Morphology evolution of the light trapping structure using atmospheric plasma textured c-Si wafer for silicon solar cells

Abstract

Applying atmospheric plasma etching to the surface texturing process of silicon solar cells is a promising strategy for the current photovoltaic manufacturing industry due to its low equipment cost and good fabrication flexibility. This paper investigates the morphology evolution of the silicon surface etched by an Ar/CF4/O2 plasma and the associated optical properties. Results show that the generation of the light trapping structure on the polished silicon surface can be divided into two stages on the basis of the multi-scale morphological images and the quantitative evaluation of roughness parameters. The initial roughening stage mainly involves the formation of high-frequency nanoroughness that can act as an effective medium layer with a gradual refractive index. The resulting optical medium effect can reduce the surface reflectance within a broad range of wavelengths. At the next texturing stage, the low-frequency and high-amplitude microroughness dominates the morphology of the etched silicon surface. It features inverted parabolic structures with a high aspect ratio, which can cause multiple reflections of the incident light. The optical medium effect resulting from the nanoroughness is also inherited. Thus, the anti-reflectance property of the etched silicon surface is greatly improved. This work demonstrates that the light trapping properties of silicon surface etched by atmospheric plasma jet are a synergy of the optical medium effect and geometrical optics. Insights into the morphology evolution and optical properties of the textured surfaces are important for developing a new surface texturing process of silicon solar cells.