Electrochromic devices incorporating biohybrid electrolytes doped with a lithium salt, an ionic liquid or a mixture of both

• Poly(ϵ-caprolactone)/siloxane biohybrid electrolytes were prepared by sol-gel chemistry.
• The electrolytes were doped with LiCF3SO3, an IL or the mixture of both.
• The IL used was 1-ethyl-3-methyl imidazolium tetrafluoroborate ([Emim]BF4).
• Prototype electrochromic devices incorporating the three electrolytes were tested.

The sol-gel method was employed in the synthesis of di-urethane cross-linked poly(ϵ-caprolactone) (PCL(530))/siloxane biohybrid ormolytes incorporating either a mixture of lithium triflate (LiCF3SO3) and the ionic liquid (IL) 1-ethyl-3-methyl imidazolium tetrafluoroborate ([Emim]BF4), or solely with [Emim]BF4 or LiCF3SO3. The ormolyte doped with [Emim]BF4 is thermally more stable and exhibits higher ionic conductivity (4 × 10−4 and 2 × 10−3 S cm−1 at 36 and 98 °C, respectively) than those containing the LiCF3SO3/[Emim]BF4 mixture or just LiCF3SO3. The three ormolytes were employed in the production of glass/ITO/ormolyte/WO3/ITO/glass electrochromic devices (ECDs) designated as ECD@Y with Y = Li-[Emim]BF4, [Emim]BF4 and Li. The three ECDs displayed fast switching speed (ca. 30 s). ECD@Li-[Emim]BF4 exhibited an electrochromic contrast of 18.4% and an optical density change of 0.11 in the visible region, the coloration efficiency attained at 555 nm was 152 and 80.2 cm2C−1 in the “on” and “off” states, respectively, and the open circuit memory was 48 hours. In the “on” state the CIE 1931 color space coordinates were x = 0.29 and y = 0.30, corresponding to blue color.

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