Energy efficient hydrogel based smart windows with low cost transparent conducting electrodes

•This work aims to fabricate affordable smart windows for light and temperature control.•Transparent heater is a vital component of a smart window.•Crackle template method provides transparent conducting plates with low fabrication costs.•HPMC hydrogel is one of the promising active materials for smart windows.

Indoor light control using thermotropic materials is an active area of research. While active materials are available to switch transmittance with temperature, large area heaters with desired transparency are not easily affordable. In this paper, the fabrication of thermochromic devices using inexpensive Sn mesh electrodes (5 Ω/□, transmission, 80%) produced by crackle lithography with hydroxypropyl methyl cellulose (HPMC) as active material is reported. When laminated and coated on the inner surface of a PET window (8×8 cm2), the mesh served as a transparent heater to cause gelation in HPMC at ~40 °C to switch from water-clear transparency to paper-white opaqueness with 1 mm thickness of the active layer. The power consumption was only 0.2 W/cm2. Few drops of a color ink produced interesting effects in this smart window prototype.

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