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

All-inorganic CsPbBr 3 perovskite has triggered great interests in photovoltaic field owing to its superior stability. However, the uncontrollable CsPbBr 3 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 CsPbBr 3 films for carbon-based planar perovskite solar cells . By precisely tuning the thickness ratio of the evaporated CsBr to PbBr 2 precursors ( r ), the dominant phase conversion of the cesium lead bromide perovskites from PbBr 2 -rich CsPb 2 Br 5 ( r  ≤ 12:7) to CsPbBr 3 ( r  = 12:8), and further to CsBr-rich Cs 4 PbBr 6 ( r  ≥ 12:9) are achieved. The optimized CsPbBr 3 perovskites are highly phase-pure and crystallized with ultra-high light absorption ability. The as-prepared CsPbBr 3 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 CsPbBr 3 cells with evaporated CsPbBr 3 light absorbers. The large-area (1 cm 2 ) devices also achieve an efficiency of 6.21%. Moreover, the unencapsulated CsPbBr 3 devices present superior moisture and thermal stabilities. Our work provides a facile approach to fabricate high-quality and large-area CsPbBr 3 films for highly efficient solar cells, light-emitting diodes and photodetectors .