(757e) Rate Orders and Rate Constants for Hybrid Perovskite Degradation with Water and Oxygen

Halide perovskites (HPs) have emerged as promising absorbing materials for photovoltaics (PVs), having achieved 25.5% record power conversion efficiency (PCE) in single junction PVs and 29.5% PCE in tandem PVs with silicon. To achieve commercial cost targets for PV devices ($0.02/kWh, per the DOE SunShot program), commercial modules made from HPs will need >30 year verifiable field lifetimes. However, HPs undergo rapid decomposition under humidity, oxygen, light, and temperature, which will limit the operational service lifetimes of HP PV modules. In order to predict long-time material stability of perovskite thin films in optoelectronic devices, it is essential to quantitatively understand the material degradation mechanisms of HPs in combinations of oxygen, moisture, and illumination. Here, we use in-situ degradation testing of methylammonium lead iodide (CH₃NH₃PbI₃, MAPbI₃) perovskite in controlled humidity, oxygen, light, and temperature to determine MAPbI₃ degradation rates over a range of environments. Using rate constants calculated from initial degradation rate, we identify two condition space regimes with different predominant modes of MAPbI₃ degradation. In dry air, MAPbI₃ degradation is dominated by a photooxidation reaction pathway that follows Arrhenius kinetics with an activation energy of 0.48 eV. In 60% RH air, MAPbI₃ decomposition is predominantly driven by humidity-accelerated photooxidation, with faster degradation rates than dry air conditions and an activation energy of 0.08 eV. In both photooxidation- and humidity-driven degradation regimes, we identify reaction rate orders for water, oxygen, and light intensity/photoexcited electrons. Using this data, we propose a unified mechanism of initial degradation of MAPbI₃ films and derive a rate expression for MAPbI₃ degradation that accurately expresses these reaction rate orders in both humidity-driven and photooxidation-driven decomposition regimes.