In-situ conductivity and Seebeck measurements of highly efficient n-dopants in fullerene C60

We present two organic dimetal complexes Cr-2(hpp)(4) and W-2(hpp)(4) as n-dopants investigated in the model system of fullerene C-60 for the application in organic electronic devices. Conductivity and Seebeck measurements on doped layers are carried out in vacuum at different doping concentrations and various substrate temperatures to compare the two dopants. Very high conductivities of up to 4 S/cm are achieved for both organic dopants. The thermal activation energy of the conductivity as well as the measured Seebeck coefficient are found to decrease with increasing doping concentration, indicating a shift of the Fermi level towards the electron transport level of the n-doped C-60. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3689778]