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Organic electronic materials are desirable due to facile and low-cost manufacturing through solution deposition. However, the inherit difficulties of reproducibility and solvent compatibility, as well as the hazards associated with the solvents, have stifled the progress of realizing practical solution-deposition methods. As a result, organic thin-films used in industry are typically produced by thermal evaporation techniques, which largely negate the benefits due to the higher cost and complexity of vacuum and evaporation equipment. Here we report the use of a conventional office laser printer to electrophotographically deposit the organic semiconductor layer in thin-film transistors. We have successfully used this solvent-free, low-cost method to produce the first laser-printed organic semiconductor layer in thin-film transistors. We printed on flexible and transparent polyethylene terephthalate (PET) substrates. We used the highly hydrophobic fluoropolymer Cytop as the dielectric in a bottom-gate, bottom-contact configuration, a feat that is not possible with traditional solution-deposition. The organic semiconductor layer consisted of a toner powder based on triisopropylsilylethynyl pentacene (TIPS Pn). Grazing incidence wide-angle X-ray scattering (GIWAXS) images indicated both edge- and face-on orientations of the semiconductor for these devices while electrical measurements revealed field-effect mobilities up to 10-3 cm2V¬-1s-1 and on/off current ratio of 103.
Our method has the combined advantages of low temperature and ambient pressure deposition while eliminating the drawbacks of solvents or the high cost of evaporation equipment. Further, as a digital printing method, the laser-printed layer is easily patternable as designed by any convenient graphics software. Since the powder is transferred in a dry state, surface dewetting is no longer an issue, which opens the door to even more substrate/dielectric materials that would otherwise reject solutions from adhering.
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