devices exhibit a power conversion efficiency of 6.6% and an external quantum efficiency of 4.4%, respectively, comparable to their commercial indium tin oxide counterparts. Solution-processed hybrid transparent electrodes are developed by spray-coating of silver nanowires and exfoliated graphene. Mechanical, chemical, and electronic properties of the silver nanowire network are improved upon the coverage of graphene layer. Uniform morphology, low surface roughness, and high conductivity at high transmittance of the film contribute to highly efficient optoelectronic devices, such as organic solar cells and polymer light-emitting diode.

Light-Driven Rotation of Plasmonic Nanomotors


Colloidal metal nanocrystals exhibit distinct plasmonic resonances that can greatly enhance optical forces and torques. This article highlights the recent application of such particles as light-driven rotary motors at the nanoscale. By using laser tweezers, it is possible to achieve unprecedented rotation performance in solution, providing a variety of exciting possibilities for applications ranging from nanomechanics to biochemical sensing. Recent developments in this emerging field are discussed, and the physics behind the rotation mechanism, the Brownian dynamics, and the photothermal heating effects influencing the performance of the plasmonic nanomotors are introduced. Possible applications, open questions, and interesting future developments are also discussed. Colloidal plasmonic nanostructures are promising candidates for constructing high-performance rotary nanomotors that can be propelled by light. Such plasmonic nanomotors controlled by laser tweezers hold great potential in providing a powerful nano-optomechanical platform for various applications. This feature article focuses on recent development of colloidal plasmonic nanomotors with emphasis on their rotation control, Brownian dynamics, photothermal effects, and molecular sensing applications.

Organic Solar Cells: Microcavity Structure Provides High-Performance (>8.1%) Semitransparent and Colorful Organic Photovoltaics (Adv. Funct. Mater. 7/2018)


In article 1703398, Jong-Hong Lu, Chih-Ping Chen and, co-workers demonstrate a Ag/ITO/Ag based microcavity (MC) structure for colorful organic photovoltaics applications. OPVs with an ultra-wide vivid color-gamut (blue, green, yellow-green, yellow, orange, and red), with PCEs as high as 8.2% for the yellow-green [CIE 1931: (0.364, 0.542)] device with a highest transmittance of 17.3% at 561 nm are demonstrated.

Actuators: Bioinspired Anisotropic Hydrogel Actuators with On–Off Switchable and Color-Tunable Fluorescence Behaviors (Adv. Funct. Mater. 7/2018)


Some animals such as octopuses not only can move, but also can tune their body colors to camouflage or communicate in specific surroundings. Inspired by that, an anisotropic polymeric hydrogel actuator with on-off switchable and color-tunable fluorescence behaviors is developed by Jiawei Zhang, Tao Chen, and co-workers in article number 1704568, which integrates color-changing and complex shape deformation abilities in one system.

Monolayer Semiconductors: Electron Field Emission of Geometrically Modulated Monolayer Semiconductors (Adv. Funct. Mater. 7/2018)


Recently, engineering of 2D semiconductors has been widely highlighted for diverse potential applications. In article number 1706113, Yi-Hsien Lee and co-workers report highly efficient and stable electron emission of monolayer semiconductors in low turn-on electric fields. Geometrical control by integrating 1D nanostructure arrays for geometrical modulation is key to this achievement.

Perovskite Solar Cells: Passivated Perovskite Crystallization via g-C3N4 for High-Performance Solar Cells (Adv. Funct. Mater. 7/2018)


In article 1705875, Zhao-Kui Wang, Peng-Fei Fang, Liang-Sheng Liao, and co-workers incorporate graphitic carbon nitride (g-C3N4) into the perovskite layer of perovskite solar cells. The additive retards the crystallization rate, improving crystalline quality and reducing the intrinsic defect density of the perovskite film. Increasing the fill factor from 0.65 to 0.74 yields a stable device with a power conversion efficiency of 19.49%.

Masthead: (Adv. Funct. Mater. 7/2018)


Contents: (Adv. Funct. Mater. 7/2018)


Recent Progress in MOF-Derived, Heteroatom-Doped Porous Carbons as Highly Efficient Electrocatalysts for Oxygen Reduction Reaction in Fuel Cells


Currently, developing nonprecious-metal catalysts to replace Pt-based electrocatalysts in fuel cells has become a hot topic because the oxygen reduction reaction (ORR) in fuel cells often requires platinum, a precious metal, as a catalyst, which is one of the major hurdles for commercialization of the fuel cells. Recently, the newly emerging metal-organic frameworks (MOFs) have been widely used as self-sacrificed precursors/templates to fabricate heteroatom-doped porous carbons. Here, the recent progress of MOF-derived, heteroatom-doped porous carbon catalysts for ORR in fuel cells is systematically reviewed, and the synthesis strategies for using different MOF precursors to prepare heteroatom-doped porous carbon catalysts, including the direct carbonization of MOFs, MOF and heteroatom source mixture carbonization, and MOF-based composite carbonization are summarized. The emphasis is placed on the precursor design of MOF-derived metal-free catalysts and transition-metal-doped carbon catalysts because the MOF precursors often determine the microstructures of the derived porous carbon catalysts. The discussion provides a useful strategy for in situ synthesis of heteroatom-doped carbon ORR electrocatalysts by rationally designing MOF precursors. Due to the versatility of MOF structures, MOF-derived porous carbons not only provide chances to develop highly efficient ORR electrocatalysts, but also broaden the family of nanoporous carbons for applications in supercapacitors and batteries. Metal-organic frameworks (MOFs) have emerged as promising precursors to synthesize metal-free or nonprecious-metal-doped porous carbon catalysts for the oxygen reduction reaction (ORR) due to their unique advantages. Here, the recent progress of MOF-derived carbon catalysts in ORR applications is systematically reviewed and the strategies to develop highly efficient carbon electrocatalysts by rationally designing MOF precursors are summarized.

