Versatile electrowetting arrays for smart window applications-from small to large pixels on fixed and flexible substrates

Versatile electrowetting (EW) arrays were fabricated with small to large pixels, on fixed glass and flexible polymer substrates, for smart window applications. EW prototypes on glass substrates were constructed with pixel sizes ranging from 50 μm×150 μm to 2 mm×2 mm. The dosing of the array with colored oil was achieved by dip coating the substrate through an oil film suspended on a water bath. The arrays can be driven by either DC or AC voltage. Optical transmission of the prototypes can be modulated from ∼5% to >70% with a relatively low applied voltage of ∼15 V. The switching speed of the prototype depends on oil properties and cell size, typically ∼10 ms for 300 μm×900 μm pixel cells. Flexible color EW array prototypes have been fabricated on polymer polyethylene terephthalate (PET) substrates, which can be switched reversibly by applying a relatively low voltage difference between the water and bottom electrode. The EW specifications are maintained even when the prototype is mechanically flexed. These results indicate the promise of EW technology for smart window applications.