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 (HTM) free carbon-based all-inorganic CsPbBr3 perovskite solar cells (PSCs) are promising for commercialization due to its low-cost, high open-circuit voltage (Voc) and superior stability. Due to the different solubility of PbBr2 and CsBr in conventional solvents, CsPbBr3 films are mainly obtained by multi-step spin-coating through the phase evolution from PbBr2 to CsPb2Br5 and then to CsPbBr3. The scalable fabrication of high-quality CsPbBr3 films has been rarely studied. Herein, an inkjet-printing method is developed to prepare high-quality CsPbBr3 films. The formation of long-range crystalline CsPb2Br5 phase can effectively improve phase purity and promote regular crystal stacking of CsPbBr3. Consequently, the inkjet-printed CsPbBr3 C-PSCs realized PCEs up to 9.09%, 8.59% and 7.81% with active areas of 0.09, 0.25 and 1 cm², 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 CsPbBr3 films. This work provides insights into the relationship between the phase evolution mechanisms and crystal growth dynamics of cesium lead bromide halide films.