Cost-Effective, Flexible, and Colorful Dynamic Displays: Removing Underlying Conducting Layers from Polymer-Based Electrochromic Devices

Electrochromic (EC) materials and devices provide a user-controlled, dynamic way of displaying information using low power, making them interesting for a range of applications in numerous markets, including logistics, retail, consumer goods, and health care. To optimize the cost while simplifying the production, expanding the color space, and enhancing the contrast and vibrancy of EC displays aimed for cost-sensitive products, we sought to reduce the number of layers as well as remove the underlying conducting layer that accounts for a substantial fraction of the cost of a printed label. Here, we show how conjugated electrochromic polymers, which are inherently semiconducting, can be used to accomplish this goal and afford printable EC displays with a flexible form factor. Using a combination of electrochemical probes, in situ spectroscopy, solid-state conductivity, and in situ conductance measurements, we have studied and compared five different EC polymers with conductivities spanning multiple orders of magnitude and colors that span most of the visible range, identifying polymers and properties that allow for switching from the colored to the clear state without an underlying conducting layer. Finally, we incorporate these EC polymers into optimized flexible devices without an underlying conductor and demonstrate that they are able to provide on-demand, reversible colored-to-clear switching on the order of seconds to minutes, with operating voltages below ±1 V, optical memories exceeding 60 min, and a shelf-life exceeding 12 months.