Search of sustainable energy resources is continued from the decades. The industrialization growth in various domains and socio-economic developments created huge demand of electrical power while the conventional resources are shrinking. This opens doors for research and developments in renewable energy resources such as, Solar, Wind, Hydro and Geothermal Energy sectors. Among these energy solar energy emerged as one of the sustainable energy resource. This research work targeted to improve the efficiency of thin film flexible Copper Indium Gallium Di-Selenide abbreviated as CIGS cell through optimization of buffer layer parameters. The proposed model used zinc sulphide (ZnS) as a potential buffer layer to make the solar cell free from toxic Cadmium (CdS) sulphide. Further the doping profile and width of buffer layers are investigated along with corresponding change in energy states and electrical permittivity of the material. The complete solar cell model is simulated using MATLAB scripting and SCAPS model. the results are compared with the existing result of CdS-CIGS. The ZnS-CIGS model is simulated with variation in thickness of buffer layer and optimized material parameters are determined.