Local optoelectronic characterization of solvent annealed lead-free bismuth-based perovskite films

Traditional organolead-halide perovskite-based devices have shown rapid improvements in their power conversion efficiency (PCE) in less than a decade, yet challenges remain for improving stability and film uniformity, as well as the elimination of lead to address toxicity issues. We fabricated lead-free methylammonium bismuth iodide (MBI) perovskite films and studied the effect of solvent annealing with dimethylformamide (DMF) on the local optoelectronic properties of the films as measured via (photo)conductive atomic force microscopy ((p)c-AFM)). We found solvent annealing to significantly increase electrical conductivity in the out-of-plane direction. Photoconductivity in both solvent-annealed and thermally-annealed MBI films was boosted in the grain interiors versus the grain boundaries (GBs). It was observed that DMF induced solvent annealing impacts charge transport through the film which can be a unique design parameter for optimizing local optoelectronic properties. By studying how solvent annealing changes the ways in which charge is transported through the film, we have developed a better understanding of how local optoelectronic properties are affected by DMF annealing.