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.