Commercial triple junction solar cell designs were modified in their junction thicknesses, contact grid densities, and anti-reflective (AR) coating thicknesses to better match the Mars surface solar spectrum. Resulting cells show up to approximately 8% relative improvement in efficiency under the Mars solar spectrum, compared to non-optimized space solar cells, in testing performed at JPL.

The Mars-optimized cells incorporated modifications to the epitaxial structure of the cells to correct for reduced content in the blue portion of the Martian 60° latitude spectrum as well as a grid design optimized for the low solar intensity. The current produced by the 60° Martian spectrum is about 15% of that produced from the Earth AM0 spectrum, which notably reduces emitter sheet resistance losses. Additional resistive power loss from the reduction of front-side grid metal is less than a quarter of a percent, while shading is reduced by almost 50%. This Mars-optimized grid design improves efficiency by about 0.75% relative.

Optimization of a commercial state-of-the-art Triple Junction solar cell for the Mars surface solar spectrum focused on the 60° latitude spectrum. A previous report showed a 4.4% relative increase in maximum power by current-matching in the top two subcells of the triple junction. The current densities in the top and middle cells are appropriately matched for the reduced blue content of the 60° latitude solar spectrum.

This work was done by Paul M. Stella, Robert L Mueller, and Nick Mardesich of Caltech; Mark A. Stan, Dan J. Aiken, A. V. Ley, and Scott P. Endicter of Emcore Photovoltaics; and Kenneth M. Edmonson, Chris Fetzer, and Andreea Boca of Spectrolab Inc. for NASA’s Jet Propulsion Laboratory. For more information, contact This email address is being protected from spambots. You need JavaScript enabled to view it.. NPO-46201

NASA Tech Briefs Magazine

This article first appeared in the December, 2014 issue of NASA Tech Briefs Magazine.

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