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

Enhanced electroluminescence (EL) from vapor deposited p-sexiphenyl (6p) la yer has been observed utilizing heterostructure of p-sexiphenyl emissive la yer and TPD hole transporting layer. The EL device consists of an indium ti n 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-me thylphenyl)-1,1'- biphenyl-4,4'-diamine (TPD) has been employed as a hole t ransporting layer. A heterostructure device with 50 nm thick p-sexiphenyl a nd 60 nm thick TPD shows the enhanced emission from the p-sexiphenyl emissi ve layer. The device emits blue light centered at 420 nm, and the EL intens ity reaches as high as 3400 cd/m(2) at an applied voltage of 10 V. The maxi mum 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 materi als. (C) 2001 Elsevier Science B.V. All rights reserved.