NASA 1998 SBIR Phase I


PROPOSAL NUMBER: 98-1 18.02-6000

PROJECT TITLE: High Efficiency InGaP/GaAs Linear Concentrator Arrays

TECHNICAL ABSTRACT (LIMIT 200 WORDS)

Spire proposes to develop two-junction In(x)Ga(1-x)P/GaAs tandems as high-efficiency concentrator solar cells. Efficiency of present In(0.49)Ga(0.51)P/GaAs tandems is below the desired 30% AM0 level. We propose to make a major change to the present design, which should result in 33% AM0 10-sun cells. The In(0.49)Ga(0.51)P/GaAs combination was chosen since it is lattice-matched. Current-matching is achieved by thinning the In(0.49)Ga(0.51)P top cell to leak light into the lower GaAs cell. The overall result is a Jsc of ~16 mA/cm2. If the bandgap of the top cell is raised from 1.85 eV to 2 eV, a Jsc of ~18 mA/cm2 is possible and the voltage should increase by ~150 mV due to the higher bandgap and another ~120 mV due to the higher solar insulation. We will investigate two different 2 eV top cells. The first option is innovative; In(0.42)Ga(0.58)P, which exhibits a 0.4% mismatch to GaAs, will be used. We believe an indium-based cell with only 0.4% mismatch may not be degraded substantially from one that is lattice-matched. The second option is an InAlGaP lattice-matched cell; the challenge here is to grow long-lifetime material (difficult due to the reactivity of aluminum with oxygen).

POTENTIAL COMMERCIAL APPLICATIONS

The proposed two-junction InGaP/GaAs concentrator cells are usable in a variety of space power systems with concentration ratios from one through ten suns. Such low concentration systems are of interest (NASA WIRE, AF MightySat) in order to lower array cost by reducing III-V solar cell area, as well as obtaining a boost in efficiency due to the higher solar insolation, while having less severe pointing requirements than high concentration systems.

NAME AND ADDRESS OF PRINCIPAL INVESTIGATOR

Steven J. Wojtczuk, Ph.D.
Spire Corporation
One Patriots Park
Bedford , MA 01730-2396

NAME AND ADDRESS OF OFFEROR

Spire Corporation
One Patriots Park
Bedford , MA 01730-2396