Super‐high‐efficiency multi‐junction solar cells

The status of Japanese development of super‐high‐efficiency In 0.49 Ga 0.51 P/In 0.01 GaAs/Ge multi‐junction solar cells is reviewed. Key issues for a successful cell design are discussed, together with the technologies that have led to efficiency values of 29.1% AM0 and >36% under concentrated 400×AM1.5 illumination. The radiation resistance of the multi‐junction solar cell is discussed, showing the degradation in performance for the InGaP, InGaAs and Ge junctions. Finally, some perspectives for further multi‐junction cell development and alternative approaches to high efficiency are outlined.