Thiazolothiazole-Based Quinoidal Compounds for High-Performance n-Channel Organic Field-Effect Transistors with Low-Cost Metal Electrodes

Thiazolothiazole-based quinoidal molecules B1 and B2 are designed and synthesized. B1 and B2 have low-lying lowest unoccupied molecular orbital energy levels of -4.47 and -4.41 eV, respectively. In thin films, B1 forms J-type aggregation while B2 adopts H-type aggregation. B1 and B2 can react with copper and silver metals and form charge transfer salts. Thin-film transistor characteristics show both compounds display n-channel field-effect behavior, and the Ag and Cu source-drain electrode-based devices exhibit similar mobility as Au source-drain electrode-based ones. B1-based transistors with Au, Cu, and Ag electrodes exhibit electron mobilities of 0.54, 0.45, and 0.39 cm(2) V-1 s(-1), respectively. The mobility of B2 is 0.061 cm(2) V-1 s(-1) for Au electrode-based devices, 0.081 cm(2) V-1 s(-1) for Cu electrode-based devices, and 0.09 cm(2) V-1 s(-1) for Ag electrode-based devices. The self-doping layer formed by the reaction of electrodes (Ag, Cu) and organic semiconductors (B1 and B2), at the interface of electrode/organic semiconductor is responsible for the high performance of Ag and Cu electrode-based devices. All these results demonstrate the introduction of self-doping layer at electrode/organic semiconductor is a general strategy to fabricate high performance transistors with low cost metals Ag and Cu as source-drain electrodes.