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PHOTOVOLTAIC MODULE FABRICATION PROCESS
FIELD OF THE INVENTION 5
This invention relates generally to photovoltaic devices. More specifically, the invention relates to the fabrication of photovoltaic panels. Most specifically, the invention relates to a method by which a large area portion of photovoltaic 1Q material may be fabricated into photovoltaic panels comprised of a plurality of electrically interconnected photovoltaic units.
BACKGROUND OF THE INVENTION
Photovoltaic devices are non-polluting and silent in operation. They are readily adapted to either a centralized, or distributed power generating system and as such, are an attractive alternative to fossil fuels and nuclear power sources. The relatively high cost of photovoltaic power has 20 been a historical limitation upon its use; however, high volume processes for the preparation of thin film semiconductor devices have now dramatically decreased the cost of photovoltaic materials. It is now possible to manufacture thin film photovoltaic devices in a continuous, roll-to-roll 25 processor. U.S. Pat. No. 4,485,125, the disclosure of which is incorporated herein by reference, describes one such process.
The output of a typical high volume process comprises a large area roll of substrate material coated with a multiplicity 30 of semiconductor layers thereupon. In order to fabricate a practical device, it is generally necessary to convert the large area material output by the roll-to-roll process into a plurality of discrete devices optimized for particular voltage and power requirements. Processing steps typically include 35 cutting the large area material into smaller area portions, testing the individual portions, applying current collecting structures such as collector grids and bus bars to the individual devices, assembling the devices into power generating modules, and affixing protective and/or support struc- 40 tures to the modules. These subsequent fabrication steps can be labor intensive, and they can possibly compromise the efficiency, and even the operability, of the resultant devices by introducing short circuits, high resistance contacts, and other defects of a like nature. It will thus be appreciated that 45 the processing of the large area material can be a bottleneck which negates many of the benefits of high volume production.
There is a need for a methodology wherein large area 5Q bodies of photovoltaic material may be efficiently fabricated into devices specifically adapted for particular end uses. The present invention provides a production line method for device fabrication which is highly efficient, both in terms of required labor, time and the economical use of photovoltaic material. These and other advantages of the present invention will be readily apparent from the drawings, discussion and description which follow.
BRIEF DESCRIPTION OF THE INVENTION
There is disclosed herein a method for the manufacture of a photovoltaic panel from a large area of photovoltaic material of the type comprising a substrate electrode, a photovoltaic body disposed atop, and in electrical communication with the substrate electrode, and a transparent 65 electrically conductive top electrode disposed atop the photovoltaic body. The method includes the steps of dividing the
material into a plurality of individual slabs, each comprising a portion of the substrate electrode, photovoltaic body, and top electrode; and isolating a photoactive area within each slab which is substantially free of any defects which could establish a short circuit current path between the top electrode and the substrate electrode of the slab. The method further includes passivating any defect regions which may be present within the photovoltaic area, affixing a first bus bar tape to the slab in electrical communication with the substrate electrode, affixing a second bus bar tape to the slab so that it is electrically insulated from the substrate electrode, providing at least one current collecting member which is coated with an electrically conductive adhesive, and bonding the member to the top electrode of the slab and to the second tape so as to establish electrical communication therebetween. The method also includes the step of applying a transparent, protective coating to the slab so as to cover the top electrode and current collecting wire. In further processing steps, a plurality of the slabs are electrically interconnected in either a series or parallel relationship; a flexible, transparent, electrically insulating encapsulant is affixed to a front surface of each photovoltaic slab in a manner which leaves the back surface of each slab free of the encapsulant; and, a common backing plate is affixed to the back surface of each of the slabs of the plurality.
The step of isolating the photovoltaic area may comprise scribing away the photovoltaic body and top electrode portion of the slab in a region which defines a perimeter of the protected area, as for example by a laser scribe, water jet scribe, or chemical etching technique. Alternatively, the photoactive area may be isolated by cutting away those edges of the slab which were defined when the slab was divided from the web, through the use of a cutting technique which prevents shards of the top electrode from creating a short circuit current path between the top electrode and the substrate electrode of the slab. Passivation of defects within the photoactive area is preferably accomplished by a biasetch passivation process. The bus bar tapes may be individually affixed to each slab, or a preformed, interconnected bus bar tape may be affixed to a plurality of slabs simultaneously whereby the steps of tape affixation and unit interconnection are carried out concomitantly. In some instances it has been found advantageous to ultrasonically bond the first tape to the substrate.
In some instances, the backing plate may comprise a preformed backing plate particularly configured for a specific end-use application. In other instances, the backing plate may be bent, drilled, or otherwise formed subsequent to its affixation to the photovoltaic slabs.
