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

Abstract

Iridium complexes with alkyl substituted 2-phenylpyridine, $\mathrm{Ir(Bu-PPy}{)}_3,$ were synthesized. Polymer light emitting diodes with Ir complexes as the guest materials and the substituted polyphenylenes as the host were fabricated. $\mathrm{Ir(Bu-PPy}{)}_3$ -doped Poly(2-(6-cyano-6-methyl)- heptyloxy-1,4-phenylene) (CNPPP) device showed generally higher quantum efficiency (QE) than that of $\mathrm{Ir(PPy}{)}_3$ -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 $\mathrm{Ir(Bu-PPy}{)}_3$ -doped CNPPP: the maximum external quantum efficiency, QE, and luminance efficiency reached 5.1% ph/el and 12 cd/A, respectively, at 800 ${\mathrm{cd/m}}^2$ and maintained at 4.2% ph/el and 10 cd/A, respectively, at 2500 ${\mathrm{cd/m}}^2.$