A-Site Cations Impact on Nonradiative Recombination, Mobility, and Defect Dynamics in Sn-Based Perovskites

Sn-based perovskites with different cations in the A-site exhibit distinct electronic structures and dynamic properties. By utilizing time-dependent density functional theory and nonadiabatic molecular dynamics, we demonstrate that larger FA cations decrease wave function overlap between initial and final states and slow down nuclear motion. In the case of FASnI₃, this alteration decreases the nonadiabatic coupling and increases the nonradiative electron-hole recombination time by 130% and 76%, respectively, compared to CsSnI₃ and MASnI₃ (CH₃NH₃SnI₃). Furthermore, A-site modification significantly improves electron mobility and changes the properties of defects in FASnI₃ (HC(NH₂)₂SnI₃), which achieves higher electron mobility through a polar optical phonon-dominated scattering mechanism and exhibits higher defect formation energy and migration barriers of A-site cations due to increased steric hindrance, relative to CsSnI₃ and MASnI₃. These results emphasize the critical function of A-site cation substitution in controlling nonradiative recombination dynamics, electron mobility, and defect characteristics in Sn-based perovskites and provide theoretical insights for the advancement of novel lead-free perovskite materials.