Effects of substrate temperature on the crystallization process and properties of mixed-ion perovskite layers

The morphology and crystalline quality of perovskite layers are crucial to fabricate high efficiency and high stability perovskite solar cells (PSCs). In this work, we investigated how the substrate temperature influences the crystallization process of the mixed-ion perovskite material (FAPbI(3))(0.85)(MAPbBr(3))(0.15). The intermediate phase formation, the following perovskite phase transformation, and the film morphology were studied by spin-coating the perovskite material onto hot substrates using microscopy and X-ray diffraction methods. The results show that elevating the substrate temperature alters the morphology of perovskite films from pure dendritic to dendritic/ island co-existing structures. The appearance of islands increases the defect density in the perovskite layer and deteriorates the device performance. The substrate temperature has to be controlled in a certain range to form a high crystallinity perovskite layer. The morphology evolution mechanism was also discussed. This work provided a better understanding of the roles of DMSO and temperature in the crystallization process, which will provide more opportunities and guidance for the upscaling of mixed-ion perovskite solar cell manufacturing.