Smart Windows with a VO₂ Thin Film as a Conductive Layer for Efficient and Independent Dual-Band Modulation

Abstract

Smart windows that can modulate the transmission of sunlight entering the room can significantly reduce energy consumption. Herein, we provide a simple structure for smart windows which can modulate the transmittance of visible (vis) light actively by an external electric field and modulate the transmittance of near-infrared (NIR) light passively by temperature. The dual-band control of vis and NIR light are achieved by polymer-dispersed liquid crystal, vanadium dioxide (VO2), and Al-doped ZnO. The VO2 thin film plays two roles: NIR light control and conductive layer. There are four optical modulation modes for this kind of smart window, that is, (1) vis and NIR light passing mode, (2) vis light blocking and NIR light passing mode, (3) vis light passing and NIR light blocking mode, and (4) vis and NIR light blocking mode. The transmittance in the vis range (T lum) can be reversibly and actively modulated between 0.38 and 39.93%, and the transmittance in solar irradiation (T solar) can be reversibly and passively modulated between 42.32 and 9.95%. In the meantime, the response time (t on) decreases from 114.5 to 5.2 ms when the VO2 thin film changes from monoclinic to rutile phase. The electro-optical measurement indicates smart windows with featured fast response time, long stability, and independent modulation ability. Besides, a house model testing proves an indoor temperature cooling of 7.7 °C. Smart windows with simple structure, large area preparation, and outstanding modulation ability are promising in energy saving in buildings and automobiles.

Facile Solution Process of VO2 Film with Mesh Morphology for Enhanced Thermochromic Performance

“…When the zinc concentration in the solution increases, the transmittance from 300 nm to 2500 nm at 20 °C remains high while the transmittance from 300 nm to 2500 nm at 90 °C decreases, leading to an enhanced solar modulation efficiency. Specifically, when the zinc concentration is 0.15 mol/L, the film shows a visible transmittance of 38.2% at 20 °C, a solar modulation efficiency of 11.3%, and an infrared modulation efficiency of 20.3%, which is better than that of most VO2 films in previous works [15][16][17]46] as shown in Table 2. The enhancement in visible transmittance and solar modulation is related to the nanostructure of LBZA.…”

Flexible Normally Transparent Smart Window Modulating Near‐Infrared Penetration under Ambient Conditions

“…VO 2 nanoparticles (d = 100-200 nm, Hongwu International Group Ltd., China) doped 3 wt% PVP (Sigma-Aldrich) aqueous were prepared at relative mass ratios of 110, 120, 130, 140, and 150%. Aluminum doped zinc oxide (AZO)-coated glass substrates prepared via radio frequency sputtering, [28] indium tin oxide (ITO)-coated glass substrates (sheet resistance ≤ 6 Ω sq −1 , Ningbo Nanotech Advanced Materials Co., Ltd) and normal glass were ultrasonically cleaned in isopropanol (IPA) and acetone (20 min…”

“…VO 2 nanoparticles ( d = 100–200 nm, Hongwu International Group Ltd., China) doped 3 wt% PVP (Sigma‐Aldrich) aqueous were prepared at relative mass ratios of 110, 120, 130, 140, and 150%. Aluminum doped zinc oxide (AZO)‐coated glass substrates prepared via radio frequency sputtering, [ 28 ] indium tin oxide (ITO)‐coated glass substrates (sheet resistance ≤ 6 Ω sq −1 , Ningbo Nanotech Advanced Materials Co., Ltd) and normal glass were ultrasonically cleaned in isopropanol (IPA) and acetone (20 min in each bath) and then hydrophilized using a digital UV ozone system (PSD UV 12, Novascan Technologies, USA). VO 2 ‐doped PVP hybrid solutions were pre‐ultrasonicated for 15 min and then spin‐coated onto the substrates, followed by a soft bake at 120 °C for 30 min and a hard bake at 220 °C for 1 h. W 0.003 V 0.997 O 2 ‐doped PVP thin layer‐coated substrates were similarly obtained after replacing VO 2 with tungsten (W) doped VO 2 nanoparticles (W 0.003 V 0.997 O 2 , SS‐VW50, Hangzhou Jikang New Materials Co., Ltd).…”

“…[20,21] Thermotropic VO 2 that modulates NIR light penetration has been used to fabricate smart windows and manage the indoor thermal environment. [22][23][24][25][26][27][28][29] However, the MIT of VO 2 occurs at 68 °C, thus far in excess of a comfortable temperature, greatly hampering VO 2 utilization. Here, we develop a dualstimulus-responsive, normally transparent, WVO-PSCLCs flexible smart window using thermally stable polymer stabilized CLCs (PSCLCs) and a flexible, thermotropic, tungsten-doped VO 2 hybrid thin layer.…”

Dual-Band Electrochromism: Plasmonic and Polaronic Mechanisms

“…This mode would be useful for operation of dual-band EC devices in cold weather where the user desires to benefit from some solar heating while controlling glare or ensuring privacy. There are some examples in the literature where the existence of this “warm” mode has been demonstrated by sandwiching polymer dispersed liquid crystals in between thin films of doped metal oxides and, by capacitively charging the lithiated phase of TiO 2 nanocrystals; however, the visible transmittance is still fairly high in these cases, and more improvement is required to give user the comfort of privacy. One unexplored approach to produce a warm mode would be to creatively combine the EC absorption characteristics of materials reported in the literature either in composite EC films or by leveraging the additive filtering effects from the cathodic EC film and the counter electrode.…”