Influence of Surface Modification of IndiumTin Oxide on Performance of Organic Light Emitting Diodes

Surface of Indium Tin Oxide (ITO) films on glass substrates were treated by ethanol, oxygen plasma, NaOH, and sulfuric acid, respectively and then analyzed by Atomic Force Microscope (AFM), X-ray Photoelectron Spectroscopy (XPS) and goniometer. Results show that ITO films treated by sulfuric acid and NaOH have low roughness, small grain radius, low contamination of carbon, and high surface energy. Double layer Organic Light-Emitting Diodes (OLEDs):ITO/NPB (15 nm)/AlQ (40 nm)/Mg:Ag (10:1,100 nm)/Ag (50 nm) were fabricated on substrates treated above. Current-voltage (J-V), brightness-voltage (B-V), and efficiency (η) characteristics of these devices were measured and discussed in details. Experimental results show that devices based on NaOH-treated and sulfuric-acid-treated substrates have better performance comparing with oxygen-plasma-treated substrate, namely lower turn-on voltage, higher electroluminescent brightness and higher efficiency.