Solution for increasing wafer sheet resistance and/or photovoltaic cell power density level
View Patent ↗Treating thin film amorphous or mono- or multi-crystalline silicon wafer substrate for use in a photovoltaic cell, the wafer substrate having at least one of a pn- or np junction and a partial phosphosilicate or borosilicate glass layer on a top surface of the wafer substrate, to increase at least one of (a) the sheet resistance of he wafer and (b) the power density level of the photovoltaic cell made from said wafer. The treatment solution being an acidic treatment solution of a buffered oxide etch (BOE) solution of at least one tetraalkylammonium hydroxide, acetic acid, at least one non-ionic surfactant, at least one metal chelating agent, a metal free source of ammonia, a metal free source, of fluoride ions, and water, mixed with an oxidizer solution and optionally water.
1. A method of treating a thin film amorphous or mono- or multi-crystalline silicon wafer substrate for use in a photovoltaic cell, the wafer substrate having at least one of a pn- or np junction and a partial phosphosilicate or borosilicate glass layer on a top surface of the wafer substrate, to increase at least one of (a) the sheet resistance and (b) the power density of the photovoltaic cell, the method comprising contacting the wafer substrate with an acidic treatment solution for a time and at a temperature sufficient to increase at least one of (a) the sheet resistance of the wafer and (b) the power density of the photovoltaic cell made from said wafer, the acidic treatment solution comprising:
a buffered oxide etch (BOE) solution of:
from about 0.1 to about 20% by weight of at least one tetraalkylammonium hydroxide,
from about 0.1 to about 5% by weight acetic acid,
from about 0.1 to about 5% by weight of at least one non-ionic surfactant,
about 0.1 to about 5% by weight of at least one metal chelating agent,
from about 0.1 to about 20% by weight of a metal free source of ammonium ions,
from about 0.01 to about 20% by weight of a metal free source of fluoride ions,
balance water to 100%,
mixed with a solution of oxidizer and optionally water in a ratio of oxidizer solution /water/BOE solution of 0.01-10/0-100/1.
2. A method according to claim 1 wherein the treatment occurs at a temperature of from about 20° to about 70° C.
3. A method according to claim 1 wherein BOE solution has a pH of from about 3 to about 6.
4. A method according to claim 3 wherein the BOE solution has a pH of from about 4.3 to about 5.
5. A method according to claim 1 wherein the oxidizer solution comprises hydrogen peroxide.
6. A method according to claim 1 wherein the BOE solution comprises tetramethylammonium hydroxide as the tetraalkylammonium hydroxide, 3,5-dimethylhex -1-yn3-ol as the at least one surfactant, and EDTA as the at least one metal chelating agent, and the oxidizer solution comprises hydrogen peroxide and water.
7. A method according to claim 6 wherein the BOE solution comprises about 3.1% tetramethylammonium hydroxide, about 1.2% acetic acid, about 2.1% HF, about 0.8% 3,5-dimethylhex -1-yn-3-ol about 0.8% ammonium hydroxide, about 0.6% EDTA, about 91.5% water.
8. A method according to claim 7 wherein the BOE solution is mixed with oxidiser solution in a ratio of BOE/water/30% hydrogen peroxide in the range 1/6/0.2-1.0.
9. A method according to claim 7 wherein the BOE solution is mixed with oxidizer solution in a ratio of BOE/water/30% hydrogen peroxide solution of about 1/6/0.8.
10. A method according to claim 7 wherein the BOE solution is mixed with oxidizer solution in a ratio of BOE/water/30% hydrogen peroxide solution of about 1/6/1.
11. A method according to claim 7 wherein the BOE solution is mixed with oxidizer solution in a ratio of BOE/water/30% hydrogen peroxide solution of about 1/6/0.2.
12. A method according to claim 11 wherein the treatment occurs at a temperature of from about 20° to about 70° C.
13. A method according to claim 1 wherein the treatment also improves the efficiency of a photovoltaic cell made from this wafer.
14. An acidic treatment solution for treating a thin film amorphous or mono- or multi-crystalline silicon wafer substrates for use in a photovoltaic cell, the wafer substrate having at least one of a pn- or np junction and a partial phosphosilicate or borosilicate glass layer on a top surface of the wafer substrate, to increase at least one of (a) the sheet resistance of the wafer and (b) the power density of the photovoltaic cell made from said wafer, the acidic treatment solution comprising a mixture of:
a buffered oxide etch (BOE) solution of:
from about 0.1 to about 20% by weight of at least one tetraalkylammonium hydroxide,
from about 0.1 to about 5% by weight acetic acid,
from about 0.1 to about 5% by weight of at least one non-ionic surfactant,
about 0.1 to about 5% by weight of at least one metal chelating agent,
from about 0.1 to about 20% by weight of a metal free source of ammonia ions,
from about 0.01 to about 20% by weight of a metal free source of fluoride ions,
balance water to 100%,
mixed with a solution of oxidizer and optionally water in a ratio of oxidizer solution/water/BOE solution of 0.01-10/0-100/1.
15. An acidic treatment solution according to claim 14 wherein the oxidizer solution comprises hydrogen peroxide.
16. An acidic treatment solution according to claim 14 wherein BOE solution has a pH of from about 3 to about 6.
17. An acidic treatment solution according to claim 16 wherein the BOE solution has a pH of from about 4.3 to about 5.
18. An acidic treatment solution according to claims 14 wherein the BOE solution comprises tetramethylammonium hydroxide as the tetraalkylammonium hydroxide, 3,5-dimethylhex-1-yn-3-ol as the at least one surfactant, and EDTA as the at least one metal chelating agent, and the oxidizer solution comprises hydrogen peroxide and water.
19. An acidic treatment solution according to claim 18 wherein the BOE solution comprises about 3.1% tetramethylammonium hydroxide, about 1.2% acetic acid, about 2.1% HF, about 0.8% 3,5-dimethylhex-1-yn-3-ol about 0.8% ammonium hydroxide, about 0.6% EDTA, about 91.5% water.
20. An acidic treatment solution according to claim 19 wherein the BOE solution is mixed with the oxidiser solution in a ratio of BOE/water/30% hydrogen peroxide solution within the range 1/6/0.2-1.0.
21. An acidic treatment solution according to claim 19 wherein the BOE solution is mixed with oxidizer solution in a ratio of BOE/water/30% hydrogen peroxide solution of about 1/6/0.2.
22. An acidic treatment solution according to claim 19 wherein the BOE solution is mixed with oxidizer solution in a ratio of BOE/water/30% hydrogen peroxide solution of about 1/6/0.8.
23. An acidic treatment solution according to claim 19 wherein the BOE solution is mixed with oxidizer solution in a ratio of BOE/water/30% hydrogen peroxide solution of about 1/6/1.