Subwavelength antireflective structure for thin-film solar cells

Consisting of a two-dimensional (2D) array of rings and pillars, the structure can improve the short-circuit current of a thin-film crystalline solar cell by over 50%, its creators say. The subwavelength AR structures are robust to certain degrees of fabrication errors, they add.

Schematic view of the silicon subwavelength AR structure used in the simulation.

Image: Northwestern Polytechnical University, Hindawi, Creative Commons License CC BY 4.0, https://bit.ly/3LuEUpE

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A group of scientists from the Northwestern Polytechnical University in China has designed a broadband surface relief subwavelength optical anti-reflective (AR) structure aimed at improving light harvesting in thin-film crystalline solar cells.

The device is claimed to have a weighted average reflectance of 4.2% over the 400–1100 nm spectral range, which the researchers said is almost an order of magnitude reduction compared with a bare silicon surface, and to be able to increase the short-circuit current of a 3 μm three-layer thick thin-film silicon solar cell by over 50%.

The structure consists of a two-dimensional (2D) array of rings and pillars. “It is a periodic structure that can be integrated onto the surface of the top silicon layer of solar cells,” they explained. “To minimize the reflection over a wide wavelength range, it is crucial to find the optimum geometric parameters of the subwavelength AR structure.”

The electromagnetic response of the device was simulated through commercially available finite-difference time-domain (FDTD) tools, which are commonly used for modeling computational electrodynamics. As a light source, a broadband (400–1100 nm) plane wave with a varying angle of incidence to the substrate was used and the typical optical dispersion property of silicon was also considered in the simulation.

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According to the research group's calculations, the AR structure would be able to increase the solar cell short-circuit current to 28.6 mA/cm2, which would be 53% more than that of a reference cell without the AR device. “Our simulations show that the averaged reflectance, weighted with the AM1.5 solar spectrum in the 400–1100 nm spectral range, can be reduced from 35% down to only 4.2%,” it concluded. “Besides, we show that the subwavelength AR structures are robust to certain degrees of fabrication errors.”

The anti-reflective tech is introduced in the paper Design of a Highly Efficient Subwavelength Antireflective Structure for Solar Cells, published in the International Journal of Optics.

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