dc.description.abstract | Indium-based transparent conductive oxide films are widely used in solar cell, touch panel, LED, and other diode elements with superior conductivity and high optical transmittance in visible region. Nowadays, radio-frequency (RF) magnetron sputtering is one common method for preparing a transparent conductive oxide films. Furthermore, compared with other methods, RF magnetron sputtering has several advantages, such as the excellent deposition rates, low temperature, and film uniformity. The indium tin oxide (ITO) thin films, the titanium-doped indium oxide (ITiO) thin films, and the indium molybdenum oxide (IMO) thin films were fabricated by RF magnetron sputtering process. In this study, we modulated the argon flow rate, radio-frequency power, process pressure, oxygen flow rate, and post-annealing temperature to investigate the thin films quality. The target to fabricate the transparent conductive oxide anti-reflection film (75~80 nm) with low sheet resistance ( < 50 Ohm/square), high mobility ( > 40 cm2/Vs), and high transmittance in visible region and near-infrared region that will be applied to amorphous silicon / crystalline silicon heterojunction solar cells. The conversion efficiency of solar cells can be improved by the reduction of series resistance and improvement of light transmittance.
The results of experiments show that indium tin oxide has low sheet resistance (30~100 Ohm/square), high mobility (40~45 cm2/Vs), and high transmittance in visible region (86~92 %). Indium molybdenum oxide has high carrier concentration (2E20~4E20 cm-3). Titanium-doped indium oxide has general optical and electrical properties. It has significant influence on transparent conductive oxide films quality by modulating the argon gas flow rate and increasing the radio-frequency power. Under the condition of argon gas flow rate = 60~80 sccm and radio-frequency power = 250 W, the indium tin oxide, the titanium-doped indium oxide, and the indium molybdenum oxide have the lowest sheet resistance of 70 (Ohm/square), 171 (Ohm/square), and 104 (Ohm/square), respectively. Modulation of oxygen gas flow rate can control the number of oxygen vacancies in films, but it is not obvious to affect the optical and electrical properties of films. In addition, increase process pressure will reduce the kinetic energy of the ions and affect films structure, resulting in deterioration of films quality. Furthermore, post-annealing process can make transparent conductive oxide films transform to crystal structure from amorphous structure, and reduce band edge defects. In particular, post-annealing process can greatly improve carrier concentration and reduce sheet resistance of the indium tin oxide thin films. The post-annealing process can also improve the indium tin oxide thin films transmittance from 87.3 % to 92.4 %. Under the condition of argon flow rate = 80 sccm, radio-frequency power = 200 W, and annealing temperature = 500 ℃, we obtained the low sheet resistance 33 (Ohm/square) and high optical transmittance 92.4 % at 400 nm~1200 nm wavelength of the tin oxide thin film, respectively.
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