ACIDIC ETCHING PROCESS FOR SI WAFERS
The present invention relates to a method for acidic surface etching of a silicon wafer, such as those used for solar cells, comprising contacting at least one surface of a silicon wafer as cut with an acidic etching agent, provided that the wafer is, prior to the acidic etching, not subjected to an alkaline etching step or process. Further, the present invention is directed to Si wafer, photovoltaic cells, PERC photovoltaic cells and solar modules produced according to the method of the present invention.
1 . A method for acidic etching of a Si wafer, comprising contacting at least one surface of a Si wafer as cut with an acidic etching agent with the proviso that the Si wafer is, prior to the acidic etching, not subjected to an alkaline etching step or process.
2 . The method according to claim 1 , wherein the Si wafer is a monocrystalline or a quasi-monocrystalline Si wafer.
3 . The method according to claim 1 , wherein the Si wafer is saw-damaged and/or cleaned prior to etching.
4 . The method according to claim 1 , wherein the acidic etching agent is an aqueous solution of an acid selected from the group consisting of HF, HCl, HBr, HI, AcOH, HNO 3 , H 3 PO 4 , H 2 SO 4 , citric acid, oxalic acid, lactic acid and mixtures Thereof.
5 . The method according to claim 1 , wherein the acid etching agent is an aqueous solution containing a mixture of AcOH, HNO 3 and HF.
6 . The method according to claim 5 , wherein the solution comprises AcOH (98 wt.-% in water), HNO3 (69 wt.-% in water), and HF (49 wt.-% in water), wherein the volume ratio of AcOH:HNO 3 :HF is 10:6:4.
7 . The method according to claim 1 , wherein the acid etching agent is a mixture of HNO 3 and HF.
8 . The method according to claim 7 , wherein the mixture consists of HNO 3 (67-70 wt.-% in water) and HF (49 wt.-% in water), wherein the volume ratio of HNO 3 :HF gradually changes over time from about 6:1 to 10:1 at the start to a final volume ratio of 2:1 to 1.2:1
9 . The method according to claims 1 to 8 , wherein the acidic etching agent is contacted with at least one surface of the Si wafer as cut once or several times.
10 . The method according to claim 1 , wherein the step of contacting an acid etching agent with at least one surface of the Si wafer comprises dipping, spraying, coating or printing.
11 . The method according to claim 1 , wherein the method further comprises generating a SiO 2 /SiN x passivation layer or an Al 2 O 3 /SiN x passivation layer on one surface of the Si wafer after the acidic etching process.
12 . The method according to claim 1 , wherein the method further comprises an alkaline etching process, preferably an alkaline texture etching process, conducted after the acidic etching of the at least one Si wafer surface and optionally after generating the SiO 2 /SiN x passivation layer or Al 2 O 3 /SiN x passivation layer on one surface of the Si wafer, or optionally after the laser ablation process to texture etch the front surface and the ablated pattern at the wafer rear-side.
13 . The method according to claim 1 , wherein the method further comprises the steps of:
doping the Si wafer with phosphorus in order to modulate the electrical properties of the wafer.
14 . The method according to claim 1 , wherein the method is a part of an in-line process.
15 . Si wafer obtainable accordingly to the method of claim 1 .
16 . Solar cell comprising the Si wafer of claim 14 .
17 . Solar module comprising a solar cell according to claim 15 .