Consideration of temperature-dependent emissivity of selective emitters in thermophotovoltaic systems
Spectral emissivity control is paramount for designing a high-efficiency selective emitter surface required for thermophotovoltaic (TPV) applications. Owing to the temperature dependency of materials optical constants, the spectral properties of a selective emitter surface changes with the emitter temperature. This paper presents the fabrication of a multilayer metal-dielectric ($${\rm Si}_{3}{\rm N}_{4}/\rm W/Si_{3}{\rm N_{4}}$$) coated tungsten selective emitter aimed for GaSb-based TPV systems and studies the dependence of its surface spectral emissivity, $$\varepsilon (\lambda)$$, upon a temperature ranging from 300 K to 1500 K. Both the simulation and experimental methods were used to characterize $$\varepsilon (\lambda)$$ as a function of temperature. For wavelengths less than 1.4 µm, $$\varepsilon (\lambda)$$ was found to have a minimal dependence on temperature. Beyond 1.4 µm, $$\varepsilon (\lambda)$$ increases with the temperature. At 1.55 µm, the simulation and experimental data estimated a $${\sim}{{4}}\%$$ greater emissivity at 1500 K than at room temperature. At 1500 K, the increased $$\varepsilon (\lambda)$$ at longer wavelengths lowered the spectral conversion efficiency of the selective emitter from 58% to 47%. The output power density, sub-bandgap loss, and TPV conversion efficiency ($${\eta _{\rm TPV}}$$) for a GaSb cell illuminated by the selective thermal emitter at 1500 K were estimated. $${\eta _{\rm TPV}}$$ drops from 13.7% to 11% due to the increased sub-bandgap emission at 1500 K. Essential approaches for mitigating the sub-bandgap losses to further improve $${\eta _{\rm TPV}}$$ are also discussed.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1649239
- Journal Information:
- Applied Optics, Vol. 59, Issue 18; ISSN 1559-128X
- Publisher:
- Optical Society of AmericaCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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