  We propose an efficient plasmonic structure consisting of metal strips and
thin-film silicon for solar energy absorption. We numerically demonstrate the
absorption enhancement in symmetrical structure based on the mode coupling
between the localized plasmonic mode in Ag strip pair and the excited waveguide
mode in silicon slab. Then we explore the method of symmetry-breaking to excite
the dark modes that can further enhance the absorption ability. We compare our
structure with bare thin-film Si solar cell, and results show that the
integrated quantum efficiency is improved by nearly 90% in such thin geometry.
It is a promising way for the solar cell.
