Electrophosphorescence from a Polymer Guest–Host System with an Iridium Complex as Guest: Förster Energy Transfer and Charge Trapping

Authors


  • This work was supported by the Mitsubishi Chemical Center for Advanced Materials at UCSB and the Air Force Office of Scientific Research through the MURI Center (“Polymeric Smart Skins”), Charles Lee, Program Officer. Synthesis of the iridium complexes was supported by a grant to G. Bazan from Kodak. X. Gong is grateful to Dr. Gang Yu of Dupont Displays for valuable discussion.

Abstract

We report high-efficiency green electrophosphorescent light-emitting diodes obtained by using tris[9,9-dihexyl-2-(phenyl-4′-(-pyridin-2″-yl))fluorene]iridium(III) (Ir(DPPF)3) as the guest, and a blend of poly(vinylcarbazole) (PVK) with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol (PBD) as the host. The electrophosphorescent emission is characteristic of Ir(DPPF)3, with its maximum at 550 nm. An external quantum efficiency of 8 % photons per electron and luminous efficiency of 29 cd A–1, with maximum brightness of 3500 cd m–2, were achieved at 1 wt.-% concentration of Ir(DPPF)3. The devices exhibited no emission from PVK or PBD, even at the lowest concentration of Ir(DPPF)3 (0.1 wt.-%). The results indicate that Förster energy transfer plays a minor role in achieving high efficiencies in these devices. Direct charge trapping appears to be the main operating mechanism.

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