Double Beneficial Role of Fluorinated Fullerene Dopants on Organic Thin Films Transistors: Structural Stability and Improved Performance

The present work assesses improved carrier injection in organic field effect transistors (OFETs) by contact doping and provides fundamental insight on the multiple impacts that the dopant/semiconductor interface details have on the long-term and thermal stability of devices. We investigate donor [1]benzothieno[3,2-b]-[1]benzothiophene (BTBT) derivatives with one and two octyl side-chains attached to the core, therefore constituting asymmetric (BTBT-C8) and symmetric (C8-BTBT-C8) molecules, respectively. Our results reveal that films formed out of the asymmetric BTBT-C8 expose the same alkyl-terminated surface as the C8-BTBT-C8 films do. In both cases, the consequence of depositing fluorinated fullerene (C60F48) as molecular p-dopant is the formation of C60F48 crystalline islands decorating the step edges of the underlying semiconductor film surface. We demonstrate that local work function changes along with a peculiar nanomorphology lead to the double beneficial effect of lowering the contact resistance and providing long-term and enhanced thermal stability of the devices.