Manipulating the antireflective properties of vertically-aligned silicon nanowires

Abstract

Vertically-aligned silicon nanowires (VA-SiNWs) realized with vacuum metal-assisted chemical etching are demonstrated to be the better candidate for optical manipulation due to their superior physical and optical properties. The length-dependent volume filling factor of as-grown VA-SiNWs agrees with the theoretically optimal conditions which lead to the lowest surface reflectance in visible spectral region. Growing a thin thermal oxide with an appropriate thickness on the surface of VA-SiNWs could further improve the antireflective performance in near-infrared wavelengths. We also demonstrated that the surface reflectance could be adjusted without sacrificing the bandwidth of its antireflective window by tuning the bundle filling factor of two-dimensional VA-SiNW bundle array. Such a flexible surface reflectance cannot be obtained by simply adjusting the physical parameters of planar VA-SiNWs. For implementing SiNW-based solar cells, a pre-patterning method is conducted to enable the formation of antireflective VA-SiNW surfaces at energy-harvesting areas while maintaining planar silicon surfaces at the metallization areas to avoid high electrical contact resistivity over SiNW surfaces. Nanowire-based solar cell shows an 18% increased short-circuit current and a 10% improved overall efficiency compared to the reference cell with a planar silicon top surface.