High-valence rhenium doping for intensifying optical and transparent thermal performance of Cs0.33WO3

In this work, high-valence rhenium (Re) was firstly used as the dopant to improve the optical and transparent thermal properties of Cs 0.33 WO 3 . Among all samples, the film with 2 mol% Re doping exhibited the best transparent thermal insulation performance, with a luminous transmittance ( T lum ) of 53.5 % and a near-infrared (NIR) shielding efficiency ( Ψ NIR ) of 70.1 %. Structural and spectroscopic analyses revealed that Re 6 + successfully substituted for W 6+ in the hexagonal lattice, inducing the formation of W 5+ species and oxygen vacancies. These defect states enhanced the free carrier concentration and promoted small polaron absorption, thereby improving the NIR shielding performance. The improved transparency was also attributed to enhanced hydrophilicity and particle dispersion. The results highlighted the potential of high-valence Re doping as an effective strategy to modulate the electronic structure and defect chemistry of Cs 0.33 WO 3 , providing a new pathway for the design of advanced energy-saving smart window coatings.