Effect of high energy proton irradiation on MAPbI3 films for space applications observed by micro-Raman spectroscopy

Abstract

Irradiation of samples with 10 MeV protons is a standard test for simulation of outer space environment in order to qualify devices and materials for space applications. Micro-Raman spectroscopy allows to determine the irradiation effect in methylammonium lead iodide (MAPbI3) thin films under ambient conditions and encapsulated. For the unprotected films, the vibrational modes matched previously reported lead oxide phonon frequencies and the appearance of superficial oxides was confirmed by EDAXS analysis. However, the Raman shifts corresponding to PbO were not observed for the irradiated encapsulated samples, indicating that oxidation occurs after surface exposure to ambient oxygen. Similar effects were observed by photooxidation where the superoxide highly reactive radical is involved in the oxidation mechanism. We propose that irradiation promotes excitation of the electronic cloud that readily reduces the surface adsorbed oxygen and later bonds to the accessible Pb atoms.