Temperature effects on surface textures of CsPbIBr2 films for perovskite solar cells

The quality of perovskite crystallization directly determines the performance of perovskite solar cells (PSCs). However, there is a lack of research on the bottom crystallization of perovskite films of PSCs. Here, by simply controlling the annealing temperature of perovskite films, CsPbIBr2 films with different surface textures on both the top and bottom sides were obtained, respectively. It is found that dimethyl sulfoxide (DMSO), which is widely used to enhance the crystallization of perovskite films, cannot be completely removed under 160 °C, leading to the formation of snowflower-like textures (SFT) composed of countless pinholes on the upper and lower surfaces of the perovskite film and the existence of obvious cavities between the perovskite layer and the TiO2 layer. This is mainly due to the dissolution of CsPbIBr2 in the residual DMSO. On the contrary, CsPbIBr2 films with compact and smooth surface textures (CST) on both the top and bottom sides can be achieved under 250 °C. For PSCs, the CST-based champion device (9.66%) exhibits higher efficiency and better stability than the SFT-based one (3.69%), primarily due to the high quality film with superior carrier separation and migration properties. The proposed understanding and accurate control of the perovskite crystal growth process are of great significance to the future development of PSCs.