In this paper,ZnO:Al(ZAO) films are deposited by using twin-target DC magnetron sputtering at room temperature,which are used as the window electrodes of flexible substrate a-Si:H solar cells.ZAO films′ structure,composition and photo-electronic properties are optimized by adjusting the Ar flow parameter from 1.67×10-7m3/s to 8.33×10-7m3/s.The experimental results show that the ideal Ar flow is 3.33×10-7m3/s.The optimized ZAO films with high crystallization structure and c-axis orientation are obtained.The films′ Hall resistivity is 4.26×10-4 Ω·cm,the carrier concentration is 1.8×1021 cm-3,and the visible region light transmittance is over 85%.Using the ZAO films in the window electrodes of flexible substrate a-Si:H solar cells,the conversion efficiency is extended to 4.26%.