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

The sol-gel method was employed in the synthesis of di-urethane cross-linked poly( 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 x 10-4 and 2 x 10-3 S cm-1 at 36 and 98 ºC, 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 159 and 80.2 cm-2 C-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.

This work was supported by Fundação para a Ciência e a Tecnologia(PTDC/CTM BPC/112774/2009, PTDC/QUI-QUI/110855/2009, EXCL/CTM-NAN/0201/2012, Pest C/CTM/LA0025/2014, Pest-C-CTM/LA0011/2013, Pest-OE/QUI/UI0616/2014 and PEst-C/QUI/UI0686/2013)) and COST Action MP1202 “Rational design of hybrid organic-inorganic interfaces”. M. Fernandes, R. Rego and R. Leones acknowledge FCT for grants (SFRH/BPD/78919/2011, SFRH/BSAB/1337/2013 and SFRH/BD/90366/2012 respectively).