Electrical and optical characteristics of polymer light-emitting devices with surface-treated indium-tin-oxide electrodes

Effects of differently surface-treated indium-tin-oxide (ITO) electrodes in poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)-based polymer light-emitting electrochemical cells (LECs) were investigated. It is found that the surface properties of ITO substrates are more effectively improved by the oxygen plasma compared with other treatments. Atomic force microscopy (AFM) measurements show that the oxygen plasma treatment reduces the roughness of the ITO surface and yields more smooth and homogeneous surface. X-ray photoelectron spectroscopy (XPS) analyses reveal that the oxygen plasma treatment increases the oxygen content and decreases the carbon content on the ITO surface. Contact angle and surface energy results indicate that the oxygen plasma treatment enhances the wettability of the ITO surface. The LECs with the oxygen plasma-treated ITO substrates exhibit the higher injection current, luminance and efficiency than that of the devices based on the ITO substrates treated in other different ways, due to the improvement of interface formation and electrical contact of the ITO electrode with the polymer blend in the LECs.