Figure 1.

Sketches of Both Types of LT Nanostructures Analyzed in This Work, Patterned on Solar Cells with a Si Absorber (either a-Si or c-Si)

(A and B) The LT elements provide a gradually varying effective refractive index, which minimizes reflection, while their geometry can interact with the incoming light to produce strong scattered fields preferentially directed into the higher index Si material with high mode density. The parameters (R, R_Z, t, d) considered for optimization are indicated by the arrows. The LT structures consist in an hexagonal array (with pitch d) of vertically aligned spheroidal-based features with radii R and R_Z, respectively, along the in-plane and normal directions. (A) TiO₂ half-prolates separated by an AZO layer with thickness t; (B) semi-prolate voids in a layer of either TiO₂ or AZO material with thickness t. At normal incidence, light impinges from the top along the spheroids' axis of revolution (z). The rear side of the Si layer is coated with a 60-nm-thick passivating AZO layer and a perfect reflecting mirror. The sketches on the right show the top views of the structures, whose symmetry allows the computed region to be reduced to the volume in red. See Section S1 in Supplemental Information for further details regarding the computational methods.