Plasmonic light-harvesting devices over the whole visible spectrum

On the basis of conformal transformation, a general strategy is proposed to design plasmonic nanostructures capable of an efficient harvesting of light over a broadband spectrum. The surface plasmon modes propagate toward the singularity of these structures where the group velocity vanishes and energy accumulates. A considerable field enhancement and confinement is thus expected. Radiation losses are also investigated when the structure dimension becomes comparable to the wavelength.