Lattice‐matched four‐junction tandem solar cell including two dilute nitride bottom junctions

• DOI: 10.1002/pip.3094
• Publication Date: 2018-12-10T09:35:35Z
• Authors: Arto Aho; Riku Isoaho; Lauri Hytönen; Timo Aho; Marianna Raappana; Ville Polojärvi; Antti Tukiainen; Jarno Reuna; Severi Mäkelä; Mircea Guina
• Keywords: 216 Materials engineering; 221 Nanotechnology; 0103 physical sciences; 216; 221; 530; 114 Physical sciences; 01 natural sciences; 7. Clean energy; 114

AbstractMonolithic four‐junction solar cells incorporating two dilute nitride (GaInNAsSb) bottom junctions are reported. The dilute nitride junctions have band gaps of 0.9 and 1.2 eV, while the top junctions have band gaps of 1.4 and 1.9 eV. By using experimental‐based parametrization, it was estimated that the four‐junction solar cell could theoretically exhibit efficiency levels of 34.7% at one sun, 43.2% at 100 suns, and 46.4% at 1000 suns for AM1.5D illumination. The most challenging subcell in terms of fabrication is the GaInNAsSb bottom junction with 0.9 eV band gap. For this subcell, a background doping level down to 5 × 1014 cm−3 and a high charge carrier lifetime up to 2 to 4 nanoseconds are reported, which reflects high values for current and voltage. An experimental AlGaAs/GaAs/GaInNAsSb/GaInNAsSb solar cell structure was fabricated by molecular beam epitaxy. At one‐sun AM1.5D illumination, the experimental cell exhibited an efficiency of 25%, an average quantum efficiency of 91%, and an open circuit voltage, which is about 87% of the estimated potential. The cell exhibited maximum efficiency of 37% at 100‐sun concentration.