The effects of doping and coating on degradation kinetics in perovskites

• Published in: Solar energy materials and solar cells 2021-09, Vol.230, p.111142, Article 111142
• Main Authors: Wincukiewicz, A., Jasinski, J.B., Tokarczyk, M., Pietruszka, R., Godlewski, M., Kaminska, M.
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Atomic layer epitaxy; Chlorine; Coating; Coatings; Degradation; Degradation mechanism; Diffusion; Diffusion barriers; Diffusion rate; Durability; Energy conversion efficiency; Iodides; Iodine; Methylammonium lead halides; Oxygen; Perovskites; Photoelectron spectroscopy; Photoelectrons; Photovoltaic cells; Photovoltaics; Solar cells; Stability analysis; X ray photoelectron spectroscopy; X-ray diffraction
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2021.111142

In the last few years, perovskite-based solar cells have seen rapid improvements of their power conversion efficiencies (PCE) that have already reached silicon cell values. The commercial use of perovskite cell technology remains, however, a challenge due to durability issues. In fact, perovskite films when exposed to moisture and oxygen undergo degradation within a couple of hours or days. In order to address these problems, several strategies have been developed in recent years, including surface passivation and coating. Herein, we analyze and compare two perovskite stability improvement approaches, each aimed at the reduction of the oxygen diffusion, one by adding chlorine to perovskite precursors in order to block iodine vacancy sites, and the other by coating the perovskite layers with protective Al2O3 films using Atomic Layer Deposition (ALD). The study provides an experimental verification of the degradation mechanism linking it to oxygen diffusion into the perovskite films. As shown by X-ray photoelectron spectroscopy (XPS) analysis, the addition of chlorine into the iodine-based perovskite film slows down the oxygen diffusion, while X-ray diffraction (XRD) measurements show improved stability of such iodide perovskite with chlorine addition. Characteristic times for oxygen diffusion into subsurface region as well as for degradation process of film volume are provided and discussed. XRD measurements are also used to show that an additional significant stability improvement can also be achieved when the films are coated with a protective ALD Al2O3 layer. [Display omitted] •A systematic study of the degradation kinetics in hybrid perovskites.•Two stability enhancement strategies applied: (i) addition of Cl during synthesis and (ii) use of a protective coating layer.•The process of degradation is successfully described by simple exponential kinetics.•The addition of chlorine slows down the oxygen diffusion-related degradation by approximately 3 times.•The use of a thin (50 nm) Al2O3 protective layer slows down the degradation by at least one order of magnitude.