Effect of Surface Plasmon on 4,4$'$-N,N$'$-Dicarbazolylbiphenyl:Tris(2-phenylpyridinate) Iridium(III)-Based Phosphorescent Organic Light-Emitting Diodes

The spectra of two organic light-emitting diodes (OLEDs), where the emission layers consisted of either 4,4'-N,N'-dicarbazolylbiphenyl (CBP) doped with tris(2-phenylpyridinate) iridium(III) [Ir(ppy)3] [CBP:Ir(ppy)3] or CBP/CBP:Ir(ppy)3 were compared. Both devices had an Ag film as a cathode. A subpeak appeared only for the OLED with CBP/CBP:Ir(ppy)3, when it was current-excited and photoexcited in the region with the Ag film. This was considered to be caused by the surface plasmon effect. Experimental results suggested that the surface plasmon enhancement of radiation was effective in an emitting material with low luminescence efficiency.