GaAs//CuInGaSe‐Based Multijunction Solar Cells with 30% Efficiency Under Low Concentrated Sunlight

Multijunction (MJ) solar cells have demonstrated very high efficiencies (>30%) owing to the effective use of solar energy. Among these, the GaAs//CuInGaSe(CIGSe)‐based MJ solar cell is unique owing to its features, such as being lightweight owing to the combination of thin cells and allowing the use of flexible substrates such as thin metal plates and polymer films. Furthermore, low‐concentration solar cells offer a practical solution with high efficiency and low cost. Previously, an efficiency of more than 30% was attained for an InGaP/GaAs//CIGSe three‐junction solar cell fabricated via mechanical stacking using Pd nanoparticle arrays and a silicone adhesive (modified smart stack). In this study, the potential of GaAs//CIGSe‐based MJ solar cells is examined for application under low‐concentration sunlight. The fabricated InGaP/Al 0.06 Ga 0.94 As//CIGSe three‐junction solar cell demonstrates a maximum efficiency of 29.73% at 2.8 suns and maintained a high efficiency of ≈30% in the low‐concentration region (<10 suns). For the in‐vehicle deployment, an efficiency of 30% is sufficient to enable independent travel for 1 day in Japan. These results demonstrate the potential of smart‐stack GaAs//CIGSe‐based MJ solar cells as next‐generation solar cells.