Flexible plasmonic cellulose papers for broadband absorption and efficient solar steam generation

Plasmonic solar absorber holds great potential in solar-powered steam generation due to its resonant absorption, rapid photo-to-heat conversion, and localized heating impact. However, expanding the absorption bandwidth of plasmonic nanoparticles is challenging. Here, we produce flexible plasmonic cellulose papers (PCPs) with broadband absorption by filling the nanogaps (between nanofibrils) of commercially available cellulose papers (CPs) with plasmonic nanoparticles. A nanoconfinement strategy is employed for the fast and easy-to-scale-up synthesis of Ag- and Cu-based PCPs. In particular, Ag-CP exhibits a broadband solar absorption efficiency of up to 93.7% at a spectrum range of 250–2500 nm and a solar-to-thermal efficiency of 85.2% under 1 kW m−2 irradiation (1 sun). The nanoconfinement effect serves as a simple and flexible platform to regulate the particle size and interspace and reduce the aggregation. By combining the analysis of structure-regulated absorption behaviors with theoretical simulations, we conclude that the unique microstructure tailors the interparticle coupling effect, the predominant cause of the strong broadband plasmonic absorption. Our work presents a nanoconfinement strategy to tune solar absorption and demonstrates an appealing plasmonic solar absorber.