We devised a method of modifying indium-tin-oxide (ITO) electrodes for organic electroluminescent devices. It consists of deposition of a nanometer-thick Cu layer on the ITO electrode and an oxygen plasma treatment. By this modification, the surface of the ITO substrate is covered with a partly oxidized Cu layer (CuOx). The CuOx-coated ITO electrode possesses strong hole-injection ability, which leads to lowered operational voltage and high luminance from the devices consisting of tris(8-quinolinato)aluminum and diamine hole-transport layers. The hole-injection ability of the CuOx-coated ITO electrode is better than that of the ITO electrode modified by conventional methods, such as insertion of a Cu-phthalocyanine buffer layer. Moreover, the CuOx layer is effective to improve the durability of the devices.

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We successfully improved quality of tin oxide (SnO2) films formed on m-plane sapphire substrates by mist chemical vapor deposition. The crystal quality was characterized mainly by the FWHM of the X-ray diffraction ω-rocking curve. We found that the use of tin acetate [Sn(CH3COO)4] solution led to the formation of high-quality SnO2 film, where FWHM was as narrow as 0.1°. Using tin chloride (SnCl4) solution, electrical and optical properties can be improved because crystal grain size was large. Therefore, on the SnO2 layer formed with the Sn(CH3COO)4 solution, the second SnO2 layer was overgrown with the SnCl4 solution to form a double-layer structure, where FWHM was also 0.1° and carbon impurity was lower than that of the first SnO2 layer. Furthermore, in case of the second SnO2 layer, we found that a growth temperature window providing the narrow FWHM of 0.1° was very wide (500 °C–800 °C).

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