Preparation of indium tin oxide anodes using energy filtrating technique for top-emitting organic light-emitting diode

Indium tin oxide (ITO) anodes were deposited by an improved magnetron sputtering technique (energy filtrating magnetron sputtering technique, EFMS) for top-emitting organic light-emitting diodes (TOLEDs). The phases, surface morphologies and optical properties were examined by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM) and spectroscopic ellipsometer. The sheet resistances were measured by the sheet resistance meter. The electrical properties were tested by the Hall measurement system. The electro-optic characteristics were examined by a special home-made measurement system. Results indicated that ITO anode deposited by EFMS had a more uniform and smoother surface with smaller grains. ITO film was prepared with the electrical property of the lowest resistivity (4.56 × 10−4 Ω cm), highest carrier density (6.48 × 1020 cm−3) and highest carrier mobility (21.1 cm2/V/s). The average transmissivity of the ITO film was 87.0% in the wavelength range of 400-800 nm. The TOLEDs based on this ITO anode had a lower turn-on voltage of 2 V (>0.02 mA/cm2), higher current density of 58.4 mA/cm2 at 30 V, higher current efficiency of 1.374 cd/A and higher luminous efficiency of 0.175 lm/W. The possible mechanism of the technique was discussed in detail.