Controlledp-type doping of polycrystalline and amorphous organic layers: Self-consistent description of conductivity and field-effect mobility by a microscopic percolation model

Abstract

We present a systematic study on p-type doping of zinc-phthalocyanine by tetrafluoro-tetracyano-quinodimethane as an example of controlled doping of thin organic films by cosublimation of matrix and dopant. The zinc-phthalocyanine layers are prepared both in polycrystalline and amorphous phase by variation of the sublimation conditions. The films are electrically characterized in situ by temperature dependent conductivity and Seebeck and field-effect measurements. In addition to previous work, we show that also amorphous phthalocyanine layers can be doped, i.e., their conductivity increases and their Seebeck coefficient decreases indicating a shift of the Fermi level towards the hole transport level. The field-effect mobility of the polycrystalline samples is in the range of ${10}^{\ensuremath{-}4}--{10}^{\ensuremath{-}3} {\mathrm{cm}}^{\ensuremath{-}2}/\mathrm{Vs}$ and increases with increasing dopant concentration. Adapting a percolation model presented by Vissenberg and Matters [Phys. Rev. B, 57, 12 964 (1998)], which assumes hopping transport within a distribution of localized states, we can quantitatively describe the conductivity (in different organic layers) and the field-effect mobility.