Water assisted formation of highly oriented CsPbI 2 Br perovskite films with the solar cell efficiency exceeding 16

Cesium lead halide perovskites are promising alternatives as light-absorbing materials for achieving perovskite solar cells with excellent thermal stability, but their inferior power conversion efficiency (PCE) and ambient instability are impeding their application. In this work, we show that liquid water can assist the formation of CsPbI 2 Br perovskites under the synergetic adsorption of H 2 O and dimethylsulfoxide (DMSO), which enabled uniform, [100] oriented CsPbI 2 Br films with a grain size up to 4.4 μm. It was found that a suitable amount of H 2 O helps desorb the DMSO molecules, and thus favours the formation of a cubic perovskite phase from DMSO complexed intermediates. Perovskite solar cells based on our strategy delivered an optimized PCE of 16.47% with a high open-voltage of 1.33 V, as well as good device stability against humidity, light and heat.