Solution processed bismuth oxyiodide (BiOI) thin films and solar cells.

Post transition metal chalcohalides are an emerging class of semiconductor materials for optoelectronic applications. Within this class, bismuth oxyiodide (BiOI) is of particular interest due to its high environmental stability, low toxicity, and defect tolerance considered typical of 'ns 2 ' materials. Here we fabricate BiOI thin films using a solution-processed method that affords pin-hole free highly pure films without any residual carbon or other contaminant species. Based on these films, solution processed all-inorganic solar cells with an architecture ITO/NiO x /BiOI/ZnO/Al are fabricated for the first time. Additional device improvements are realised by templating BiOI thin film growth to attain efficiencies that rival some of the best vacuum deposited devices. The BiOI thin films and devices outlined here are an excellent platform for the further development of solution processed bismuth chalcohalide optoelectronic devices.