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Cloaked contact grids on solar cells by coordinate transformations: Designs and prototypes
: Schumann, M.F.; Wiesendanger, S.; Goldschmidt, J.C.; Bläsi, B.; Bittkau, K.; Paetzold, U.W.; Sprafke, A.; Wehrspohn, R.B.; Rockstuhl, C.; Wegener, M.
Nontransparent contact fingers on the sun-facing side of solar cells represent optically dead regions which reduce the energy conversion per area. We consider two approaches for guiding the incident light around the contacts onto the active area. The first approach uses graded-index metamaterials designed by two-dimensional Schwarz–Christoffel conformal maps, and the second uses freeform surfaces designed by one-dimensional coordinate transformations of a point to an interval. We provide proof-of-principle demonstrators using direct laser writing of polymer structures on silicon wafers with opaque contacts. Freeform surfaces are amenable to mass fabrication and allow for complete recovery of the shadowing effect for all relevant incidence angles.