Interfacial Gradient-Energy-Band-Alignment Modulation via a Vapor-Phase Anion-Exchange Reaction toward Lead-Free Perovskite Photodetectors with Excellent UV Imaging Capability

Bi-based inorganic perovskites have attracted great attention in optoelectronics, as they feature similar photoelectric properties but have high stability and lead-free merits. Unfortunately, due to the high exciton binding energy and small Bohr radius, their photodetection performance still largely lags behind that of Pb-based counterparts. Herein, using a vapor-phase chloride ion-substitution strategy, Cs3Bi2Br9 photodetectors (PDs) with gradient energy band alignment were delicately modulated, contributing to a high carrier separation/collection efficiency. The optimized Bi-based perovskite ACCT (Al2O3/Cs3Bi2Br9/Cs3Bi2ClxBr9-x/TiO2) PDs exhibit outstanding performance, the ON/OFF ratio and linear dynamic range (LDR) are significantly improved by 20 and 2.6 times, respectively. Significantly, we further demonstrate the high-SNR (signal-to-noise ratio) UV imaging based on the optimized device, which shows 21.887 dB higher than that of the pristine device. Finally, the vapor-phase anionexchange modified perovskite PDs show long-term stability and high UV resistance. Vapor-phase ion-substitution is a promising approach for the synergistic effect of matched energy band alignment and interface passivation, which can be applied to other perovskite-based optoelectronic devices.

Photoacoustic Communication from the Air to Underwater Based on Low-Cost Passive Relays

With the development of ocean research, communications from the air to underwater (e.g., aircraft to submarines) are especially important. However, the existing communication methods have their own limitations and wireless communication between underwater and the air has remained an unsolved problem. In this article, we propose a photoacoustic communication based on low-cost passive relays, which is capable of not only minimizing the energy loss both in water and in the air-water interface, but also relieving the difficulty of target seeking. Thus, we can get a six order of magnitude reduction of laser energy (25 J vs. 27 mu J) using passive relays whose cost is less than US$1.00. It is also demonstrated that our photoacoustic communication can work decently under complex water situations including waving and pollution. This creationary photoacoustic application may become a practical way to communicate from the air to underwater.

Tunneling-assisted highly sensitive and stable lead-free Cs3Bi2I9 perovskite photodetectors for diffuse reflection imaging

Lead-free perovskites exhibit low toxicity and have been investigated as new active materials for photoconversion applications. Among them, Cs3Bi2I9 perovskites have received extensive attention due to their eco-friendliness, excellent stability and high photosensitivity. Herein, the optical and electronic bandgap of Cs3Bi2I9 thin films are determined to be 2.19 eV and 2.55 eV, providing insights into strong excitonic photodetection materials. Furthermore, we introduce an ultrathin Al2O3 layer into the interface of Cs3Bi2I9 perovskite PDs using the atomic layer deposition (ALD). The ON/OFF ratio can be significantly improved by 20-fold using an Al2O3 layer with an optimal thickness of 1.5 nm due to the interfacial-tunneling-effect. Moreover, the unsealed Cs3Bi2I9 perovskite PDs exhibit excellent stability, and can retain 90% of their original performance after 30 days under ambient conditions (25 degrees C, RH = 60%). Furthermore, the potential application in diffuse reflection imaging has been explored based on Cs3Bi2I9 perovskite PDs without encapsulation, confirming a high-resolution and high-contrast imaging demonstration.

Importance of Bi-O Bonds at the Cs2AgBiBr6 Double-Perovskite/Substrate Interface for Crystal Quality and Photoelectric Performance

Interface interactions between perovskite materials and substrates are of great significance for the development of high-quality perovskite materials. Herein, we have successfully prepared Cs2AgBiBr6 double-perovskite films via a one-step spin-coating process and demonstrated a novel approach that modifies the surface of substrates with an ultrathin metal oxide (MOx) layer to promote the film quality and photoelectric performance. Characterization results strongly suggest that the improvement is attributed to the Bi-O interfacial interaction at substrate/perovskite interface. Benefiting from this interface interaction, the average grain size of Cs2AgBiBr6 films has remarkably risen up to similar to 500 nm, which is nearly four times larger than the one directly deposited on a commercial fluorine-doped tin oxide substrate. Meanwhile, the pin hole surface area ratio has reduced from 2.61 to 0.60%. Furthermore, the corresponding photodetectors (PDs) have been fabricated and the performance has significantly improved owing to the enhanced Cs2AgBiBr6 film quality. The on-off ratio of the optimized PD has a boost of almost 10 times. In addition, the minimum detected irradiation has decreased from 9.7 X 10(-8) to 1.9 X 10(-9) W cm(-2), as well as the maximum detectivity has increased from 3.3 X 10(11) to 1.2 x 10(13) Jones. These results suggest a feasible method for crystallization improvement of double-perovskite films and indicate promising promotion of photoelectric performance.

