Development of molecular dynamics force field parameters for hybrid perovskites

Sebastian Potthoff

Lead halide perovskites, especially the CH3NH3PbI3 compound, have attracted a great deal of attention. Its use in photovoltaic devices has increased their efficiency from 3.9% to almost 20% in the last five years. They have a much higher optical absorption than thin film solar cell absorbers, a band-gap that allows it to absorb most of the visible light, efficient electron hole pair separation and bipolar diffusion of carriers. They can be easily produced and are made of inexpensive materials. In addition they present ferroelectric and geometrical phase transition behaviour. Most of the theoretical description focuses on the electronic properties of these materials and use computationally intensive methods, which limits its study to small systems. In this work we aim at developing molecular dynamics force field parameters to be able to describe the dynamics of large-scale perovskite systems and interfaces. The force field parameters that we are developing shall describe the elastic properties of the inorganic PbI2 cage, the organic cation and the interaction of both of them. The description of the system ranges from relatively weak van der Waals interactions among the organic components to hydrogen bonding interactions between the organic and inorganic components (as well as among the organic molecules), and stronger ionic and covalent interactions within the metal halide cage.