Influence of DMSO/DMF ratio on the crystal growth and optical properties of Sn-based perovskite films

Perovskite solar cells (PSCs) are promising candidates for next-generation photovoltaic technology because of their high power conversion efficiency (PCE) and low production cost. However, the presence of lead in most PSCs raises concerns about their environmental impact. Tin (Sn)-based PSCs offer a less toxic alternative, but their performance still lags behind lead (Pb)-based counterparts. This study investigates the impact of solvent composition and annealing temperature on the crystal growth and optoelectronic properties of Sn-based perovskite (MA_0.2FA_0.8SnI₃) thin films. By varying the ratio of dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF) in the precursor solution, we systematically controlled the crystallization process, guided by the LaMer model. X-ray diffraction (XRD) and microscopy analyses revealed that solvent ratio and annealing temperature significantly influence the crystallinity and morphology of the films. High DMSO ratios promoted larger crystal formation, while high DMF ratios induced smaller crystals. Optical characterization revealed a correlation between film morphology and band gap, with deviations from the theoretical value attributed to voids and incomplete surface coverage. Our findings demonstrate the critical role of solvent engineering in optimizing the quality of tin-based perovskite films for enhanced solar cell performance.