Towards high-efficiency and low-cost epitaxial CIGSu/Si tandem solar cells

We propose to explore tandem junctions associating single crystalline silicon bottom cell (Eg = 1.12 eV) and wide bandgap (1.7 eV) CuIn0.75Ga0.25S2 (pure-sulfide CIGSu) top cell, using GaP intermediate layer. Our purpose is to grow CIGSu films under epitaxial conditions on GaP/Si(001) to improve the top cell efficiency, thanks to a reduction of the structural defects density detrimental for the cell performance, so that CIGSu/Si tandem cells can emerge as cost competitive for the next generation of PV modules. Record efficiency on standard AZO/ZnMgO/CdS/CIGSu/Mo/Glass solar cell and epitaxy of CIGSsu on GaP/Si are demonstrated.