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Abstract
Optical absorbance is used to study the kinetics of methylammonium lead iodide (MAPbI3) thin film degradation in response to combinations of moisture, oxygen, and illumination over a range of temperatures. 105 degradations were conducted over 41 unique environmental conditions. We discover that water acts synergistically with oxygen in a water-accelerated photo-oxidation (WPO) pathway. This pathway is the dominant pathway at 25 °C and is 10, 100, 1000, and >1000 times faster than dry photooxidation (DPO), degradation via hydrate formation, thermal degradation, and blue light degradation, respectively. We find that the rate determining step for DPO is proton abstraction from methylammonium while for WPO it is proton abstraction from water, which occurs at a faster rate and results in water acting as an accelerant for photooxidation of MAPbI3. A full kinetic rate equation is derived and fitted to the data to determine activation energies and rate constants.
Supplementary materials
Title
Supporting Information for Water-Accelerated Photo-oxidation of CH3NH3PbI3 Perovskite: Mechanism, rate orders, and rate constants
Description
Experimental details; supporting discussion and text; quantification of absorbance and reflectance as a function of degradation extent; thickness-dependent degradation rate; degradation rates in dark environments; how convective flow rate of MAPbI3 impacts degradation rate; raw ΔA vs time data and linear fits of all data used in Figures 2-4, quantifying “pre-anneal” used to dry thin films before limiting case experiments; J-V curves of devices made from MAPbI3 films and morphology; illumination intensity vs photoconductivity plot.
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