Recent Advances in Perovskite Photodetectors for Image Sensing

Mitigation of Parasitic and Drift Capacitance-Induced Nonlinear Current Responses for Stable and Sensitive Perovskite X-ray Detectors

The development of perovskite direct X-ray detectors shows potential for advancing medical imaging and industrial inspection precision. To ensure the optimal energy conversion efficiency of X-rays for reducing radiation doses, it is necessary for perovskites with thicknesses reaching hundreds of micrometers or even several millimeters to be utilized. However, the nonlinear current response becomes uncertain with such high thicknesses. For instance, the prevailing theory regarding the rapid trapping and release of charges by shallow-level defects falls short in explaining the nonlinear current response observed in high-quality single-crystal samples. Moreover, a significant nonlinear current response can degrade the detection performance. Here, we elucidate peculiar parasitic and drift capacitance-induced nonlinear current responses in perovskites, which arise from bulk structural deficiencies and interface junction width variation in addition to shallow-level defects. Both theoretical analysis and experimental findings demonstrate the effective suppression of nonlinear current responses by establishing bulk heterojunctions and refining interface junctions. Consequently, we have successfully developed highly linear current-responsive detectors based on polycrystalline MAPbI3 thick films. Notably, these detectors achieve a record sensitivity of 2.3 × 104 μC·Gyair-1·cm-2 under 100 kVp X-ray irradiation with a low bias of 0.1 V/μm, enabling enduring and high-resolution X-ray imaging for high-density objects. Successful fabrication and testing of a 64 × 64-pixel flat-panel prototype detector affirm the widespread applicability of these strategies in rectifying nonlinear current responses in perovskite-based X-ray detectors.

Highly Emissive Lanthanide-Based 0D Metal Halide Nanocrystals for Efficient Ultraviolet Photodetector

Recently, lanthanide-based 0D metal halides have attracted considerable attention for their applications in X-ray imaging, light-emitting diodes (LEDs), sensors, and photodetectors. Herein, lead-free 0D gadolinium-alloyed cesium cerium chloride (Gd3+-alloyed Cs3CeCl6) nanocrystals (NCs) are introduced as promising materials for optoelectronic application owing to their unique optical properties. The incorporation of Gd3+ in Cs3CeCl6 (CCC) NCs is proposed to increase the photoluminescence quantum yield (PLQY) from 57% to 96%, along with significantly enhanced phase and chemical stability. The structural analysis is performed by density functional theory (DFT) to confirm the effect of Gd3+ in Cs3Ce1- xGdxCl6 (CCGC) alloy system. Moreover, the CCGC NCs are applied as the active layer in UVPDs with different Gd3+ concentration. The excellent device performance is shown at 20% of Gd3+ in CCGC NCs with high detectivity (7.938 × 1011 Jones) and responsivity (0.195 A W-1) at -0.1 V at 310 nm. This study paves the way for the development of lanthanide-based metal halide NCs for next-generation UVPDs and other optoelectronic applications.

Programmable, High-resolution Printing of Spatially Graded Perovskites for Multispectral Photodetectors

Micro/nanostructured perovskites with spatially graded compositions and bandgaps are promising in filter-free, chip-level multispectral, and hyperspectral detection. However, achieving high-resolution patterning of perovskites with controlled graded compositions is challenging. Here, a programmable mixed electrohydrodynamic printing (M-ePrinting) technique is presented to realize the one-step direct-printing of arbitrary spatially graded perovskite micro/nanopatterns for the first time. M-ePrinting enables in situ mixing and ejection of solutions with controlled composition/bandgap by programmatically varying driving voltage applied to a multichannel nozzle. Composition can be graded over a single dot, line or complex pattern, and the printed feature size is down to 1 µm, which is the highest printing resolution of graded patterns to the knowledge. Photodetectors based on micro/nanostructured perovskites with halide ions gradually varying from Br to I are constructed, which successfully achieve multispectral detection and full-color imaging, with a high detectivity and responsivity of 3.27 × 1015 Jones and 69.88 A W-1, respectively. The presented method provides a versatile and competitive approach for such miniaturized bandgap-tunable perovskite spectrometer platforms and artificial vision systems, and also opens new avenues for the digital fabrication of composition-programmable structures.

Spectrally Tunable Lead-Free Perovskite Rb2ZrCl6:Te for Information Encryption and X-ray Imaging

A series of lead-free Rb2ZrCl6:xTe4+ (x = 0%, 0.1%, 0.5%, 1.0%, 2.0%, 3.0%, 5.0%, 10.0%) perovskite materials were synthesized through a hydrothermal method in this work. The substitution of Te4+ for Zr in Rb2ZrCl6 was investigated to examine the effect of Te4+ doping on the spectral properties of Rb2ZrCl6 and its potential applications. The incorporation of Te4+ induced yellow emission of triplet self-trapped emission (STE). Different luminescence wavelengths were regulated by Te4+ concentration and excitation wavelength, and under a low concentration of Te4+ doping (x ≤ 0.1%), different types of host STE emission and Te4+ triplet state emission could be achieved through various excitation energies. These luminescent properties made it suitable for applications in information encryption. When Te4+ was doped at high concentrations (x ≥ 1%), yellow triplet state emission of Te4+ predominated, resulting in intense yellow emission, which stemmed from strong exciton binding energy and intense electron-phonon coupling. In addition, a Rb2ZrCl6:2%Te4+@RTV scintillating film was fabricated and a spatial resolution of 3.7 lp/mm was achieved, demonstrating the potential applications of Rb2ZrCl6:xTe4+ in nondestructive detection and bioimaging.

