Structural Disorder and Spin Dynamics Study in Millimeter-Sized All-Inorganic Lead-Free Cesium Bismuth Halide Perovskite Single Crystals

Perovskite single crystals have emerged as potential candidates in the field of optoelectronic devices because of their low trap state densities, long diffusion lengths, and high charge carrier mobilities. However, the presence of lead (Pb) in perovskite causes serious concerns due to lead’s high-perceived toxicity and poor environmental stability. Therefore, development of lead-free perovskites as a potential alternative material and an environment-friendly candidate has received critical attention. Here, we report the synthesis of all-inorganic millimeter-sized lead-free bismuth-based halide perovskite Cs3Bi2X9 (X = Cl, Br, I) single crystals and their structural disorderness, optical, and spin relaxation properties in detail. Higher Urbach energy in Cs3Bi2X9 single crystals reveals a high degree of local structural disorderness and a short range of crystallinity. We show that structural disorder affects not only the optical properties but also the magnetic and spin relaxation properties. We observe that increased structural disorder leads to enhanced smearing of local energy bands and high spin–orbit coupling. The spin relaxation time is determined in the picoseconds time scale, which corresponds to fast charge carrier dynamics. Our work provides a design strategy and in-depth understanding to develop environment-friendly lead-free and stable perovskite-based optoelectronics and spintronic devices.