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

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.