Low-voltage modulated inorganic smart windows using solid polymer electrolyte

We have developed a low-voltage modulated inorganic electrochromic device using a solid polymer electrolyte (SPE). UV-cured electrolytes with various ferrocene (Fc) concentrations of 0, 0.05, and 0.1 M were developed. The electrochromic evaluation of the device using an Fc concentration of 0.1 M indicated high transmittance changes of >60% under a low potential change of 2.5 V due to the Fc in the electrolyte assisting with ion transfer to thin films, resulting in the lowest resistance within the device. Moreover, this electrochromic device, with an excellent self-bleaching effect, showed improved transmittance by 37% for 2000 s. We have fabricated a large smart window with a size of 20 × 20 cm2 using the optimized conditions, with stable cyclic transmittance change up to 100 cycles upon a potential change of 2.5 V. Therefore, an electrochromic device with high transmittance difference and stable switching performance was successfully demonstrated using 0.1 M Fc-based SPE. •WO3 electrochromic and ATO ion storage layers were deposited on the FTO-glass using a kinetically sprayed process.•The electrochromic device with Ferrocene shows low resistance, resulting in a transmittance change of >60% upon low voltage.•The ECD with 0.1 M Fc showed the highest self-bleaching effect for cyclic transmittance without additional external voltage.•We have proven that a large-area smart window was fabricated and operated under the low voltage change of 2.5 V.