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 simila r to 0.8 eV can be determined from the photoresponse of single layer d iodes consisting of tris (8-hydroxyquinoline) aluminium (Alq) sandwich ed between protonated ITO and aluminium electrodes. Due to the chemica l treatment, the contact between the protonated hole injecting oxide e lectrode and Alq becomes ohmic. Under an applied electric field, the e fficient injection of holes produces a positive space charge in the or ganic layer which enhances the emission of electrons from the cathode. (C) 1998 Elsevier Science B.V.