Effect of Annealing Temperature on the Electrochromic Properties of Tungsten Oxide Films by Sol-Gel Method
Electrochromism is a phenomenon in which the optical properties of a material are altered due to the embedding of ions in an electrolyte when the material is subjected to an applied electric field.This phenomenon can be utilised in a variety of scenarios,including architectural insulation,decoration and information display.Tungsten oxide(WO₃),a widely researched mechanism-free electrochromic material,still exhibits high costs when used in large-scale mechanism-free electrochromic films in photothermal modulation scenarios.This is due to the stringent preparation process requirements and the costly price of the transparent conductive substrate,despite the material being widely available in our country.In this study,tungsten oxide(WO3)thin films were prepared by sol-gel method,and the crystalline and amorphous states were prepared by changing the annealing temperature,and the electrochromic properties were tested.The experimental results showed that the films gradually changed from amorphous to crystalline state and the internal structure of the films gradually densified with the increase of annealing temperature.At four annealing temperatures(200℃,250℃,300℃,350℃),the films annealed at 200℃showed the best electrochromic properties with good reversibility.The optical contrast at 633 nm was 79%in 1 mol∙L-1 AlCl3 solution with-0.5 V applied.The other annealing temperature of the films,due to the internal structure of the films tends to be dense,in the application of forward voltage,the embedded ions can not be de-embedded in a short period of time,making it difficult to return to the initial state of the optical properties of the films,the colouring fading response speed decreased;also led to the film in the state of the colouring of the optical contrast has a varying degree of degradation.One of the samples annealed at 350℃showed differentiation in optical contrast,which may be attributed to the crystallization of the film,with fine grain boundaries providing more reaction sites.This study provides a simple and low-cost method to prepare WO3 thin films and investigates the influence of the electrochromic properties of the films at different sub-treatment temperatures for large area application of electrochromic materials.
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