Direct drop-casting synthesis of all-inorganic lead and lead-free halide perovskite microcrystals for high-performance photodetectors

Due to the exciting photoelectric properties, better stability, and environmental-friendly nature, all-inorganic halide perovskites (AIHPs), especially the lead-free perovskites, have attracted worldwide attention. However, the film quality of AIHPs fabricated by typical spin-coating and subsequent high-temperature annealing is still not satisfactory, restricting their further development. Herein, we demonstrate a simple low-temperature solution-processed drop-casting method to achieve highly-crystalline cubic CsPbBr3 and lead-free layer-structured Cs3Sb2I9 microcrystals (MCs). This drop-casting technique not only consumes the less amount of precursor solution but also eliminates the high-temperature annealing as compared with those of spin coating. When these MCs are configured into photodetectors, they exhibit superior device performance, which is in distinct contrast to the one of spin-coated counterparts. Specifically, the responsivity of CsPbBr3 MCs is found to be as large as 8,990 mA/W, being 13 times larger than the spin-coated films and even better than many state-of-the-art solution-processed AIHPs devices. This device performance enhancement is attributed to the better film quality and phase purity obtained by the drop-casting method. All these results can evidently fill the "technology gap" for further enhancing the material quality of solution-processed AIHPs and breaking down the barriers that hinder the development of AIHPs based optoelectronic devices.