Enhanced blue light electroluminescence utilizing heterostructure of p-sexiphenyl and TPD

Enhanced electroluminescence (EL) from vapor deposited p-sexiphenyl (6p) layer has been observed utilizing heterostructure of p-sexiphenyl emissive layer and TPD hole transporting layer. The EL device consists of an indium tin oxide (ITO) anode, a TPD hole transporting layer, a p-sexiphenyl emissive layer, and a magnesium containing silver cathode. N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1'- biphenyl-4,4'-diamine (TPD) has been employed as a hole transporting layer. A heterostructure device with 50 nm thick p-sexiphenyl and 60 nm thick TPD shows the enhanced emission from the p-sexiphenyl emissive layer. The device emits blue light centered at 420 nm, and the EL intensity reaches as high as 3400 cd/m(2) at an applied voltage of 10 V. The maximum efficiency reaches up to 0.4 cd/A at an emission intensity of 2200 cd/m(2), or at an injection current of 0.6 A/cm(2). The heterostructure device emits two orders of magnitude higher intensity than the conventional single layer device. The mechanism of enhanced emission from the heterostructure device has been discussed utilizing the energy band diagram of these materials. (C) 2001 Elsevier Science B.V. All rights reserved.