Low Reflection and Low Surface Recombination Rate Nano-Needle Texture Formed by Two-Step Etching for Solar Cells.

Chia-Hsun Hsu,Xiao-Ying Zhang,Sam Zhang,Shui-Yang Lien,Song-Yan Chen,Yun-Shao Cho,Wen-Zhang Zhu,Yan-Hua Huang,Shih-Mao Liu

doi:10.3390/nano9101392

Abstract

In this study, needle-like and pyramidal hybrid black silicon structures were prepared by performing metal-assisted chemical etching (MACE) on alkaline-etched silicon wafers. Effects of the MACE time on properties of the black silicon wafers were investigated. The experimental results showed that a minimal reflectance of 4.6% can be achieved at the MACE time of 9 min. The height of the nanostructures is below 500 nm, unlike the height of micrometers needed to reach the same level of reflectance for the black silicon on planar wafers. A stacked layer of silicon nitride (SiNx) grown by inductively-coupled plasma chemical vapor deposition (ICPCVD) and aluminum oxide (Al2O3) by spatial atomic layer deposition was deposited on the black silicon wafers for passivation and antireflection. The 3 min MACE etched black silicon wafer with a nanostructure height of less than 300 nm passivated by the SiNx/Al2O3 layer showed a low surface recombination rate of 43.6 cm/s. Further optimizing the thickness of ICPCVD-SiNx layer led to a reflectance of 1.4%. The hybrid black silicon with a small nanostructure size, low reflectance, and low surface recombination rate demonstrates great potential for applications in optoelectronic devices.

Highlights

Silicon reflects a significant amount of incident light on its surface because of its high refractive index of about 3 to 4 in the visible wavelength region
The low surface recombination rates for the samples in this study demonstrate a high surface passivation quality because of the atomic layer deposition (ALD) Al2O3 layer
Needle-like nanostructures were prepared on pyramidal surfaces of c-Si using metal-assisted chemical etching (MACE) processes

Summary

Introduction

Silicon reflects a significant amount of incident light on its surface because of its high refractive index of about 3 to 4 in the visible wavelength region. A dielectric layer is deposited to further reduce the reflection based on the quarter-wavelength design and is optimized only for a given wavelength [1] Another way is to make nanostructures on a silicon surface (known as black Si [2,3]). In order to obtain sufficiently low reflectance, the etching depth needs to be deep, and sharp, long nanostructures are produced. These structures increase the difficulties of the doping process and passivation of silicon surface. Sharp nanowires produced by traditional MACE on planar wafers, the small sized nanostructures in turn mean a smaller amount of increase in surface area, and passivation will be relatively easier. Low reflectance and high passivation on silicon wafers with small-sized nanostructures can be achieved

Materials and Methods

Findings

Conclusions