Indium tin oxide (ITO) is widely used for opto-electronic products such as organic light-emitting diodes, organic photovoltaic devices and liquid crystal displays due to its high transparency and electrical conductivity. Since there is a trade-off between the conductivity and transparency of ITO, it is necessary to optimize performances of opto-electronic products by balancing the sheet resistance and transmittance. Both sheet resistance and transmittance are affected by a number of factors such as working temperature, working pressure, oxygen-to-argon ratio during the fabricating process, and thickness. In our study, ITO thin films were deposited on glass substrates by dc sputtering. Effects of ITO with different thicknesses, sheet resistances, and transmission spectra on the performance of bulk heterojunction photovoltaic devices were investigated.