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Energy level alignment of electrically doped hole transport layers with transparent and conductive indium tin oxide and polymer anodes

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8 Author(s)
Fehse, K. ; Institut für Angewandte Photophysik, Technische Universität Dresden, D-01062 Dresden, Germany ; Olthof, Selina ; Walzer, Karsten ; Leo, Karl
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Using ultraviolet photoemission spectroscopy, we investigated the energy level alignment at the interfaces of typical anodes used in organic electronics, indium tin oxide (ITO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), with the oligomeric hole transport material N,N,N,N-tetrakis(4-methoxyphenyl)-benzidine (MeO-TPD), and studied the influence of electrical interface doping by the strong electron acceptor tetrafluoro tetracyanoquinodimethane (F4-TCNQ). The fundamentally different anode materials with work functions of 4.40 eV (ITO) and 4.85 eV (PEDOT:PSS) show different hole injection barriers, which also depend on the thickness of the F4-TCNQ interface dopant layer. PEDOT:PSS anodes exhibit a consistently lower hole injection barrier to MeO-TPD compared to ITO by 0.1 eV. We attribute this low hole injection barrier to additional charge transfer reactions at the PEDOT:PSS/MeO-TPD interface. In contrast, the deposition of the electron acceptor at the interface helps significantly to lower the hole injection barrier for ITO anodes.

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Journal of Applied Physics  (Volume:102 ,  Issue: 7 )