Flexible　CZTSSe　solar　cells　have　attracted　much　attention　due　to　their　earth-abundant　elements,　high　stability,　and　wide　application　prospects.　However,　the　environmental　problems　caused　by　the　high　toxicity　of　the　Cd　in　the　buffer　layers　restrict　the　development　of　flexible　CZTSSe　solar　cells.　Herein,　we　develop　a　Cd-free　flexible　CZTSSe/ZnO　solar　cell.　The　influences　of　the　ZnO　films　on　device　performances　are　investigated.　The　light　absorption　capacity　of　flexible　CZTSSe　solar　cells　is　enhanced　due　to　the　removal　of　the　CdS　layer.　The　optimal　thickness　of　the　ZnO　buffer　layers　and　the　appropriate　annealing　temperature　of　the　CZTSSe/ZnO　are　100　nm　and　200　C-?.　Ultimately,　the　optimum　flexible　CZTSSe/ZnO　device　achieves　an　efficiency　of　5.0%,　which　is　the　highest　efficiency　for　flexible　CZTSSe/ZnO　solar　cells.　The　systematic　characterizations　indicate　that　the　flexible　CZTSSe/ZnO　solar　cells　based　on　the　optimal　conditions　achieved　quality　heterojunction,　low　defect　density　and　better　charge　transfer　capability.　This　work　provides　a　new　strategy　for　the　development　of　the　environmentally　friendly　and　low-cost　flexible　CZTSSe　solar　cells.