Method for producing a solar cell
The embodiments relate to a method for producing a solar cell having a rear-side contact with a tunnel barrier. A monocrystalline wafer having a front side and a rear side may be provided with silicon and a dopant. A tunnel barrier is produced on the wafer, and a polycrystalline or amorphous layer is deposited on the tunnel barrier. The polycrystalline or amorphous layer includes silicon and a dopant. The polycrystalline or amorphous layer is removed on the front side by gas-phase etching.
1 . A method for producing a solar cell having a rear-side contact with a tunnel barrier, the method comprises:
providing a monocrystalline wafer having a front side and a rear side, the wafer comprising silicon and a dopant;
producing a first tunnel barrier on the front side of the wafer and producing a second tunnel barrier on the rear side of the wafer;
depositing a polycrystalline or amorphous layer on the first and second tunnel barriers, wherein the polycrystalline or amorphous layer comprises silicon; and
removing the polycrystalline or amorphous layer on the front side by gas-phase etching, wherein an etchant for the gas-phase etching comprises F 2 ,
wherein for the gas-phase etching, the wafer rests on a conveyor belt and
wherein the gas-phase etching is stopped upon reaching the first tunnel barrier at the front side.
2 . The method according to claim 1 , wherein for the gas-phase etching, the wafer is heated to a temperature from about 120° C. to about 260° C.
3 . The method according to claim 2 , wherein for gas-phase etching, the wafer is heated to a temperature from about 190° C. to about 200° C.
4 . The method according to claim 1 , wherein the gas-phase etching is carried out with a gas phase, and the F 2 concentration is about 20% to about 30%.
5 . The method according to claim 4 , wherein the gas-phase etching is carried out with a gas phase which is supplied with F 2 at a flow rate from about 5 slm to about 7 slm.
6 . The method according to claim 1 wherein the gas-phase etching is carried out with a gas phase which is supplied with N 2 at a flow rate from about 0.75 slm to about 1.25 slm.
7 . The method according to claim 6 , wherein the gas-phase etching is carried out between about 15 sec. and about 35 sec.
8 . The method according to claim 1 , wherein the gas-phase etching is carried out in a gas phase which has a pressure from about 960 mbar to about 1040 mbar.
9 . The method according to claim 1 , wherein the gas-phase etching is continued when reaching the tunnel barrier at the front side so that a surface patterning is produced on the front side of the wafer.
10 . The method according to claim 1 , further comprising:
diffusing boron into the wafer; and
removing the boron-containing layer on the rear side.
11 . The method according to claim 10 , wherein the borosilicate glass layer forming when boron is diffused on the rear side and/or on the front side of the wafer is removed in a wet chemical process.
12 . The method according to claim 10 , wherein the tunnel barrier has a thickness from about 1 nm to about 5 nm.
13 . The method according to claim 12 , wherein the polycrystalline or amorphous layer has a thickness from about 30 nm to about 300 nm.
14 . The method according to claim 13 , wherein the tunnel barrier comprises SiO x wherein 1≤x≤2.
15 . The method according to claim 1 , wherein the polycrystalline or amorphous layer further contains at least one dopant.