In polycrystalline thin films, the inherent grain boundaries that contain abundant charge traps can cause adverse effect on optoelectronic properties of perovskite materials, and defect passivation is necessary for efficient polycrystalline PSCs. [3] In contrast, perovskite single crystals offer an opportunity to further improve the efficiency of PSCs, due to the absence of grain boundaries as well as their orders of magnitude lower defect density and longer carrier diffusion length than those in their polycrystalline counterparts. [4] Recently, the efficiency of smallarea single-crystal PSCs based on 20 µm thick MAPbI 3 (MA = CH 3 NH 3 + ) absorber layer has reached 21.9% by using a low-temperature (<90 °C) inverse temperature crystallization (ITC) method. [5] Moreover, the near-infrared response of the devices can be expanded by incorporating FA (FA = CH(NH 2 ) 2 + ) into MAPbI 3 crystals, leading to a high PCE of up to 22.8%. [6] To construct large-area single-crystal PSCs, Liu et al. developed a refreshing-reiteration method to grow perovskite bulk single crystals with dimension as large as 120 mm. [7] Besides, they established a diamond-wire-sawing process to produce inchsized single-crystal perovskite wafers for fabrication of inchsized single-crystal PSCs. [8] For photovoltaic application, growth of micrometer-thick lead-iodide perovskite single crystals is necessary to promote carrier transport and collection. [9] Liu et al. designed an ultrathin geometry-defined dynamic-flow reaction system and realized the growth of large-area single-crystal perovskite wafers with controllable thickness, which provides a universal and effective strategy for application of perovskite single crystals in optoelectronic device design and fabrication. [10] In this method, a mass concentration of defects would unavoidably be generated at the interface due to the lattice mismatch between perovskite and hole transport layer (HTL). Huang et al. found that the trap density in perovskite single crystals increased by five orders of magnitude from interior to surface/interface, and most deep traps were detected near the HTL/perovskites interface. [11] On the other hand, the ion diffusion rate in the confined space is limited by the interaction between substrates and solvated Perovskite single crystals have recently been regarded as emerging candidates for photovoltaic application due to their improved optoelectronic properties and stability compared to their polycrystalline counterparts. However, high interface and bulk trap density in micrometer-thick thin single crystals strengthen unfavorable nonradiative recombination, leading to large open-circuit voltage (V OC ) and energy loss. Herein, hydrophobic poly(3-hexylthiophene) (P3HT) molecule is incorporated into a hole transport layer to interact with undercoordinated Pb 2+ and promote ion diffusion in a confined space, resulting in higher-quality thin single crystals with reduced interface and bulk defect density, suppressed nonradiative recombination, accelerated charge transp...

Self‐powered perovskite X‐ray detectors have drawn increasing attention due to the merits of low noise, low power consumption as well as high portability and adaptability. However, the active layer thickness is usually compromised by the small carrier diffusion length, which leads to inefficient X‐ray attenuation and hence low sensitivity of the detectors. Herein, self‐powered and highly sensitive single‐crystal perovskite X‐ray detectors are achieved by finely controlling the crystal thickness and optimizing their carrier transport properties. Perovskite single crystals with thickness of around 800 µm are grown by a two‐step crystal growth process to realize the full attenuation of hard X‐ray with the energy of 80 keV. And the incorporation of formamidinium (FA) (FA = CH(NH2)2+) cation into methylammonium lead triiodide (MAPbI3) (MA = CH3NH3+) increases the mobility‐lifetime (µτ) product of the single crystals by nearly one order of magnitude, leading to a record X‐ray detection sensitivity of 8.7 × 104 µC Gyair−1 cm−2 under zero bias. Moreover, the eliminated external bias and reduced trap density weaken the field‐driven ion migration effect, and therefore result in a low detection limit of 27.7 nGy s−1. This work represents an effective way to achieve self‐powered perovskite X‐ray detectors with both high sensitivity and low detection limit.

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.

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