Improved electrochromic performance of potentiostatically electrodeposited nanogranular WO3 thin films

The main goal was to build electrochromic (EC) smart windows with large areas, low cost, durability, and multi-functionality to meet various technological challenges. EC nanostructured materials are promising for displays, rear-view mirrors, and smart windows owing to their long cycle life and chemical stability. In this scenario, the potentiostatically electrodeposited WO3 thin films were used to fabricate an EC device to eliminate the need for expensive heating or vacuum treatment. Different electrodeposited cycles were evaluated to optimize the structural, morphological, optical, and electrochromic properties. X-ray diffraction showed a small change in the hump intensity on all samples with identical diffraction orientations. Field emission scanning electron microscopy suggested that the deposited WO3 thin film has a nanogranular morphology composed of many particles. Raman spectroscopy showed that tungsten oxide thin films undergo stretching and vibrational modes to form a pure WO3 phase. The reversible insertion/extraction of Li+ ions in WO3 confirmed its transformation to LixWO3. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy revealed the presence of W and O in the deposits. Moreover, cyclic voltammetry and in-situ transmittance measurements were performed to assess the electrochromic performance of electrodeposited WO3 thin films using a 1 M LiClO4 + PC electrolyte. An electrochromic device, 4 × 3 cm2 in size, was fabricated using nanogranular WO3. The device showed the highest optical modulation (80 %), better Li-ion diffusion coefficient (1.71 × 10–9 cm2/s), excellent reversibility (98 %), fast switching time of 3.5 s and 6.0 s for coloration and bleaching, respectively, and a remarkable CE (98.89 cm2/C).