The present invention also includes a particular design of bus bar tape configured to be affixed to a plurality of distinct slabs of photovoltaic material, and to electrically interconnect those slabs in a preselected series or parallel relationship.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic depiction of a web of photovoltaic material which has been divided into a plurality of individual slabs;
FIG. 2 is a cross-sectional view of one of the slabs;
FIG. 3a is a top plan view of one of the slabs having a photoactive area thereof isolated;
FIG. 3b is a cross-sectional view of the slab of FIG. 3a taken along line 3—3;
FIG. 4a is a cross-sectional view of a portion of a slab
having its photoactive area isolated by a back side severing process;
FIG. 4b is a cross-sectional view of a portion of a slab having its photoactive area isolated by a front surface severing process; 5
FIG. 5 is a top plan view of a slab with bus bar tapes affixed thereto;
FIG. 6 is a cross-sectional view of the slab of FIG. 5 taken along lines 6—6; 10
FIG. 7 is an illustration of one embodiment of tapered bus bar tapes in accord with the present invention;
FIG. 8 is top plan view of a slab having current collecting wires affixed to the second bus bar tapes thereof;
FIG. 9a is a cross-sectional view of one embodiment of 15 current collecting wire;
FIG. 9b is a cross-sectional view of another embodiment of current collecting wire;
FIG. 10 is a cross-sectional view of the device of FIG. 8 2Q taken along lines 10—10;
FIG. 11 is a top plan view of three electrically interconnected photovoltaic slabs;
FIG. 12 is an enlarged view of a portion of two of the slabs of FIG. 11 that illustrate the interconnection thereof; 25
FIG. 13 is an enlarged view of a portion of two electrically interconnected slabs which include tapered bus bars;
FIG. 14a is a bottom plan view of a portion of one of the photovoltaic slabs illustrating a back side terminal strip;
FIG. 14b is a cross-sectional view of the device of FIG. 14a taken along lines 14—14;
FIG. 15 is a cross-sectional view of three photovoltaic slabs having a front surface encapsulant member affixed thereto; 35
FIG. 16 is a cross-sectional view of three photovoltaic slabs generally similar to those of FIG. 15 and further including a backing plate afExed thereto;
FIG. 17 is a cross-sectional depiction of the photovoltaic slabs of 40
FIG. 16 further illustrating one manner in which the backing plate may be formed to provide a roofing panel;
FIG. 18 is a depiction of three photovoltaic slabs electrically interconnected by a preformed bus bar tape in accord 45 with the present invention;
FIG. 19 is a cross-sectional view of the bus bar tape of FIG. 18 taken along lines 19—19;
FIG. 20 is a cross-sectional view of the bus bar tape of FIG. 18 taken along lines 20—20; 50
FIG. 21 is a cross-sectional view of the bus bar tape of FIG. 18, taken along lines 21—21;
FIG. 22 is a schematic depiction, partially in cross-section of an apparatus for coating a current-collecting wire; and
FIG. 23 is a cross-sectional view of an orifice which is employed in the apparatus of FIG. 22.
Detailed Description of the Invention
The present invention relates to the efficient manufacture of high quality photovoltaic panels from a starting material which is a large area photovoltaic material generally in the form of a flexible, elongated web. As was described hereinabove, it is now possible to deposit layers of high quality 65 semi-conductor material upon a flexible substrate in a continuous, plasma energized, roll to roll deposition process.
The output of such processes typically comprises a coated web of substrate material which is approximately one foot wide and up to several hundred feet long. This coated web may be considered to be one single, very large area photovoltaic cell, and prior to its use it is desirable to process it into smaller area devices to suit particular applications.
FIG. 1 depicts a large area web of photovoltaic material 2 which has been subdivided into a plurality of smaller area slabs 4A-4C. The web is typically formed upon a stainless steel, or other metallic, substrate base; and, the subdividing is typically accomplished by shearing, slitting, sawing, or any other such method as is well known in the sheet metal working art. In some instances, as will be detailed hereinbelow, the substrate may comprise a polymer, a sheet of glass or ceramic, or another such electrically insulating material, with an electrically conductive electrode layer supported thereupon.
Referring now to FIG. 2, there is shown a cross-sectional view of a typical slab 4 as employed in the present invention. This slab includes a substrate electrode 8, a photovoltaic body 12 disposed atop, and in electrical communication with, the substrate electrode 8, and a top electrode 16 disposed atop the photovoltaic body 12. The photovoltaic body, as is known in the art, operates to absorb incident photons and provide a photocurrent in response thereto. The current is collected at the substrate electrode 8 and the top electrode 16. In one preferred device, the substrate electrode 8 is a metallic electrode, and in the illustrated embodiment, the substrate electrode 8 comprises a sheet of stainless steel. As is known in the art, the substrate electrode may include additional layers to enhance its reflectivity, modify its texture or control its current carrying capacity. In some embodiments, the substrate electrode is comprised of a thin, electrically conductive layer which is supported upon an insulating substrate. All of the foregoing are encompassed within the disclosure of a substrate electrode. It will be appreciated that there are a variety of photovoltaic materials which may be employed in the practice of the present invention. One particularly preferred group of materials includes the thin film alloys of Group IV semiconductors, particularly the disordered alloys of silicon and germanium. However, it is to be understood that the present invention is not limited to such materials and may be practiced with equal advantage with other photovoltaic materials, including thin film materials such as CdS, CuInSe2, organic materials, and the like.
In the illustrated embodiment, photovoltaic body 12 preferably comprises one or more triads of p-i-n configuration, wherein a layer of substantially intrinsic semiconductor material 5 is interposed between oppositely doped semiconductor layers 7, 9. A number of such triads may be stacked in a series relationship to enhance the efficiency of the device.
The top electrode 16 is fabricated from a transparent, electrically conductive material, typically a transparent conductive oxide (TCO) such as indium oxide, tin oxide, zinc oxide, cadmium oxide, and various combinations of the foregoing. It should be noted that in the various figures accompanying this disclosure, the vertical dimensions of the various layers have been preferentially distorted to better illustrate the semiconductor and electrode layers. The substrate electrode usually comprises a body of stainless steel of approximately 5 mils thickness, while the total thickness of the photovoltaic body 12 is less than 1 micron, as is the thickness of the top electrode 16.
It has been found that the step of dividing the web into a