Pre-Texturing Thermal Treatment for Saw-Damage-Removal-Free Wet Texturing of Monocrystalline Silicon Wafers

Yujin Jung,Kwanhong Min,Donghwan Kim,Haeseok Lee,Soohyun Bae,Myeongseob Sim,Yoonmook Kang

doi:10.3390/en13246610

Abstract

The etching of Si wafers significantly influences the efficiency of photovoltaic devices. Texturing can effectively decrease front surface reflection and improve device performance. Saw damage removal (SDR) is necessary to yields uniform random pyramidal surfaces without the appearance of saw marks, it entails significant consumption of chemical solutions and complicated cleaning steps. Herein, an alternative process of pre-texturing thermal treatment was carried out at 800 °C for 10 min, followed by anisotropic texturing, and a uniform pyramidal surface over a large area of the textured surface was obtained without saw marks. Compared with that of as-cut mono-Si wafers (30.7%), the weighted average reflectance of the samples textured with or without thermal treatment decreased to 11.2% and 11.9%, respectively, and further to 3% and 3.4%, respectively, when anti-reflection coatings were applied. In addition, saw marks on the wafer surface were used as gettering sites during thermal treatment, and the bulk lifetime was more than doubled from 42.6 µs before the treatment to 93.8 µs after. The simple, SDR-free method presented herein for enhancing the textural uniformity of Si wafers and, hence, solar cell performance, can be employed on an industrial scale without necessitating additional investment in equipment.

Highlights

Minimizing the degree of surface reflection during fabrication increases the short-circuit current and conversion efficiency of solar cells [1]
We proposed a pre-texturing thermal treatment process to obtain a uniform pyramidal surface over a large area of the textured surface of DWS monocrystalline Si (mono-Si) wafers without necessitating any additional chemical treatment
We investigated a method for obtaining a uniform pyramidal surface over a large area of the textured surface of the DWS mono-Si wafer to increase its light absorption rate

Summary

Introduction

Minimizing the degree of surface reflection during fabrication increases the short-circuit current and conversion efficiency of solar cells [1]. This is achieved via texturing in which arbitrary pyramids are formed on the wafer surface. In the global market for solar cells, crystalline Si (c-Si) accounts for more than 95%, of which monocrystalline Si (mono-Si) constitutes approximately 78% [2]. Wet etching processes using sodium hydroxide (NaOH), potassium hydroxide (KOH), and tetramethylammonium hydroxide (TMAH)-based solutions are widely employed to increase the light absorption rate of mono-Si solar cells. The process typically entails selective anisotropic etching of (100) Si surfaces to yield a texture of Energies 2020, 13, 6610; doi:10.3390/en13246610 www.mdpi.com/journal/energies

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Conclusion