Surface Texturing of Silicon {100} in an Extremely Low Concentration TMAH for Minimized Reflectivity

Abstract

Micro-texturing of silicon front surface which consists of geometrical array of structures is needed to reduce the overall reflectance and to increase light trapping by multiple internal reflections of incident light for solar cell application. A wet anisotropic etching technique based on the alkaline solution is widely used to form micro-sized pyramidal structures on the silicon surface. In this work, an extremely low concentration tetramethylammonium hydroxide (TMAH) is employed for texturing the surface of {100} oriented monocrystalline silicon without adding any additive and agitation during etching to investigate the surface roughness and thereby reflectance. TMAH concentration is varied from 1.0-0.1 wt% in a step of 0.1 wt%. For each concentration, time of etching is also varied from 20–100 min with an interval of 20 min at a fixed temperature of 70°C. Surface morphology and surface roughness for as-textured silicon surfaces are analyzed by scanning electron microscope (SEM) and 3D laser scanning microscope, respectively. SEM images of etched silicon surface with 0.5 wt% TMAH confirm uniform and dense pyramidal structures. As measured by UV-Vis spectrometer using integrating sphere mode, we were able to achieve the lowest reflectance of 8.3% at 570 nm and solar weighted reflectance (RSW) of 9.7% in visible range after 80 min of etching in 0.5 wt% TMAH solution at 70°C.

Fabrication and Characterization of Inverted Silicon Pyramidal Arrays with Randomly Distributed Nanoholes

“…Light-trapping films can improve the absorption of their composite devices by modifying its surface microstructure in the wavelength range of 300–1100 nm [ 17 , 25 , 26 ]. Compared to bare silicon or silicon with other structures, silicon with pyramidal structures can have reduced reflectance and a simple and stable fabrication process [ 21 , 27 ]. Anisotropic wet etching [ 28 ] takes advantage of the fact that different crystal orientations of Si have different etching rates in alkaline solutions, and, thus, allows for the preparation of large-area micro-nano pyramidal array structures on the surface of monocrystalline silicon.…”