In the production of solar cells, velvet making is the first process of crystalline silicon cells. The engineer mentioned that for monocrystalline silicon, the purpose of velvet production is to extend the propagation path of light on the surface of the battery, thereby improving the absorption efficiency of solar cells for light. The main method for producing single crystal silicon velvet is to corrode the surface of silicon wafers with alkali (NaOH, KOH). Due to the different internal structures of silicon wafers, anisotropic alkaline fluff is mainly used to form a pyramid shaped fluff on the surface of monocrystalline silicon with uniform crystal orientation, effectively enhancing the absorption of incident sunlight by the silicon wafer and thereby increasing the photogenerated current density. For textured surfaces that can achieve low surface reflectivity and are beneficial for the subsequent production process of solar cells, the pyramid size should be uniform, with individual cell sizes ranging from 2 to 10 μ Between m, there is no gap between adjacent pyramids, indicating a coverage rate of 100%. The formation of ideal quality velvet surface is influenced by many factors, such as the surface state of the silicon wafer before corrosion, the composition of the velvet solution, the content of each component, temperature, reaction time, etc. In industrial production, the influencing factors on this process are more complex, such as the number of silicon wafers processed, the volatilization of alcohols, the accumulation of reaction products in the solution, and the changes in the components of the velvet making solution. In order to maintain good reproducibility in production and achieve high production efficiency. It is necessary to have a thorough understanding of the formation mechanism of pyramid velvet, control the factors that have a significant impact on the velvet making process, and form high-quality pyramid velvet in a short period of time.

The process of single crystal velvet production is quite complex, and different companies have their own unique velvet production methods. There are several methods for alkaline velvet production, including NaOH+IPA, NaOH+IPA+NaSiO3, NaOH+CH3CH2OH, etc. There are generally two types of chemical additives used, one is IPA (isopropanol), and the other is industrial alcohol. After adding isopropanol, the reaction can be accelerated, mainly to eliminate bubbles. After adding industrial alcohol, the quality and aesthetics of the silicon wafer surface will be improved.
The widely accepted method in industrial large-scale production is NaOH+IPA+NaSiO3. The process requires NaSiO3: NaOH to be between 1:3.5 and 1:3, and NaOH: IPA to be around 1:6. The NaOH concentration should be adjusted between 2% and 4%. In the velvet making process, temperature and the ratio of solution are the main parameters. Time is secondary. Maintaining the stability of the process is crucial for large-scale production. This is usually achieved through the methods of draining and replenishing fluids. For the second process method, the optimal working temperature for velvet production is 83 ℃± 1 ℃. The temperature is too low and the IPA ratio is too small to make a textured surface, or in other words, the silicon wafer has already been consumed before the textured surface is formed. IPA is too numerous to form a textured surface, and it cannot regulate the rate of crystal orientation reaction.