Electronic and spin functions of pi-electron interface in organic field-effect devices

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In this study, field-induced electron spin resonance (FI-ESR) method is applied to directly detect the spins of charge carries at the interface of organic FETs. Microscopic information such as electronic and spin states of charge carries and local molecular orientation is obtained, which is crucial in understanding the device functions. In high-mobility thin-film transistors of a thienothiophene-based molecule C8-BTBT , FI-ESR has provided evidence for the charge carrier motion even at 4K within highly crystalline domains. Correlation between mobility anisotropy and uniaxial orientation of polymer chains has been clarified in ultrathin polymeric transistors and correlation between the interface chemical treatments and mobility enhancement has been revealed in crystalline transistors of rubrene. Further, in high-density carrier injections, crossover from polarons with spins to spinless bipolarons or polaron pairs is suggested in both polymeric and molecular FETs.