The effects of post p-n junction formation processes, namely transparent conducting oxide (TCO) layer deposition conditions on Cu(ln,Ga)Se-2 (CIGS) and CuGaSe2 (CGS) solar cell device properties were comparatively studied. It was found that CIGS devices were relatively insensitive to the presence of oxygen and heat during TCO layer deposition, whereas CGS devices were extremely sensitive to oxygen and heat, resulting in a degradation of device performance in the presence of them. The use of the relatively low TCO deposition temperature (T-s) of 80 degrees C led to significant improvements in the fill factor values of CGS devices compared to the case for Ts similar to 180 degrees C, though the open circuit voltage was reduced. These results suggest that TCO deposition conditions can be an important parameter which critically affects ternary CGS solar cell device properties. It is, therefore, suggested that TCO layer deposition conditions for CGS devices should be optimized independently of that for conventional narrow-gap CIGS devices. (C) 2016 Elsevier B.V. All rights reserved.