Drop‐Casting Halide Microcrystals Enabled by Green Glycol Solvent for High‐Performance Photodetectors

Halide perovskites have attracted significant recent attention due to their remarkable photoelectric properties; however, the poor structural and moisture stability limit their use for practical utilization. Interestingly, binary halides, such as BiI 3 and PbI 2 , are the typical constituents of halide perovskites, where they do not only have the similar outstanding properties of perovskites but also the superior stability. Herein, the synthesis of layered BiI 3 and PbI 2 microcrystals by simple drop‐casting is investigated and their enhanced photoelectric performance compared to the thin‐film counterparts obtained by conventional spin‐coating is demonstrated. For the formation of high‐quality layered microcrystals, the keys are adopting glycol as a green solvent and appropriate temperature during processing. Once configured into photodetectors, the BiI 3 and PbI 2 microcrystals exhibit a higher photocurrent, on/off current ratio, responsivity, and other performance parameters than their thin‐film devices. These improved performances of microcrystals can be attributed to their superior crystallinity, thanks to the excellent solvent properties of glycol and the optimal growth temperature chosen. This work proposes a more simple and effective solution processing technique to fabricate layered binary halides with higher quality than the conventional spin‐coating method, enabling the further development of halides‐based optoelectronic devices.