Near‐Perfect Ultrathin Nanocomposite Absorber with Self‐Formed Topping Plasmonic Nanoparticles

Nanocomposites, consisting of metallic nanoparticles embedding in a dielectric host, can significantly enhance light–matter interactions in solar energy conversion and optical applications. In this contribution, a class of scalable ultrathin nanocomposite films with self‐formed topping plasmonic nanoparticles is proposed. Just by controlling the high‐throughput co‐sputtering process, the nanocomposite absorbers can achieve near 100% light absorption in the wavelength ranges from 300 to 800 nm. Through systematic experiments and numerical studies, three mechanisms for this near‐perfect absorption are further revealed: impedance matching of ultrathin nanocomposite film with tunable filling factor, excitation of localized surface plasmon induced by self‐formed topping nanoparticles, and near‐field coupling between the topping nanoparticles and bottom metallic reflective layer. With these merits, the proposed ultrathin nanocomposite absorbers have demonstrated their outstanding omnidirectional absorptance over the wide solar irradiance spectrum ranging from 250 to 2000 nm.