image: High performance polycrystalline as Functional modulation layer of F-P resonant cavities.
Credit: Tao Zhao and Prof. Yao Li from Harbin Institute of Technology.
A research team from the Harbin Institute of Technology have fabricated tungsten-doped vanadium dioxide (WₓV₁₋ₓO₂) films that exhibit exceptional dynamic radiative properties, paving the way for innovative thermal management systems. The integration of advanced in situ characterization methodologies, the team has elucidated the fundamental relationships between fabrication process parameters and the temperature-dependent optoelectronic properties of the film.
The new polycrystalline WₓV₁₋ₓO₂ films demonstrated a remarkable ability to modulate infrared radiation in response to temperature changes. By precisely controlling oxygen flow rates and post-annealing temperatures during fabrication, scientists have achieved materials capable of dynamically adjusting their emissivity range from 0.25 to 0.87 within the atmospheric transparency window. This significant range allows buildings and devices to optimize heat loss or retention adaptively, greatly reducing energy consumption.
In recent years, dynamic radiant thermal management (DRTM) based on WₓV₁₋ₓO₂ has attracted much attention due to its energy efficiency and environmental benefits, and it is a breakthrough in the field of radiative cooling technology. Radiative cooling is a natural process by which objects or surfaces release heat energy into space through the emission of infrared radiation. This process allows objects to stay cooler than their surroundings, especially during clear nights when the sky acts like a cold reservoir.
These properties demonstrates a great potential for passive thermal regulation; however, existing high-quality WₓV₁₋ₓO₂ thin films are mainly in single-crystal or quasi-single-crystal form and are mainly prepared by relying on pulsed laser deposition (PLD) technology, which is a high-cost and severe-conditioned process that has greatly limited the wide application of DRTM.
The Solution: The researchers reported a highly polycrystalline WₓV₁₋ₓO₂ film with resistivity variations of up to three orders of magnitude can be achieved through high-power impulsed magnetron sputtering (HiPIMS). The optical properties of the film at varying temperatures are characterized using in-situ techniques, including scanning near-field optical microscopy (SNOM), absorption spectroscopy, grazing-incidence X-ray diffraction (GIXRD), and Raman scattering spectroscopy. The results reveal that the insulating dimerized state undergoes a transition to a metallic state at a threshold temperature of 39.4℃ in WₓV₁₋ₓO₂, driven by thermal excitation of electrons from the d∥ bonding state to the π* anti-bonding state. This process disrupts the V–V dimers due to the collapse of molecular orbitals, leading to notable changes in optical absorption and enhanced IR radiation properties of WₓV₁₋ₓO₂. As expected, a DRTM reflector based on polycrystalline WₓV₁₋ₓO₂ exhibits a remarkable dynamic emissivity tunability, varying from 0.25 to 0.87 within the 7-13 μm range. Simulated results show that integrating our DRTM reflector into buildings roof can reduce HVAC energy consumption by over 8% in five climate zones worldwide, with seasonally distinct zones achieving reduction of up to 48.95 MJ cm-2 annually. This work provides a novel strategy for fabricating high-performance WₓV₁₋ₓO₂ polycrystalline films and offer a promising route for advancing dynamic radiant thermal management, enhancing energy efficiency and promoting sustainability in buildings.
The Future: Future research will explore more focus on the stability and selective regulation of DRTM in complex ground or space environments, and promote its practical applications in energy and space.
The Impact: This work offers a promising pathway to achieving high-performance WₓV₁₋ₓO₂ films but also pave the way for sustainable energy solutions in the face of global climate challenges.
The research has been recently published in the online edition of Materials Futures, a prominent international journal in the field of interdisciplinary materials science research.
Reference:Tao Zhao, Yanyu Chen, Xingquan Guo, Chenchen Geng, Qianqian Zhao, Hongyi Ouyang, Shuliang Dou, Jinxin Gu, Jiupeng Zhao and Yao Li. High Performance Tungsten-Doped VO2 Polycrystalline for Advanced Dynamic Radiant Thermal Management[J]. Materials Futures, 2025, DOI: 10.1088/2752-5724/adea8a.
Journal
Materials Futures