Environment-friendly　flexible　Cu2ZnSn(S,Se)(4)　(CZTSSe)　solar　cells　show　great　potentials　for　indoor　photovoltaic　market.　Indoor　lighting　is　weak　and　multi-directional,　thus　the　researches　of　photovoltaic　device　structures,　techniques　and　performances　face　new　challenges.　Here,　we　design　symmetrical　bifacial　CZTSSe　solar　cells　on　flexible　Mo-foil　substrate　to　efficiently　harvest　the　indoor　energy.　Such　devices　are　fabricated　by　double-sided　deposition　techniques　to　ensure　bifacial　consistency　and　save　cost.　We　report　9.3%　and　9%　efficiencies　for　the　front　and　back　sides　of　the　flexible　CZTSSe　solar　cell　under　the　standard　sun　light.　Considering　the　indoor　environment,　we　verify　weak-light　response　performance　of　the　devices　under　LED　illumination　and　flexibility　properties　after　thousands　of　bending.　Bifacial　CZTSSe　solar　cells　in　parallel　achieve　the　superposition　of　double-sided　output　current　from　multi-directional　light,　significantly　enhancing　the　area　utilization　rate.　The　present　results　and　methods　are　expected　to　expand　indoor　photovoltaic　applications.　Indoor　lighting　is　weak　and　multi-directional,　thus　the　requirement　for　photovoltaic　differs　from　that　designed　for　outdoor.　To　efficiently　harvest　the　indoor　energy,　the　authors　designed　CZTSSe　bifacial　solar　cells　on　flexible　Mo　substrate　using　double-sided　deposition　to　ensure　consistency　and　to　save　cost.