Smart Window for Controllable Visible/NIR Dual Band Absorbance

Abstract

Due to using massive energy, efficient energy saving devices are strongly needed. Smart windows capable of blocking near infra-red (NIR) wavelengths have gained much attention as a candidate for energy saving windows. However, it is difficult for a single window to modulate selectively the optical properties of visible light and NIR region. Here, we prepared smart windows that can absorb visible light and NIR selectively by introducing phosphonated viologen anchored TiO2 film as a visible light absorbing layer while VO2 film was used as an NIR absorbing layer. The exhibited color of viologen/TiO2 electrode was tuned by controlling the electron affinity of viologen species and applied voltage. We synthesized three types of viologen species according to electron affinity (2PV, CF3V and CNV). For, CF3V and CNV, one electrode could exhibit up to two colors in response to applied voltage. After fabricating hybrid windows by introducing viologen/TiO2 and VO2 electrode, it absorbed visible light and NIR selectively according to applied voltage. Our smart window can be applied to energy saving windows owing to the ability to block NIR of sunlight at daytime, and privacy protecting windows by blocking visible light. Furthermore, we can modulate visible light and NIR independently and provide more abundant colors by utilizing tandem system.