Abstract
We have investigated a new type of redirection waveguides for concentration solar-cell systems. The solar cell units are to be placed in the peripheral region of the waveguide. The redirection waveguide converts three-dimensionally propagating (3D) photons into 2D photons that propagate in a planar waveguide which serves as the mainstream of the redirection waveguide. In this new type, the cladding layer on one side of the planar waveguide, not being spatially continuous, tangentially touches the core of the planar waveguide which, having an open geometry, is connected, through tributary waveguides, to the bottom plane where the 3D-photons come in vertically. Based on simulations, we have shown not only that good mainstream-to-mainstream propagation of light-wave can be obtained but also that the light propagation from the tributary waveguides to the mainstream is well done. We also have confirmed that light-waves from the tributary waveguides are well merged with those from the mainstream waveguide at the junction of the cores of the mainstream and the tributary waveguides. Light-waves injected from tributary waveguides propagates well in the core of the mainstream waveguide passing those junctions. The light-wave merging can be fulfilled in the waveguide with the discrete translational symmetry. Photons are shown to be well conveyed in the new waveguide losslessly for a distance of ~1 mm. The redirection waveguide is promising for the concentration photovoltaic systems with solar-cell units placed at its periphery.
Highlights
Many types of conventional solar cells studied so far [1,2,3], including tandem solar cells, have difficulty in converting the full spectrum of sunlight into electrical energy
We have shown that the first layer of the redirection waveguide, i.e., a thin slab with densely packed paraboloids can make those photons that come with various angles go, to a good approximation, perpendicularly to the 2D waveguide that is to convey the light to the solar cell units located at the periphery of the redirection waveguide
As for the second function of the redirection waveguide, we have proposed a new asymmetric waveguide with discrete translational symmetry
Summary
Many types of conventional solar cells studied so far [1,2,3], including tandem solar cells, have difficulty in converting the full spectrum of sunlight into electrical energy. Except for a couple of studies [7,8], direction of the photon propagation being orthogonal to its PN junction, the photo-carrier diffusion is parallel to the photon propagation In those structures, we need a thick layer to fully absorb the solar light, while we need to have a layer thin enough to collect photo-generated electrons and as many holes as possible, because the lifetimes of those carriers are finite. Photons are absorbed in the direction perpendicular to that of the carrier drift/diffusion, and the aforementioned trade-off between the light absorption and the photocarrier collection trade-off could be avoided. Exploiting the and orthogonality, we collection can makecould the and the aforementioned between the light absorption the photocarrier semiconductor stripe wide to absorb allcan themake photons the distance between the to pbe avoided. Figure order that the incoming photons firstand meet the widest gap semiconductor, in medium-gaps, the
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