Photoelectric Detectors Based on Inorganic p-Type Semiconductor Materials

Elucidating the Chirality-Induced Spin Selectivity Effect of Co-Doped NiO Deposited on Ni Foam for Highly Stable Zn-Air Batteries

The urgent need to alleviate global warming and limit the consumption of fossil fuels has prompted the development of rechargeable Zn-air batteries (ZABs) considering their superior energy density, safety, and cost-effectiveness. However, the sluggish reaction kinetics of the oxygen evolution reaction (OER) and the unfavorable properties of conventional OER catalysts (including low electrical conductivity and the use of active site-blocking binders) hinder the development of practically viable ZABs. Herein, we report a distinct approach for directly synthesizing cobalt-doped nickel oxide (Co-NiO) with a chiral structure on porous Ni foam via a one-step hydrothermal process. The chirality-induced spin selectivity (CISS) boosts the OER kinetics, while Co doping elevates the electrical conductivity and the abundance of active sites on the catalyst. The chiral Co-NiO demonstrates an OER current density of 10 mA cm-2 at 1.58 V versus the reversible hydrogen electrode, outperforming both achiral Co-NiO and undoped NiO. Furthermore, a chiral Co-NiO-based rechargeable ZAB demonstrates a high open-circuit potential (1.57 V), a low charge/discharge overpotential (0.71 V), and excellent stability for 960 h (40 days) because the CISS effect mitigates the production of the corrosive singlet oxygen. These results represent a prominent pathway for the advancement of ZABs using the low-cost oxygen evolution catalyst modulated by the CISS effect and heteroatomic doping.

Investigation of the GO effect on CdS quantum dot sensitized PV-cells based on the GO-TiO2 nanocomposite photoanode: modeling using the Lambert function

Titanium dioxide (TiO2) and graphene oxide-TiO2 (GO-TiO2) photoanode nanocomposite solar cells, incorporating CdS quantum dots, were analyzed. The current and power density versus voltage characteristics of the fabricated photovoltaic (PV) cells were measured under different power densities. A fourfold increase in short-circuit current density, from 0.481 mA cm-2 to 2 mA cm-2, was observed by adding 0.12 g of graphene. This increase in performance is attributed to the enhanced electrical and optical properties provided by graphene, which generates more charge carriers and increases the density of electron-hole pairs by absorbing white light. Quantum dots were also employed to improve the solar cell performance. The capacitance-frequency characteristics of the graphene-TiO2 composite photoanode, based on CdS quantum dots, were studied with graphene. The negative capacitance behavior of PV cells with graphene was investigated, revealing that graphene significantly influences these values. As a result, adding graphene enhanced the inductive behavior of the quantum dot-sensitized solar cells (QDSSCs). The electrical characteristics of the solar cells were studied, and the experimental data for current and power density versus voltage were simulated using the Lambert function to explain the effect of graphene on the inductive behavior of TiO2/CdS-based cells.

Engineering n-Type and p-Type BiOI Nanosheets: Influence of Mannitol on Semiconductor Behavior and Photocatalytic Activity

Photocatalytic technology holds significant promise for sustainable development and environmental protection due to its ability to utilize renewable energy sources and degrade pollutants efficiently. In this study, BiOI nanosheets (NSs) were synthesized using a simple water bath method with varying amounts of mannitol and reaction temperatures to investigate their structural, morphological, photoelectronic, and photocatalytic properties. Notably, the introduction of mannitol played a critical role in inducing a transition in BiOI from an n-type to a p-type semiconductor, as evidenced by Mott-Schottky (M-S) and band structure analyses. This transformation enhanced the density of holes (h+) as primary charge carriers and resulted in the most negative conduction band (CB) position (-0.822 V vs. NHE), which facilitated the generation of superoxide radicals (·O2-) and enhanced photocatalytic activity. Among the samples, the BiOI-0.25-60 NSs (synthesized with 0.25 g of mannitol at 60 °C) exhibited the highest performance, characterized by the largest specific surface area (24.46 m2/g), optimal band gap energy (2.28 eV), and efficient photogenerated charge separation. Photocatalytic experiments demonstrated that BiOI-0.25-60 NSs achieved superior methylene blue (MB) degradation efficiency of 96.5% under simulated sunlight, 1.14 times higher than BiOI-0-70 NSs. Additionally, BiOI-0.25-60 NSs effectively degraded tetracycline (TC), 2,4-dichlorophenol (2,4-D), and rhodamine B (Rh B). Key factors such as photocatalyst concentration, MB concentration, and solution pH were analyzed, and the BiOI-0.25-60 NSs demonstrated excellent recyclability, retaining over 94.3% of their activity after three cycles. Scavenger tests further identified ·O2- and h+ as the dominant active species driving the photocatalytic process. In this study, the pivotal role of mannitol in modulating the semiconductor characteristics of BiOI nanomaterials is underscored, particularly in promoting the n-type to p-type transition and enhancing photocatalytic efficiency. These findings provide a valuable strategy for designing high-performance p-type photocatalysts for environmental remediation applications.

High-Sensitivity and Fast-Response Photomultiplication Type Photodetectors Based on Quasi-2D Perovskite Films for Weak-Light Detection

Photovoltaic photodiodes often face challenges in effectively harvesting electrical signals, especially when detecting faint light. In contrast, photomultiplication type photodetectors (PM-PDs) are renowned for their exceptional sensitivity to weak signals. Here, an advanced PM-PD is introduced based on quasi 2D Ruddlesden-Popper (Q-2D RP) perovskites, optimized for weak light detection at minimal operating voltages. The abundant traps at the Q-2D RP surface capture charge carriers, inducing a trap-assisted tunneling mechanism that leads to the photomultiplication (PM) effect. Deep-lying trap states within the Q-2D RP bulk accelerate charge carrier recombination, resulting in an outstanding rise/fall time of 1.14/1.72 µs for the PM-PDs. The PM-PD achieves a remarkable response level of up to 45.89 A W-1 and an extraordinary external quantum efficiency of 14400% at -1 V under an illumination of 1 µW cm- 2. The intrinsic high resistance of the Q-2D perovskite results in a low dark current, enabling an impressive detectivity of 4.23 × 1012 Jones based on noise current at -1 V. Furthermore, the practical application of PM-PDs has been demonstrated in weak-light, high-rate communication systems. These findings confirm the significant potential of PM-PDs based on Q-2D perovskites for weak light detection and suggest new directions for developing low-power, high-performance PM-PDs for future applications.

Zr-Doping Strategy of High-Quality Cu2O/β-Ga2O3 Heterojunction for Ultrahigh-Performance Solar-Blind Ultraviolet Photodetection

β-Ga2O3, as an ultrawide band gap semiconductor, has emerged as the most promising candidate in solar-blind photodetectors. The practical application of β-Ga2O3, however, suffers from intrinsic defects and suboptimal crystal quality within the devices. In this work, high-quality β-Ga2O3 was successfully synthesized by employing the Zr-doping strategy, which has facilitated the development of ultrahigh-performance solar-blind photodetectors based on Cu2O/β-Ga2O3 heterostructures. Structural analyses indicate that the strong Zr-O covalent bond effectively stabilizes the material, thereby eliminating oxygen vacancy defects. The Cu2O/β-Ga2O3 heterostructure photodetector demonstrates an ultrahigh responsivity and detectivity coupled with an external quantum efficiency. Furthermore, the device exhibits a photocurrent-to-dark current ratio of 3 × 105, showcasing its superior capability in detecting low-intensity deep ultraviolet signals, markedly surpassing previous heterostructure ultraviolet photodetectors. These exceptional performances are attributed to the effective elimination of oxygen vacancy defects in β-Ga2O3 and the variation of band alignment at the interface, which facilitate rapid separation of photogenerated electron-hole pairs under reverse bias. This study not only provides an enhanced and easy route to mitigate oxygen vacancy defects in oxide materials but also propels further exploration into the next generation of flexible, high-performance, solar-blind ultraviolet photodetectors.

