Two-step W and N co-doping in VO2: Synergistically reducing phase transition temperature while enhancing thermochromic performance

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The inherent performance trade-offs of VO 2 materials have remained the key challenge hindering their smart window applications, with no viable solution developed to date. Herein, we propose a cation/anion co-doping strategy by sequentially incorporating W and N via a two-step process for the first time. A novel phenomenon of W-facilitated N incorporation is uncovered in prepared W/N co-doped VO 2 . Integrated experimental and theoretical calculations demonstrate that W-doping enhances NH 3 adsorption, reduces transition-state energy barriers, and induces lattice expansion, thereby facilitating more effective nitrogen incorporation. This synergistic effect achieves a phase transition temperature reduction dramatically exceeding the sum of individual contributions from W and N. The W/N co-doped VO 2 exhibits a broad tunability in onset phase transition temperature ( T o ) spanning from 44.4 to 4.3 °C, enabling exceptional climate adaptability. Leveraging N doping on decreasing haze and enhancing crystallinity, W/N co-doped VO 2 demonstrates both superior luminous transmittance ( T lum ) and solar-energy modulation performance ( ΔT sol ) than reported co-doped VO 2 . W0.5-300-20-5 sample (0.5 at.%W + 1.38 at.%N) exhibits optimal thermochromic performance with T o = 44.2 °C, T lum = 64.6 %, and ΔT sol = 9.5 %. This study offers valuable design insight and feasible technical references for overcoming the multiple performance trade-offs of VO 2 smart windows. • Synthesized W/N co-doped VO 2 for the first time via a two-step doping strategy • Uncovered a novel synergistic effect of W-facilitated N incorporation by DFT and TEM • Achieved transition temperature decline exceeding the sum of single-doping effects • Realized synergistic enhancement of thermochromic performance in W/N co-doped VO 2 • Provided references for overcoming performance trade-offs of VO 2 smart windows