Inkjet‐Printing Controlled Phase Evolution Boosts the Efficiency of Hole Transport Material Free and Carbon‐Based CsPbBr₃ Perovskite Solar Cells Exceeding 9%

Hole transport material free carbon‐based all‐inorganic CsPbBr 3 perovskite solar cells (PSCs) are promising for commercialization due to its low‐cost, high open‐circuit voltage ( V oc ) and superior stability. Due to the different solubility of PbBr 2 and CsBr in conventional solvents, CsPbBr 3 films are mainly obtained by multi‐step spin‐coating through the phase evolution from PbBr 2 to CsPb 2 Br 5 and then to CsPbBr 3 . The scalable fabrication of high‐quality CsPbBr 3 films has been rarely studied. Herein, an inkjet‐printing method is developed to prepare high‐quality CsPbBr 3 films. The formation of long‐range crystalline CsPb 2 Br 5 phase can effectively improve phase purity and promote regular crystal stacking of CsPbBr 3 . Consequently, the inkjet‐printed CsPbBr 3 C‐PSCs realized PCEs up to 9.09%, 8.59% and 7.81% with active areas of 0.09, 0.25, and 1 cm 2 , respectively, demonstrating the upscaling potential of our fabrication method and devices. This high performance is mainly ascribed to the high purity, strong crystal orientation, reduced surface roughness and lower trap states density of the as‐printed CsPbBr 3 films. This work provides insights into the relationship between the phase evolution mechanisms and crystal growth dynamics of cesium lead bromide halide films.