Microcavity Structure Provides High-Performance (>8.1%) Semitransparent and Colorful Organic Photovoltaics


High-performance colored aesthetic semitransparent organic photovoltaics (OPVs) featuring a silver/indium tin oxide/silver (Ag/ITO/Ag) microcavity structure are prepared. By precisely controlling the thickness of the ITO layer, OPV devices exhibiting high transparency and a wide and high-purity color gamut are obtained: blue (B), green (G), yellow-green (YG), yellow (Y), orange (O), and red (R). The power conversion efficiencies (PCEs) of the G, YG, and Y color devices are greater than 8% (AM 1.5G irradiation, 100 mW cm−2) with maximum transmittances (TMAX) of greater than 14.5%. An optimized PCE of 8.2% was obtained for the YG OPV [CIE 1931 coordinates: (0.364, 0.542)], with a value of TMAX of 17.3% (at 561 nm). As far as it is known, this performance is the highest ever reported for a transparent colorful OPV. Such high transparency and desired transmitted colors, which can perspective see the clear images, suggest great potential for use in building-integrated photovoltaic applications. High-performance colored aesthetic semitransparent organic photovoltaics (OPVs) featuring a silver/indium tin oxide/silver microcavity structure are demonstrated. Colored OPVs of high purity and a wide color gamut are obtained: blue, green, yellow-green, yellow, orange, and red. The highest power conversion efficiency was 8.2% for the yellow-green device, with CIE 1931 coordinates of (0.364, 0.542) and a transmittance of 17.3% at 561 nm.

Bioinspired Anisotropic Hydrogel Actuators with On–Off Switchable and Color-Tunable Fluorescence Behaviors


An effective approach to develop a novel macroscopic anisotropic bilayer hydrogel actuator with on–off switchable fluorescent color-changing function is reported. Through combining a collapsed thermoresponsive graphene oxide-poly(N-isopropylacrylamide) (GO-PNIPAM) hydrogel layer with a pH-responsive perylene bisimide-functionalized hyperbranched polyethylenimine (PBI-HPEI) hydrogel layer via macroscopic supramolecular assembly, a bilayer hydrogel is obtained that can be tailored and reswells to form a 3D hydrogel actuator. The actuator can undergo complex shape deformation caused by the PNIPAM outside layer, then the PBI-HPEI hydrogel inside layer can be unfolded to trigger the on–off switch of the pH-responsive fluorescence under the green light irradiation. This work will inspire the design and fabrication of novel biomimetic smart materials with synergistic functions. A macroscopic anisotropic bilayer hydrogel actuator integrating complex shape-changing and fluorescent color-changing functions is explored. The thermoresponsive shape deformation can trigger the on–off switch of the pH-responsive fluorescence change, which will inspire the design of novel biomimetic smart materials with synergistic functions.

Electron Field Emission of Geometrically Modulated Monolayer Semiconductors


Electron field emission, electrons emitted from solid surfaces under high electric field, offers significant scientific interests in materials sciences and potential optoelectronics applications. 2D atomic layers, such as MoS2, exhibit fascinating properties for diverse applications in next-generation nanodevices and rich physical phenomena for fundamental research. However, the study on field emission of semiconducting monolayers is lacking owing to its low efficiency and stability of electron emission. Here, electron field emission of the geometrically modulated monolayer semiconductors suspended with 1D nanoarrays is demonstrated. Chemical vapor deposition synthesis of two prototype monolayers of transition metal dichalcogenides (TMD), MoS2 and MoSe2, is presented and their diverse band structures offer an ideal platform to explore the fundamental process of the electron emission in the TMD. Geometrical modulation and charge transfer of the semiconducting monolayers can be significantly tuned with the structural suspension with the 1D ZnO nanoarrays. Possible mechanisms on the enhanced electron emission of the 2D monolayers are discussed. With geometrical control of the monolayers, a highly efficient and stable electron emission of TMD monolayers is achieved in low turn-on electric fields, enabling applications on electrons sources and opening a new avenue toward geometrically tuned atomic layers. Electron field emission generated from the geometrically modulated MoS2 and MoSe2 monolayers is demonstrated. Geometrical modulation and charge transfer of the monolayers can be significantly tuned using structural suspension and the 1D nanoarrays. With geometrical control of the monolayers, a highly efficient and stable electron emission of different monolayers is achieved in low turn-on electric fields.

