Optics and calculated efficiencies of mechanically stacked two-junction solar cells

Journal Article · Wed Jul 15 00:00:00 EDT 1987 · J. Appl. Phys.; (United States)

DOI:https://doi.org/10.1063/1.339744· OSTI ID:6587004

Partain, L D; Fraas, L M; McLeod, P S; Cape, J A; Kuryla, M S

Mechanically stacked two-junction solar cells avoid the multijunction problems of interfering growth conditions, shorting layers, and current matching. They also allow the use of well-developed Si and GaAs junctions. Doping the top junction substrates at 2(10/sup 17/) cm/sup -3/ reduces measured free-carrier absorption by up to a factor of 5 compared to doping at 8(10/sup 17/) cm/sup -3/. Separately measured quantum-yield spectra, open-circuit voltages, and fill factors provide the basis to calculate stack efficiencies of 24%--28% for Si stacked under GaAsP and GaAs top junctions for a direct air mass 1.5 (AM1.5D)= terrestrial sunlight spectra and a 400 x light concentration. The GaAs is a preferred top junction because it has a direct gap, operates at near its theoretical limits, and minimizes transmission loss effects by contributing over 70% of the total stack output without compromising potential stack performance. The open-circuit voltages of GaAs and Si cells are measured to vary with light intensity as predicted by the standard model with a junction ideality factor equal to 1.0. This and other experimental junction data provide the basis to calculate 400 x , AM1.5D stack efficiencies of 29% for GaAs stacked on Ge and 30% for GaAs stacked on GaSb. Device improvements are suggested to project GaAs/Ge stack efficiencies of 30% and GaAs/GaSb stack efficiencies of 34% for 400 x , AM1.5D. The 400 x , AM0 efficiencies for space are 0.88 to 0.91 times the corresponding, terrestrial AM1.5D values.

• Research Organization: Chevron Research Company, Richmond, California 94802
• OSTI ID: 6587004
• Journal Information: J. Appl. Phys.; (United States), Vol. 62:2
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
GALLIUM ARSENIDE SOLAR CELLS
EFFICIENCY
OPTICS
GALLIUM PHOSPHIDE SOLAR CELLS
SILICON SOLAR CELLS
CRYSTAL DOPING
ELECTRIC POTENTIAL
EXPERIMENTAL DATA
JUNCTIONS
DATA
DIRECT ENERGY CONVERTERS
EQUIPMENT
INFORMATION
NUMERICAL DATA
PHOTOELECTRIC CELLS
PHOTOVOLTAIC CELLS
SOLAR CELLS
SOLAR EQUIPMENT
140501* - Solar Energy Conversion- Photovoltaic Conversion