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2 June 1994 Carrier tunneling and device characteristics in polymer light-emitting diodes
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This paper demonstrates that the characteristics of light- emitting diodes (LEDs) based upon MEH-PPV, (more fully known as poly(2-methoxy,5-(2'-ethyl-heroxy)-1,4-phenylene-vinylene)), are determined by tunneling of both the holes and the electrons through interface barriers caused by the band offset between the polymer and the electrodes. It is shown that manipulating these offsets can control the useful operating-voltage of the device as well as its efficiency. A Model is developed which clearly explains the device characteristics of a wide range of diodes based upon MEH-PPV. The turn-on voltage for an ideal device is shown to be equal to the band-gap, i.e. 2.1eV for MEH-PPV, and is slightly lower at 1.8eV for an indium-tin oxide/MEH-PPV/Ca device. If there is a significant difference in the barrier height, the smaller of the two barriers controls the I-V characteristics while the larger barrier determines the device efficiency. In ITO/MEH-PPV/Ca devices, the barrier to hole injection is 0.2eV and the barrier to electron injection is only 0.1eV. We show that reducing the hold barrier to 0.1eV using a polyaniline anode halves the operating voltage and increases device efficiency.
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ian D. Parker "Carrier tunneling and device characteristics in polymer light-emitting diodes", Proc. SPIE 2144, Advanced Photonics Materials for Information Technology, (2 June 1994);

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