Effect of Water on the Structural, Optical, and Hot-Carrier Cooling Properties of the Perovskite Material MASnI3

Understanding the stability, carrier transport, and relaxation of Sn-based hybrid perovskite CH3NH3SnI3 is of high interest to develop lead-free perovskite solar cells. In this study, we perform first-principles and nonadiabatic ab initio molecular dynamics simulations to address the electronic and optical properties as well as hot-carrier relaxation dynamics of pristine CH3NH3SnI3 and its monohydrated phase CH3NH3SnI3·H2O. Our results show that the water molecules interact strongly with the organic part [CH3NH3]+ of the material by forming hydrogen bonding. They also interact with the inorganic lattice (mostly with iodide ions). Our study also indicates a profound effect of water molecules on the optical properties of the perovskite materials. For example, the water molecules reduce the absorption of the system mostly in the visible range of the solar spectrum. The presence of water molecules also leads to faster hot-carrier cooling and enhanced polarization of the material.