Flexible organic-inorganic hybrid photodetectors with n-type phenyl-C61-butyric acid methyl ester （PCBM） and p-type pearl-like GaP nanowires

Flexible photodetectors have become a focus of current researches because they may offer some unique applications in various new areas that require flexible, lightweight, and mechanical shock-resistive sensing elements. In this work, we designed flexible organic-inorganic hybrid photodetectors on various flexible substrates, including polyethylene terephthalate （PET）, common Sellotape and polydimethylsiloxane （PDMS）, with n-type phenyl-C61-butyric acid methyl ester （PCBM） and p-type pearl-like GaP nanowires （NWs） as the active materials. The as-fabricated hybrid devices exhibited an optimized performance superior to the device made of pristine GaP NWs, with a fast response time （43 ms） and high on/off ratio （-170）. Under different bending conditions, the flexible hybrid photodetectors demonstrated excellent flexibility and electrical stability, which make them very promising for further large-scale, high sensitivity and high speed photodetector applications.     

Perovskite-Inspired Lead-Free Ag2BiI5 for Self-Powered NIR-Blind Visible Light Photodetection

In recent years,solution-processible semiconductors with perovskite or perovskite-inspired structures have been extensively investigated for optoelectronic applications.In particular,silver-bismuth-halides have been identified as especially promising because of their bulk properties and lack of heavily toxic elements.This study investigates the potential of Ag2BiI5 for near-infrared(NIR)-blind visible light photodetection,which is critical to emerging applications(e.g.,wearable optoelectronics and the Internet of Things).Self-powered photodetectors were realized and provided a near-constant≈100 mA W−1 responsivity through the visible,a NIR rejection ratio of>250,a long-wavelength responsivity onset matching standard colorimetric functions,and a linear photoresponse of>5 orders of magnitude.The optoelectronic characterization of Ag2BiI5 photodetectors additionally revealed consistency with one-center models and the role of the carrier collection distance in self-powered mode.This study provides a positive outlook of Ag2BiI5 toward emerging applications on low-cost and low-power NIR-blind visible light photodetector.     

All-inorganic lead-free NiOx/Cs3Bi2Br9 perovskite heterojunction photodetectors for ultraviolet multispectral imaging

Bismuth-based perovskites are considered to be promising candidates to substitute the toxic lead-based perovskite in optoelectronics due to their excellent optoelectronic properties,high environmental friendliness,and(moisture,light,and heat)stability.However,there are still few reports about high performance bismuth-based perovskite ultraviolet photodetectors,and is more lacking in ultraviolet imaging demonstration.Herein,we reported a self-powered NiO_x/Cs₃Bi₂Br₉ heterojunction photodetector with excellent photodetection performance by electrochemical depositing NiOx as the hole transport layer.The optimized NiO_x/CsaBi₂Brg heterojunction photodetector exhibits excellent ultraviolet detection performance with a fast response speed of 3.04/4.65 ms,wide linear dynamic range of 116.6 dB,decent responsivity of 4.33 mA·W^-1 at 0 V bias,and high detectivity of 1.3×10¹¹ jones.The outstanding performance of the optimized NiO_x/Cs₃Bi₂Br₉ heterojunction photodetector is enough to meet the high-quality ultraviolet imaging.Therefore,we further integrated the optimized NiO_x/Cs₃Bi₂Br₉ heterojunction photodetector to the transmission mode ultraviolet multispectral imaging system,achieving admirable imaging results at weak light condition.This work will play a positive role in promoting the development of bismuth-based ultraviolet photodetection and ultraviolet multispectral imaging.     

