HF-HCL-CL2溶液的生成及表面纹理对PERC太阳能电池光吸收影响的模拟

The Texturization of crystalline silicon wafers by wet-chemical treatment is commonly used for the  enhancement of light absorption in solar cells. Recent studies of anisotropic acidic etchants based on HF-HCl-Cl₂ led to an  innovative random inverted pyramid surface structure. By using the ‘wafer ray tracer’ of pvlighthouse.com.au the  theoretical light absorption properties of the random inverted pyramid structure were compared to the well-known textures for PERC solar cells. We simulated pyramidal and inverted pyramidal structures with monomodal sizes and with various  average pyramid widths. Besides, simulation of a PERC solar cell on the roof top (30°, south) of our building in Freiberg  (N 50°55'32.16'', E 13°19'58.43'') on June 21st, 2016 (solstitium) was performed. The results encourage further  development of new textures on monocrystalline silicon wafers by maskless acidic wet chemical treatment with HF-HCloxidant mixtures.

Theoretical discussions on the texture of monocrystalline silicon wafers have been made since the  1980s. These studies led to powerful Monte-Carlo  simulation tools like OPAL 2 and the ‘wafer ray tracer’, which are based on assumptions of various ray paths  and give the share of reflection, transmission and  absorption of light for photogeneration of charge carriers.

The goal of the present study was to identify ideal  textures for a PERC solar cell. We examined four different  types of surface structures on monocrystalline silicon  wafers. Random inverted pyramid structures, recently  found by HF-HCl-Cl₂-treatment, are compared to the well-known types of surface structures on monocrystalline  silicon wafers: regular upright, random upright and regular  inverted (Figure 1).  

For preparing the etching mixtures hydrochloric acid  (37 wt%, analytical grade, VWR), hydrofluoric acid (48  wt%, analytical grade, Sigma-Aldrich) and deionized (DI)  water were mixed in a PFA beaker. Dried gaseous chlorine  was bubbled into the etching solution. Silicon wafer pieces  of approximately 1 cm x 1 cm ((100) orientation, boron  doped, thickness of 190 μm, resistivity of 0.5 − 2.0 Ω cm−1,  Deutsche Solar GmbH, Freiberg, Germany) were placed  with tweezers for 20 minutes in 30 mL of the etching  mixture.

Fig1

The simulations were performed with the ‘wafer ray  tracer’ of pvlighthouse.com.au. Parameters like wafer  thickness, front and rear films were kept constant. Surface  morphologies were varied as shown in Figure 1. Parameters for the Zenith and Azimuth were used from  www.suncalc.org. The given values for absorption and  reflectivity are average values for the wavelengths  between 300 nm and 1200 nm.

Using HF-HCl-Cl₂ mixtures for treatment of  monocrystalline silicon wafers, random inverted  pyramidal structures are generated without masking or  lithographic processes. Silicon etching rates up to 0.35 µm  min-1 are observed during etching of monocrystalline,  diamond wire-sawn wafers at room temperature. SEM  pictures show pyramid edge widths between 2 and 20 µm  (Figure 3). On the Inside of the inverted pyramids a  microstructure is observed.