Structural study of several amorphous silicon (a-Si:H) films deposited by rf-PECVD from a silane-argon mixture have revealed that the 90% argon diluted sample has the lowest microstructure and defect density. This sample has been further compared with a-Si:H layer deposited from undiluted silane by using each of them as the intrinsic (i) layer in p-i-n solar cells. The output characteristics of these devices have been studied experimentally and by theoretical modeling. These studies demonstrate that the improvement in the stabilized output characteristics of the cell with argon diluted i-layer results both from the structural improvement of the a-Si:H layer, as well as a reduction of the p/i interface defects.