The role of the dielectric interface in organic transistors: A combined device and photoemission study

Here the device performance is shown to be directly related to the measured electronic level alignment at the dielectric interface in C-60 organic field effect transistors (OFETs). We compare C-60 on two dielectrics: Al2O3 and a divinyltetramethyldisiloxane-bis(benzocyclobutene) (BCB)-Al2O3 bilayer. The improved transistor performance and the lowering of the threshold voltage by 0.8 V due to the BCB interlayer are rejected in the ultra-violet photoemission data. These show a 0.8 eV difference in the work function and a concomitant shift in the C-60 valence band. By following the work function the improvement is shown to be due to the dipole at the organic BCB-C-60 interface. (C) 2009 Elsevier B.V. All rights reserved.