Additional post-glass-removal processes for enhanced cell efficiency in the production of solar cells

Abstract

A method is provided for the production of solar cells from raw crystalline p-type silicon wafer material. The surface condition prior to SiNx deposition is improved by providing additional process steps following the phosphorous glass removal and prior to the SiNx anti-reflection coating deposition. In one embodiment, the wafer is submitted to a thermal anneal under oxygen atmosphere followed by a wet-chemical oxide removal. The anneal reduces the surface phosphorous concentration by diffusion, reduces lattice defects in the emitter and oxidizes the silicon surface. In another embodiment, both a surface oxide is obtained and subsequently removed with wet chemistry. This sequence allows for an integration of the phosphorous glass removal, the wet-chemical oxidation, and the SiOx removal into a single machine.

Description

FIELD OF THE INVENTION[0001]This invention relates to the process sequence in the production of solar cells from raw crystalline p-type silicon wafer material.[0002]Process tests show that the cell efficiencies obtained with the current production lines can be improved significantly by inserting one or more additional process steps.BACKGROUND OF INVENTION[0003]The process sequence of the existing production lines is shown in FIG. 1. The saw-damage and impurities present on the raw silicon wafers are removed with a wet etching. Simultaneously with this process a defined surface texture is obtained. A phosphorous containing precursor is deposited that serves as the phosphorous source during the emitter diffusion in a horizontal passage furnace. A phosphorous glass layer is formed during diffusion. This layer is removed with wet etching prior to the deposition of a SiNx anti-reflection coating. Front- and back-side metallization is realized by screen printing and firing of metallizatio...

AI Technical Summary

Benefits of technology

[0009]It is, therefore, an object of the present invention to provide an improved process sequence for the production of solar cells from raw crystalline p-type silicon wafer material.

[0011](a) removing any saw-damage on the wafer by a wet-chemical etching process, thereby defining surface texture on the wafer;

Problems solved by technology

The cell efficiency obtained with the process sequence described in FIG. 1 is limited by the surface condition that is obtained after the phosphorous glass removal.