Copper-silver chalcporyites as top cell absorbers in tandem photovoltaic and hybrid photovoltaic/photoelectrochemical devices

Bandgap tuneability with copper chalcopyrites offers convenient opportunities to use this material in tandem solar cells. While single-junction photovoltaic cells have performed remarkably well, the use of tandem cells can more efficiently utilize the solar spectrum by converting different portions of it with multiple cells, resulting in devices with higher voltages and possibly greater efficiencies. While it might be expected to be analogous to lower-bandgap materials, higher-bandgap copper chalcopyrites (like CuGaSe₂ where E_g~1.65eV) do not form efficient junctions with back contacts and buffer/window layers due to band edge misalignments and material differences (like lattice mismatching). The addition of silver to replace part or all of the copper in chalcopyrites may offer an avenue of improvement providing higher bandgaps, more favorable band edge alignments, and better junctions with back contacts and buffer/window layers in tandem PV devices. The different band edge positions resulting from the addition of silver also offers itself well to tandem hybrid photovoltaic/photoelectrochemical cells where the top photoelectrochemical cell drives a chemical reaction like splitting water into hydrogen and oxygen gases.