Se-S bonded non-metal elementary substance heterojunction activating photoelectrochemical water splitting

Non-metal elements are often merely regarded as electronic modulators, yet their intrinsic characteristics are frequently overlooked. Indeed, non-metal elements possess notable advantages in high-abundance, excellent hydrogen adsorption and the ability of active sites to be inversely activated, rendering them potential photoelectrochemical (PEC) materials. However, weak non-metal interbinding, susceptibility to photocorrosion, and high photogenerated carrier recombination rates hinder their practical applications. Herein, for the first time, we report a novel non-metal elementary substance heterojunction Se/S based on interfacial bonding engineering strategy. Atomic-level tight coupling of sulfonyl-rich sulfur quantum dots (SQDs) with selenium microtube arrays (Se-MTAs) enhances the structural stability of Se/S and introduces crucial Se-S heterointerfacial bonds, which not only endow Se/S with robust internal electronic interactions, but also provide high-speed channels for charge separation via unique bridging. Consequently, Se/S achieves optimal photocurrent density of 3.91 mA cm-2 at 0 VRHE, accompanied by long-term stability over 24 h. It is the highest value reported to date for Se-based photocathodes without co-catalyst and outperforms most metal-selenide-based photoelectrodes. Furthermore, the direct Z-scheme charge transport mechanism is exposed by in-depth spectroscopic analyses. Our work fills the gap in application of non-metal elementary substance heterojunction for PEC, poised for potential expansion into other new-energy devices.

Compact Physical Implementation of Spiking Neural Network Using Ambipolar WSe2 n-Type/p-Type Ferroelectric Field-Effect Transistor

Spiking neural networks (SNNs) are attracting increasing interests for their ability to emulate biological processes, offering energy-efficient computation and event-driven processing. Currently, no devices are known to combine both neuronal and synaptic functions. This study presents an experimental demonstration of an ambipolar WSe2 n-type/p-type ferroelectric field-effect transistor (n/p-FeFET) integrated with ferroelectric Hf0.5Zr0.5O2 (HZO) to achieve both volatile and nonvolatile properties in a single device. The nonvolatile n-FeFET, driven by the stable ferroelectric properties of HZO, exhibits highly linear synaptic behavior. In contrast, the volatile p-FeFET, influenced by electron self-compensation in the ambipolar WSe2, enables self-resetting leaky-integrate-and-fire neurons. Integrating neuronal and synaptic functions in the same device allows for compact neuromorphic computing applications. Additionally, simulations of SNNs using experimentally calibrated synaptic and neuronal models achieved a 93.8% accuracy in MNIST digit recognition. This innovative approach advances the development of SNNs with high biomimetic fidelity and reduced hardware costs.

TexSe1-x Shortwave Infrared Photodiode Arrays with Monolithic Integration

TexSe1-x shortwave infrared (SWIR) photodetectors show promise for monolithic integration with readout integrated circuits (ROIC), making it a potential alternative to conventional expensive SWIR photodetectors. However, challenges such as a high dark current density and insufficient detection performance hinder their application in large-scale monolithic integration. Herein, we develop a ZnO/TexSe1-x heterojunction photodiode and synergistically address the interfacial elemental diffusion and dangling bonds via inserting a well-selected 0.3 nm amorphous TeO2 interfacial layer. The optimized device achieves a reduced dark current density of -3.5 × 10-5 A cm-2 at -10 mV, a broad response from 300 to 1700 nm, a room-temperature detectivity exceeding 2.03 × 1011 Jones, and a 3 dB bandwidth of 173 kHz. Furthermore, for the first time, we monolithically integrate the TexSe1-x photodiodes on ROIC (64 × 64 pixels) with the largest-scale array among all TexSe1-x-based detectors. Finally, we demonstrate its applications in transmission imaging and substance identification.

Role of growth temperature on microstructural and electronic properties of rapid thermally grown MoTe2thin film for infrared detection

In the field of electronic and optoelectronic applications, two-dimensional materials are found to be promising candidates for futuristic devices. For the detection of infrared (IR) light, MoTe2possesses an appropriate bandgap for which p-MoTe2/n-Si heterojunctions are well suited for photodetectors. In this study, a rapid thermal technique is used to grow MoTe2thin films on silicon (Si) substrates. Molybdenum (Mo) thin films are deposited using a sputtering system on the Si substrate and tellurium (Te) film is deposited on the Mo film by a thermal evaporation technique. The substrates with Mo/Te thin films are kept in a face-to-face manner inside the rapid thermal-processing furnace. The growth is carried out at a base pressure of 2 torr with a flow of 160 sccm of argon gas at different temperatures ranging from 400 °C to 700 °C. The x-ray diffraction peaks appear around 2θ= 12.8°, 25.5°, 39.2°, and 53.2° corresponding to (002), (004), (006), and (008) orientation of a hexagonal 2H-MoTe2structure. The characteristic Raman peaks of MoTe2, observed at ∼119 cm-1and ∼172 cm-1, correspond to the in-plane E1gand out-of-plane A1gmodes of MoTe2, whereas the prominent peaks of the in-plane E12gmode at ∼234 cm-1and the out-of-plane B12gmode at ∼289 cm-1are also observed. Root mean square (RMS) roughness is found to increase with increasing growth temperature. The bandgap of MoTe2is calculated using a Tauc plot and is found to be 0.90 eV. Electrical characterizations are carried out using current-voltage and current-time measurement, where the maximum responsivity and detectivity are found to be 127.37 mA W-1and 85.21 × 107Jones for a growth temperature of 600 °C and an IR wavelength illumination of 1060 nm.

Multimodal Artificial Synapses for Neuromorphic Application

The rapid development of neuromorphic computing has led to widespread investigation of artificial synapses. These synapses can perform parallel in-memory computing functions while transmitting signals, enabling low-energy and fast artificial intelligence. Robots are the most ideal endpoint for the application of artificial intelligence. In the human nervous system, there are different types of synapses for sensory input, allowing for signal preprocessing at the receiving end. Therefore, the development of anthropomorphic intelligent robots requires not only an artificial intelligence system as the brain but also the combination of multimodal artificial synapses for multisensory sensing, including visual, tactile, olfactory, auditory, and taste. This article reviews the working mechanisms of artificial synapses with different stimulation and response modalities, and presents their use in various neuromorphic tasks. We aim to provide researchers in this frontier field with a comprehensive understanding of multimodal artificial synapses.

Metal-Organic Framework-Based Photodetectors

The unique and interesting physical and chemical properties of metal-organic framework (MOF) materials have recently attracted extensive attention in a new generation of photoelectric applications. In this review, we summarized and discussed the research progress on MOF-based photodetectors. The methods of preparing MOF-based photodetectors and various types of MOF single crystals and thin film as well as MOF composites are introduced in details. Additionally, the photodetectors applications for X-ray, ultraviolet and infrared light, biological detectors, and circularly polarized light photodetectors are discussed. Furthermore, summaries and challenges are provided for this important research field.

