Improvement of organic electroluminescent device performance by in situ plasma treatment of indium-tin-oxide surface

Indium-tin-oxide (ITO) surface treated by Ar-50% O-2 plasma has been in situ analyzed using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS), to investigate the relations between the properties of the ITO surface and the properties of organic electroluminescent (EL) devices. The plasma treatment of the ITO surface lowered the operating voltage of the organic EL device. The UPS measurements revealed that the plasma treatment resulted in the increase of the work function of the TTO surface by more than 1 eV. The XPS measurements showed that the plasma treatment effectively removed carbon contaminants from the ITO surface. The work function was correlated with the surface carbon concentration. From these results, the lowering of the operating voltage in the EL devices is attributed to the increase of the work function resulting from the carbon removal by the plasma treatment. (C) 2000 Elsevier Science B.V. All rights reserved.