In situ sol–gel synthesis of tungsten trioxide networks in polymer electrolyte: Dual-functional solid state chromogenic smart film

The novel electro-photochromic solid electrolyte films were successfully synthesized by in situ sol–gel synthesis of tungsten trioxide (WO₃) working electrode within gelatin/lithium cosolvent system. The transparent free-standing single-layer film with adhesiveness and flexibility, darken significantly under the UV radiation with photo-response time of 30 s and gradually reversed once the source of UV was blocked. Moreover, casted film on the indium tin oxide (ITO) glass showed electrochromic (EC) behavior as well in presence of ion storage counter electrode. X-ray diffraction analysis indicates the amorphous nature of an in situ synthesized gelatin-based film. The prepared film containing 30 wt% LiClO₄ and 10 wt% WO₃ (sample designated as GLi30W10) shows ionic conductivity value of 1.1 × 10^?4 S/cm. The EC performances of the device with the following configuration; ITO/GLi30W10/NiO/ITO, was investigated by means of UV and cyclic voltammograms. Good performances and fast electro-response times (2 s/1 s) of the device were demonstrated with coloration efficiency of 51.54 cm²/C.