Recently, surface plasmons have been employed in a variety of methods to increase the efficiency of solar cells. Surface plasmons are oscillations of electrons that arise from surface effects of light interaction with materials that have appreciable free carrier densities; their resonance is confined to a region that depends on the dielectric response of the medium. It has been observed that noble metals exhibit this resonance within visible- near IR range, making them an attractive candidate for silicon solar cells whose primary absorption bands are in this region. Research in silicon-based plasmonic solar cells has utilized the high scattering cross section and favorable angular distributions of noble metal nanoparticle-scattered radiation to increase absorption of thin silicon devices, which are normally weakly absorbing for photons of energy below 2 eV. The interaction is subject to interface effects, interferences of scattered and incident radiation, and the dielectric nature of the embedding medium or surface. In addition, perturbations caused by the longitudinal field of the metal nanoparticle may theoretically enhance the direct interband transitions of free carriers near the particle surface, further enhancing the photocurrent. This latter possibility has yet to be fully explored experimentally in crystalline silicon photovoltaics.
Absorption Enhancement in Ultrathin Crystalline Silicon Solar Cells with Antireflection and Light-Trapping Nanocone Gratings
