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Mobile-Ion-Induced Degradation of Organic Hole-Selective Layers in Perovskite Solar Cells

Zhao, Yicheng, Zhou, Wenke, Tan, Hairen, Fu, Rui, Li, Qi, Lin, Fang, Yu, Dapeng, Walters, Grant, Sargent, Edward H., Zhao, Qing
The Journal of Physical Chemistry C 2017 v.121 no.27 pp. 14517-14523
cations, electric field, photovoltaic cells, physical chemistry, semiconductors
Organometal halide perovskites are mixed electronic–ionic semiconductors. It is imperative to develop a deeper understanding of how ion-migration behavior in perovskites impacts the long-term operational stability of solar cells. In this work, we found that ion penetration from the perovskite layer into the adjacent organic hole-selective layer is a crucial cause of performance degradation in perovskite solar cells. The monovalent cation, namely, methylammonium (MA⁺), is the main ion species that penetrates into the organic hole-selective layer of Spiro-MeOTAD because of the built-in electric field during operation. The incorporation of MA⁺ induces deep-level defects in the Spiro-MeOTAD layer and thereby deteriorates the hole-transporting ability of Spiro-MeOTAD, degrading solar cell performance. Our work points to two ways to improve the stability of perovskite solar cells: one is to insert a compact ion-blocking layer between Spiro-MeOTAD and perovskite, and the other is to find a hole-selective layer that is insensitive to extraneous ions (MA⁺).