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.