Recent Progress on Synthesis,Intrinsic Properties and Optoelectronic Applications of Perovskite Single Crystals

Metal halide perovskite have shown great potential for applications in photovoltaics, light-emitting diodes and photon detectors, mainly owing to their superb optoelectronic properties, low-cost raw materials and facile fabrication process. Although, polycrystalline perovskite thin-films have been actively investigated for preparing various optoelectronic devices, the presence of detrimental defects at grain boundaries, serious ion migration and limited stability unfortunately hinder their device performance and practical application. As a contrast, perovskite single crystals (SCs) exhibit no grain boundaries, much lower trap density and much improved stability, hence providing a more attractive choice for not only optoelectronic device applications but also fundamental research. In this review, recent progress in the growth methods of perovskite SCs is summarized, followed by giving a detailed introduction of the intrinsic properties of perovskite SCs including optical properties, defects, charge carrier dynamics, ion migration and stability. On these base, the applications of perovskite SCs in various optoelectronic devices like solar cells, photodetectors, and radiation detectors are discussed, where the relationship between the composition, device architecture and device performance is highlighted. Finally, a tentative discussion on the current challenges and future opportunities in the development of perovskite SCs and optoelectronic devices is presented.     

Perovskite Single Crystals: Synthesis,Properties, and Applications

Perovskite single crystals have gained enormous attention in recent years due to their facile synthesis and excellent optoelectronic properties including the long carrier diffusion length, high carrier mobility, low trap density, and tunable absorption edge ranging from ultra-violet (UV) to near-infrared (NIR), which offer potential for applications in solar cells, photodetectors (PDs), lasers, etc. In this review, we summarized the synthesis, properties, and applications of organic-inorganic mixed and all-inorganic perovskite single crystals, particularly those through the solution synthesis approach. Challenges towards the crystal growth and stability with future perspectives were also briefly described at the end of this paper.     

Metal Halide Perovskite Arrays: From Construction to Optoelectronic Applications

Inorganic semiconductor arrays revolutionize many areas of electronics, optoelectronics with the properties of multifunctionality and large-scale integration. Metal halide perovskites are emerging as candidates for next-generation optoelectronic devices due to their excellent optoelectronic properties, ease of processing, and compatibility with flexible substrates. To date, a series of patterning technologies have been applied to perovskites to realize array configurations and nano/microstructured surfaces to further improve device performances. Herein, various construction methods for perovskite crystal or thin film arrays are summarized. The optoelectronic applications of the perovskite arrays are also discussed, in particular, for photodetectors, light-emitting diodes, lasers, and nanogratings.     

Reversible Transformation between CsPbBr3 Perovskite Nanowires and Nanorods with Polarized Optoelectronic Properties

CsPbX₃ (X = Cl, Br, I) perovskite nanowires and nanorods are important 1D and quasi 1D semiconductor nanomaterials. They have shown significant prospect in optic and optoelectronic applications, especially for their adaptability to flexible devices, good carrier transport performance, polarized absorption, and emission properties. Due to the high dependence of the property to the morphology, it is crucial to develop synthesis methods with continuous diameter and length tunability of the 1D/quasi 1D perovskites. In this report, a feasibly room temperature synthesis method was developed for ultrathin CsPbX₃(X = Cl, Br, I) perovskite nanowires. By aging the CsPbBr₃ nanowires (≈2*500 nm) under ambient condition with proper concentration and time, the nanowires are transformed to nanorods with controllable diameter and length. Reversibly, the nanorods can be transformed back to nanowires. Equilibrium mechanism is adopted to understand the morphology evolution, and hopefully could be generally applied to many other nano materials. The polarized optoelectronic properties of the nanowires and nanorods are interpreted by a model based on the two-channel anisotropies measurement. Polarized light detectors constructed by oriented assembled nanowires are fabricated to demonstrate their application potentials.     

Direct Growth of Pyramid‐Textured Perovskite Single Crystals: A New Strategy for Enhanced Optoelectronic Performance

Even though there have been a few reports of substrate surface texturing of thin film perovskite solar cells to enhance their light trapping, there has been no direct texturing of the perovskite material, let alone perovskite single crystals (SCs). Herein, a method to prepare a pyramid‐structured perovskite CH₃NH₃PbX₃ (CH₃NH₃⁺ = MA, X = I, Br) SC surface with minimized light reflection and maximized incident light harvesting is reported. Specifically, a hard template is used to directly transfer the pyramidal texture onto the MAPbX₃ SC during its growth. A well‐shaped pyramidal texture is formed on the single‐crystal surface leading to improved light trapping. The textured MAPbBr₃ SC shows good crystallinity, prolonged carrier lifetime, and improved carrier mobility. Furthermore, the photodetector made from the textured SC shows enhanced responsivity of 321 A W^?1 and external quantum efficiency of 7191%, about two times higher than that of a control device. This method may be used to directly fabricate desired textures on general single crystal surfaces.     

