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. This paper presents 3 high‐performance CI(G)S thin film solar cells with bandgaps as low as 0.95 to 1.07 eV. Two of the cells were certified achieving efficiencies around 16%. One of the 2 CIGS cells has a certified efficiency of 16.6% and is at the moment the best low bandgap cell reported. Measuring the 3 cells under a 780‐nm longpass filter, corresponding to the bandgap of a typical top cell in tandem applications, they achieved efficiencies of 7.4% to 8.3% with the potential to achieve 23.5% to 24.4% stacked with an efficient high bandgap top cell in tandem applications. Admittance measurements showed no recombination active deep defects.