Plasma treatment of ITO surfaces to improve luminescence characteristics of organic light-emitting devices with dopants

Indium-tin-oxide (ITO) surfaces were treated with O₂ and H₂ plasmas. The contact angle of water, X-ray photoelectron spectroscopy (XPS) spectra, and luminescence characteristics of organic light-emitting devices (OLEDs) fabricated on plasma-treated ITO surfaces using poly(N-vinylcarbazole) (PVK) films doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) or Nile Red were investigated.Using O₂ plasma treatment, the contact angle was reduced from 35° to 13°. The luminance of OLEDs with rubrene was significantly improved. The luminous color of an OLED inserted poly (3,4-ethylenedioxythiophene)-polystyrene sulphonic acid (PEDOT-PSS) layer between Nile Red-doped PVK film and O₂-plasma-treated ITO surface turned white as the applied voltage increased.