Efficient solution-processed electrophosphorescent devices using ionic iridium complexes as the dopants

Efficient solution-processed electrophosphorescent devices using two blue-emitting ionic iridium complexes (complex I and complex 2) were fabricated, with poly(N-vinylcarbazole) (PVK):1,3-bis(5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl)benzene (OXD-7) as the host and CS2CO3/Al as the cathode. Using complex I as the dopant, we obtained efficient blue-green electrophosphorescence from single-layer devices with a maximum efficiency of 12.2 cd A(-1), a maximum brightness of 12,600 cd m(-2) and CIE (Commission Internationale de l'Eclairage) coordinates of (0.19, 0.45). And the maximum efficiency of the device based on complex I can be further improved to 20.2 cd A(-1), when a thin 1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBI) layer was inserted between the light-emitting layer and the cathode. Using complex 2 as the dopant, we obtained deep-blue electrophosphorescence with the emission peak at 458 nm and CIE coordinates of (0.16, 0.22). Our work suggests that ionic iridium complexes are promising phosphors for obtaining efficient electrophosphorescence in the blue region. (C) 2008 Elsevier B.V. All rights reserved.