title: Optical absorption enhancement in amorphous silicon nanowire and nanocone arrays.
abstract: Hydrogenated amorphous Si (a-Si:H) is an important solar cell material. Here we demonstrate the fabrication of a-Si:H nanowires (NWs) and nanocones (NCs), using an easily scalable and IC-compatible process. We also investigate the optical properties of these nanostructures. These a-Si:H nanostructures display greatly enhanced absorption over a large range of wavelengths and angles of incidence, due to suppressed reflection. The enhancement effect is particularly strong for a-Si:H NC arrays, which provide nearly perfect impedance matching between a-Si:H and air through a gradual reduction of the effective refractive index. More than 90% of light is absorbed at angles of incidence up to 60 degrees for a-Si:H NC arrays, which is significantly better than NW arrays (70%) and thin films (45%). In addition, the absorption of NC arrays is 88% at the band gap edge of a-Si:H, which is much higher than NW arrays (70%) and thin films (53%). Our experimental data agree very well with simulation. The a-Si:H nanocones function as both absorber and antireflection layers, which offer a promising approach to enhance the solar cell energy conversion efficiency.
authors.affiliation: Department of Electrical Engineering, Department of Applied Physics, Department of Materials Science and Engineering, and Department of Chemistry, Stanford University, Stanford, California 94305, USA.
authors.forename: Jia
authors.initials: J
authors.lastname: Zhu
authors.forename: Zongfu
authors.initials: Z
authors.lastname: Yu
authors.forename: George F
authors.initials: GF
authors.lastname: Burkhard
authors.forename: Ching-Mei
authors.initials: CM
authors.lastname: Hsu
authors.forename: Stephen T
authors.initials: ST
authors.lastname: Connor
authors.forename: Yueqin
authors.initials: Y
authors.lastname: Xu
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.forename: Michael
authors.initials: M
authors.lastname: McGehee
authors.forename: Shanhui
authors.initials: S
authors.lastname: Fan
authors.forename: Yi
authors.initials: Y
authors.lastname: Cui
mesh_terms: D003460:Crystallization / Q000379:methods*; D008027:Light; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D012031:Refractometry; D012542:Scattering, Radiation; D012825:Silicon / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D046911:Macromolecular Substances; D012825:Silicon