In Situ Growth of 120 cm2 CH3 NH3 PbBr3 Perovskite Crystal Film on FTO Glass for Narrowband-Photodetectors

Filter-Less Color-Selective Photodetector Derived from Integration of Parallel Perovskite Photoelectric Response Units

Color-selective photodetectors (PDs) play an indispensable role in spectral recognition, image sensing, and other fields. Nevertheless, complex filters and delicate optical paths in such devices significantly increase their complexity and size, which subsequently impede their integration in smart optoelectronic chips for universal applications. This work demonstrates the successful fabrication of filter-less color-selective perovskite PDs by integrating three perovskite units with different photoresponse on a single chip. The variation in photoresponse is attributed to different quantities of SnO2 nanoparticles, synthesized through controlled ultrasonic treatment on the surface of the electron transportation layer SnS2, which selectively absorb short-wavelength light, thus increasing the relative transmittance of long-wavelength light and enhancing the photoresponse of the units to long wavelengths. By integrating any two units and deriving the formula for the wavelength to the responsivity ratio, a wavelength sensor is developed which can accurately identify incident light in the range of 400-700 nm with a minimum error <3 nm. Furthermore, the device integrating three units with different photoresponse can identify red, green and blue in polychromatic light to achieve color imaging with a relative error <6%. This work provides valuable insights into wavelength identification and color imaging of perovskite PDs.

Multidimensional vision sensors for information processing

The visual scene in the physical world integrates multidimensional information (spatial, temporal, polarization, spectrum and so on) and typically shows unstructured characteristics. Conventional image sensors cannot process this multidimensional vision data, creating a need for vision sensors that can efficiently extract features from substantial multidimensional vision data. Vision sensors are able to transform the unstructured visual scene into featured information without relying on sophisticated algorithms and complex hardware. The response characteristics of sensors can be abstracted into operators with specific functionalities, allowing for the efficient processing of perceptual information. In this Review, we delve into the hardware implementation of multidimensional vision sensors, exploring their working mechanisms and design principles. We exemplify multidimensional vision sensors built on emerging devices and silicon-based system integration. We further provide benchmarking metrics for multidimensional vision sensors and conclude with the principle of device-system co-design and co-optimization.

Space-Confined Growth for Thickness-Controlled Cs3Bi2I9 Perovskite Single Crystal Wafers for X-Ray Detectors

The Cs3Bi2I9 single crystal, as an all-inorganic non-lead perovskite, offers advantages such as stability and environmental friendliness. Its superior photoelectric properties, attributed to the absence of grain boundary influence, make it an outstanding X-ray detection material compared to polycrystals. In addition to material properties, X-ray detector performance is affected by the thickness of the absorption layer. Addressing this, a space-confined method is proposed. The temperature field is determined through finite element simulation, effectively guiding the design of the space-confined method. Through this innovative method, a series of thickness-controlled perovskite single crystal wafers (PSCWs) are successfully prepared. Corresponding X-ray detectors are then prepared, and the impact of single crystal thickness on device performance is investigated. With an increase in single crystal thickness, a rise followed by a decline in device sensitivity is observed, reaching an optimal value at 0.7 mm thickness at 40V mm-1 with a device performance of 11313.6µC Gy-1 cm-2. This space-confined method enables the direct growth of high-quality perovskite single crystals with specified thickness, eliminating the need for slicing or etching.

Gas-Liquid Interface Route to Hybrid Copper Bromine Perovskite Single-Crystal Membrane with Dielectric Transitions and Ferromagnetic Exchanges

Single-crystal membranes (SCMs) show great promise in the fields of sensors, light-emitting diodes, and photodetection. However, the growth of a large-area single-crystal membranes is challenging. We report a new organic-inorganic SCMs [HCMA]2CuBr4 (HCMA = cyclohexanemethylamine) crystallized at the gas-liquid interface. It also has low-temperature ferromagnetic order, high-temperature dielectric anomalies, and narrow band gap indirect semiconductor properties. Specifically, the reversible phase transition of the compound occurs at 350/341 K on cooling/heating and exhibits dielectric anomalies and stable switching performance near the phase transition temperature. The ferromagnetic exchange interaction in the inorganic octahedra and the organic layer enables ferromagnetic ordering at low-temperature 10 K. Finally, the single crystal exhibits an indirect semiconducting property with a narrow band gap of 0.99 eV. Such rich multichannel physical properties make it a potential application in photodetection, information storage and sensors.

Can thick metal-halide perovskite single crystals have narrower optical bandgaps with near-infrared absorption?

Metal-halide perovskite (MHP) single crystals are emerging as potential competitors to their polycrystalline thin-film counterparts. These materials have shown the specific feature of extended absorbance towards the near-infrared (NIR) region, which promises further extension of their applications in the field of photovoltaics and photodetectors. This notable expansion of absorbance has been explained by the narrower effective optical bandgap of MHP single crystals promoted by their large thickness over several micrometres to millimetres. Herein, the attributes of the material's thickness and the measurement technique used to estimate these characteristics are discussed to elucidate the actual origins of the extended absorbance of MHP single crystals. Contrary to the general belief of the narrower bandgap of the MHP single crystals, we demonstrate that the extended NIR absorption in the MHP single crystals mainly originates from the combination of unique below-bandgap absorption of MHPs, the thickness of single crystals, and the technical limitation of the spectrophotometer, with the key attributes of (i) significantly large thickness of the MHP single crystals by suppressing the transmitted light and (ii) the detector's limited dynamic range. Combining the theoretical and experimental characterizations, we clarify the significant role of the large thickness together with the limited sensitivity of the detector in promoting the well-known red shift of the absorption onset of the MHP single crystals. The observations evidently show that in some special circumstances, the acquired absorption spectrum cannot reliably represent the optical bandgap of MHP materials. This highlights some misinterpretations in the estimation of the narrower optical bandgap of the MHP single crystals from conventional optical methods, while the optical bandgap is an inherent property independent of the thickness. The proposed broad applications of the MHP single crystals are dictated by their fascinating properties, and therefore, a deep insight into these features should be considered besides device applications, because much of their property-function relationships are still ambiguous and a subject of debate.