Structure and Piezoelectric Properties of Lead-Free Na_(0.5)Bi_(0.5)TiO_3 Nanofibers Synthesized by Electrospinning

Lead-free Na_(0.5)Bi_(0.5)TiO_3(NBT) nanofibers with the perovskite structure were prepared by the electrospinning method.The nanofibers were about 200-300 nm in diameter and up to several hundred microns in length.The crystal structures and morphologies of the nanofibers were characterized by X-ray diffraction(XRD),Raman spectroscopy,scanning electron microscopy(SEM),and transmission electron microscopy(TEM).The effective piezoelectric property of individual NBT nanofiber was examined by piezoresponse force microscopy(PFM).The NBT nanofibers crystallized in pure perovskite phase after annealing above 700℃in air and comprised a great number of fine particles with size of 60-80 nm.In addition,the electromechanical energy conversion models for NBT nanofibers were built and demonstrated high voltage output as high as several millivolts.Such a result qualifies NBT nanofibers as a promising candidate for leadfree electromechanical conversion devices.     

Controllable printing of large-scale compact perovskite films for flexible photodetectors

Perovskite materials are promising candidates for the next generation of wearable optoelectronics.However,due to uncontrolled crystallization and the natural brittle property of crystals,it remains a great challenge to fabricate large-scale compact and tough perovskite film.Here we report a facile method to print large-scale perovskite films with high quality for flexible photodetectors.By introducing a soluble polyethylene oxide(PEO)layer during the inkjet printing process,the nucleation and crystal growth of perovskite is well controlled.Perovskite films can be easily printed in large scale and patterned in high resolution.Moreover,this method can be extended to various kinds of perovskite materials,such as MAPbb(MA=methylammonium),MA₃Sb₂l₉,and(BA)₂PbBr₄(BA=benzylammonium).The printed perovskite films show high quality and excellent mechanical performance.The photodetectors based on the MAPbBr3 perovskite films show a responsivity up to -1,036 mAA/V and maintain over 96.8%of the initial photocurrent after 15,000 consecutive bending cycles.This strategy provides a facile approach to prepare large-scale flexible perovskite films.It opens up new opportunities for the fabrication of diverse wearable optoelectronic devices.     

Low-Temperature Aging Provides 22% E cient Bromine-Free and Passivation Layer-Free Planar Perovskite Solar Cells

Previous reports of formamidinium/methylamine(FAMA)-mixed halide perovskite solar cells have focused mainly on controlling the morphology of the perovskite film and its interface—for example,through the inclusion of bromine and surface passivation.In this paper,we describe a new processing pathway for the growth of a high-quality bromine-free FAMAPbI3 halide perovskites via the control of intermediate phase.Through low-temperature aging growth(LTAG)of a freshly deposited perovskite film,α-phase perovskites can be seeded in the intermediate phase and,at the same time,prevent beta-phase perovskite to nucleate.After postannealing,large grain-size perovskites with significantly reduced PbI2 presence on the surface can be obtained,thereby eliminating the need of additional surface passivation step.Our pristine LTAG-treated solar cells could provide PCEs of greater than 22%without elaborate use of bromine or an additional passivation layer.More importantly,when using this LTAG process,the growth of the pure alpha-phase FAMAPbI3 was highly reproducible.     

Capping CsPbBr<Subscript>3</Subscript> with ZnO to improve performance and stability of perovskite memristors

The rapid development of information technology has led to an urgent need for devices with fast information storage and processing,a high density,and low energy consumption.Memristors are considered to be next-generation memory devices with all of the aforementioned advantages.Recently,organometallic halide perovskites were reported to be promising active materials for memristors,although they have poor stability and mediocre performance.Herein,we report for the first time the fabrication of stable and high-performance memristors based on inorganic halide perovskite (CsPbBr3,CPB).The devices have electric field-induced bipolar resistive switching (ReS) and memory behaviors with a large on/off ratio (＞105),low working voltage (＜1 V) and energy consumption,long data retention (＞104 s),and high environmental stability,which are achieved via ZnO capping within the devices.Such a design can be adapted to various devices.Additionally,the heterojunction between the CPB and ZnO endows the devices with a light-induced ReS effect of more than 103 with a rapid response speed (＜1 ms),which enables us to tune the resistance state by changing the light and electric field simultaneously.Such multifunctional devices achieved by the combination of information storage and processing abilities have potential applications for future computing that transcends traditional architectures.     