Recent progress of group III-V materials-based nanostructures for photodetection

Due to the suitable bandgap structure, efficient conversion rates of photon to electron, adjustable optical bandgap, high electron mobility/aspect ratio, low defects, and outstanding optical and electrical properties for device design, III-V semiconductors have shown excellent properties for optoelectronic applications, including photodiodes, photodetectors, solar cells, photocatalysis, etc. In particular, III-V nanostructures have attracted considerable interest as a promising photodetector platform, where high-performance photodetectors can be achieved based on the geometry-related light absorption and carrier transport properties of III-V materials. However, the detection ranges from Ultraviolet to Terahertz including broadband photodetectors of III-V semiconductors still have not been more broadly development despite significant efforts to obtain the high performance of III-V semiconductors. Therefore, the recent development of III-V photodetectors in a broad detection range from Ultraviolet to Terahertz, and future requirements are highly desired. In this review, the recent development of photodetectors based on III-V semiconductor with different detection range is discussed. First, the bandgap of III-V materials and synthesis methods of III-V nanostructures are explored, subsequently, the detection mechanism and key figures-of-merit for the photodetectors are introduced, and then the device performance and emerging applications of photodetectors are provided. Lastly, the challenges and future research directions of III-V materials for photodetectors are presented.

Element Diffusion Induced Carrier Transport Enhancement in High-Performance CZTSSe Self-Powered Photodetector

Cu2ZnSn(S,Se)4 (CZTSSe) has attracted great interest in thin-film solar cells due to its excellent photoelectric performance in past decades, and recently is gradually expanding to the field of photodetectors. Here, the CZTSSe self-powered photodetector is prepared by using traditional photovoltaic device structure. Under zero bias, it exhibits the excellent performance with a maximum responsivity of 0.77 A W-1, a high detectivity of 8.78 × 1012 Jones, and a wide linear dynamic range of 103 dB. Very fast response speed with the rise/decay times of 0.576/1.792 µs, and ultra-high switching ratio of 3.54 × 105 are obtained. Comprehensive electrical and microstructure characterizations confirm that element diffusion among ITO, CdS, and CZTSSe layers not only optimizes band alignment of CdS/CZTSSe, but also suppresses the formation of interface defects. Such a suppression of interface defects and spike-like band alignment significantly inhibit carrier nonradiative recombination at interface and promote carrier transport capability. The low trap density in CZTSSe and low back contact barrier of CZTSSe/Mo could be responsible for the very fast response time of photodetector. This work definitely provides guidance for designing a high performance self-powered photodetector with high photoresponse, high switching ratio, fast response speed, and broad linear dynamic range.

First principles calculation of interface interactions and photoelectric properties of ZnSe/SnSe heterostructure

Heterostructure engineering is an effective technology to improve photo-electronic properties of two dimensional layered semiconductors. In this paper, based on first principles method, we studied the structure, stability, energy band, and optical properties of ZnSe/SnSe heterostructure change with film layer. Results show that all heterostructures are the type-II band arrangement, and the interlayer interaction is characterized by van der Waals. The electron concentration and charge density difference implies the electron (holes) transition from SnSe to monolayer ZnSe. By increasing the layer of SnSe films, the quantum effects are weakened leading to the band gap reduced, and eventually show metal properties. The optical properties also have obvious change, the excellent absorption ability of ZnSe/SnSe heterostructures mainly near the infrared spectroscopy. These works suggest that ZnSe/SnSe heterostructure has significant potential for future optoelectronic applications.

Redox-Sensitive NiOx Stabilizing Perovskite Films for High-Performance Photovoltaics

Metal halide perovskite materials inherently possess imperfections, particularly under nonequilibrium conditions, such as exposure to light or heat. To tackle this challenge, we introduced stearate ligand-capped nickel oxide (NiOx), a redox-sensitive metal oxide with variable valence, into perovskite intermediate films. The integration of NiOx improved the efficiency and stability of perovskite solar cells (PSCs) by offering multifunctional roles: (1) chemical passivation for ongoing defect repair, (2) energetic passivation to bolster defect tolerance, and (3) field-effect passivation to mitigate charge accumulation. Employing a synergistic approach that tailored these three passivation mechanisms led to a substantial increase in the devices' efficiencies. The target cell (0.12 cm2) and module (18 cm2) exhibited efficiencies of 24.0 and 22.9%, respectively. Notably, the encapsulated modules maintained almost 100 and 87% of the initial efficiencies after operating for 1100 h at the maximum power point (60 °C, 50% RH) and 2000 h of damp-heat testing (85 °C, 85% RH), respectively. Outdoor real-time tests further validated the commercial viability of the NiOx-assisted PSMs. The proposed passivation strategy provides a practical and uncomplicated approach for fabricating high-efficiency and stable photovoltaics.

Suppressing Carrier Recombination in BiVO4/PEDOT:PSS Heterojunction for High-Performance Photodetector

The organic-inorganic hybrid heterojunction is introduced for the first time to break through the performance bottleneck of BiVO4-based photodetectors. Through a facile solution process, a p-n heterojunction is established at the BiVO4/PEDOT:PSS interface, and the built-in electric field is designed to separate photogenerated charge carriers. The hybrid heterojunction outputs a significantly increased photocurrent, which is 24 000 times larger than that of the bare BiVO4 thin film. The photodetector shows a satisfactory performance with a responsivity (R) and specific detectivity (D*) of 107.8 mA/W and 4.13 × 1010 Jones at 482 nm illumination. In addition to the fast response speed (100 ms), the device also exhibits an impressive long-term stability with a negligible attenuation in photocurrent after more than 700 cycles. This work provides a novel strategy to suppress carrier recombination of BiVO4, and the coupling of metal oxides and organic semiconductors opens up a new avenue for fabricating high-performance photodetectors.

Dipole Field-Driven Organic-Inorganic Heterojunction for Highly Sensitive Ultraviolet Photodetector

Developing high-performance organic-inorganic ultraviolet (UV) photodetectors (PDs) has attracted considerable attention. However, this development has been hindered due to poor directional charge-transfer ratios in transport layers, excessive costs, and an ambiguous underlying mechanism. To tackle these challenges, we constructed a heterojunction of economic Mg-doped ZnO (MgZnO) nanorods and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) [PEDOT:PSS (P:P)] that utilizes dipole field-driven spontaneous polarization to enhance photogenerated charge kinetics. As a result, the proposed heterojunction has an improved noise equivalent power of 3.16 × 10-11 W Hz-1/2), a normalized detection rate (D*) of 8.96 × 109 jones, and external quantum efficiency comparable to other ZnO-based devices. Notably, the prepared PDs showed a photocurrent of 4.8 × 10-3 μA under a faint UV light having an intensity of 1 × 10-5 W cm-2, exceeding the performance of the most state-of-the-art ZnO-based UV sensors. The introduction of Mg into ZnO is responsible for the high performance, as it causes a lattice mismatch and distortion of the Mg-doped ZnO unit cell. It results in improved dipole movement and the creation of a dipole field, accelerating the directional electron-transfer process. Using a dipole field to manipulate the migration and transport of photogenerated carriers represents a promising approach for achieving outstanding performance in UV PDs.

