Investigation of the Structural Disorder and Spin Dynamics in the Bismuth Halide Perovskite Single Crystals*

Recently, development of lead free perovskites as a potential alternative material and environment friendly candidate has received critical attention. Here, we report the synthesis of all inorganic millimeter size lead-free bismuth based halide perovskites Cs₃Bi₂X₉ (X= Cl, Br, I) single crystals and their structural disorderness, optical, and spin relaxation properties in details. Higher Urbach energy in Cs₃Bi₂X₉ single crystals reveals high degree of local structural disorderness and short range of crystallinity. We show structural disorder not only affect the optical properties but also impacts 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 new design strategy and in-depth understanding to develop environmental friendly lead free and stable perovskite based optoelectronics and spintronic devices.