For laboratory scale devices the transfer of the Cu(In,Ga)Se2 (CIGSe) thin film technology from a rigid float glass substrate to flexible titanium foil is achieved. Here we will highlight the effect of the rough, flexible substrate on the electrical and optical characteristics of the transparent window layers of such devices. The roughness of the substrate may give rise to changes in sheet resistance of the transparent front contact and in the reflectivity of the completed device. However, the devices deposited onto the kind of titanium foil substrate used in this work are smooth enough not to affect the sheet resistance; nevertheless optical effects are enough to affect the process window for an antireflective coating. With the use of an antireflective coating, a maximum efficiency of 17.4% could be reached for 0.5 cm2 area devices on glass.