Crumpled graphene ball-based broadband solar absorbers.

Sheet-like graphene tends to stack with each other in thin films, resulting in relatively smooth microstructures with increased reflection as the thickness increases. In contrast, when the sheets are crumpled into a shape like paper balls, reflection is greatly reduced. In this work, crumpled graphene balls are found to be strong light absorbers in the visible and near-infrared regions. Average absorption of thin films made of crumpled graphene balls can reach up to 97.4% in the wavelength region of 350-2500 nm. When crumpled graphene balls are used as the solar absorber for the interfacial evaporation system, an evaporation efficiency of 84.6% was obtained under one sun at ambient pressure. Enhanced solar absorption of crumpled graphene balls, coupled with their aggregation-resistance and universal solution processability, makes them promising candidates for solar heating/distillation applications.