Modification of the hole injection barrier in organic light-emitting devices studied by ultraviolet photoelectron spectroscopy

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Abstract
Ultraviolet photoelectron spectroscopy has been applied to the investigation of modified hole injection barriers in organic light-emitting devices(OLEDs). Different from those reported previously, the indiumtin oxide (ITO) surfacetreatedin situ by oxygen plasma possesses a work function of 5.2 eV, and the organic ITO interface thereafter formed shows a 0.5 eV smaller hole injection barrier compared to that on untreated ITO. Insertion of an ultrathin SiO 2 layer between the organic and ITO results in a similar reduction of the barrier. This indicates that improved hole injection favors efficient operation of OLEDs, as manifested by enhanced efficiency by the SiO 2 insertion.