Facile and Scalable Synthesis of Crystalline BiOI Nanoflake Films via LiTFSI-Assisted Conversion of Porous BiI3 for Functional Applications

Abstract

Bismuth oxyiodide (BiOI) has garnered significant attention due to its unique morphological, optical and electronic properties, making it a promising candidate for diverse applications in optoelectronics and energy-related fields. In this study, we report a novel and facile method for synthesizing crystalline BiOI nanoflake films via lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-assisted conversion of porous bismuth triiodide (BiI3) precursors. The synthesis involves formulating a stable BiI3 paste using LiTFSI as a structural template and gamma-butyrolactone (GBL) or dimethyl sulfoxide (DMSO) as solvents. The paste is deposited on flat substrates to form a film and subsequently hydrolyzed in deionized water under mild conditions, yielding BiOI films. The paste-based approach enables efficient material utilization and reproducible large-area synthesis. The resulting BiOI films were systematically characterized using scanning electron microscopy, X-ray diffraction, ultraviolet-visible spectroscopy, photoluminescence spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller surface area analysis and pore size distribution measurements. The films synthesized using GBL and DMSO exhibited well-defined nanoflake morphology, with average flake thicknesses of 24.3 and 17.5 nm, direct bandgap values of 2.07 and 1.95 eV, and surface areas of 19.57 and 16.71 m2/g, respectively. This robust and versatile synthesis strategy offers a promising pathway for the scalable production of high-quality BiOI films toward future optoelectronic and environmental photocatalytic applications.