Graphene‐Based Nanomaterials: Synthesis,Properties, and Optical and Optoelectronic Applications

Graphene, a two‐dimensional, single‐atom‐thick carbon crystal arranged in a honeycomb lattice, shows extraordinary electronic, mechanical, thermal, optical, and optoelectronic properties, and has great potential in next‐generation electronics, optics, and optoelectronics. Graphene and graphene‐based nanomaterials have witnessed a very fast development of both fundamental and practical aspects in optics and optoelectronics since 2008. In this Feature Article, the synthesis techniques and main electronic and optical properties of graphene‐based nanomaterials are introduced with a comprehensive view. Recent progress of graphene‐based nanomaterials in optical and optoelectronic applications is then reviewed, including transparent conductive electrodes, photodetectors and phototransistors, photovoltaics and light emitting devices, saturable absorbers for ultrafast lasers, and biological and photocatalytic applications. In the final section, perspectives are given and future challenges in optical and optoelectronic applications of graphene‐based nanomaterials are addressed.     

Single Crystal Perovskite Solar Cells: Development and Perspectives

The efficiency of perovskite solar cells has increased to a certified value of 25.2% in the past 10 years, benefiting from the superior properties of metal halide perovskite materials. Compared with the widely investigated polycrystalline thin films, single crystal perovskites without grain boundaries have better optoelectronic properties, showing great potential for photovoltaics with higher efficiency and stability. Additionally, single crystal perovskite solar cells are a fantastic model system for further investigating the working principles related to the surface and grain boundaries of perovskite materials. Unfortunately, only a handful of groups have participated in the development of single crystal perovskite solar cells; thus, the development of this area lags far behind that of its polycrystalline counterpart. Therefore, a review paper that discusses the recent developments and challenges of single crystal perovskite solar cells is urgently required to provide guidelines for this emerging field. In this progress report, the optical and electrical properties of single crystal and polycrystalline perovskite thin films are compared, followed by the recent developments in the growth of single crystal perovskite thin films and the photovoltaic applications of this material. Finally, the challenges and perspectives of single crystal perovskite solar cells are discussed in detail.     

Composition Engineering of Perovskite Single Crystals for High-Performance Optoelectronics

Composition engineering, with its advantages to effectively tune semiconductor properties by regulating chemical stoichiometry, is a proven strategy to boost the efficiency and stability of ABX₃ perovskite photoelectronic devices. Compared with its counterpart polycrystalline perovskite film, single crystalline is the ideal model for exploring its fundamental scientific issues. In this review, a critical overview of recent advances of the growth strategies, properties, and functional applications of multicomponent perovskite single crystals (SCs) is presented. First, the underlying advantages of composition engineering of perovskite SCs are discussed and then the different composition tuning strategies, including A-site, B-site, X-site, and simultaneous A- and X-site engineering, are systematically summarized. Subsequently, the benefits of composition engineering are highlighted for optimizing photovoltaic and photoelectronic devices. Lastly, controversies and remaining challenges for the development of composition engineering of perovskite SCs are discussed and a brief perspective regarding further investigation in this field is provided.     

Self-Cleaning Perovskite Single Crystals Fabricated with Bis(trifluoromethylsulfonyl)imide Derived Ionic Liquid Toward High-Performance Photodetection

Surface defects are crucial to perovskite single crystals (SCs) for versatile optoelectronic applications, whereas suffers from the intricate post-treatments and unsatisfactory reproducibility within solution growth strategy due to the residue solvent corrosion and adsorbed precursors deposition. Here, an ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMITFSI) is demonstrated, assisted solution growth approach for fabricating high-quality self-cleaning perovskite single crystals with no need for any post-treatment. Benefiting from the in situ assembling in crystalline surface, BMITFSI can effectively decrease the crystallographic trap density by simultaneously introducing the self-cleaning effect and optimizing the crystalline growth process. Particularly, as fabricated MAPbI₃ single crystal exhibits an impressive photodetection performance with a specific detectivity of 2.83 × 10¹² Jones in visible-IR spectrum and a sensitivity of 7.24 × 10⁴ µC Gy_air⁻¹ cm⁻² in X-ray detection, which is as good as the conventionally fabricated crystal with elaborate post-treatments. Based on the chemical composition independent universality, this work paves an easy but efficient route to improve the current crystallization methodology toward high-quality perovskite SCs fabrication.     

