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. The proposed technology as demonstrated in the Phase I program overcomes this limitation by optimizing light absorption through the incorporation of quantum dot (QD) nanostructures while maintaining traditional lattice spacings between layers allowing for high quality multilayer devices. The resulting improvements in current matching for the overall device will result in large efficiency gains. During the Phase II program, we propose triple junction cells with efficiencies of approximately 40%. For larger stacks, which will be much easier to fabricate than in traditional multijunction cells, efficiencies greater than 60% are predicted.