Guided CdTe Nanowires Integrated into Fast Near-Infrared Photodetectors

Infrared photodetectors are essential devices for telecommunication and night vision technologies. Two frequently used materials groups for this technology are III-V and II-VI semiconductors, notably, mercury-cadmium-telluride alloys (MCT). However, growing them usually requires expensive substrates that can only be provided on small scales, and their large-scale production as crystalline nanostructures is challenging. In this paper, we present a two-stage process for creating aligned MCT nanowires (NWs). First, we report the growth of planar CdTe nanowires with controlled orientations on flat and faceted sapphire substrates via the vapor-liquid-solid (VLS) mechanism. We utilize this guided growth approach to parallelly integrate the NWs into fast near-infrared photodetectors with characteristic rise and fall times of ∼100 μs at room temperature. An epitaxial effect of the planar growth and the unique structure of the NWs, including size and composition, are suggested to explain the high performance of the devices. In the second stage, we show that cation exchange with mercury can be applied, resulting in a band gap narrowing of up to 55 meV, corresponding to an exchange of 2% Cd with Hg. This work opens new opportunities for creating small, fast, and sensitive infrared detectors with an engineered band gap operating at room temperature.

Effect of copper doping on plasmonic nanofilms for high performance photovoltaic energy applications

In the current era, alternative but environment-friendly sources of energy have gained attention to meet the growing energy demands. In particular, the focus of research has been solar energy and using it to fulfill energy demands. Solar energy is either directly converted into electrical energy or stored for later use. Solar cells are a practical way to turn solar energy into electrical energy. Various materials are being investigated to manufacture solar cell devices that can absorb a maximum number of photons present in sunlight. The present study reports thermally evaporated in situ Cu-doped SnS photon absorber thin films with tunable physical properties. This study mainly explored the effects of changing Cu concentrations on the physical features of light absorption of SnS thin films. The thin films were formed by simultaneous resistive heating of Cu and SnS powders on glass substrates at 150 °C. The X-ray diffraction patterns revealed pure SnS thin films having orthorhombic polycrystalline crystal structures oriented preferentially along the (111) plane. Raman spectroscopy confirmed this phase purity. Photoconductivity studies showed phase dependence on Cu content that improved with increasing concentrations of Cu. The optical bandgap energy was also found to be dependent on Cu content and was observed at 1.10-1.47 eV for SnS thin films with variation in the Cu content, i.e., 0-18%. According to the hot probe method, all films displayed p-type conductivity for the substitution of Cu metal atoms. These findings demonstrated that the prepared thin films are substantial candidates as low-cost, suitably efficient, thin-film solar cells featuring environmentally-friendly active layers that absorb sunlight.

Significant increase of the photoresponse range and conductivity for a chalcogenide semiconductor by viologen coating through charge transfer

Widening the photoresponse range while enhancing the electrical properties of semiconductors could reduce the complexity and cost of photodetectors or increase the power conversion efficiency of solar cells. Surface doping through charge transfer with organic species is one of the most effective and widely used approaches to achieve this aim. It usually features easier preparation over other doping methods but is still limited by the low physicochemical stability and high cost of the used organic species or low improvement of electrical properties. This work shows unprecedented surface doping of semiconductors with highly stable, easily obtained, and strong electron-accepting viologen components, realizing the significant improvement of both the photoresponse range and conductivity. Coating the chalcogenide semiconductor KGaS2 with dimethyl viologen dichloride (MV) yields a charge-transfer complex (CTC) on the surface, which broadens the photoresponse range by nearly 300 nm and improves the conductivity by 5 orders of magnitude. The latter value surpasses all records obtained by surface doping through charge transfer with organic species.

Design Strategy for Improving Detection Sensitivity in a Bromoplumbate Photochromic Semiconductor

Reducing the dark current of photodetectors is an important strategy for enhancing the detection sensitivity, but hampered by the manufacturing cost due to the need for controlling the complex material composition and processing intricate interface. This study reports a new single-component photochromic semiconductor, [(HDMA)4 (Pb3 Br10 )(PhSQ)2 ]n (1, HDMA = dimethylamine cation, PhSQ = 1-(4-sulfophenyl)-4,4'-bipyridinium), by introducing a redox-active monosubstituted viologen zwitterion into inorganic semiconducting skeleton. It features yellow to green coloration after UV irradiation with the sharply dropping intrinsic conductivity of 14.6-fold, and the photodetection detection sensitivity gain successfully doubles. The reason of decreasing conductivity originates from the increasing the band gap of the inorganic semiconducting component and formation of Frenkel excitons with strong Coulomb interactions, thereby decreasing the concentration of thermally excited intrinsic carriers.

High performance self-powered photodetector based on van der Waals heterojunction

Self-powered photodetectors that do not require external power support are expected to play a key role in future photodetectors due to their low power characteristics, but achieving high responsivity remains a challenge. 2D van der Waals heterojunctions are a promising technology for high-performance self-powered photodetectors due to their excellent optical and electrical properties. Here, we fabricate a self-powered photodetector based on In2Se3/WSe2/ReS2van der Waals heterojunction self-powered photodetector. Due to the presence of ReS2layer, photocurrent is enhanced as a result of the increase in light absorption efficiency and the effective region for generating photogenerated carriers. The built-in electric field is enhanced by a negative 'back-gate voltage' along the p-n junction vertical direction generated by the electrons in the photo-generated electrons accumulation layer. Accordingly, the optical responsivity and the photoresponse speed of this heterojunction self-powered photodetector are greatly boosted. The proposed self-powered photodetector based on the In2Se3/WSe2/ReS2heterojunction exhibits a high responsivity of 438 mA W-1, which is 17 times higher compared to the In2Se3/WSe2photodetector, a self-powered current (1.1 nA) that is an order of magnitude higher than that of the In2Se3/WSe2photodetector, and a fast response time that is 250% faster. Thus the self-powered photodetector with a stronger built-in electric field and a wider depletion zone can provide a new technological support for the fabrication of high responsivity, low power consumption and high speed self-powered photodetectors based on van der Waals heterojunctions.

Broadband SnS/Te photodetector to long-wavelength infrared: breaking the spectrum limit through alloy engineering

Materials based on group IV chalcogenides, are considered to be one of the most promising materials for high-performance, broadband photodetectors due to their wide bandgap coverage, intriguing chemical bonding and excellent physical properties. However, the reported photodetectors based on SnS are still worked at relatively narrow near-infrared band (as far as 1550 nm) hampered by the nonnegligible bandgap of 1.1-1.5 eV. Here, a novel photodetector based on Te alloyed SnS thin film was demonstrated with an ultra-broadband response up to 10.6 µm. By controlling the Te alloyed concentration in SnS increasing to 37.64%, the bandgap narrows to 0.23 eV, exhibiting a photoresponse potential at long-wavelength infrared excitation. Our results show Te-alloying can remarkably enhance the detection properties of SnS/Te photodetectors. The photoresponsivity and detectivity of 1.59 mA/W and 2.3 × 108 Jones were realized at 10.6 µm at room temperature. Moreover, the nonzero photogain was observed generated by nonlinearly increased photocurrent density, resulting in a superlinear dependency between photoresponsivity and light intensity. Our studies successfully broaden photoresponse spectrum of SnS toward the mid-infrared range for the first time. It also suggests that alloying is an effective technique for tuning the band edges of group IV chalcogenides, contributing deep implications for developing future optoelectronic applications.

