Polymer light-emitting devices using ionomers as an electron injecting andhole blocking layer

The effect of ion concentration, neutralization level and counterions in io nomers was systematically studied to obtain the optimal electroluminescent (EL) characteristics in polymer light-emitting diodes using poly[2-methoxy- 5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) for the emissive lay er and sulfonated polystyrene (SPS) ionomers for the electron-injecting lay er. The optimum ion concentration of NaSPS was determined to be at 6.7 mol %. Ionomers with a higher neutralization level make the EL device more effi cient, with the highest efficiency being at 200% overneutralization. The io nomer with a smaller metal counter ion greatly enhances the efficiency of E L devices with the indium-tin-oxide/MEH-PPV/LiSPS/Al device having the high est EL quantum efficiency, 1.18% photons/electron. The dominant factor in e nhancing the luminance is the number of ionic dipoles near the cathode irre spective of the type of metal counterions, while the hole blocking mostly d epends on the restriction of chain segmental motion in ionomers. (C) 2001 A merican Institute of Physics.