The　optimization　of　the　back　interface　is　an　important　means　of　improving　the　power　conversion　efficiency　(PCE)　of　Cu2ZnSn(S,Se)4　(CZTSSe)　solar　cells.　Here,　a　CuO　sacrificial　layer　is　introduced　into　the　Mo/CZTSSe　back　interface　to　improve　device　efficiency.　The　insertion　of　the　CuO　sacrificial　layer　inhibits　the　formation　of　Sn(S,Se)2　secondary　phases　in　the　CZTSSe　film.　Meanwhile,　the　interfacial　trap　state　(N　IT)　is　reduced　by　about　22%.　Furthermore,　the　75　nm　CuO　sacrificial　layer　can　reduce　the　thickness　of　the　MoSe2　layer,　leading　to　a　33.18　meV　reduction　in　the　back　interfacial　barrier.　This　design　enhances　the　back　interfacial　transport　characteristics　and　suppresses　defects.　Finally,　the　flexible　CZTSSe　solar　cell　achieve　the　efficiency　of　10.57%.