We report on high-performance thermochromic ZrO2/V0.982W0.018O2/ZrO2 coatings with a low transition temperature prepared on glass by a low-temperature scalable deposition technique. The V0.982W0.018O2 layers were deposited by a controlled high-power impulse magnetron sputtering of V target, combined with a simultaneous pulsed DC magnetron sputtering of W target to reduce the transition temperature to 20–21 °C, at a low substrate surface temperature of 330 °C in an argon–oxygen gas mixture. ZrO2 antireflection layers both below and above the thermochromic V0.982W0.018O2 layers were deposited at a low substrate temperature (< 100 °C). A coating design utilizing a second-order interference in the ZrO2 layers was applied to increase both the luminous transmittance (Tlum) and the modulation of the solar transmittance (ΔTsol). The ZrO2/V0.982W0.018O2/ZrO2 coatings exhibit Tlum up to 60% at ΔTsol close to 6% for a V0.982W0.018O2 thickness of 45 nm, and Tlum up to 50% at ΔTsol above 10% for a V0.982W0.018O2 thickness of 69 nm.
The ion-flux characteristics at a substrate position and the corresponding discharge characteristics were investigated during controlled low-temperature (300 °C) reactive highpower impulse magnetron sputtering (HiPIMS) depositions of thermochromic VO 2 films onto conventional soda-lime glass substrates without any substrate bias voltage and without any interlayer. It was shown that the phase composition of the films correlates with the (V + + V 2+ ) ion fraction and the (V + + V 2+ ):(2O + 2 + O + ) ion ratio in the total ion flux onto the substrate. Setting the amount of oxygen in the gas mixture allowed us to control not only the phase composition of the films but also their crystallinity. It was found that an appropriate composition of the total ion flux and high ion energies (up to 50 eV relative to ground potential) support the crystallization of the thermochromic phase in the VO 2 films. We achieved a high modulation of the transmittance at 2500 nm (between 51% and 8%) and of the electrical resistivity (changed 350 times) for a 88 nm thick VO 2 film.
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