ZrS₂ is transition metal dichalcogenides (TMDCs) which is believed one of the most talented applicants to fabricate photovoltaics. Therefore, we present here for the first-time numerical simulation of novel inorganic ZrS₂/CuO heterojunction solar cells employing SCAPS-1D. The influence of the thickness, carrier concentration, and bandgap for both the window and absorber layers on the solar cell fundamental parameters was explored intensely. Our results reveal that the solar cell devices performance is mainly affected by many parameters such as the depletion width (W_d), built-in voltage (V_bi), collection length of charge carrier, the minority carrier lifetime, photogenerated current, and recombination rate. The η of 23.8% was achieved as the highest value for our simulated devices with the V_oc value of 0.96 V, the J_sc value of 34.2 mA/cm², and the FF value of 72.2%. Such efficiency was obtained when the CuO band gap, thickness, and carrier concentration were 1.35 eV, 5.5 µm, and above 10¹⁸ cm⁻³, respectively, and for the ZrS₂ were 1.4 eV, 1 µm, and less than 10²⁰ cm⁻³, respectively. Our simulated results indicate that the inorganic ZrS₂/CuO heterojunction solar cells are promising to fabricate low-cost, large-scale, and high-efficiency photovoltaic devices.