Integration of Large-Area Halide Perovskite Single Crystals and Substrates via Chemical Welding Using an Ionic Liquid for Applications in X-ray Detection

The large carrier lifetime mobility product and strong stopping power for high-energy X-rays make halide perovskites an attractive candidate for next-generation X-ray detectors. In particular, high-energy X-rays in the range of several tens of keV require halide perovskite absorber layers with thicknesses exceeding a few millimeters. To avoid carrier scattering caused by grain boundaries at such thicknesses, the utilization of single crystals is desirable. Large-area single crystals are predominantly grown in a freestanding form, and integration onto a substrate is necessary for the fabrication of commercial devices. However, an effective method for integrating large single crystals onto a substrate has not yet been developed. In this study, a large-area (20 cm2) MAPbBr3 single crystal is bonded to an indium tin oxide (ITO) substrate using an ionic liquid, showing strong adhesion strength of 164 kPa. X-ray detectors based on ITO/MAPbBr3 single crystal bonded by methylammonium acetate achieved excellent sensitivity of 91,200 μC Gyair-1 cm-2, the highest among substrate-integrated halide perovskite single crystal X-ray detectors.

Fast Response, High Spectral Rejection Ratio, Self-Filtered Ultranarrowband Photodetectors Based on Perovskite Single-Crystal Heterojunctions

Narrowband photodetectors have wide application potential in high-resolution imaging and encrypted communication, due to their high-precision spectral resolution capability. In this work, we report a fast response, high spectral rejection ratio, and self-filtered ultranarrowband photodetector with a new mechanism, which introduces bulk recombination by doping Bi3+ and cooperates with surface recombination for further quenching photogenerated charges generated by short-wavelength-light excitation in perovskite single-crystal. A perovskite film focused on collecting charges is fabricated on the single crystal by a lattice-matched solution-processed epitaxial growth method. Due to the formation of PN heterojunctions, a narrowband photodetector in this mechanism has remarkable spectral selectivity and detection performance with an ultranarrow full width at half-maximum (FWHM) of 7.7 nm and a high spectral rejection ratio of 790, as well as a high specific detectivity up to 1.5 × 1010 Jones, a fast response speed with a rise time and fall time of ∼8 and 137 μs. The ultrafast and ultranarrow spectra response of self-filtered narrowband photodetector provides a new strategy in high-precision and high-resolution photoelectric detection.

Thermodynamically and Kinetically Controlled Nucleation and Growth of Halide Perovskite Single Crystals

Halide perovskites are ideal for next-generation optical devices and photovoltaics. Although perovskite single-crystals show reproducible optoelectronic properties, significant variations in the crystal size, anisotropy, density, defects, photoluminescence (PL), and carrier lifetime affect the sample properties and device performances. Homogenous size and shape FA/MAPbBr3 single microcrystals (MCs) with controlled edge lengths, crystal densities, PL lifetimes, and PL intensities are prepared by thermodynamically controlling and kinetically separating the crystal nucleation-growth processes using optimum N-cyclohexyl-2-pyrrolidone (CHP) concentration. The crystal growth kinetics at different CHP concentrations and temperatures are estimated spectroscopically by measuring the concentration of Pb (II). High-density cubic MCs with a homogenous size distribution, high PL intensities, and long PL lifetimes are obtained within minutes at high temperatures by the controlled addition of the pyrrolidone derivative. Conversely, the crystal size nonlinearly increases with time at low temperatures. The isotropically grown high-density single crystals at controlled nucleation-growth rates at 190 °C with 20% CHP show the highest PL intensity and the longest PL lifetimes. This method offers thermodynamic and kinetic control of perovskite single-crystal growth with shape control.

3D-Heterojunction Based on Embedded Perovskite Micro-Sized Single Crystals for Fast Photomultiplier Photodetectors with Broad/Narrowband Dual-Mode

A fast photomultiplier photodetector with a broad/narrowband dual mode is implemented using a new 3D heterostructure based on embedded perovskite micro-sized single crystals. Because the single-crystal size is smaller than the electrode size, the active layer can be divided into a perovskite microcrystalline part for charge transport and a polymer-embedded part for charge storage. This induces an additional radial interface in the 3D heterojunction structure, and allows a photogenerated built-in electric field in the radial direction, especially when the energy levels between the perovskite and embedding polymer are similar. This type of heterojunction has a small radial capacitance that can effectively reduce carrier quenching and accelerate the carrier response. By controlling the applied bias direction, up to 300-1000% external quantum efficiency (EQE) and microsecond response can be achieved not only in the wide range of ultraviolet to visible light from 320 to 550 nm, but also in the narrow-band response with a full width at half minimum (FWHM) of 20 nm. This shows great potential for applications in integrated multifunctional photodetectors.

Perovskite single-crystal thin films: preparation, surface engineering, and application

Perovskite single-crystal thin films (SCTFs) have emerged as a significant research hotspot in the field of optoelectronic devices owing to their low defect state density, long carrier diffusion length, and high environmental stability. However, the large-area and high-throughput preparation of perovskite SCTFs is limited by significant challenges in terms of reducing surface defects and manufacturing high-performance devices. This review focuses on the advances in the development of perovskite SCTFs with a large area, controlled thickness, and high quality. First, we provide an in-depth analysis of the mechanism and key factors that affect the nucleation and crystallization process and then classify the methods of preparing perovskite SCTFs. Second, the research progress on surface engineering for perovskite SCTFs is introduced. Third, we summarize the applications of perovskite SCTFs in photovoltaics, photodetectors, light-emitting devices, artificial synapse and field-effect transistor. Finally, the development opportunities and challenges in commercializing perovskite SCTFs are discussed.

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.

