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Optical designs for improved solar cell performance

Citation

Kosten, Emily Dell (2014) Optical designs for improved solar cell performance. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:05222014-154510725

Abstract

The solar resource is the most abundant renewable resource on earth, yet it is currently exploited with relatively low efficiencies. To make solar energy more affordable, we can either reduce the cost of the cell or increase the efficiency with a similar cost cell. In this thesis, we consider several different optical approaches to achieve these goals. First, we consider a ray optical model for light trapping in silicon microwires. With this approach, much less material can be used, allowing for a cost savings. We next focus on reducing the escape of radiatively emitted and scattered light from the solar cell. With this angle restriction approach, light can only enter and escape the cell near normal incidence, allowing for thinner cells and higher efficiencies. In Auger-limited GaAs, we find that efficiencies greater than 38% may be achievable, a significant improvement over the current world record. To experimentally validate these results, we use a Bragg stack to restrict the angles of emitted light. Our measurements show an increase in voltage and a decrease in dark current, as less radiatively emitted light escapes. While the results in GaAs are interesting as a proof of concept, GaAs solar cells are not currently made on the production scale for terrestrial photovoltaic applications. We therefore explore the application of angle restriction to silicon solar cells. While our calculations show that Auger-limited cells give efficiency increases of up to 3% absolute, we also find that current amorphous silicion-crystalline silicon heterojunction with intrinsic thin layer (HIT) cells give significant efficiency gains with angle restriction of up to 1% absolute. Thus, angle restriction has the potential for unprecedented one sun efficiencies in GaAs, but also may be applicable to current silicon solar cell technology. Finally, we consider spectrum splitting, where optics direct light in different wavelength bands to solar cells with band gaps tuned to those wavelengths. This approach has the potential for very high efficiencies, and excellent annual power production. Using a light-trapping filtered concentrator approach, we design filter elements and find an optimal design. Thus, this thesis explores silicon microwires, angle restriction, and spectral splitting as different optical approaches for improving the cost and efficiency of solar cells.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Solar Cell, Photovoltaic, Optics, Detailed Balance
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Atwater, Harry Albert
Group:Resnick Sustainability Institute
Thesis Committee:
  • Atwater, Harry Albert (chair)
  • Roukes, Michael Lee
  • Cross, Michael Clifford
  • Schwab, Keith C.
Defense Date:15 May 2014
Record Number:CaltechTHESIS:05222014-154510725
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05222014-154510725
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1039/C3EE43584ADOIExperimental demonstration of enhanced photon recycling in angle-restricted GaAs solar cells
http://dx.doi.org/10.1117/12.2024275DOISpectrum splitting photovoltaics: Light trapping filtered concentrator for ultrahigh photovoltaic efficiency
http://dx.doi.org/10.1038/lsa.2013.1DOIHighly efficient GaAs solar cells by limiting light emission angle
http://dx.doi.org/10.1364/OE.19.003316DOIRay optical light trapping in silicon microwires: exceeding the 2n2 intensity limit
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8259
Collection:CaltechTHESIS
Deposited By: Emily Kosten
Deposited On:29 May 2014 21:25
Last Modified:25 Apr 2016 23:12

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