Degradation by Exposure of Co-Evaporated CH3NH3PbI3 Thin Films

TL;DR

This study investigates the stability of co-evaporated CH3NH3PbI3 thin films under various environmental exposures, revealing their resistance to oxygen and dry air but susceptibility to water-induced degradation beyond a specific exposure threshold.

Contribution

It provides detailed analysis of the degradation mechanisms of CH3NH3PbI3 films under different environmental conditions using XPS and XRD techniques.

Findings

CH3NH3PbI3 is insensitive to oxygen and dry air.

Water exposure causes decomposition above a certain threshold.

Degradation results in PbI2, amorphous C, and O contamination.

Abstract

Degradation of co-evaporated CH3NH3PbI3 thin films was investigated with x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD) as the films were subjected to exposure of oxygen, dry air, ambient, or H2O. The co-evaporated thin films have consistent stoichiometry and crystallinity suitable for detailed surface analysis. The results indicate that CH3NH3PbI3 is not sensitive to oxygen. Even after 10^13 Langmuire (L, one L equals 10^-6 torr sec) oxygen exposure, no O atoms could be found on the surface. The film is not sensitive to dry air as well. A reaction threshold of about 2*10^10 L is found for H2O exposure, below which no CH3NH3PbI3 degradation takes place and the H2O acts as an n-dopant. Above the threshold, the film begins to decompose, and the amount of N and I decrease quickly, leaving the surface with PbI2, amorphous C and O contamination.