20 February 2013 Simulation and development of sub-wavelength textured ARCs for CPV applications
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Abstract
In high X III-V concentrator applications sunlight is focused onto the surface of cell with a wide angular distribution that limits the effectiveness of conventional thin-film AR coatings. Furthermore the transmission properties are generally degraded non-uniformly over the electromagnetic spectrum which in the case of multi-junction solar cells leads to additional sub-cell current matching related losses. Here, and in an attempt to identify a better alternative to the conventional dual layer ARCs, we have undertaken a systematic analysis of design parameters and angular dependent antireflective properties of dielectric grating formed through the implementation of sub-wavelength arrays of 2D pyramidal and hemispherical textures. The evaluation indicates that through a careful selection of the design and dielectric material these structures can significantly surpass the performance of planar double layer ARCs (i.e. MgF2/ZnS), and the total number of reflected photons over the 380-2000 nm wavelength range can be reduced to less than 2%. Finally it is shown that the implementation of these structures for a typical 3 or 4 junction solar cells (i.e. inverted metamorphic) and for acceptance angles ranging from 0-60 degrees, reduces total losses of reflected photons for each subcell (and to some extent the resulting current degradation) to less than 4%. Anti-reflection and angular tolerant properties of 2D TiO2 surface texturing made by nano imprinting technique were simulated and measured in this work. It has been proved that from both simulation and experimental work textured surface surpasses both antireflection and angular tolerant characters of planar ARC, which supplies a potential candidate AR structure for concentrated photovoltaic system.
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Wei Wang, Paul Narchi, Alex Freundlich, "Simulation and development of sub-wavelength textured ARCs for CPV applications", Proc. SPIE 8620, Physics, Simulation, and Photonic Engineering of Photovoltaic Devices II, 86200P (20 February 2013); doi: 10.1117/12.2004612; https://doi.org/10.1117/12.2004612
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