Trap levels and effect of oxygen in poly[2-methoxy-5- (2′-ethyl-hexyloxy)-1,4-phenylene vinylene] diodes

Kazˇukauskas, V.; Tzeng, H.; Chen, S. A.
March 2002
Applied Physics Letters;3/18/2002, Vol. 80 Issue 11, p2017
Academic Journal
We investigated carrier transport and capture in poly[2-methoxy-5-(2'-ethyl-hexyloxy)1,4-phenylene vinylene] Schottky diodes by thermally stimulated currents and current-voltage characteristics. Two main charge traps were found after the white light excitation. Their effective activation energies were in the ranges 0.207-0.355 eV and 0.75-0.91 eV, and the total charges were up to (2-8) x 10[sup 14] cm[sup -3] and ∼(1-2) x 10[sup 16] cm[sup -3] respectively. The activation energy and level filling could be increased significantly by exposing the sample to the air. The deeper trap is likely located near the surface, meanwhile the shallower trap is most probably distributed over the sample depth. As far as these traps are related to the oxygen, both of them 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 nonexponential depolarization lasted for several thousands of seconds and was not thermally activated even above the glass transition temperature. These facts make it necessary to include into analysis other possible physicochemical mechanisms, e.g., reversible chemical reactions or chain structure reorganization induced by electric field.


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