Growth of AlGaAsSb/GaAsSb monolithic, cascade solar cells

Thesis/Dissertation · Sat Jan 01 04:00:00 EST 1983

OSTI ID:5803777

Timmons, M L

Modeling has shown that the optimum bandgaps for two-junction, monolithic, cascade solar cells are 1.8 and 1.2 eV for cells intended for the high temperature environment found in terrestrial 400- to 1000-sun concentrator systems. These values can be obtained employing Al/sub 0/ /sub 44/Ga/sub 0/ /sub 56/As/sub 0/ /sub 87/Sb/sub 0/ /sub 13/ for the high- and low- bandgap junctions, respectively, at the same lattice constant. Using these alloys, photojunctions were developed; with Al/sub 0/ /sub 44/Ga/sub 0/ /sub 56/As/sub 0/ /sub 87/Sb/sub 0/ /sub 13/ tunnel junctions as cell interconnects, cascade structures have been grown by liquid phase epitaxy which show voltage addition for the two photojunctions. Measured conversion efficiencies were less than or equal to 2%, far short of the 30% goal described by the models. The cell shortcomings have three sources: 1) there is a 1% lattice mismatch between GaAs substrates and GaAs/sub 0/ /sub 87/Sb/sub 0/ /sub 13/, low bandgap junctions; 2) the required AlGaAsSb compositions are near a miscibility gap, resulting in questionable material homogeneity and difficult crystal nucleation; these problems are manifested by the appearance of a second, Sb-rich solid phase in x-ray diffraction spectra and poor growth reproducibility and morphology; and 3) the heavy Ge doping in the p/sup +/ tunnel-junction layers contracts the lattice constant, impeding lattice matching to bottom cells, and results in second phase formation observed by x-ray diffraction.

• OSTI ID: 5803777
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140501* -- Solar Energy Conversion-- Photovoltaic Conversion
ALLOYS
ALUMINIUM ADDITIONS
ALUMINIUM ALLOYS
ANTIMONY ADDITIONS
ANTIMONY ALLOYS
CASCADE SOLAR CELLS
CRYSTAL DOPING
DIRECT ENERGY CONVERTERS
EFFICIENCY
ELEMENTS
EQUIPMENT
GALLIUM ARSENIDE SOLAR CELLS
GERMANIUM
GRADED BAND GAPS
METALS
PHOTOELECTRIC CELLS
PHOTOVOLTAIC CELLS
PNICTIDES
SOLAR CELLS
SOLAR EQUIPMENT