Steric Hindrance Enhancement Prolongs Charge Carrier Lifetimes in Two-Dimensional Ruddlesden–Popper Perovskites

Experiments reveal that the steric hindrance of A-site cations significantly affects carrier dynamics in two-dimensional (2D) perovskites. However, these cations simultaneously introduce hydrogen bonding and steric hindrance. Thus, it is essential to decouple these dual effects to understand their respective impacts on carrier dynamics. In this study, we systematically investigate the role of steric hindrance on carrier dynamics through nonadiabatic molecular dynamics simulations in (C8H12N)2PbI4 (S-MBA2PbI4) and (C8H18N)2PbI4 (S-CHEA2PbI4) perovskites. Our results show that while S-MBA and S-CHEA exhibit nearly identical hydrogen bonding strength, they display different steric hindrance. Enhancing the steric hindrance of A-site cations suppresses atomic motion and weakens nonadiabatic coupling, resulting in prolonged hot carrier relaxation and charge recombination times. This study provides critical theoretical insights into how steric hindrance modulates charge carrier dynamics in 2D perovskites. These findings offer valuable guidelines for designing high-performance solar cells and other optoelectronic devices by strategically controlling the molecular steric properties.