Abstract: Disclosed is a photovoltaic device comprising: a substrate; a III-V solar cell structure having one p-n junction on the substrate; a first semiconductor window layer on the III-V solar cell structure; a second semiconductor window layer on the first semiconductor window layer; an anti-reflective layer on the second semiconductor window layer; a contact layer disposed in the anti-reflective layer and on the second semiconductor window layer; and an electrode on the contact layer, wherein the second semiconductor window layer does not contain aluminum.