Passivated Perovskite Crystallization via g-C3N4 for High-Performance Solar Cells


Organometallic halide perovskite films with good surface morphology and large grain size are desirable for obtaining high-performance photovoltaic devices. However, defects and related trap sites are generated inevitably at grain boundaries and on surfaces of solution-processed polycrystalline perovskite films. Seeking facial and efficient methods to passivate the perovskite film for minimizing defect density is necessary for further improving the photovoltaic performance. Here, a convenient strategy is developed to improve perovskite crystallization by incorporating a 2D polymeric material of graphitic carbon nitride (g-C3N4) into the perovskite layer. The addition of g-C3N4 results in improved crystalline quality of perovskite film with large grain size by retarding the crystallization rate, and reduced intrinsic defect density by passivating charge recombination centers around the grain boundaries. In addition, g-C3N4 doping increases the film conductivity of perovskite layer, which is beneficial for charge transport in perovskite light-absorption layer. Consequently, a champion device with a maximum power conversion efficiency of 19.49% is approached owing to a remarkable improvement in fill factor from 0.65 to 0.74. This finding demonstrates a simple method to passivate the perovskite film by controlling the crystallization and reducing the defect density. Graphitic carbon nitride (g-C3N4) is incorporated into the perovskite precursor solution to modify the perovskite film by controlling the perovskite crystallization, reducing the intrinsic defect density, and improving the film conductivity. As a result, a champion device with a maximum power conversion efficiency of 19.49% is approached.

Coordinating Thermogel for Stem Cell Spheroids and Their Cyto-Effectiveness


A polymer (mP) with thermogelling and metal coordinating properties is prepared by pyridine-dicarboxylate (PDC) connected poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) triblock copolymers. Tonsil-derived mesenchymal stem cells (TMSCs) are incorporated in the mP hydrogel by increasing the temperature of the cell-suspended aqueous mP solution to 37 °C. The TMSCs are randomly embedded in the in situ formed hydrogel at first; however, they aggregated to form live cell spheroids on day 7. In contrast, the spheroid formation is blocked in the Fe3+-incorporating mP thermogel. Compared with the conventional 2D-cultured stem cells, the stem cell spheroid in the 3D mP culture system exhibits significantly enhanced stemness biomarkers, angiogenic biomarkers, and anti-inflammatory biomarkers in the growth medium. In addition, the stem cell spheroid exhibits significantly greater biomarker expression for osteogenic, chondrogenic, and adipogenic differentiations than the stem cells cultured in the 2D system in each induction medium. This study suggests that a simple injection of stem cells suspended in the current aqueous mP solution can lead to the spontaneous formation of stem cell spheroids with excellent multipotency and retention in the in situ formed thermogel, and thus opens a direct injectable method for the application of the stem cells at a target site. Stem cell spheroids formation is controlled by Fe3+ in a metal coordinating thermogel, where the stem cell spheroid not only exhibits significantly enhanced biomarker expression for stemness, angiogenicity, and anti-inflammation, but also its multipotency toward osteogenic, chondrogenic, and adipogenic differentiation is much more effective than the traditional 2D-cultured stem cells.

Controlling Spatiotemporal Mechanics of Supramolecular Hydrogel Networks with Highly Branched Cucurbit[8]uril Polyrotaxanes


Attempts to rationally tune the macroscopic mechanical performance of supramolecular hydrogel networks through noncovalent molecular interactions have led to a wide variety of supramolecular materials with desirable functions. While the viscoelastic properties are dominated by temporal hierarchy (crosslinking kinetics), direct mechanistic studies on spatiotemporal control of supramolecular hydrogel networks, based on host–guest chemistry, have not yet been established. Here, supramolecular hydrogel networks assembled from highly branched cucurbit[8]uril-threaded polyrotaxanes (HBP-CB[8]) and naphthyl-functionalized hydroxyethyl cellulose (HECNp) are reported, exploiting the CB[8] host–guest complexation. Mechanically locking CB[8] host molecules onto a highly branched hydrophilic polymer backbone, through selective binary complexation with viologen derivatives, dramatically increases the solubility of CB[8]. Additionally, the branched architecture enables tuning of material dynamics of the supramolecular hydrogel networks via both topological (spatial hierarchy) and kinetic (temporal hierarchy) control. Relationship between macroscopic properties (time- and temperature-dependent rheological properties, thermal stability, and reversibility), spatiotemporal hierarchy, and chain dynamics of the highly branched polyrotaxane hydrogel networks is investigated in detail. Such kind of tuning of material mechanics through spatiotemporal hierarchy improves our understanding of the challenging relationship between design of supramolecular polymeric materials and their complex viscoelasticity, and also highlights a facile strategy to engineer dynamic supramolecular materials. Formation of hydrogel networks through a two-component strategy from highly branched CB[8]-threaded polyrotaxanes, exploiting the dynamic CB[8]-based heteroternary host–guest complexation. The branched architecture enables tuning of the hydrogel network dynamics via both topological (spatial hierarchy) and kinetic (temporal hierarchy) control.

