Cu(In, Ga)Se2 thin film solar cells grown at low temperatures

Cu(In, Ga)Se2 (CIGS) thin film solar cells were grown on polyimide (PI) and soda lime glass (SLG) substrates at low substrate temperatures between 400 °C and 500 °C. Different material properties of the CIGS thin films and photovoltaic performances of the solar cells were systematically investigated. It is found that the (112), (220)/(204) and (116)/(312) peaks from X-ray diffraction (XRD) patterns show double-peak patterns as the substrate temperature decreases. The CIGS thin films grown on both PI and SLG substrates shows layered structures. The bottom and surficial layers of CIGS thin films display small size polycrystalline grains while the middle layers show large size polycrystalline grains. Both types of CIGS thin film solar cells exhibit similar efficiencies while CIGS thin film solar cells grown on PI substrates show lower open circuit voltage and fill factor but higher short circuit current density, as compared to those of CIGS thin film solar cells on SLG substrates. The highest efficiency of 6.14% has been achieved for the CIGS thin film solar cells on PI with the structure of PI/Mo/CIGS/CdS/i-ZnO/ZnO:Al/Al grid here.