Flexible　Cu2ZnSn(S,Se)(4)　(CZTSSe)　solar　cells　have　wide　application　prospects.　N-type　window　layers　and　contact　among　the　layers　have　an　important　effect　on　the　properties　of　flexible　CZTSSe　solar　cells.　Here,　we　present　a　modified　structure　for　flexible　CZTSSe　solar　cells　with　window　layers　(CdS/ITO)　instead　of　the　traditional　window　layers　(CdS/ZnO/ITO)　for　higher　performance　and　lower　cost.　The　flexible　CZTSSe　device　realizes　9.2%　efficiency　with　an　improved　fill　factor　(FF)　from　57.7　to　63.6%.　Systematic　physical　measurements　show　that　the　increase　in　FF　comes　from　a　significant　decrease　in　series　resistance　(R-s).　To　enhance　the　antireflective　function　of　the　window　layers,　we　introduce　MgF2　antireflection　coatings　on　the　surfaces　of　solar　cells.　The　average　J(sc)　of　devices　is　significantly　enhanced　6%　due　to　the　antireflective　effect.　A　champion　device　achieves　an　efficiency　of　9.7%　with　the　highest　FF　of　64.0%　in　the　flexible　CZTSSe　solar　cells.　The　present　investigation　will　provide　a　new　strategy　for　the　development　of　flexible　CZTSSe　solar　cells.