De Novo Studies of Working Mechanisms for Self-Driven Narrowband Perovskite Photodetectors

Self-driven narrowband perovskite photodetectors have recently attracted significant attention due to their simple preparation, high performance, and amenability for system integration. However, the origin of narrowband photoresponse and the related regulation mechanisms still remains elusive. To address these issues, we herein perform a systematic investigation by formulating an analytic model in conjunction with finite element simulation. The optical and electrical simulations have resulted in design principles for perovskite narrowband photodetectors in terms of the dependence of external quantum efficiency (EQE) on perovskite layer thickness, doping concentration, and band gap as well as trap state concentration. Careful investigations on the profiles of electric field, current, and optical absorption reveal the dependence of narrowband EQE on the direction of incident light and perovskite doping types: only p-type perovskite can yield the narrowband photoresponse for illumination from the hole transport layer (HTL) side. The simulation results demonstrated in this study shed new light on the mechanism of perovskite-based narrowband photodetectors and provide valuable guidance for their design.

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.

Stabilization and Performance Enhancement Strategies for Halide Perovskite Photocatalysts

Solar-energy-powered photocatalytic fuel production and chemical synthesis are widely recognized as viable technological solutions for a sustainable energy future. However, the requirement of high-performance photocatalysts is a major bottleneck. Halide perovskites, a category of diversified semiconductor materials with suitable energy-band-enabled high-light-utilization efficiencies, exceptionally long charge-carrier-diffusion-length-facilitated charge transport, and readily tailorable compositional, structural, and morphological properties, have emerged as a new class of photocatalysts for efficient hydrogen evolution, CO₂ reduction, and various organic synthesis reactions. Despite the noticeable progress, the development of high-performance halide perovskite photocatalysts (HPPs) is still hindered by several key challenges: the strong ionic nature and high hydrolysis tendency induce instability and an unsatisfactory activity due to the need for a coactive component to realize redox processes. Herein, the recently developed advanced strategies to enhance the stability and photocatalytic activity of HPPs are comprehensively reviewed. The widely applicable stability enhancement strategies are first articulated, and the activity improvement strategies for fuel production and chemical synthesis are then explored. Finally, the challenges and future perspectives associated with the application of HPPs in efficient production of fuels and value-added chemicals are presented, indicating the irreplaceable role of the HPPs in the field of photocatalysis.

A Simple-Structured Perovskite Wavelength Sensor for Full-Color Imaging Application

In this study, simple-structured wavelength sensors were developed by depositing two back-to-back Au/MAPbI₃/Au photodetectors on an MAPbI₃ single crystal. This sensor could quantitatively distinguish wavelengths. Further device analysis showed that both photodetectors possess entirely disparate optoelectronic properties. Consequently, the as-developed wavelength sensor could accurately distinguish incident-light wavelengths ranging from 265 to 860 nm with a resolution of less than 1.5 nm based on the relation between the photocurrent ratios of both photodetectors and the incident light wavelengths. Notably, a high resolution and wide detection range are among the optimum reported values for such sensors and enable full-color imaging. Furthermore, technology computer-aided design (TCAD) simulations showed that a mechanism involved in distinguishing wavelengths is attributed to the wavelength-dependent photon generation rate in MAPbI₃ single crystals. The high-performance MAPbI₃ wavelength sensor can potentially drive the research progress of perovskites in wavelength recognition and full-color imaging.

Synthetic approaches for perovskite thin films and single-crystals

Halide perovskites are compelling candidates for the next generation of photovoltaic technologies owing to an unprecedented increase in power conversion efficiency and their low cost, facile fabrication and outstanding semiconductor properties.

Tunable Multiband Halide Perovskite Tandem Photodetectors with Switchable Response

Photodetectors with multiple spectral response bands have shown promise to improve imaging and communications through the switchable detection of different photon energies. However, demonstrations to date have been limited to only two bands and lack capability for fast switching in situ. Here, we exploit the band gap tunability and capability of all-perovskite tandem solar cells to demonstrate a new device concept realizing four spectral bands of response from a single multijunction device, with fast, optically controlled switching between the bands. The response to monochromatic light is highly selective and narrowband without the need for additional filters and switches to broader response bands on applying bias light. Sensitive photodetection above 6 × 10¹¹ Jones is demonstrated in all modes, with rapid switching response times of <250 ns. We demonstrate proof of principle on how the manipulation of the modular multiband detector response through light conditions enables diverse applications in optical communications with secure encryption.

Organic-Inorganic Lead Halide Perovskite Single Crystal: From Synthesis to Applications

Organic-inorganic lead halide perovskite is widely used in the photoelectric field due to its excellent photoelectric characteristics. Among them, perovskite single crystals have attracted much attention due to its lower trap density and better carrier transport capacity than their corresponding polycrystalline materials. Owing to these characteristics, perovskite single crystals have been widely used in solar cells, photodetectors, light-emitting diode (LED), and so on, which have greater potential than polycrystals in a series of optoelectronic applications. However, the fabrication of single-crystal devices is limited by size, thickness, and interface problems, which makes the development of single-crystal devices inferior to polycrystalline devices, which also limits their future development. Here, several representative optoelectronic applications of perovskite single crystals are introduced, and some existing problems and challenges are discussed. Finally, we outlook the growth mechanism of single crystals and further the prospects of perovskite single crystals in the further field of microelectronics.

Epitaxial Perovskite Single-Crystalline Heterojunctions for Filter-Free Ultra-Narrowband Detection with Tunable Spectral Responses

Narrowband photodetectors (NPDs) with the capability of detecting light within a selective wavelength range are in high demand for numerous emerging applications such as imaging systems, machine vision, and optical communication. Halide perovskite materials have been developed for eliminating the current complex filtering systems in NPDs due to their beneficial properties, while currently NPDs using perovskite materials are limited by hardly fully eliminated short wavelength response, low charge collection efficiency (CCE), complex fabrication process, and so forth. Herein, a series of perovskite single-crystalline heterojunctions (PSCHs) with a structure of Bi-MAPbX3/MAPbY3 are fabricated by liquid phase epitaxy for filter-free narrowband detection. By varying the halide component in the PSCH, the PSCH-based NPDs can realize continuously tunable spectral response range from blue to NIR regions and ultra-narrow full width at half-maximum (FWHM) of <20 nm. Specifically, the PSCH-based NPD with a high CCE under a large electric filed shows a high spectra rejection ratio of >1000, a fast response speed with rise/fall time of ∼160/∼225 μs, and long-term stability more than 3 months in ambient air. This work provides a simple strategy for designing low-cost and high-performance filter-free NPDs with a tunable spectral response.