Optoelectronic insights of lead-free layered halide perovskites

Two-dimensional organic-inorganic halide perovskites have emerged as promising candidates for a multitude of optoelectronic technologies, owing to their versatile structure and electronic properties. The optical and electronic properties are harmoniously integrated with both the inorganic metal halide octahedral slab, and the organic spacer layer. The inorganic octahedral layers can also assemble into periodically stacked nanoplatelets, which are interconnected by the organic ammonium cation, resulting in the formation of a superlattice or superstructure. In this perspective, we explore the structural, electronic, and optical properties of lead-free hybrid halides, and the layered halide perovskite single crystals and nanostructures, expanding our understanding of the diverse applications enabled by these versatile structures. The optical properties of the layered halide perovskite single crystals and superlattices are a function of the organic spacer layer thickness, the metal center with either divalent or a combination of monovalent and trivalent cations, and the halide composition. The distinct absorption and emission features are guided by the structural deformation, electron-phonon coupling, and the polaronic effect. Among the diverse optoelectronic possibilities, we have focused on the photodetection capability of layered halide perovskite single crystals, and elucidated the descriptors such as excitonic band gap, effective mass, carrier mobility, Rashba splitting, and the spin texture that decides the direct component of the optical transitions.

A Double Perovskite Single Crystal CsCuAgI3

Eco-friendly halide double perovskites are attracting significant attention as potential substitutes for traditional lead-based halide perovskites. However, their typically wide or indirect band gap limits further technological advancement. This study presents a new, eco-friendly, all-inorganic millimeter-scale CsCuAgI3 single crystal (SC). The crystal exhibits a direct band gap of 2.02 eV at the G-point, markedly superior to that of traditional double perovskites. The absorption and photoluminescence spectra further corroborate its band gap attributes. Owing to the B-site Cu-Ag disorder, the crystal possesses a higher Urbach energy (119 meV), indicative of structural disorder. CsCuAgI3 exhibits a wide Stokes shift of 230 nm, a wide full width at half-maximum (fwhm) of 152 nm, a long fluorescence lifetime of 7.29 μs, and excellent stability. In addition, a photoelectric detection prototype was prepared using a CsCuAgI3 single crystal. Using a 375 nm laser as the excitation source, the device showed a very sensitive photoelectric response, clocking in at (0.37/0.21) seconds. This work offers new insights into developing novel lead-free double perovskite single crystals and exploring their potential applications.

A Polarization-Sensitive Photodetector with Patterned CH3NH3PbCl3 Film

Perovskite photodetectors with polarization-sensitive properties have gained significant attention due to their potential applications in fields such as imaging and remote sensing. Most perovskite photodetectors concentrate on iodine (I) or bromine (Br)-based materials, primarily due to their straightforward fabrication techniques. The utilization of chloride (Cl)-based perovskites with wider bandgaps, such as CH3NH3PbCl3, is relatively limited. In this work, polarized perovskite photodetectors are prepared by a patterned spatially confined method with polarization sensitivity and excellent optoelectronic properties. The patterned perovskite photodetectors (PP-PDs) not only exhibit outstanding photoelectric conversion performance but also demonstrate polarization sensitivity. PP-PDs showcase remarkable performance, including on/off ratios of 3.4 × 104, an extremely low dark current of 1.56 × 10-11 A, and a rapid response time of microseconds. The responsivity and detectivity of PP-PDs reach 10.6 A W-1 and 3 × 1012 Jones, respectively, positioning them as among the highest-performing MAPbCl3-based photodetectors reported to date. Furthermore, polarization layered imaging sensing is achieved using stepwise scanning of the device. This work provides innovative ideas for realizing high-performance polarized perovskite photodetectors.

Solar-Blind Photodetector Arrays Fabricated by Weaving Strategy

The quest for solar-blind photodetectors (SBPDs) with exceptional optoelectronic properties for imaging applications has prompted the investigation of SBPD arrays. Ga2O3, characterized by its ultrawide bandgap and low growth cost, has emerged as a promising material for solar-blind detection. In this study, SBPD arrays were fabricated by weaving Sn-doped β-Ga2O3 microbelts (MBs). These MBs, which have a conductive core surrounded by a high-resistivity depletion surface layer resulting from the segregation of Sn and oxygen, are woven into a grid structure. Each intersection of the MBs functions as a photodetector pixel, with the intersecting MBs serving as the output electrodes of the pixel. This design simplifies the readout circuit for the photodetector array. The solar-blind photodetector array demonstrates superior solar-blind detection performance, including a dark current of 0.5 pA, a response time of 38.8 μs, a light/dark current ratio of 108, and a responsivity of 300 A/W. This research may provide a feasible strategy for the fabrication of photodetector arrays, thus pushing forward the application of photodetectors in imaging.

MXene based flexible photodetectors: progress, challenges, and opportunities

The growing interest in applying 2D transition-metal carbides and nitrides (MXenes) to diverse application fields such as energy storage and harvesters, catalysts, sensors, optoelectronics, electromagnetic interference shielding and antennas since its first discovery in 2011 is clearly evident. Their intrinsic high conductivity limits the development of MXenes in photodetectors that rely on the semiconducting properties of active materials, while the abundant functional groups on the surface of MXenes provide opportunities for using MXenes as sensing materials in the fabrication of flexible photodetectors. Considerable studies on MXene based photodetectors have been carried out, but the main obstacles include seeking novel semiconducting materials in MXene families, the manufacturing technology, etc. This review highlights the progress, challenges and opportunities in MXene based flexible photodetectors and discusses novel materials, architectures, and approaches that capitalize on our growing understanding of MXenes.

Interface Energy Alignment between Lead Halide Perovskite Single Crystals and TIPS-Pentacene

At present, there is a huge development in optoelectronic applications using lead halide perovskites. Considering that device performance is largely governed by the transport of charges across interfaces and, therefore, the interfacial electronic structure, fundamental investigations of perovskite interfaces are highly necessary. In this study, we use high-resolution soft X-ray photoelectron spectroscopy based on synchrotron radiation to explore the interfacial energetics for the molecular layer of TIPS-pentacene and lead halide perovskite single crystals. We perform ultrahigh vacuum studies on multiple thicknesses of an in situ formed interface of TIPS-pentacene with four different in situ cleaved perovskite single crystals (MAPbI3, MAPbBr3, FAPbBr3, and CsxFA1-xPbBryI3-y). Our findings reveal a substantial shift of the TIPS-pentacene energy levels toward higher binding energies with increasing thickness, while the perovskite energy levels remain largely unaffected regardless of their composition. These shifts can be interpreted as band bending in the TIPS-pentacene, and such effects should be considered when assessing the energy alignment at perovskite/organic transport material interfaces. Furthermore, we were able to follow a reorganization on the MAPbI3 surface with the transformation of the surface C 1s into bulk C 1s.

