We present a modelling study of thin silicon based solar cells endowed with periodic and decoupled front/back textures. After careful optimization, the proposed device models exhibit absorption beyond the Lambertian light trapping limit for a wide range of light angles of incidence. The advanced light management scheme is applied to (nano)crystalline silicon solar cells, where the benefits of texturing the absorber rather than the supporting layers is clear and to barium (di)silicide solar cells, which could achieve an implied photocurrent densityof41.1 mA/cm2 for a thickness of only 2 \mum.

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We present the study of an advanced light trapping scheme applied to thin-film silicon-based solar cells, overcoming the broadband Green absorption limit, that is the generalized case of the 4n² classical absorption limit for all wavelengths. This result is achieved by the 3-dimensional optical modelling of a fully functional thin-film hydrogenated nano-crystalline silicon (nc-Si:H) solar cell endowed with decoupled front and back textures. Our results stem from rigorously characterized optical properties of state-of-the-art materials, optimized geometric nano-features on the front and rear surfaces of the solar cell, and thickness optimization of the front transparent oxide. The simulated improvements derive from a gain in light absorption, especially in the near-infrared part of the spectrum close to the band gap of nc-Si:H. In this wavelength region, the material is weakly absorbing, whereas we now find significant absorptance peaks that can only be explained by the concurrent excitation of guided resonances by front and rear textures. This insight indicates the need to modify the temporal coupled-mode theory, which fails to predict the absorption enhancement achieved in this work, extending its validity to the case of decoupled front/back texturing. Our approach results in substantially high photocurrent density (>36 mA/cm²), creating a platform suitable for high efficiency single and multi-junction thin-film solar cells based either on typical silicon alloys or on the novel and promising barium (di)silicide (BaSi₂) absorber. In the latter case, using the same advanced light trapping employed for nc-Si:H, we demonstrate a very high implied photocurrent density of 41.1 mA/cm², for a device endowed with 2-μm thick absorber.

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The effect of decoupled front/back textures and the application of photonic and plasmonic nanostructures on the performance of thin silicon solar cells was studied. New light trapping concepts based on diffraction on periodic photonic nanostructures and scattering using plasmonic structures have potential to outperform the currently used randomly textured structures. The study demonstrates that supporting layers of solar cells, such as transparent conductive oxides, doped layers and back reflectors, are responsible for significant parasitic absorption losses that prevent achieving 4n2 enhancement of light absorption in solar cells with silicon absorbers.@en