Engineering Chemical Vapor Deposition for Lead‐Free Perovskite‐Inspired MA₃Bi₂I₉ Self‐Powered Photodetectors with High Performance and Stability

Abstract Lead‐free perovskite‐inspired materials (PIMs) have attracted great interest in optoelectronics, as they feature electronic properties similar to mainstream lead‐based perovskites but are not burdened by the same toxicity issues. However, PIM photodetectors to date have not delivered efficiencies and stability on par with benchmark technologies. With a focus on methylammonium bismuth iodide (MA₃Bi₂I₉)—a prominent lead‐free PIM—this study overcomes this challenge by growing the photoactive material through an engineered chemical vapor deposition (CVD) approach. While the commonplace one‐tube (1T)‐CVD approach delivers films with disconnected grains and large pinholes, a two‐tube (2T)‐CVD approach is developed that enables the growth of smoother films with superior, compact morphology. The considerable optoelectronic potential of 2T‐CVD MA₃Bi₂I₉ films is demonstrated by realizing high‐performance self‐powered photodetectors, which deliver a responsivity and specific detectivity as high as 0.28 A W^–1 and 8.8 × 10¹² Jones, respectively, under UV illumination—i.e., approximately twice as large as the 1T‐CVD counterparts. Further, nonencapsulated 2T‐CVD devices exhibit considerable long‐term moisture stability, with an attenuation of their photoresponse of ≤3% over 100 days. These results demonstrate that 2T‐CVD offers a promising platform that can catalyze the development of high‐performance lead‐free perovskite‐inspired optoelectronics.