Flexible Stacked Perovskite Photodetectors for High-Efficiency Multicolor Fluorescence Detection

A flexible, multicolor detector based on stacked perovskite layers with graded band gaps was presented. Different perovskite layers generate a series of photocurrents corresponding to light intensities at different wavelengths. Experimentally, the flexible detector demonstrated acceptable long-term stability and temperature stability in the bending state. To demonstrate the advantages of the flexible multicolor detector in biological applications, a tubular-shaped multicolor fluorescence detector that embraces the sample cell was constructed. As a result, the detection limits of three kinds of CdTe quantum dots (QDs) with central wavelengths of 545, 625, and 730 nm were 0.52, 0.85, and 0.43 nM, respectively, which was significantly improved by more than 10 times compared to those of planar detectors. Additionally, the detector was able to detect three kinds of QDs simultaneously in a mixed solution, and the relative deviation was smaller than 10% compared to the preset concentration. These results demonstrate that the flexible stacked perovskite detector and the tubular-shaped detection configuration hold promise for the simultaneous fluorescent detection of multiple biomolecules.

A platform for integrated spectrometers based on solution-processable semiconductors

Acquiring real-time spectral information in point-of-care diagnosis, internet-of-thing, and other lab-on-chip applications require spectrometers with hetero-integration capability and miniaturized feature. Compared to conventional semiconductors integrated by heteroepitaxy, solution-processable semiconductors provide a much-flexible integration platform due to their solution-processability, and, therefore, more suitable for the multi-material integrated system. However, solution-processable semiconductors are usually incompatible with the micro-fabrication processes. This work proposes a facile and universal platform to fabricate integrated spectrometers with semiconductor substitutability by unprecedently involving the conjugated mode of the bound states in the continuum (conjugated-BIC) photonics. Specifically, exploiting the conjugated-BIC photonics, which remains unexplored in conventional lasing studies, renders the broadband photodiodes with ultra-narrowband detection ability, detection wavelength tunability, and on-chip integration ability while ensuring the device performance. Spectrometers based on these ultra-narrowband photodiode arrays exhibit high spectral resolution and wide/tunable spectral bandwidth. The fabrication processes are compatible with solution-processable semiconductors photodiodes like perovskites and quantum dots, which can be potentially extended to conventional semiconductors. Signals from the spectrometers directly constitute the incident spectra without being computation-intensive, latency-sensitive, and error-intolerant. As an example, the integrated spectrometers based on perovskite photodiodes are capable of realizing narrowband/broadband light reconstruction and in-situ hyperspectral imaging.

Photosensitive Dielectric 2D Perovskite Based Photodetector for Dual Wavelength Demultiplexing

Stacked 2D perovskites provide more possibilities for next generation photodetector with more new features. Compared with its excellent optoelectronic properties, the good dielectric performance of metal halide perovskite rarely comes into notice. Here, a bifunctional perovskite based photovoltaic detector capable of two wavelength demultiplexing is demonstrated. In the Black Phosphorus/Perovskite/MoS₂ structured photodetector, the comprehensive utilization of the photosensitive and dielectric properties of 2D perovskite allows the device to work in different modes. The device shows normal continuous photoresponse under 405 nm, while it shows a transient spike response to visible light with longer wavelengths. The linear dynamic range, rise/decay time, and self-powered responsivity under 405 nm can reach 100, 38 µs/50 µs, and 17.7 mA W^-1 , respectively. It is demonstrated that the transient spike photocurrent with long wavelength exposure is related to the illumination intensity and can coexist with normal photoresponse. Two waveband-dependent signals can be identified and used to reflect more information simultaneously. This work provides a new strategy for multispectral detection and demultiplexing, which can be used to improve data transfer rates and encrypted communications. This work mode can inspire more multispectral photodetectors with different stacked 2D materials, especially to the optoelectronic application of the wide bandgap, high dielectric photosensitive materials.

Self-adaptive fusion method for scientific CMOS image sensors with variable gain ratios and background values

Image diagnosis is an important technique in transient process research of high-energy physics. High dynamic range scenes require high linear dynamic range imaging systems. Scientific CMOS (sCMOS) image sensors have widely been used in high-energy physics, nuclear medical imaging, and astronomical observation because of their advantages in the high linear dynamic range. In this paper, we study the gain ratio variation and background value variation of commercial sCMOS image sensors. A self-adaptive fusion method is proposed to realize the fusion of high linear dynamic range images. The proposed method only uses the high gain image and the low gain image of the sCMOS image sensor to evaluate the gain ratio and the background compensation. The measured results show that the error rates of the evaluated gain ratio and background compensation are less than 2% and 6%. Test results show that the self-adaptive fusion method realizes well the fusion effects, which efficiently avoids the influence of gain ratio variation and background value variation.

A Universal Microscopic Patterned Doping Method for Perovskite Enables Ultrafast, Self-Powered, Ultrasmall Perovskite Photodiodes

Novel metal halide perovskite is proven to be a promising optoelectronic material. However, fabricating microscopic perovskite devices is still challenging because the perovskite is soluble with the photoresist, which conflicts with conventional microfabrication technology. The size of presently reported perovskite devices is about 50 µm. Limited by the large size of perovskite optoelectronic devices, they cannot be readily adopted in the fields of imaging, display, etc. Herein a universal microscopic patterned doping method is proposed, which can realize microscale perovskite devices. Rather than by the conventional doping method, in this study the local Fermi level of perovskite is modulated by the redistributing intrinsic ion defects via a polling voltage. A satisfactorily stable polarized ion distribution can be achieved by optimization of the perovskite material and polling voltage, resulting in ultrafast (40 µs), self-powered microscale (2 µm) photodiodes. This work sheds light on a route to fabricate integrated perovskite optoelectronic chips.