Importance of Bi–O Bonds at the Cs2AgBiBr6 Double-Perovskite/Substrate Interface for Crystal Quality and Photoelectric Performance

Reducing the dark current of cuprous oxide/Au schottky photodetector for high signal-to-noise ratio imaging

Photodetectors (PDs) as image sensors have been widely used in imaging system due to their outstanding photosensitivity. The improvement of imaging quality (signal-to-noise ratio (SNR)) can be realized by reducing the dark current of PDs. Conventionally, interfacial engineering can effectively suppress the dark current of PDs. Nevertheless, these techniques are hard to be applied in practical imaging systems owing to their complicated process. In this work, we proposed a facile method to reduce the dark current of Cu2O/Au Schottky PDs, and further demonstrated its application in high SNR imaging system. By applying a small external bias of -120 mu V, the dark current of PDs decreases from 27 nA to 0.6 nA, with 4023% improvements of ON/OFF ratio. Additonaly, a model based on free carriers generated by rich trap-state and thermal excitation under asymmetric internal electric field was proposed to understand this phenomenon. Finally, a high-resolution image with high SNR (48 dB) was acquired, which is close to that of commercial Si-CDD and CMOS. Our results provide a convenient way to reduce the dark current and improve the image quality, also suggest Cu2O is potentially an attractive candidate to be applied in optical imaging applications.

Controllable fabrication of alpha-Ni(OH)(2) thin films with preheating treatment for long-term stable electrochromic and energy storage applications

Although dual-functional electrochromic energy storage (EES) materials are important for the development of smart windows for energy-saving applications, few EES materials simultaneously possess fast switching time, long-term stability and high capacitance, which are among the most important characteristics for their applications. Herein, we present the controllable synthesis of pure alpha-Ni(OH)(2) via an improved one-step electrodeposition process. The as-deposited Ni(OH)(2) EES electrodes exhibited significantly enhanced performances with broad-range optical modulation of 78.6% at 550 nm, fast switching time of 0.9 s for coloration and 1.2 s for bleaching, as well as excellent stability (45000 cycles). Meanwhile, the EES electrodes exhibited an excellent energy storage performance with an areal capacitance of 154.05 mF cm(-2), and could light up a green light-emitting diode for 20 min. The improved EES performance is mainly attributed to the phase-controllable fabrication of uniform and compact alpha-Ni(OH)(2) thin films with a small charge-transfer resistance, which exhibit a stable structure, allowing for fast ion intercalation/de-intercalation during the reversible redox reactions. The scalable and cost-effective fabrication of alpha-Ni(OH)(2) materials is expected to expand the EES applications to other metal hydroxide materials.

Interfacial engineering to boost photoresponse performance and stability of V2O5/n-Si heterojunction photodetectors

Transitional metal oxides (TMOs) have demonstrated as a promising alternative to doped layers in highefficient crystalline silicon heterojunction solar cells. However, the unintentional oxidation causes serious carrier recombination at the interface, which accounts for the low photoelectric conversion efficiency and poor stability. Herein, a self-powered, broad-band, fast-response V2O5/n-Si heterojunction photodetectors (PDs) are fabricated by thermal evaporation of an ultrathin V2O5 thin films on nanoporous pyramid silicon structures. By interfacial engineering with structural optimization and surface methyl passivation, the photodetection performance and stability of V2O5/n-Si PDs can be significantly enhanced. The V2O5/n-Si heterojunction PDs demonstrate a high on/off ratio of 1.4x10(4), fast-response speed of 9.5 is, high responsivity of 185 mA W-1(@940 nm) and high specific detectivity (1.34x10(12) Jones). Based on the energy band alignment analysis, the excellent photoresponse performance is mainly attributed to the efficient carrier separation after surface passivation by methyl group. Additionally, the built-in electric field at the interface also accelerates the charge carrier separation. Our work would contribute to the fabrications of other TMOs-based heterojunctions, and give some enlightening insights into the understanding of carrier transportation in heterojunctions. (C) 2019 Elsevier B.V. All rights reserved.

Controllable fabrication of α-Ni(OH)2 thin films with preheating treatment for long-term stable electrochromic and energy storage applications

Long-term stable, fast switching α-Ni(OH)2 electrodes for electrochromic energy storage application has been fabricated by one-step preheating treatment. The cost-effective fabrication is expected to expand to other metal hydroxide materials.