Preparation of a novel Bi9O7.5S6/SnS composite film with improved photoelectric properties

Atomically thin two-dimensional (2D) bismuth oxychalcogenides have been considered as promising candidates for high-speed and low-power photoelectronic devices due to their high charge carrier mobility and excellent environmental stability. However, the photoelectric performance of their bulk materials still falls short of expectations. Herein, a novel Bi9O7.5S6/SnS composite film with a type-II heterojunction was successfully prepared by combining hydrothermal and knife-coating techniques. The crystal structure, morphology, and optical properties were systematically investigated. Under 1 V bias voltage, the photocurrent of the Bi9O7.5S6/SnS composite film can be obtained as 107 μA cm-2, which is about 29.9 times and 93.9 times higher than that of bare Bi9O7.5S6 and SnS, respectively. The type-II heterojunction has played a significant role in improving the photoelectric performance of the Bi9O7.5S6/SnS composite film by facilitating the separation and transfer of photo-generated carriers. This work sheds light on the design and development of new bismuth-based composite materials for advanced photoelectric and photocatalytic applications.

Ultrathin Crystalline Silicon Nano and Micro Membranes with High Areal Density for Low-Cost Flexible Electronics

Ultrathin crystalline silicon is widely used as an active material for high-performance, flexible, and stretchable electronics, from simple passive and active components to complex integrated circuits, due to its excellent electrical and mechanical properties. However, in contrast to conventional silicon wafer-based devices, ultrathin crystalline silicon-based electronics require an expensive and rather complicated fabrication process. Although silicon-on-insulator (SOI) wafers are commonly used to obtain a single layer of crystalline silicon, they are costly and difficult to process. Therefore, as an alternative to SOI wafers-based thin layers, here, a simple transfer method is proposed for printing ultrathin multiple crystalline silicon sheets with thicknesses between 300 nm to 13 µm and high areal density (>90%) from a single mother wafer. Theoretically, the silicon nano/micro membrane can be generated until the mother wafer is completely consumed. In addition, the electronic applications of silicon membranes are successfully demonstrated through the fabrication of a flexible solar cell and flexible NMOS transistor arrays.

Engineering graphitic carbon nitride for next-generation photodetectors: a mini review

Semiconductor photodetectors, as photoelectric devices using optical-electrical signal conversion for detection, are widely used in various fields such as optical communication, medical imaging, environmental monitoring, military tracking, remote sensing, etc. Compared to the conventional photodetector materials including silicon, III-V semiconductors and metal sulfides, graphitic carbon nitride (g-C3N4) as a metal-free polymeric semiconductor, has many advantages such as low-price, easy preparation, efficient visible light response, and relatively good thermal stability. In the meantime, the polymer characteristics also endow the g-C3N4 with good mechanical properties. Apart from being used for photo(electro)catalysts during the past decades, the potential use of g-C3N4 in photodetectors has attracted great research interests very recently. In this review, we first briefly introduce the structure and properties of g-C3N4 and the key performance parameters of photodetectors. Then, combining the very recent progress, the review focuses on the active materials, fabrication methods and performance enhancement strategies for g-C3N4 based photodetectors. The existing challenges are discussed and the future development of g-C3N4 based photodetectors is also forecasted.

Wafer-Scale Synthesis of 2D Materials by an Amorphous Phase-Mediated Crystallization Approach

The interest in the wafer-scale growth of two-dimensional (2D) materials, including transition metal dichalcogenides (TMDCs), has been rising for transitioning from lab-scale devices to commercial-scale systems. Among various synthesis techniques, physical vapor deposition, such as pulsed laser deposition (PLD), has shown promise for the wafer-scale growth of 2D materials. However, due to the high volatility of chalcogen atoms (e.g., S and Se), films deposited by PLD usually suffer from a lack of stoichiometry and chalcogen deficiency. To mitigate this issue, excess chalcogen is necessary during the deposition, which results in problems like uniformity or not being repeatable. This study demonstrates a condensed-phase or amorphous phase-mediated crystallization (APMC) approach for the wafer-scale synthesis of 2D materials. This method uses a room-temperature PLD process for the deposition and formation of amorphous precursors with controlled thicknesses, followed by a post-deposition crystallization process to convert the amorphous materials to crystalline structures. This approach maintains the stoichiometry of the deposited materials throughout the deposition and crystallization process and enables the large-scale synthesis of crystalline 2D materials (e.g., MoS2 and WSe2) on Si/SiO2 substrates, which is critical for future wafer-scale electronics. We show that the thickness of the layers can be digitally controlled by the number of laser pulses during the PLD phase. Optical spectroscopy is used to monitor the crystallization dynamics of amorphous layers as a function of annealing temperature. The crystalline quality, domain sizes, and the number of layers were explored using nanoscale and atomistic characterization (e.g., AFM, STEM, and EDS) along with electrical characterization to explore process-structure-performance relationships. This growth technique is a promising method that could potentially be adopted in conventional semiconductor industries for wafer-scale manufacturing of next-generation electronic and optoelectronic devices.

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.

Enhanced Spectral Response of ZnO-Nanorod-Array-Based Ultraviolet Photodetectors by Alloying Non-Isovalent Cu-O with CuAlO2 P-Type Layer

CuAlO₂ was synthesized by a hydrothermal method, in which the Cu-O dimers were incorporated by simply altering the ratio of the reactants and the temperature. The incorporation process increases the grain size in CuAlO₂, and modulates the work function and binding energies for CuAlO₂ due to the partial substitution of Cu⁺ 3d¹⁰ with Cu²⁺ 3d⁹ orbitals in the valence band maximum by alloying non-isovalent Cu-O with a CuAlO₂ host. Based on the ZnO nanorod arrays (NRs) ultraviolet photodetector, CuAlO₂/Cu-O fabricated by the low-cost drop-coating method was used as the p-type hole transport layer. The incorporation of the Cu-O clusters into CuAlO₂ lattice to enhance the conductivity of CuAlO₂ is an effective way for improving ZnO NRs/CuAlO₂ device performance. The photodetectors exhibit significant diode behavior, with a rectification ratio approaching 30 at ±1 V, and a dark saturation current density 0.81 mA cm^-2. The responsivity of the ZnO-NRs-based UV photodetector increases from 13.2 to 91.3 mA/W at 0 V bias, with an increase in the detectivity from 2.35 × 10¹⁰ to 1.71 × 10¹¹ Jones. Furthermore, the ZnO NRs/[CuAlO₂/Cu-O] photodetector exhibits a maximum responsivity of 5002 mA/W at 1.5 V bias under 375 nm UV illumination.

Rapid Response Solar Blind Deep UV Photodetector with High Detectivity Based On Graphene:N/βGa2 O3 :N/GaN p-i-n Heterojunction Fabricated by a Reversed Substitution Growth Method

This work reports a high-detectivity solar-blind deep ultraviolet photodetector with a fast response speed, based on a nitrogen-doped graphene/βGa₂ O₃ /GaN p-i-n heterojunction. The i layer of βGa₂ O₃ with a Fermi level lower than the central level of the forbidden band of 0.2 eV is obtained by reversed substitution growth with oxygen replacing nitrogen in the GaN matrix, indicating the majority carrier is hole. X-ray diffractometershows that the transformation of GaN into βGa₂ O₃ with (-201) preferred orientation at temperature above 900 °C in an oxygen ambient. The heterojunction shows enhanced self-powered solar blind detection ability with a response time of 3.2 µs (rise)/0.02 ms (delay) and a detectivity exceeding 10¹² Jones. Under a reverse bias of -5 V, the photoresponsivity is 8.3 A W^-1 with a high I_light /I_dark ratio of over 10⁶ and a detectivity of ≈9 × 10¹⁴ Jones. The excellent performance of the device is attributed to 1) the continuous conduction band without a potential energy barrier, 2) the larger built-in potential in the heterojunction because of the downward shift of Fermi energy level in β-Ga₂ O₃ , and 3) an enhanced built-in electric field in the βGa₂ O₃ due to introducing p-type graphene with a high hole concentration of up to ≈10²⁰ cm^-3 .

