PVP-Engineered WO/TiO Heterostructures for High-Performance Electrochromic Applications with Enhanced Optical Modulation and Stability.

In response to escalating global energy demands and environmental challenges, electrochromic (EC) smart windows have emerged as a transformative technology for adaptive solar modulation. Herein, we report the rational design and fabrication of a bilayer WO/TiO heterostructure via a synergistic two-step strategy involving the electrochemical deposition of amorphous WO and the controlled hydrothermal crystallization of TiO. Structural and morphological analyses confirm the formation of phase-pure heterostructures with a tunable TiO crystallinity governed by reaction time. The optimized WTi-5 configuration exhibits a hierarchically organized nanostructure that couples the fast ion intercalation dynamics of amorphous WO with the interfacial stability and electrochemical modulation capability of crystalline TiO. Electrochromic characterization reveals pronounced redox activity, a high charge reversibility (98.48%), and superior coloration efficiency (128.93 cm/C). Optical analysis confirms an exceptional transmittance modulation (ΔT = 82.16% at 600 nm) and rapid switching kinetics (coloration/bleaching times of 15.4 s and 6.2 s, respectively). A large-area EC device constructed with the WTi-5 electrode delivers durable performance, with only a 3.13% degradation over extended cycling. This study establishes interface-engineered WO/TiO bilayers as a scalable platform for next-generation smart windows, highlighting the pivotal role of a heterostructure design in uniting a high contrast, speed, and longevity within a single EC architecture.