Antimony　sulfide　(Sb2S3)　with　a　1D　molecular　structure　has　strong　bending　characteristics,　showing　great　application　potential　in　flexible　devices.　Herein,　the　flexible　substrate-structured　Sb2S3　solar　cells　is　developed　and　improve　device　performances　by　the　back　interface　selenization.　The　high-quality　Sb2S3　film　with　an　optimal　thickness　of　1.8 µm,　ensuring　efficient　spectra　utilization,　is　deposited　on　flexible　Mo　foils　by　the　rapid　thermal　evaporation　technique.　To　solve　the　issues　of　back　interfacial　recombination　and　charge　transport,　the　20 nm　MoSe2　layer　between　Sb2S3　film　and　Mo　foil　is　fabricated　by　substrate　selenization　in　the　tube　furnace.　Further　investigations　indicate　that　the　MoSe2　layer　improves　the　interfacial　energy　band　alignments　and　induces　the　[hk1]　orientation　of　Sb2S3　film,　thereby　passivating　defects　and　enhancing　the　carrier　transport　capacity.　The　flexible　solar　cell　in　the　structure　of　Mo　foil/MoSe2/Sb2S3/CdS/ITO/Ag,　exhibiting　good　flexibility　to　stand　thousands　of　bending,　achieves　an　efficiency　of　3.75%,　which　is　the　highest　for　Sb2S3　devices　in　substrate　configuration.　The　presented　flexible　structure　and　back　interfacial　selenization　study　will　provide　new　prospects　for　inorganic　Sb2S3　thin　film　solar　cells.　©　2023　Wiley-VCH　GmbH.