Abstract
Solar cells can strongly benefit from optical strategies capable of providing the desired broadband absorption of sunlight and consequent high conversion efficiency. While many diffractive light-trapping structures prove high absorption enhancements, their industrial application rather depends on simplicity concerning the integration to the solar cell concept and the process technology. Here, we show how simple grating lines can perform as well as advanced light-trapping designs. We use a shallow and periodic grating as the basic element of a quasi-random structure, which is highly suitable for industrial mass production. Its checkerboard arrangement breaks the mirror symmetry and is shown, for instance, to enhance the bulk current of a 1 µm slab of crystalline silicon by 125%. We explain its excellent performance by drawing a direct link between a structure’s Fourier series and the implied photocurrent, derived from a large and diverse set of structures. Our design rule thus meets all relevant aspects of light-trapping for solar cells, clearing the way for simple, practical, and yet outstanding diffractive structures, with a potential impact beyond photonic applications.
Highlights
Broadband absorption of sunlight is key for solar cell technologies, so nanophotonic structures have emerged as a promising technique for their efficiency improvement
For a direct comparison of light-trapping performance, we follow the strategy set out in previous works [33,37,40,41], employing a test solar cell structure composed of a crystalline silicon (c-Si) absorber material [42] with an ideal back reflector:
The thickness of the c-Si slab is set to 1 μm
Summary
Broadband absorption of sunlight is key for solar cell technologies, so nanophotonic structures have emerged as a promising technique for their efficiency improvement. One-dimensional (1D) surface gratings have become one of the most studied diffractive structures. Simple grating lines serve as test vehicles for theoretical concepts and fabrication methods [2,3]. While their superposition facilitates the analysis of more complicated designs [2,4], gratings are commonly used in monochromators, spectrometers, wavelength-division multiplexing, cavity lasers, and sensors [5]. Some studies proved their suitability for broadband mirrors [6] and radiative cooling applications [7]
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