Cross-Correlation Between Crystallinity and Optoelectronic Properties of Mixed-Perovskite Thin Films Through Multiple Time-Resolved Spectroscopy

A power conversion efficiency (PCE) exceeding 25% is achievable using perovskite solar cells (PSCs), with compositional engineering as the most effective strategy for high-efficiency PSCs. However, the understanding of structural properties, charge-carrier dynamics, and photoelectric properties, crucial for solar cell performance, still remains insufficient to establish a correlation with device performance for improving the PCE and stability of PSCs. This study uncovers the crucial links between structural disorder, charge-carrier dynamics, and photoelectric properties of mixed-perovskite (FAPbI₃)_1-x(MAPbBr₃)_x thin films by investigating device performance for different mol%. Structural and morphological analyses reveal that the mixed perovskite-thin-film disorder exhibits composition dependence in the form of a checkmark trend, with a minimum near 0.8 mol%. Time-resolved transient absorption spectroscopy demonstrates that charge-carrier dynamics and optoelectronic properties exhibit a corresponding dependence on disorder. As the disorder of the perovskite thin film decreases, the trap density decreases, charge-carrier loss decreases during the thermalization process, and the carrier lifetime is prolonged. Optical pump-THz probe measurements show 20% effective mobility and a diffusion length of 34%. The device performance shows composition dependence and superior PCE is achieved at 0.8 mol%. This study highlights the significance of charge-carrier dynamics in optimizing mixed perovskite composition for enhanced PCE and stability of PSCs.