Abstract: Solar Photovoltaic (PV) technologies are undoubtedly going to merge with mainstream energy harvesting technologies for mankind around the globe in near future. The promises that various photovoltaic options provide to date include high conversion efficiency with low manufacturing cost. Solar manufacturing industries are in the midst of an argument over which material to dominate the future for harvesting sunlight. Solar panels based on silicon currently account for more than 90% of the production with some limitations. However, much attention has been paid to alternatives like thin film semiconductor materials such as amorphous silicon, cadmium telluride and copper-indium-gallium-diselenide based solar cells due to the promises in cost efficiency. Attributed to some recent breakthrough in copper-indium-gallium-diselenide (CIS, thereafter) based solar cell efficiency, commercialization has got momentum around the world. Here, progresses in Cu (In, Ga) Se2 thin film solar cells technologies are discussed here in regard to material properties of the Cu (In, Ga) Se2 absorber layer, fabrication method of the complete device and the current CIGS research challenges. The scope of this review aims to elucidate the basics of CIGS solar cells fabricated by co-evaporation method which yields the highest conversion efficiency so far.