From Kitchen Garden to Multifunctionality: Leek-inspired Surface Structures Introduce Optical and Self-cleaning Properties to Cellulose-based Films

Abstract A bioinspired approach to produce all-biobased films with high anisotropic light scattering and superhydrophobicity is presented as a route toward sustainable light management layers for photovoltaics. The multifunctional films are achieved by replicating leek leaves onto cellulose acetate, producing hierarchical surface structures. The free-standing films show a transmittance of ≈ 94% and a haze of ≈ 54% at the wavelength of 550 nm. Inspired by leek’s epicuticular wax, surface hydrophobicity was achieved through tailoring carnauba wax coatings. The surfaces show anisotropic advancing contact angles of up to 160° and 156° in cross directions, due to the periodical surface roughness and low-surface-energy carnauba wax secondary features. Using the replica as the light management layer on perovskite solar cells improved the power conversion efficiency by 6 ± 0.3%. Meanwhile, the surface water repellency facilitates self-cleaning, which tackles dirt accumulation, ensures maximum incident light, and maintains photovoltaic performance over time. Hence the developed films are suitable candidates as organic light management layers for improving the lifetime and efficiency of solar cells and other optoelectronics. Furthermore, the method can be potentially employed to fabricate substrates from virtually any leaf or patterned surface as the initial replication template.