Plasma nanotexturing of silicon surfaces for photovoltaics applications: influence of initial surface finish on the evolution of topographical and optical properties

Abstract

Using a plasma to generate a surface texture with feature sizes on the order of tens to hundreds of nanometers (“nanotexturing”) is a promising technique being considered to improve efficiency in thin, high-efficiency crystalline silicon solar cells. This study investigates the evolution of the optical properties of silicon samples with various initial surface finishes (from mirror polish to various states of micron-scale roughness) during a plasma nanotexturing process. It is shown that during said process, the appearance and growth of nanocone-like structures are essentially independent of the initial surface finish, as quantified by the auto-correlation function of the surface morphology. During the first stage of the process (2 min to 15 min etching), the reflectance and light-trapping abilities of the nanotextured surfaces are strongly influenced by the initial surface roughness; however, the differences tend to diminish as the nanostructures become larger. For the longest etching times (15 min or more), the effective reflectance is less than 5 % and a strong anisotropic scattering behavior is also observed for all samples, leading to very elevated levels of light-trapping.

A Low-Cost, Non-hazardous Protocol for Surface Texturing of Glass Particles

“…Surface texturing methods for flat materials (metals/ alloys, polymers, and glass) have evolved rapidly over the years. Techniques such as abrasive [15], chemical [16], and laser etching [17], as well as abrasive polishing [18,19], blasting [20], mechanical press [21], electrical discharge machining [22], electron beam lithography [23], photolithography [24], and plasma nano-texturing [25] have all been applied to produce either random or structured rough surfaces. In contrast, established techniques for roughening batches of mm-scale particles is limited.…”

Excitation of Ar, O2, and SF6/O2 plasma discharges using tailored voltage waveforms: control of surface ion bombardment energy and determination of the dominant electron excitation mode

“…Very low reflectance (around 3% compared to 37% initially) can be obtained after 10 min of process for an ion energy of 115 eV, while lower values of ion energy lead to a smaller decrease in reflectance. This effect is directly linked to the morphological evolution of the silicon surface [26,27], as is illustrated by the scanning electron microscopy (SEM) images of selected samples in figure 2(b). Sample A (processed 10 min at a maximal ion energy of 85 eV) shows a smooth surface only altered by sparse, nanometer-scale holes, indicated by the white arrows in figure 2(b).…”