Highly efficient electrophosphorescent devices based on conjugated polymers doped with iridium complexes

Iridium complexes with alkyl substituted 2-phenylpyridine, Ir(Bu-PPy)(3), were synthesized. Polymer light emitting diodes with Ir complexes as the guest materials and the substituted polyphenylenes as the host were fabricated. Ir(Bu-PPy)(3)-doped Poly(2-(6-cyano-6-methyl)- heptyloxy-1,4-phenylene) (CNPPP) device showed generally higher quantum efficiency (QE) than that of Ir(PPy)(3)-doped device for a given dopant concentration. More importantly, the addition of butyl group into phenylpyridine ligand significantly suppresses the decay of device efficiency at high current density. For instance, for devices made with Ir(Bu-PPy)(3)-doped CNPPP: the maximum external quantum efficiency, QE, and luminance efficiency reached 5.1% ph/el and 12 cd/A, respectively, at 800 cd/m(2) and maintained at 4.2% ph/el and 10 cd/A, respectively, at 2500 cd/m(2). (C) 2002 American Institute of Physics.