Highly efficient polymer light-emitting devices using ambipolar phosphorescent polymers

Suzuki, Mitsunori; Tokito, Shizuo; Sato, Fumio; Igarashi, Takeshi; Kondo, Kunio; Koyama, Tamami; Yamaguchi, Tetsuhiko
March 2005
Applied Physics Letters;3/7/2005, Vol. 86 Issue 10, p103507
Academic Journal
We report on highly efficient polymer light-emitting devices (PLEDs) achieved using a phosphorescent polymer, which is a copolymer that has bis(2-phenylpyridine)iridium (acetylacetonate) [Ir(ppy)2(acac)], N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as a side group. The phosphorescent polymer has an ambipolar charge-transport ability. An increase in PBD unit concentration allows an improvement in the efficiency of the PLEDs. Ba and Cs were used for electron-injection layers as well as Ca, to improve the electron injection. An external quantum efficiency of 11.8% and a power efficiency of 38.6 lm/W were obtained by using Cs. The results indicate that this can be attributed to an improvement in the charge balance of electrons and holes.


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