A facile one‐step solution synthesis of Cs2SnI6−xBrx using less‐toxic methanol solvent for application in dye‐sensitized solar cells

Summary Cs2SnX6 (X = I, Br, and Cl), a vacancy‐ordered double perovskite, has recently emerged as a promising lead‐free perovskite for optoelectronic applications. The low quality of solution‐processed Cs2SnX6 perovskites, on the other hand, precludes further improvement of their performance in the devices. In this work, we developed a facile one‐step solution strategy for synthesizing high‐quality Cs2SnI6−xBrx material with the less‐toxic methanol solvent. A series of Cs2SnI6−xBrx perovskites was synthesized by carefully tuning each stage of the process and using thorough structural and optical characterizations as feedback. We identified two critical parameters that affect the quality of perovskite material through this detailed characterization: the reactant ratio and the annealing temperature. The optimal precursor ratio for the synthesized perovskite was determined to be 1:1 with an annealing temperature of 100°C. Leveraging this, we investigated the optimized perovskite material as a hole transport material (HTM) in a dye‐sensitized solar cell (ss‐DSSC) and achieved an outstanding PCE of 3.2% without using any modifiers. We envisage that our findings may open the door for the growth of nonhazardous synthesis approaches for Sn‐based optoelectronic devices. Novelty Statement The preparation methods and high costs associated with the organic HTMs and the use of toxic solvents are the major obstacles to developing efficient materials for photovoltaic applications. With the possibility of commercialization of solution‐processable solar cells, it is critical to find less hazardous perovskite formation approaches. Leveraging this, we developed a facile one‐step solution method and investigated the potential of Cs2SnI6−xBrx perovskite as a promising hole transport material (HTM) for solid‐state dye‐sensitized solar cell (ss‐DSSC). Schematics illustrating the facile synthesis of Cs2SnI6−xBrx perovskite in a less‐toxic methanol solvent, as well as the highest IV‐parameters obtained when used as HTM in dye‐sensitized solar cells.