In this research work, the tungsten diselenide (WSe2)-based thin-film solar cell with a copper thiocyanate (CuSCN) hole transport layer (HTL) has been designed and studied by using the Solar Cell Capacitance Simulator in One Dimension software program (SCAPS-1D). A comparative numerical study between Al/ITO/CdS/WSe2/Ni and Al/ITO/CdS/WSe2/CuSCN/Ni has been done. The SCAPS-1D simulator has been utilized to investigate photovoltaic parameters such as open circuit voltage, short-circuit current density, fill-factor, power conversion efficiency and quantum efficiency of heterojunction solar cell due to the variation of thickness, doping density, bulk defect density, defect density at buffer/absorber and absorber/HTL interfaces, operating temperature, band alignment and back surface recombination velocity. The conversion efficiency of 17.33% has been determined for the WSe2 solar cell without HTL. On the contrary, the efficiency of the proposed solar cell with CuSCN HTL has been found to be 24.20% at the optimal device structure. These numerical findings of the present study may therefore provide an intuitive approach to fabricate an economically feasible and highly efficient WSe2-based heterojunction thin-film solar cell.