Role of Moisture and Oxygen in Defect Management and Orderly Oxidation Boosting Carbon-Based CsPbI2 Br Solar Cells to a New Record Efficiency

Large energy loss (E_loss ) caused by defect-assisted recombination makes the photovoltaic performance of carbon-based perovskite solar cells (C-PSCs) inferior to that of metal-electrode ones. Herein, the influence of environmental factors (moisture and oxygen) on defect management during re-annealing process of CsPbI₂ Br crystalline films is systematically studied. Density functional theory and experimental results indicate that moisture in the air can significantly reduce the oxidation kinetics of crystalline films, resulting in orderly oxidation. Concomitantly, the oxidation decomposition products PbO and CsPbIBr₂ are enriched at grain boundaries, passivating surface defects efficiently. Simultaneously, energy band coupling between CsPbI₂ Br and CsPbIBr₂ improves the hole extraction efficiency. The photovoltage of corresponding C-PSCs is increased from 1.05 to 1.32 V, indicating a reduced E_loss derived from orderly oxidation strategy. Correspondingly, the champion cell achieves an efficiency of 15.27%, and a certified efficiency of 14.7%, which is a new record efficiency for CsPbI₂ Br C-PSCs.

Surface-Passivated Single-Crystal Micro-Plates for Efficient Perovskite Solar Cells

Perovskite solar cells (PeSCs) prepared with single crystals (SCs) ideally exhibit higher power conversion efficiencies (PCEs) because they possess a lower density of structural imperfection and superior charge transport. However, the density of the surface defects on the SCs is still very high, thereby inevitably affecting the device performance. Herein, perovskite single-crystal micro-plates were grown on a hole-transporting material, poly[bis(4-phenyl)(2,4,6-trimethylphenyl) amine], through a space-limited inverse temperature crystallization method. The surfaces of the as-prepared SCs were passivated using trioctylphosphine oxide (TOPO) during the device fabrication to alleviate the impact of surface defects. The PCE values are averagely improved from 11.90 ± 0.30% to 14.76 ± 0.65% after the surface passivation; the champion device even exhibits a PCE of 15.65%. The results from photoluminescence and hole-only devices reveal that TOPO treatments effectively reduce the number of surface defects on the single crystals, thereby improving the photovoltaic performance. The surface passivation also inhibits the hysteresis behavior due to the lower defect density. Finally, the TOPO treatment also improves the stability of the single-crystal PeSCs, presumably due to the hydrophobic long alkyl chains. Thus, this work provides an effective approach to achieving high efficiencies of single-crystal PeSCs.

Halide perovskite single crystals: growth, characterization, and stability for optoelectronic applications

Recently, metal halide perovskite materials have received significant attention as promising candidates for optoelectronic applications with tremendous achievements, owing to their outstanding optoelectronic properties and facile solution-processed fabrication. However, the existence of a large number of grain boundaries in perovskite polycrystalline thin films causes ion migration, surface defects, and instability, which are detrimental to device applications. Compared with their polycrystalline counterparts, perovskite single crystals have been explored to realize stable and excellent properties such as a long diffusion length and low trap density. The development of growth techniques and physicochemical characterizations led to the widespread implementation of perovskite single-crystal structures in optoelectronic applications. In this review, recent progress in the growth techniques of perovskite single crystals, including advanced crystallization methods, is summarized. Additionally, their optoelectronic characterizations are elucidated along with a detailed analysis of their optical properties, carrier transport mechanisms, defect densities, surface morphologies, and stability issues. Furthermore, the promising applications of perovskite single crystals in solar cells, photodetectors, light-emitting diodes, lasers, and flexible devices are discussed. The development of suitable growth and characterization techniques contributes to the fundamental investigation of these materials and aids in the construction of highly efficient optoelectronic devices based on halide perovskite single crystals.

Spray-Coating Thick Films of All-Inorganic Halide Perovskites for Filterless Narrowband Photodetectors

A significant challenge facing perovskite narrowband photodetectors is making high-quality and thick enough films. Here, we report a facile one-step spray-coating approach to deposit cesium lead halide perovskite thick films for filterless narrowband photodetectors, which exhibited a specific detectivity of 2.43 × 10¹⁰ Jones at 655 nm with an fwhm of 25 nm. We demonstrated that both substrate temperature and deposition time during the spray-coating process are key factors that govern the thickness and morphology of perovskite films. The photodetection behavior was dependent on the film thickness, and the narrowband photoresponse was recorded at a 3.9 μm thickness. We discovered that the internal electric field also plays a critical role in determining the narrowband photoresponse behavior. A distinct photoresponse behavior was observed when respectively applying a reverse bias and a forward bias, which is ascribed to the trade-off between the charge-trapping effect and charge extraction under the internal built-in electric field in different biased conditions. Through changing the halogen composition of perovskites from CsPbCl₂Br to CsPbI₂Br, the peak position of the narrowband spectral photoresponse was observed to shift from 460 to 660 nm. This study not only offers a controllable spray-coating approach to develop thick perovskite films but also provides an important guidance for the rational design of filterless narrowband photodetectors for practical applications in industrial control, visual imaging, and biological sensing.

