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Nature's evolution provides a multitude of answers to scientific and key technological challenges such as the light harvesting. In this work, we investigate the optical properties of the unique texture of viola petals for the purpose of improved light harvesting in photovoltaics. We find that crystalline silicon solar cells encapsulated with a transparent coating show a 6% improvement in power conversion efficiency if the viola petal texture is replicated onto the front surface. This gain is based on a broadband enhancement in current generation that originates from the exceptional optical properties of the viola surface texture, combining micro-and nanotexture. The microcones of this hierarchical texture demonstrate strong and broadband light incoupling effects as well as retroreflection capabilities, and the nanowrinkles further decrease the reflection losses. Using rigorous optical simulation, we analyze and explain the working principle ruling the light harvesting properties of this dual-scale texture.

Abstract:We introduce laser interference lithography (LIL) as a tool to fabricate hierarchical photonic nanostructures inspired by blue Morpho butterflies. For that, we utilize the interference pattern in vertical direction in addition to the conventional horizontal one. The vertical interference creates the lamellae by exploiting the back reflection from the substrate. The horizontal interference patterns the ridges of the hierarchical Christmas tree like structure. The artificial Morpho replica produced with this technique feature a brilliant blue iridescence up to an incident angle of 40 • .

Decreasing the absorber layer thickness of thin‐film solar cells can be an effective solution for cost reduction of photovoltaic electricity generation. Unfortunately, this reduction leads to detrimental effects such as incomplete photon absorption and increased charge carrier recombination at the rear electrode. To tackle these losses in ultra‐thin 0.5 µm Cu(In,Ga)Se2 (CIGS) solar cells, we developed different passivation structures made of MgF2 and Al2O3 at the molybdenum–CIGS interface, leading to localized back contacts. The influence of the distance between those contacts on the cell performance was studied by varying the periodicity of the applied 1D patterns from 6 μm to 30 μm. Thus, an increase in performance was measured for microstructured layers with a periodicity of up to 12 µm. More precisely, a MgF2 layer yielded an increase in power conversion efficiency (PCE) of up to 9%rel compared to an unpassivated cell design, and a passivation layer comprising Al2O3 led to up to a 5%rel increase in PCE. The gains were primarily attributed to an increased reflectivity of the back contact, while the formation of a negative backside field in the case of Al2O3 might have contributed to this increase by preventing electrons from recombining at the backside interface. Our findings indicate a high lateral conductivity for holes inside the multicrystalline CIGS compound over few tens of micrometres, which allows an independent design of future back contacts and light‐trapping schemes.