Carrier Transport Properties of Monodisperse Glassy-Nematic Oligofluorenes in Organic Field-Effect Transistors

A heptafluorene, F(Pr)5F(MB)2, a dodecafluorene, F(MB)10F(EH)2, and poly(9,9‘-dioctylfluorene), PFO, were used to prepare field-effect transistors. Monodomain and polydomain glassy-nematic films as well as glassy-amorphous films were prepared for the measurement of hole mobility. In a monodomain film, the μ ∥ value is determined by the chain length in oligofluorene and the persistence length in polyfluorene. Mobility in a polydomain film lies between μ ∥ and μ ⊥ of a monodomain film. Amorphous films possess the lowest mobility of all presumably because of the geometric and energetic disorder. The OFET containing a monodomain glassy-nematic film of F(MB)10F(EH)2 exhibits a field-effect mobility of 0.012 cm 2 /Vs with an on/off current ratio of 1.0 × 10 4, a substantial improvement over a monodomain glassy-nematic film of PFO.