Electrode Spacing as a Determinant of the Output Performance of Planar-Type Photodetectors Based on Methylammonium Lead Bromide Perovskite Single Crystals

Methylammonium lead bromide is a very perspective hybrid semiconductor material, suitable for high-sensitive, filter-free photodetection of electromagnetic radiation. Herein, we studied the effect of electrode spacing on the output performance and stability of planar-type photodetectors based on high-quality MAPbBr₃ single crystals. Such crystals, as large as 4.5×4.5×1.2 mm³ were synthesized via the inverse temperature crystallization method and were further used for the fabrication of planar Au/MAPbBr₃/Au photodetectors with variable electrode spacing (in the range between 125 and 25 μm). We report that the electrode spacing has a profound impact on photocurrent densities and key detector parameters (responsivity R, external quantum efficiency EQE, and specific detectivity D*). In the studied fivefold electrode spacing, the photocurrent density increased over 4 times, with decreasing active area of the devices. This effect is attributed to intrinsic photocurrent amplification. Based on the transient photocurrent measurements and calculated key parameters, we determined the device sample with the best output performance. The champion sample with an electrode spacing of 50 μm exhibited great detection ability, especially for a low light intensity of 200 nWcm^-2, for which we calculated the R of 19.55 A W^-1, EQE of 4253%, and D* of 3.42 × 10¹² Jones (cm Hz^1/2 W^-1). Moreover, the functional stability of this device showed a minimal reduction of photodetection ability after 2000 cycles, which makes it very promising for the next generation of optoelectronic devices.

High-Luminance Microsized CH3NH3PbBr3 Single-Crystal-Based Light-Emitting Diodes via a Facile Liquid-Insulator Bridging Route

Micro-/nanosized organic-inorganic hybrid perovskite single crystals (SCs) with appropriate thickness and high crystallinity are promising candidates for high-performance electroluminescent (EL) devices. However, their small lateral size poses a great challenge for efficient device construction and performance optimization, causing perovskite SC-based light-emitting diodes (PSC-LEDs) to demonstrate poor EL performance. Here, we develop a facile liquid-insulator bridging (LIB) strategy to fabricate high-luminance PSC-LEDs based on single-crystalline CH₃NH₃PbBr₃ microflakes. By introducing a blade-coated poly(methyl methacrylate) (PMMA) insulating layer to effectively overcome the problems of leakage current and possible short circuits between electrodes, we achieve the reliable fabrication of PSC-LEDs. The LIB method also allows us to systematically boost the device performance through crystal growth regulation and device architecture optimization. Consequently, we realize the best CH₃NH₃PbBr₃ microflake-based PSC-LED with an ultrahigh luminance of 136100 cd m^-2 and a half-lifetime of 88.2 min at an initial luminance of ∼1100 cd m^-2, which is among the highest for organic-inorganic hybrid perovskite LEDs reported to date. Moreover, we observe the strong polarized edge emission of the microflake-based PSC-LEDs with a high degree of polarization up to 0.69. Our work offers a viable approach for the development of high-performance perovskite SC-based EL devices.

Color-tunable persistent luminescence in 1D zinc–organic halide microcrystals for single-component white light and temperature-gating optical waveguides

Information security of photonic communications has become an important societal issue and can be greatly improved when photonic signals are propagated through active waveguides with tunable wavelengths in different time and space domains. Moreover, the development of active waveguides that can work efficiently at extreme temperatures is highly desirable but remains a challenge. Herein, we report new types of low-dimensional Zn(ii)–organic halide microcrystals with fluorescence and room-temperature phosphorescence (RTP) dual emission for use as 1D color-tunable active waveguides. Benefiting from strong intermolecular interactions (i.e., hydrogen bonds and π–π interactions), these robust waveguide systems exhibit colorful photonic signals and structural stability at a wide range of extreme simulated temperatures (>300 K), that covers natural conditions on Earth, Mars, and the Moon. Both experimental and theoretical studies demonstrate that the molecular self-assembly can regulate the singlet and triplet excitons to allow thermally assisted spectral separation of fluorescence and RTP, in combination with the single-component standard white-light emission. Therefore, this work demonstrates the first use of metal–organic halide microcrystals as temperature-gating active waveguides with promising implications for high-security information communications and high-resolution micro/nanophotonics.

1D zinc–organic halide microcrystals exhibiting thermally assisted spectral separation of fluorescence and phosphorescence could be used as single-component standard white-light and temperature-gating active waveguides.

Monocrystalline Methylammonium Lead Halide Perovskite Materials for Photovoltaics

Lead halide perovskite solar cells have been gaining more and more interest. In only a decade, huge research efforts from interdisciplinary communities enabled enormous scientific advances that rapidly led to energy conversion efficiency near that of record silicon solar cells, at an unprecedented pace. However, while for most materials the best solar cells were achieved with single crystals (SC), for perovskite the best cells have been so far achieved with polycrystalline (PC) thin films, despite the optoelectronic properties of perovskite SC are undoubtedly superior. Here, by taking as example monocrystalline methylammonium lead halide, the authors elaborate the literature from material synthesis and characterization to device fabrication and testing, to provide with plausible explanations for the relatively low efficiency, despite the superior optoelectronics performance. In particular, the authors focus on how solar cell performance is affected by anisotropy, crystal orientation, surface termination, interfaces, and device architecture. It is argued that, to unleash the full potential of monocrystalline perovskite, a holistic approach is needed in the design of next-generation device architecture. This would unquestionably lead to power conversion efficiency higher than those of PC perovskites and silicon solar cells, with tremendous impact on the swift deployment of renewable energy on a large scale.

Biphasic Liquid-Liquid Interface Limit Architecture of High-Quality Perovskite Single-Crystal Sheets for UV Photodetection

Thin organic-inorganic MAPbX₃ perovskite single-crystal sheets have become the hotspot of smart photodetectors because of their low number of trap states, high carrier mobility, long diffusion length, and effective light-receiving area. However, MAPbX₃ single crystals are so fragile that single-crystal perovskite sheets with a thickness of ≤100 μm are hard to obtain by cutting. Thin single-crystal MAPbX₃ sheets were synthesized by the biphasic liquid-liquid interface limit method with dimethicone/DMSO biphasic films and could be obtained with an adjustable thickness of 1-50 μm and improved crystal quality of the perovskite sheets. The thin MAPbX₃ single-crystal sheet-based photodetector exhibits a superior responsivity of 0.88 A W^-1, an external quantum efficiency of 276.8%, and an ultrahigh detectivity of 2.26 × 10¹¹ Jones under 395 nm irradiation at 3 V. These values are more than 500% as high as those of the bulk-crystal-based photodetector. In particular, the sheet-based photodetector could retain long-time stability after 4200 on-off cycles.

