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

Abstract

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.