Sequentially vacuum evaporated high-quality CsPbBr3 films for efficient carbon-based planar heterojunction perovskite solar cells

All-inorganic CsPbBr3 perovskite has triggered great interests in photovoltaic field owing to its superior stability. However, the uncontrollable CsPbBr3 film growth in solution always leads to a poor film quality with low phase-purity as well as many surface and bulk defects. Herein, we demonstrate an environmentally friendly non-solution route to fabricate high-quality CsPbBr3 films for carbon-based planar perovskite solar cells. By precisely tuning the thickness ratio of the evaporated CsBr to PbBr2 precursors (r), the dominant phase conversion of the cesium lead bromide perovskites from PbBr2-rich CsPb2Br5 (r <= 12:7) to CsPbBr3 (r = 12:8), and further to CsBr-rich Cs4PbBr6 (r >= 12:9) are achieved. The optimized CsPbBr3 perovskites are highly phase-pure and crystallized with ultra-high light absorption ability. The as-prepared CsPbBr3 films also exhibit a dense and uniform morphology with large grain sizes and monolayer-vertical aligned grains. The corresponding devices deliver a champion PCE of 7.58%, which is an excellent efficiency among carbon-based CsPbBr3 cells with evaporated CsPbBr3 light absorbers. The large-area (1 cm(2)) devices also achieve an efficiency of 6.21%. Moreover, the unencapsulated CsPbBr3 devices present superior moisture and thermal stabilities. Our work provides a facile approach to fabricate high-quality and large-area CsPbBr3 films for highly efficient solar cells, light-emitting diodes and photodetectors.