Air‐Stabilized Lead‐Free Hexagonal Cs3Bi2I9 Nanocrystals for Ultrahigh‐Performance Optical Detection

Broadband photodetectors possess enormous potentials for diverse applications while it is generally subjected to a lack of active materials with high performances under user‐friendly conditions. Bismuth‐based perovskites are promising and demonstrate better air stability than lead halide perovskites against moisture, heat, and light. In the present work, lead‐free all‐inorganic hexagonal Cs3Bi2I9 perovskite nanocrystals are successfully fabricated via a modulated colloidal synthetic route. The Cs3Bi2I9 nanocrystals are monodispersed with a size of ≈28 nm, which are applied for the construction of flexible Cs3Bi2I9 detector and vertical heterogeneous structured photodetector of p‐Si/Cs3Bi2I9/graphene. The flexible detector not only demonstrates excellent detective performance, but also yields high‐resolution photographs as an imaging sensor. The p‐Si/Cs3Bi2I9/graphene photodetector exhibits broad spectral response from ultraviolet to infrared light (254−1064 nm) with microsecond response time (31/34 µs). In particular, it performs with a high responsivity of 23.6 A W−1 and a high specific detectivity of 1.75 × 1013 Jones under 650 nm illumination even in weak light intensity as low as 1 µW cm−2, and exhibits excellent stability in ambient air, which is obviously ahead of the previously reported work. In addition, finite element analysis further demonstrates the excellent optoelectronic properties of Cs3Bi2I9 materials and the broad spectral response of vertical heterojunctions. The authors synthesize high quality Pb‐free Cs3Bi2I9 hexagonal nanocrystals using a modulated colloidal synthetic approach and demonstrate a broad‐spectrum detector from the ultraviolet to near‐infrared range with an exceptional photodetection performance. Further, the flexible Cs3Bi2I9 photodetector serving as an image sensor is able to yield high‐resolution images.