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

In this study, we employed lock-in amplifier-based surface photovoltage (SPV) spectroscopy to identify bandgap excitations, bound exciton states, and defect excitations in Cs 3 Bi 2 I 9 . 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 Cs 3 Bi 2 I 9 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 Cs 3 Bi 2 I 9 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 Cs 3 Bi 2 I 9 are preparation-dependent, leading to broad tailing absorption and enabling the conversion of SPV signals via wavelength modulation. These results highlight the potential of Cs 3 Bi 2 I 9 in advanced optoelectronic applications.