Mechanically Stacked GaAs/GaInAsP Dual-Junction Solar Cell with High Conversion Efficiency of More than 31%

We successfully fabricated high-performance GaAs and GaInAsP (band gap = 0.95 eV) single-junction solar cells with an area of 1×1 cm2. The conversion efficiencies of the GaAs and GaInAsP cells were 25.0 and 19.3%, respectively, under 1-sun air-mass 1.5 global (AM1.5G) conditions. The GaInAsP cell as the bottom cell under the mechanically stacked GaAs top cell also showed a high efficiency of 6.1%, and a total efficiency of 31.1% was achieved for the GaAs/GaInAsP tandem cell. This is the highest efficiency obtained under 1-sun AM1.5G conditions among the dual-junction cells ever reported.