Engineering the Structure–Performance Relationship of WO3 Thin Films Through PVP–Mn Synergy for Electrochromic Applications

The electrochromic (EC) behavior of tungsten oxide (WO3) is strongly influenced by its nanoscale architecture and local chemical environment, which determine the efficiency of ion–electron transport during switching. Here, a systematic polyvinylpyrrolidone (PVP)–Manganese (Mn) synergistic engineering approach was developed using bare WO3 (WO), PVP-assisted WO3 (P-WO), Mn-doped WO3 (Mn-WO), and PVP-assisted Mn-doped WO3 (P-Mn-WO) to clarify the individual and combined effects of PVP and Mn on EC performance. All films retained the amorphous WO3 structure, while morphological evolution revealed a transition from compact nanoparticle assemblies to an interconnected porous architecture in P-Mn-WO. The optimized P-Mn-WO film exhibited enhanced Li+ transport, with diffusion coefficients of 0.45 × 10−10 and 4.08 × 10−10 cm2/s for oxidation and reduction, respectively. This favorable transport environment enabled 75.8% optical modulation at 635 nm, a coloration efficiency of 142.63 cm2/C, and 92.59% charge reversibility, with only 5.24% degradation during repeated switching. At the device level, P-Mn-WO delivered 82.30% bleached transmittance, 12.02% colored transmittance, and 70.28% optical modulation, while showing only 4.5% degradation over 2000 s of continuous operation. These results demonstrate that coupling PVP-assisted growth with Mn doping provides effective control over WO3 morphology, Li+ transport, charge utilization, and optical switching, establishing a promising route toward a durable, high-contrast WO3-based EC smart-window.