New electrolyte for electrochromic devices

The paper presents the results of the research on a new polymer-gel electrolyte for electrochromic devices. In the performed studies, various electrolytes were used. They all contained an ionic conductor, a matrix of polymer gel and organic solvent or mixture of polar organic solvents. The electrolyte which had the best properties contained 8% LiCF₃SO₃ as an ionic conductor, a matrix consisting of two polymers: 10% PMMA, 6% PEO, and a mixture of the following two polar organic solvents: 38% propylene carbonate and 38% ethylene carbonate. The high conductivity (σ = 4.8 mS/cm), which provides easy deposition in layers, gives stability (resistance) in time and high transmittance value of radiation in the visible region makes the electrolyte very useful for electrochromic devices. A seven-layer electrochromic device with this new gel electrolyte was assembled according to the following formula: glass ₁ /ITO/WO₃/electrolyte/BP/ITO/glass ₂, where ITO was an indium-tin film oxide, WO₃ was an electrochemically deposited tungsten oxide film and BP an electrochemically deposited film of prussian blue. The density of the current flowing through the unit and the transmittance at the wavelength ʎ = 550 nm are given in the paper as a function of sinusoidal voltage. The transmittance varies from 70–50% (coloured) to 25–10% (for fully bleached) in the range of visible radiation and the colouration efficiency is high (above 100 cm²/C). These results are considerably better than those reported in the other similar studies.