Graphene-carbon nanotube hybrid films for high-performance flexible photodetectors

Graphene is being actively explored as a candidate material for flexible and stretchable devices.However,the development of graphene-based flexible photonic devices,i.e.photodetectors,is hindered by the low absorbance of the single layer of carbon atoms.Recently,van der Waals bonded carbon nanotube and graphene hybrid films have demonstrated excellent photoresponsivity,and the use of vein-like carbon nanotube networks resulted in significantly higher mechanical strength.Here,we report for the first time,a flexible photodetector with a high photoresponsivity of ～ 51 A/W and a fast response time of ～ 40 ms over the visible range,revealing the unique potential of this emerging all-carbon hybrid films for flexible devices.In addition,the device exhibits good robustness against repetitive bending,suggesting its applicability in large-area matrix-array flexible photodetectors.     

Chemical vapor deposition growth of single-crystalline cesium lead halide microplatelets and heterostructures for optoelectronic applications

Orgaruc-inorganic hybrid halide perovskites,such as CH3NH3PbI3,have emerged as an exciting class of materials for solar photovoltaic applications;however,they are currently plagued by insufficient environmental stability.To solve this issue,all-inorganic halide perovskites have been developed and shown to exhibit significantly improved stability.Here,we report a single-step chemical vapor deposition growth of cesium lead halide (CsPbX3) microcrystals.Optical microscopy studies show that the resulting perovskite crystals predominantly adopt a square-platelet morphology.Powder X-ray diffraction (PXRD) studies of the resulting crystals demonstrate a highly crystalline nature,with CsPbC13,CsPbBr3,and CsPbI3 showing tetragonal,monoclinic,and orthorhombic phases,respectively.Scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies show that the resulting platelets exhibit well-faceted structures with lateral dimensions of the order of 10-50 μm,thickness around 1 μm,and ultra-smooth surface,suggesting the absence of obvious grain boundaries and the single-crystalline nature of the individual microplatelets.Photoluminescence (PL) images and spectroscopic studies show a uniform and intense emission consistent with the expected band edge transition.Additionally,PL images show brighter emission around the edge of the platelets,demonstrating a wave-guiding effect in high-quality crystals.With a well-defined geometry and ultra-smooth surface,the square platelet structure can function as a whispering gallery mode cavity with a quality factor up to 2,863 to support laser emission at room temperature.Finally,we demonstrate that such microplatelets can be readily grown on a variety of substrates,including silicon,graphene,and other two-dimensional materials such as molybdenum disulfide,which can readily allow the construction of heterostructure optoelectronic devices,including a graphene/perovskite/ graphene vertically-stacked photodetector with photoresponsivity ＞ 105 A/W.The extraordinary optical properties of CsPbX3 platelets,combined with their ability to be grown on diverse materials to form functional heterostructures,can lead to exciting opportunities for broad optoelectronic applications.     

Solution-processed,flexible and broadband photodetector based on CsPbBr_3/PbSe quantum dot heterostructures

Due to their promising applications in foldable displays,optical communication equipment and environmental monitoring systems,flexible and broadband optoelectronic devices have gained extensive attention in recent years.Here,a flexible and broadband photodetector based on CsPbBr₃/PbSe quantum dot(QD) heterostructures is firstly presented.The integrated QD heterostructures possess consecutive detection range from ultraviolet(UV) to long-wave length infrared(LW-IR) regions with efficient light absorption and chemical stability,in comparison with the pristine PbSe QDs.Systematic material characterizations reveal the improved exciton dissociation,carrier transport and carrier lifetime of the QD heterostructures.Flexible photodetector Ag/CsPbBr₃/PbSe/Ag demonstrate a high responsivity of 7.17 A/W with a specific detectivity of 8.97 × 10¹² Jones under 25 μW/cm² 365 nm illumination at 5 V.Furthermore,it could maintain 91.2 %(or 94.9 %) of its initial performance even after bending for thousands of times(or exposing in ambient air for 4 weeks).More importantly,its re s ponse time is shortened more than three orders of magnitude as that of pristine PbSe QDs-based photodetectors.Therefore,it provides a feasible and promising method for the next-generation high-performance broadband photodetectors via constructing heterostructures of various QDs.     

