Observation of field-induced charge carriers in high-mobility organic transistors of a thienothiophene-based small molecule: Electron spin resonance measurements

Electron spin resonance (ESR) measurements are performed on field-induced charge carriers in high-mobility organic transistors of polycrystalline dioctylbenzothieno[2,3-b]benzothiophene (C-8-BTBT) films. The angular dependences of the ESR spectra are well fitted by orthorhombic g values with the largest component of g(Y) = 2.0110 nearly parallel to the normal direction of the substrate but tilted by 5 degrees. The results indicate a highly organized end-on alignment of C-8-BTBT molecules at the device interface. The ESR linewidth exhibits motional narrowing down to 4 K, providing microscopic evidence for high carrier mobilities within the crystalline domains of C-8-BTBT.