CuSCN/Si heterojunction near-infrared photodetector based on micro/nano light-trapping structure

In this paper, high-performance CuSCN/Si heterojunction near-infrared photodetectors were successfully prepared using nanoscale light-trapping optical structures. Various light-trapping structures of ortho-pyramids, inverted pyramids and silicon nanowires were prepared on silicon substrates. Then, CuSCN films were spin-coated on silicon substrates with high crystalline properties for the assembly of CuSCN/Si photodetectors. Their reflectance spectra and interfacial passivation properties were characterized, demonstrating their superiority of light-trapping structures in high light response. Under the irradiation of 980 nm near-infrared light, a maximum responsivity of 2.88 A W^-1at -4 V bias and a specific detectivity of 5.427 × 10¹⁰Jones were obtained in the CuSCN/Si heterojunction photodetectors prepared on planner silicon due to 3.6 eV band gap of CuSCN. The substrates of the light-trapping structure were then applied to the CuSCN/Si heterojunction photodetectors. A maximum responsivity of 10.16 A W^-1and a maximum specific detectivity of 1.001 × 10¹¹Jones were achieved under the 980 nm near-infrared light irradiation and -4 V bias, demonstrating the advanced performance of CuSCN/Si heterojunction photodetectors with micro-nano light-trapping substrates in the field of near-infrared photodetection compared to other silicon-based photodetectors.

Advanced Stretchable Photodetectors: Strategies, Materials and Devices

Past decades have witnessed the generation of new stretchable photodetectors in electronic eyes, health sensing, wearable devices, intelligent monitoring and other fields. Stretchable devices require not only outstanding performance but also excellent flexibility, adaptability and stability. Innovative strategies have been proposed to realize the stretchability of devices. In addition, novel functional materials including zero-dimensional nanomaterials, one-dimensional inorganic nanomaterials, two-dimensional layered materials, organic materials, and organic-inorganic composite materials with excellent properties are emerging to continuously improve the performance of devices. Here, the recent research progress of stretchable photodetectors in terms of both various design methods and functional materials is outlined. The optical performance and stretchable properties are also comprehensively reviewed. Finally, a summary and the challenges associated with the application of stretchable photodetectors are presented.

Hybrid mixed-dimensional WTe2/CsPbI3perovskite heterojunction for high-performance photodetectors

Perovskites have showed significant potential for the application in photodetectors due to their outstanding electrical and optical properties. Integrating two-dimensional (2D) materials with perovskites can make full use of the high carrier mobility of 2D materials and strong light absorption of perovskite to realize excellent optoelectrical properties. Here, we demonstrate a photodetector based on the WTe₂/CsPbI₃heterostructure. The quenching and the shortened lifetime of photoluminescence (PL) for CsPbI₃perovskite confirms the efficient charge transfer at the WTe₂/CsPbI₃heterojunction. After coupled with WTe₂, the photoresponsivity of the CsPbI₃photodetector is improved by almost two orders of magnitude due to the high-gain photogating effect. The WTe₂/CsPbI₃heterojunction photodetector reveals a large responsivity of 1157 A W^-1and a high detectivity of 2.1 × 10¹³Jones. The results pave the way for the development of high-performance optoelectronic devices based on 2D materials/perovskite heterojunctions.

Self-Powered and Broadband Bismuth Oxyselenide/p-Silicon Heterojunction Photodetectors with Low Dark Current and Fast Response

Inorganic nanomaterials such as graphene, black phosphorus, and transition metal dichalcogenides have attracted great interest in developing optoelectronic devices due to their efficient conversion between light and electric signals. However, the zero band gap nature, the unstable chemical properties, and the low electron mobility constrained their wide applications. Bismuth oxyselenide (Bi₂O₂Se) is gradually showing great research significance in the optoelectronic field. Here, we develop a bismuth oxyselenide/p-silicon (Bi₂O₂Se/p-Si) heterojunction and design a self-powered and broadband Bi₂O₂Se/p-Si heterojunction photodetector with an ultrafast response (2.6 μs) and low dark current (10^-10 A without gate voltage regulation). It possesses a remarkable detectivity of 4.43 × 10¹² cm Hz^1/2 W^-1 and a self-powered photoresponse characteristic at 365-1550 nm (ultraviolet-near-infrared). Meanwhile, the Bi₂O₂Se/p-Si heterojunction photodetector also shows high stability and repeatability. It is expected that the proposed Bi₂O₂Se/p-Si heterojunction photodetector will expand the applications of Bi₂O₂Se in practical integrated circuits in the field of material science, energy development, optical imaging, biomedicine, and other applications.

Surface Engineering in SnO2/Si for High-Performance Broadband Photodetectors

Silicon-based photodetectors are important optoelectronic devices in many fields. Many investigations have been conducted to improve the performance of silicon-based photodetectors, such as spectral responsivity and sensitivity in the ultraviolet band. In this study, we combine the surface structure engineering of silicon with wide-bandgap semiconductor SnO₂ films to realize textured Si-based heterojunction photodetectors. The obtained SnO₂/T-Si photodetectors exhibit high responsivity ranging from ultraviolet to near-infrared light. Under a bias voltage of 1 V, SnO₂/T-Si photodetectors (PDs) with an inverted pyramid texture show the best performance, and the typical responsivities to ultraviolet, visible, and near-infrared light are 0.512, 0.538, 1.88 (800 nm, 67.7 μW/cm²) A/W@1 V, respectively. The photodetectors exhibit short rise and decay times of 18.07 and 29.16 ms, respectively. Our results demonstrate that SnO₂/T-Si can serve as a high-performance broadband photodetector.

Photoactive Nanomaterials for Wireless Neural Biomimetics, Stimulation, and Regeneration

Nanomaterials at the neural interface can provide the bridge between bioelectronic devices and native neural tissues and achieve bidirectional transmission of signals with our brain. Photoactive nanomaterials, such as inorganic and polymeric nanoparticles, nanotubes, nanowires, nanorods, nanosheets or related, are being explored to mimic, modulate, control, or even substitute the functions of neural cells or tissues. They show great promise in next generation technologies for the neural interface with excellent spatial and temporal accuracy. In this review, we highlight the discovery and understanding of these nanomaterials in precise control of an individual neuron, biomimetic retinal prosthetics for vision restoration, repair or regeneration of central or peripheral neural tissues, and wireless deep brain stimulation for treatment of movement or mental disorders. The most intriguing feature is that the photoactive materials fit within a minimally invasive and wireless strategy to trigger the flux of neurologically active molecules and thus influences the cell membrane potential or key signaling molecule related to gene expression. In particular, we focus on worthy pathways of photosignal transduction at the nanomaterial-neural interface and the behavior of the biological system. Finally, we describe the challenges on how to design photoactive nanomaterials specific to neurological disorders. There are also some open issues such as long-term interface stability and signal transduction efficiency to further explore for clinical practice.

