Chalcopyrite solar cells——state-of-the-art and options for improvement

Chalcopyrite solar cells will have to play an important role to mitigate the climate crisis, because of their particularly low carbon emissions. Doping in these semiconductors is due to native defects and intentional alkali impurities. The recent progress in efficiency has been made possible by post-deposition treatments with heavy alkalis. Tail states and band gap distribution are the main limitations for the open circuit voltage in state-of-the-art chalcopyrite solar cells. Further efficiency limitations are due to the increased diode factor because of metastable defect transitions. Alloying with Ag opens new possibilities of band-edge engineering, as well as seems to improve the diode factor. In state-of-the-art cells the back contact is passivated by a Ga gradient;considerable research has been done to passivate the back contact by structured or continuous dielectric layers. A leap forward in efficiency can be expected from tandem cells. Chalcopyrite solar cells show promising potential as bottom cells as well as top cells.