Tuned emission from organic light emitting devices based upon divalent osmium complexes.

摘要

Electrophosphorescence tuned from the green to red (522 nm ― 650 nm) was achieved from double-layer light emitting devices using osmium (Os) complexes doped blend of either poly(vinylcarbazole) and 2-fe?t-butylpnenyl-5-biphenyl-1,3,4-oxadiazole (PVK:PBD), or poly(vinyl naphthalene) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PVN:PBD) as the emitting layer. Blending PVN with PBD greatly suppresses the electromer emission of PVN. The PVN:PBD blend emanates a short wavelength EL emission peaking at around 375 nm, which well overlaps with the absorption spectra of the Os complexes and ensures very efficient energy transfer to the Os complex dopants. PVK:PBD has an EL emission around 450 nm which does not overlap the absorption bands of the osmium complexes and also produces devices of lower efficiency, but PVK is a better transport layer and therefore produces brighter devices. The best external quantum efficiency of the double-layer devices was 2.2%, with a photometric efficiency of 1.9 cd/A. The brightest device achieved was 1,600 cd/m~2.