Perovskite/CIGS Spectral Splitting Double Junction Solar Cell with 28% Power Conversion Efficiency

The highest theoretical efficiency of double junction solar cells is predicted for architectures with the bottom cell bandgap ( E g ) of approximately 0.9–1.0 eV, which is lower than that of a typical Si cell (1.1 eV). Cu(In,Ga)(Se,S) 2 (CIGS) solar cells exhibit a tunable E g depending on their elemental composition and depth profile. In this study, various CIGS solar cells with E g ranging from 1.02 to 1.14 eV are prepared and a spectrum splitting system is used to experimentally demonstrate the effect of using lower- E g cells as the bottom cell of two-junction solar cells. The four-terminal tandem cell configuration fabricated using a mixed-halide perovskite top cell ( E g = 1.59 eV; stand-alone efficiency = 21.0%) and CIGS bottom cell ( E g = 1.02 eV; stand-alone efficiency = 21.5%) with a 775-nm spectral splitting mirror exhibits an efficiency of 28.0% at the aperture area of 1 cm 2 .