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 (MHP) single crystals are promising candidates for photovoltaics and related optoelectronic devices. They afford optical and charge transport properties superior to those of their polycrystalline counterparts. Despite this advantage, MHP single crystals are less widely adopted. Traditional bulk growth methods do not lend single-crystal MHPs to device integration as readily as their polycrystalline analogues, which are amenable to a multitude of approaches for deposition and growth. Fortunately, diverse shape-control approaches for MHP single crystals have been recently reported, enabling tunable optoelectronic properties and expanding the potential for single-crystal applications. In this review, we summarize recent developments in the shape control of MHP single crystals, including those pertaining to microcrystals, single-crystal thin films, nano-/microplates, nano-/microrods, and nanocrystals. We highlight strategies for optimizing the synthesis of these crystals to achieve targeted materials properties and device performance. This review aims to guide the future of shape design in MHP single crystals for various optoelectronic applications. assisted length control of perovskite nanowires. The inset of (b) shows a photograph of a CsPbBr3 nanowire under UV light (λ = 365 nm). (a) Reproduced with permission. 145

Metal halide perovskite single crystals have become emerging candidates for photovoltaic applications due to their better optoelectronic properties and higher stability than their polycrystalline thin-film counterparts. However, in contrast to the rapid enhancement of power conversion efficiency (PCE), the operational stability of single-crystal perovskite solar cells (PSCs) remains far lagging behind. Herein, it is discovered that widely investigated 20 μm-thick single-crystal PSCs show poor operational stability, which is assigned to low crystal quality of these thin single crystals. Subsequently, the crystal quality of formamidinium0.55methylammonium0.45 lead triiodide (FA0.55MA0.45PbI3) thin single crystals are optimized by adjusting the ion diffusion velocity in confined space, leading to lower trap density, larger ion migration activation energy, and reduced light-induced degradation of material properties. As a result, stable single-crystal PSCs with no efficiency degradation after 330 h of continuous operation at the maximum power point under 1 sun illumination are achieved. Moreover, thickness-dependent device efficiency discloses an ultralong carrier transport length of 200 μm in FA0.55MA0.45PbI3 thin single crystals, which is instructive for developing lateral-structure solar cells.

Metal halide perovskite single crystals are a promising candidate for X-ray detection due to their large atomic number and high carrier mobility and lifetime. However, it is still challenging to grow large-area and thin single crystals directly onto substrates to meet real-world applications. In this work, millimeter-thick and inch-sized methylammonium lead tribromide (MAPbBr3) single-crystal wafers are grown directly on indium tin oxide (ITO) substrates through controlling the distance between solution surface and substrates. The single-crystal wafers are polished and treated with O3 to achieve smooth surface, lower trap density, and better electrical properties. X-ray detectors with a high sensitivity of 632 µC Gyair−1 cm−2 under –5 V and 525 µC Gyair−1 cm−2 under –1 V bias can be achieved. This work provides an effective way to fabricate substrate-integrated, large-area, and thickness-controlled perovskite single-crystal X-ray detectors, which is instructive for developing imaging application based on perovskite single crystals.