Novel Structure for High Performance UV Photodetector Based on BiOCl/ZnO Hybrid Film

A novel type of high performance ultraviolet (UV) photodetector (PD) based on a ZnO film has been prepared by incorporating a BiOCl nanostructure into the film. The responsivity of the BiOCl/ZnO hybrid film PD in UV region can reach 182.87 mA W^?1, which is about 2.72 and 6.87 times for that of TiO₂/ZnO hybrid film PD and pure ZnO film PD. The rise/decay time of BiOCl/ZnO hybrid film PD is 25.83/11.25 s, which is much shorter than that of TiO₂/ZnO hybrid film PD (51.94/26.05 s) and pure ZnO film PD (69.34/>120 s). The BiOCl nanostructure can inject photogenerated electrons into the ZnO film under UV light illumination, leading to the increase of photocurrent, and forms barriers to block the straight transmission of electrons between electrodes, resulting in the decrease of decay time. The results of control experiment show that the transfer path of photogenerated electrons formed by p–n junction will be cut off after depositing gold nanoparticles on the film surface, which means this hybrid film is a unique and novel structure to improve the optoelectronic performance of photodetectors. This novel BiOCl/ZnO hybrid structure paves new route for the development of film PDs based on ZnO film.     

ZnO Film UV Photodetector with Enhanced Performance: Heterojunction with CdMoO4 Microplates and the Hot Electron Injection Effect of Au Nanoparticles

A novel CdMoO₄–ZnO composite film is prepared by spin‐coating CdMoO₄ microplates on ZnO film and is constructed as a heterojunction photodetector (PD). With an optimized loading amount of CdMoO₄ microplates, this composite film PD achieves a ≈18‐fold higher responsivity than pure ZnO film PD at 5 V bias under 350 nm (0.15 mW cm⁻²) UV light illumination, and its decay time shortens to half of the original value. Furthermore, Au nanoparticles are then deposited to modify the CdMoO₄–ZnO composite film, and the as‐constructed photodetector with an optimized deposition time of Au nanoparticles yields an approximately two‐fold higher photocurrent under the same condition, and the decay time reduces by half. The introduced CdMoO₄ microplates form type‐II heterojunctions with ZnO film and improve the photoelectric performance. The hot electrons from Au nanoparticles are injected into the CdMoO₄–ZnO composite film, leading to the increased photocurrent. When the light is off, the Schottky barriers formed between Au nanoparticles and CdMoO₄–ZnO composite film block the carrier transportation and accelerate the decay process of current. The study on Au‐nanoparticle‐modified CdMoO₄–ZnO composite film provides a facile method to construct ZnO film based PD with novel structure and high photoelectric performance.     

Enhanced Performance of a Self‐Powered Organic/Inorganic Photodetector by Pyro‐Phototronic and Piezo‐Phototronic Effects

Self‐powered photodetectors (PDs) have long been realized by utilizing photovoltaic effect and their performances can be effectively enhanced by introducing the piezo‐phototronic effect. Recently, a novel pyro‐phototronic effect is invented as an alternative approach for performance enhancement of self‐powered PDs. Here, a self‐powered organic/inorganic PD is demonstrated and the influences of externally applied strain on the pyro‐phototronic and the photovoltaic effects are thoroughly investigated. Under 325 nm 2.30 mW cm^‐2 UV illumination and at a ‐0.45% compressive strain, the PD's photocurrent is dramatically enhanced from ≈14.5 to ≈103 nA by combining the pyro‐phototronic and piezo‐phototronic effects together, showing a significant improvement of over 600%. Theoretical simulations have been carried out via the finite element method to propose the underlying working mechanism. Moreover, the pyro‐phototronic effect can be introduced by applying a ‐0.45% compressive strain to greatly enhance the PD's response to 442 nm illumination, including photocurrent, rise time, and fall time. This work provides in‐depth understandings about the pyro‐phototronic and the piezo‐phototronic effects on the performances of self‐powered PD to light sources with different wavelengths and indicates huge potential of these two effects in optoelectronic devices.     

