Tandem　solar　cells　usually　use　a　wide　band　gap　absorber　for　top　cell.　The　band　gap　of　CuIn(1-x)GaxSe2　can　be　changed　from　1.04　eV　to　1.68　eV　with　the　ratio　of　Ga/(In+Ga)　from　0　to　1.　When　the　ratio　of　Ga/(In+Ga)　is　over　0.7,　the　band　gap　of　CIGS　absorber　is　over　1.48　eV.　CIGS　absorber　with　a　high　Ga　content　is　a　possible　candidate　one　for　the　top　cell.　In　this　work,　CuInGa　precursors　were　prepared　by　magnetron　sputtering　with　CuIn　and　CuGa　targets,　and　CIGS　absorbers　were　prepared　by　selenization　annealing.　The　Ga/(In+Ga)　is　changed　by　changing　the　thickness　of　CuIn　and　CuGa　layers.　Additionally,　CIGS　solar　cells　were　prepared　using　CdS　buffer　layer.　The　effects　of　Ga　content　on　CIGS　thin　film　and　CIGS　solar　cell　were　studied.　The　band　gap　was　measured　by　PL　and　EQE.　The　results　show　that　using　structure　of　CuIn/CuGa　precursors　can　make　the　band　gap　of　CIGS　present　a　gradient　band　gap,　which　can　obtain　a　high　open　circuit　voltage　and　high　short　circuit　current　of　the　device.　With　the　decrease　in　Ga　content,　the　efficiency　of　the　solar　cell　increases　gradually.　Additionally,　the　highest　efficiency　of　the　CIGS　solar　cells　is　11.58%　when　the　ratio　of　Ga/(In+Ga)　is　0.72.　The　value　of　Voc　is　702　mV.　CIGS　with　high　Ga　content　shows　a　great　potential　for　the　top　cell　of　the　tandem　solar　cell.