Limits...
Impacts of propagating, frustrated and surface modes on radiative, electrical and thermal losses in nanoscale-gap thermophotovoltaic power generators.

Bernardi MP, Dupré O, Blandre E, Chapuis PO, Vaillon R, Francoeur M - Sci Rep (2015)

Bottom Line: Results reveal that surface mode mediated nano-TPV power generation with the Drude radiator outperforms the tungsten radiator, dominated by frustrated modes, only for a vacuum gap thickness of 10 nm and if both electrical and thermal losses are neglected.It is shown that the power output of a tungsten-based device increases by 6.5% while the cell temperature decreases by 30 K when applying a high energy cutoff at 1.45 eV.This work demonstrates that design and optimization of nano-TPV devices must account for radiative, electrical and thermal losses.

View Article: PubMed Central - PubMed

Affiliation: Radiative Energy Transfer Lab, Department of Mechanical Engineering, University of Utah, Salt Lake City, UT 84112, USA.

ABSTRACT
The impacts of radiative, electrical and thermal losses on the performances of nanoscale-gap thermophotovoltaic (nano-TPV) power generators consisting of a gallium antimonide cell paired with a broadband tungsten and a radiatively-optimized Drude radiator are analyzed. Results reveal that surface mode mediated nano-TPV power generation with the Drude radiator outperforms the tungsten radiator, dominated by frustrated modes, only for a vacuum gap thickness of 10 nm and if both electrical and thermal losses are neglected. The key limiting factors for the Drude- and tungsten-based devices are respectively the recombination of electron-hole pairs at the cell surface and thermalization of radiation with energy larger than the cell absorption bandgap. A design guideline is also proposed where a high energy cutoff above which radiation has a net negative effect on nano-TPV power output due to thermal losses is determined. It is shown that the power output of a tungsten-based device increases by 6.5% while the cell temperature decreases by 30 K when applying a high energy cutoff at 1.45 eV. This work demonstrates that design and optimization of nano-TPV devices must account for radiative, electrical and thermal losses.

No MeSH data available.


Coupled effects of radiative, electrical and thermal losses on the power output of nano-TPV power generators.
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f1: Coupled effects of radiative, electrical and thermal losses on the power output of nano-TPV power generators.

Mentions: Figure 1 shows how the coupled effects of radiative, electrical and thermal losses negatively affect nano-TPV power output. Note that losses are defined relative to the power absorbed by the cell. Reflection by the cell is not a radiative loss for nano-TPV systems, as reflected radiation can be absorbed by the radiator. Yet, reflection should be minimized in order to maximize radiation absorption by the cell. Additionally, transmission is negligible for a micrometer-thick cell. Radiation absorbed by the cell with energy E below its bandgap Eg does not generate electron-hole pairs (EHPs) and is classified as a radiative loss. Since this energy is dissipated as heat via absorption by the lattice and the free carriers, it also contributes to thermal losses resulting in an increase of the cell temperature Tcell. As Tcell increases, the dark current increases thereby decreasing the power output25. The radiative properties and the absorption bandgap of the cell are temperature-dependent, such that there is a feedback component, shown by the dashed arrow 1 in Fig. 1, affecting the absorption characteristics and therefore the radiative losses. Radiation absorbed by the cell with energy E equal to or larger than Eg generates EHPs. Electrical losses arise when the photogenerated EHPs recombine before being separated at the depletion region of the cell, thus reducing the power output. Electrical losses include recombination within the volume and at the surfaces of the cell. These mechanisms also contribute to thermal losses since the EHPs that undergo non-radiative recombination dissipate their energy as heat. As the electrical properties of the cell are temperature-dependent, an increase in Tcell also affects recombination of EHPs; this coupling is represented by the dashed arrow 2 in Fig. 1. Radiation with energy E larger than the bandgap Eg dissipates its excess energy as heat through thermalization, thus contributing to thermal losses. There is a feedback component to this loss mechanism, shown by the dashed arrow 3 in Fig. 1, as increasing Tcell lowers the absorption bandgap of the cell and modifies its radiative properties. Clearly, accounting for thermal losses substantially increases the complexity of the problem as the loss mechanisms are strongly coupled to each other.