Orthorhombic Ti2O3: A Polymorph-Dependent Narrow-Bandgap Ferromagnetic Oxide


Magnetic semiconductors are highly sought in spintronics, which allow not only the control of charge carriers like in traditional electronics, but also the control of spin states. However, almost all known magnetic semiconductors are featured with bandgaps larger than 1 eV, which limits their applications in long-wavelength regimes. In this work, the discovery of orthorhombic-structured Ti2O3 films is reported as a unique narrow-bandgap (≈0.1 eV) ferromagnetic oxide semiconductor. In contrast, the well-known corundum-structured Ti2O3 polymorph has an antiferromagnetic ground state. This comprehensive study on epitaxial Ti2O3 thin films reveals strong correlations between structure, electrical, and magnetic properties. The new orthorhombic Ti2O3 polymorph is found to be n-type with a very high electron concentration, while the bulk-type trigonal-structured Ti2O3 is p-type. More interestingly, in contrast to the antiferromagnetic ground state of trigonal bulk Ti2O3, unexpected ferromagnetism with a transition temperature well above room temperature is observed in the orthorhombic Ti2O3, which is confirmed by X-ray magnetic circular dichroism measurements. Using first-principles calculations, the ferromagnetism is attributed to a particular type of oxygen vacancies in the orthorhombic Ti2O3. The room-temperature ferromagnetism observed in orthorhombic-structured Ti2O3, demonstrates a new route toward controlling magnetism in epitaxial oxide films through selective stabilization of polymorph phases. Epitaxial Ti2O3 (Ti3+: 3d1) thin films on Sapphire are systematically investigated, and, more interestingly, a new stabilized orthorhombic phase is fabricated. Depending on extensive physical and optical properties measurements, the new orthorhombic Ti2O3 is confirmed to be a narrow band-gap (≈0.11 eV) n-type semiconductor with emergent ferromagnetism, while the corundum Ti2O3 is a p-type antiferromagnetic semiconductor with a trigonal structure.

Directional and Continuous Transport of Gas Bubbles on Superaerophilic Geometry-Gradient Surfaces in Aqueous Environments


Due to the direct and sufficient contacting with the aqueous environment, the directional and continuous transport of gas bubbles on open surface without energy input will advance a variety of applications in heat transfer, selective aeration, water electrolysis, etc. Unfortunately, the behaviors of gas bubbles in aqueous environment are mainly dominated by the buoyancy moving gas bubbles upward, resulting in their difficult manipulation. Therefore, realizing the directional and continuous transport of gas bubbles on open surface still remains a great challenge. Herein, a novel strategy integrating the superaerophilic wettability with geometry-gradient structure is proposed, which can engender high driving force and low hysteresis resistance force acting on the gas bubbles. In experiment, these fabricated superaerophilic geometry-gradient polyethylene surfaces demonstrate distinguished performance of directionally and continuously transporting gas bubbles on open surfaces without energy input. In addition, the antibuoyancy bubble transportation device and the underwater bubble microreactor are successfully prepared in this manuscript, both of which illustrate the feasibility in the applications of complex environment and gas-related fields. It can be envisioned that this study will promote the understanding and development of underwater functional superwettability materials to achieve the directional and continuous transport of gas bubbles on the open surface. Superaerophilic geometry-gradient surfaces can be facilely fabricated by utilizing the techniques of laser cutting, sandpaper rubbing, and surface superhydrophobic coating. Benefiting from the superaerophilic wettability and geometry-gradient morphology, the prepared surfaces are facilitated with low hysteresis resistance force and high driving force, which can accomplish the directional and continuous transport of underwater gas bubbles.

Tunable Förster Resonance Energy Transfer in Colloidal Nanoparticles Composed of Polycaprolactone-Tethered Donors and Acceptors: Enhanced Near-Infrared Emission and Compatibility for In Vitro and In Vivo Bioimaging


A near-infrared (NIR) fluorescent donor/acceptor (D/A) nanoplatform based on Förster resonance energy transfer is important for applications such as deep-tissue bioimaging and sensing. However, previously reported D/A nanoparticles (NPs) often show limitations such as aggregation-induced fluorescence quenching and poor interfacial compatibility that reduces the efficiency of the energy transfer and also leads to leaching of the small molecular fluorophores from the NP matrix. Here highly NIR-fluorescent D/A NPs with a fluorescence quantum yield as high as 46% in the NIR region (700–850 nm) and robust optical stability are reported. The hydrophobic core of each NP is composed of donor and acceptor moieties both of which are tethered with polycaprolactone (PCL), while the hydrophilic corona is composed of poly[oligo(ethylene glycol) methyl ether methacrylate] to offer colloidal stability and “stealthy” effect in aqueous media. The PCL matrix in each colloidal NP not only offers biocompatibility and biodegradability but also minimizes the aggregation-caused fluorescence quenching of D/A chromophores and prevents the leakage of the NIR fluorophores from the NPs. In vivo imaging using these NIR NPs in live mice shows contrast-enhanced imaging capability and efficient tumor-targeting through enhanced permeability and retention effect. Near-infrared fluorescent colloidal nanoparticles composed of polycaprolactone-tethered donors/acceptors show efficient Förster resonance energy transfer and enhanced fluorescence quantum yield as high as 46% in the NIR region (700–850 nm) and a large Stokes shift of 233 nm. The good biocompatibility, robust structural integrity, and bright near-infrared fluorescence make them promising for bioimaging applications.

