The reason why so-called wide-bandgap CuIn1?xGaxSe2 (CIGSe with x\textgreater0.4) based solar cells show hindered performance compared with theoretical expectations is still a matter of debate. In the present Letter, atom probe tomography studies of CuIn1?xGaxSe2 polycrystalline thin films with x varying from 0 to 1 are reported. These investigations confirm that the grain boundaries (GBs) of low gallium containing (x\textless0.4) CIGSe layers are Cu-depleted compared with grains inte- rior (GI). In contrast, it is observed that the GBs of widest band gap CIGSe films (x\textgreater0.8) are Cu- enriched compared with GI. For intermediate gallium contents (0.4\textlessx\textless0.8), both types of GBs are detected. This threshold value of 0.4 surprisingly coincides with solar cells output voltage devi- ation from theoretical expectations, which suggests modifications of GBs properties could partici- pate in the loss of photovoltaic performance.