IZO thin films have been deposited on poly(ethylene terephthalate) flexible substrate under varying radio frequency (rf) power, process pressure and thickness of IZO films using rf magnetron sputtering under Ar/O2 gas mix. As the process pressure increased, the deposition rate was slightly increased and the transmittance showed little change, but the resistivity was increased. With increasing rf power, the great increase in deposition rate was observed but the transmittance showed a slight change only, and the resistivity was decreased. In addition, an attempt was made to find the optimal thickness of IZO films under varying the thickness of IZO films at the process conditions of 1 mTorr pressure and 90 W rf power, which showed lowest resistivity. IZO thin films with the thickness of 1,500 Å showed lowest resistivity and also showed highest transmittance around the wavelength zone of the maximum absorption. The power conversion efficiency of solar cells fabricated using various transparent electrodes with different thicknesses were measured and the solar cell with IZO electrode of 1,500 Å showed the maximum conversion-efficiency of 2.88 %.