XPS evidence of degradation mechanism in hybrid halide perovskites

TL;DR

This study uses XPS measurements to investigate degradation in hybrid halide perovskites, revealing PbI2 formation and identifying degradation thresholds under light and heat exposure.

Contribution

It provides detailed XPS analysis correlating degradation with specific spectral changes and establishes degradation time thresholds for irradiation and annealing.

Findings

Decrease in I:Pb ratio indicates PbI2 formation during degradation.

Degradation thresholds are 500 hours for light and 200 hours for heat.

XPS spectra combined with DFT calculations elucidate degradation mechanisms.

Abstract

The paper presents the results of measurements of XPS valence band spectra of SiO2/MAPbI3 hybrid perovskites subjected to irradiation with visible light and annealing at an exposure of 0-1000 hours. It is found from XPS survey spectra that in both cases (irradiation and annealing) a decrease in the I:Pb ratio is observed with aging time, which unambiguously indicates PbI2 phase separation as a photo and thermal product of degradation. The comparison of the XPS valence band spectra of irradiated and annealed perovskites with density functional theory calculations of the MAPbI3 and PbI2 compounds have shown a systematic decrease in the contribution of I 5p-states and allowed us to determine the threshold for degradation, which is 500 hours for light irradiation and 200 hours for annealing.