The electrodeposition of indium on copper substrates is studied in an acid sulfate solution for applications in CuInS2 (CIS) and Cu (InGa) Se2 (CIGS) solar cells. The study is focused on the film morphology and thickness uniformity on the nanometer scale. A two-step film growth behavior was observed, a conformal smooth film growth followed by a three-dimensional island growth. A hypothesis involving the Cu-In alloy formation and the Cu-In interdiffusion is proposed. While the room temperature alloy formation promotes the conformal deposition of a few monolayers of alloy, the fast interdiffusion between Cu and In further extends this alloy formation to a thicker layer and delays the typical island formation-growth phenomenon. © 2010 The Electrochemical Society.