Doped N-Type Organic Field-Effect Transistors Based on Faux-Hawk Fullerene

Faux-hawk fullerenes are promising candidates for high-performance organic field-effect transistors (OFETs). They show dense molecular packing and high thermal stability. Furthermore, in contrast to most other C-60 derivates, functionalization of the fullerene core by the fluorinated group C6F4CF2 does not increase their lowest unoccupied orbital position, which allows the use of air-stable molecular n-dopants to optimize their performance. The influence of n-doping on the performance of OFETs based on the faux-hawk fullerene 1,9-C-60(cyclo-CF2(2-C6F4)) (C60FHF) is studied. An analytic model for n-doped transistors is presented and used to clarify the origin of the increase in the subthreshold swing usually observed in doped OFETs. It is shown that the increase in subthreshold swing can be minimized by using a bulk dopant layer at the gate dielectric/C60FHF layer instead of a mixed host:dopant layer. Following an optimization of the OFETs, an average electron mobility of 0.34 cm(2) V-1 s(-1), a subthreshold swing below 400 mV dec(-1) for doped transistors, and a contact resistance of 10 k omega cm is obtained, which is among the best performance for fullerene based n-type semiconductors.