5:00 PM - EP11.06.08
Absorption Enhancement of the Solar Spectrum with Arrays of Subwavelength Silicon Trumpet Non-Imaging Light Concentrators
Ankit Chauhan1,Ashish Prajapati1,Dor Keizman1,Gil Shalev2
Ben-Gurion University of the Negev1,The Ilse-Katz Institute for Nanoscale Science & Technology, Ben-Gurion University of the Negev2
Light trapping and the broadband absorption of the solar radiation are important for photonic and nanophotonic applications ranging from sensing to harvesting of the solar energy. For example, appropriate light trapping supports the realization of ultra-thin photovoltaic cells with enhanced efficiencies1-3. Efficient light trapping was demonstrated with surface arrays of subwavelength structures such as nanopillar (NP) arrays, nanocone arrays, etc4. In the current study we numerically explore light trapping based on surface arrays of subwavelength trumpet non-imaging light (NLC) concentrators (henceforth, trumpet arrays)5. Non-imaging optics was formulated in the regime of geometrical optics in the early 1970s. There are various members to the NLC family such as light cone (LC) NLC, paraboloid NLC, compound parabolic concentrators (CPC) and its derivatives, etc. The trumpet NLC (or hyperboloid NLC) is an important NLC with an ideal concentration ratio as it accounts for both meridional rays as well as skew rays.
We use finite-difference time-domain (FDTD) electromagnetic calculations to examine light trapping and broadband absorption of the solar radiation for laterally infinite cubic-tiled substrate-less silicon trumpet array under normal illumination. The absorptivity spectra of trumpet arrays are characterized by strong absorption peaks, some of which are just below the Yablonovitch limit, which is solely attributed to efficient
occupation of the array Mie modes. We show that the absorption enhancement at the near infrared is an order of magnitude higher than that of optimized NP arrays. We show superior broadband absorption of the solar radiation in trumpet arrays (with unoptimized geometry) compared with that of optimized nanopillar arrays (~26% enhancement). We show that low reflectivity is governed by modal excitations at the upper part of the trumpets (which is also supported by the weak dependency of the reflectivity on the array height), whereas the transmissivity is governed by modal excitation at the lower part of the trumpets. We show that the strong absorption peaks of trumpet arrays are governed by the interplay between reflectivity and transmissivity, and the corresponding excitations, which is tuned by adequate selection of the trumpet bottom diameter. The higher optical absorption in trumpet array is governed by low transmissivity, in contrast with nanopillar array in which the absorption is governed by low reflectivity6.
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