In this research, a numerical simulation and analysis of the second generation thin film solar cell Copper Indium Gallium diselenide, Cu(In,Ga)Se2 or, CIGS, is conducted in order to optimize its performance and compare among the cells using different materials for buffer and window layers. The one-dimensional solar cell simulation program SCAPS-1D (Solar Cell Capacitance Simulator) is used for the simulation and analysis purpose. The effects of variation of bandgap, concentration and thickness of the p-type CIGS absorber layer on the efficiency of CIGS solar cell are investigated. The change in CIGS solar cell efficiency with change in temperature is studied, too. Two different buffer layers namely CdS and In2S3 are considered for the simulation of the CIGS solar cell. The thickness of the buffer layer, its bandgap and concentration are taken into consideration for optimization. As for the window layer, ZnO and SnO2 are employed for the numerical simulation. The thickness of the window layer is varied and its effect on the efficiency of the solar cell is investigated. The open-circuit voltage, short-circuit current density, fill factor and quantum efficiency of the CIGS solar cell are observed from the SCAPS simulation besides the solar cell efficiency. A comparison among the different CIGS cell structures employing different buffer layers and window layers is performed in terms of efficiency and other essential parameters as mentioned above. The solar cell performances of the structures explored in this work were also put in comparison against some laboratory research cell output. The simulation result shows a possible better performance for all the simulated CIGS cell structures compared to the experimental results. In2S3 appears to increase efficiency and thus poses a great potential for non-toxic CIGS solar cell. Though CIGS absorber layer requires more thickness for desired output, successful application of much thinner SnO2 replacing ZnO buffer layer paves the way to less thicker CIGS thin film solar cell.