A soluble self-doped conducting polyaniline graft copolymer as a hole injection layer in polymer light-emitting diodes

We demonstrate that a novel soluble self-doped conducting polyaniline graft copolymer can be used for a hole injection layer (HIL) in polymer light-emitting diodes (PLEDs). The work function of the material (5.18 eV) was similar to that (5.20 eV) of a conventional conducting polymer dispersion, poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonate (PSS). When we fabricated PLEDs by using this material, the current-voltage-luminescence characteristics were very similar to those of the device using the PEDOT/PSS. When the material was blended with PSS, the luminous efficiency was further improved up to 11.9 cd/A. Since this kind of soluble type HIL has advantages over the conventional PEDOT/PSS dispersion in terms of the solution processibility and film quality, this soluble graft-type conducting polymer can be one of the promising candidates for a HIL in PLEDs.