Electro-Optical Analysis of Carrier Dynamics in Lead-Free Cs₃Bi₂I₉ Perovskite

In this study, we examined carrier conduction in a Cs₃Bi₂I₉ (CBI) perovskite through a dual-probe approach using both optical and electrical measurements. We observed that the open-circuit voltage and photocurrent with light intensity follow the V_OC ∝ I^0.06 and J_SC ∝ I^0.94 relationships, attributed to nonradiative recombination losses and trapping of carriers. Excitation power-dependent photoluminescence behavior indicates the influence of the self-trapped exciton (STE) and strong phonon perturbation at high excitation powers in the CBI lattice. Transient absorption measurements as a function of excitation power and energy provide insights about exciton trapping and polaron formation. At higher powers, polaron formation and lattice distortion increase, broadening the photoinduced absorption band at the low-energy side. Exciton generation was more efficient near the excitonic absorption peak, while a higher energy caused greater lattice distortion and electron-phonon coupling. This study advances the understanding of the optoelectronic behavior of CBI perovskites and provides insights into carrier dynamics in similar materials.