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Microsol International Texture Process Article PV Magazine 11.11
Microsol International’s researchers investigate fabrication process of textured wafers.
Stable texturization process by carbohydrates
Stable texturization: Photovoltaic industries widely use the standard texturization method with NaOH/KOH and IPA (Isopropyl alcohol) to reduce reflectivity of mono crystalline silicon ( crystal orientation) wafers. IPA promotes the formation of uniform pyramidal structure but leads to unstable process. In this work, Microsol International’s Md. Al-Amin, A.K.M. Rahmatul Alam, Kiran Turlapati and BarathBaskaranathan have investigated carbohydrates as an additive in the etchant solution. It has no evaporation loss and thus leads to a stable process.
The etching rates of different concentrations of carbohydrates, surface morphology, reflectance factor and processstability were analyzed. A batch of 156Pseudo-Square mono c-Si solar cells with17.1 to 17.2 percent efficiencies was fabricated with new texturization additive and compared with standard cells. This technology is yet to be incorporated into Microsol’s production lines.
In the commercial solar cell process, oriented single crystal silicon wafers are used for texturization and appropriate ARC (anti-reflective coating) to re-duce reflection. After removing the saw damage, the wafer’s reflection of incident light is more than 35 percent [Tom Mark-vart, Luis Castaner, Solar Cells Material,Manufacturing and Operation; Elsevier,2005]. Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are well recognized etchants of silicon. Typically the etching rate depends on the process time,temperature and concentration of the solution. The surface development during etching depends on the reaction mechanism, which is not fully understood in detail. The following chemical reactions during the etching process are generally accepted.
The etching rate needs to be control ledin order to get selective etching. Pyramid formation will not take place without an additive because of poor wet ability of the silicon surface that leads to in sufficient pyramid nucleation [U. Gangopadhyay,K. Kim, A. Kandol, J. Yi, H. Saha, Role of hydrazine mono hydrate during texture
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