We report the results of an effort to understand the effect of surface electronic structure of indium tin oxide (ITO) on luminance efficiency of organic light-emitting devices (OLED)s. Nitric oxide (NO) plasma was used to modify the ITO. NO plasma induced an increase in the sheet resistance of ITO. The surface electronic structure of ITO was studied using X-ray photoelectron spectroscopy. An approximately 4-nm thick low conductivity layer with a production of N-O type species was formed near the ITO surface region. It is demonstrated that the barrier for hole-injection from an ITO anode to a hole transporting layer can be engineered by NO plasma treatment. The increase in luminance efficiency of the OLEDs reflects an improved current balance in the device.
Antimony doped tin oxide films have been deposited on flexible substrates such as polyimide and polypropylene adipate. And the structural properties of the films have been investigated. The XRD measurements reveal that all of the obtained films were polycrystalline with the rutile structure. With increasing the substrate temperature and film thickness, the crystallinity of the resulting films is improved and the crystalline size becomes larger. The substrate temperature and film thickness dependence of crystallinity for the SnO2:Sb films were further revealed by their atomic force micrographs, which is consistent with the XRD observations. The XPS details of the SnO2:Sb films are also given. The tin core levels Sn 3d5/2 are observed at 486.5 and 494.9 eV, respectively, while the O 1s peak is obtained at 530.6 eV. It can be seen that the oxygen peak in the spectra is asymmetric, which is due to the concealed Sb 3d peak. The gap between the Sn 3d5/2 and Sn 3d3/2 levels is approximately the same as in the standard spectrum of Sn.