Nucleation Engineering in Sprayed MA 3 Bi 2 I 9 Films for Direct-Conversion X-ray Detectors.

Metal halide perovskite and its derivatives show great promise in X-ray detection. However, large-scale fabrication of high-quality thick perovskite films is still full of challenges due to the complicated crystal nucleation process that always introduces lots of cracks or pinholes in the final perovskite film. Here, a MA 3 Bi 2 I 9 film was fabricated by the cost-effective, scalable spraying process, and MACl was used as an additive to effectively tune the crystallization process. As a result, a dense MA 3 Bi 2 I 9 film constituted by large grains was obtained, which has a high carrier mobility of ∼1 cm 2 V -1 s -1 and a large activation energy ( E a ) for ion migration of 0.91 eV. Thanks to the outstanding optoelectronic characteristics, X-ray detectors with a configuration of ITO/MA 3 Bi 2 I 9 /Au show a sensitivity of 35 μC Gy air -1 cm -2 and a limit of detection (LoD) of 0.14 μGy air s -1 , which is outstanding compared with commercial α-Se detectors.