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2 September 2008 Electronic structure of doping in organic semiconductor
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We investigated the electronic structure of organic thin films doped with alkali metal using photoemission and inverse photoemission spectroscopy (UPS, XPS and IPES). We found that doping induces energy level shift, which can be seen as in two different stages. The first stage is predominantly due to the Fermi level moving in the energy gap as a result of the doping of electrons from the alkaline metal to the organic, and the second stage is characterized by the significant modification of organic energy levels such as the introduction of a new gap state, new core level components, and change of binding energies with respect to the frontier orbital. In addition, we observed that the energy level shift in the first stage depended approximately in a semi-logarithmic fashion on the doping concentration, whose slope could not be explained by the conventional model used in inorganic semiconductors. The lowest unoccupied molecular orbital (LUMO) is observed to diminish as doping progresses. Furthermore, we observed that the doping induced modification can be compensated by depositing Au or O2 on alkali metal doped organic films. The modification of the electronic structure by other inorganic or organic dopants will also be discussed.
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Huanjun Ding and Yongli Gao "Electronic structure of doping in organic semiconductor", Proc. SPIE 7051, Organic Light Emitting Materials and Devices XII, 705111 (2 September 2008);

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