DEPENDENCE OF PHOTOVOLTAGES OF SPRAY-DEPOSITED INDIUM TIN OXIDE SILICON-OXIDE SILICON JUNCTION SOLAR-CELLS ON SPRAY SOLVENTS

The photovoltages of spray-deposited indium tin oxide/silicon oxide/n-Si junction solar cells are found to depend strongly on the spray solvents such as methanol, ethanol, ethyl acetate, water, etc. It is also found that the work function of the indium tin oxide (ITO) films is dependent on the spray solvents, and the higher the work function of the ITO films, the larger the photovoltage. X-ray photoelectron spectroscopy (XPS) measurements indicate that an In-OH species, probably formed by reactions of the ITO film with the spray solvents, is present in the deposited film in cases where its work function is high. The resistivity of the ITO films produced using the organic spray solvents is in the range of 2 - 4 X 10(-4) OMEGA cm, leading to high fill factors of the solar cells, while that of the films deposited using water as a spray solvent is as high as 1.2 x 10(-3) OMEGA cm, resulting in low fill factors. On the basis of the XPS measurements, the high resistivity of the latter ITO films is attributed to a small amount of tin ions in the films. X-ray diffraction measurements show that the crystal orientation of the ITO films also depends on the spray solvents, indicating that the film formation mechanism varies with the spray solvents. By use of a mixed solvent of methanol:ethyl acetate:water = 5:5:1, the photovoltage becomes the highest, and the conversion efficiency of 14% is achieved.