Recent Progress on Wavelength-Selective Perovskite Photodetectors for Image Sensing

Spectral sensing plays a crucial part in imaging technologies, optical communication, and other fields. However, complicated optical elements, such as prisms, interferometric filters, and diffraction grating, are required for commercial multispectral detectors, which hampers their advance toward miniaturization and integration. In recent years, metal halide perovskites have been emerging for optical-component-free wavelength-selective photodetectors (PDs) because of their continuously tunable bandgap, fascinating optoelectronic properties, and simple preparation processes. In this review, recent advances in wavelength-selective perovskite PDs, including narrowband PDs, dual-band PDs, multispectral-recognizable PDs, and X-ray PDs, are highlighted, with an emphasis on device structure designs, working mechanisms, and optoelectronic performances. Meanwhile, the applications of wavelength-selective PDs in image sensing for single-/dual-color imaging, full-color imaging, and X-ray imaging are introduced. Finally, the remaining challenges and perspectives in this emerging field are presented.

Recent advances in inkjet-printing technologies for flexible/wearable electronics

The rapid development of flexible/wearable electronics requires novel fabricating strategies. Among the state-of-the-art techniques, inkjet printing has aroused considerable interest due to the possibility of large-scale fabricating flexible electronic devices with good reliability, high time efficiency, a low manufacturing cost, and so on. In this review, based on the working principle, recent advances in the inkjet printing technology in the field of flexible/wearable electronics are summarized, including flexible supercapacitors, transistors, sensors, thermoelectric generators, wearable fabric, and for radio frequency identification. In addition, some current challenges and future opportunities in this area are also addressed. We hope this review article can give positive suggestions to the researchers in the area of flexible electronics.

Highly efficient and stable near-infrared photodetectors enabled from passivated tin-lead hybrid perovskites

Tin-lead perovskite-based photodetectors have a wide light-absorption wavelength range, which spans 1000 nm. However, the preparation of the mixed tin-lead perovskite films faces two great obstacles, namely easy oxidation of Sn²⁺to Sn⁴⁺and fast crystallization from tin-lead perovskite precursor solutions, thus further resulting in poor morphology and high density of defects in tin-lead perovskite films. In this study, we demonstrated a high-performance of near-infrared photodetectors prepared from a stable low-bandgap (MAPbI₃)_0.5(FASnI₃)_0.5film modified with 2-fluorophenethylammonium iodide (2-F-PEAI). The addition engineering can efficiently improve the crystallization of (MAPbI₃)_0.5(FASnI₃)_0.5films through the coordination binding between Pb²⁺and N atom in 2-F-PEAI, and resulting in a uniform and dense (MAPbI₃)_0.5(FASnI₃)_0.5film. Moreover, 2-F-PEAI suppressed Sn²⁺oxidation and effectively passivated defects in the (MAPbI₃)_0.5(FASnI₃)_0.5film, thereby significantly reducing the dark current in the PDs. Consequently, the near-infrared photodetectors showed a high responsivity with a specific detectivity of over 10¹²Jones at 800 to near-1000 nm. Additionally, the stability of PDs incorporated with 2-F-PEAI has been significantly improved under air conditions, and the device with the 2-F-PEAI ratio of 400:1 retained 80% of its initial efficiency after 450 h storage in air without encapsulation. Finally, 5 × 5 cm²photodetector arrays were fabricated to demonstrate the potential utility of the Sn-Pb perovskite photodetector in optical imaging and optoelectronic applications.

Soft Fiber Electronics Based on Semiconducting Polymer

Fibers, originating from nature and mastered by human, have woven their way throughout the entire history of human civilization. Recent developments in semiconducting polymer materials have further endowed fibers and textiles with various electronic functions, which are attractive in applications such as information interfacing, personalized medicine, and clean energy. Owing to their ability to be easily integrated into daily life, soft fiber electronics based on semiconducting polymers have gained popularity recently for wearable and implantable applications. Herein, we present a review of the previous and current progress in semiconducting polymer-based fiber electronics, particularly focusing on smart-wearable and implantable areas. First, we provide a brief overview of semiconducting polymers from the viewpoint of materials based on the basic concepts and functionality requirements of different devices. Then we analyze the existing applications and associated devices such as information interfaces, healthcare and medicine, and energy conversion and storage. The working principle and performance of semiconducting polymer-based fiber devices are summarized. Furthermore, we focus on the fabrication techniques of fiber devices. Based on the continuous fabrication of one-dimensional fiber and yarn, we introduce two- and three-dimensional fabric fabricating methods. Finally, we review challenges and relevant perspectives and potential solutions to address the related problems.

Exploring the Limits: Degradation Behavior of Lead Halide Perovskite Films under Exposure to Ultrahigh Doses of γ Rays of Up to 10 MGy

Herein, we show that thin films of MAPbI₃, FAPbI₃, (CsMA)PbI₃, and (CsMAFA)PbI₃, where MA and FA are methylammonium and formamidinium cations, respectively, tolerate ultrahigh doses of γ rays approaching 10 MGy without significant changes in their absorption spectra. However, among the studied materials, FAPbI₃ was the only one that did not form metallic lead due to its extreme radiation hardness. Infrared near-field optical microscopy revealed the radiation-induced depletion of organic cations from the grains of MAPbI₃ and their accumulation at the grain boundaries, whereas FAPbI₃ on the contrary lost FA cations from the grain boundaries. The multication (CsMAFA)PbI₃ perovskite underwent a facile phase segregation to domains enriched with MA and FA cations, which is a principally new radiation-induced degradation pathway. Our findings suggest that the radiation hardness of the rationally designed perovskite semiconductors could go far beyond the impressive threshold of 10 MGy we set herein for FAPbI₃ films, which opens many exciting opportunities for practical implementation of these materials.