有机半导体薄膜的光学和电学性质研究

采用真空热蒸镀技术制备了NPB有机半导体薄膜和单层夹心结构器件,通过透射谱测量研究了薄膜的光学能隙、折射率和消光系数等光学性质,结果表明有机半导体薄膜具有直接带隙半导体的光学性质,并且其折射率色散性质遵循单振子模型.另外,通过分析器件的电流-电压特性研究了薄膜的电导率、载流子迁移率和载流子浓度等电学性质.这些实验结果对于有机光电子器件的结构设计具有一定的参考价值.     

Fabrication of MAPbBr3 Single Crystal p‐n Photodiode and n‐p‐n Phototriode for Sensitive Light Detection Application

In this study, MAPbBr₃ single crystal (MSC) p‐n perovskite homojunction photodiode and n‐p‐n phototriode are successfully fabricated through controlled incorporation of Bi³⁺ ions in solution. Optoelectronic analysis reveals that the photodiode shows typical photovoltaic behavior and the best photovoltaic performance can be achieved when the n‐type MSC is grown in 0.3% Bi³⁺ feed solution. The as‐assembled p‐n MSC photovoltaic detector displays obvious sensitivity to 520 nm illumination, with a high responsivity of up to 0.62 A W^‐1 and a specific detectivity of 2.16 × 10¹² Jones, which surpass many those of MSC photodetectors previously reported. Further performance optimization can be realized by constructing an n‐p‐n phototriode using the same growth method. The photocurrent magnification rate of the as‐fabricated n‐p‐n phototriode can reach a maximum value of 2.9 × 10³. Meanwhile, a higher responsivity of 14.47 A W^‐1, specific detectivity of 4.67 × 10¹³ Jones, and an external quantum efficiency of up to 3.46 × 10³ are achieved under an emitter–collector bias of 8 V. These results confirm that the present p‐n and n‐p‐n MSC homojunctions are promising device configurations, which may find potential application in future optoelectronic devices and systems.     

Optoelectronic Perovskite Synapses for Neuromorphic Computing

Simulating the human brain for neuromorphic computing has attractive prospects in the field of artificial intelligence. Optoelectronic synapses have been considered to be important cornerstones of neuromorphic computing due to their ability to process optoelectronic input signals intelligently. In this work, optoelectronic synapses based on all‐inorganic perovskite nanoplates are fabricated, and the electronic and photonic synaptic plasticity is investigated. Versatile synaptic functions of the nervous system, including paired‐pulse facilitation, short‐term plasticity, long‐term plasticity, transition from short‐ to long‐term memory, and learning‐experience behavior, are successfully emulated. Furthermore, the synapses exhibit a unique memory backtracking function that can extract historical optoelectronic information. This work could be conducive to the development of artificial intelligence and inspire more research on optoelectronic synapses.     

AIN膜及其在半导体光电器件中的应用

本文报道溅射AlN膜及其应用于半导体光电器件的实验研究结果。测定了不同条件下溅射的AlN膜厚度、淀积速率、折射率和击穿电场强度。首次用AlN膜做器件的端面保护和减反射膜以及表面钝化膜均获得成功。几种常用介质膜的实验数据对比分析表明AlN膜在半导体光电器件领域将有广阔应用前景。     

Optoelectronic Synapses and Photodetectors Based on Organic Semiconductor/Halide Perovskite Heterojunctions: Materials,Devices, and Applications

Both photodetectors (PDs) and optoelectronic synaptic devices (OSDs) are optoelectronic devices converting light signals into electrical responses. Optoelectronic devices based on organic semiconductors and halide perovskites have aroused tremendous research interest owing to their exceptional optical/electrical characteristics and low-cost processability. The heterojunction formed between organic semiconductors and halide perovskites can modify the exciton dissociation/recombination efficiency and modulate the charge-trapping effect. Consequently, organic semiconductor/halide perovskite heterojunctions can endow PDs and OSDs with high photo responsivity and the ability to simulate synaptic functions respectively, making them appropriate for the development of energy-efficient artificial visual systems with sensory and recognition functions. This article summarizes the recent advances in this research field. The physical/chemical properties and preparation methods of organic semiconductor/halide perovskite heterojunctions are briefly introduced. Then the development of PDs and OSDs based on organic semiconductor/halide perovskite heterojunctions, as well as their innovative applications, are systematically presented. Finally, some prospective challenges and probable strategies for the future development of optoelectronic devices based on organic semiconductor/halide perovskite heterojunctions are discussed.     

