Thin film and core-shell nanowire heterostructures containing copper indium gallium sulfide Cu(In,Ga)S-2 (CIGS) as light absorber are fabricated by low cost, solution based processes. The unique structures consist of ZnO and CdS or (Zn,Mg)O core-shell nanowire arrays embedded inside CIGS thin films for solar cell applications. Nontoxic (Zn,Mg)O buffer layer deposited by atomic layer deposition is proven to be suitable for replacing solution grown CdS for fabricating CIGS nanowire solar cells. A systemic comparison of device performance is made between the CIGS nanowire solar cells and their thin film counterparties with different final treatment temperatures. Overall, the nanowire devices show higher efficiency than the corresponding planar structures fabricated under similar conditions. Effect of nanowire on the solar cell performance is further studied by using nanowires of various lengths, which reveals that the longer nanowire arrays resulted in a higher short circuit current. This study represents the first working CIGS nanowire solar cells reported so far and provides an opportunity for investigating the mechanism of nanowire solar cells using a well-defined material system. (C) 2015 Published by Elsevier B.V.