Control Synthesis and Alloying of Ambient Stable Pb-Free Cs₃Bi₂Br_{9(1- x)}I_{9 x}(0 ≤ x ≤ 1) Perovskite Nanocrystals for Photodetector Application

We represent a facile colloidal synthesis of halide tunable, structurally distorted Cs3Bi2Br9(1-x)I9x (0 ≤ x ≤ 1) nanocrystals. The detail structural characterization establishes phase purity of the as-synthesized perovskite nanocrystals. The lattice parameters follow a linear trend in agreement with Vegard's law, confirming the homogeneous gradient alloying of the nanocrystals through entropic halide mixing up to a certain degree of alloying. Systematic Raman analysis also proves the complete homogeneous solid solution formation across the entire compositional window. Simultaneous optical and cyclic voltammetry measurements corroborate a band gap variation in the range of 1.97-2.72 eV, consistent with the pure end (x = 0 and 1) compounds. A stable photodetector was fabricated with pristine and alloyed nanocrystals where the best performance was achieved for Cs3Bi2I9. The functionality in the form of a fast photodetector suggests that these Cs3Bi2Br9(1-x)I9x nanocrystals are prospective optoelectronic materials. The present study provides an evidence of tunable optical window for mixed halide all-inorganic bismuth halide perovskites toward photodetector applications.