High-Performance Self-Powered Photodetector Based on the Lateral Photovoltaic Effect of All-Inorganic Perovskite CsPbBr3 Heterojunctions

CsPbBr₃, an inorganic halide perovskite, has attracted great interest in recent years due to its excellent photoelectric properties. In this paper, we report a high-performance position-sensitive detector and laser communication sensor based on a CsPbBr₃/4H-SiC heterojunction that effectively exploits the lateral photovoltaic (LPV) effect. The X-ray diffraction, X-ray photoelectron spectra, and photoluminescence data indicate that a high-quality CsPbBr₃ film has been successfully obtained using pulsed laser deposition. The thickness of the CsPbBr₃ film is shown to play a key role in the open-circuit voltage and linear LPV. A large position sensitivity (up to 827 mV/mm) of the LPV with a fast relaxation time is observed. Moreover, the shortest relaxation time of only 0.34 μs for 532 nm laser irradiation among counterparts is achieved in the detector under consideration. Furthermore, the position sensitivity and relaxation time of the LPV in the CsPbBr₃/4H-SiC heterojunction show a weak dependence on the laser wavelength from 266 to 532 nm. The robust characteristics of fast relaxation time and high position sensitivity of the LPV make the CsPbBr₃ junction a promising candidate for both laser communication sensors and self-powered high-performance position-sensitive detectors.

A Perovskite Photodetector Crossbar Array by Vapor Deposition for Dynamic Imaging

With the development of perovskite photodetectors, integrating photodetectors into array image sensors is the next target to pursue. The major obstacle to integrating perovskite photodiodes for dynamic imaging is the optoelectrical crosstalk among the pixels. Herein, a perovskite photodiode-blocking diode (PIN-BD) crossbar array with pixel-wise rectifying property by the vapor deposition method is presented. The PIN-BD shows a large rectification ratio of 3.3 × 10² under illumination, suppressing electrical crosstalk to as small as 8.0% in the imaging array. The fast response time of 72.8 ns allows real-time image acquisition by over 25 frames per second. The imaging sensor exhibits excellent imaging capability with a large linear dynamic range of 112 dB with 4096 gray levels and weak light sensitivity under 1.2 lux.

Halide Perovskite: A Promising Candidate for Next-Generation X-Ray Detectors

In the past decade, metal halide perovskite (HP) has become a superstar semiconductor material due to its great application potential in the photovoltaic and photoelectric fields. In fact, HP initially attracted worldwide attention because of its excellent photovoltaic efficiency. However, HP and its derivatives also show great promise in X-ray detection due to their strong X-ray absorption, high bulk resistivity, suitable optical bandgap, and compatibility with integrated circuits. In this review, the basic working principles and modes of both the direct-type and the indirect-type X-ray detectors are first summarized before discussing the applicability of HP for these two types of detection based on the pros and cons of different perovskites. Furthermore, the authors expand their view to different preparation methods developed for HP including single crystals and polycrystalline materials. Upon systematically analyzing their potential for X-ray detection and photoelectronic characteristics on the basis of different structures and dimensions (0D, 2D, and 3D), recent progress of HPs (mainly polycrystalline) applied to flexible X-ray detection are reviewed, and their practicability and feasibility are discussed. Finally, by reviewing the current research on HP-based X-ray detection, the challenges in this field are identified, and the main directions and prospects of future research are suggested.

Fabrication of ZnO dual electron transport layer via atomic layer deposition for highly stable and efficient CsPbBr3perovskite nanocrystals light-emitting diodes

Electron transport layers (ETLs) are important components of high-performance all-inorganic perovskite nanocrystals light-emitting diodes (PNCs-LED). Herein, atomic layer deposition (ALD) of inorganic ZnO layer is combined to the organic 1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) to form dual ETLs to enhance both the efficiency and stability of PNCs-LED simultaneously. Optimization of ZnO thickness suggested that 10 cycles ALD yields the best performance of the devices. The external quantum efficiency of the device reaches to 7.21% with a low turn-on voltage (2.4 V). Impressively, the dual ETL PNCs-LED realizes maximumT₅₀lifetime of 761 h at the initial luminance of 100 nit, which is one of the top lifetimes among PNCs-LEDs up to now. The improved performance of dual ETL PNCs-LED is mainly due to the improved charge transport balance with favorable energy level matching. These findings present a promising strategy to modify the function layer via ALD to achieve both highly efficient and stable PNCs-LED.

High-Performance UV-Vis Broad-Spectra Photodetector Based on a β-Ga2O3/Au/MAPbBr3 Sandwich Structure

The UV-vis photodetector (PD), a detector that can simultaneously detect light in the ultraviolet region and the visible region, has a wide range of applications in military and civilian fields. Currently, it is very difficult to obtain good detection performance in the UV region (especially in the solar-blind range) like in the visible region with most UV-vis PDs. This severely affects the practical application of UV-vis broad-spectra PDs. Here, a simple sandwich structure PD (SSPD) composed of β-Ga₂O₃, Au electrodes, and the MAPbBr₃ perovskite is designed and fabricated to simultaneous enhance the detection performance in the UV and visible light regions. The β-Ga₂O₃/Au/MAPbBr₃ SSPD exhibits enhanced optoelectronic performance with high responsivities of 0.47 and 1.43 A W^-1 at 240 and 520 nm under a bias of 6 voltage (V), respectively, which are 8.5 and 23 times than that of the metal-semiconductor-metal (MSM) structure MAPbBr₃ PD at 6 V, respectively. The enhanced performance was attributed to the effective suppression of carrier recombination due to the efficient interface charge separation in the device structure. In addition, the self-powered response characteristic is also realized by forming a type-II heterojunction between β-Ga₂O₃ and MAPbBr₃, which gives the β-Ga₂O₃/Au/MAPbBr₃ SSPD superior single-pixel photo-imaging ability without an external power supply. This work provides a simple and effective method for the preparation of high-performance self-powered imaging PDs in the UV-visible region.

