Lotus Leaf Structured Fluoropolymer Foils for Superhydrophobicity and Enhanced Light Management in Photovoltaic Devices

Reflection losses and soiling of photovoltaic devices are well-known challenges that suppress their full operational potential. Multifunctional self-cleaning light management foils offer a concurrent solution to both subjects. Here we demonstrate a simple processing method to fabricate a lotus leaf textured fluoropolymer foil by nanoimprint lithography and hot embossing. We employ nanoimprinted molds for hot embossing, bypassing the conventional electroforming process to enable facile prototyping. Light management qualities as well as superhydrophobic properties are investigated by comparing nontextured foils with lotus leaf structured and random micro-pyramid foils. One dimensional optical simulation verified the anti-reflective properties of the lotus texture. Implementing the lotus leaf textured foil to the sun-facing air-glass interface of liquid-phase-crystallized silicon thin-film solar cells was found to induce a broadband antireflective effect and increase the short-circuit current density J_sc up to 3.4% (relative). At the same time, the water contact angle of the planar glass superstrate was improved from 47° to superhydrophobic 157° by the attached lotus foil.