Effects of Solvent Coordination Strength on the Morphology of Solution-Processed BiI₃ Thin Films

The remarkable performance of Pb halide perovskites in optoelectronic devices is complicated by concerns over their toxicity, which has motivated a search for Pb-free alternatives that have similar performance. Bi halides and halide perovskites have been predicted to be among the most promising Pb-free alternatives; however, their performance in devices has fallen short of expectations. One of the major challenges in fabricating efficient devices based on these Bi-based alternatives has been poor control over the morphology of thin films. Using BiI3 as a model system, we demonstrate that the film morphology and surface coverage are strongly dependent on the Lewis basicity of solvents that are used during deposition. We demonstrate that coordinating BiI3 with strong Lewis bases in tetrahydrofuran results in conformal films that have been difficult to achieve using conventional deposition techniques