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

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 indium tin oxide (ITO) surface treated in 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 SiO2 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 SiO2 insertion.