Influence of pyramid size on reflectivity of silicon surfaces textured using an alkaline etchant

Abstract

Surface texturing of p-type monocrystalline silicon (100) is well known as one of the best methods to reduce reflection losses and to increase light trapping and light absorption probability. Pyramid surface textures play a major role in reducing the reflectance of monocrystalline silicon surfaces. In this paper, the size of pyramids formed on the surface of p-type silicon substrates and by changing the etching characteristics during the texturing process of silicon were studied and evaluated. The pyramids that formed on the crystalline silicon surface formed light traps that led to increased light absorption efficiency. The pyramid size effects on the percent reflectivity were evaluated at normal incidence and an inverse relationship between the percent reflectivity and the pyramid size was found. The size of the pyramids was controlled by controlling the texturing process by changing the concentrations of potassium hydroxide (KOH) and isopropyl alcohol (IPA) and by controlling the etching process time. In this work, the optimized etching conditions were determined as a solution prepared with 20 wt% KOH and 3 wt% IPA for wet etching at a reaction temperature of $80^{\circ }\hbox {C}$ and an etching time of 40 min. The lowest value for percent reflectivity of the patterned surfaces was 9.7% and it was achieved for pyramid bases close to $4~\upmu \hbox {m}$ as measured at a wavelength of 650 nm.