Formation of gap states and enhanced current injection efficiency in organic light emitting diodes incorporated with subphthalocyanine

The improvement of current injection efficiency in organic light emitting diodes is demonstrated with incorporation of SubPc-doped NPB as hole injection layers. The photoemission spectra illustrate the presence of gap states and the occurrence of axial reaction on SubPc with NPB. Quantum chemistry calculation provides simulated valence-band spectra indicating that the formation of gap states is due to the HOMOs of new complexes created from the reaction of SubPc and NPB, which facilitate the hole injection at the anode interfaces.