Metamorphic GayIn1-yP/Ga1-xInxAs tandem solar cells for space and for terrestrial concentrator applications at C>1000 suns

The use of Ga1-xInxAs instead of GaAs as a bottom solar cell in a GayIn1-yP/ Ga1-xInxAs tandem structure increases the flexibility of choosing the optimum bandgap combination of materials for a multijunction solar cell. Higher theoretical efficiencies are calculated and different cell concepts are suggested for space and terrestrial concentrator applications. Various GayIn1-yP/Ga1-xInxAs material combinations have been investigated for the first time and efficiencies up to 24.1% (AM0) and 27.0% (AM1.5 direct) have been reached under one-sun conditions. An efficiency of 30.0-31.3% was measured for a Ga0.35In0.65P/Ga0.83In0.17As tandem concentrator cell with prismatic cover at 300 suns. The top and bottom cell layers of this structure are grown lattice-matched to each other but a large mismatch is introduced at the interface to tire GaAs substrate. This cell structure is well suited for the use in next-generation terrestrial concentrators working at high concentration ratios. For the first time a cell efficiency up to 29-30% has been measured at concentration levels rep to 1300 suns, A small prototype concentrator with Fresnel lenses and four tandem solar cells working at C=120 has been constructed with art outdoor efficiency of 23%. Copyright (C) 2001 John Wiley & Sons, Ltd.