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A two-step acidic texturization procedure for the manufacture of low-reflective multi-crystalline silicon solar wafer.

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Title: A two-step acidic texturization procedure for the manufacture of low-reflective multi-crystalline silicon solar wafer.
Authors: Meinel, B.1 (AUTHOR), Langner, T.1 (AUTHOR), Preis, P.2 (AUTHOR), Sieber, T.1 (AUTHOR), Wefringhaus, E.2 (AUTHOR), Acker, J.1 (AUTHOR) joerg.acker@b-tu.de
Source: Solar Energy. Nov2019, Vol. 193, p395-402. 8p.
Subjects: Hydrofluoric acid, Silicon wafers, Surface topography, Solar cells, Ammonium hydroxide, Nitric acid
Abstract: • Development of a novel two-step texturization process for acidic texturization. • A low-rate etching step pre-shapes the texture. • A subsequent high-rate etching removes the saw damage and finalizes the texture. • The final texture is characterized by a large surface area and by a low reflectivity. Texturization of multi-crystalline silicon wafers for photovoltaic application comprises the removal of the saw damage and shaping the topography of the bulk surface to create a surface with a low reflectivity, the so-called texture. Etching of multi-crystalline silicon wafers is usually carried out with acid mixtures consisting of hydrofluoric acid (HF), nitric acid (HNO 3) and hexafluorosilicic acid (H 2 SiF 6). The present study reveals that such acid mixtures diluted by water or modified by the addition of ammonia solution, NH 3 (added as ammonium hydroxide solution, NH 4 OH) can create textures with a significantly increased surface area exceeding that obtained by standard etching mixtures by a factor of 2.5–3. This yields a significantly reduced reflectivity of the etched wafer surface. However, the addition of water or NH 3 causes a very low etching rate, which makes such mixtures inapplicable for industrial application. To overcome this disadvantage, a two-step etching regime was developed to produce surface-enlarged solar wafers within a timespan typical for industrial production lines. This procedure comprises a first step of slow etching with a NH 3 -modified etching mixture to pre-shape the as-cut wafer surface. The second etching step is performed with a typical HF/HNO 3 /H 2 SiF 6 etching mixture that finalizes the texturization. Electrical measurements made on solar cells produced from such etched wafer confirm the improved surface quality of the two-step etched wafer compared to the reference wafer. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:• Development of a novel two-step texturization process for acidic texturization. • A low-rate etching step pre-shapes the texture. • A subsequent high-rate etching removes the saw damage and finalizes the texture. • The final texture is characterized by a large surface area and by a low reflectivity. Texturization of multi-crystalline silicon wafers for photovoltaic application comprises the removal of the saw damage and shaping the topography of the bulk surface to create a surface with a low reflectivity, the so-called texture. Etching of multi-crystalline silicon wafers is usually carried out with acid mixtures consisting of hydrofluoric acid (HF), nitric acid (HNO 3) and hexafluorosilicic acid (H 2 SiF 6). The present study reveals that such acid mixtures diluted by water or modified by the addition of ammonia solution, NH 3 (added as ammonium hydroxide solution, NH 4 OH) can create textures with a significantly increased surface area exceeding that obtained by standard etching mixtures by a factor of 2.5–3. This yields a significantly reduced reflectivity of the etched wafer surface. However, the addition of water or NH 3 causes a very low etching rate, which makes such mixtures inapplicable for industrial application. To overcome this disadvantage, a two-step etching regime was developed to produce surface-enlarged solar wafers within a timespan typical for industrial production lines. This procedure comprises a first step of slow etching with a NH 3 -modified etching mixture to pre-shape the as-cut wafer surface. The second etching step is performed with a typical HF/HNO 3 /H 2 SiF 6 etching mixture that finalizes the texturization. Electrical measurements made on solar cells produced from such etched wafer confirm the improved surface quality of the two-step etched wafer compared to the reference wafer. [ABSTRACT FROM AUTHOR]
ISSN:0038092X
DOI:10.1016/j.solener.2019.09.051