In situ Near‐Ambient Pressure X‐ray Photoelectron Spectroscopy Reveals the Influence of Photon Flux and Water on the Stability of Halide Perovskite

• Published in: ChemSusChem Vol. 13; no. 21; pp. 5722 - 5730
• Main Authors: Kot, M., Kegelmann, L., Köbler, H., Vorokhta, M., Escudero, C., Kúš, P., Šmíd, B., Tallarida, M., Albrecht, S., Abate, A., Matolínová, I., Schmeißer, D., Flege, J. I.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 06-11-2020; John Wiley and Sons Inc
• Subjects: Energy conversion efficiency; Field emission microscopy; field emission scanning electron microscopy; Field emission spectroscopy; Flux; Frenkel defects; Hysteresis; Illumination; Moisture content; near-ambient pressure X-ray photoelectron spectroscopy; perovskite; Perovskites; Photoelectron spectroscopy; Photoelectrons; photon-induced degradation; Photons; Photovoltaic cells; Pressure; Solar cells; Spectrum analysis; Stability; Water vapor
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.202001527

For several years, scientists have been trying to understand the mechanisms that reduce the long‐term stability of perovskite solar cells. In this work, we examined the effect of water and photon flux on the stability of CH3NH3PbI3 perovskite films and solar cells using in situ near‐ambient pressure X‐ray photoelectron spectroscopy (NAP‐XPS), field emission scanning electron microscopy (FESEM), and current density–voltage (J–V) characterization. The used amount of water vapor (up to 1 mbar) had a negligible impact on the perovskite film. The higher the photon flux, the more prominent were the changes in the NAP‐XPS and FESEM data; also, a faster decline in power conversion efficiency (PCE) and a more substantial hysteresis in the J‐V characteristics were observed. Based on our results, it can be concluded that the PCE decrease originates from the creation of Frenkel pair defects in the perovskite film under illumination. The stronger the illumination, the higher the number of Frenkel defects, leading to a faster PCE decline and more substantial hysteresis in the J‐V sweeps.
Solar cell deactivation: For similar exposures, the soaking of light proves more detrimental to the perovskite film than water vapor. Absorbed photons create Frenkel defects in the perovskite crystal. The number of created Frenkel defects depends strongly on the used illumination. The higher the photon flux, the higher the creation of Frenkel defects, and thus the stronger the degradation of power conversion efficiency and the stronger the hysteresis in the J–V characteristics.