Flexible and Robust Ultrablack Elastomers with a Dual-Gradient Design for Broadband and Efficient Light Management

Engineering flexible broadband light absorbers is crucial to various applications ranging from dark-level reduction to light harvesting. However, developing solvent free, ultrablack elastomers with high light-absorption performance and broad absorption band remains a challenge. Here, a class of composite elastomers is fabricated for ultrablack sheet materials. The fabrication process involves a fast photo-polymerization of acrylates in the presence of gradient deposited polypyrrole (PPy) nanoparticles. The resultant film shows a dual-gradient structure (i.e., lower side features lower polymer chain density while higher concentration of deposited PPy). Such structure design critically contributes to the formation of bio-mimetic, hierarchical surface microstructures for efficient light trapping. As a result, lower side of the film exhibits incident-light-angle independent, high light absorptivity of 98.43% at 250-2400 nm. Moreover, flexible and mechanically robust absorbers have been demonstrated to offer versatile solar energy related applications, such as sunlight heater, photoactuator, pattern display, and anticounterfeiting. Rather than tedious processing ways generally used in carbon nanotube forests or plasmonic involved ultrablack materials, dual-gradient design principle is concise and compatible with polymer thin-film fabrication process, and applicable to various elastic substrates, thus will provide guidance for fabricating various flexible ultrablack sheet materials and devices in a cost-effective and large scalable way.