White organic light-emitting diodes based on tandem structures

White organic light-emitting diodes made of two electroluminescent (EL) units connected by a charge generation layer were fabricated. Thus, with a tandem structure of indium tin oxide/N,N-'-di(naphthalene-1-yl)-N,N-'-diphenyl-benzidine (NPB)/9,10-bis-(beta-naphthyl)-anthrene (ADN)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/tris(8-hydroxyquinoline) aluminum (Alq(3))/BCP:Li/V2O5/NPB/Alq(3):4-(dicyanomethylene)-2-t-butyle-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB)/Alq(3)/LiF/Al, a stable white light with Commission Internationale De L'Eclairage chromaticity coordinates from (0.35, 0.32) at 18 V to (0.36, 0.36) at 50 V was generated. It was clearly seen that the EL spectra consist of red band at 600 nm due to DCJTB, green band at 505 nm due to Alq(3), and blue band at 435 nm due to ADN, and the current efficiency and brightness equal basically to the sum of the two EL units. As a result, the tandem devices showed white light emission with a maximum brightness of 10 200 cd/m(2) at a bias of 40 V and a maximum current efficiency of 10.7 cd/A at a current density of 3.5 mA/cm(2). (C) 2005 American Institute of Physics.