Preparation and optical/electrical properties of vanadium pentoxide films on fluorine-doped SnO2 (FTO) substrates through sol–gel route

Abstract

V₂O₅ films were formed via sol–gel spin coating and thermal annealing with fluorine-doped SnO₂ (FTO) glass as substrates. The impacts of annealing temperature, time and spin-coating number on surface morphology, structure and optical/electrical properties of V₂O₅/FTO composite films were mainly studied. The results demonstrated that increasing annealing temperature, time and spin-coating number could contribute to increases in the film compactness, grain size and crystallinity, but too high temperatures or too long times would degrade the film compactness, and too large spin-coating numbers would cause grain/particle agglomeration and cracking phenomena. The film transmittance and sheet resistance depended on the combined effect of these factors. It was determined that a uniform and compact V₂O₅ film could be formed on the FTO substrate under spin-coating four times and annealing at 400 °C for 60 min. The as-obtained composite film exhibited ideal optical/electrical properties, with an average transmittance (600–1100 nm) of 73.83%, a sheet resistance of 25.42 kΩ/sq, an optical band gap energy of 2.751 eV and an average transmittance (1250–1600 nm) change amplitude of 14.2% before and after phase transition that accompanied by a reversible thermotropic color change from yellow to orange. This work offers useful insights for preparing V₂O₅-based composite films.