Abstract
White polymer phosphorescent light-emitting diodes (WPLEDs) have been fabricated
employing poly(ethylene glycol) dimethyl ether blended in the single active layer to
enhance the emission efficiency. The devices have a simple sandwich architecture of
ITO/poly((3,4-ethylenedioxythiophene): poly(styrenesulfonate)/emissive layer/CsF/Al. The
emissive layer uses a blend of poly(9-vinylcarbazole), 1,3-bis[(4-tert-
butylphenyl)-1,3,4-oxidiazolyl]phenylene, two or three phosphorescent dopants with
complementary colors. The addition of poly(ethylene glycol) dimethyl ether enhances
electron injection, transport, and the balance of densities of electrons and holes. The
measured current efficiency in the front viewing direction is 17.5 cd/A at 1800
cdcm<sup>2</sup> for the two complementary WPLEDs, and 35.7 cd/A at 3000
cd/m<sup>2</sup> for the three complementary color WPLEDs. The current efficiencies
remain high even at brightness levels up to 30,000 cd/m<sup>2</sup>. The high current
efficiency is ascribed to the improved electron injection ability from the metal
cathode, the enhanced charge carrier transport ability and the enhanced red emitting
intensity by blending with PEG-DME. Also the low roll-off of the current efficiency was
due to the lower triplet-polaron annihilation and the electric field-induced triplet
exciton quenching by increased charge carrier transport in unipolar device and broadened
recombination zone. The improved charge carrier injection at the interface and the
enhanced charge carrier transport were resulted from specific interfacial interactions
between PEG-DME and aluminum and higher electric field by blending with
PEG-DME.
© 2013 IEEE
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