Molecular Insights into Water Vapor Adsorption and Interfacial Moisture Stability of Hybrid Perovskites for Robust Optoelectronics

SC Lin and C Chen and LL Zhao and MC Wang and JF Wang and HH Zhou and CY Zhao, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 175, 121334 (2021).

DOI: 10.1016/j.ijheatmasstransfer.2021.121334

Understanding interfacial mass transfer processes, such as the water vapor adsorption-induced degradation of hybrid perovskites, is vital for improving the durability and performance of their optoelectronic devices in the ambient atmosphere with humidity. In this paper, vapor adsorption on prototypical MAPbI(3), terminated by MAI(0) and PbI2(0) surface, at different relative humidity (RH) levels is studied using grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The resulting vapor adsorption isotherms match the Brunauer-Emmett- Teller (BET) adsorption model with heats of adsorption of 0.510 and 0.609 eV, respectively, for water monolayers on MAI(0) and PbI2(0). The formation of water monolayer on MAI(0) (for RH >= 30%) is consistent with its lower hydrophilicity compared to PbI2(0) (for RH >= 10%), reflected from the larger water contact angle predicted. Based on predicted water surface coverages at various RHs, the moisture- induced surface degradation kinetics is studied using MD simulations and transition-state theory. Humidity has a minor impact on the degradation energy barriers due to the similar ion removal pathway by water solvation, but strongly affects the ion dissociation rates through the frequency of attempts to attack surface ions. MAI(0) is more vulnerable against water than PbI2(0), despite its lower hydrophilicity, implying that long-term exposed MAPbI(3) are mostly terminated by PbI2(0). Furtherly, averaged degradation material loss rates of 5.8 similar to 13.1 mu m/s are estimated at 30 similar to 80% RH levels and 300 K, which is consistent with experiment observations. Finally, we offer a picture for the water-diffusion-based degradation mechanism and elucidate interesting hydrogen-bonding features at the vapor-MAPbI(3) interface. This research provides quantitative insights into the inherent vapor-perovskite interactions and addresses the moisture instability mechanisms in metal halide perovskites towards the rational design of water-resistant, long term stable and efficient optoelectronic devices. (C) 2021 Elsevier Ltd. All rights reserved.

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