Broadband light absorption enhancement in thin-film solar cells by combining front dielectric and back metal gratings

Abstract

We numerically study the absorption enhancement of amorphous Si (alpha-Si) solar cells, in which a dual grating structure combining front dielectric grating and back metal grating is proposed to improve light absorption in the 300-900 nm wavelength range. The front dielectric grating scatters the incident light into active layer which can reduce reflection without much energy loss, especially at the short wavelengths. The back metal grating causes the absorption enhancement at long wavelengths due to the excitation of surface plasmon polaritons (SPPs) at the interface of metal/semiconductor and/or photonic modes in the active layer. When these two gratings are combined, a large, broadband absorption enhancement over the entire spectrum can be realized. For better comparison, the flat structure without any gratings is chosen as a reference. In our work, the absorption enhancement of the solar cells with dual gratings is superior to the structures with a front dielectric or back metal grating alone in almost over the entire wavelength range 300-900 nm. For wavelengths in the range 300-900 nm, 72.4% absorptivity is observed for 100-nm-thickness flat a-Si solar cell, 76.9% and 75.1% for front and back grating cases, and up to 82.6% for dual grating case at the grating period of 360 nm.