Optical Absorption Enhancement in Amorphous Silicon Nanowire and Nanocone Arrays

TLDR

Hydrogenated amorphous silicon is a key material for solar cells. The study aims to fabricate a‑Si:H nanowires and nanocones and examine their optical properties. They use a scalable, IC‑compatible fabrication process to produce a‑Si:H nanowires and nanocones. The nanocone arrays achieve over 90 % absorption up to 60° incidence, outperforming nanowires and thin films, and match simulations, indicating strong potential to boost solar‑cell efficiency.

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.