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We investigate theoretically the role of carrier trapping on the efficiency of single-layer organic light-emitting diodes (OLEDs) by incorporating traps into the OLED device model of Davids et al. [J. Appl. Phys. 82, 6319 (1997)]. Carrier trapping directly affects the density and mobility balance between electrons and holes through its effects on injection and mobility. In addition, trap-mediated changes in density alter recombination rates and spatial profiles of recombination that become important when excited state quenching at metallic contacts is considered. We illustrate these various influences of traps on device efficiency through computations on a series of model devices. Good agreement is obtained with previous experiments by Menon et al. [Chem. Mater. 14, 3668 (2002)], where energetic disorder from transport traps was shown to reduce device efficiency. Our model, however, predicts circumstances where traps will improve device efficiency as well and can assist with selection of contacts to realistic organic materials. [ABSTRACT FROM AUTHOR]

Thin polycrystalline films of perylenetetracarboxylic dianyhydride (PTCDA), an organic molecular solid, exhibits substantial anisotropies in its electronic transport properties. Only electrons transport in the directions along molecular planes, while mainly holes transport in the direction normal to molecular planes. A series of measurements on both field effect transistors with PTCDA active layers and light emitting diodes with PTCDA transport layers documents the anisotropy seen in the electronic transport in thin films of PTCDA. © 1997 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which examined the interface between evaporated aluminum and poly(p-phenylenevinylene) (PPV) in situ using x-ray photoelectron spectroscopy. Materials and methods used; Description of the spectrum of a PPV film; Characteristics of the spectra after aluminum metal deposition.

Energetic disorder plays a critical role in governing the performance of organic light-emitting diodes (OLEDs). This is particularly true for polymer-based OLEDs in which disorder can be controlled but not eliminated. Contrary to the common assumption that energetic disorder has only a negative effect on performance, we provide experimental evidence of improved efficiency when the energetic disorder is increased upon deliberate addition of traps via an increase in polymer chain length distribution. We use numerical calculations to extract the mechanisms responsible for the observed improvements and discuss the general conditions under which traps can be introduced to increase device efficiency. [ABSTRACT FROM AUTHOR]