AVS 47th International Symposium
    Organic Films and Devices Wednesday Sessions
       Session OF-WeP

Paper OF-WeP3
Controlled Doping of Polycrystalline and Amorphous Molecular Organic Layers: Physics and Device Prospects

Wednesday, October 4, 2000, 11:00 am, Room Exhibit Hall C & D

Session: Poster Session
Presenter: T. Fritz, TU Dresden, Institut fuer Angewandte Photophysik, Germany
Authors: X. Zhou, TU Dresden, Institut fuer Angewandte Photophysik, Germany
B. Maennig, TU Dresden, Institut fuer Angewandte Photophysik, Germany
M. Pfeiffer, TU Dresden, Institut fuer Angewandte Photophysik, Germany
J. Blochwitz, TU Dresden, Institut fuer Angewandte Photophysik, Germany
T. Fritz, TU Dresden, Institut fuer Angewandte Photophysik, Germany
K. Leo, TU Dresden, Institut fuer Angewandte Photophysik, Germany
Correspondent: Click to Email
Organic dyes with a conjugated electron system are currently investigated intensively for optoelectronic applications. In contrast to classical silicon technology, the materials used for both research and devices such as organic light-emitting diodes (OLED) are usually prepared in a nominally undoped form, leading to scattering of device parameters and higher operating voltages as compared to e.g. polymeric devices. Shifting the Fermi level towards the transport states by doping can reduce ohmic losses, ease carrier injection from contacts and increase the built-in potential of Schottky- or pn-junctions. We present here the results of a comprehensive study of controlled p-type doping of various polycrystalline and amorphous organic materials by the strong organic acceptor F4-TCNQ (tetrafluoro-tetracyano-quinodimethane). It turns out that doping is more efficient for the polycrystalline materials like the phthalocyanines where doping enhances the conductivity by up to eight orders of magnitude (10@super -2@ S/cm). Nevertheless, we could show for the first time that also amorphous phthalocyanine layers (deposited onto cooled substrates) and amorphous wide-gap materials can be doped, i.e. their conductivity increases and their Seebeck coefficient decreases indicating a shift of the Fermi level towards the hole transport state. Amorphous wide gap materials like TDATA or TPD are commonly used as hole transport materials in OLEDs because they form smooth and stable layers. We show here that controlled intentional doping of these layers strongly reduces the operating voltages of OLEDs.