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 C60 organic field effect transistors (OFETs). We compare C60 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 reflected in the ultra-violet photoemission data. These show a 0.8 eV difference in the work function and a concomitant shift in the C60 valence band. By following the work function the improvement is shown to be due to the dipole at the organic BCB–C60 interface.