Cu(In,Ga)Se2 solar cells and mini-modules fabricated on thin soda-lime glass substrates

In this paper, we report a recent progress in Cu(In,Ga)Se2 (CIGS) solar cells and mini-modules demonstrated on soda-lime glass (SLG) substrates, which are one of the most common and cost effective substrate materials for chalcopyrite photovoltaics. CIGS absorber layers grown by the three-stage co-evaporation process was used with an optimized [Se]/[metal] flux ratio and preferable substrate temperatures for SLG substrate thicknesses. SLG substrates of 0.28-1.1 mm in thickness, which are thinner than that generally used in laboratories and industries (∼2-3 mm), were employed to develop techniques for further reductions of material cost and module weight. Solar cell and mini-module efficiencies of >19% and >17%, respectively, with relatively high open circuit voltages (Voc) and fill factors (FF) (Voc 0.77 V and FF 0.79 for cells, and Voc 0.77 V and FF 0.74 for mini-modules) were demonstrated using a composition ratio [Ga]/([In]+[Ga]) of 0.45 for the CIGS absorber layers. Key techniques and future directions toward highly efficient CIGS solar cells and modules with high values of Voc and FF are discussed.