Atomically thin 2D layered semiconductor materials such as Transition Metal Di-Chalcogenides (TMDCs) have great potential for use as flexible, ultra-thin photovoltaic materials in solar cells due to their favorable photon absorption and electronic transport properties. The electronic properties, such as band structure and bandgap, and optical absorption properties of Tungsten Disulfide (WS2) were obtained from Density Functional Theory (DFT) calculations; the properties of WS2 make it a favorable photovoltaic material. Using these properties, we have modelled, using numerical calculations and simulations, a solar cell based on monolayer and bulk WS2 together with amorphous silicon (a-Si). The maximum efficiency of this cell is 23.26% with V-OC of 0.843 V and J(SC) of 33.49 mA/cm(2). The performance of our solar cell is comparable to many commercial cells. The results show how monolayer WS2 can serve as a suitable photovoltaic material, opening possibilities to develop solar cells based on 2D TMDC materials.