GOALI:Cooperative Integration of High Efficiency Multijunction Solar Cell Structures

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The objective of this research is to develop a multijunction solar cell which has the potential to exceed the current record solar-to-electric energy conversion efficiency of 41.6%. This cell uses a tandem germanium/gallium arsenide/indium gallium phosphide structure, which is limited by the current generated in the top two cells. The approach is to integrate strained layer superlattices into both of these cells in order to reduce the bandgap. The resulting potentially significant increase in the current generated by the top and middle cells with only a small decrease in voltage, should improve the efficiency of the multijunction photovoltaic device.This work will impact the science of photovoltaic devices and strained layer superlattices. The ability to extend the optical absorption of the solar spectrum beyond that of conventional GaAs solar cells has been a long-standing problem since the demonstration of the first multijunction PV device. The proposed work will extend this absorption region while maintaining lattice matching of dissimilar materials, and thus carrier lifetimes. Strained layer superlattices have wide applicability in other applications as well, such as photodetectors and optical modulators for high frequency communications and sensing.Photovoltaic materials have the potential to provide a clean and renewable energy source. The project will train students in a number of skills used in the semiconductor industry such as growth, fabrication, characterization and device modeling. This will include the participation of undergraduate, minority students, and high school students and teachers.