In this paper, we discuss the surface doping in sexithiophene (T6) organic
field-effect transistors by PDI-8CN2. We show that an accumulation
heterojunction is formed at the interface between the organic semiconductors
and that the consequent band bending in T6 caused by PDI-8CN2 deposition can be
addressed as the cause of the surface doping in T6 transistors. Several
evidences of this phenomenon have been furnished both by electrical transport
and photoemission measurements, namely the increase in the conductivity, the
shift of the threshold voltage and the shift of the T6 HOMO peak towards higher
binding energies.Comment: 5 pages, 5 figure
