Reaction‐Diffusion and Crystallization Kinetics Modulation of Two‐Step Deposited Tin‐Based Perovskite Film via Reducing Atmosphere

The two‐step deposition method effectively mitigates the efficiency decline observed in tin‐based perovskite solar cells (TPVSCs) with increasing cell area, stemming from film in‐homogeneity. However, the high solubility of SnI2 in the conventionally used solvent isopropyl alcohol, coupled with the absence of effective modulation of reaction‐diffusion process, results in inadequate film coverage and conversion. In this study, we introduce formic acid as the second‐step solvent and introduce dithiothreitol (DTT) to regulate reaction‐diffusion/crystallization kinetics meticulously. Moreover, this research underscores a fundamental principle that the suitable binding energy ranging from ‐1.38 to ‐10.10 kcal/mol between ligands and Sn2+ significantly enhances the effectiveness of two‐step crystallization control. Notably, a uniform perovskite film is achieved on large‐scale substrate, and TPVSCs processed with DTT exhibit the highest efficiencies of 12.68% for 0.04 cm2 device and 11.30% for 1 cm2 device among tin‐based perovskite devices in two‐step sequential deposition method, even in the absence of dimethyl sulfoxide. This study lays the groundwork for the potential scale‐up development of lead‐free perovskite solar cells.