Full metadata
Title
Wavelength-Selective Light Trapping for Enhanced Photogeneration, Radiative Cooling and Sub-Bandgap Reflection
Description
This work investigates the impact of wavelength-selective light trapping on photovoltaic efficiency and operating temperature, with a focus on GaAs and Si devices. A nanostructure array is designed to optimize the efficiency of a III-V narrow-band photonic power converter (PPC). Within finite-difference time-domain (FDTD) simulations, a nanotextured GaInP window layer yields a 25× path-length enhancement when integrated with a rear dielectric-metal reflector. Then, nanotexturing of GaInP is experimentally achieved with electron-beam lithography (EBL) and Cl2/Ar plasma etching. Time-resolved photoluminescence (TRPL) measurements show that the GaAs absorber lifetime does not drop due to the nanotexturing process, thus indicating a path to thinner, higher-efficiency PPCs. Next, wavelength-selective light management is examined for enhanced radiative cooling. It is shown that wavelength-selective optimizations of a module’s emissivity can yield 60-65% greater radiative cooling benefits compared to comparative changes across a broader wavelength range. State-of-the-art Si modules that utilize microtextured cover glass are shown to already achieve 99% of the radiative cooling gains that are possible for a photovoltaic device under full sunlight. In contrast, the sub-bandgap reflection (SBR) of Si modules is shown to be far below ideal. The low SBR of modules with textured Si cells (15%-26%) is shown to be the primary reason for their higher operating temperatures than modules with planar GaAs cells (SBR measured at 77%). For textured cells, typical of Si modules, light trapping amplifies parasitic absorption in the encapsulant and the rear mirror, yielding greater heat generation. Optimization of doping and the rear mirror of a Si module could increase the SBR to a maximum of 63%, with further increases available only if parasitic absorption in the encapsulation materials can be reduced. For thin films, increased heat generation may outweigh the photogeneration benefits that are possible with light trapping. These investigations motivate a wavelength-selective application of light trapping: light trapping for near- to above-bandgap photons to increase photogeneration; and out-coupling of light in mid- to far-infrared wavelengths to increase the emission of thermal radiation; but light trapping should ideally be avoided at sub-bandgap energies where there is substantial solar radiation to limit heat generation and material degradation.
Date Created
2023
Contributors
- Irvin, Nicholas P. (Author)
- Honsberg, Christiana B. (Thesis advisor)
- King, Richard R. (Thesis advisor)
- Nemanich, Robert J. (Committee member)
- Smith, David J. (Committee member)
- Arizona State University (Publisher)
Topical Subject
Resource Type
Extent
152 pages
Language
Copyright Statement
In Copyright
Primary Member of
Peer-reviewed
No
Open Access
No
Handle
https://hdl.handle.net/2286/R.2.N.187424
Level of coding
minimal
Cataloging Standards
Note
Partial requirement for: Ph.D., Arizona State University, 2023
Field of study: Physics
System Created
- 2023-06-06 07:36:20
System Modified
- 2023-06-06 07:36:25
- 11 months ago
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