Giant optical pathlength enhancement in plasmonic thin film solar cells using core-shell nanoparticles

In this paper, a finite-difference time-domain method is adopted to investigate the light scattering properties of core (metal)-shell (dielectric) nanoparticles, with varying shell thickness and refractive index. Adding a shell coating can shift the resonance to above the solar material bandgap when compared with a bare nanoparticle that has resonance outside of the useful solar radiation. The front-located core-shell metal-dielectric nanoparticles on thin Si substrates demonstrate enhanced forward scatterings with suppressed backward scatterings. The fraction of light scattered into the substrate and the maximum optical path length enhancement can be as high as 0.999 and 3133, respectively, if properly engineered, while the maximum optical path length enhancements of an ideal Lambertian and dipole source are only similar to 100. This light scattering property can be ascribed to the constructive interference of the electric and magnetic dipoles. The giant fraction of light scattered into the substrate and the maximum optical path length enhancement in core-shell nanoparticle based plasmonic solar cells provides an insight into addressing the out-coupling and poor pathlength in thin film photovoltaic technology.