III-V//CuxIn1-yGaySe2 Multijunction Solar Cells with 27.2% Efficiency Fabricated using Modified Smart Stack Technology with Pd Nanoparticle Array and Adhesive Material
Multijunction (MJ) solar cells achieve high efficiencies by effectively utilizing the solar spectrum. Previously, we have developed III-V MJ solar cells using smart stack technology, a mechanical stacking technology that uses a Pd nanoparticle array. In this study, we fabricated an InGaP/AlGaAs//CuxIn1−yGaySe2 three-junction solar cell by applying modified smart stack technology with a Pd nanoparticle array and adhesive material. Using adhesive material (silicone adhesive), the bonding stability was improved conspicuously. The total efficiency achieved was 27.2% under AM 1.5 G solar spectrum illumination, which is a better performance compared to our previous result (24.2%) for a two-terminal solar cell. The performance was achieved by optimizing the structure of the upper GaAs-based cell and by using a CuxIn1−yGaySe2 solar cell with a specialized performance for an MJ configuration. In addition, we assessed the reliability of the InGaP/AlGaAs//CuxIn1−yGaySe2 three-junction solar cell through a heat cycle test (from −40°C to +85°C; 50 cycles) and were able to confirm that our solar cells show high resistivity under severe conditions. The results demonstrate the potential of III-V//CuxIn1−yGaySe2 MJ solar cells as next-generation photovoltaic cells for applications such as vehicle-integrated photovoltaics; they also demonstrate the effectiveness of modified smart stack technology in fabricating MJ cells.