Stable and High-Efficiency Methylammonium-Free Perovskite Solar Cells.

Gao, Xiao-Xin; Luo, Wen; Zhang, Yi; Hu, Ruiyuan; Zhang, Bao; Züttel, Andreas; Feng, Yaqing; Nazeeruddin, Mohammad Khaja · Adv Mater · 2020

basic_science · Level V

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Abstract

Organic-inorganic metal halide perovskite solar cells (PSCs) have achieved certified power conversion efficiency (PCE) of 25.2% with complex compositional and bandgap engineering. However, the thermal instability of methylammonium (MA) cation can cause the degradation of the perovskite film, remaining a risk for the long-term stability of the devices. Herein, a unique method is demonstrated to fabricate highly phase-stable perovskite film without MA by introducing cesium chloride (CsCl) in the double cation (Cs, formamidinium) perovskite precursor. Moreover, due to the suboptimal bandgap of bromide (Br<sup>-</sup> ), the amount of Br<sup>-</sup> is regulated, leading to high power conversion efficiency. As a result, MA-free perovskite solar cells achieve remarkable long-term stability and a PCE of 20.50%, which is one of the best results for MA-free PSCs. Moreover, the unencapsulated device retains about 80% of the original efficiencies after a 1000 h aging study. These results provide a feasible approach to enhance solar cell stability and performance simultaneously, paving the way for commercializing PSCs.