Halide perovskites scintillators: unique promise and current limitations

The widespread use of X- and gamma-rays in a range of sectors including healthcare, security and industrial screening is underpinned by the efficient detection of the ionising radiation. Such detector applications are dominated by indirect detectors in which a scintillating material is combined with a photodetector. Halide perovskites have recently emerged as an interesting class of semiconductors, showing enormous promise in optoelectronic applications including solar cells, light-emitting diodes and photodetectors. Here, we discuss how the same superior semiconducting properties that have catalysed their rapid development in these optoelectronic devices, including high photon attenuation and fast and efficient emission properties, also make them promising scintillator materials. By outlining the key mechanisms of their operation as scintillators, we show why reports of remarkable performance have already emerged, and describe how further learning from other optoelectronic devices will propel forward their applications as scintillators. Finally, we outline where these materials can make the greatest impact in detector applications by maximally exploiting their unique properties, leading to dramatic improvements in existing detection systems or introducing entirely new functionality.

Indium-antimony-halide single crystals for high-efficiency white-light emission and anti-counterfeiting

Although single-source white emissive perovskite has emerged as a class of encouraging light-emitting material, the synthesis of lead-free halide perovskite materials with high luminous efficiency is still challenging. Here, we report a series of zero-dimensional indium-antimony (In/Sb) alloyed halide single crystals, BAPPIn_2-2x Sb_2x Cl₁₀ (BAPP = C₁₀H₂₈N₄, x = 0 to 1), with tunable emission. In BAPPIn_1.996Sb_0.004Cl₁₀, bright yellow emission with near 100% photoluminescence quantum yield (PLQY) is yielded when it was excited at 320 nm, which turns into bright white-light emission with a PLQY of 44.0% when excited at 365 nm. Combined spectroscopy and theoretical studies reveal that the BAPP⁴⁺-associated blue emission and inorganic polyhedron-afforded orange emission function as a perfect pair of complementary colors affording white light in BAPPIn_1.996Sb_0.004Cl₁₀ Moreover, the interesting afterglow behavior, together with excitation-dependent emission property, makes BAPPIn_2-2x Sb_2x Cl₁₀ as high-performance anti-counterfeiting/information storage materials.

High-Responsivity, Fast, and Self-Powered Narrowband Perovskite Heterojunction Photodetectors with a Tunable Response Range in the Visible and Near-Infrared Region

In recent years, narrowband photodetectors (PDs) have been widely used in color imaging, spectral detection or discrimination, defense, and scientific research due to their special spectral selective responses. In this work, by combining organic-inorganic hybrid perovskite layers of different band gaps and thicknesses, a series of narrowband perovskite heterojunction PDs with a continuously adjustable spectral range in the visible and near-infrared range are designed and prepared. The PDs can achieve a narrowband photoresponse with a full width at half-maximum (FWHM) of less than 50 nm and a light rejection ratio (between 780 and 532 nm) of over 1100 and exhibit excellent photoresponse performances with an external quantum efficiency (EQE), responsivity (R), and detectivity (D*) as high as 50.3%, 0.331 A/W, and 4.27 × 10¹⁰ Jones, respectively. More importantly, the photoresponses of the PDs at zero bias are as good as those at the reverse bias voltages, indicating the outstanding self-powered property. In addition, a fast response time of ∼180/∼200 μs is obtained in the narrowband perovskite heterojunction, and the response speed nearly remains constant for different PDs in the whole tunable wavelength range, demonstrating the suitable and stable structure of the heterojunction, as well as the high crystalline quality of the perovskite layers. This work definitely provides a simple strategy for designing low-cost, high-photoresponsivity, fast speed, and self-powered narrowband PDs with a tunable spectral range.

Oriented Halide Perovskite Nanostructures and Thin Films for Optoelectronics

Oriented semiconductor nanostructures and thin films exhibit many advantageous properties, such as directional exciton transport, efficient charge transfer and separation, and optical anisotropy, and hence these nanostructures are highly promising for use in optoelectronics and photonics. The controlled growth of these structures can facilitate device integration to improve optoelectronic performance and benefit in-depth fundamental studies of the physical properties of these materials. Halide perovskites have emerged as a new family of promising and cost-effective semiconductor materials for next-generation high-power conversion efficiency photovoltaics and for versatile high-performance optoelectronics, such as light-emitting diodes, lasers, photodetectors, and high-energy radiation imaging and detectors. In this Review, we summarize the advances in the fabrication of halide perovskite nanostructures and thin films with controlled dimensionality and crystallographic orientation, along with their applications and performance characteristics in optoelectronics. We examine the growth methods, mechanisms, and fabrication strategies for several technologically relevant structures, including nanowires, nanoplates, nanostructure arrays, single-crystal thin films, and highly oriented thin films. We highlight and discuss the advantageous photophysical properties and remarkable performance characteristics of oriented nanostructures and thin films for optoelectronics. Finally, we survey the remaining challenges and provide a perspective regarding the opportunities for further progress in this field.

Controllable, Self-Powered, and High-Performance Short-Wavelength Infrared Photodetector Driven by Coupled Flexoelectricity and Strain Effect

Mechanical deformation-induced strain gradients and coupled spontaneous electric polarization field in centrosymmetric materials, known as the flexoelectric effect, can generate ubiquitous mechanoelectrical functionalities, like the flexo-photovoltaic effect. Concurrently, nano/micrometer-scale inhomogeneous strain reengineers the electronic arrangements and in turn, could alter the fundamental limits of optoelectronic performance. Here, the flexoelectric effect-driven self-powered giant short-wavelength infrared (λ ≤ 1800 nm) photoresponse from centrosymmetric bulk silicon, indeed far beyond the fundamental bandgap (λ = 1100 nm) is demonstrated. Particularly, large on/off ratio (≈10⁵ ), extremely high sensitivity (2.5 × 10⁸ %), good responsivity of 96 mA W^-1 , decent specific detectivity of ≈1.54 × 10¹⁴ Jones, and a rapid response speed of ≈100 µs, even at nanoscale (<30 nm), are measured at λ = 1620 nm. The infrared response sensitivity is tuned in a wide range (up to 1.4 × 10⁸ %) by controlling the applied pointed force from 1 to 10 µN. These results confirm that emerging mechanoelectrical coupling not only sheds to achieve tunable optoelectronic performance beyond the fundamental limit, but also offers innovative numerous applications like mechanoptical switch, photovoltaic, sensors, and self-driving vehicles.

