Binary solvents of anhydrous ethanol and propylene carbonate for electrolytes of amorphous WO3 films to improve electrochromic performance

Abstract

In this study, amorphous WO₃ thin films were deposited on indium-tin oxide substrates using radio frequency magnetron sputtering. Anhydrous ethanol (AE) and propylene carbonate (PC) served as binary solvents, with the WO₃ films evaluated in AE + PC-LiClO₄ electrolytes. By adjusting the volume percentage of AE, the physical properties of the electrolytes were modified to improve the fluidity and wetting behavior. The analysis of several aspects, such as migration of ions, capillary flow of electrolyte and electrochemical reaction rate, highlights the important influence of AE + PC binary solvent in reducing the response time. Notably, WO₃ films in AE + PC-LiClO₄ electrolyte with a 7/8 volume percentage of AE demonstrated exceptional optical modulation (ΔT = 75.7 %) and fast response times (t_c = 6.41 s, t_b = 2.29 s), alongside shortened the diffusion path, increased ion diffusion coefficients (D_a=4.4678 × 10⁻¹⁰ cm²/s, D_c = 8.2968 × 10⁻¹⁰ cm²/s) and electrochemical active area. Based on these efforts, the feasibility of applying AE + PC binary solvent to WO₃ electrochromic thin films has been confirmed. These results offer valuable insights for the development of efficient electrolytes and their application in electrochromic devices.