Design rules for defect-free 3D perovskite-perovskite interfaces

Abstract

The understanding of defect dynamics at all 3D (bulk phase) hybrid organic-inorganic perovskite heterojunctions is necessary for improving the stability and performance of perovskite based devices. In this work, using density functional theory calculations, we study the effect of interfacial defects on the stability and electronic properties of a bromine based lead-tin perovskite heterojunction. We find that antisite defects are not stable at this interface and relax to form Pb/Sn interstitial and halide vacancy defects. Interstitial Pb/Sn defects result in the formation of dimer bonds along with associated mid bandgap states. The halide vacancy defects enhance the interaction between the neighboring B site cations at the interface and result in the formation of charge localizing mid bandgap states. Our results indicate that the bulk Pb-Sn perovskite heterojunction is vulnerable to the formation of charge localizing interfacial defects and adopting a Br rich synthesis condition is necessary to obtain a heterojunction with promising optoelectronic properties.