The effect of ion bombardment on photovoltaic characteristics, induced during the sputtering deposition of In<inf>2</inf>O<inf>3</inf>:Sn (ITO) layers, has been investigated using hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction solar cells with double-layered ITO structures. The experimental results indicate that the significant decrease in the fill factor (FF) induced at a sputtering rf power higher than 30 W is attributed to the increase in series resistance (R<inf>s</inf>), which is caused by property degradation in the ITO/a-Si:H interface region. Furthermore, it has been found that the impact of the sputter-induced ion bombardment on the property degradation reaches the ITO/a-Si:H interface region through the deposited ITO layer even up to a thickness of 20 nm.