Examination of the Photo-Physical Properties of Single Layer and Multiple Layer Two-Dimensional Hybrid Lead Halide Perovskites

Lead halide perovskites are being studied due to their favorable properties for light emitting and photovoltaic devices. The main challenge currently limiting the application of perovskite solar cells is the long-term stability, which has thermal, photo, and moisture stability weaknesses. This has led to the examination of two-dimensional inorganic-organic hybrid perovskites which offer increased stability and higher tunability of physical properties. However, these materials offer a decreased efficiency compared to their three-dimensional versions. Here we use density functional theory and excited state dynamics to examine the effects that varying the thickness of the perovskite layer has on the ground state and excited state photo-physical properties of the materials. Density matrix-based equation of motion is used to calculate the dynamics of electronic degrees of freedom. Nonadiabatic couplings were computed based on the on-the-fly approach along a molecular dynamics trajectory. We find that single perovskite layer models offer tunability, where the smaller perovskite layers have a larger bandgap, but show similar trends for non-radiative relaxation. As a method to compensate for the decreased efficiency that is observed for the two-dimensional hybrid perovskites, we take our single layer models and combine them into multiple layer models where we have two perovskite layers of different thickness separated by the organic layer of our model. Performing the same calculations as were performed on the single layer models we attempt to determine if our multiple layer models show photo-physical properties that would be indicative of the two single layer models separately.