Protonated metal-oxide electrodes for organic light emitting diodes

Protonation of the indium tin oxide (ITO) electrode surface by nitric acid vapor gives rise to an ionic double layer producing an important increase in the effective electrode workfunction. This shift of ∼0.8 eV can be determined from the photoresponse of single layer diodes consisting of tris (8-hydroxyquinoline) aluminium (Alq) sandwiched between protonated ITO and aluminium electrodes. Due to the chemical treatment, the contact between the protonated hole injecting oxide electrode and Alq becomes ohmic. Under an applied electric field, the efficient injection of holes produces a positive space charge in the organic layer which enhances the emission of electrons from the cathode.