Prospects of Z-Scheme Photocatalytic Systems Based on Metal Halide Perovskites

Considering the attractive optoelectronic properties of metal halide perovskites (MHPs), their introduction to the field of photocatalysis was only a matter of time. Thus far, MHPs have been explored for the photocatalytic generation of hydrogen, carbon dioxide reduction, organic synthesis, and pollutant degradation applications. Of growing research interest and possible applied significance are the currently emerging developments of MHP-based Z-scheme heterostructures, which can potentially enable efficient photocatalysis of highly energy-demanding redox processes. In this Perspective, we discuss the advantages and limitations of MHPs compared to traditional semiconductor materials for applications as photocatalysts and describe emerging examples in the construction of MHP-based Z-scheme systems. We discuss the principles and material properties that are required for the development of such Z-scheme heterostructure photocatalysts and consider the ongoing challenges and opportunities in this emerging field.

High speed growth of MAPbBr3 single crystals via low-temperature inverting solubility: enhancement of mobility and trap density for photodetector applications

There has been growing interest in organic-inorganic hybrid perovskites as a promising candidate for optoelectronic applications due to their superior physical properties. Despite this, most of the reported perovskite devices based on polycrystalline thin films suffer immensely from poor stability and high trap density owing to grain boundaries limiting their performance. Perovskite single crystal structures have been recently explored to construct stable devices and reduce the trap density compared to their thin-film counterparts. We present a novel method of growing sizable CH₃NH₃PbBr₃ single crystals based on the high solubility characteristic of hybrid perovskites at low temperatures within inverse temperature crystallization. We compared both the crystallinity of perovskite single crystal structures and optoelectronic charge transport of single crystal photodetectors as a function of dissolution temperature. The performance of the photodetector fabricated with our large-scaled single crystal with high quality demonstrated low trap density, high mobility, and high photoresponse.

Recent Advances in Perovskite Photodetectors for Image Sensing

In recent years, metal halide perovskites have been widely investigated to fabricate photodetectors for image sensing due to the excellent photoelectric performance, tunable bandgap, and low-cost solution preparation process. In this review, a comprehensive overview of the recent advances in perovskite photodetectors for image sensing is provided. First, the key performance parameters and the basic device types of photodetectors are briefly introduced. Then, the recent developments of image sensors on the basis of different dimensional perovskite materials, including 0D, 1D, 2D, and 3D perovskite materials, are highlighted. Besides the device structures and photoelectric properties of perovskite image sensors, the preparation methods of perovskite photodetector arrays are also analyzed. Subsequently, the single-pixel imaging of perovskite photodetectors and the strategies to fabricate narrowband perovskite photodetectors for color discrimination are discussed. Finally, the potential challenges and possible solutions for the future development of perovskite image sensors are presented.

High-Performance and Self-Powered Alternating Current Ultraviolet Photodetector for Digital Communication

Self-powered ultraviolet photodetectors offer great potential in the field of optical communication, smart security, space exploration, and others; however, achieving high sensitivity with maintaining fast response speed has remained a daunting challenge. Here, we develop a titanium dioxide-based self-powered ultraviolet photodetector with high detectivity (≈1.8 × 10¹⁰ jones) and a good photoresponsivity of 0.32 mA W^-1 under pulsed illumination (λ = 365 nm, 4 mW cm^-2), which demonstrate an enhancement of 114 and 2017%, respectively, due to the alternating current photovoltaic effect compared to the conventional direct current photovoltaic effect. Further, the photodetector demonstrated a high on/off ratio (≈10³), an ultrafast rise/decay time of 112/63 μs, and a noise equivalent power of 5.01 × 10^-11 W/Hz^1/2 under self-biased conditions. Photoconductive atomic force microscopy revealed the nanoscale charge transport and offered the possibility to scale down the device size to a sub-10-nanometer (∼35 nm). Moreover, as one of the practical applications, the device was successfully utilized to interpret the digital codes. The presented results enlighten a new path to design energy-efficient ultrafast photodetectors not only for the application of optical communication but also for other advanced optoelectronic applications such as digital display, sensing, and others.

Revealing Charge Carrier Mobility and Defect Densities in Metal Halide Perovskites via Space-Charge-Limited Current Measurements

Space-charge-limited current (SCLC) measurements have been widely used to study the charge carrier mobility and trap density in semiconductors. However, their applicability to metal halide perovskites is not straightforward, due to the mixed ionic and electronic nature of these materials. Here, we discuss the pitfalls of SCLC for perovskite semiconductors, and especially the effect of mobile ions. We show, using drift-diffusion (DD) simulations, that the ions strongly affect the measurement and that the usual analysis and interpretation of SCLC need to be refined. We highlight that the trap density and mobility cannot be directly quantified using classical methods. We discuss the advantages of pulsed SCLC for obtaining reliable data with minimal influence of the ionic motion. We then show that fitting the pulsed SCLC with DD modeling is a reliable method for extracting mobility, trap, and ion densities simultaneously. As a proof of concept, we obtain a trap density of 1.3 × 10¹³ cm^-3, an ion density of 1.1 × 10¹³ cm^-3, and a mobility of 13 cm² V^-1 s^-1 for a MAPbBr₃ single crystal.