Precise Phase Control of Large-Scale Inorganic Perovskites via Vapor-Phase Anion-Exchange Strategy

Anion exchange offers great flexibility and high precision in phase control, compositional engineering, and optoelectronic property tuning. Different from previous successful anion exchange process in liquid solution, herein, a vapor-phase anion-exchange strategy is developed to realize the precise phase and bandgap control of large-scale inorganic perovskites by using gas injection cycle, producing some perovskites such as CsPbCl3 which has never been reported in thin film morphology. Ab initio calculations also provide the insightful mechanism to understand the impact of anion exchange on tuning the electronic properties and optimizing the structural stability. Furthermore, because of precise control of specific atomic concentrations, intriguing tunable photoluminescence is observed and photodetectors with tunable photoresponse edge from green to ultraviolet light can be realized accurately with an ultrahigh spectral resolution of 1 nm. Therefore, a new, universal vapor-phase anion exchange method is offered for inorganic perovskite with fine-tunable optoelectronic properties.

Unveiling the electrochromic mechanism of Prussian Blue by electronic transition analysis

Prussian blue (PB) represents a class of metal-organic coordinated compounds with fascinating electrochromic properties. Although the electronic structure has been studied intensively, its electrochromic mechanism remains unresolved due to the lack of electronic-transition analysis. Herein, we investigate the electrochromism of Prussian blue (PB) and its derivatives by combining optical characterization and density functional theory (DFT) calculations. We unambiguously determine the optical gaps of PB-related derivatives and construct a smart window exhibiting excellent electrochromic performance and temperature control. DFT calculations demonstrate that the coloring of Prussian yellow (PY) is critically governed by two absorption bands centered at ca. 2.4 eV and 3.0 eV respectively. The former is weak and is generated by the charge-transfer transitions from the Fe(I)-t(2g) (Fe ions connected with C) band to the Fe(II)-t(2g) (Fe ions connected with N) band. The latter is strong and is induced by the electronic excitations from the Fe(I)-t(2g) band to the antibonding Fe(II)-eg band. The color change from yellow to blue is induced by the reduction of Fe(I) ions, which redshifts and enhances the former transitions but suppresses the latter transitions. In contrast, the color change from blue to transparency (Prussian white) is induced by the reduction of Fe(II) ions, which enlarges the bandgap and permits transmittance of visible light. The band-edge transition oscillator strengths are critically governed by the state weight of C-p, which provides opportunities for optical modulation via anionic doping. The insights obtained in this work are fundamental for understanding and controlling the opto-electronic properties of PB-related compounds for intelligent applications.

Reducing current fluctuation of Cs3Bi2Br9 perovskite photodetectors for diffuse reflection imaging with wide dynamic range

Recently, the newly booming metal halide perovskites have attracted extensive attention worldwide due to their outstanding optoelectronic performance, and are expected to be ideal candidates for photodetectors (PDs). However, there is still lack of perovskite PDs-based imaging devices coming into commercialization stage, due to some practical reasons including toxicity brought by lead-based perovskites and the large light current fluctuations. In this paper, for the first time we fabricate a lead-free Cs3Bi2Br9 perovskite PD, and build a prototype of this perovskite PD-based imaging system with diffuse reflection imaging mode. Moreover, we propose a new parameter F related to light current fluctuation to evaluate imaging performance of a PD especially for weak diffuse light condition, and prove its usability by comparison of unoptimized lead-free Cs(3)Bi(2)Br(9 )perovskite PD and atomic layer deposition (ALD) optimized Cs3Bi2Br9 PD. ALD-optimization can improve the quality of perovskite film and suppress the dark current and current fluctuation. Finally, we obtain satisfactory diffuse reflection images of 2D and 3D objects with wide dynamic range. Therefore, the ALD-optimized Cs3Bi2Br9 PD has addressed two major concerns about perovskite PDs-based imaging devices, that may extend application of perovskite materials and improve imaging quality. (C) 2020 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.

Solution-Processed High-Quality Cu2O Thin Films as Hole Transport Layers for Pushing the Conversion Efficiency Limit of Cu2O/Si Heterojunction Solar Cells

Cuprous oxide (Cu2O) is a nontoxic and earth-abundant semiconductor material, which is a promising candidate for low-cost photovoltaic applications. Although Cu2O-based solar cells have been studied for a few decades, they still suffer from disappointing photovoltaic performance due to its high trap-state density and inferior carrier collection efficiency. Herein, a facile solution method is demonstrated to synthesize high-quality Cu2O films with low defects as hole transport layers (HTLs) and the Cu2O/Si heterojunction solar cells are fabricated. Moreover, a variety of interfacial engineering and light management strategies are adopted to push the efficiency limit of Cu2O/Si solar cells, including a Ag transparent conductive layer, HNO3 passivation, Mg electrode back contact, and MoOx antireflection layer, which enable the boosting of carrier separation and reduce the loss of incident solar light, yielding a record high power conversion efficiency of 9.54%. This work may pave the way for economical and environment-friendly use of Cu2O/Si heterojunction solar cells in daily life.

