Carrier trapping and efficient recombination of electrophosphorescent device with stepwise doping profile

Byung Doo Chin; Min Chul Suh; Mu-Hyun Kim; Seong Taek Lee; Hye Dong Kim; Ho Kyoon Chung
March 2005
Applied Physics Letters;3/28/2005, Vol. 86 Issue 13, p133505
Academic Journal
We have presented a physical concept for enhancing efficiency and lifetime of doped electrophosphorescent organic light-emitting devices. In order to provide a control parameter for higher device performance, a stepwise doping concentration profile at the emission layer was prepared. A more than 30% improvement of power efficiency was obtained for green electrophosphorescent device with a higher doping ratio at the emission layer-hole transport layer interface. We explained the carrier trapping and transport mechanism with direct recombination of an exciton in an iridium-based dopant system. When compared to green device, phosphorescent red devices showed a more significant charge trapping effect at low doping concentration, which is responsible for shifting the recombination zone far from the emission layer-hole transport layer interface. Therefore, charge trapping by doping control in an emission layer could be utilized for a charge-balancing technique for the confinement of a triplet exciton.


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