The use of plasmonic nanostructures for creating broadband absorbers is demonstrated in Nature Communications this week. The proposed structures may help enhance the performance of photovoltaic cells which are used widely in solar panels.

The development of materials with high absorption across the visible light spectrum is important for a number of optical devices, including solar cells. Existing schemes based on plasmonics only work in narrow frequency ranges and for certain polarisations of light. Koray Aydin and colleagues have overcome these problems by building ultrathin metal-insulator-metal stacks with the top metal layer shaped into a grid of trapezoids just tens of nanometres wide. This provides them with an average of 70% absorption across the visible spectrum, independent of the incident light polarisation and for a wide range of incidence angles.

These stacks are only 260nm thick, making them an attractive possibility to enhance the light-harvesting capability of photovoltaics or to improve thermal emitters and absorbers.