Rubrene Single-Crystal Transistors with Perfluoropolyether Liquid Dielectric: Exploiting Free Dipoles to Induce Charge Carriers at Organic Surfaces

We report the use of perfluoropolyether (PFPE) as a liquid dielectric for use in rubrene single-crystal transistors. In particular, we explore the effect of the free, permanent dipoles in PFPE on the charge carrier accumulation and transport at the rubrene/PFPE interface. This provides a complementary approach to ionic liquid dielectrics where charge accumulation is achieved via mobile ions. Large hysteresis (i.e., a memory effect) in transistor transfer curves and peaks in the gate displacement current curves are observed and interpreted in terms of the dipolar response of PFPE to the gate electric field. The orientation of free dipoles in PFPE is found to have a significant influence on the formation and annihilation of the rubrene conducting channel. Hole densities on the order of 10 11 cm –2 are achieved at the surface of rubrene, and a transition from band-like to hopping transport near the freezing point of PFPE is evidenced by temperature-dependent Hall effect and resistance measurements. Overall, the dipole-induced memory effect and the possibility of further increase in charge accumulation by increasing the dipole density suggest that liquids with free, permanent dipoles may be interesting dielectrics for use in field-effect transport experiments.