Efficient blue organic light-emitting diodes with simple structure based on N, N′-bis (1-naphthyl)-N, N′-biphenyl-1, 1′-biphenyl-4,4′-diamine

Small molecular Organic light-emitting diodes (OLEDs) with high efficiency composed of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and N, N'-bis-(1-naphthyl)-N, N'-biphenyl-1,1'-biphenyl-4,4-diamine (NPB) as an electron transporting layer and an emitting layer, respectively were studied. Two devices of indium-tin-oxide (ITO)/NPB/BCP/8-hydroxyquinoline aluminum (Alq(3))/Mg:Ag and ITO/NPB/BCP/ Mg:Ag with unique simple structure were fabricated. The luminance-voltage and current density-voltage characteristics of devices were investigated. The results demonstrated that the maximum luminance of the double and triple-layer devices is 11500cd/m(2) and 5000 cd/m(2) at 15V, respectively. The maximum luminous power efficiency is 1.21m/W at the luminance of 300cd/m(2) and the luminous efficiency of 2.7cd/A. The peak of Electroluminescence (EL) spectrum locates at 433nm and the Commissions Internationale d'Eclairage (CIE) coordinates are (0.18, 0.17), which is consistent with the Photoluminescent (PL) spectrum of NPB. The bright blue light emission is independent on the variation of bias voltage. The diversity of device performance with two different structures was discussed.