Antimony sulfide (Sb₂S₃) thin films possess n-type and p-type conductivity. Design and defect analysis on promising light-harvesting material Sb₂S₃ homojunction solar cells with various electron transport layers and hole transport layers are performed by using wxAMPS. The device structure consisting of glass/FTO/ZnS/(n)Sb₂S₃/(p)Sb₂S₃/Spiro-OMeTAD/Au is proposed. In Sb₂S₃ homojunction solar cells, a built-in electric field is formed that increase the bending of the energy band and therefore leads to the increase of open-circuit voltage. Bulk defects in the (p)Sb₂S₃ have stronger impact on the device performance than that in the (n)Sb₂S₃, but defects at ZnS/(n)Sb₂S₃ interface and (p)Sb₂S₃/Spiro-OMeTAD interface have the same effects on device performance. When the bulk defect density in (n)Sb₂S₃ and (p)Sb₂S₃ is 10¹⁵ cm^-3, and the interface defect density at ZnS/(n)Sb₂S₃ interface and (p)Sb₂S₃/Spiro-OMeTAD interface is 10⁹ cm^-2, then the optimized conversion efficiency of the solar cells can reach 23.96%. Simulation results show that device design with Sb₂S₃ based homojunction is an effective structure to achieve highly efficient solar cells.