How Cation Rigidity and Dipole Moment Prolong Hot-Carrier Lifetime in 2D Perovskites.

Abstract

2D Dion-Jacobson perovskites are promising solar cells due to high efficiency and stability yet are limited by poor charge dynamics and energy loss. Using density functional theory, ab initio molecular dynamics, and nonadiabatic molecular dynamics simulations to explore the cation rigidity and dipole moment of cations can extend hot-carrier lifetime and slow down charge recombination. Specifically, increasing the cation dipole moment strengthens hydrogen bonding between the organic spacer and the inorganic lattice, while a rigid cation enhances lattice stiffness. These factors strengthen thermal coupling between the organic and [PbI₆]^4- inorganic framework, reduce atomic fluctuations, and induce phonon softening. This suppresses nonadiabatic coupling and shifts dominant electron-phonon interactions of high-frequency modes to low-frequency modes, thereby prolonging hot-carrier lifetime and reducing nonradiative recombination. Thus, dipole engineering primarily enhances hot-carrier lifetime by suppressing nonradiative pathways, rather than accelerating hot-carrier cooling. Our finding provides guidelines for designing more efficient and stable perovskite solar cells.