PROCESS FOR THE MANUFACTURE OF SOLAR CELLS

Abstract

The present invention relates to a method for manufacturing a solar cell from a silicon wafer comprising a step of etching the silicon wafer with specific gas mixtures comprising fluorine, hydrogen fluoride, one or more inert gases and optionally one or more a further gases, to silicon wafers produced using said method as well as to the use of said gas mixtures.

Claims

1. A method for manufacturing a solar cell from a silicon wafer comprising a step of etching the silicon wafer with a gas mixture consisting of 0.1 to 20 vol % F.sub.2, 2.5 to 1.000 ppmv HF, optionally a further gas with one or more inert gases being the balance to 100 vol %.

2. The method according to claim 1 wherein the gas mixture consists of 0.5 to 5 vol % F.sub.2, 5 to 100 ppmv HF with one or more inert gases being the balance to 100 vol %.

3. The method of claim 1 wherein the gas mixture consists of 1 to 5 vol % F.sub.2, 10 to 50 ppmv HF with one or more inert gases being the balance to 100 vol %.

4. The method according to claim 1 wherein the step of etching the silicon wafer with the gas mixture is a step of texturing the surface of the solar wafer said step being suitable to increase the efficiency of the solar cell.

5. The method according to claim 1 wherein the one or more inert gas is chosen from N.sub.2 or Ar.

6. The method according to claim 1 wherein the optionally further gas is selected from the group consisting of O.sub.2, N.sub.2O, NO, NO.sub.2, NO.sub.3 and NF.sub.3.

7. The method according to claim 1 wherein the step of etching the silicon wafer with the gas mixture is performed thermally.

8. A method for manufacturing a solar panel wherein two or more solar cells manufactured by the method according to claim 1 are assembled.

9. A solar cell obtained by the process of claim 1.

10. A solar panel obtained by the process of claim 8.

11. A method for texturing the surface of a silicon wafer, the method comprising using a gas mixture with a defined content of HF.

12. The method of claim 11 wherein the gas mixture consists of 0.1 to 20 vol % F.sub.2, 2.5 to 1.000 ppmv HF, optionally a further gas with one or more inert gases being the balance to 100 vol %.

13. The method according to claim 5 wherein the one or more inert gas is nitrogen.

14. The method according to claim 7 wherein the step of etching the silicon wafer with the gas mixture is performed thermally at a temperature from 200 to 400° C.

Description

EXAMPLES

Example 1

Texturing of a Silicon Wafer

[0031] A 200 mm plain silicon wafer without structure is dry etched in a microwave plasma etcher manufactured by Secon Semiconductor Equipment GmbH, Austria. The wafers are weighed before and after etching, the difference in weight indicates the etch rate. The etch depth achieved by the texturing is measured by optical laser measuring and can be performed on a Proforma 200SA (MTI instruments inc.).

[0032] The wafer is placed in the etching chamber and the heater maintained a temperature of 300° C. Thermal etching, i.e. etching with the plasma source being switched off, commences with a gas mixture consisting of 20 vol % F.sub.2, 200 ppmv HF, and N.sub.2 being the balance to 100 vol % at a flow rate of 20 sccm at atmospheric pressure (755 Torr). The thermal etching process is performed for 60 s. A control experiment is conducted using the same parameters as described above using an ultrapure gas mixture consisting of 20 vol % F.sub.2 and 80 vol % N.sub.2 with an HF content of below 1 ppm.

[0033] Etch depth analysis shows that the etch depth achieved with the gas mixture comprising 200 ppmv HF shows an up to fourfold improvement compared to the ultrapure gas mixture comprising 1 ppmv HF.

Example 2

Applying Electrodes to the Treated Wafer

[0034] A silicon wafer treated according to the procedure outlined in example 1 is further processes to apply electrodes as described in EP-A-0 542148. A paste containing silver and, as inorganic binder, lead oxide and silicon dioxide is applied on the front side of the wafer by screen printing according to the desired pattern of the electrode structure. On the back side, a similar electrode paste is applied which further contains aluminium. The wafer is then fired at around 800° C. The pattern is then galvanized in a bath containing silver chloride and sodium thiosulfate.

[0035] The solar cell thus manufactured shows an improved efficiency compared to a solar cell manufactured using untreated silicon wafers.