High‐performance low bandgap thin film solar cells for tandem applications

Thin film tandem solar cells provide a promising approach to achieve high efficiencies.
These tandem cells require at least a bottom low bandgap and an upper high bandgap
solar cell. In this contribution, 2 high‐performance Cu(In,Ga)Se2 cells with bandgaps as
low as 1.04 and 1.07 eV are presented. These cells have shown certified efficiencies
of 15.7% and 16.6% respectively. Measuring these cells under a 780‐nm longpass filter,
corresponding to the bandgap of a typical top cell in tandem applications
(1.57 eV), they achieved efficiencies of 7.9% and 8.3%. Admittance measurements
showed no recombination active deep defects. One additional high‐performance
CuInSe2 thin film solar cell with bandgap of 0.95 eV and efficiency of 14.1% is presented.
All 3 cells have the potential to be integrated as bottom low bandgap cells
in thin film tandem applications achieving efficiencies around 24% stacked with an
efficient high bandgap top cell.