A-site Cation Effects on Hot Carrier Relaxation in Perovskites by Nonadiabatic Molecular Dynamics Simulations

In recent years , perovskites have become a research hotspot in the field of solar cells due to their excellent optical and electrical properties. A large number of experiments reported that hot carries relaxation times follow the trend CsPbBr3> MAPbBr(3) (MA = CH3NH3) > FAPbBr(3) [FA = HC (NH2) (2)]. However, the underlying mechanism of the A-site cation( Cs+, MA(+), FA(+)) effects on the relaxation time remains unclear, the hot electrons and holes relaxation of the three perovskiteswere investigated using time-domain density functional theory combined with nonadiabatic molecular dynamics. The obtained time scales agreed well with experiment. This is because A-site cation affects electronic-vibrational coupling with the inorganic Pb-Br framework via electrostatic interaction and hydrogen bond , leading to the strength of nonadiabatic coupling decreasing from FAPbBr(3) to MAPbBr(3), to CsPbBr3. As a result, the hot carrier relaxation times decreases as the same trend. The study suggests that rational choice of A-site cations provides an excellent strategy to the optimize the perfkifmance of perovskite solar cells.