Polyaniline-Based Conducting Polymer Compositions with a High Work Function for Hole-Injection Layers in Organic Light-Emitting Diodes: Formation of Ohmic Contacts

It is a great challenge to develop solution‐processed, polymeric hole‐injection layers (HILs) that perform better than small molecular layers for realizing high‐performance small‐molecule organic light‐emitting diodes (SM‐OLEDs). We have greatly improved the injection efficiency and the current efficiency of SM‐OLEDs by introducing conducting polymer compositions composed of polyaniline doped with polystyrene sulfonate and perfluorinated ionomer (PFI) as the HIL. During single spin‐coating of conducting polymer compositions, the PFI layer was self‐organized at the surface and greatly increased the film work function. It enhanced hole‐injection efficiency and current efficiency by introducing a nearly ohmic contact and improving electron blocking. Our results demonstrate that solution‐processed polyaniline HILs with tunable work functions are good candidates for reducing process costs and improving OLED performance. The perfect blend: The current efficiencies of small‐molecule organic light‐emitting diodes can be improved by using a blend composed of a polyaniline‐based conducting polymer (PANI:PSS) and a perfluorinated ionomer (PFI) in the hole‐injection layer produced by a single spin‐coating process (see figure).