White-electrophosphorescent devices based on copper complexes using 2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole as chromaticity-tuning layer

摘要

Efficient white organic light-emitting diodes based on copper complex, [Cu(bis[2-(diphenylphosphino)phenyl]ether)(6,7-dicyanodipyrido[2,2-d: 2', 3'-f]quinoxaline)]BF_4 [Cu(I) complex], in which the white emission composed of yellow emission from Cu(I) complex doped 4,4'-N,N'-dicarbazole-biphenyl (CBP) layer and blue emission from N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-benzidine)-4,4'-diamine layer, were fabricated. A thin 2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole (Bu-PBD) layer sandwiched between the two emission layers acts as a chromaticity-tuning layer. The white device with 10 nm, 2 wt % Cu(I) complex doped CBP layer and 2 nm Bu-PBD layer shows CIE coordinates of (0.33,0.36) at applied bias of 10 V, a maximum luminance of 2466 cd/m~2, and a maximum current efficiency of 6.76 cd/A, corresponding to the power efficiency of 3.85 lm/W. The efficient white emission is attributed to the simultaneous exciton formation in both emission layer. The working mechanism of the thin Bu-PBD layer for achieving white emission was also discussed.