High efficiency polymer light emitting diodes based on poly(phenylene vinylene)s with balanced electron and hole fluxes

We have synthesized the yellow light emitting polymers by modifying the green emission alkoxyphenyl-substituted poly(phenylene vinylene)s (PPVs) through copolymeration with the short side chain comonomer [(2,5-dimethoxy-p-phenylene)vinylene] (DMeOPV) to allow a more locally ordered main chain structure. Through the charge carrier flux measurements on single carrier devices, it is found that the limiting factor that determines the overall rate of charge transport is the inter-chain charge transport, which is greatly affected by chain structure and morphology. The local order can promote the electron mobility and flux, which allows an adjusting of the electron and hole carriers fluxes to some extent such that an improvement in the device performance can be made. The maximum brightness of the yellow light emitting polymers with 10 and 25% of comonomer (DMeOPV) are 57,000 (at 15 V/90 nm) and 73,000 (at 13 V/83 nm) cd/m(2); and the maximum luminous efficiencies are 15.5 (at 7 V/90 nm) and 11.9 cd/A (at 5.5 V/83 nm), respectively. (C) 2002 Elsevier Science B.V. All rights reserved.