Fig. 3: Formation mechanism of homogeneous structural perovskite films.

a Real-time monitoring of perovskite wet films morphology evolutions over time with an optical microscope in air (RH～65%, T～25 °C). Scalebars, 200 µm. b Real-time PL intensity at 760 nm of perovskite wet films during high-speed spin-coating in air, simulating the process of VASP. c Real-time PL intensity at 760 nm of semi-wet films during annealing in air. d Solvent evolution in the upper, lower, and whole layers of control and PZ-treated perovskite precursor films, tracked by GD-OES. e Proposed mechanism for scalable perovskite film preparation with homogeneous structure, integrating solvent evolution, crystallization kinetics, and colloidal distribution. The schematic illustrates that when the crystallization rates of the upper and lower layers of the wet films are more consistent, it is prone to form large, monolithic grains. However, even with notable differences in crystallization rates, it is still probabilistic to form such grain structures within a specific range.