| Summary: | Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. === This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. === Cataloged from student-submitted PDF version of thesis. === Includes bibliographical references (pages 67-70). === Solar power has unmatched ability to provide greater security and reduced environmental impact for the energy sector. Photovoltaic (PV) systems provide the most popular method used today for harnessing this power. However, the costs of these systems are still higher than traditional fossil fuel generation, leading to limited adoption. One of the major drivers of cost is the efficiency with which PV systems convert solar energy to electricity. Systems that rely on a single semiconducting material to absorb sunlight are fundamentally limited in how efficiently they can convert it to electricity, so efforts have been made to incorporate multiple absorber materials into a single system. One approach is to use an optical component to split the solar spectrum and guide high-energy light to absorber materials with a wide band gap and low-energy light to absorbers with a narrower band gap. This thesis uses two-dimensional technology computer aided design (TCAD) simulations to develop design guidelines for optical components used for this purpose. Two optical parameters, spectral fidelity -- the fraction of photons that are absorbed by the intended material -- and spatial uniformity -- the uniformity of light intensity over the surface of the solar cell -- are considered. A sensitivity analysis of these parameters is performed for a system using two absorber materials: crystalline silicon (Si) and cuprous oxide (Cu2O). The spectral fidelity of the low-energy spectral band was found to have a strong impact on device performance, the fidelity of the high-energy spectral band was found to have a small impact, and the spatial uniformity was found to have almost no impact. While the detailed analysis is valid strictly for this combination of absorbers, the findings bear relevance for systems with more absorbers and different materials, and the sensitivity analysis approach can be applied to any system. === by David Berney Needleman. === S.M.
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