High-performance planar heterojunction perovskite solar cells： Preserving long charge carrier diffusion lengths and interracial engineering

We demonstrate that charge carrier diffusion lengths of two classes of perovskites, CH3NH3PbI3-xClx and CH3NH3PbI3, are both highly sensitive to film processing conditions and optimal processing procedures are critical to preserving the long carrier diffusion lengths of the perovskite films. This understanding, together with the improved cathode interface using bilayer-structured electron transporting interlayers of [6,6]-phenyl-C61-butyric acid methyl ester （PCBM）/ZnO, leads to the successful fabrication of highly efficient, stable and reproducible planar heterojunction CH3NH3PbI3-xCl2 solar cells with impressive power-conversion efficiencies （PCEs） up to 15.9%. A 1-square-centimeter device yielding a PCE of 12.3% has been realized, demonstrating that this simple planar structure is promising for large-area devices.     

Interface engineering of high efficiency perovskite solar cells based on ZnO nanorods using atomic layer deposition

Despite the considerably improved efficiency of inorganic-organic metal hybrid perovskite solar cells (PSCs),electron transport is still a challenging issue.In this paper,we report the use of ZnO nanorods prepared by hydrothermal selfassembly as the electron transport layer in perovskite solar cells.The efficiency of the perovskite solar cells is significantly enhanced by passivating the interfacial defects via atomic layer deposition of A12O3 monolayers on the ZnO nanorods.By employing the A12O3 monolayers,the average power conversion efficiency of methylammonium lead iodide PSCs was increased from 10.33％ to 15.06％,and the highest efficiency obtained was 16.08％.We suggest that the passivation of defects using the atomic layer deposition of monolayers might provide a new pathway for the improvement of all types of PSCs..     

Single-crystal microplates of two-dimensional organic–inorganic lead halide layered perovskites for optoelectronics

Organic-inorganic hybrid perovskites attract considerable attention owing to their applications in high-efficiency solar cells and light emission.Compared with three-dimensional perovskites,two-dimensional (2D) layered hybrid perovskites have a higher exciton binding energy and potentially higher light-emission efficiency.The growth of high-quality crystalline 2D perovskites with a well-defined nanoscale morphology is desirable because they can be suitable building blocks for integrated optoelectronics and (nano)photonics.Herein,we report the facile solution growth of single-crystal microplates of 2D perovskites based on a 2-phenylethylammonium (C6H5CH2CH2NH3+,PEA) cation,(PEA)2PbX4 (X =Br,I),with a well-defined rectangular geometry and nanoscale thickness through a dissolution-recrystallization process.The crystal structures of (PEA)2PbX4 are first confirmed using single-crystal X-ray diffraction.A solution-phase transport-growth process is developed to grow microplates with a typical size of tens of micrometers and thickness of hundreds of nanometers on another clean substrate different from the substrate coated with lead-acetate precursor film.Surface-topography analysis suggests that the formation of the 2D microplates is likely driven by the wedding-cake growth mechanism.Through halide alloying,the photoluminescence emission of (PEA)2Pb(Br,I)4 perovskites with a narrow peak bandwidth is readily tuned from violet (～410 nm) to green (～530 nm).     