UV-vis-IR Broad Spectral Photodetectors Based on VO2-ZnO Nanocrystal Films

As a narrow band semiconductor at room temperature and a metallic material above ∼68 °C, functional VO₂ films are widely investigated for smart windows, whereas their potential for ultraviolet-visible-infrared (UV-vis-IR) broad spectral photodetectors has not been efficiently studied. In this report, photodetectors based on VO₂-ZnO nanocrystal composite films were prepared by nanocrystal-mist (NC-mist) deposition. An enhanced photodetection switching ratio was achieved covering the ultraviolet to infrared wavelength. Due to the synergetic effect of nanosize, surface, phase transition, percolation threshold, and the band structure of the heterojunction, the transfer and transport of photogenerated carriers modulate the device performance. This study probes new chances of applying VO₂-semiconductor-based nanocomposites for broad spectral photodetectors.

High-Quality Patterning of CsPbBr3 Perovskite Films through Lamination-Assisted Femtosecond Laser Ablation toward Light-Emitting Diodes

Metal halide perovskites have exhibited promising potential for practical applications such as image sensors and displays benefiting from their outstanding optoelectronic properties. However, owing to the instability of the perovskite materials, producing patterned perovskite films with adequately high quality and high precision for such practical applications poses a challenge for existing patterning methods. Herein, the lamination-assisted femtosecond laser ablation (LA-FsLA) technique was successfully applied to fabricate patterned CsPbBr₃ films with sufficiently high quality and high precision. A sandwich-laminated structure (glass/CsPbBr₃/glass) was introduced to avoid the impact of debris on the patterned perovskite film. As a result, arbitrarily patterned perovskite films with high quality, submicron precision, and well-defined edges were successfully prepared. Moreover, the light-emitting diodes (LEDs) based on the patterned perovskite films also exhibit good emission characteristics. This work provides a promising strategy for the fabrication of patterned perovskite films with adequately high quality and high precision toward perovskite-based optoelectronic devices.

Stable and flexible photodetector based on liquid-phase exfoliated titanium disulfide nanosheets

Herein, the TiS₂nanosheets (NSs) are prepared from the TiS₂bulk by the liquid-phase exfoliation to fabricate photoelectrochemical-type (PEC) photodetector. SEM images and Raman spectra show the successful acquisition of the TiS₂NSs. The as-prepared TiS₂photodetector shows self-powered ability with an applicable photoresponsivity that is about 0.37μA W^-1under zero bias potential and 80 mW cm^-2visible light, and the response time of rise is 0.67 s and the decay time is 2.81 s. In this case, the photodetector is made of ITO-coated polyethylene terephthalate (PET), so it can maintain stable performance under the bending conditions. These results display that the as-prepared photodetector has excellent photoelectric properties, which facilitates the development of TiS₂NSs in optoelectronic devices.

Flexible Self-Powered Weak Light Detectors Based on ZnO/CsPbBr3/γ-CuI Heterojunctions

Halide perovskites (HPs) with marvelous optical and electrical properties are regarded as one of the competitive candidates for building next-generation photodetectors (PDs). However, combining their excellent properties with satisfactory long-term robustness is still challenging, ultimately limiting the practical applications of HP-based PDs. Herein, a high vacuum deposition system is employed to fabricate flexible self-powered PDs with a ZnO/CsPbBr₃/γ-CuI structure, which shows excellent stability and outstanding performance in weak light detection. Benefiting from the improved crystallinity and optimized device structure, a high detectivity of 8.1 × 10¹³ Jones and a rapid response speed (rise/decay time of 3.9/1.8 μs) are obtained in this self-powered device. Furthermore, the unencapsulated device exhibits intriguing environmental stability and mechanical flexibility. The photocurrent remains unchanged after 7000 s of continuous operation or 100 bending cycles. Furthermore, a 15 × 15 PD array is fabricated as an image sensor. A high contrast image of the target object can be obtained owing to the high sensitivity and uniformity of the self-powered PDs. These results demonstrate the feasibility and practicality of the ZnO/CsPbBr₃/γ-CuI heterojunction for applications in weak light detection and image formation.

Flexible Artificial Optoelectronic Synapse based on Lead-Free Metal Halide Nanocrystals for Neuromorphic Computing and Color Recognition

Optoelectronic synapses combining optical-sensing and synaptic functions are playing an increasingly vital role in the neuromorphic computing systems development, which can efficiently process visual information and complex recognition, memory, and learning. Metal halides are considered promising candidates for synaptic devices due to their excellent optoelectronic properties. However, the toxicity of lead and the further development of device functions are the recognized problems at present. Herein, a flexible optoelectronic synapses system based on high-quality lead-free Cs₃ Bi₂ I₉ nanocrystals is demonstrated, in which the carrier confinement caused by the band mismatching between the Cs₃ Bi₂ I₉ and the organic semiconductor layer provides the possibility to simulate synaptic behaviors. The synaptic functions including long/short-term memory and learning-forgetting-relearning are demonstrated in this device and visual perception, visual memory, and color recognition functions are successfully implemented. Additionally, the flexible device exhibits excellent robustness and can realize imaging of light distribution under curved hemispheres similar to the human eye. Finally, through the simulation based on an artificial neural network algorithm, the device successfully realizes the high-precision recognition of handwritten digital images and possesses a strong fault tolerant capability even in bending states. These results are expected to drive the practical progress of metal halide for neuromorphic computing.

