Temperature dependent optical properties of methylammonium lead iodine perovskite: Influence of the initial degradation process

Abstract

The degradation of methylammonium lead iodine perovskite was studied by analyzing its optical properties at temperatures ranging from room temperature to 13 K, on three different days. After the measurements, X-ray diffraction analysis revealed the presence of trace amounts of PbI2, indicating degradation. We identified primarily blue light exposure and secondarily air exposure as possible environmental degradation factors. A phase transition from tetragonal (high temperature) to orthorhombic (low temperature) is observed. The phase transition temperature increases from 110 K to 140 K as the degradation progresses. The photoluminescence spectra present a single emission peak for the tetragonal phase due to free exciton recombination. At the orthorhombic phase the photoluminescence intensity increases without accompanying the shift associated with the phase change, and a second lower energy peak emerges at temperatures of 60 K and below, that is assigned to the localization of the exciton in defects. As the degradation progresses, the low energy peak becomes visible at higher temperatures, reaching 120 K for the third day. Conversely, the high energy peak initially visible even at 15 K, disappearing at temperatures below 80 K during the third day.