Optimizing power conversion in photon-enhanced thermionic emission solar energy converters
Abstract/Contents
- Abstract
- Photon-Enhanced Thermionic Emission (PETE) is a recently demonstrated physical mechanism for direct conversion of solar energy to electricity. PETE has attracted significant attention for its high theoretical conversion efficiencies that are well in excess of thermodynamic limits for traditional single-junction photovoltaic devices. In a PETE device, photoexcited electrons in a semiconductor cathode are thermionically emitted into vacuum, and collected at an anode with lower temperature and work function. In effect, PETE combines the advantages of both photovoltaic cells and Thermionic Energy Converters (TECs). Realizing these high theoretical efficiencies requires significant engineering of materials and device geometries to maximize electron emission, transport, and collection while simultaneously maintaining or raising the output voltage. The critical component in a PETE device is a well-designed PETE cathode. In this dissertation I discuss a simple analytical model for PETE cathodes relating emission yield to a number of material parameters that can be tuned during device fabrication, and the implications of this new model for PETE cathode design. Our model predicts reasonable efficiency at high temperatures across a range of values for surface recombination, electron affinity, and cathode thickness. Operating in this high temperature regime requires thermal stability of electron emission, which has not been well established for commonly used photocathode materials. Here, I will present a series of measurements of photoemission yield from different cathode materials over a range of temperatures. I will then discuss potential material choices and constraints for highly efficient PETE cathodes based on these measurements. Efficient PETE device operation relies on more than just maximizing the electron emission current from the cathode. Emitted electrons can suffer significant losses associated with space-charge build-up in the vacuum gap between the cathode and anode. Traditionally, in-gap plasmas have been used to mitigate these losses and boost device current. These plasmas, however, result in a significant drop in output voltage. I will therefore discuss experimental results in TECs with microbead-defined micron-scale gaps showing vastly improved current and minimal voltage reduction, resulting in greater power conversion efficiencies. The TEC is used as a model system, and these results will be equally applicable to PETE devices. I conclude with a discussion of the outlook for PETE as an energy conversion technology.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2016 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Sahasrabuddhe, Kunal Atul |
|---|---|
| Associated with | Stanford University, Department of Applied Physics. |
| Primary advisor | Melosh, Nicholas A |
| Primary advisor | Shen, Zhi-Xun |
| Thesis advisor | Melosh, Nicholas A |
| Thesis advisor | Shen, Zhi-Xun |
| Thesis advisor | Hwang, Harold Yoonsung, 1970- |
| Advisor | Hwang, Harold Yoonsung, 1970- |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Kunal Atul Sahasrabuddhe. |
|---|---|
| Note | Submitted to the Department of Applied Physics. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2016. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2016 by Kunal Atul Sahasrabuddhe
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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