Tuning solvent co-ordination in Cs2SnI6 perovskite solution via the co-solvent dilution strategy for energy-efficient broadband photodetector arrays

With the advancement of perovskite research, there is a growing urgency to address the imperative need for practical applications while simultaneously tackling the enduring challenges of material reliability and lead (Pb) toxicity. The crystallization, morphology and optical properties of the resultant film and device performance during solution processing are heavily influenced by the solution-based intermediate, a state determined using the coordination between solute and solvent. Solvent-solute coordination is closely correlated with solvent characteristics including ionization capabilities, dielectric constant, hydrolysis, and reactivity with solutes. Deionized water (D-water) characterized by its high polarity, ionization capability, and dielectric constant, when used as a co-solvent with dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), facilitates stronger coordination with CsI/SnI4 species in Cs2SnI6 precursor solution. This enhanced coordination leads to improved solvation, precursor reactivity, and solution homogeneity. Incorporating an appropriate amount of D-water as a co-solvent into Cs2SnI6 precursor solution allows for tuning solvent coordination and control over the resulting thin film crystallization and morphology. The co-solvent diluted optimized Cs2SnI6 thin film leads to the fabrication of energy-efficient broadband 4 x 3 photodetector arrays ranging from UV to NIR giving a responsivity of 5.5 A W-1 at a substantially lower bias voltage of -0.1 V with stable operation stability in ambient air. These findings underscore the potential advantages of solution-processed Cs2SnI6 perovskites in various optoelectronic applications.