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).