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Europium-Doped CsPbI2Br for Stable and Highly Efficient Inorganic Perovskite Solar Cells

2019    Xiang, Wanchun; Wang, Zaiwei; Kubicki, Dominik J.; Tress, Wolfgang; Luo, Jingshan; Prochowicz, Daniel; Akin, Seckin; Emsley, Lyndon; Zhou, Jiangtao; Dietler, Giovanni; Graetzel, Michael; Hagfeldt, Anders

All-inorganic perovskite films hold promise for improving the stability of perovskite solar cells (PSCs). However, the 3D alpha phase of narrow-bandgap inorganic perovskites is thermodynamically unstable at room temperature, limiting the development of high-performance inorganic PSCs. Here, we show that europium doping of CsPbI2Br stabilizes the alpha phase of this inorganic perovskite at room temperature. We rationalize it by using solid-state nuclear magnetic resonance and high-angle annular dark-field scanning transmission electron microscopy, which show that europium is incorporated into the perovskite lattice. We demonstrate amaximum power-conversion efficiency of 13.71% for an inorganic PSC with the CsPb0.95Eu0.05I2Br perovskite and alpha stable power output of 13.34%. Using electroluminescence we show that incorporation of europium reduces non-radiative recombination, resulting in high open-circuit voltage of 1.27 V. The devices retain 93% of the initial efficiency after 370 hr under 100 mW cm(-2) continuous white light illumination under maximum-power point-tracking measurement.