Additive-Morphology Interplay and Loss Channels in “All-Small-Molecule” Bulk-heterojunction (BHJ) Solar Cells with the Nonfullerene Acceptor IDTTBM


Achieving efficient bulk-heterojunction (BHJ) solar cells from blends of solution-processable small-molecule (SM) donors and acceptors is proved particularly challenging due to the complexity in obtaining a favorable donor–acceptor morphology. In this report, the BHJ device performance pattern of a set of analogous, well-defined SM donors—DR3TBDTT (DR3), SMPV1, and BTR—used in conjunction with the SM acceptor IDTTBM is examined. Examinations show that the nonfullerene “All-SM” BHJ solar cells made with DR3 and IDTTBM can achieve power conversion efficiencies (PCEs) of up to ≈4.5% (avg. 4.0%) when the solution-processing additive 1,8-diiodooctane (DIO, 0.8% v/v) is used in the blend solutions. The figures of merit of optimized DR3:IDTTBM solar cells contrast with those of “as-cast” BHJ devices from which only modest PCEs <1% can be achieved. Combining electron energy loss spectrum analyses in scanning transmission electron microscopy mode, carrier transport measurements via “metal-insulator-semiconductor carrier extraction” methods, and systematic recombination examinations by light-dependence and transient photocurrent analyses, it is shown that DIO plays a determining role—establishing a favorable lengthscale for the phase-separated SM donor–acceptor network and, in turn, improving the balance in hole/electron mobilities and the carrier collection efficiencies overall. A set of structurally analogous small-molecule (SM) donors with distinct side-chain manifolds shows significant differences in their performance patterns in bulk-heterojunction (BHJ) devices with the nonfullerene SM acceptor IDTTBM. Reducing the lengthscale of the phase-separated network between donor and acceptor effectively suppresses nongeminate recombination in the BHJ active layers and improves the carrier mobility balance.

Room-Temperature-Operated Ultrasensitive Broadband Photodetectors by Perovskite Incorporated with Conjugated Polymer and Single-Wall Carbon Nanotubes


In this work, room-temperature-operated ultrasensitive solution-processed perovskite photodetectors (PDs) with near infrared (NIR) photoresponse are reported. In order to enable perovskite PDs possessing extended NIR photoresponse, novel n-type low bandgap conjugated polymer, poly[(N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalene diimide-2,6-diyl) (2,5-dioctyl-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione-5,5′-diyl)] (NDI-DPP), which has strong absorption in the NIR region, is developed and then employed in perovskite PDs. By the formation of type II band alignment between NDI-DPP with single-wall carbon nanotubes (SWCNTs), the NIR absorption of NDI-DPP is exploited, which contributes to the NIR photoresponse for the perovskite PDs, where perovskite is incorporated with NDI-DPP and SWCNTs as well. In addition, SWCNTs incorporated with perovskite active layer can offer the percolation pathways for high charge-carrier mobility, which tremendously boosts the charge transfer in the photoactive layer, and consequently improves the photocurrent in the visible region. As a result, the perovskite PDs exhibit the responsivities of ≈400 and ≈150 mA W−1 and the detectivities of over 6 × 1012 Jones (1 Jones = 1 cm Hz1/2 W−1) and over 2 × 1012 Jones in the visible and NIR regions, respectively. This work reports the development of perovskite PDs with NIR photoresponse, which is terrifically beneficial for the practical applications of perovskite PDs. Room temperature operated uncooled broadband ultrasensitive photodetectors with the responsivities of 400 and 150 mA W-1 and the detectivities of over 6 × 1012 and 2 × 1012 Jones in the visible and near infrared regions are realized by utilization of perovskite incorporated with novel n-type low-bandgap conjugated polymer and single-wall carbon nanotubes through type II band alignment.

A Self-Healable, Highly Stretchable, and Solution Processable Conductive Polymer Composite for Ultrasensitive Strain and Pressure Sensing


Mimicking human skin's functions to develop electronic skins has inspired tremendous efforts in design and synthesis of novel soft materials with simplified fabrication methods. However, it still remains a great challenge to develop electronically conductive materials that are both stretchable and self-healable. Here it is demonstrated that a ternary polymer composite comprised of polyaniline, polyacrylic acid, and phytic acid can exhibit high stretchability (≈500%) and excellent self-healing properties. The polymer composite with optimized composition shows an electrical conductivity of 0.12 S cm−1. On rupture, both electrical and mechanical properties can be restored with ≈99% efficiency in a 24 h period, which is enabled by the dynamic hydrogen bonding and electrostatic interactions. It is further shown that this composite is both strain and pressure sensitive, and therefore can be used for fabricating strain and pressure sensors to detect a variety of mechanical deformations with ultrahigh sensitivity. The sensitivity and sensing range are the highest among all of the reported self-healable piezoresistive pressure sensors and even surpass most flexible mechanical sensors. Notably, this composite is prepared via a solution casting process, which potentially allows for large-area, low-cost fabrication electronic skins. Artificial skin: mimicking human skin's functions to develop skin-like electronics has inspired tremendous efforts in developing novel soft materials. It is shown that a ternary polymer composite comprised of polyaniline, polyacrylic acid, and phytic acid can exhibit high stretchability (≈500%) and excellent self-healing properties for electronic skin applications with ultrahigh sensitivity.

