We report on a fabrication route based on hot embossing lithography to replicate the surface texture of plants into large-area polymeric foils, with a view to developing multifunctional photovoltaic cover layers. Our approach is demonstrated by reproducing the complex texture of rose petals with a high fidelity from the nano-to the centimeter scale into different polymers, including poly(methyl methacrylate) (PMMA), polycarbonate (PC) and fluorinated ethylene propylene (FEP). We show that the hot embossed PMMA and PC foils, applied as a cover layer onto a copper indium gallium diselenide (Cu(In,Ga)Se2) thin-film solar cell, improve its light harvesting properties compared to (unencapsulated) devices based on an optimized MgF2 antireflective coating, especially at large angles of incidence (>50°). By employing a low surface free energy polymer like FEP, we further demonstrate that the textured cover layer can achieve strong hydrophobicity (with water contact angle around 135°) without any additional surface treatment. This wetting property results in droplets hitting the foil rapidly bouncing off its surface, which can be exploited for self-cleaning purposes. The bioreplication route presented herein can be extended to other biological surfaces, polymers, photovoltaic technologies or to other optical systems to introduce a light harvesting scheme operating efficiently in outdoor conditions.
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