Solvent-induced orientation of FAPbI₃ single crystals for highly efficient self-powered X-ray detectors

Perovskites are promising materials for use in self-powered X-ray detectors. However, the presence of defects causes unsatisfactory sensitivity in the prepared devices. Tuning crystal orientation has been confirmed to be an effective means of reducing the defects of perovskites. Here, we report the co-development of (100), (110) and (111) crystal orientations in FAPbl₃ SCs for the first time by inducing the target facets to be the lowest surface energy facets within the selected solvents. The size of the formed facets is large enough to evaluate their properties without interference from non-dominant facets. Compared to (110)- and (111)-oriented FAPbI₃ SCs, the (100)-oriented one manifests reduced trap-state density and suppression of ionic migration. It thus promotes charge collection, demonstrating superior response performance under both visible-light and X-ray illuminations. Moreover, such orientation engineering enables FAPbI₃ SCs to be excellent candidates for self-powered X-ray detectors. High sensitivity close to 5000 μC Gy_air ^-1 cm^-2 was achieved when using 30 keV of X-ray energy, which is the record value among all the self-powered X-ray detectors constructed exclusively by perovskites, even surpassing the devices assisted by heterojunctions. Hence, our findings confirm that solvent-induced orientation engineering has great potential to enable perovskite SCs to be the superior choice for self-powered X-ray photodetectors with high performance.