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Soluble Electroluminescent Poly(phenylene vinylene)s with Balanced Electron- and Hole Injections
journal contribution
posted on 2001-02-14, 00:00 authored by Yuh-Zheng Lee, Xiwen Chen, Show-An Chen, Pei-Kuen Wei, Wun-Shain FannWe report a new route for the design of efficient soluble electroluminescent PPV-based copolymers
bearing electron-deficient oxadiazole (OXD) moieties on side chains. The introduction of OXD through a
long alkylene spacer with PPV backbone provides a molecular dispersion of OXD in the film; both the side
chain OXD and the main chain PPV do retain their own electron-transport and emissive properties, respectively.
The use of phenylene vinylene derivatives with asymmetric and branched substituents and a long spacer provides
solubility for ease of device fabrication as well as amorphous structure to allow a well-mixing of OXD groups
with the main chains. By properly adjusting the OXD content through copolymerization, we can tailor the
chemical structure of electroluminescent material to give a balance of hole- and electron injections for various
metal cathodes, such that the quantum efficiency is significantly improved and the turn-on voltage is reduced
for the devices with aluminum and calcium. For the device with calcium fabricated in open air, a maximum
brightness of 15000 cd/m2 at 15 V/100 nm and a maximum luminance efficiency of 2.27 cd/A can be obtained,
respectively, about 30 times brighter and 9.4 times more efficient than those with the corresponding
homopolymer, poly[2-methoxy-5-(2‘-ethylhexyloxy)-p-phenylenevinylene] (MEH−PPV). The use of physical
blends to simulate the copolymers provides no significant improvement, since phase-separation structures appear,
causing an inefficient utilization of OXD and sometimes voltage-dependent emission spectra. The present
route permits a fabrication of single layer PLED with high brightness, high efficiency, and low turn-on voltage.
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emissive properties9.4 timesmetal cathodesside chain OXDHole Injectionselectron injectionsluminance efficiencyphenylene vinylene derivativeslayer PLEDOXD contentquantum efficiencyalkylene spacerchemical structureOXD groupsMEHdevice fabricationchain PPV30 timesside chainselectroluminescent materialPPV backbone
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