Sol-Gel coated WO3 thin films based complementary electrochromic smart windows

•The WO3 films exhibit the anodic/ cathodic diffusion coefficient of 2.31/4.79 × 10−12 cm2/s.•Electrochromic smart windows with the following structures were fabricated and tested.•(i) G/FTO/NiO/PMMA-PC-H+/WO3/FTO/G (EC1).•(ii) G/FTO/Ni0.95Co0.05O/PMMA-PC-H+/WO3/FTO/G (EC2).•(iii) G/FTO/NiO/PMMA-PC-Li+/WO3/FTO/G(EC3) and.•(iv) G/FTO/Ni0.95Co0.05O/PMMA-PC-Li+/WO3/FTO/G (EC4). The WO3 films were prepared via sol- gel dip coating method. The optical, structural, morphological, electrochemical and electrochromic properties of the prepared films were studied. The WO3 film coated on glass substrate exhibits 74% transmission at 550 nm. XRD studies indicate the WO3 films in the amorphous state. FTIR spectrum confirms the formation of WO3. The FESEM image confirms the formation of smooth surface. The cyclic voltammetric study reveals the anodic/cathodic diffusion coefficients of 2.31/4.79 × 10−12 cm2/s for WO3 films. The film thickness was about 260 nm. The same film shows a change in optical transmission of 55.37% at 550 nm. The sol–gel coated WO3 films were used to develop the complementary electrochromic smart windows in conjugation with NiO and Ni0.95Co0.05O as an anode. A five layered EC windows were developed and studied with Li+ and H+ conducting gel electrolytes.