Mid-infrared emissivity of crystalline silicon solar cells

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2017-10-13Author
Mellor, A.
Alonso Alvarez, D.
Ferre Llin, L.
Guarracino, I.
Markides, C. N.
Paul, D. J.
Ekins-Daukes, N.
Suggested citation
Riverola Lacasta, Alberto;
Mellor, A.;
Alonso Alvarez, D.;
Ferre Llin, L.;
Guarracino, I.;
Markides, C. N.;
...
Ekins-Daukes, N..
(2017)
.
Mid-infrared emissivity of crystalline silicon solar cells.
Solar Energy Materials and Solar Cells, 2017, vol. 174, p. 607-615.
https://doi.org/10.1016/j.solmat.2017.10.002.
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The thermal emissivity of crystalline silicon photovoltaic (PV) solar cells plays a role in determining the operating temperature of a solar cell. To elucidate the physical origin of thermal emissivity, we have made an experimental measurement of the full radiative spectrum of the crystalline silicon (c-Si) solar cell, which includes both absorption in the ultraviolet to near-infrared range and emission in the mid-infrared. Using optical modelling, we have identified the origin of radiative emissivity in both encapsulated and unencapsulated solar cells. We find that both encapsulated and unencapsulated c-Si solar cells are good radiative emitters but achieve this through different effects. The emissivity of an unencapsulated c-Si solar cell is determined to be 75% in the MIR range, and is dominated by free-carrier emission in the highly doped emitter and back surface field layers; both effects are greatly augmented through the enhanced optical outcoupling arising from the front surface texture. An encapsulated glass-covered cell has an average emissivity around 90% on the MIR, and dips to 70% at 10 µm and is dominated by the emissivity of the cover glass. These findings serve to illustrate the opportunity for optimising the emissivity of c-Si based collectors, either in conventional c-Si PV modules where high emissivity and low-temperature operation is desirable, or in hybrid PV-thermal collectors where low emissivity enables a higher thermal output to be achieved.
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Solar Energy Materials and Solar Cells, 2017, vol. 174, p. 607-615European research projects
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