We have investigated the characteristics of flexible indium zinc oxide (IZO) electrode grown on polyethylene terephthalate (PET) substrates using a specially designed roll-to-roll (RTR) sputtering system for use in flexible optoelectronics It was found that both electrical and optical properties of the flexible IZO electrode were critically dependent on the DC power and Ar/O(2) flow ratio during the roll-to-roll sputtering process At optimized conditions (constant working pressure of 3 mTorr.Ar/O(2) flow ratio of Ar at only 30 sccm, DC power 800 W and rolling speed at 0 1 cm/s) the flexible IZO electrode exhibits a sheet resistance of 17 25 Omega/sq and an optical transmittance of 89 45% at 550 nm wavelength. Due to the low PET substrate temperature, which is effectively maintained by cooling drum system, all IZO electrodes showed an amorphous structure regardless of the DC power and Ar/O(2) flow ratio Furthermore. the IZO electrodes grown at optimized condition exhibited superior flexibility than the conventional amorphous ITO electrodes due to its stable amorphous structure This indicates that the RTR sputter grown IZO electrode is a promising flexible electrode that can substitute for the conventional ITO electrode, due to its low resistance, high transparency, superior flexibility and fast preparation by the RTR process. (C) 2009 Elsevier B.V All rights reserved