Broadband near-field effects for improved thin film Si solar cells on randomly textured substrates

We show the superior performance in terms of light management of n-doped mixed phase silicon oxide in direct contact with Ag with respect to the established ZnO/Ag back reflector in thin film Si tandem solar cells on randomly textured substrates. Based on coexisting larger quantum efficiency and amplification of the optical Raman mode of Si, we propose that, in spite of a simple cell design, near-field concentrated light radiated at metal nanoprotrusions on the back interface is harvested. The effect is a remarkable 10% increase of the generated current density in the bottom cell, holding promise for significant conversion efficiency gain in matched devices.

► n-SiOx:H/Ag and ZnO/Ag back reflectors (BR) in micromorph solar cells are compared.
► n-SiOx:H, vital layer of the bottom junction, also plays a major role in the BR.
► Up to 10% larger current density in the bottom cell is found with n-SiOx:H/Ag BR.
► Amplified optical Raman mode of Si is observed on the same cells.
► Absorption of near-field light radiated by the back Ag nanoprotrusions is proposed.