Fresnel lens based on silicon nanowires

Silicon nanowire reflective Fresnel lenses are demonstrated and their focusing and lensing properties characterizations are shown. The Fresnel lenses were fabricated using conventional lithography and metal-assisted chemical etching. The lenses have dark zones made of sub-wavelength silicon nanowires and bright zones formed by polished silicon surface. High intensity contrast exists between the bright and the dark zones, leading to an efficient focusing performance in the spectrum of visible light. The reflective Fresnel lens has the potential to reflect and focus light onto photosensitive dye in dye-sensitive solar cells in order to improve their light absorption efficiency and hence, the photocurrent.