“…36,38,114,115 In a one-step spin coating process, the subtle changes in characteristics of perovskite precursor solution, involving precursor concentration, stoichiometric ratio, existence state of solute, and solvent choice enable a substantial variation in perovskite crystallization, which could determine the microstructure of a final perovskite crystal. 38,116–118 For example, the concentration-dependent grain growth of perovskite thin films was observed in the perovskite precursor solutions with different concentrations. 119 During perovskite nucleation, slightly larger nuclei tend to appear at higher precursor concentrations due to an increased system entropy Δ S .…”