White-emitting organic diode with a doped blocking layer between hole- and electron-transporting layers

A new white-emitting organic diode was realized simply by inserting a doped hole-blocking layer between the hole-transporting layer (HTL) and the electron-transporting layer (ETL). The structure of this device is ITO/CuPc/NPB/blocking layer:rubrene/Alq/MgAg. Copper phthalocyanine (CuPc) was used as a buffer layer; N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1.1'-biphenyl-4-4'-diamine (NPB) was the HTL; the tris(8-quinolinolato)aluminium complex (Alq) was the ETL; and the trimer of N-arylbenzimidazole (TPBi), 2-(4-biphenylyl-5-(4-tertbutylphenyl)-1,2,3-oxadiazole (PBD) or the 1,2,4-triazole derivative (TAZ) were used as the blocking layers, in which rubrene is doped. The emission spectrum of this device covers a wide range of the visible region and can be sensitively adjusted by the concentration of rubrene. The white emission with CIE (Commission international de l'Eclairage) coordinates x = 0.31, y = 0.32, a maximum luminance of 8635 cd m(-2) and maximum luminous efficiency 1.39 lm w(-1) (4.9 V) were obtained in the device with a concentration of 1.5% rubrene in TPBi.