HIGHLY EFFICIENT AND BRIGHT ORGANIC ELECTROLUMINESCENT DEVICES WITH AN ALUMINUM CATHODE

The electron injection process, which limits the electroluminescent pe rformance of organic devices, has been enhanced tremendously by insert ing a layer of LiF with appropriate thickness between the cathode and a quinacridone doped organic layer, Devices with an Al/LiF cathode dem onstrated a luminance in excess of 20000 cd/m(2) and an external quant um efficiency of 3%. which is comparable to devices with a Mg/LiF cath ode. These devices show maximum luminance of 45 000 cd/m(2) prior to f ailure in continuous bias operation. For the same LiF thickness, the o perating voltage for devices with Al/LiF was lower than the correspond ing operating voltage for devices with Mg/LiF or Mg alone. Tunneling t heory is used to explain this enhancement. (C) 1997 American Institute of Physics.