Al doped zinc oxide (AZO) films were prepared by mid-frequency magnetron sputtering for silicon (Si) thin film solar cells. Then, the influence of deposition parameters on the electrical and optical properties of the films was studied. Results showed that high conductive and high transparent AZO thin films were achieved with a minimum resistivity of 2.45 * 10^–4 Ω?cm and optical transmission greater than 85% in visible spectrum region as the films were deposited at a substrate temperature of 225°C and a low sputtering power of 160 W. The optimized films were applied as back reflectors in a-SiGe:H solar cells. A relative increase of 19% in the solar cell efficiency was achieved in comparison to the cell without the ZnO films doped with Al (ZnO:Al).