Impacts of propagating, frustrated and surface modes on radiative, electrical and thermal losses in nanoscale-gap thermophotovoltaic power generators.

Bernardi MP, Dupré O, Blandre E, Chapuis PO, Vaillon R, Francoeur M - Sci Rep (2015)

Coupled effects of radiative, electrical and thermal losses on the power output of nano-TPV power generators.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4481525&req=5

f1: Coupled effects of radiative, electrical and thermal losses on the power output of nano-TPV power generators.
Mentions: Figure 1 shows how the coupled effects of radiative, electrical and thermal losses negatively affect nano-TPV power output. Note that losses are defined relative to the power absorbed by the cell. Reflection by the cell is not a radiative loss for nano-TPV systems, as reflected radiation can be absorbed by the radiator. Yet, reflection should be minimized in order to maximize radiation absorption by the cell. Additionally, transmission is negligible for a micrometer-thick cell. Radiation absorbed by the cell with energy E below its bandgap Eg does not generate electron-hole pairs (EHPs) and is classified as a radiative loss. Since this energy is dissipated as heat via absorption by the lattice and the free carriers, it also contributes to thermal losses resulting in an increase of the cell temperature Tcell. As Tcell increases, the dark current increases thereby decreasing the power output25. The radiative properties and the absorption bandgap of the cell are temperature-dependent, such that there is a feedback component, shown by the dashed arrow 1 in Fig. 1, affecting the absorption characteristics and therefore the radiative losses. Radiation absorbed by the cell with energy E equal to or larger than Eg generates EHPs. Electrical losses arise when the photogenerated EHPs recombine before being separated at the depletion region of the cell, thus reducing the power output. Electrical losses include recombination within the volume and at the surfaces of the cell. These mechanisms also contribute to thermal losses since the EHPs that undergo non-radiative recombination dissipate their energy as heat. As the electrical properties of the cell are temperature-dependent, an increase in Tcell also affects recombination of EHPs; this coupling is represented by the dashed arrow 2 in Fig. 1. Radiation with energy E larger than the bandgap Eg dissipates its excess energy as heat through thermalization, thus contributing to thermal losses. There is a feedback component to this loss mechanism, shown by the dashed arrow 3 in Fig. 1, as increasing Tcell lowers the absorption bandgap of the cell and modifies its radiative properties. Clearly, accounting for thermal losses substantially increases the complexity of the problem as the loss mechanisms are strongly coupled to each other.

Bottom Line: Results reveal that surface mode mediated nano-TPV power generation with the Drude radiator outperforms the tungsten radiator, dominated by frustrated modes, only for a vacuum gap thickness of 10 nm and if both electrical and thermal losses are neglected.It is shown that the power output of a tungsten-based device increases by 6.5% while the cell temperature decreases by 30 K when applying a high energy cutoff at 1.45 eV.This work demonstrates that design and optimization of nano-TPV devices must account for radiative, electrical and thermal losses.

View Article: PubMed Central - PubMed

Affiliation: Radiative Energy Transfer Lab, Department of Mechanical Engineering, University of Utah, Salt Lake City, UT 84112, USA.

ABSTRACT
The impacts of radiative, electrical and thermal losses on the performances of nanoscale-gap thermophotovoltaic (nano-TPV) power generators consisting of a gallium antimonide cell paired with a broadband tungsten and a radiatively-optimized Drude radiator are analyzed. Results reveal that surface mode mediated nano-TPV power generation with the Drude radiator outperforms the tungsten radiator, dominated by frustrated modes, only for a vacuum gap thickness of 10 nm and if both electrical and thermal losses are neglected. The key limiting factors for the Drude- and tungsten-based devices are respectively the recombination of electron-hole pairs at the cell surface and thermalization of radiation with energy larger than the cell absorption bandgap. A design guideline is also proposed where a high energy cutoff above which radiation has a net negative effect on nano-TPV power output due to thermal losses is determined. It is shown that the power output of a tungsten-based device increases by 6.5% while the cell temperature decreases by 30 K when applying a high energy cutoff at 1.45 eV. This work demonstrates that design and optimization of nano-TPV devices must account for radiative, electrical and thermal losses.

No MeSH data available.