Efficient electrophosphorescent polymer light-emitting devices using a Cs/Al cathode

Efficient electrophosphorescent polymer light-emitting devices have been developed using a Cs/Al cathode. The materials used were a molecularly doped poly(9-vinylcarbazole)-emissive layer with electrophosphorescent complexes: $bis[2-(2′-benzothienyl)-pyridinato-N,C3′](acetylacetonate)Ir(III)$ as a red emitter, fac-tris(2-phenylpyridyl)Ir(III) as a green emitter, and $bis[(4,6-difluorophenyl)-pyridinato-N,C2](picolinato)Ir(III)$ as a blue emitter. The red, green, and blue electrophosphorescent emitting devices exhibited efficient emissions of 4, 31, and 14 cd/A, respectively. An inspection of secondary ion mass spectroscopy (SIMS) profiles confirmed that Cs diffuses into both Al and the emissive layer. Also, a Cs concentration of approximately 1 atomic% was estimated to be present at the interface from x-ray photoelectron spectroscopy (XPS) profiles.