Exploring New Convergences between PV Technologies for High Efficiency Tandem Solar Cells

A new concept is proposed to develop efficient tandem cells based on silicon bottom cells and wide band gap Cu(In,Ga,Al)(S,Se)2 (noted CIGS) top cells. It consists in introducing an epitaxial III-V buffer layer at the interface. The benefit of this configuration is discussed in terms of lattice and band offsets matching between CIGS and III-V's. Selected combinations are proposed, with AlGaAs and GaAlP buffer layers. Preliminary results with CuGaSe2 on various sustrates confirm the influence if the substraqte on the growth of CGS and PV propoerties. Epitacial growth on GaP and possible selective back contact effect with GaAlAs are evidenced. Preliminary results on using advanced characterization methods are presented (quantum efficiency, x-ray diffraction, secondary ion mass spectroscopy, nanoAuger, cathodoluminescence).