All‐Inorganic CsPb 1− x Ge x I 2 Br Perovskite with Enhanced Phase Stability and Photovoltaic Performance

Compared with organic‐inorganic perovskites, all‐inorganic cesium‐based perovskites without volatile organic compounds have gained extensive interests because of the high thermal stability. However, they have a problem on phase transition from cubic phase (active for photo‐electric conversion) to orthorhombic phase (inactive for photo‐electric conversion) at room temperature, which has hindered further progress. Herein, novel inorganic CsPb 1− x Ge x I 2 Br perovskites were prepared in humid ambient atmosphere without a glovebox. The phase stability of the all‐inorganic perovskite was effectively enhanced after germanium addition. In addition, the highest power conversion efficiency of 10.8 % with high open‐circuit voltage ( V OC ) of 1.27 V in a planar solar cell based on CsPb 0.8 Ge 0.2 I 2 Br perovskite was achieved. Furthermore, the highest V OC up to 1.34 V was obtained by CsPb 0.7 Ge 0.3 I 2 Br perovskite, which is a remarkable record in the field of all‐inorganic perovskite solar cells. More importantly, all the photovoltaic parameters of CsPb 0.8 Ge 0.2 I 2 Br perovskite solar cells showed nearly no decay after 7 h measurement in 50–60 % relative humidity without encapsulation.