Probe Decomposition of Methylammonium Lead Iodide Perovskite in N2 and O2 by in Situ Infrared Spectroscopy.

Packaging methylammonium lead iodide perovskite (MAPbI3)-based solar cells with N2 or dry air is a promising solution for its application in outdoor photovoltaics. However, the effect of N2 and O2 on the decomposition chemistry and kinetics of MAPbI3 is not yet well-understood. With in situ Fourier transform infrared spectroscopy measurements, we show that the effective activation energy for the degradation of MAPbI3 in N2 is ∼120 kJ/mol. The decomposition of MAPbI3 is greatly accelerated by exposure to O2 in the dark. As a result of the synergistic effect between O2 and a HeNe laser (633 nm), the degradation rate is further increased with photon flux. This synergistic effect reduces the effective activation energy of degradation of MAPbI3 to ∼50 kJ/mol. The solid decomposition products after annealing in N2 and O2 at 150 °C or below do not have absorbance between 650 and 4000 cm-1.