An organic electronic paper display technology (see Figure and also inside front cover) is presented. The electrochromic display cell together with the addressing electrochemical transistor form simple smart pixels that are included in matrix displays, which are achieved on coated cellulose‐based paper using printing techniques. The ion‐electronic technology presented offers an opportunity to extend existing use of ordinary paper.

Novel electrochemical transistors, based on the conductive polymer PEDOT, operating at driving voltages of only a few volts in bulk material, and with little demand on substrate planarity, are described by the authors. The underlying polymer ion pair PEDOT:PSS is conductive in both oxidized and reduced state. Two transistor architectures, a bi‐stable and a dynamic transistor (the first electrochemical specimen of its kind) with an on/off ratio of 105 and 200 Hz modulation speed, were realized.

Over-oxidative degradation of polythiophenes, which breaks the conjugation and destroys the electronic conductivity of the polymer, is well documented as a liability in these materials. We use this 'weakness', via controlled electrochemical over-oxidation, in a novel subtractive patterning technique compatible with high-speed reel-to-reel printing technology. We demonstrate the use of electrochemical over-oxidation to pattern PEDOT:PSS films via an x-y plotter, silk-screen and high-resolution photolithographic techniques, resulting in patterning down to a resolution of 2 µm and a conduction contrast between unpatterned and patterned areas of up to 10 8 .

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