Epitaxial Growth of Lead-Free 2D Cs3 Cu2 I5 Perovskites for High-Performance UV Photodetectors

The all-inorganic lead-free Cu-based halide perovskites represented by the Cs-Cu-I system, have sparked extensive interest recently due to their impressive photophysical characteristics. However, successive works on their potential application in light emission diodes and photodetectors rely on tiny polycrystals, in which the grain boundaries and defects may lead to the performance degradation of their embodied devices. Here, 2D all-inorganic perovskite Cs₃ Cu₂ I₅ single crystals are epitaxially grown on mica substrates, with a thickness down to 10 nm. The strong blue emission of the Cs₃ Cu₂ I₅ flakes may originate from the radiative transition of self-trapped excitons associated with a large Stocks shift and long (microsecond) decay time. Ultravioelt (UV) photodetectors based on individual Cs₃ Cu₂ I₅ nanosheets are fabricated via a swift and etching-free dry transfer approach, which reveal a high responsivity of 3.78 A W^-1 (270 nm, 5 V bias), as well as a fast response speed (τ_rise  ≈163 ms, τ_decay  ≈203 ms), outperforming congeneric UV sensors based on other 2D metal halide perovskites. This work therefore sheds light on the fabrication of green optoelectronic devices based on lead-free 2D perovskites, vital for the sustainable development of photoelectric technology.

2D Material and Perovskite Heterostructure for Optoelectronic Applications

Optoelectronic devices are key building blocks for sustainable energy, imaging applications, and optical communications in modern society. Two-dimensional materials and perovskites have been considered promising candidates in this research area due to their fascinating material properties. Despite the significant progress achieved in the past decades, challenges still remain to further improve the performance of devices based on 2D materials or perovskites and to solve stability issues for their reliability. Recently, a novel concept of 2D material/perovskite heterostructure has demonstrated remarkable achievements by taking advantage of both materials. The diverse fabrication techniques and large families of 2D materials and perovskites open up great opportunities for structure modification, interface engineering, and composition tuning in state-of-the-art optoelectronics. In this review, we present comprehensive information on the synthesis methods, material properties of 2D materials and perovskites, and the research progress of optoelectronic devices, particularly solar cells and photodetectors which are based on 2D materials, perovskites, and 2D material/perovskite heterostructures with future perspectives.

Ultrathin, Transparent, and High Density Perovskite Scintillator Film for High Resolution X-Ray Microscopic Imaging

Inorganic perovskite quantum dots CsPbX₃ (X = Cl, Br, and I) has recently received extensive attention as a new promising class of X-ray scintillators. However, relatively low light yield (LY) of CsPbX₃ and strong optical scattering of the thick opaque scintillator film restrict their practical applications for high-resolution X-ray microscopic imaging. Here, the Ce³⁺ ion doped CsPbBr₃ nanocrystals (NCs) with enhanced LY and stability are obtained and then the ultrathin (30 µm) and transparent scintillator films with high density are prepared by a suction filtration method. The small amount Ce³⁺ dopant greatly enhances the LY of CsPbBr₃ NCs (about 33 000 photons per MeV), which is much higher than that of bare CsPbBr₃ NCs. Moreover, the scintillator films made by these NCs with high density realize a high spatial resolution of 862 nm thanks to its thin and transparent feature, which is so far a record resolution for perovskite scintillator-based X-ray microscopic imaging. This strategy not only provides a simple way to increase the resolution down to nanoscale but also extends the application of as-prepared CsPbBr₃ scintillator for high resolution X-ray microscopic imaging.

A high-performance polarization-sensitive and stable self-powered UV photodetector based on a dendritic crystal lead-free metal-halide CsCu2I3/GaN heterostructure

Polarization-sensitive photodetectors are the core of optics applications and have been successfully demonstrated in photodetectors based on the newly-emerging metal-halide perovskites. However, achieving high polarization sensitivity is still extremely challenging. In addition, most of the previously reported photodetectors were concentrated on 1D lead-halide perovskites and 2D asymmetric intrinsic structure materials, but suffered from being external bias driven, lead-toxicity, poor stability and complex processes, severely limiting their practical applications. Here, we demonstrate a high-performance polarization-sensitive and stable polarization-sensitive UV photodetector based on a dendritic crystal lead-free metal-halide CsCu₂I₃/GaN heterostructure. By combining the anisotropic morphology and asymmetric intrinsic structure of CsCu₂I₃ dendrites with the isotropic material GaN film, a high specific surface area and built-in electric field are achieved, exhibiting an ultra-high polarization selectivity up to 28.7 and 102.8 under self-driving mode and -3 V bias, respectively. To our knowledge, such a high polarization selectivity has exceeded those of all of the reported perovskite-based devices, and is comparable to, or even superior to, those of the conventional 2D heterostructure materials. Interestingly, the unsealed device shows outstanding stability, and can be stored for over 2 months, and effectively maintained the performance even after repeated heating (373K)-cooling (300K) for different periods of time in ambient air, indicating a remarkable temperature tolerance and desired compatibility for applications under harsh conditions. Such excellent performance and simple method strongly show that the CsCu₂I₃/GaN heterojunction photodetector has great potential in practical applications with high polarization-sensitivity. This work provides a new insight into designing novel high-performance polarization-sensitive optoelectronic devices.

Vertical Heterogeneous Integration of Metal Halide Perovskite Quantum-Wires/Nanowires for Flexible Narrowband Photodetectors

Charge collection narrowing (CCN) has been reported to be an efficient strategy to achieve optical filter-free narrowband photodetection (NPD) with metal halide perovskite (MHP) single crystals. However, the necessity of utilizing thick crystals in CCN limits their applications in large scale, flexible, self-driven, and high-performance optoelectronics. Here, for the first time, we fabricate vertically integrated MHP quantum wire/nanowire (QW/NW) array based photodetectors in nanoengineered porous alumina membranes (PAMs) showing self-driven broadband photodetection (BPD) and NPD capability simultaneously. Two cutoff detection edges of the NPDs are located at around 770 and 730 nm, with a full-width at half-maxima (fwhm) of around 40 nm. The optical bandgap difference between the NWs and the QWs, in conjunction with the high carrier recombination rate in QWs, contributes to the intriguing NPD performance. Thanks to the excellent mechanical flexibility of the PAMs, a flexible NPD is demonstrated with respectable performance. Our work here opens a new pathway to design and engineer a nanostructured MHP for novel color selective and full color sensing devices.

