Bulk limited conduction in electroluminescent polymer devices

Citation
Aj. Campbell et al., Bulk limited conduction in electroluminescent polymer devices, J APPL PHYS, 84(12), 1998, pp. 6737-6746
Citations number
27
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science
Journal title
JOURNAL OF APPLIED PHYSICS
ISSN journal
0021-8979 → ACNP
Volume
84
Issue
12
Year of publication
1998
Pages
6737 - 6746
Database
ISI
SICI code
0021-8979(199812)84:12<6737:BLCIEP>2.0.ZU;2-T
Abstract
The current-voltage (J-V) characteristics of ITO/polymer film/Al or Au stru ctures of poly(phenylene vinylene) (PPV) and a dialkoxy PPV copolymer have been recorded for a range of different film thickness d and temperatures T. At high applied bias all the characteristics can be fitted over a given ra nge to a power law J = KVm, where m increases with decreasing T, log( K) is proportional to m, and K is proportional to d(-a m), where alpha similar t o 2 (ITO/polymer film/Al devices) and similar to 1 (ITO/polymer film/Au dev ices). Different single carrier space charge limited conduction;1 theories have been used to try and explain this behavior. The analytical theory in w hich the carrier density is decreased by an exponential trap distribution l ying below effectively isoelectronic transport states is in good agreement, but cannot explain the thickness dependence of the ITO/polymer film/Au dev ices and can be criticized as being physically unreasonable. A numerical an alysis in which the mobility has the field and temperature dependence found for hopping transport in disordered systems is also in good agreement, but can only fit a small range of J and cannot explain the magnitude of K, the temperature dependence of m or the abrupt change in slope in the J-V chara cteristics with increasing bias. Mixed models are equally good but cannot e xplain the deviations from experiment. We consider that further experimenta l studies of carrier mobilities and the nature of the traps present in such materials is required to distinguish between these models and resolve the nature of bulk limited conduction in conjugated polymers. (C) 1998 American Institute of Physics. [S0021-8979(98)03424-0].