Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener Upscaling the fabrication routine of bioreplicated rose petal light harvesting layers for photovoltaic modules Benjamin Fritz a, ⁎ , Ruben Hünig b , Markus Guttmann c , Marc Schneider c , K.M. Samaun Reza a , Oliver Salomon b , Philip Jackson b , Michael Powalla b , Uli Lemmer a,c , Guillaume Gomard a,c a Light Technology Institute (LTI), Karlsruhe Institute of Technology (KIT), Engesserstrasse 13, 76131 Karlsruhe, Germany b Center for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW), Meitnerstraße 1, 70563 Stuttgart, Germany c Institute of Microstructure Technology (IMT), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany ARTICLE INFO Keywords: Bioreplication Hot embossing Light harvesting coating Polymeric antireflective layer Hierarchical texture Petal epidermal cells ABSTRACT The hierarchical micro-/nanotextures adorning the petal surfaces of certain flower species exhibit outstanding sunlight harvesting properties, which can be exploited for photovoltaic (PV) applications via a direct replication approach into polymeric cover layers. This route has been so far hampered by the restricted size of the original bio-template and by the limited number of replication cycles when a polymeric mold is used. Here, we therefore introduce an upscaling strategy allowing the fabrication of mechanically stable, temperature resistant and large area nickel mold inserts which can be employed for hot embossing lithography, and ultimately for the mass production of bioreplicated films that improve light management in PV modules. As a proof-of-concept, we laminate the thus produced textured foils, here corresponding to rose petal replicas, onto glass encapsulated copper indium gallium diselenide (CIGS) solar modules with a surface of 100 cm 2 . We demonstrate an increase of the power output of 5.4% with respect to a device with an uncoated glass cover layer (measured in outdoor operating conditions). This improvement is notably attributed to the excellent light in-coupling properties of the replicated texture at high oblique incidence angles. 1. Introduction The interface between photovoltaic (PV) modules and their en- vironment is pivotal for controlling their light harvesting properties and long-term performance. Accordingly, it can be textured with the aim of introducing an efficient light management and self-cleaning scheme. Considering the multifunctional role of PV cover layers, their design can strongly benefit from the latest advances in the field of biomimetics (Senthil and Yuvaraj, 2018; Vüllers et al., 2016; Kong et al., 2019), as animals and plants have evolved to optimize their interaction with the environment, in particular with sunlight. Thus, synthetic anti-reflective surfaces and coatings inspired by the subwavelength structures found on the compound eyes or on the transparent wings of insects (Choi et al., 2019; Hasan et al., 2019) have been successfully tested as solar cell antireflective layers (Shin et al., 2011; Luo et al., 2019), and have eventually reached the (pre-) production stage (Zhang et al., 2017). Fused silica substrates, decorated by moth eye inspired nanotextures on their two sides, have achieved reflection losses as low as 0.2% (Diao et al., 2016) at normal incidence over the visible and near-infrared range. Hierarchical micro/nanostructures can further improve sunlight harvesting beyond the sole reduction of surface reflection losses. However, the fabrication of bioinspired hierarchical structures often involves sophisticated processes (Liu et al., 2017), which motivates the direct replication of optical biostructures over areas that are compatible with real-world PV applications. In that respect, the hierarchical tex- tures developed by certain plant species, be it for enhancing the color saturation of petals (Noda et al., 1994; Whitney et al., 2011; Gorton and Vogelmann, 1996) or for fostering photosynthesis in the leaves (Bone et al., 1985), are particularly well-suited since they can cover a few cm 2 and result in outstanding antireflective properties (Schulte et al., 2009; Schulte, 2012; Hünig et al., 2016; Huang et al., 2015; Huang et al., 2018). The latter mainly originate from disordered microcones, which improve light in-coupling and allow the backward propagating light to be retro-reflected towards the solar cells (Hünig et al., 2016; Fritz et al., 2017; Fritz et al., 2018; Schmager et al., 2017; Li et al., 2018). These mechanisms are particularly efficient owing to the 100% packing fraction of these microcones (Deinega et al., 2011), to their various orientations as well as to the waviness of the surface that ameliorate sunlight collection under various incidence angles. While a great https://doi.org/10.1016/j.solener.2020.03.020 Received 23 September 2019; Received in revised form 20 February 2020; Accepted 5 March 2020 ⁎ Corresponding author. E-mail address: benjamin.fritz@kit.edu (B. Fritz). Solar Energy 201 (2020) 666–673 Available online 20 March 2020 0038-092X/ © 2020 Published by Elsevier Ltd on behalf of International Solar Energy Society. T