Design and roles of RGO-wrapping in charge transfer and surface passivation in photoelectrochemical enhancement of cascade-band photoanode

Fast charge transfer and anti-photocorrosion are two crucial factors for developing efficient,durable photoanodes for photoelectrochemical (PEC) cells.Reduced graphene oxide (RGO) is a promising photoanode element that can provide both of these.In this study,we elucidated the roles of RGO in the charge transfer and surface passivation of photoanodes by the precise design of a RGO-wrapped photoanode and examination of its PEC properties.Arrays of hetero-nanorods (HNRs) with three different designs were fabricated as photoanodes using RGO,CdSe nanopartides (NPs),and ZnO nanorods (NRs) as building blocks.CdSe@ZnO HNRs were prepared by decorating ZnO NRs with CdSe NPs.Finite-element analysis and experimental studies demonstrated that in the CdSe@ZnO HNRs,if only the ZnO NRs were wrapped by RGO,the conductivity between CdSe and ZnO was enhanced by RGO to shuttle charges.If RGO only surrounded the outside of the CdSe@ZnO HNRs,the corrosion was slowed owing to the passivation effect of RGO,which increased the electron lifetime of the photoanode.If both CdSe and ZnO were fully wrapped by RGO,the advantages of the two aforementioned cases were both obtained.RGO-wrapped CdSe@ZnO HNRs with position-controlled designs are promising photoanode materials with a high PEC efficiency,and the developed synthesis process can be applied to explore the design and fabrication of next-generation photoanodes using RGO as a building block.     

Moisture-driven phase transition for improved perovskite solar cells with reduced trap-state density

We report a mechanistic understanding of a moisture-driven intermediate-phase transition that improves the quality of perovskite thin films based on a lead-acetate precursor,improving the power-conversion efficiency.We clarify the composition of the intermediate phase and attribute the transition of this phase to the hygroscopic nature of the organic product,i.e.,methylammonium acetate.Thermal annealing aids in the coarsening of the grains.These decoupled processes result in better crystal formation with a lower spatial and energetic distribution of traps.Thermal annealing of the films without exposure to air results in a faster intermediate-phase transition and grain coarsening,which occur simultaneously,leading to disorder in the films and a higher deep trap-state density.Our results indicate the need for a humid environment for the growth of high-quality perovskite films and provide insight into intermediate-phase dissociation and conversion kinetics.Thus,they are useful for the large-scale production of efficient solution-processed perovskite solar cells.     

Structural,optical, and electrical properties of phase-controlled cesium lead iodide nanowires

Cesium lead iodide (CsPbI3),in its black perovskite phase,has a suitable bandgap and high quantum efficiency for photovoltaic applications.However,CsPbI3 tends to crystalize into a yellow non-perovskite phase,which has poor optoelectronic properties,at room temperature.Therefore,controlling the phase transition in CsPbI3 is critical for practical application of this material.Here we report a systematic study of the phase transition of one-dimensional CsPbI3 nanowires and their corresponding structural,optical,and electrical properties.We show the formation of perovskite black phase CsPbI3 nanowires from the non-perovskite yellow phase through rapid thermal quenching.Post-transformed black phase CsPbI3 nanowires exhibit increased photoluminescence emission intensity with a shrinking of the bandgap from 2.78 to 1.76 eV.The perovskite nanowires were photoconductive and showed a fast photoresponse and excellent stability at room temperature.These promising optical and electrical properties make the perovskite CsPbI3 nanowires attractive for a variety of nanoscale optoelectronic devices.     

Nanosized-bismuth-embedded 1D carbon nanofibers as high-performance anodes for lithium-ion and sodium-ion batteries

Bi is a promising candidate for energy storage materials because of its high volumetric capacity,stability in moisture/air,and facile preparation.In this study,the electrochemical performance of nanosized-Bi-embedded one-dimensional (1D) carbon nanofibers (Bi/C nanofibers) as anodes for Li-ion batteries (LIBs) and Na-ion batteries (NIBs) was systematically investigated.The Bi/C nanofibers were prepared using a single-nozzle electrospinning method with a specified Bi source followed by carbothermal reduction.Abundant Bi nanoparticles with diameters of approximately 20 nm were homogeneously dispersed and embedded in the 1D carbon nanofibers,as confirmed by structural and morphological characterization.Electrochemical measurements indicate that the Bi/C nanofiber anodes could deliver a long cycle life for LIBs and a preferable rate performance for NIBs.The superior electrochemical performances of the Bi/C nanofiber anodes are attributed to the 1D carbon nanofiber structure and uniform distribution of Bi nanoparticles embedded in the carbon matrix.This unique embedded structure provides a favorable electron carrier and buffering matrix for the effective release of mechanical stress caused by volume change and prevents the aggregation of Bi nanoparticles.     

