In heterojunction solar cells consisting of hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si), suppression of epitaxial growth at the heterointerface is found to be Crucial to achieve high solar cell efficiencies. In order to avoid the epitaxial growth, wide-gap hydrogenated amorphous silicon oxide (a-SiO:H) has been applied to the heterojunction solar cells. We have fabricated a-SiO:H/c-Si solar cells using n-type and p-type c-Si substrates and demonstrated that incorporation of the a-SiO:H i layer prevents the harmful epitaxial growth at the heterointerface completely. (C) 2008 Elsevier B.V. All rights reserved.