Lattice matchable alloy for solar cells

Abstract

An alloy composition for a subcell of a solar cell is provided that has a bandgap of at least 0.9 eV, namely, Ga1-xInxNyAs1-y-zSbz with a low antimony (Sb) content and with enhanced indium (In) content and enhanced nitrogen (N) content, achieving substantial lattice matching to GaAs and Ge substrates and providing both high short circuit currents and high open circuit voltages in GaInNAsSb subcells for multijunction solar cells. The composition ranges for Ga1-xInxNyAs1-y-zSbz are 0.07≦x≦0.18, 0.025≦y≦0.04 and 0.001≦z≦0.03.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS[0001]NOT APPLICABLESTATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]NOT APPLICABLEREFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK[0003]NOT APPLICABLEBACKGROUND OF THE INVENTION[0004]The present invention relates to multijunction solar cells, and in particular to high efficiency solar cells comprised of III-V semiconductor alloys.[0005]Multijunction solar cells made primarily of III-V semiconductor alloys are known to produce solar cell efficiencies exceeding efficiencies of other types of photovoltaic materials. Such alloys are combinations of elements drawn from columns III and V of the standard Periodic Table, identified hereinafter by their standard chemical symbols, names and abbreviation. (Those of skill in the art can identify their class of semiconductor properties by class without specific reference to their column.) The high...

AI Technical Summary

Benefits of technology

[0010]The invention described herein reflects a further refinement of work described in U.S. patent application Ser. No. 12 / 217,818, including the discovery and identification of specific ranges of elements, i.e., a specific alloy mix of the various elements in GaInNAsSb that improve significantly the performance of the disclosed solar cells.

Problems solved by technology

This structure is not optimal for efficiency, in that the bottom junction can generate roughly twice the short circuit current of the upper two junctions, as reported by J. F. Geisz et al., “Inverted GaInP / (In)GaAs / InGaAs triple junction solar cells with low-stress metamorphic bottom junctions,”Proceedings of the 33rd IEEE PVSC Photovoltaics Specialists Conference, 2008.

This extra current capability is wasted, since the net current must be uniform through the entire stack, a design feature known as current matching.

This has been attributed to low minority carrier diffusion lengths that prevent effective photocarrier collection.

Devices reported in that paper have short circuit currents far too low for integration into multijunction solar cells.

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