Benchmarking the Stability of Hole-Transport Materials for p–i–n Perovskite Solar Cells: The Importance of Interfacial Reactions

Practical implementation of hybrid perovskite solar cells (PSCs) depends on achieving decent lifetimes under realistic operational conditions. The degradation pathways in PSCs are effectively mitigated using charge-transport interlayers, which are usually designed based on empiric considerations. Herein, we present a systematic comparative study of a series of hole-transport materials for p–i–n perovskite solar cells such as CuI, CuSCN, MnS, CuOx, MoOx, VOx, WOx, and PTAA and reveal their influence on the light-induced degradation of MAPbI3 as a model perovskite absorber material. Using a set of complementary techniques, we demonstrate that WOx enables the best stack stability, while CuOx, on the contrary, strongly facilitates the degradation of the perovskite material due to the formation of PbO and other aging products. Furthermore, we show that such materials as CuOx, CuI, and CuSCN undergo severe intermixing with the deposited above perovskite absorber and, hence, could not form efficient hole-extraction layers in p–i–n perovskite solar cells. The obtained results provide important guidelines for the rational design of hole-transport materials for perovskite solar cells and feature the most promising candidates, which could enable the long-term operational stability of PSCs.