Long-range ordered amino acid assemblies exhibit effective optical-to-electrical transduction and stable photoluminescence

Bio-endogenous peptide molecules are ideal components for fabrication of biocompatible and environmentally friendly semiconductors materials. However, to date, their applications have been limited due to the difficulty in obtaining stable, high-performance devices. Herein, simple amino acid derivatives fluorenylmethoxycarbonyl-leucine (Fmoc-L) and fluorenylmethoxycarbonyl-tryptophan (Fmoc-W) are utilized to form long-range ordered supramolecular nanostructures by tight aromatic stacking and extensive hydrogen bonding with mechanical, electrical and optical properties. For the first time, without addition of any photosensitizers, pure Fmoc-L microbelts and Fmoc-W microwires exhibit Young's modulus up to 28.79 and 26.96 GPa, and unprecedently high values of photocurrent responses up to 2.2 and 2.3 μA/cm², respectively. Meanwhile, Fmoc-W microwires with stable blue fluorescent emission under continuous excitation are successfully used as LED phosphors. Mechanism analysis shows that these two amino acids derivatives firstly formed dimers to reduce the bandgap, then further assemble into bioinspired semiconductor materials using the dimers as the building blocks. In this process, aromatic residues of amino acids are more conducive to the formation of semiconducting characteristics than fluorenyl groups. STATEMENT OF SIGNIFICANCE: Long-range ordered amino acid derivative assemblies with mechanical, electrical and optical properties were fabricated by a green and facile biomimetic strategy. These amino acid assemblies have Young's modulus comparable to that of concrete and exhibit typical semiconducting characteristics. Even without the addition of any photosensitizer, pure amino acid assemblies can still produce a strong photocurrent response and an unusually stable photoluminescence. The results suggest that amino acid structures with hydrophilic C-terminal and aromatic residues are more conducive to the formation of semiconducting characteristics. This work unlocks the potential for amino acid molecules to self-assemble into high-performance bioinspired semiconductors, providing a reference for customized development of biocompatible and environmentally friendly semiconductor materials through rational molecular design.

Zero Bias Operation: Photodetection Behaviors Obtained by Emerging Materials and Device Structures

Zero-biased photodetectors have desirable characteristics for potentially next-generation devices, including high efficiency, rapid response, and low power operation. In particular, the detector efficiency can be improved simply by changing the electrode contact geometry or morphological structure of materials, which give unique properties such as energy band bending, photo absorbance and electric field distribution. In addition, several combinations of materials enable or disable the operation of selective wavelengths of light detection. Herein, such recent progresses in photodetector operating at zero-bias voltage are reviewed. Considering the advantages and promises of these low-power photodetectors, this review introduces various zero-bias implementations and reviews the key points.

Visible-Light-Stimulated Synaptic Phototransistors Based on CdSe Quantum Dot/In-Ga-Zn-O Hybrid Channels

Light-stimulated synaptic devices are promising candidates for the development of artificial intelligence systems because of their unique properties, which include broad bandwidths, low power consumption, and superior parallelism. The key to develop such devices is the realization of photoelectric synaptic behavior in them. In this work, visible-light-stimulated synaptic transistors based on CdSe quantum dot (CdSe QD)/amorphous In-Ga-Zn-O hybrid channels are proposed. This design can not only improve the charge separation efficiency of the photogenerated carriers, but also can induce delayed decay of the photocurrent. The improved charge separation efficiency enhances the photoelectric properties significantly, while the delayed decay of the photocurrent led to the realization of photoelectric synaptic behaviors. This simple and efficient method of fabricating light-stimulated phototransistors may inspire new research progress into the development of artificial intelligence systems.

Solution-processed transparent p-type orthorhombic K doped SnO films and their application in a phototransistor

The exploitation of p-type oxide semiconductors with excellent optoelectrical properties as well as a simple preparation process is still challenging owing to the difficulty in producing hole carriers which results from strong hole localization in p-type oxide semiconductors. In this work, we succeeded in using ethylene glycol as a reductant to prepare orthorhombic structure SnO films using a sol-gel method and through K doping the optical and electrical properties of the films were improved. When the orthorhombic K doped SnO (K-SnO) films were applied in a phototransistor, it presented ultra-broadband photosensing from the ultraviolet to infrared region (300-1000 nm), demonstrating a photoresponsivity of 349 A W^-1 and a detectivity of 5.45 × 10¹² Jones at 900 nm under a light intensity of 0.00471 mW cm^-2. In particular, infrared photosensing was for the first time reported in the SnO based phototransistors. This work not only provides a simple method to fabricate high-performance and low-cost p-type K-SnO films and phototransistors, but may also suggest a new way to improve the p-type characteristics of other oxide semiconductors and devices.

Recent Advances in Ferroelectric Materials-Based Photoelectrochemical Reaction

Inorganic perovskite ferroelectric-based nanomaterials as sustainable new energy materials, due to their intrinsic ferroelectricity and environmental compatibility, are intended to play a crucial role in photoelectrochemical field as major functional materials. Because of versatile physical properties and excellent optoelectronic properties, ferroelectric-based nanomaterials attract much attention in the field of photocatalysis, photoelectrochemical water splitting and photovoltaic. The aim of this review is to cover the recent advances by stating the different kinds of ferroelectrics separately in the photoelectrochemical field as well as discussing how ferroelectric polarization will impact functioning of photo-induced carrier separation and transportation in the interface of the compounded semiconductors. In addition, the future prospects of ferroelectric-based nanomaterials are also discussed.

Robust Spin-Dependent Anisotropy of Circularly Polarized Light Detection from Achiral Layered Hybrid Perovskite Ferroelectric Crystals

Circularly polarized light (CPL) detection has sparked overwhelming research interest for its widespread chiroptoelectronic and spintronic applications. Ferroelectric materials, especially emerging layered hybrid perovskite ferroelectrics, exhibiting striking bulk photovoltaic effect (BPVE) present significant possibilities for CPL detection by a distinctive working concept. Herein, for the first time, we demonstrate the realization of robust angular anisotropy of CPL detection in a new layered hybrid perovskite ferroelectric crystal (CPA)₂FAPb₂Br₇ (1, CPA is chloropropylammonium, FA is formamidinium), which crystallized in an optically active achiral polar point group. Benefiting from the notable spontaneous polarization (5.1 μC/cm²) and excellent semiconducting characteristics, single crystals of 1 exhibit remarkable BPVE under light illumination, with a high current on/off switching ratio (ca. 10³). More intriguingly, driven by the angular carrier drift originating from spin-dependent BPVE in optically active ferroelectrics, 1 displays highly sensitive self-powered CPL detection performance, showing a robust angular anisotropy factor up to 0.98, which is far more than those achieved by material intrinsic chirality. This work provides an unprecedented approach for realizing highly sensitive CPL detection, which sheds light on the further design of optically active ferroelectrics for chiral photonic applications.

