Single‐crystalline domain Ta‐doped VO ₂ films and the application in the excellent thermochromic film assembly

Abstract It still remains a challenge to prepare a room‐temperature responsive VO 2 ‐based thermochromic film assembly that could balance high visible light transmittance ( T lum ) and solar light modulation efficiency (Δ T sol ). In the current research, Ta‐doped VO 2 films, composed of large single‐crystalline domains, were prepared through magnetron sputtering and postvacuum annealing; their structural, electrical, and optical properties were deeply analyzed. The doped films showed distinct semiconductor‐to‐metal transition (SMT) behaviors, and it was seen that the resistance change across the SMT was still near 100 times when the SMT temperature ( T c ) was decreased to ∼35°C. The analysis indicated that the Ta dopants formed shallow donors 0.1–0.14 eV below the conduction band for semiconductor phase. The n and k were obtained from the regressive analysis of the optical spectra, which were further used to obtained absorption coefficients and gap energies, based on which the electronic structure was discussed. Under the guidance of optical designs, a four‐layer SiO 2 /TiO 2 /Ta‐VO 2 /TiO 2 /substrate was fabricated; this obtained the average T lum of ∼53% and the Δ T sol of ∼14%, while the T c was reduced to ∼35°C. A remarkable balance between the high T lum and high Δ T sol was achieved for the multilayer film assemblies, which can be increased by further tuned the layer thicknesses and VO 2 structures.