Atomic-Layer Deposition-Assisted Double-Side Interfacial Engineering for High-Performance Flexible and Stable CsPbBr3 Perovskite Photodetectors toward Visible Light Communication Applications

Self-powered photodetectors (PDs) based on inorganic metal halide perovskites are regarded as promising alternatives for the next generation of photodetectors. However, uncontrollable film growth and sluggish charge extraction at interfaces directly limit the sensitivity and response speed of perovskite-based photodetectors. Herein, by assistance of an atomic layer deposition (ALD) technique, CsPbBr3 perovskite thin films with preferred orientation and enlarged grain size are obtained on predeposited interfacial modification layers. Thanks to improved film quality and double side interfacial engineering, the optimized CsPbBr3 (Al2O3/CsPbBr3/TiO2, ACT) perovskite PDs exhibit outstanding performance with ultralow dark current of 10(-11) A, high detectivity of 1.88 x 10(13) Jones and broad linear dynamic range (LDR) of 172.7 dB. Significantly, excellent long-term environmental stability (ambient conditions >100 d) and flexibility stability (>3000 cycles) are also achieved. The remarkable performance is credited to the synergistic effects of high carrier conductivity and collection efficiency, which is assisted by ALD modification layers. Finally, the ACT PDs are successfully integrated into a visible light communication system as a light receiver on transmitting texts, showing a bit rate as high as 100 kbps. These results open the window of high performance all-inorganic halide perovskite photodetectors and extends to rational applications for optical communication.

Significantly Enhancing Response Speed of Self-Powered Cu2ZnSn(S,Se)4 Thin Film Photodetectors by Atomic Layer Deposition of Simultaneous Electron Blocking and Electrode Protective Al2O3 Layers

High performance MoO3−x/Si heterojunction photodetectors with nanoporous pyramid Si arrays for visible light communication application

Self-powered, fast-response heterojunction photodetectors based on nanoporous pyramid Si arrays are successfully developed. The photodetector is further integrated into a visible light communication system as an optical signal receiver.

Valence-State Controllable Fabrication of Cu2–xO/Si Type-II Heterojunction for High-Performance Photodetectors

Significantly Enhanced Detectivity of CIGS Broadband High-Speed Photodetectors by Grain Size Control and ALD-Al2O3 Interfacial-Layer Modification

Solution‐Processed High‐Quality Cu 2 O Thin Films as Hole Transport Layers for Pushing the Conversion Efficiency Limit of Cu 2 O/Si Heterojunction Solar Cells

Reliable Information Encryption and Digital Display Applications Based on Multistate Smart Windows

In situ plasmonic optical fiber detection of the state of charge of supercapacitors for renewable energy storage

Visualized UV Photodetectors Based on Prussian Blue/TiO2 for Smart Irradiation Monitoring Application

Facile synthesis of TiO2/Mn3O4 hierarchical structures for fiber-shaped flexible asymmetric supercapacitors with ultrahigh stability and tailorable performance

A flexible fiber-shaped electrode based on a hierarchical TiO2/Mn3O4 structure was successfully fabricated via a facile synthesis method.

Rational design of carbon shell endows TiN@C nanotube based fiber supercapacitors with significantly enhanced mechanical stability and electrochemical performance

Electrochromic Asymmetric Supercapacitor Windows Enable Direct Determination of Energy Status by the Naked Eye

Tailorable pseudocapacitors for energy storage clothes

All-solid-state tailorable supercapacitors based on flexible carbon nanotube (CNT)–polymer and CNT–metal oxide hybrid electrodes are successfully demonstrated.

Tailorable and Wearable Textile Devices for Solar Energy Harvesting and Simultaneous Storage

Interface Engineering To Boost Photoresponse Performance of Self-Powered, Broad-Bandwidth PEDOT:PSS/Si Heterojunction Photodetector

Combining Bulk/Surface Engineering of Hematite To Synergistically Improve Its Photoelectrochemical Water Splitting Performance

WO3 nanoflowers with excellent pseudo-capacitive performance and the capacitance contribution analysis

WO3 nanoflower based negative electrodes demonstrate excellent balance between areal and gravimetric specific capacitances.

Flexible electrochromic supercapacitor hybrid electrodes based on tungsten oxide films and silver nanowires

The flexible electrochromic supercapacitor electrode exhibits good electrochemical performances (13.6 mF cm−2, 138.2 F g−1) and high coloration efficiency (80.2 cm2 C−1).

Flexible honeycomb-like NiMn layered double hydroxide/carbon cloth architecture for electrochemical energy storage

BiOI–BiVO 4 photoanodes with significantly improved solar water splitting capability: p–n junction to expand solar adsorption range and facilitate charge carrier dynamics

Self-Powered, High-Speed and Visible–Near Infrared Response of MoO3–x/n-Si Heterojunction Photodetector with Enhanced Performance by Interfacial Engineering