A higher efficiency of photovoltaic cells can be attained by optimizing their design, selecting the appropriate materials, and implementing of effective passivation process. The present study investigates the influence of the thickness and band gap of different layers of the solar cell and resuting opto-electric performance parameters of both single junction heterojunction (HJ) and heterojunction with intrinsic thin layer (HIT) cells. These cells are made up of a crystalline silicon (c-Si) active layer having back surafce field layer. The reported simulated work was conducted using AFORS-HET, an automated program specifically designed for simulating heterostructures. An efficiency of 26.86% has been attained for a HJ solar cell, this efficiency was further improved to 29.38% for the HIT solar cell by optimising all parameters. These cells require an emitter layer with a bandgap of around 1.4 eV. The optimal values of open-circuit voltage (V
OC), short-circuit current density (JSC), and fill factor are determined and found to be: 631.2 mV, 51.16 mA cm−2, and 83.16% for HJ solar cell, and 683 mV, 52.74 mA cm−2, and 81.55% for HIT solar cell. Moreover, the J-V curve, spectral response and quantum efficiency analysis have also been studied.