Impact of Spin-Coating Temperature on Morphology of Pb-Based Mixed Ion Perovskite Films and Their Solar Cell Performance

Abstract

Performance of metal halide perovskite solar cells depends largely on the perovskite film quality. Here, we demonstrate the impact of spin-coating temperature under anhydrous conditions on Pb-based mixed ion perovskite film morphology, crystal structure, optical properties, and their solar cell performance. The perovskite films prepared at spin-coating temperatures of ≤27 °C under anhydrous conditions showed pinhole-free and dense grain structures, while the perovskite films prepared at ≥35 °C showed formation of island/particles with void areas. This temperature dependence of the film formation mechanism can be explained by classical heterogeneous nucleation and growth theory with modified LaMer diagrams. In contrast, indistinguishable temperature dependence was found for charge carrier dynamics including electron and hole transfer rates and yield and charge carrier mobility inside the perovskite films. The highest solar cell performance was obtained for a solar cell based on a perovskite film prepared at around 25 (22–27) °C, suggesting that the solar cell performance is essentially controlled by the perovskite film morphology, but not by the charge carrier dynamics. These results also suggest that the process to preheat precursor solution is not required to obtain pinhole-free and dense perovskite films under anhydrous conditions. Furthermore, the optimum temperature to obtain pinhole-free perovskite films under anhydrous conditions was compared with the optimum temperature previously obtained under different humidity conditions, indicating that the optimum temperature rises with the increase in humidity.