Effect of Etching Temperature on the Surface Texturing of Si{100} in an Extremely Low Concentration Tmah for Minimized Reflectivity

Abstract

Among various renewable energy resources, solar energy is one of the most abundant energy available in nature. The solar energy can be utilized by converting photon energy into electrical energy by using solar cells as energy harvesters. Silicon-based solar cells dominate the current photovoltaic market because of its higher efficiency, excellent stability, non-toxicity, lower processing cost and excellent reliability in the outdoor conditions.1 However, the silicon solar cell efficiency can be further increased by reducing the front surface reflection from silicon, which is greater than 35%. In order to reduce the reflection from silicon surface, surface texturing is done where silicon surface is intentionally made rough. Wet anisotropic etching is most widely used in surface texturing of silicon because of its high throughput and lower cost. Potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) are two most extensively used alkaline solution for surface texturing of silicon. 2-4 In these two etchants, TMAH is preferred because it is fully compatible with CMOS process and also provide high etch selectivity between silicon and silicon dioxide. Surface texturing using low concentration TMAH (<5%) results in high surface roughness. This is a remarkable observation that can be applied in solar cell industries to minimize the reflection from silicon front surface.In this work, we have studied the effect of very low concentration TMAH (1.0-0.1 wt%) without adding any additive and agitation during etching for surface texturing of Si{100} surface. The main objective of this study is to achieve an optimized etched surface topography at lowest possible etching concentration and etching time to minimize the reflectance for application in solar cells. The average solar weighted reflectance (Rsw) of around 10% is obtained in a very mild etching conditions. Compared to the previous results reported in literatures and also the mild etching conditions, reflectance values obtained in this work are quite promising for large area surface texturing of silicon solar cell panels for enhancement in their efficiency. In addition, the use of very low concentration TMAH minimizes the chemical waste. This also helps in adopting the technique for fabricating anti-reflective silicon surfaces at large scale.