In the solar cell production process, cleaning and texturing is one of the important links. Optimization and technological upgrading of the texturing process can improve the conversion efficiency of solar cells and reduce production costs. The formation of texturing suede is affected by NaOH concentration, residence time, temperature during the process and other factors.

    Why do silicon wafers need texturing?

    First, cleaning and texturing can remove stains on the surface of the silicon wafer and reduce the occurrence of defective products. Secondly, a better pyramid must be small and uniform, and cover the entire silicon wafer surface. This increases the silicon wafer surface area, which also means increasing the PN junction area.

The most important thing is that texturing can form an uneven textured surface, which produces a light trapping effect, increases the absorption of sunlight by the silicon wafer, reduces the light reflectivity of the silicon surface, increases the short-circuit current Isc, and maximizes the utilization of light. converted into electrical energy.

  Best results for texturing

At a suitable corrosion rate, nucleation and growth reach a balance, forming a pyramid structure of appropriate size, complete structure, and densely distributed on the entire silicon wafer surface. At this time, the pyramid structure is relatively optimized and has the best anti-reflection effect.

If the corrosion rate is high, the growth of the pyramid will be greater than the nucleation, and the texture structure will be a large pyramid, and there will be unnucleated areas on the surface. The gaps between the pyramids will increase the surface reflectivity. When the corrosion rate is too low, pyramid nucleation is greater than growth, manifesting as incomplete, dense and stacked pyramids.

The corrosion rate is determined by three reaction rates. One is the movement rate of the corrosive liquid to the surface of the corroded object; the second is the reaction rate of the chemical reaction between the corrosive liquid and the surface of the corroded object; the third is the transfer rate of the products from the surface of the corroded object. rate of departure.

Factors affecting texturing

1.Influence of NaOH concentration

NaOH concentration has an important impact on the reaction rate of silicon wafers. During the texturing process, since the NaOH concentration used is a low alkali concentration, as the NaOH concentration increases, the corrosion rate of the silicon wafer increases relatively. At the same time, as the NaOH concentration changes, the AF of the silicon wafer reaction also changes. Therefore, the NaOH concentration also has an important impact on the pyramid's pyramid angle.

 2. Temperature effect

If the temperature is too high, the reaction AF value will decrease, the continuity of the suede surface will decrease, and the corrosion rate will be too fast, making control difficult;

If the temperature is too low, the corrosion rate will be too slow and the texturing cycle will be extended. Usually the texturing temperature is controlled at 75°C-85°C.

3. Time impact

Texturing includes the process of pyramid nucleation and growth, so texturing time has an important impact on the morphology of the texture and the amount of silicon wafer corrosion.

After the damaged layer is removed by hot and concentrated alkali, many corrosion pits are left on the surface of the silicon wafer;

In heated low-concentration alkali texturing liquid:

After 1 minute, pyramids sprouted like bamboo shoots after a rain, popping up sporadically;

After 5 minutes, the surface of the silicon wafer is basically covered by small pyramids, and a few have begun to grow. We call this change in the early stage of suede surface pyramid nucleation;

After 10 minutes, the dense pyramidal suede surface has been formed, but the size is uneven, and the reflectivity has also dropped to a relatively low level;

As time goes by, the pyramid expands and merges outwards, the volume gradually expands, and the size tends to be uniform. If the time is too long, the uniformity of the suede structure will decrease.