Self-Powered Organometal Halide Perovskite Photodetector with Embedded Silver Nanowires

Metal-semiconductor-metal (MSM) configuration of perovskite photodetectors (PPDs) suggests easy and low-cost manufacturing. However, the basic structures of MSM PPDs include vertical and lateral configurations, which require the use of expensive materials such as transparent conductive oxides or/and sophisticated fabrication techniques such as lithography. Integrating metallic nanowire-based electrodes into the perovskite photo-absorber layer to form one-half of the MSM PPD structure could potentially resolve the key issues of both configurations. Here, a manufacturing of solution-processed and self-powered MSM PPDs with embedded silver nanowire electrodes is demonstrated. The embedding of silver nanowire electrode into the perovskite layer is achieved by treating the silver nanowire/perovskite double layer with a methylamine gas vapor. The evaporated gold layer is used as the second electrode to form MSM PPDs. The prepared MSM PPDs show a photoresponsivity of 4 × 10-5 AW-1 in the UV region and 2 × 10-5 AW-1 in the visible region. On average, the devices exhibit a photocurrent of 1.1 × 10-6 A under white light (75 mW cm-2) illumination with an ON/OFF ratio of 83.4. The results presented in this work open up a new method for development and fabrication of simple, solution-processable MSM self-powered PPDs.

All-inorganic perovskite nanocrystals: next-generation scintillation materials for high-resolution X-ray imaging

With super strong penetrability, high-energy X-rays can be applied to probe the inner structure of target objects under nondestructive situations. Scintillation materials can down-convert X-rays into visible light, enabling the reception of photon signals and photoelectric conversion by common sensing arrays such as photomultiplier tubes and amorphous-Si photodiode matrixes. All-inorganic perovskite nanocrystals are emerging photovoltaic and scintillation materials, with tremendous light-conversion efficiency and tunable luminous properties, exhibiting great potential for high-quality X-ray imaging. Recent advancements in nanotechnology further accelerate the performance improvement of scintillation materials. In this review, we will provide a comprehensive overview of novel all-inorganic perovskite nano-scintillators in terms of potential applications in low-dose X-ray medical radiography. Compared with conventional scintillators, the merits/drawbacks, challenges, and scintillation performance control will be the focus of this article.

GaS:WS2 Heterojunctions for Ultrathin Two-Dimensional Photodetectors with Large Linear Dynamic Range across Broad Wavelengths

Two-dimensional (2D) photodetectors based on photovoltaic effect or photogating effect can hardly achieve both high photoresponsivity and large linear dynamic range at the same time, which greatly limits many practical applications such as imaging sensors. Here, the conductive-sensitizer strategy, a general design for improving photoresponsivity and linear dynamic range in 2D photodetectors is provided and experimentally demonstrated on vertically stacked bilayer WS₂/GaS_0.87 under a parallel circuit mode. Owing to successful band alignment engineering, the isotype type-II heterojunction enables efficient charge carrier transfer from WS₂, the high-mobility sensitizer, to GaS_0.87, the low-mobility channel, under illumination from a broad visible spectrum. The transferred electron charges introduce a reverse electric field which efficiently lowers the band offset between the two materials, facilitating a transition from low-mobility photocarrier transport to high-mobility photocarrier transport with increasing illumination power. We achieved a large linear dynamic range of 73 dB as well as a high and constant photoresponsivity of 13 A/W under green light. X-ray photoelectron spectroscopy, cathodoluminescence, and Kelvin probe force microscopy further identify the key role of defects in monolayer GaS_0.87 in engineering the band alignment with monolayer WS₂. This work proposes a design route based on band and interface modulation for improving performance of 2D photodetectors and provides deep insights into the important role of strong interlayer coupling in offering heterostructures with desired properties and functions.

Perovskite photodetectors and their application in artificial photonic synapses

Organic-inorganic hybrid perovskites exhibit superior optoelectrical properties and have been widely used in photodetectors. Perovskite photodetectors with excellent detectivity have great potential for developing artificial photonic synapses which can merge data transmission and storage. They are highly desired for next generation neuromorphic computing. The recent progress of perovskite photodetectors and their application in artificial photonic synapses are summarized in this review. Firstly, the key performance parameters of photodetectors are briefly introduced. Secondly, the recent research progress of photodetectors including photoconductors, photodiodes, and phototransistors is summarized. Finally, the applications of perovskite photodetectors in artificial photonic synapses in recent years are highlighted. All these demonstrate the great potential of perovskite photonic synapses for the development of artificial intelligence.

Cost-Effective Strategy for the Synthesis of Air-Stable CH3NH3PbX3 (X = Cl, Br, and I) Quantum Dots with Bright Emission

Lead halide perovskite quantum dots (QDs) are known as prospective optoelectronic device materials because of their excellent luminescence, extraordinary photoelectric performance, and specific octahedron framework. Herein, we report a cost-effective approach for synthesizing highly stable CH₃NH₃PbBr₃ QDs in low-polarity binary solvents without nitrogen protection. The CH₃NH₃PbBr₃ QDs are tunable from 1.2 to 4.2 nm by adjusting the proportion of oleic acid and oleylamine as capping ligands. The photoluminescence quantum yield of CH₃NH₃PbBr₃ QDs can reach 87.4%. The fluorescence can maintain over 80% of its earliest emission intensity under the atmosphere after 5 days, which is much better than that (∼10%) of QDs with ligand-assisted reprecipitation. The possible reaction mechanism of preparing CH₃NH₃PbBr₃ QDs was also addressed. Notably, such a strategy can be applied extensively in the preparation of other lead halide perovskite QDs. Furthermore, the as-prepared thick PMMA-coated CH₃NH₃PbBr₃ QDs were further conjoined with a red luminescence powder on a blue InGaN chip to obtain a powerful efficiency (45.4 lm W^-1) warm white light-emitting diode.