Ultrahigh Detailed Balance Efficiencies for Single Junction Solar Cells with Structured Emission
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The promise of solar powered energy is highly attractive, generating research efforts into the physical understanding of photovoltaic devices and how a greater knowledge of these systems can be applied to improving their overall performance. The study presented here uses the model of detailed balance to calculate the efficiencies of single junction solar cells with the inclusion of angular restriction methods that rely on the anisotropic emission of ideal radiating rod shaped materials. The proposal of a device that utilizes the sin2 emission pattern of a dipole is described and adaptations of the detailed balance model are discussed for the inclusion of angular dependent restriction provided by this type of “structured emitter.” When radiative recombination is considered as the only source of energy loss, the highest efficiency a single junction cell may reach is 33.7%; however, constraining the angular range of emitted light promotes light trapping and photon recycling within the semiconductor and increases this maximum to 45.1%. Here a strategy is presented for implementing a single junction device with 60.0% efficiency, by placing anisotropic optical emitters with a dipole radiation pattern optically in-series with a conventional cell. The analysis further considers application of so called “structured emission” to the inclusion of non-radiative losses incurred by real material properties of GaAs. The Auger losses of GaAs systems are dominant in power conversion efficiencies; however, a broadening in the range of maximum efficiency results from the modified emission and implies less reliance on external optics to track the maximum intensity of the sun. This increase in maximum efficiency angles allows for less intensive solar tracking, which can be reflected in decreased device complexity and cost. Additionally, real material properties of nanocrystal photoluminescence are described with a bandwidth addition to the band gap of the cell. For Auger-limited GaAs cells, nanorod inclusion provides a linear decrease in efficiency associated with the decreased absorptivity occurring in the near band gap region. Arbitrary band gap cells are limited to the best angle restricted efficiency commonly reported; however, they show a trend of decreasing band gap shifts for the point at which maximum efficiency occurs.
Martin, Jarett C (2016). Ultrahigh Detailed Balance Efficiencies for Single Junction Solar Cells with Structured Emission. Master's thesis, Texas A & M University. Available electronically from