We report on transparent and conductive ZnO:Al films deposited by reactive AC magnetron sputtering for large area a-Si:H thin film solar cells. Up to now, the highest efficiency of a-Si:H thin film solar cells has been achieved using ceramic ZnO:Al2O3 target material. We have developed the reactive AC magnetron sputtering for the large area in-line deposition of ZnO:Al films on glass substrates as a competitive high rate and low cost technology. These films with minimum resistivity of 260 (A Wem allow for reproducible initial cell efficiencies of more than 9% for single junction amorphous silicon solar cells on commercial float glass substrates. © 2005 Society of Vacuum Coaters.