An All-Organic Self-Powered Photodetector with Ultraflexible Dual-Polarity Output for Biosignal Detection

Endowing photodetectors with mechanically flexibility and actual functionality are current research issues in developing optoelectronic devices. However, rigid metal-based or metal-oxide-based electrodes remain a block to the realization of ultraflexible electronics. Thus, an ultraflexible all-organic photodetector (all-OPD) is designed by innovatively introducing symmetrical organic electrodes PH1000/PH1000 to substitute the widely applied indium-doped tin oxide (ITO)/Ag electrodes. Specifically, this all-OPD exhibits a high self-powered responsivity (R) of over 100 mA W^-1 among 500-600 nm and the photocurrent remains about 80% of the original performance after being bent 20 000 circles, and can output steady biosignals for photo-plethysmography (PPG) application. More importantly, this all-OPD outputs dual-polarity photocurrent as it is flipped or folded. Benefitting from the ordered phase distribution and designed Schottky barrier heights, the photogenerated holes will be transferred and collected by nearer electrode, while electrons will be trapped in the thick bulk heterojunction (BHJ) as a result of the long channel. This work offers a new avenue toward developing a multifunctional and ultraflexible all-OPD with a straightforward all-solution method, and it is expected to be more compatible in complex application scenarios.

Application of Nanostructured TiO2 in UV Photodetectors: A Review

As a wide-bandgap semiconductor material, titanium dioxide (TiO₂ ), which possesses three crystal polymorphs (i.e., rutile, anatase, and brookite), has gained tremendous attention as a cutting-edge material for application in the environment and energy fields. Based on the strong attractiveness from its advantages such as high stability, excellent photoelectric properties, and low-cost fabrication, the construction of high-performance photodetectors (PDs) based on TiO₂ nanostructures is being extensively developed. An elaborate microtopography and device configuration is the most widely used strategy to achieve efficient TiO₂ -based PDs with high photoelectric performances; however, a deep understanding of all the key parameters that influence the behavior of photon-generated carriers, is also highly required to achieve improved photoelectric performances, as well as their ultimate functional applications. Herein, an in-depth illustration of the electrical and optical properties of TiO₂ nanostructures in addition to the advances in the technological issues such as preparation, microdefects, p-type doping, bandgap engineering, heterojunctions, and functional applications are presented. Finally, a future outlook for TiO₂ -based PDs, particularly that of further functional applications is provided. This work will systematically illustrate the fundamentals of TiO₂ and shed light on the preparation of more efficient TiO₂ nanostructures and heterojunctions for future photoelectric applications.

Atomically-thin Schottky-like photo-electrocatalytic cross-flow membrane reactors for ultrafast remediation of persistent organic pollutants

The remediation of persistent organic pollutants in surface and ground water represents a major environmental challenge worldwide. Conventional physico-chemical techniques do not efficiently remove such persistent organic pollutants and new remediation techniques are therefore required. Photo-electro catalytic membranes represent an emerging solution that can combine photocatalytic and electrocatalytic degradation of contaminants along with molecular sieving. Herein, macro-porous photo-electro catalytic membranes were prepared using conductive and porous stainless steel metal membranes decorated with nano coatings of semiconductor photocatalytic metal oxides (TiO₂ and ZnO) via atomic layer deposition, producing highly conformal and stable coatings. The metal - semiconductor junction between the stainless steel membranes and photocatalysts provides Schottky - like characteristics to the coated membranes. The PEC membranes showed induced hydrophilicity from the nano-coatings and enhanced electro-chemical properties due to the Schottky junction. A high electron transfer rate was also induced in the coated membranes as the photocurrent efficiency increased by 4 times. The photo-electrocatalytic efficiency of the TiO₂ and ZnO coated membranes were demonstrated in batch and cross flow filtration reactors for the degradation of persistent organic pollutant solution, offering increased degradation kinetic factors by 2.9 and 2.3 compared to photocatalysis and electrocatalysis, respectively. The recombination of photo-induced electron and hole pairs is mitigated during the photo-electrocatalytic process, resulting in an enhanced catalytic performance. The strategy offers outstanding perspectives to design stimuli-responsive membrane materials able to sieve and degrade simultaneously toxic contaminants towards greater process integration and self-cleaning operations.

Earth-abundant and environmentally benign Ni-Zn iron oxide intercalated in a polyaniline based nanohybrid as an ultrafast photodetector

Nickel-zinc iron oxide (NZF) was introduced into a polyaniline (PANI) matrix by an in situ chemical oxidation polymerization approach. The surface composition and chemical states were investigated by X-ray photoelectron spectroscopy (XPS), which revealed an Fe 2p spectrum with the two peak positions of Fe 2p_3/2 and Fe 2p_1/2 at 711.00 and 724.48 eV, respectively. Deconvolution of the Fe 2p_3/2 peak revealed two components with binding energies of 713.98 and 718.16 eV, corresponding to the presence of Fe cations in the octahedral and tetrahedral sites. Additionally, the Rietveld refinement of NZF showed a cubic system with the Fd₃m space group. High-resolution transmission electron microscopy (HRTEM) analysis showed that the NZF material strongly interacts with polyaniline, while the selected area electron diffraction (SAED) pattern perfectly matched with the XRD data. Lognormal distribution was used to determine the particle size, which was found to be in the range of 1-100 nm. A flexible photodetector device utilizing the NZF-PANI nanohybrid was fabricated on an environmentally friendly, biodegradable cellulose paper substrate and the device exhibited excellent performance, i.e., a responsivity of 0.069 A W^-1 and detectivity of 7.258 × 10¹⁰ Jones at a very low voltage of 0.1 V. The non-stretched device showed a responsivity of 24.980 A W^-1 at 5 V, whereas at 2 cm^-1 bending curvature, the device showed a responsivity of 20.175 A W^-1, which was much higher than the responsivity of a commercial photodetector (<0.5 A W^-1).

Ag metal interconnect wires formed by pseudoplastic nanoparticles fluid imprinting lithography with microwave assistant sintering

Nanoimprint technology has the advantages of low cost, high precision, high fidelity and high yield. The metal nanoparticle fluid is non-Newtonian fluid, which is used as the imprint transfer medium to realize high fidelity of pattern because of its shear thinning effect. In order to functionalize the metal nanoparticles microstructure, the subsequent sintering step is required to form a metal interconnect wire. Metal interconnect wire with fewer grain boundaries and fewer holes have excellent mechanical and electronic properties. In this paper, the pseudoplastic metal nanoparticle fluid was formed by Ag nanoparticle and precursor solution, and then the thermal diffusion process was completed by microwave sintering after interconnects were embossed. The influence of microwave and thermal atmosphere on the microstructure and performance of Ag Interconnect wires was analyzed and discussed, and the Ag Interconnect wires performance was determined under the influence of time and temperature parameters. In our experiments, the interconnects after microwave sintering can achieve 39% of the conductivity of bulk silver. The microwave sintering module might be integrated as the heat treatment module of the metal micro/nano pattern directly imprint lithography.

Heterojunction Nanomedicine

Exogenous stimulation catalytic therapy has received enormous attention as it holds great promise to address global medical issues. However, the therapeutic effect of catalytic therapy is seriously restricted by the fast charge recombination and the limited utilization of exogenous stimulation by catalysts. In the past few decades, many strategies have been developed to overcome the above serious drawbacks, among which heterojunctions are the most widely used and promising strategy. This review attempts to summarize the recent progress in the rational design and fabrication of heterojunction nanomedicine, such as semiconductor-semiconductor heterojunctions (including type I, type II, type III, PN, and Z-scheme junctions) and semiconductor-metal heterojunctions (including Schottky, Ohmic, and localized surface plasmon resonance-mediated junctions). The catalytic mechanisms and properties of the above junction systems are also discussed in relation to biomedical applications, especially cancer treatment and sterilization. This review concludes with a summary of the challenges and some perspectives on future directions in this exciting and still evolving field of research.