Recent R&D topics on concentrator multi-junction solar cells and materials under innovative solar cells´s project

III-V compound multi-junction solar cells have great potential for space and terrestrial applications because they have high efficiency potential of more than 50% and superior radiation-resistance. We have been studying concentrator multi-junction solar cells under Japanese Innovative Photovoltaic R&D program started since FY2008. This paper presents our new achievements in super high-efficiency multi-junction and concentrator solar cells. We have obtained promising results: 1) 35.8% efficiency InGaP/GaAs/InGaAs 3-junction cells, 2) high quality (In)GaAsN material with higher mobility by chemical beam epitaxy compared to those grown by the other growth methods.