Defect characterization and prospective applications of Cs₃Bi₂I₉ perovskite: Insights from surface photovoltage...

In this study, we employed lock-in amplifier-based surface photovoltage (SPV) spectroscopy to identify bandgap excitations, bound exciton states, and defect excitations in Cs₃Bi₂I₉. This method, combined with SPV phase spectroscopy, enabled the evaluation of deep-level and shallow-level defects, correlating with charge-transfer transitions and defect-induced broad tailing absorption observed in the absorption spectrum. We found that deep-level defects in Cs₃Bi₂I₉ films can produce both positive and negative SPV signals, allowing for the simulation of excitatory and inhibitory synapses in neural networks and potential applications in robotic eye implants. By integrating Cs₃Bi₂I₉ thin films rich in deep-level defects, robotic eyes can generate execution and cancellation commands based on SPV responses to different light wavelengths. Our results demonstrate that defect states in Cs₃Bi₂I₉ are preparation-dependent, leading to broad tailing absorption and enabling the conversion of SPV signals via wavelength modulation. These results highlight the potential of Cs₃Bi₂I₉ in advanced optoelectronic applications.