Nanocrystalline Perovskite Hybrid Photodetectors with High Performance in Almost Every Figure of Merit


Conversion of photon into electron is a phenomenon of great importance in nature. Photodetectors based on this principle have immense potential applications at the frontiers of both scientific and industrial communities, thus affecting the daily life. Herein, a novel class of high-quality organic–inorganic trihalide perovskite nanoscale hybrid photodetectors is presented based on carbon electrode−molecule junctions working at mild conditions. Almost every figure of merit with high performance, such as highest responsivity, highest photogain, high detectivity, high linear dynamic range, and a broad spectral response, could be achieved simultaneously in a single device under different biases. These significant achievements benefit from rational choices of novel energy loss-prevented hybrid perovskite nanocrystals as active materials and optimized carbon electrode−molecule junctions as device architectures, which leads to a hybridization mechanism of photodiodes and photoconductors. These investigations demonstrate a useful photodetector platform that might lead to many future photoelectric conversion applications in the practical way. A new class of photodetectors working at mild conditions by using organic–inorganic trihalide perovskites as active materials and carbon electrode−molecule junctions as device architectures is demonstrated. The high performances, such as highest responsivity, highest photogain, high detectivity, high linear dynamic range, and a broad spectral response, could be achieved simultaneously in a single device under different biases.

Strong Photoacoustic Signal Enhancement by Coating Gold Nanoparticles with Melanin for Biomedical Imaging


Photoacoustics is a powerful biomedical imaging and detection technique, because it is a noninvasive, nonionizing, and low-cost method facilitating deep tissue penetration. However, suitable contrast agents need to be developed to increase the contrast for in vivo imaging. Gold nanoparticles are often discussed as potential sonophores due to their large absorption cross-section and their tunable plasmon resonance. However, disadvantages such as toxicity and low photoacoustic efficiency in the tissue transparency window prevail, preventing their clinical application. As a result, there remains a strong need to develop colloidal photoacoustic contrast agents which absorb in the tissue transparency window, exhibit high photoacoustic signal, and are biocompatible. Here, a facile synthetic approach is presented to produce melanin shells around various gold nanoparticle geometries, from spheres to stars and rods. These hybrid particles show excellent dispersability, better biocompatibility, and augmented photoacoustic responses over the pure melanin or pristine gold particles, with a rod-shape geometry leading to the highest performance. These experimental results are corroborated using numerical calculations and explain the improved photoacoustic performance with a thermal confinement effect. The applicability of melanin coated gold nanorods as gastrointestinal imaging probes in mouse intestine is showcased. Here, the preparation of melanin coated gold particles is presented. The melanin coating provides enhanced colloidal stability, improved biocompatibility, and augmented photoacoustic contrast. The reasons for these improvements are analyzed experimentally and theoretically and it is found that a thermal confinement effect leads to enhanced photothermal efficiency, which is exploited for intestinal photoacoustic imaging.

Bio-Inspired Anisotropic Wettability Surfaces from Dynamic Ferrofluid Assembled Templates


The biomimetic principle of harnessing topographical structures to determine liquid motion behavior represents a cutting-edge direction in constructing green transportation systems without external energy input. Here, inspired by natural Nepenthes peristome, a novel anisotropic wettability surface with characteristic structural features of periodically aligned and overlapped arch-shaped microcavities, formed by employing ferrofluid assemblies as dynamic templates, is presented. The magnetic strength and orientation are precisely adjustable during the generation process, and thus the size and inclination angle of the ferrofluid droplet templates could be tailored to make the surface morphology of the resultant polymer replica achieve a high degree of similarity to the natural peristome. The resultant anisotropic wettability surface enables autonomous unidirectional water transportation in a fast and continuous way. In addition, it could be tailored into arbitrary shapes to induce water flow along a specific curved path. More importantly, based on the anisotropic wettability surface, novel pump-free microfluidic devices are constructed to implement multiphase flow reactions, which offer a promising solution to building low-cost, portable platform for lab-on-a-chip applications. An anisotropic wettability surface with Nepenthes peristome inspired structures is fabricated through dynamic ferrofluid assembly. It enables autonomous unidirectional water transportation and could be tailored into arbitrary shapes to induce water flow along a specific curved path. Novel pump-free microfluidic devices are constructed for multiphase flow reactions, which offer a promising solution in building low-cost, portable platform for lab-on-a-chip applications.

