The heterojunction (HJ) solar cell is one of the best possible options to upgrade the conventional single homo-junction c-Si solar cell. In this work, a single HJ solar cell based on crystalline silicon (c-Si) wafer with zinc oxide (ZnO) is designed to reduce the loss of power conversion owing to the reflection of incident photons by the top surface of silicon. A PC1D simulation is used to evaluate the optimum numerical value of key photovoltaic parameters for HJ-based c-Si solar cells. The average reflectance for ZnO/Si HJ-based c-Si is 7.65% in the wavelength range of 400-1000 nm. The highest efficiency (η = 24.8%) of the ZnO/Si HJ-based c-Si solar is obtained with a 400 μm base thickness, 20 μm emitter thickness, doping concentration of 1.1 × 1017 cm−3 in the base and a doping concentration of 5.1 x 1016 cm−3 in the emitter. The proposed ZnO/Si HJ-based c-Si solar cell with high efficiency would be one of the best possible alternative HJ device to the conventional single homo-junction c-Si solar cell.