Self‐Powered Si/CdS Flexible Photodetector with Broadband Response from 325 to 1550 nm Based on Pyro‐phototronic Effect: An Approach for Photosensing below Bandgap Energy

Cadmium sulfide (CdS) has received widespread attention as the building block of optoelectronic devices due to its extraordinary optoelectronic properties, low work function, and excellent thermal and chemical stability. Here, a self‐powered flexible photodetector (PD) based on p‐Si/n‐CdS nanowires heterostructure is fabricated. By introducing the pyro‐phototronic effect derived from wurtzite structured CdS, the self‐powered PD shows a broadband response range, even beyond the bandgap limitation, from UV (325 nm) to near infrared (1550 nm) under zero bias with fast response speed. The light‐induced pyroelectric potential is utilized to modulate the optoelectronic processes and thus improve the photoresponse performance. Lasers with different wavelengths have different effects on the self‐powered PDs and corresponding working mechanisms are carefully investigated. Upon 325 nm laser illumination, the rise time and fall time of the self‐powered PD are 245 and 277 µs, respectively, which are faster than those of most previously reported CdS‐based nanostructure PDs. Meanwhile, the photoresponsivity R and specific detectivity D* regarding to the relative peak‐to‐peak current are both enhanced by 67.8 times, compared with those only based on the photovoltaic effect‐induced photocurrent. The self‐powered flexible PD with fast speed, stable, and broadband response is expected to have extensive applications in various environments.     

Improved Dual-Polarity Response via Pyro-phototronic Effect for Filterless Visible Light Communication

Dual-polarity response photodetectors (PDs) take full advantage of the directivity of the photocurrent to identify optical information. The dual-polarity signal ratio, a key parameter that represents the equilibrium degree of responses to different lights, is proposed for the first time. The synchronous enhancement of dual-polarity photocurrents and the amelioration of the dual-polarity signal ratio are beneficial to the practical applications. Herein, based on the selective light absorption and energy band structure design, a self-powered CdS/PEDOT:PSS/Au heterojunction PD consisting of a p-n junction and a Schottky junction exhibits unique wavelength-dependent dual-polarity response, where the photocurrent is negative and positive in the short and long wavelength regions, respectively. More importantly, the pyro-phototronic effect inside the CdS layer significantly improves the dual-polarity photocurrents with the maximum enhancement factors of 120%, 343%, 1167%, 1577%, and 1896% at 405, 450, 532, 650, and 808 nm, respectively. Furthermore, the dual-polarity signal ratio tends to 1:1 due to different degrees of the enhancement. This work provides a novel design strategy for dual-polarity response PDs with a simple working principle and improved performance, which can supply a substitution for two traditional PDs in the filterless visible light communication (VLC) system.     

Controlled Vectorial Electron Transfer and Photoelectrochemical Applications of Layered Relay/Photosensitizer‐Imprinted Au Nanoparticle Architectures on Electrodes

Two configurations of molecularly imprinted bis‐aniline‐bridged Au nanoparticles (NPs) for the specific binding of the electron acceptor N,N′‐dimethyl‐4,4′‐bipyridinium (MV²⁺) and for the photosensitizer Zn(II)‐protoporphyrin IX (Zn(II)‐PP‐IX) are assembled on electrodes, and the photoelectrochemical features of the two configurations are discussed. Configuration I includes the MV²⁺‐imprinted Au NPs matrix as a base layer, on which the Zn(II)‐PP‐IX‐imprinted Au NPs layer is deposited, while configuration II consists of a bilayer corresponding to the reversed imprinting order. Irradiation of the two electrodes in the presence of a benzoquinone/benzohydroquinone redox probe yields photocurrents of unique features: (i) Whereas configuration I yields an anodic photocurrent, the photocurrent generated by configuration II is cathodic. (ii) The photocurrents obtained upon irradiation of the imprinted electrodes are substantially higher as compared to the nonimprinted surfaces. The high photocurrents generated by the imprinted Au NPs‐modified electrodes are attributed to the effective loading of the imprinted matrices with the MV²⁺ and Zn(II)‐PP‐IX units and to the effective charge separation proceeding in the systems. The directional anodic/cathodic photocurrents are rationalized in terms of vectorial electron transfer processes dictated by the imprinting order and by the redox potentials of the photosensitizer/electron acceptor units associated with the imprinted sites in the two configurations.     

Photoelectrochemical properties of sol–gel-derived anatase and rutile TiO2 films

Anatase and rutile film electrodes with comparable porosities were prepared by the sol–gel dip-coating method, and the photoelectrochemical properties were studied based on photocurrent measurement and impedance analysis in a three-electrode wet cell. The photocurrent was found to increase with the donor density, both in anatase and rutile electrodes. For the same donor density, however, rutile electrodes exhibited higher photocurrents than anatase electrodes, which was ascribed to the more beneficial bandgap structure of the former.     

