- 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 (HNO₃) and hexafluorosilicic acid (H₂SiF₆). The present study reveals that such acid mixtures diluted by water or modified by the addition of ammonia solution, NH₃ (added as ammonium hydroxide solution, NH₄OH) 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 NH₃ 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 wafersTexturization 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 (HNO₃) and hexafluorosilicic acid (H₂SiF₆). The present study reveals that such acid mixtures diluted by water or modified by the addition of ammonia solution, NH₃ (added as ammonium hydroxide solution, NH₄OH) 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 NH₃ 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 NH₃-modified etching mixture to pre-shape the ascut wafer surface. The second etching step is performed with a typical HF/HNO₃/H₂SiF₆ 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.…
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