Design guidelines for efficient plasmonic solar cells exploiting the trade-off between scattering and metallic absorption

We report on the role of plasmonic resonances in determining the delicate balance between scattering and absorption of light in nanometric particle arrays applied to the front surface of solar cells. Strong parasitic absorption is shown to be dependent upon the excitation of localized surface plasmon resonances and prohibits efficient scattering into the underlying semiconductor. Via detailed analytical and numerical investigations we obtain the dependence of scattering and absorption in nanoparticles upon their complex refractive index. These results provide an insight into the optimum material properties required to minimize parasitic optical absorption, while maintaining high scattering cross-section efficiency, thus providing a general design guideline for efficient light trapping with scattering nanoparticles. The work is extended to include comprehensive optoelectronic simulations of plasmonic solar cells in which the scattering metals are made from either Au, Ag or Al. We show that Al particles provide the closest approximation to the optimized particle refractive index and therefore exhibit the smallest parasitic absorption and correspondingly lead to the greatest solar cell efficiency enhancements. Indeed, for the Al particles we report a full-band enhancement of external quantum efficiency over the reference device.