Dyadic Green’s functions of thin films: Applications within plasmonic solar cells

Abstract

Optimization and design of silicon solar cells by exploiting light scattering from metal nanoparticles to increase the efficiency is addressed in the small particle limit from a fundamental point of view via the dyadic Green's function formulation. Based on the dyadic Green's function (Green's tensor) of a three-layer geometry, light scattering from electric point dipoles (representing small metal scatterers) located within a thin layer sandwiched between a substrate and a superstrate is analyzed. Starting from the full dyadic Green's function we derive analytical near- and far-field approximations. The far-field approximations enable efficient, exact, and separate evaluation of light scattering into waves that propagate in the substrate or the superstrate. Based on the near-field approximation we present a semianalytical expression for the total near-field absorption in the substrate. The theoretical approach is used to analyze realistic configurations for plasmon-assisted silicon solar cells. We show that by embedding metal nanoscatterers in a thin film with a high refractive index (rutile TiO${}_{2}$ with $n\ensuremath{\approx}2.5$) on top of the silicon, the fraction of scattered light that couples into the solar cell can become larger than 96%, and an optical path length enhancement of more than 100 can be achieved.