Effect of Annealing Temperature on Morphology and Electrochromic Performance of Electrodeposited WO₃ Thin Films

The purpose of this study was to investigate the effect of annealing temperature on the structural, morphological, and electrochemical properties of tungsten trioxide (WO3) films, fabricated via electrodeposition and annealed at 50 °C, 250 °C, and 450 °C. Structural analysis using X-ray diffraction (XRD) revealed temperature-induced modifications, transitioning from amorphous to crystalline phases. Morphological studies by field emission scanning electron microscopy (FESEM) demonstrated an increase in grain size with temperature (31 nm, 48 nm, and 53 nm) and the formation of cracks at higher annealing temperatures. Electrochemical characterization showed that the WO3 film annealed at 250 °C exhibited superior redox activity, enhanced ion diffusion, and excellent reversibility. Optical studies highlighted its exceptional performance, with 79.35% optical modulation, a coloration efficiency of 97.91 cm2/C, and rapid switching times (9.8 s for coloration and 7.5 s for bleaching). Furthermore, long-term cycling tests confirmed minimal degradation after 5000 cycles, demonstrating durability. This work provides a comprehensive understanding of the annealing temperature’s impact on WO3 films and underscores the novelty of achieving optimal electrochromic (EC) performance through temperature tuning, advancing the design of energy-efficient smart materials.