Novel surface modification of indium-tin-oxide films using ion implantation for organic light-emitting diodes

Indium-tin-oxide (ITO) films doped using an ion implantation system were used as the anode electrode of organic light-emitting diodes (OLEDs). Changes in the characteristics of the doped ITO films were observed and measured in terms of sheet resistance, Hall mobility, contact angle, roughness, transmittance and work function. Boron dopant was used as an impurity to modify the surface of the ITO films. The depth profile of boron concentration was monitored by secondary ion mass spectrometry (SIMS) as a function of dose. Optimum dose was 5 x 10(14) atoMS/cm(3) at which resistance was lowest. The resistance variation from 16 Omega/sq. of the conventional ITO to 11Omega/sq. of doped ITO shows that the doped ITO films become more conductive after doping and thermal annealing. The Hall mobility and carrier concentration of boron-doped ITO was 40.4 cm(2) /Vs and -9.32 x 10(20)/cm(3) respectively. Contact angle and roughness were investigated by the sessile drop technique and atomic force microscopy (AFM). After doping, the water contact angle of the film surface was changed from 55degrees to 38degrees and the root-mean- square roughness of the films was similar to that of conventional ITO. Transmittance in the visible spectrum range was increased from 91% to 96%. Work function was improved from 4.66 eV to 4.86 eV. An OLED device fabricated with a multilayer, boron-doped-ITO/CuPc/NPD/Alq3:C545T/Alq3/LiF/Al, was tested. The device had a luminance of 780cd/m(2) and the lifetime was also increased by approximately 25% compared with those of ITO devices produced under the same conditions.