In recent years, research on organic‐inorganic lead halide two‐dimensional (2D) perovskites has been blossoming. 2D perovskites have completely different layered structures from three‐dimensional perovskites, with interleaved organic and inorganic layers, leading to 2D perovskite materials being more stable and possessing anisotropic electrical transport. Meanwhile, 2D organic‐inorganic lead halide perovskite single crystals are receiving increasing attention because of their remarkable properties, such as long charge carrier lifetime, low defect density, and high photoluminescence quantum yield, increasing their potential for optoelectronic applications. Previously, a series of material systems based 2D perovskites single crystals has been synthesized and applied in various device applications. In this review, the preparation methods of organic‐inorganic lead halide 2D perovskite single crystals, the growth principles, their photoelectric properties and several device applications are discussed.

Generally, growing phase pure CsPbBr3 single crystals is challenging, and CsPb2Br5 or Cs4PbBr6 by‐products are usually formed due to the different solubilities of CsBr and PbBr2 in the single solvent. Herein, the growth of high‐quality phase pure CsPbBr3 perovskite single crystals at room temperature by a humidity controlled solvent evaporation method is reported first. Meanwhile, the room temperature phase transition process from three dimensional (3D) cubic CsPbBr3 to two dimensional (2D) layered tetragonal CsPb2Br5 and the detailed mechanism induced by humidity are revealed. Moreover, compared with the organic–inorganic perovskite, the prepared CsPbBr3 single crystals are much more stable under high humidity, which satisfies the long‐term working conditions of X‐ray detectors. The X‐ray detectors based on CsPbBr3 single crystals show a high sensitivity and a low detection limit of 1.89 μGyair s–1, all of which meet the needs of medical diagnosis.

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Lead halide perovskites have attracted increasing attention in photovoltaic devices, light-emitting diodes, photodetectors, and other fields due to their excellent properties. Besides optoelectronic devices, growing numbers of studies have focused on the perovskite-based electrical devices in the past few years, such as transistors and resistive random access memories (RRAMs). Here, this article summarizes the recent progress the researchers have made of RRAM devices. Primarily, the working mechanism and the key parameters of RRAM are introduced. Generally, the working principles, including the conductive filament model (containing the types of the model of the metal cationsinduced filament and the model of the ions migration in bulk), the interface effect, and the electronic effect are the origins of the RRAM behaviors, and hence, various factors that affect the device performance are explored. Then, RRAMs based on organolead halide perovskite and all-inorganic perovskite are discussed in terms of different structures, different compositions, and different fabrication methods. Finally, a brief conclusion and a broad outlook are given on the progress and challenges in the field of perovskite-based RRAMs. K E Y W O R D S all-inorganic perovskites, conductive filament models, organolead halide perovskites, resistive random access memories, resistive switching Jiayu Di and Jianhui Du contributed equally to this work.

CsPbBR 3 PEROVSKITE SINGLE CRYSTALSHigh quality phase pure CsPbBr 3 perovskite single crystals are grown by solvent evaporation method under controlled humidity conditions. Meanwhile, the humidity is revealed as a key factor affecting the phase transformation of CsPbBr 3 at room temperature. Moreover, the prepared CsPbBr 3 single crystals are applied for the long-term working high performance X-ray detectors. More details can be found in article number 2103482 by Jingjing Chang and co-workers.