Exploring the Fundamental Optical Properties of Methyl-Ammonia Lead Iodide Solar Cell Materials...

"Exploring the Fundamental Optical Properties of Methyl-Ammonia Lead Iodide Solar Cell Materials: A Computational Study" -- Joshua Leveillee, University of Illinois Urbana-Champaign

Methyl-ammonia lead-iodide (MAPbI3) perovskite solar cells have rapidly increased in photo-conversion efficiency and engineering synthesis viability over the past four years. Despite experimental progress, the underlying physics of how creation, lifetime, and separation of light-induced electron-hole pairs and the connection to high device efficiency in these unique materials is still heavily debated in the scientific community. In this study, we take a first principles approach to understanding the fundamental electronic-optical behavior of these perovskite solar cell materials. We use density functional theory (DFT) to obtain equilibrium atomic geometries and calculate the ground state of the different organic-metal halide perovskite material. Then, we use the Bethe-Salpeter equation (BSE) to calculate the optical polarization function. Finally, we compute optical and absorption spectra including excitonic effects. The Blue Waters Super Computer allows our team to rapidly compute large excitonic Hamiltonians, using the entire memory of several tens of nodes, and in some cases even pushing the memory available. We find that the organic cation, methyl-ammonia, potentially plays a central role by contributing high lattice screening of to the electron-hole interaction. This effect allows easier separation of electrons and holes. Charges may then flow freely, leading to efficient solar cell materials.