无机钙钛矿CsPbX3晶体的低温溶液生长及应用研究进展

无机钙钛矿材料CsPbX₃(X=Cl,Br,I)具有光吸收系数高、发射谱线宽度窄、发光效率高等优异的光电性能,与目前在光伏领域大放异彩的有机-无机杂化钙钛矿材料相比,其在化学稳定性和热稳定性方面更胜一筹。文章就CsPbBr₃晶体的低温制备方法及其在光电探测器、发光二极管、激光、高能射线探测等领域的应用研究进展进行了分析和总结。     

Recent Progress of Bismuth Effect on All-Inorganic Lead-Free Metal Halide Derivatives: Crystals Structure,Luminescence Properties,and Applications

Bismuth (Bi³⁺)-included lead-free metal halide (LFMH) materials attract much attention in lighting, display, photodetectors, X-ray detectors, and photovoltaic fields, due to the tunable luminescence and optoelectronic performance in response to crystal and electronic structure, morphology, and particle sizes. This review summarizes Bi³⁺-included LFMH materials about their preparation approach, crystal and electronic structure properties, luminescence performance, and emerging applications. Notably, Bi³⁺ ions not only can act as framework cation to construct stable LFMH structure, but can also incorporate into LFMH materials as activators or sensitizers to generate remarkable luminescence tuning and band engineering. The Bi³⁺ effect on the luminescence and optoelectronic properties of LFMH materials, including, promotion of exciton localization, enhancement of light absorption in near-ultraviolet region, action as sensitizer ions to transfer energy to rare earth or transition metal ions and emission of highly-efficient light is systematically summarized. The proposed structure-luminescence relationship offers guidance for the optimization of current Bi³⁺-included LFMH materials and the exploitation of new LFMH derivatives.     

Mitigating Surface Deficiencies of Perovskite Single Crystals Enables Efficient Solar Cells with Enhanced Moisture and Reverse-Bias Stability

Metal halide perovskite single crystals are promising for diverse optoelectronic applications due to their outstanding properties. In comparison to the bulk, the crystal surface suffers from high defect density and is moisture sensitive; however, surface modification strategies of perovskite single crystals are relatively deficient. Herein, solar cells based on methylammonium lead triiodide (MAPbI₃) thin single crystals are selected as a prototype to improve single-crystal perovskite devices by surface modification. The surface trap passivation and protection against moisture of MAPbI₃ thin single crystals are achieved by one bifunctional molecule 3-mercaptopropyl(dimethoxy)methylsilane (MDMS). The sulfur atom of MDMS can coordinate with bare Pb²⁺ of MAPbI₃ single crystals to reduce surface defect density and nonradiative recombination. As a result, the modified devices show a remarkable efficiency of 22.2%, which is the highest value for single-crystal MAPbI₃ solar cells. Moreover, MDMS modification mitigates surface ion migration, leading to enhanced reverse-bias stability. Finally, the cross-link of silane molecules forms a protective layer on the crystal surface, which results in enhanced moisture stability of both materials and devices. This work provides an effective way for surface modification of perovskite single crystals, which is important for improving the performance of single-crystal perovskite solar cells, photodetectors, X-ray detectors, etc.     

ICP刻蚀技术及其在光电子器件制作中的应用

简单介绍了ICP(inductively coupled plasma)刻蚀设备的结构和刻蚀机理，报道了ICP刻蚀硅、二氧化硅和Ⅲ—Ⅴ族材料的一些最新进展，重点介绍ICP刻蚀技术在光电子器件制作方面的进展和应用前景。     

Self-Assembled Perovskite Nanoislands on CH3NH3PbI3 Cuboid Single Crystals by Energetic Surface Engineering

Organometal perovskite single crystals have been recognized as a promising platform for high-performance optoelectronic devices, featuring high crystallinity and stability. However, a high trap density and structural nonuniformity at the surface have been major barriers to the progress of single crystal-based optoelectronic devices. Here, the formation of a unique nanoisland structure is reported at the surface of the facet-controlled cuboid MAPbI₃ (MA = CH₃NH₃⁺) single crystals through a cation interdiffusion process enabled by energetically vaporized CsI. The interdiffusion of mobile ions between the bulk and the surface is triggered by thermally activated CsI vapor, which reconstructs the surface that is rich in MA and CsI with reduced dangling bonds. Simultaneously, an array of Cs-Pb-rich nanoislands is constructed on the surface of the MAPbI₃ single crystals. This newly reconstructed nanoisland surface enhances the light absorbance over 50% and increases the charge carrier mobility from 56 to 93 cm² V⁻¹ s⁻¹. As confirmed by Kelvin probe force microscopy, the nanoislands form a gradient band bending that prevents recombination of excess carriers, and thus, enhances lateral carrier transport properties. This unique engineering of the single crystal surface provides a pathway towards developing high-quality perovskite single-crystal surface for optoelectronic applications.