Study of Structure and Electronic Properties of Hetero-Interfaces for Photovoltaic Applications

The photovoltaic performance of hybrid halide perovskite is linked to the atomic and electronic structure at the interface between carrier generating perovskite layer and the electron transport layer (ETL). With the help of ab-initio molecular dynamics simulations and density functional theory calculations, we have determined the structure, electronic, and transport properties at the perovskite/ETL interface. As a model system, we used CH₃NH₃PbI₃ hybrid halide perovskite and phenyl-C61-butyric acid methyl ester (PCBM) as the ETL. Our results reveal that PCBMs prefer to attach to the perovskite surface via the ester moiety. However, bonding at the interface is sensitive to the chemical composition at the surface termination (CH₃NH₃I vs. PbI₂) of the perovskite. For PbI₂ terminations, the carbonyl O atom of PCBM forms a bond with Pb atom on perovskite surface, whereas for CH₃NH₃I terminations methyl H on PCBM site forms bonds with I atom on the perovskite surface. Different preferences in bonding at the interface leads to distinct electronic and transport properties across two chemical terminations.