Bulletin of the American Physical Society
2023 Fall Meeting of the APS Eastern Great Lakes Section
Friday–Saturday, October 20–21, 2023; Cleveland State University, Cleveland, Ohio
Session L04: Applied, Condensed Matter, and Chemical Physics
9:15 AM–10:27 AM,
Saturday, October 21, 2023
Cleveland State University
Room: SI 148
Chair: Niklas Manz, College of Wooster
Abstract: L04.00001 : Analysis of Thermoradiative Thermal Energy Conversion*
9:15 AM–9:27 AM
Presenter:
Geoffrey A Landis
(NASA John H. Glenn Research Center)
Author:
Geoffrey A Landis
(NASA John H. Glenn Research Center)
The power and efficiency can be calculated as a function of bandgap in the Shockley-Queisser detailed-balance limit, in which the thermal emissivity of the cell is due to the recombination of electron-hole pairs, and all other recombination losses are ignored. The current produced is directly proportional to the recombination radiation. The fundamental loss mechanism for the thermoradiative cell is the energy carried by the infrared radiation into space from band-to-band recombination of carriers injected across the junction. In an ideal cell, to maximize the efficiency, the emission energy of these photons would precisely equal the bandgap. This can be achieved, for example, using dielectric filters or meta-material filters to recycle emission at other wavelengths back into the cell.
The voltage is proportional to the external bias. These two constraints allow optimization of the optimum bias point for maximum power. Unlike photovoltaic cells, the maximum power operating point is not the same as the maximum efficiency point, and higher efficiency can be achieved at a higher (negative) bias in the ideal case. Incorporating non-ideal losses, however, shifts the maximum efficiency point toward lower bias. Unlike in photovoltaic cells, non-radiative recombination (e.g., Auger losses) will reduce the output current, but will not reduce the conversion efficiency, since the recombination energy is retained in the cell in the form of heat.
Since a thermoradiative cell operates by radiating directly to space, the current produced by themoradiative cells will increase as Stefan-Boltzmann radiation; roughly the fourth power of the temperature. Thus, the power produced is highest at high operating temperatures, and, unlike conventional thermal conversion, increasing radiator temperature increases, the efficiency. Thus, the choice of technology will be toward semiconductors resistant to degradation at high temperature.
*NASA Innovative Advanced Concepts
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