A Self‐Powered and Flexible Organometallic Halide Perovskite Photodetector with Very High Detectivity

Flexible and self‐powered photodetectors (PDs) are highly desirable for applications in image sensing, smart building, and optical communications. In this paper, a self‐powered and flexible PD based on the methylammonium lead iodide (CH₃NH₃PBI₃) perovskite is demonstrated. Such a self‐powered PD can operate even with irregular motion such as human finger tapping, which enables it to work without a bulky external power source. In addition, with high‐quality CH₃NH₃PBI₃ perovskite thin film fabricated with solvent engineering, the PD exhibits an impressive detectivity of 1.22 × 10¹³ Jones. In the self‐powered voltage detection mode, it achieves a large responsivity of up to 79.4 V mW^?1 cm^?2 and a voltage response of up to ≈90%. Moreover, as the PD is made of flexible and transparent polymer films, it can operate under bending and functions at 360 ° of illumination. As a result, the self‐powered, flexible, 360 ° omnidirectional perovskite PD, featuring high detectivity and responsivity along with real‐world sensing capability, suggests a new direction for next‐generation optical communications, sensing, and imaging applications.     

Decoupling the Effects of Self‐Assembled Monolayers on Gold,Silver, and Copper Organic Transistor Contacts

In bottom‐contact organic field‐effect transistors (OFETs), the functionalization of source/drain electrodes leads to a tailored surface chemistry for film growth and controlled interface energetics for charge injection. This report describes a comprehensive investigation into separating and correlating the energetic and morphological effects of a self‐assembled monolayers (SAMs) treatment on Au, Ag, and Cu electrodes. Fluorinated 5,11‐bis(triethylsilylethynyl) anthradithiophene (diF‐TES‐ADT) and pentafluorobenzenethiol (PFBT) are employed as a soluble small‐molecule semiconductor and a SAM material, respectively. Upon SAM modification, the Cu electrode devices benefit from a particularly dramatic performance improvement, closely approaching the performance of OFETs with PFBT‐Au and PFBT‐Ag. Ultraviolet photoemission spectroscopy, polarized optical microscopy, grazing‐incidence wide‐angle X‐ray scattering elucidate the metal work function change and templated crystal growth with high crystallinity resulting from SAMs. The transmission‐line method separates the channel and contact properties from the measured OFET current–voltage data, which conclusively describes the impact of the SAMs on charge injection and transport behavior.     

Chain-length dependence of photoelectric conversion from a porphyrin monolayer modified electrode

The photoelectrochemistry of a series of porphyrins containing an alkyl chain terminated with imidazolyl, is described. Indium–tin oxide electrodes deposited with porphyrins using the Langmuir–Blodgett (LB) technique exhibit high photocurrent values under ambient condition. Action spectra of the photocurrent generation are coincident with the absorption of the LB film-modified electrodes, indicating that the dye aggregates in the LB film are responsible for the photocurrent. The bias voltages that may influence the photocurrent have also been investigated. The photocurrents varied with the side chain length; the compound with a longer chain but not with the shortest chain generated the maximum photocurrent. To interpret such a special case, a possible mechanism is suggested.     

聚苯胺/TiO2复合纳米膜电极的制备及其光电性能

采用原位化学氧化法,在酸性TiO2溶胶中未加分散剂制备了聚苯胺修饰的TiO2稳定溶胶,并以涂刮法在柔性导电塑料薄膜上成膜。利用FT-IR、XRD、TEM、选区电子衍射、紫外-可见光谱、光电流-电压曲线对所制备的复合溶胶及复合膜进行了表征。结果表明TiO2与聚苯胺之间实现了结构上的复合,聚苯胺的引入改善了TiO2膜对太阳光的利用率,提高了TiO2膜的光电响应性能。这种用复合溶胶制备聚苯胺/TiO2复合膜的方式扩大了成膜基底的范围。     

Wire-shaped quantum dots-sensitized solar cells based on nanosheets and nanowires

Wire-shaped quantum dots-sensitized solar cells (WS-QDSCs) based on nanosheets and nanowires were fabricated and investigated for this paper. The nanosheets grown on stainless steel (SS) wire by electrodeposition were mainly composed of Zn?(OH)?Cl?·H?O and most of the Zn?(OH)?Cl?·H?O was converted to ZnO by post-treatment, and ZnO nanowires were directly grown on SS wire by the hydrothermal method. CdS QDs were deposited on nanosheets and nanowires by successive ionic layer adsorption and reaction method. The results of photoelectrochemical performance indicated that WS-QDSCs showed a similar conversion efficiency in polysulfide and Na?SO? electrolytes, while the WS-QDSCs based on the Cu2S counter electrode achieved much higher performance than those based on SS and Cu counter electrodes. By optimizing electrodeposition duration, the WS-QDSCs based on nanosheets presented the highest conversion efficiency of 0.60% for the duration of 20 min. Performance comparison indicated that the WS-QDSC based on nanosheets showed very superior performance to that based on the nanowires with similar film thickness.     

