Regensburg 2010 – scientific programme

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O: Fachverband Oberflächenphysik

O 86: Organic, electronics and photovoltaics

O 86.1: Talk

Friday, March 26, 2010, 11:15–11:30, H40

WO3 under, in and on CuPc - A doping mechanism for organic semiconductors — •Corinna Hein, Eric Mankel, Thomas Mayer, and Wolfram Jaegermann — TU Darmstadt, FG Oberflächenforschung, Petersenstraße 32, 64287 Darmstadt

Doping of organic semiconductors plays an important role for the development of organic devices like photovoltaic cells or organic light emitting diodes. P-doping of CuPc which is frequently used as hole conductor was performed successfully by coevaporation of the CuPc matrix and the WO3 dopant showing good doping efficiency and limit. The Fermi level determined by synchrotron induced photoemission shifts gradually with the concentration of dopant up to 690meV. To clarify the doping mechanism band alignment of both CuPc/WO3 and WO3/CuPc interfaces was determined. The work function difference of the two materials is overcome by band bending and an interface dipole. The dipole is 2eV for CuPc/WO3 and 1.4eV for WO3/CuPc lowering the amount of transferred charge and therefore limiting the doping efficiency. The sum of band bending at the interface adds up to 0.5eV for the CuPc/WO3 interface and 1.1eV for CuPc deposited on WO3. The Fermi level shift in the composites fits to this range in accord to a doping model assuming cluster growth of WO3 within CuPc. The model could be directly proofed by transmission electron microscopy distinguishing the two phases of CuPc and WO3 with a cluster size of approximately 5nm.