How to assess light trapping structures versus a Lambertian Scatterer for solar cells?

Abstract

We propose a new figure of merit to assess the performance of light trapping nanostructures for solar cells, which we call the light trapping efficiency (LTE). The LTE has a target value of unity to represent the performance of an ideal Lambertian scatterer, although this is not an absolute limit but rather a benchmark value. Since the LTE aims to assess the nanostructure itself, it is, in principle, independent of the material, fabrication method or technology used. We use the LTE to compare numerous proposals in the literature and to identify the most promising light trapping strategies. We find that different types of photonic structures allow approaching the Lambertian limit, which shows that the light trapping problem can be approached from multiple directions. The LTE of theoretical structures significantly exceeds that of experimental structures, which highlights the need for theoretical descriptions to be more comprehensive and to take all relevant electro-optic effects into account.

Sunlight-thin nanophotonic monocrystalline silicon solar cells

“…They noted that the LTE of experimental cells is significantly lower than that of theoretical structures, which can approach the Lambertian limit, LTE=1. The present nanophotonic cell, and that of [14], present a clear improvement compared to the reported results of [37], by advancing from 0.2-0.3 to 0.56 and 0.57 respectively. We further focus on the lowly-absorbed photons and evaluate the light-path enhancement factor of the nanophotonic cells following the same method as in [14].…”

Photonic light trapping and electrical transport in thin-film silicon solar cells

“…To conclude, we note that the differences between the curves corresponding to light trapping and the single-pass case are larger for thicknesses ranging from a few hundreds of nm to a few microns [51], where there is a crossover between Ray and Wave Optics. This range of thickness is thus the most interesting one for investigating the light trapping properties of photonic patterns.…”

Light trapping in thin-film solar cells measured by Raman spectroscopy

“…An alternative definition of the so-called light-trapping efficiency, based on the J SC enhancement, is described and calculated for relevant lighttrapping structures in Ref. 11. Both the J SC and EQE are sensitive to the cell electronic quality.…”