Ultra-high Efficiency Multijunction Solar Cells Using Quantum Dots

There is continuous pressure to improve the performance and reduce the cost of space solar arrays. However, further improvements in existing state of the art multijunction devices will likely yield only incremental improvements. Multijunction devices are currently limited by the inability to optimize the light absorption of the various layers due to the fact that materials in adjacent layers must be lattice matched, thus restricting the choices of semiconductors. We propose to dramatically increase solar cell efficiencies by developing a next generation device that incorporates quantum dot (QD) nanostructures in multijunction solar cells. The QDs will allow the optimal light absorption for the various sub-cells but will not create problems with lattice mismatches between the layers. The resulting improvements in current matching for the overall device will result in large efficiency gains. For triple junction cells we expect that efficiencies in excess of 40% will be attainable. For larger stacks, which will be much easier to fabricate than in traditional multijunction cells, efficiencies greater than 60% are predicted.