GaAs//CuIn_1−yGa_ySe₂ Three-Junction Solar Cells With 28.06% Efficiency Fabricated Using a Bonding Technique Involving Pd Nanoparticles and an Adhesive

Multijunction (MJ) solar cells haveattracted attention as next-generation solar cells. In particular, III–V-based MJ solar cells connected with heterogeneous cells, such as GaAs//Si and GaAs//CIGSe (CuIn _1−y Ga _y Se ₂ ), are expected to be highly efficient and low cost. In this article, we demonstrate a highly efficient InGaP/Al _0.06 Ga _0.94 As//CIGSe three-junction solar cell. The key technology used to fabricate this solar cell is a bonding method that uses a Pd nanoparticle array and an adhesive material (silicone adhesive) for the bonding interface, which is modified for our previous “smart stack” technology. This modified smart stack technology contributes to enhancing the bonding strength between the GaAs-based cell and the CIGSe cell. Using this technology, total efficiency of 28.06% was attained, as certified by the National Institute of Advanced Industrial Science and Technology. This value is superior to that obtained in our previous result (27.2%) and represents the highest efficiency ever reported for two-terminal GaAs//CIGSe-based tandem solar cells.