Trifunctional Self‐Supporting Cobalt‐Embedded Carbon Nanotube Films for ORR,OER, and HER Triggered by Solid Diffusion from Bulk Metal

The development of robust and efficient trifunctional catalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen reaction (HER) is central to regenerative metal–air batteries and overall water splitting. It is still a big challenge to achieve an efficient integration of three functions in one freestanding electrode. Herein, a facile and upscalable strategy is demonstrated, to construct cobalt nanoparticle‐encapsulated 3D conductive films (Co/CNFs), which were induced by in situ solid diffusion from bulk cobalt metal. Under high‐temperature, volatile cobalt species from bulk cobalt foil are trapped by the contacted nitrogen‐rich carbons, followed by catalytic growth of interconnected carbon tubes, forming the 3D structured film. This resulting film can be directly preformed as self‐supporting and binder‐free electrode, which simultaneously facilitates the ORR, OER, and HER with excellent activities and superior stability. Furthermore, such “all‐in‐one” film also exhibits remarkable performance for Zn–air batteries and overall water splitting, demonstrating its feasibility for practical applications.     

Fabrication of Cu2S on Cu film electrode and its application in lithium ion battery

Cu₂S film electrode direct growth on Cu foil is prepared by a simple hydrothermal approach. The electrochemical properties of the as-prepared Cu₂S electrode are investigated via conventional discharge and charge tests. When applying a current density of 0.1 mA cm^− 2, the as-prepared Cu₂S electrode exhibits discharge and charge capacity of 0.27, 0.32, 0.35, 0.34 and 0.34 mAh cm^− 2 at the 100th, 200th, 300th, 400th and 500th cycle, respectively. Such good performance of the as-prepared Cu₂S electrode is attributed to the fine electric contact between Cu₂S and Cu foil and the possible hollow structure of Cu₂S film.     

Hydrogen Terminated Germanene for a Robust Self‐Powered Flexible Photoelectrochemical Photodetector

As a rising star in the family of graphene analogues, germanene shows great potential for electronic and optical device applications due to its unique structure and electronic properties. It is revealed that the hydrogen terminated germanene not only maintains a high carrier mobility similar to that of germanene, but also exhibits strong light–matter interaction with a direct band gap, exhibiting great potential for photoelectronics. In this work, few‐layer germanane (GeH) nanosheets with controllable thickness are successfully synthesized by a solution‐based exfoliation–centrifugation route. Instead of complicated microfabrication techniques, a robust photoelectrochemical (PEC)‐type photodetector, which can be extended to flexible device, is developed by simply using the GeH nanosheet film as an active electrode. The device exhibits an outstanding photocurrent density of 2.9 µA cm^?2 with zero bias potential, excellent responsivity at around 22 µA W^?1 under illumination with intensity ranging from 60 to 140 mW cm^?2, as well as short response time (with rise and decay times, t_r = 0.24 s and t_d = 0.74 s). This efficient strategy for a constructing GeH‐based PEC‐type photodetector suggests a path to promising high‐performance, self‐powered, flexible photodetectors, and it also paves the way to a practical application of germanene.     

Stretchable Thin‐Film Electrodes for Flexible Electronics with High Deformability and Stretchability

Flexible and stretchable electronics represent today's cutting‐edge electronic technologies. As the most‐fundamental component of electronics, the thin‐film electrode remains the research frontier due to its key role in the successful development of flexible and stretchable electronic devices. Stretchability, however, is generally more challenging to achieve than flexibility. Stretchable electronic devices demand, above all else, that the thin‐film electrodes have the capacity to absorb a large level of strain (>>1%) without obvious changes in their electrical performance. This article reviews the progress in strategies for obtaining highly stretchable thin‐film electrodes. Applications of stretchable thin‐film electrodes fabricated via these strategies are described. Some perspectives and challenges in this field are also put forward.     

