XPS evidence of degradation mechanism in CH 3 NH 3 PbI 3 hybrid perovskite

• Published in: Journal of physics. Condensed matter 2020-02, Vol.32 (9), p.095501
• Main Authors: Zhidkov, Ivan S, Poteryaev, Alexander I, Kukharenko, Andrey I, Finkelstein, Larisa D, Cholakh, Seif O, Akbulatov, Azat F, Troshin, Pavel A, Chueh, Chu-Chen, Kurmaev, Ernst Z
• Format: Article
• Language: English
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/1361-648X/ab576f

In this study, we investigate the photo-/thermal degradation mechanism of hybrid perovskites by using x-ray photoelectron (XPS) valence band (VB) spectra coupling with density functional theory (DFT) calculations. Herein, CH NH PbI is respectively subjected to irradiation with visible light and annealing at an exposure of 0-1000 h. 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 the formation of PbI as the product of photo/thermal degradation. The comparison of the XPS VB spectra of irradiated and annealed perovskites with the DFT calculations of CH NH PbI and PbI compounds have showed a systematic decrease in the contribution of I-5p states, which allows us to determine the respective threshold for degradation, which is 500 h for light irradiation and 200 h for annealing. This discrepancy might be due to the fact that the relaxation of thermal excitations of the system is carried out only by the phonons (which are non-radiative physical processes) while the radiative processes occurred during the photoexcitation will elastically or inelastically divert part of the external energy from the system to reduce its impact on perovskite degradation.