Self-Standing Porous LiCoO2 Nanosheet Arrays as 3D Cathodes for Flexible Li-Ion Batteries


Self-standing electrodes are the key to realize flexible Li-ion batteries. However, fabrication of self-standing cathodes is still a major challenge. In this work, porous LiCoO2 nanosheet arrays are grown on Au-coated stainless steel (Au/SS) substrates via a facile “hydrothermal lithiation” method using Co3O4 nanosheet arrays as the template followed by quick annealing in air. The binder-free and self-standing LiCoO2 nanosheet arrays represent the 3D cathode and exhibit superior rate capability and cycling stability. In specific, the LiCoO2 nanosheet array electrode can deliver a high reversible capacity of 104.6 mA h g−1 at 10 C rate and achieve a capacity retention of 81.8% at 0.1 C rate after 1000 cycles. By coupling with Li4Ti5O12 nanosheet arrays as anode, an all-nanosheet array based LiCoO2//Li4Ti5O12 flexible Li-ion battery is constructed. Benefiting from the 3D nanoarchitectures for both cathode and anode, the flexible LiCoO2//Li4Ti5O12 battery can deliver large specific reversible capacities of 130.7 mA h g−1 at 0.1 C rate and 85.3 mA h g−1 at 10 C rate (based on the weight of cathode material). The full cell device also exhibits good cycling stability with 80.5% capacity retention after 1000 cycles at 0.1 C rate, making it promising for the application in flexible Li-ion batteries. This work gives a novel approach to fabricate porous LiCoO2 nanosheet arrays on Au-coated stainless steel substrates. The trivial transformation on crystal structure is the key to build 3D nanoarray electrode. The all-nanosheet array based LiCoO2//Li4Ti5O12 full cell exhibits outstanding performance and good flexibility.

Local Built-In Electric Field Enabled in Carbon-Doped Co3O4 Nanocrystals for Superior Lithium-Ion Storage


In this work, a novel concept of introducing a local built-in electric field to facilitate lithium-ion transport and storage within interstitial carbon (C-) doped nanoarchitectured Co3O4 electrodes for greatly improved lithium-ion storage properties is demonstrated. The imbalanced charge distribution emerging from the C-dopant can induce a local electric field, to greatly facilitate charge transfer. Via the mechanism of “surface locking” effect and in situ topotactic conversion, unique sub-10 nm nanocrystal-assembled Co3O4 hollow nanotubes (HNTs) are formed, exhibiting excellent structural stability. The resulting C-doped Co3O4 HNT-based electrodes demonstrate an excellent reversible capacity ≈950 mA h g−1 after 300 cycles at 0.5 A g−1 and superior rate performance with ≈853 mA h g−1 at 10 A g−1. Carbon-doped Co3O4 hollow nanotubes composed of sub-10 nm nanocrystals are rationally designed to offer a local built-in electric field to enhance fast charge/discharge capability. This anode material exhibits superior rate capability with the achieved reversible capacity ≈853 mA h g−1 at high current density of 10 A g−1.

Fully Reversible Multistate Fluorescence Switching: Organogel System Consisting of Luminescent Cyanostilbene and Turn-On Diarylethene


Multicolor tunable and multistate switchable organogel is reported, which consists of a cyanostilbene organogelator showing aggregation-induced enhanced emission and a turn-on type photochromic diarylethene dye. The mixed organogel can be reversibly switched among four different states (blue-emitting gel, nonemissive sol, green-emitting gel, and green-emitting sol) modulated by a combination of orthogonal stimuli of heat and light. It is interestingly noted that this four-state switching constitutes a combinational logic circuit consisting of two stimuli inputs and three outputs. Reversible fluorescence writing, switching, erasing, and image patterning processes on this mixture gel system are demonstrated. Multistate addressable fluorescent organogel is constructed by mixing the aggregation-induced enhanced emission organogelator and fluorescent turn-on diarylethene. Through its reversible and orthogonal stimuli-responsiveness, an integrated logic circuit, where thermal- and optical-inputs can be translated into four different outputs (blue-emitting gel, nonemissive sol, green-emitting gel, and green-emitting sol), is demonstrated.

Ultralong 20 Milliseconds Charge Separation Lifetime for Photoilluminated Oligophenylenevinylene–Azafullerene Systems


