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

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)]BF4 [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 10nm, 2wt% Cu(I) complex doped CBP layer and 2nm Bu-PBD layer shows CIE coordinates of (0.33,0.36) at applied bias of 10V, a maximum luminance of 2466cd∕m2, and a maximum current efficiency of 6.76cd∕A, corresponding to the power efficiency of 3.85lm∕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.