Management of light absorption in extraordinary optical transmission based ultra-thin-film tandem solar cells

Although ultra-thin-film solar cells can be attractive in reducing the cost, they suffer from low absorption as the thickness of the active layer is usually much smaller than the wavelength of incident light. Different nano-photonic techniques, including plasmonic structures, are being explored to i...

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Bibliographic Details
Published in:Journal of applied physics 2016-05, Vol.119 (19)
Main Authors: Mashooq, Kishwar, Talukder, Muhammad Anisuzzaman
Format: Article
Language:English
Subjects:
ABSORPTION
Applied physics
BUTYRIC ACID
Cadmium
CADMIUM SELENIDES
Cadmium telluride
CADMIUM TELLURIDES
Circuits
CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS
CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
COPPER
Copper indium gallium selenides
COPPER SELENIDES
ELECTRICAL FAULTS
Electromagnetic absorption
ELECTRONS
GALLIUM SELENIDES
GEOMETRY
HOLES
Holes (electron deficiencies)
Incident light
INDIUM SELENIDES
Intermetallic compounds
LAYERS
Light
PERIODICITY
Photonics
Photovoltaic cells
Short circuit currents
SOLAR CELLS
SPECTRA
Surface defects
SURFACES
Tellurides
Thickness
THIN FILMS
WAVELENGTHS
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Summary:Although ultra-thin-film solar cells can be attractive in reducing the cost, they suffer from low absorption as the thickness of the active layer is usually much smaller than the wavelength of incident light. Different nano-photonic techniques, including plasmonic structures, are being explored to increase the light absorption in ultra-thin-film solar cells. More than one layer of active materials with different energy bandgaps can be used in tandem to increase the light absorption as well. However, due to different amount of light absorption in different active layers, photo-generated currents in different active layers will not be the same. The current mismatch between the tandem layers makes them ineffective in increasing the efficiency. In this work, we investigate the light absorption properties of tandem solar cells with two ultra-thin active layers working as two subcells and a metal layer with periodically perforated holes in-between the two subcells. While the metal layer helps to overcome the current mismatch, the periodic holes increase the absorption of incident light by helping extraordinary optical transmission of the incident light from the top to the bottom subcell, and by coupling the incident light to plasmonic and photonic modes within ultra-thin active layers. We extensively study the effects of the geometry of holes in the intermediate metal layer on the light absorption properties of tandem solar cells with ultra-thin active layers. We also study how different metals in the intermediate layer affect the light absorption; how the geometry of holes in the intermediate layer affects the absorption when the active layer materials are changed; and how the intermediate metal layer affects the collection of photo-generated electron-hole pairs at the terminals. We find that in a solar cell with 6,6-phenyl C61-butyric acid methyl ester top subcell and copper indium gallium selenide bottom subcell, if the periodic holes in the metal layer are square or polygon, total absorption remains approximately the same. However, the total absorption suffers significantly if the holes are triangle. The transmission spectra of incident light into the bottom subcell, and hence the absorption, change significantly for square and circle holes if the active materials change to cadmium selenide (CdSe) and cadmium telluride (CdTe) in the top and bottom subcells, respectively. Although the intermediate metal layer may induce electron-hole pair recombination due to
ISSN:0021-8979
1089-7550
DOI:10.1063/1.4949588