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Nano-imprinted rear-side diffraction gratings for absorption enhancement in solar cells

: Mellor, A.; Hauser, H.; Guttowski, A.; Wellens, C.; Bläsi, B.; Tobías, I.; Martí, A.; Luque, A.


VanSant, K. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
High and low concentrator systems for solar electric applications VII : 13 - 15 August 2012, San Diego. Part of SPIE optics + photonics
Bellingham, WA: SPIE, 2012 (Proceedings of SPIE 8471)
ISBN: 978-0-8194-9185-5
Paper 84710O
Conference "High and Low Concentrator Systems for Solar Electric Applications" <2012, San Diego/Calif.>
Fraunhofer ISE ()

As wafer-based solar cells become thinner, light-trapping textures for absorption enhancement will gain in importance. In this work, crystalline silicon wafers were textured with wavelength-scale diffraction grating surface textures by nanoimprint lithography using interference lithography as a mastering technology. This technique allows fine-tailored nanostructures to be realized on large areas with high throughput. Solar cell precursors were fabricated, with the surface textures on the rear side, for optical absorption measurements. Large absorption enhancements are observed in the wavelength range in which the silicon wafer absorbs weakly. It is shown experimentally that bi-periodic crossed gratings perform better than uni-periodic linear gratings. Optical simulations have been made of the fabricated structures, allowing the total absorption to be decomposed into useful absorption in the silicon and parasitic absorption in the rear reflector. Using the calculated sil icon absorption, promising absorbed photocurrent density enhancements have been calculated for solar cells employing the nano-textures. Finally, first results are presented of a passivation layer deposition technique that planarizes the rear reflector for the purpose of reducing the parasitic absorption.