8 August 2003 Oxygen-related defects in MEH-PPV polymer light-emitting diodes
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Proceedings Volume 5122, Advanced Organic and Inorganic Optical Materials; (2003) https://doi.org/10.1117/12.515718
Event: 2003 Chapter books, 2003, Bellingham, WA, United States
We investigated carrier transport and capture in poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) Schottky diodes by thermally stimulated currents and current-voltage characteristics. Experimentally in the region from 80 K up to 450 K two distinct current peaks were found after the white light excitation. Their maxima were located in the temperature regions 214 - 244 K and 304 - 394 K respectively. The detailed numerical modeling revealed that the full TSC is a superposition of at least six traps and/or other thermally stimulated processes with different parameters. We observed effect of oxygen on these traps that was never reported before. The filling of three of these levels could be increased significantly by exposing the sample to the air. The two deepest traps with activation energies at about 0.76 - 0.8 eV and 0.76 - 0.9 eV are likely located nearby surface. Meanwhile the mid-deep trap with an activation energy 0.45 - 0.55 eV is most probably distributed over the sample depth. As far as these traps are related to the oxygen they could be identified as electron traps. In contrast none of the traps could be recharged by applied voltage. Instead the injected carriers created a long-living sample polarization. The non-exponential depolarization lasted for several thousands seconds and was not thermally activated even above the glass transition temperature. These facts make it necessary to include into analysis other possible physico-chemical mechanisms, e.g., reversible chemical reactions or chain structure reorganization induced by electric field.
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Vaidotas Kazukauskas, Vaidotas Kazukauskas, } "Oxygen-related defects in MEH-PPV polymer light-emitting diodes", Proc. SPIE 5122, Advanced Organic and Inorganic Optical Materials, (8 August 2003); doi: 10.1117/12.515718; https://doi.org/10.1117/12.515718

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