Abstract
Perovskite solar cells fabricated by the two-step spin-coating method are highly sensitive to processing conditions, yet the role of precursor solution temperature remains poorly understood. Here, we systematically investigate how the temperatures of PbI(2) and formamidinium iodide (FAI) precursor solutions affect crystallization dynamics, surface morphology, phase formation, and optoelectronic properties of FAPbI(3) thin films. By combining microscopic characterization with in situ photoluminescence (PL) monitoring during annealing, we reveal distinct temperature-dependent nucleation, ripening, and film densification processes. PbI(2) solutions at intermediate temperatures (50-70 °C) yield compact underlayers that promote homogeneous conversion and suppress residual PbI(2), while low-temperature FAI solutions favor stabilization of the photoactive α-phase. Quantitative analysis of the in situ PL evolution clarifies the correlation between crystallization stages and optical out-coupling behavior. These results establish precursor solution temperature as a critical and practical parameter for controlling perovskite film formation in two-step deposition processes.