In the present work, device modeling of tungsten disulfide-based thin-film solar cell with copper iodide as hole transport layer has been performed using the Solar Cell Capacitance Simulator in One Dimension software program (SCAPS-1D). The SCAPS-1D simulator is also utilized to investigate the photovoltaic performances of tungsten disulfide (WS₂)-based solar cells. This numerical study provides a comparison of the performances between the reference WS₂-based solar cell structure without hole transport layer (HTL) consisting of Al/FTO/CdS/WS₂/Ni and the proposed configuration of Al/FTO/CdS/WS₂/CuI/Ni. The influences of thickness, doping density, bulk defect density, defect density at buffer/absorber and absorber/HTL interfaces, operating temperature, series and shunt resistances, and back surface recombination velocity on the solar cell output parameters have also been analyzed. It is revealed that the carrier recombination at the back side has notable effects on the overall photovoltaic performances of the WS₂ heterojunction solar cell without HTL. The carrier recombination loss at the back surface can be reduced by incorporation of an ultra-thin 0.1 μm copper iodide (CuI) HTL into the reference WS₂-based solar cell and thus improves the overall performances of the proposed photovoltaic device. The conversion efficiency of 22.09% has been found for the reference WS₂ solar cell without HTL. On the other hand, the efficiency of the proposed solar cell with CuI HTL has been obtained to be 29.87% at the optimized device structure. Therefore, these findings may contribute insightful approach to fabricate viable, inexpensive, and highly efficient heterojunction thin-film solar cell.