The synthesis and characterization of oligophenylenevinylene (OPV)–azafullerene (C59N) systems in the form of OPV–C59N donor–acceptor dyad 1 and C59N–OPV–C59N acceptor–donor–acceptor triad 2 is accomplished. Photoinduced electronic interactions between OPV and C59N within 1 and 2 are assessed by UV–vis and photoluminescence. The redox properties of 1 and 2 are investigated, revealing a set of one-electron oxidation and three one-electron reduction processes owed to OPV and C59N, respectively. The electrochemical bandgap for 1 and 2 is calculated as 1.44 and 1.53 eV, respectively, and the free energy for the formation of the charge-separated state for 1 and 2 via the singlet-excited state of OPV is found negative, proving a thermodynamically favorable the process. Photoexcitation assays are performed in toluene and o-dichlorobenzene (oDCB) and the reactions are monitored with time-resolved absorption and emission spectroscopies. Competitive photoinduced energy and electron transfer are identified to occur in both systems, with the former being dominant in 2. Markedly, the charge-separated state in oDCB exhibits a much longer lifetime compared to that in toluene, reaching 20 ms for 1, the highest ever reported value for fullerene-based materials. These unprecedented results are rationalized by considering conformational phenomena affecting the charge-separated state. Charge separation lasting for 20 ms in ortho-dichlorobenzene is registered for oligophenylenevinylene–azafullerene donor–acceptor dyad. The synthesis, structural characterization, photophysical, and electrochemical properties for the dyad as well as for the azafullerene–oligophenylenevinylene–azafullerene triad are reported.

Self-Healing Shape Memory PUPCL Copolymer with High Cycle Life


New polyurethane-based polycaprolactone copolymer networks, with shape recovery properties, are presented here. Once deformed at ambient temperature, they show 100% shape fixation until heated above the melting point, where they recover the initial shape within 22 s. In contrast to current shape memory materials, the new materials do not require deformation at elevated temperature. The stable polymer structure of polyurethane yields a copolymer network that has strength of 10 MPa with an elongation at break of 35%. The copolymer networks are self-healing at a slightly elevated temperature (70 °C) without any external force, which is required for existing self-healing materials. This allows for the new materials to have a long life of repeated healing cycles. The presented copolymers show features that are promising for applications as temperature sensors and activating elements. New polyurethane-based polycaprolactone copolymer networks are presented here. The TOC image shows the representative high cycle shape recovery phenomenon at a temperature higher than Tc or Tm of the material after 100% shape fixation with potential applications into actuating elements and artificial muscles while lifting a heavier weight 20 times the weight of copolymer networks.

“Trade-Off” Hidden in Condensed State Solvation: Multiradiative Channels Design for Highly Efficient Solution-Processed Purely Organic Electroluminescence at High Brightness


Actualizing highly efficient solution-processed thermally activated delayed fluorescent (TADF) organic light-emitting diodes (OLEDs) at high brightness becomes significant to the popularization of purely organic electroluminescence. Herein, a highly soluble emitter benzene-1,3,5-triyltris((4-(9,9-dimethylacridin-10(9H)-yl)phenyl)methanone was developed, yielding high delayed fluorescence rate (kTADF > 105 s−1) ascribed to the multitransition channels and tiny singlet–triplet splitting energy (ΔEST ≈ 32.7 meV). The triplet locally excited state is 0.38 eV above the lowest triplet charge-transfer state, assuring a solely thermal equilibrium route for reverse intersystem crossing. Condensed state solvation effect unveils a hidden “trade-off”: the reverse upconversion and triplet concentration quenching processes can be promoted but with a reduced radiative rate from the increased dopant concentration and the more polarized surroundings. Striking a delicate balance, corresponding vacuum-evaporated and solution-processed TADF-OLEDs realized maximum external quantum efficiencies (EQEs) of ≈26% and ≈22% with extremely suppressed efficiency roll-off. Notably, the wet-processed one achieves to date the highest EQEs of 20.7%, 18.5%, 17.1%, and 13.6%, among its counterparts at the luminance of 1000, 3000, 5000, and 10 000 cd m−2, respectively. Hidden “trade-off” among highly radiative rate, rapid reverse upconversion, and suppressed concentration quenching is reached by condensed state solvation. With multitransition channels design for thermally activated delayed fluorescence rate surpassing 105 s−1, solution-processed organic light-emitting diodes achieve to date the best ext[...]

Superhydrophobic Shape Memory Polymer Arrays with Switchable Isotropic/Anisotropic Wetting


Smart surfaces with tunable wettability have aroused much attention in the past few years. However, to obtain a surface that can reversibly transit between the lotus-leaf-like superhydrophobic isotropic and rice-leaf-like superhydrophobic anisotropic wettings is still a challenge. This paper, by mimicking microstructures on both lotus and rice leaves, reports such a surface that is prepared by creating micro/nanostructured arrays on the shape memory polymer. On the surface, the microstructure shapes can be reversibly changed between the lotus-leaf-like random state and the rice-leaf-like 1D ordered state. Accordingly, repeated switch between the superhydrophobic isotropic and anisotropic wettings can be displayed. Research results indicate that the smart controllability is ascribed to the excellent shape memory effect of the polymer, which endows the surface with special ability in memorizing different microstructure shapes and wetting properties. Meanwhile, based on the smart wetting performances, the surface is further used as a rewritable functional platform, on which various droplet transportation programmes are designed and demonstrated. This work reports a superhydrophobic surface with switchable isotropic/anisotropic wettings, which not only provides a novel functional material but also opens a new avenue for application in controlled droplet transportation. A novel surface that can reversibly transit between the superhydrophobic isotropic and anisotropic wetting states is reported by creating micro/nanostructured pillars on the shape memory polymer. Based on the smart controllability, the surface can be used as the rewritable functional platform, on which[...]