White organic light-emitting devices using a thin layer of tris (8-hydroxyquinoline) aluminum doped with 4-(dicyanomethylene)-2-t-butyl-6-(1,1, 7,7-tetramethyyulolidyl-9-enyl) as chromaticity-tuning layer

Abstract

Efficient white organic light-emitting devices are demonstrated by inserting a thin layer of tris (8-hydroxyquinoline) aluminum (Alq) doped with 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl) (DCJTB) into N,N′ -diphenyl-N,N′ -bis(1-naphthyl)-(1,1′ -biphenyl)-4,4′-diamine (NPB) layer. Alq without doping is used as an electron-transporting layer and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine or BCP) as an exciton-blocking layer. NPB layers are separated by the doped Alq layer, the layer that sandwiched between BCP and doped Alq layers acts as a blue-emitting layer, and the other as a hole-transporting layer. The doped Alq layer acts as a red and green-emitting as well as chromaticity-tuning layer, whose thickness and position as well as the concentration of DCJTB in Alq permit the tuning of the device spectrum to achieve a balanced white emission with Commission Internationale De L'Eclairage coordinates of (0.33, 0.33), which are largely insensitive to the applied voltages, especially at high brightness (>1000cd/m2). The device have maximum luminance and efficiency of 6745 cd/m2 and 2.56 cd/A, respectively.