Energy transfer and white emitting organic thin film electroluminescence

Energy transfer between in N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-bipheny l-4-4'-diamine (NPB) and rubrene was investigated. The device ITO/CuPc/NPB: rubrene/blocking layer /Alq/MgAg, in which copper phthalocyanine (CuPc) is used as buffer layer, NPB as the hole transporting layer (HTL), trimer of N -arylbenzimidazoles (TPBi) [or 2-(4-biphenylyl)-5-(4-tertbutylphenyl)-1,2,3 -oxadiazole(PBD) or 1,2,3-triazolederivative(TAZ)] as the blocking layer, T ris(8-quinolinolato)aluminum complex (Alq) as electron transporting layers (ETL), can not give white emitting light. White emitting light can be reali zed in a new device with the structure ITO/CuPc/NPB/blocking layer:rubene/A lq/MeAg, in which rubrene is doped in blocking layer instead of in NPB. The emission spectrum of this device covers a wide range of visible region and can be adjusted by the concentration of rubrene. The white emitting device s with CIE coordinates x = 0.31, y = 0.32, maximum luminance 8635 cd/m(2) a nd luminous efficiency 1.39 Lm/w, were obtained with the blocking layer TPB i doped with 1.5% rubrene. (C) 2000 Elsevier Science S.A. All rights reserv ed.