Metal on metal oxide nanowire Co-catalyzed Si photocathode for solar water splitting

We report a systematic study of Si|ZnO and Si|ZnO| metal photocathodes for effective photoelectrochemical cells and hydrogen generation. Both ZnO nanocrystalline thin films and vertical nanowire arrays were studied. Si|ZnO electrodes showed increased cathodic photocurrents due to improved charge separation by the formation of a p/n junction, and Si|ZnO:Al (n(+)-ZnO) and Si|ZnO(N(2)) (thin films prepared in N(2)/Ar gas) lead to a further increase in cathodic photocurrents. Si|ZnONW (nanowire array) photocathodes dramatically increased the photocurrents and thus photoelectrochemical conversion efficiency due to the enhanced light absorption and enlarged surface area. The ZnO film thickness and ZnO nanowire length were important to the enhancements. A thin metal coating on ZnO showed increased photocurrent due to a catalyzed hydrogen evolution reaction and Ni metal showed comparable catalytic activities to those of Pt and Pd. Moreover, photoelectrochemical instability of Si|ZnO electrodes was minimized by metal co-catalysts. Our results indicate that the metal and ZnO on p-type Si serve as co-catalysts for photoelectrochemical water splitting, which can provide a possible low-cost and scalable method to fabricate high efficiency photocathodes for practical applications in clean solar energy harvesting.     

A New Route to Low Resistance Contacts for Performance‐Enhanced Organic Electronic Devices

The barrier to charge carrier injection across the semiconductor/electrode interface is a key parameter in the performance of organic transistors and optoelectronic devices, and the work function of the electrode material plays an important role in determining the size of this barrier. We present a new, chemical route for making metal surfaces with low work functions, by functionalizing gold surfaces with self‐assembled monolayers of n,n‐dialkyl dithiocarbamates. Ultraviolet photoemission spectroscopy measurements show that work functions of 3.2 eV ± 0.1 eV can be achieved using this surface modification. Electronic structure calculations reveal that this low work function is a result of the packing‐density, polarization along the N‐C bond, and charge rearrangement associated with chemisorption. We demonstrate that electrodes functionalized with these monolayers significantly improve the performance of organic thin‐film transistors and can potentially be employed in charge selective contacts for organic photovoltaics.     

Facile Synthesis of Ant‐Nest‐Like Porous Duplex Copper as Deeply Cycling Host for Lithium Metal Anodes

Suppressing the dendrite formation and managing the volume change of lithium (Li) metal anode have been global challenges in the lithium batteries community. Herein, a duplex copper (Cu) foil with an ant‐nest‐like network and a dense substrate is reported for an ultrastable Li metal anode. The duplex Cu is fabricated by sulfurization of thick Cu foil with a subsequent skeleton self‐welding procedure. Uniform Li deposition is achieved by the 3D interconnected architecture and lithiophilic surface of self‐welded Cu skeleton. The sufficient space in the porous layer enables a large areal capacity for Li and significantly improves the electrode–electrolyte interface. Simulations reveal that the structure allows proper electric field penetration into the connected tunnels. The assembled Li anodes exhibit high coulombic efficiency (97.3% over 300 cycles) and long lifespan (>880 h) at a current density of 1 mA cm^?2 with a capacity of 1 mAh cm^?2. Stable and deep cycling can be maintained up to 50 times at a high capacity of 10 mAh cm^?2.     

Flexible ultrasonic transducers

Flexible ultrasonic transducers (UTs) consisting of a metal foil, a piezoelectric ceramic film, and a top electrode have been developed. The flexibility is realized owing to the porosity of piezoelectric film and the thinness of metal foil. In this paper, the stainless steel (SS), lead-zirconate-titanate (PZT)/PZT composite and silver paste were chosen as metal foil, piezoelectric film, and top electrode materials, respectively. The SS foil serves as both substrate and bottom electrode. The PZT/PZT piezoelectric composite film is made by the sol-gel spray technique. PZT/PZT films of thicknesses from 40 to 70 microm were fabricated onto SS foils. The capability of these flexible sensors operated in the pulse-echo mode for nondestructive testing on flat and curved surfaces of different materials at room temperature and 160 degrees C has been demonstrated. Numerical simulations of the effects of the metal foil thickness on the ultrasonic performance of flexible UTs also were carried out, and the results are in reasonable agreement with experimental data. In addition, a PZT/PZT flexible transducer showed a signal strength comparable with that obtained by a commercial room temperature broad bandwidth transducer.