Technology Review – A new nanostructured material that absorbs a broad spectrum of light from any angle could lead to the most efficient thin-film solar cells ever. Atwater and Aydin demonstrated this broadband effect in a 260-nanometer-thick film made of a layer of silver topped with a thin layer of silicon dioxide and finished with another thin layer of silver carved with arrays of wedges that are 40 nanometers at their tips. Atwater says they chose these materials because they are particularly challenging: in their unpatterned state, they’re both highly reflective; but the patterned films can absorb an average of 70 percent of the light across the entire visible spectrum.
Resonant plasmonic and metamaterial structures allow for control of fundamental optical processes such as absorption, emission and refraction at the nanoscale. Considerable recent research has focused on energy absorption processes, and plasmonic nanostructures have been shown to enhance the performance of photovoltaic and thermophotovoltaic cells. Although reducing metallic losses is a widely sought goal in nanophotonics, the design of nanostructured ‘black’ super absorbers from materials comprising only lossless dielectric materials and highly reflective noble metals represents a new research direction. Here we demonstrate an ultrathin (260 nm) plasmonic super absorber consisting of a metal–insulator–metal stack with a nanostructured top silver film composed of crossed trapezoidal arrays. Our super absorber yields broadband and polarization-independent resonant light absorption over the entire visible spectrum (400–700 nm) with an average measured absorption of 0.71 and simulated absorption of 0.85. Proposed nanostructured absorbers open a path to realize ultrathin black metamaterials based on resonant absorption