Reflection distributions of textured monocrystalline silicon: implications for silicon solar cells

Abstract

A common misconception is that alkaline textured silicon solar cell surfaces are characterised by features that are pyramidal and bounded by {111} planes. In preference to the typical approach of observing scanning electron microscope images, we analyse reflection distributions from various pyramidal textures and find that {111} faceted pyramids are a poor approximation to the features on such surfaces. We conclude that features are hillocks, with an octagonal base. Furthermore, the characteristic base angle of the texture depends on the etchant and is closer to 50–52° than the commonly accepted value of 54.74°. Analyses of antireflection, light trapping, photogeneration and surface recombination properties of textured surfaces should take this feature morphology into account. The base angle has a strong influence on the hemispherical reflectance of the textured surface, with higher angles resulting in reduced reflectance. The influence of this reflection enhancement upon device performance is smallest when an optimised antireflection coating is applied; compared with an array of {111} faceted pyramids, a hillock morphology with 50° base angle results in a 0.2% reduction in photogenerated current in a typical cell. Additionally, as base angle is reduced, an encapsulant of increasingly higher refractive index is required to drive internal reflection at the air–glass interface of light initially reflected from the cell surface. The development of texturing processes resulting in higher base angles is encouraged. Copyright © 2012 John Wiley & Sons, Ltd.

Calibration of Electrochemical Capacitance-voltage Method on Pyramid Texture Surface Using Scanning Electron Microscopy

“…The top angle is 75.0º which is larger than 70.5º when the micro facet is a perfect (111) plane. It is also reported by BakerFinch et al [11] that it is closer to 76º-80º than the commonly accepted value 70.5º.…”

Optical properties of screen-printed aluminum contacts

“…In this work, the focus is on PERC cells made from 180 µm thick ptype mono-Si wafers and featuring an anisotropically etched front side with a silicon nitride (SiN x ) anti-reflection coating (ARC) and emitter passivation layer. Random upright pyramids formed by the anisotropic etching result in a characteristic base angle (α) that is commonly assumed to be 54.74°, but in actuality is around 50-52° for industrial cells [9]. At normal incidence, ≈76% of the total incident light (primary ray) is transmitted into the wafer at an angle (θ 1 in Fig.…”

Optical modeling of the internal back reflectance of various c-Si dielectric stacks featuring AlOx, SiNx, TiO2 and SiO2

“…This means the surface wave and evanescent losses are the dominant loss mechanisms for internal BR with these types of cell configurations. For textured monocrystalline wafers, the characteristic base angle (α) of the well-known pyramid structures is commonly taken to be 54.74°, although recent work has shown that in industrial cells this is actually around 50-52° depending on the etchant used [17]. Assuming α = 54.74° and a SiO2 frontside coating, Kray et al show that at normal incidence, the two primary rays transmitted through the cell have an angle of incidence (AOI) on the backside of 41.4° and 59.1°, the former (Ray A) being the primary ray, which carries 76.4% of the total incident flux and the latter (Ray B) carrying 19.4% [13].…”