Impact of Organic Spacers on the Carrier Dynamics in 2D Hybrid Lead-Halide Perovskites

We have carried out nonadiabatic molecular dynamics simulations combined with time-dependent density functional theory calculations to compare the properties of the two-dimensional (2D) (BA)(2)(MA)Pb2I7 and three-dimensional (3D) MAPbI(3) (where MA = methylammonium and BA = butylammonium) materials. We evaluate the different impacts that the 2D-confined spacer layer of butylammonium cations and the 3D-confined methylammonium cations have on the charge carrier dynamics in the two systems. Our results indicate that, while both the MA(+) and BA(+) cations play important roles in determining the carrier dynamics, the BA(+) cations exhibit stronger nonadiabatic couplings with the 2D perovskite framework. The consequence is a faster hot-carrier decay rate in 2D (BA)(2)(MA)Pb2I7 than in 3D MAPbI(3). Thus, tuning of the functional groups of the organic spacer cations in order to reduce the vibronic couplings between the cations and the Pb-I framework can offer the opportunity to slow down the hot-carrier relaxations and increase the carrier lifetimes in 2D lead-halide perovskites.