Surface passivated halide perovskite single-crystal for efficient photoelectrochemical synthesis of dimethoxydihydrofuran

Halide perovskite single-crystals have recently been widely highlighted to possess high light harvesting capability and superior charge transport behaviour, which further enable their attractive performance in photovoltaics. However, their application in photoelectrochemical cells has not yet been reported. Here, a methylammonium lead bromide MAPbBr₃ single-crystal thin film is reported as a photoanode with potential application in photoelectrochemical organic synthesis, 2,5-dimethoxy-2,5-dihydrofuran. Depositing an ultrathin Al₂O₃ layer is found to effectively passivate perovskite surface defects. Thus, the nearly 5-fold increase in photoelectrochemical performance with the saturated current being increased from 1.2 to 5.5 mA cm⁻² is mainly attributed to suppressed trap-assisted recombination for MAPbBr₃ single-crystal thin film/Al₂O₃. In addition, Ti³⁺-species-rich titanium deposition has been introduced not only as a protective film but also as a catalytic layer to further advance performance and stability. As an encouraging result, the photoelectrochemical performance and stability of MAPbBr₃ single-crystal thin film/Al₂O₃/Ti-based photoanode have been significantly improved for 6 h continuous dimethoxydihydrofuran evolution test with a high Faraday efficiency of 93%.

Perovskite single-crystal thin films inherit the advantages of low trap-states, well-defined thickness and remarkable stability. Now, researchers successfully employed MAPbBr₃ single-crystal thin film as photoanode in the photoelectrochemical production of organic 2,5-dimethoxy-2,5-dihydrofuran.

Dielectric confinement for designing compositions and optoelectronic properties of 2D layered hybrid perovskites

Two dimensional (2D) layered hybrid lead halide perovskites are a fascinating class of semiconductors displaying a plethora of interesting optoelectronic properties with potential for application in solar cells, light emitting diodes, etc. Most of these properties can be linked to their repeating quantum well-like structures providing 2D excitons. In this perspective, we discuss how dielectric confinement of excitons originates in these layered hybrid perovskites, and then, how it can be used to tune the excitonic properties. In particular, we discuss the recent theoretical and experimental advances correlating dielectric confinement with chemical composition, excitonic binding energy, and optoelectronic property. The freedom from the restrictions of the Goldsmith tolerance factor allows the synthesis of hundreds of compositions of 2D layered hybrid perovskites by independently varying the organic and inorganic layers. We envisage that the combination of this compositional flexibility with the concepts of dielectric confinement discussed in this perspective would be a path forward for designing novel optoelectronic materials.

Room-temperature synthesis, growth mechanisms and opto-electronic properties of organic–inorganic halide perovskite CH3NH3PbX3 (X = I, Br, and Cl) single crystals

Growth of MAPbX₃ (X = I, Br, and Cl) single crystals by room temperature crystallization (RTC) method, and the crystallization pathway illustrated by the solubility curve of MAPbCl₃ in DMSO, compared with inverse temperature crystallization (ITC) method.

Self-Driven Perovskite Narrowband Photodetectors with Tunable Spectral Responses

Narrowband photodetectors with tunable spectral responses are highly desirable for applications in image sensing, machine vision, and optical communication. Herein, a filterless and self-driven perovskite narrowband photodetector (PNPD) based on the defect-assisted charge collection narrowing (CCN) mechanism is reported, which is enabled by a high-quality thick perovskite film. By adjusting the halide component of the perovskite layer, the bandgap is successfully modulated and the corresponding narrowband photodetectors show a wide spectral response range from the red to the near-infrared (NIR), all with full-widths at half maximum (FWHMs) below 30 nm. Specifically, the methylammonium lead iodide (MAPbI₃ ) narrowband photodetector exhibits a characteristic detection peak at 800 nm with a very low noise current of ≈0.02 pA Hz^-1/2 , a high specific detectivity up to 1.27 × 10¹² Jones, and a fast response speed with rise/fall time of 12.7/6.9 µs. Impressively, these values are among the highest of their kind reported previously, and allow demonstration of narrowband imaging. The excellent performance of self-driven PNPDs lights up their prospect in high-efficiency optoelectronic devices without external power sources.

Emerging Light-Emitting Materials for Photonic Integration

The arrival of the information explosion era is urging the development of large-bandwidth high-data-rate optical interconnection technology. Up to now, the biggest stumbling block in optical interconnections has been the lack of efficient light sources despite significant progress that has been made in germanium-on-silicon (Ge-on-Si) and III-V-on-silicon (III-V-on-Si) lasers. 2D materials and metal halide perovskites have attracted much attention in recent years, and exhibit distinctive advantages in the application of on-chip light emitters. Herein, this Progress Report reviews the recent progress made in light-emitting materials with a focus on new materials, i.e., 2D materials and metal halide perovskites. The report briefly introduces the current status of Ge-on-Si and III-V-on-Si lasers and discusses the advances of 2D and perovskite light-emitting materials for photonic integration, including their optical properties, preparation methods, as well as the light sources based on these materials. Finally, challenges and perspectives of these emerging materials on the way to the efficient light sources are discussed.

Halide Perovskite Single Crystals: Optoelectronic Applications and Strategical Approaches

Halide perovskite is one of the most promising semiconducting materials in a variety of fields such as solar cells, photodetectors, and light-emitting diodes. Lead halide perovskite single crystals featuring long diffusion length, high carrier mobility, large light absorption coefficient and low defect density, have been attracting increasing attention. Fundamental study of the intrinsic nature keeps revealing the superior optoelectrical properties of perovskite single crystals over their polycrystalline thin film counterparts, but to date, the device performance lags behind. The best power conversion efficiency (PCE) of single crystal-based solar cells is 21.9%, falling behind that of polycrystalline thin film solar cells (25.2%). The oversized thickness, defective surfaces, and difficulties in depositing functional layers, hinder the application of halide perovskite single crystals in optoelectronic devices. Efforts have been made to synthesize large-area single crystalline thin films directly on conductive substrates and apply defect engineering approaches to improve the surface properties. This review starts from a comprehensive introduction of the optoelectrical properties of perovskite single crystals. Then, the synthesis methods for high-quality bulk crystals and single-crystalline thin films are introduced and compared, followed by a systematic review of their optoelectronic applications including solar cells, photodetectors, and X-ray detectors. The challenges and strategical approaches for high-performance applications are summarized at the end with a brief outlook on future work.