Ionic liquid-modified perovskite films for enhanced solar cell stability

Abstract

Halide perovskites have emerged as promising candidates for photovoltaic applications due to their remarkable device efficiencies. Despite this progress, their commercial viability is hindered by structural instability under high temperature and humidity. Here, the stability of mixed-halide perovskites is enhanced by incorporating the ionic liquids (ILs) 1-Butyl-3-methylimidazolium tetrafluoroborate (BMIMBF 4 ) and 1-Butyl-3-methylimidazolium chloride (BMIMCl). The resistance of the IL-modified films to heat and moisture is investigated using X-ray Photoelectron Spectroscopy (XPS), Near Edge X-ray Absorption Fine Structure (NEXAFS), Hard X-ray Photoelectron Spectroscopy (HAXPES) and Near-Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS). Additionally, the role of a SnO 2 electron transport layer (ETL) is investigated for improving the stability of the IL-modified films. Results indicate that the IL-modified perovskite films on SnO 2 demonstrate enhanced thermal stability, withstanding temperatures of at least 300 °C. BMIMBF 4 -modified films demonstrate superior thermal stability, attributed to the formation of an IL overlayer which protects the underlying perovskite layer. Conversely, in BMIMCl-modified films, BMIM + and Cl - ions diffuse into perovskite grain boundaries, enhancing crystallinity and neutralising surface defects. HAXPES results show that IL-modification protects the perovskite films from surface degradation. NAP-XPS results indicate that BMIMCl-modified films show greater resistance to water penetration than BMIMBF 4 -modified films. It is inferred that the combined use of ILs and SnO 2 significantly enhances the thermal and moisture stability of perovskites, advancing their potential for commercial application.