Omnidirectional and Broadband Antireflection Effect with Tapered Silicon Nanostructures Fabricated with Low-Cost and Large-Area Capable Nanosphere Lithography

Abstract

In this report, we present a process for the fabrication and tapering of a silicon (Si) nanopillar (NP) array on a large Si surface area wafer (2-inch diameter) to provide enhanced light harvesting for Si solar cell application. From our N,N-dimethyl-formamide (DMF) solvent-controlled spin-coating method, silica nanosphere (SNS in 310 nm diameter) coating on the Si surface was demonstrated successfully with improved monolayer coverage (>95%) and uniformity. After combining this method with a reactive ion etching (RIE) technique, a high-density Si NP array was produced, and we revealed that controlled tapering of Si NPs could be achieved after introducing a two-step RIE process using (1) CHF3/Ar gases for SNS selective etching over Si and (2) Cl2 gas for Si vertical etching. From our experimental and computational study, we show that an effectively tapered Si NP (i.e., an Si nanotip (NT)) structure could offer a highly effective omnidirectional and broadband antireflection effect for high-efficiency Si solar cell application.

Optical Simulation of Nanostructured Silicon Surfaces

“…Unlike surfaces with nanocylinders, for which the refractive index change is abrupt, for surfaces with nanocones, the change occurs smoothly. It is well known that in this case, the antireflective behavior of the surfaces and films is more effective [11,13]. Moreover, with an increase in 𝑓 and ℎ, the area of the light-receiving surface increases and the refractive index changes more smoothly, which together leads to a decrease in 𝑅(𝜆) and WAR.…”

“…Therefore, it can be assumed that the second mechanism is predominant for the simulated surfaces. In this case, the refractive index gradient change is described by the following expression [13]:…”

Properties of Black Silicon Layers Fabricated by Different Techniques for Solar Cell Applications

“…In addition, from top to bottom along the thickness of the RIA BS with nanocones, the refractive index increases smoothly, but in the case of MACE BS with nanocolumns, it practically does not change. [42,43] It is well known that the antireflective behavior of surfaces and multilayer films with a gradient change in the refractive index is more effective. [44,45] Table 1 summarizes the 1 sun average photovoltaic parameter values of the processed solar cells with antireflective frontal BS layers fabricated by different techniques.…”