We demonstrate the printing of a complex smart integrated system using only five functional inks: the fluoropolymer
P(VDF:TrFE) (Poly(vinylidene fluoride trifluoroethylene) sensor ink, the conductive polymer PEDOT:PSS (poly(3,4
ethylenedioxythiophene):poly(styrene sulfonic acid) ink, a conductive carbon paste, a polymeric electrolyte and SU8 for
separation. The result is a touchless human-machine interface, including piezo- and pyroelectric sensor pixels (sensitive
to pressure changes and impinging infrared light), transistors for impedance matching and signal conditioning, and an
electrochromic display. Applications may not only emerge in human-machine interfaces, but also in transient
temperature or pressure sensing used in safety technology, in artificial skins and in disposable sensor labels.
We will present organic electrochemical transistors that show both bi-stable and dynamic current modulation. In electrochemical devices, both ions and electrons are used as charge carriers. The device is all-organic and has been realized using common printing techniques, such as screen-printing. As the substrate, both cellulose-based paper and polyester foil have been used. PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulphonic acid)) is used as the conducting and electrochemical active material. PEDOT:PSS is switched between different redox states, corresponding to semi-conducting and conducting states. Operating voltages is below 2V and on/off ratios up to 105 have been reached (typical value is 5000). The operation of these devices does not depend on any critical dimensions; typical dimensions used are around 200 microns. With a certain geometrical design the dynamic transistor can be employed for frequency doubling. For the bi-stable transistor the modulation of the current is done by direct electronic contact, compared to the dynamic transistor that is modulated by induction of electrochemistry. The electrolyte in these devices can either be solidified or a liquid. The bi-stable device in combination with a layer of Nafion as electrolyte demonstrates humidity sensor functionality. Since substrates based on paper and common printing techniques can be used for fabrication, this give rise to an environmental friendly and non-expensive device setup.
Here, we report on devices based on patterned thin films of the conducting polymer system poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulphonic acid) (PEDOT:PSS) combined with patterns of solid electrolyte. The key device functionalities base on the updating of the RedOx state of PEDOT. This results in control of
the electronic properties of this conjugated polymer, i.e. the conductivity and optical properties are updated. Based on this we have achieved electric current rectifiers, transistors and display cells. Also, matrix addressed displays will be presented. Electrochemical switching is taking place when the oxidation and reduction potentials are overcome respectively. Therefore, these devices operate at voltage levels less then 2 Volts. Low voltage operation is achieved in devices not requiring any extremely narrow dimensions, as is the case for field effect driven devices. All devices reported can or has been made using standard printing techniques on flexible carriers.
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