Mechanism of Reversible Trap Passivation by Molecular Oxygen in Lead-Halide Perovskites

Abstract

The long lifetime and diffusion lengths of carriers and the defect tolerance of lead-halide perovskites are at the heart of their high efficiency in solar cell devices. Drastic photoluminescence quantum yield enhancements upon exposure of perovskites to molecular oxygen have been reported. Despite the general consensus about a direct role of oxygen in tuning the optical properties of perovskites, the microscopic origin of this effect is still under debate. On the basis of state-of-the-art density functional theory modeling, we propose a mechanism whereby oxygen effectively inactivates deep hole traps associated with iodide interstitials by forming moderately stable oxidized products. The small energy gain associated with trap passivation is in agreement with the reversibility of the process. Vibrational analysis points at the emergence of new active modes related to oxidized defect products, spanning the 300–700 cm–1 frequency range, which may be probed experimentally.