Ultrafast Exciton Dynamics in Thin Films of a Two-Dimensional Pb-Free CsBi₃I₁₀ Perovskite

CsBi3I10 perovskite films were synthesized by an antisolvent-assisted spin-coating method. The morphology and crystal structure of the CsBi3I10 perovskite film were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy, confirming its crystallinity and purity. Ultraviolet–visible (UV–vis) absorption spectra revealed two excitonic peaks peaked at 496 and 626 nm. Femtosecond transient absorption spectroscopy (TAS) was utilized to probe the exciton dynamics that reveal three dominant processes attributed to hot electron cooling, trapping to trap states, electron–hole recombination, and a possible dissociative pathway or high density of defect states coupled with the first excited electronic state or conduction band (CB), which lead an overall short-lived photoinduced charge carrier or exciton. A kinetic model was proposed to simulate and explain these processes that lead to an overall short exciton lifetime.