The rising costs of traditional fossil fuels and the impact of their emissions on the environment has caused a shift in energy production toward more environmentally conscience and renewable sources. One energy technology that displays great potential for contributing to a cleaner energy grid is solar energy. While there are many different solar technologies and materials systems, the technology and system with the greatest promise to reach the $1/W goal set by the Sunshot Initiative, a price point that will make solar energy competitive with fossil fuels, is the Multi-Junction (MJ) Concentrator Photo Voltaics (CPV). The advantage of using MJ over other solar technologies is in the division of the solar spectrum into several spectral regions and converting each region with a subcell which possess a bandgap tuned to said region. This distribution of energies in the cell results in considerable efficiency when compared to single junction (SJ) solar cells in addition to avoiding the usual tradeoff between voltage and current associated with SJ solar cells. This is of importance because efficiency is the most important parameter of a solar cell in CPV systems, as the area of the cell can be decreased considerably, thus greatly reducing the impact that the expensive MJ cell cost per area has on the final CPV system. However, despite the promise of MJ cells they are not without their issues which include lattice matching and current matching among the junctions. Currently, the Ge bottom subcell of MJ solar cells produces approximately twice the current as the middle GaAs subcell. For example the InGaP/GaAs/Ge MJ solar cell, the most studied structure, is very well lattice matched but is not optimally current matched. This current mismatch limits the potential efficiency of the total cell, and it is this current mismatch that must be addressed in order to achieve the $1/W goal.
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