Spectrolab has fabricated a direct semiconductor bonded space solar cell with an efficiency of 3S.8% under the AMO space spectrum. Using a similar technology, Spectrolab has achieved as-junction (SJ) direct bonded terrestrial cell with a record efficiency of 38.8% under the one-sun AM1.SG terrestrial spectrum. Efforts to further improve the SJ cell efficiency have focused on development of the top 3 junctions (T3J) grown on GaAs. Experiments with top 3J isotype cells have yielded an improvement of 1 % in current and 100 mV in voltage for the T3J. Spectrolab has also made significant improvements in its direct bonding process. The improved process has increased bond strengths by more than a factor of S and eliminated issues with large voids.
Spectrolab has demonstrated a 2.2/1.7/1.4/1.05/ 0.73 eV 5J cell with an efficiency of 37.8% under 1 sun AM1.5G spectrum and 35.1% efficiency for 1 sun AM0. The top three junctions and bottom two junctions were grown on GaAs and InP substrates, respectively, by metal organic vapor phase epitaxy. The GaAs-and InP-based cells were then direct bonded to create a lowresistance, high-transmissive interface. Both the space and terrestrial cells have high 1 sun V o c between 4.75 and 4.78 V. Initial tests of the terrestrial cells at concentration are promising with efficiencies increasing up to 10× concentration to a maximum value close to 41%.
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