Back polishing method of PERC battery

Abstract

The invention relates to a back polishing method of a PERC battery. The method comprises the following steps: S1, pretreating a silicon wafer before polishing; S2, polishing the back surface of the silicon wafer, wherein the step S2 comprises the steps that a silicon wafer is placed in an HF / H2SO4 / HNO3 / H2O mixed solution to be subjected to back face polishing, and a texturing face of a quasi-square or rectangular structure is formed, the volume ratio of HF:H2SO4:HNO3:H2O is 1:0.3-1.5:2.6-3.0:1-1.8, the polishing temperature is 112 DEG C, and the polishing time is 2070 s; and S3, post-processing the silicon wafer. According to the PERC battery back polishing method provided by the invention, a new acid polishing ratio, namely the ratio of rich sulfuric acid to low nitric acid, is adopted toform a microscopic quasi-square or rectangular structure on the back surface of the silicon wafer so as to improve the flatness of the microstructure on the back surface of the silicon wafer, so thatthe loss of long-wave photons and the loss of recombination are solved. And meanwhile, the light reflectivity of the back surface of the silicon wafer, the passivation capability of the battery pieceand the electrical property of the battery piece are improved.

Description

technical field [0001] The present disclosure relates to the field of solar cells, in particular to a back polishing method for PERC cells. Background technique [0002] The current PERC process flow is: texturing-diffusion-selective emitter-etching-annealing-backside alumina passivation-coating-screen printing, in which the backside of the PERC cell needs to be etched and back-polished Using hydrofluoric acid, nitric acid and water) to form a wormhole-shaped structure, the back reflectivity of the battery structure formed by this process is 28%-33%, and the low back reflectivity will reduce the reflection of long-wavelength photons, thereby reducing the light effective use. In addition, the wormhole-shaped structure will also lead to uneven field passivation on the back surface, thereby increasing the minority carrier recombination probability on the back surface and reducing the conversion efficiency of solar cells. [0003] How to improve the light reflection on the bac...

AI Technical Summary

Problems solved by technology

In order to improve the reflectivity of the back of the battery, alkali polishing is used in the industry - adding water to potassium hydroxide or sodium hydroxide, which can replace acid polishing under high temperature conditions. Alkali polishing can achieve a high reflectivity of 50%, but alkali polishing needs to be replaced. Some acid polishing machines, and alkali polishing requires an additional oxidation process, as well as an increase in the reflectivity of the back, which will lead to a decrease in the efficiency of the back of the double-sided battery

[0004] In order to improve the reflectivity of the etched backside and at the same time take into account the power generation efficiency of the backside of the double-sided battery, measures to increase the weight reduction are adopted to increase the corrosion depth. However, because acid polishing is isotropic corrosion, only by increasing the reduction Heavy, defects will form in some areas of the back surface, resulting in severe recombination centers

Therefore, although this method can achieve high reflectivity on the back, it will also increase the recombination of electrons on the back of the battery, and the two cannot be taken into account at the same time.

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