Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
1997-03-25
2001-08-21
Lam, Cathy (Department: 1775)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
C136S252000, C136S259000
Reexamination Certificate
active
06278053
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to decals and methods for manufacturing decals for use in solar cells. More particularly, the invention relates to decals and methods for manufacturing decals having an antireflective coating and metallization for use in forming a solar cell.
BACKGROUND
Solar cells are semiconductor devices that convert sunlight into electricity. The principle barrier to wider use of solar cells as a source of electrical power is their cost. To lower the cost of manufacturing solar cells, it is important to develop manufacturing methods which involve very few steps and very little handling and which are capable of very high throughput rates.
One method for lowering the manufacturing cost of solar cells is to reduce the number of overall processing steps. Each step requires a considerable amount of handling, resulting in higher labor cost and adding to the risk of reducing yield. Another method for lowering the manufacturing cost is to simplify each processing step.
By way of background, a crystalline silicon solar cell is made by forming a p-n junction on a silicon substrate, applying front and rear electrical contacts to the solar cell, and covering the front surface of the solar cell with an antireflective coating. The metallization step for the front contact, the metallization step for the rear contact, and the antireflective coating step are performed as separate processes, thereby adding complexity and cost. Also, the antireflective coating step is sometimes performed after the metallization step for the front contact, resulting in the antireflective coating covering the front contact. In such a case, another step, to remove portions of the antireflective coating, is required to access the front contact.
In order to increase light trapping and conversion efficiency, a single crystalline silicon solar cell can be textured using a chemical etching process. When etched, such a solar cell substrate reveals pyramid structures which reflect the incident light back into the solar cell. A polycrystalline silicon solar cell, however, cannot be textured by the chemical etching process due to its various crystallographic orientations. One solution to this problem is texturing an antireflective coating placed on a surface of the polycrystalline silicon solar cell. A known method of texturing an antireflective coating is through a two layer chemical vapor deposition process, which is expensive and slow.
Therefore, a need exists for a method for forming electrical contacts and antireflective coatings on solar cells that is simple and inexpensive.
SUMMARY OF THE INVENTION
The present invention features decals and decal methods for forming electrical contacts and antireflective coatings on solar cells. The invention facilitates the production of solar cells, with high device yield and low manufacturing cost, by reducing the demand for labor, by eliminating the need for a specialized equipment, and by providing a simple procedure that can be performed rapidly. The invention is elegant, yet simple, and amenable to automation and mass production.
In one aspect, the invention features a decal for use in forming a solar cell. The decal comprises an antireflective precursor material and a patterned electrically conductive material. At least a portion of the electrically conductive material is disposed adjacent the antireflective precursor material. The antireflective precursor material, which can be textured, can be disposed over a base material. The antireflective precursor material can be one or more layers of paste which form an antireflective coating upon being fired. The base material can be a water-sensitive paper, or a polymer material, or comprise a wax coating. A cover layer can be disposed over the electrically conductive material. Alternatively, the patterned electrically conductive material can be placed over the base material, and the antireflective precursor material can be placed over the electrically conductive material.
In another aspect, the invention features a method of manufacturing a decal for use in forming a solar cell. An antireflective precursor material is formed (e.g., by printing and drying) over a base material. A patterned electrically conductive material is formed (e.g., by printing and drying) over the antireflective precursor material. A cover layer can be formed (e.g., by printing and drying) over the electrically conductive material. Alternatively, the placement of the antireflective precursor material and the electrically conductive material may be reversed.
In another aspect, the invention features a method of manufacturing a decal for use in forming a solar cell. An antireflective precursor material is formed (e.g., by printing and drying) of multiple layers of materials that form a graded layer of antireflective coating. A patterned electrically conductive material is formed (e.g., by printing and drying) adjacent the antireflective precursor material and a cover layer can be formed (e.g., by printing and drying) over the antireflective precursor material and the electrically conductive material.
In another aspect, the invention features a method of forming an antireflective precursor material on a solar cell. A decal having a base material and an antireflective precursor material disposed over the base material is provided. A patterned die is placed in contact with the antireflective precursor material to form a textured pattern in the antirefiective precursor material. The patterned die can be capable of mechanically texturing the antireflective precursor material. The decal is positioned on at least one surface of a solar cell. The decal is processed (e.g., fired) to convert the antireflective precursor material into a textured antireflective coating. In this case, the antireflective precursor is made to be considerably thicker than in other embodiments.
In another aspect, the invention features a method of manufacturing a solar cell using a decal comprising an antireflective precursor and a patterned electrically conductive material disposed adjacent to the antireflective precursor material The decal is placed on at least one surface of the solar cell. The decal is processed to remove organic matter, form an antireflective coating, and form an ohmic contact for the solar cell.
In another aspect, a portion of the decal can be wrapped around at least one edge of the solar cell for contacting a second surface of the solar cell. In one embodiment for this configuration, the patterned electrically conductive material forms a front contact on the first surface of the solar cell and another patterned electrically conductive material forms a rear contact on a second surface of the solar cell. The antireflective precursor is disposed adjacent the front contact. In another embodiment, the patterned electrically conductive material is capable of forming a wraparound contact such that a first portion (e.g. the fingers) of the contact is disposed adjacent a first surface of the solar cell and a second portion (e.g. the busbar) of the contact is wrapped around at least one edge of the solar cell to a second surface of the solar cell. In this embodiment, the antireflective precursor is disposed adjacent the first portion of the contact.
The antireflective precursor can be sprayed onto the base material. In such cases, spraying can be done after the front metal contact is formed on the decal. Alternatively, the antireflective precursor can be printed over the front metal contact after the contact has been printed onto the base material. In such cases, the antireflective precursor can be printed so as not to cover the busbars of the front metal contact or the rear metal contact.
In yet another aspect, the invention features a solar cell assembly and method of forming such an assembly. The assembly comprises a solar cell, a textured antireflective coating and a patterned electrical contact. The textured antireflective coating can be disposed on a first surface of the solar cell. The patterned electrical contact is disposed on the textured
Hanoka Jack I.
Lord Brynley E.
Ma Xinfa
Mrowka Mark T.
Evergreen Solar Inc.
Lam Cathy
Testa Hurwitz & Thibeault LLP
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