(171a) Solution-Processed, Lead-Free Metal Iodide Thin Films for Photovoltaic Applications
We have synthesized and deposited metal iodide films of materials such as BiI3Â and SbI3 thin films were using solution-based methods. We have found that Lewis bases such as THF and DMF readily form Lewis acid-base adducts with BiI3, which gives them high solubility in these solvents at high concentrations (<400 mg/mL) suitable for spincoating thin films of BiI3. We find that exposure to solvent during processing can have a dramatic effect on film morphology. For example, solvent annealing BiI3 thin films under relatively mild temperatures (â?¤ 100 Â°C) resulted in pronounced grain growth and recrystallization of the film. The thin films were chemically stable for at least several months and can withstand extended (several hours) annealing at temperatures below 150 Â°C. Annealing in air after spincoating was found to be beneficial to photovoltaic device performance due to the formation of a BiOI layer at the BiI3 surface which facilitates hole transport. In non-optimized BiI3 solar cells, we have achieved power conversion efficiencies of 1.0 % demonstrating the potential of BiI3 as a nontoxic, all-inorganic metal halide photovoltaic absorber layer.