Non-uniform doping concentration CIGS absorber profile for highefficiency solar cells

The quaternary chalcopyrite semiconductor alloy Cu(In,Ga)Se2 (CIGS) is nowadays commonly considered one of the most suitable materials to fabricate cost-effective and high-efficiency photovoltaic cells. Thanks to the optical and structural properties of the absorber layer and to the tunable bandgap, thin-film CIGS cells have reached efficiencies around 20%, not far from the maximum values of traditional crystalline silicon cells. This high efficiency, together with the conceivable low fabrication costs, makes CIGS cells a promising alternative to silicon technology for large-scale production. In order to further improve the cells performance, in a previous work we have already proposed a simple structure having a linear graded carrier concentration absorber profile, which allows to induce a quasi-electrical field directed towards the back-contact, like CIGS cells with a Ga back-graded profile. Thanks to the increase of Ec and Ev towards the backcontact, while keeping the energy gap constant along the depth, the generation process is even more efficient in our structure, thus improving cells performance (efficiency over 21%). Herein, we investigate on other non-uniform doping concentration profiles that can be technologically easily realised, still maintaining the already demonstrated high-efficiency values.