Displays

The display is structured as an electrochemical cell with a pixel electrode and a counter electrode bridged by a solid electrolyte. The electrodes, which are made from PEDOT:PSS, serve both as electrochromic material and electrical conductor. When a voltage is applied across the electrodes, a redox reaction occurs, in which the reduced electrode becomes dark blue, while the oxidized electrode brightens. The display is paper-like in the sense that it works in reflective mode, that is, no backlight is used to light up the pixels.

The viewing angle is large, weight and cost are low. Energy is mainly consumed when the display is switched. The required voltage is low, typically 1-3 V, which allows for standard battery operation. Keeping the display updated only takes a small sustain current. The display is flexible and it can be folded without damage.

The display elements can be combined into a passive or active matrix addressed display [1, 2]. An arbitrary message or image can be presented in such matrix displays by applying a specific voltage pattern across the rows and columns. The most recent research activities have resulted in improved switching characteristics of the electrochemical addressing transistors, improved colour contrast of the electrochromic pixels and a novel patterning technique that can be used in the manufacturing process.

[1] Andersson, P., Nilsson, D., Svensson, P.-O., Chen, M., Malmström, A., Remonen, T., Kugler T. and Berggren, M., "Active Matrix Displays Based on All-Organic Electrochemical Smart Pixels Printed on Paper", Advanced Materials, 14, 1460-1464, 2002. Abstract

[2] Andersson, P., Forchheimer, R., Tehrani, P. and Berggren, M., "Printable All-Organic Electrochromic Active-Matrix Displays", Advanced Functional Materials, 17, 3074-3082, 2007. Abstract