This paper aims to present computational modelling of thin film fullerene-based Polymer Solar Cell (PSC) based on regioregular P3HT: PCBM, which is also known as organic solar cell (OSC). The structure is numerically modelled in such a way to boost the electrical photovoltaic parameters by modulating the thickness of active layer which is the combination of donor and acceptor (D/A) material. The obtained results strongly suggest that thickness of the active layer is one of most important and key parameter for obtaining high performance from the device. The simulated structure delivered the highest energy efficiency of 4.58 with open circuit voltage of 0.816 (V), and fill factor of 82.71 . The paper is also featured with the optical absorption of photons. The proposed architecture can be helpful for the potential applications of solar energy harvesting devices. © 2020 IEEE.