Hierarchical TiO2/ZnO Nanostructure as Novel Non-precious Electrocatalyst for Ethanol Electrooxidation

Metal oxides have a higher chemical stability in comparison to metals,so they can be utilized as electrocatalysts if the activity could be enhanced.Besides the composition,the morphology of the nanostructures has a considerable impact on the electrocatalytic activity.In this work,zinc oxide nano branches-attached titanium dioxide nanofibers were investigated as an economic and stable catalyst for ethanol electrooxidation in the alkaline media.The introduced material has been synthesized by electrospinning process followed by hydrothermal technique.Briefly,electrospinning of colloidal solution consisting of titanium isopropoxide,poly(vinyl acetate) and zinc nanoparticles was performed to produce nanofibers embedding solid nanoparticles.In order to produce TiO_2 nanofibers containing ZnO nanoparticles,the obtained electrospun nanofiber mats were calcined in air at 600 °C.The formed ZnO nanoparticles were exploited as seeds to outgrow ZnO branches around the TiO_2 nanofibers using the hydrothermal technique at sub-critical water conditions in the presence of zinc nitrate and bis-hexamethylene triamine.The morphology of the final product,as well as the electrochemical measurements indicated that zinc nanoparticles content in the original electrospun nanofibers has a significant influence on the electrocatalytic activity as the best performance was observed with the nanofibers synthesized from electrospun solution containing 0.1 g Zn,and the corresponding current density was 37 mA/cm~2.Overall,this study paves a way to titanium dioxide to be exploited to synthesize effective and stable metal oxide-based electrocatalysts.     

High-detectivity InAs nanowire photodetectors with spectral response from ultraviolet to near-infrared

InAs is a direct, narrow band gap （0.354 eV） material with ultrahigh electron mobility, and is potentially a good optoelectronic device candidate in the wide UV-visible-near-infrared region. In this work we report the fabrication of InAs nanowire-based photodetectors, which showed a very high photoresponse over a broad spectral range from 300 to 1,100 nm. The responsivity, external quantum efficiency and detectivity of the device were respectively measured to be 4.4 × 103 AW , 1.03 × 106%, and 2.6 × 1011 Jones to visible incident light. Time dependent measurements at different wavelengths and under different light intensities also demonstrated the fast, reversible, and stable photoresponse of our device. Theoretical calculations of the optical absorption and the electric field component distribution were also performed to elucidate the mechanism of the enhanced photoresponse. Our results demonstrate that the single-crystalline InAs NWs are very promising candidates for the design of high sensitivity and high stability nanoscale photodetectors with a broad band photoresponse.     

Dimethylammonium iodide stabilized bismuth halide perovskite photocatalyst for hydrogen evolution

Metal halide perovskites have emerged as novel and promising photocatalysts for hydrogen generation.Currently,their stability in water is a vital and urgent research question.In this paper a novel approach to stabilize a bismuth halide perovskite[(CH₃)₂NH₂]₃[Bil₆](DA₃Bil₆)in water using dimethylammonium iodide(DAI)without the assistance of acids or coatings is reported.The DA3Bil6 powder exhibits good stability in DAI solutions for at least two weeks.The concentration of DAI is found as a critical parameter,where the I^-ions play the key role in the stabilization.The stability of DA3Bil6 in water is realized via a surface dissolution-recrystallization process.Stabilized DA3Bil6 demonstrates constant photocatalytic properties for visible light-induced photo-oxidation of I^-ions and with PtCI4 as a co-catalyst(Pt-DA₃Bil₆),photocatalytic H2 evolution with a rate of 5.7μmol·h^-1from HI in DAI solution,obtaining an apparent quantum efficiency of 0.83%at 535 nm.This study provides new insights on the stabilization of metal halide perovskites for photocatalysis in aqueous solution.