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405a

Water-Dispersible, Conductive Polyaniline Makes Better Electrical Contacts to P-Type Organic Semiconductors in Otfts

Lynn Loo1, Kwangseok Lee1, Joung Eun Yoo1, Timothy Smith2, and Keith Stevenson2. (1) Chemical Engineering, The University of Texas at Austin, CPE Building, C0400, Austin, TX 78712, (2) Chemistry, The University of Texas at Austin, CPE Building, C0400, Austin, TX 78712

We present the first detailed report that directly correlates the reduced contact resistance in organic thin-film transistors with fundamental structural and morphological characterization at the organic semiconductor-conducting polymer interface.

Using stamp-and-spin-cast, a patterning technique for depositing water-dispersible, conductive polyaniline, we have successfully fabricated bottom-contact thin-film transistors with pentacene (p-type) as the organic semiconductors. To compare the performance of polyaniline electrodes with gold electrodes, we also fabricated reference organic thin-film transistors with analogous dimensions and geometry that use gold electrodes. Structural and electrical studies on these two batches of thin-film transistors reveal dramatic morphological differences at the channel-electrode interface that influence the linear regime current-voltage characteristics of the devices. Specifically, in bottom-contact thin-film transistors with polyaniline electrodes, the pentacene grains are similar in size and are continuous across the channel-electrode interface. On a molecular level, the fused rings of pentacene are oriented perpendicular to the surface both in the channel and on polyaniline electrodes. Accordingly, the current varies linearly with the source-drain voltage, an indication that the contact resistance is small in such devices. In thin-film transistors with gold electrodes, however, the pentacene grains are different in size and are discontinuous across the channel-electrode interface. Further, the fused rings of pentacene are oriented perpendicular to the channel surface and parallel to the gold surface. Such differences across the channel-electrode interface leads to structural and electronic disorder, which in turn results in current-voltage characteristics that deviate from linearity. Surface scanning potential measurements suggests that this deviation occurs at the channel-electrode interface and constitutes large contact resistance in devices with gold electrodes.