Electropolymerization as a Method to Create Irreversible Electrochromic Indicators

Irreversible Visual Indicators (IVIs) are devices that display information on-demand or in response to an external signal, with applications in monitoring labels, product status, digital signage, security, and sensors. IVIs display information permanently, while using minimal energy and are impossible to erase. This work builds on previous studies into such devices and aims to develop IVIs that can display information in a wide array of colors. IVIs employ the use of electrochromism, when a material or device changes color in response to application of a small voltage or current. The mechanism explored in this work to create devices is in situ electropolymerization, in which small conjugated organic heterocyclic monomers are dispersed in an ionically conducting gel. Upon applying bias across the device, the monomers are oxidized and coupled to form conjugated chains that deposit onto a transparent electrode. This conjugation allows the resulting polymers to absorb visible light, providing a wide spectrum of colors that varies based on the original monomer used. These devices are tested to determine their final color, as well as probed for irreversibility. Testing conditions are standardized so that the polymerization occurs over five minutes or less, with a 3 V oxidizing voltage, followed by a short -1.5 V reducing voltage. By varying the structure of the molecule in the device, it is demonstrated that IVIs can switch from 100% transparent to red, orange, green, blue, purple, and black. Additional molecules are being tested for more vibrant colors and uniformity of layer. This work details the steps of electrochromic device fabrication specifically for irreversible indicators and strives to create straightforward processing methods for IVIs.