WO2011160257A1

WO2011160257A1 - Method and apparatus for bonding composite solar cell structure

Info

Publication number: WO2011160257A1
Application number: PCT/CN2010/000932
Authority: WO
Inventors: Yong Shen; Yuqiang Li; Shuangyan Xu; Genbao Xu; Charles Gay
Original assignee: Applied Materials, Inc.
Priority date: 2010-06-24
Filing date: 2010-06-24
Publication date: 2011-12-29

Abstract

A method and apparatus for bonding a composite solar cell structure is provided. In one embodiment, the apparatus for bonding a solar cell structure includes a preparation module and a bonding module. The preparation module is configured to prepare the composite solar cell structure by placing a bonding material over a device substrate having solar cell devices formed thereon and placing a back substrate over the bonding material and the device substrate, wherein the bonding material is an asphalt-based and/or tar-based material. The bonding module is configured to apply heat and pressure to the composite solar cell structure to bond the back substrate to the device substrate.

Description

METHOD AND APPARATUS FOR BONDING COMPOSITE

SOLAR CELL STRUCTURE

BACKGROUND OF THE INVENTION

Field of the invention

[0001] The present invention relates to a method and apparatus for bonding a composite solar cell structure and, more particularly, to a method and apparatus for bonding a composite solar cell structure using an asphalt-based and/or tar-based bonding material.

Description of the prior art

[0002] Photovoltaic devices (PV) or solar cells are devices which convert sunlight into direct current (DC) electrical power. PV or solar cells typically have one or more p-i-n junctions. Each p-i-n junction includes a p-type layer, an intrinsic type layer, and a n-type layer. When the p-i-n junction of the PV cell is exposed to sunlight (consisting of energy from photons), the sunlight is converted to electricity through the PV effect. PV solar cells may be tiled into larger modules. PV modules are created by connecting a number of PV solar cells and are then joined into panels with specific frames and connectors.

[0003] Typically, a PV solar cell includes active regions and a transparent conductive oxide (TCO) film disposed as a front electrode and/or as a back electrode. The photoelectric conversion unit includes a p-type silicon layer, a n-type silicon layer, and an intrinsic type (i-type) silicon layer sandwiched between the p-type and n-type silicon layers. Several types of silicon films including microcrystalline silicon film ^c-Si), amorphous silicon film (a-Si), polycrystalline silicon film (poly-Si) and the like may be utilized to form the p-type, n-type, and/or i-type layers of the photoelectric conversion unit. The backside contact may contain one or more conductive layers. There is a need to improve the forming process of a PV solar cell that has good interfacial contact, low contact resistance and provides a high overall electrical device performance of the PV solar cells.

[0004] Conventionally, during PV solar cell manufacture, solar cell devices such as the transparent conductive oxide, the active regions, the backside contact and the like are built on a substrate thus becoming a device substrate. Furthermore, the device substrate is bonded to a back substrate using a bonding material. [0005] To bond a solar cell composite structure, the device substrate, the back substrate, and the bonding material are transported into a bonding module to bond the back substrate to the device substrate. During the bonding process, the bonding material, such as Polyvinyl Butyral (PVB) or Ethylene Vinyl Acetate (EVA), is sandwiched between the back substrate and the device substrate. Heat and pressure are applied to the structure to form a bonded and sealed device using various heating elements and other devices found in the bonding module. The device substrate, the back substrate, and the bonding material thus form a composite solar cell structure that at least partially encapsulates the active regions of the solar cell device.

[0006] Polyvinyl Butyral (PVB) or Ethylene Vinyl Acetate (EVA) is widely used in an encapsulation as the bonding material. However, PVB materials are expensive. Additionally, due to high water absorption, PVB requires special storage and process environment for controlling humidity and temperature, further driving up the cost to use PVB.

[0007] Moreover, to ensure the quality of the bonding of the composite solar cell structure, the composite solar cell structure may be further put into a separate autoclave module to remove trapped gasses in the bonded structure and assure that a sufficient bond is formed. During the autoclaving process, a bonded solar cell structure is placed in the autoclave module where heat is delivered to reduce the amount of trapped gas and improve the properties of the bond between the device substrate, the back substrate, and the bonding material. The processes performed in the autoclave are also useful to assure that the stress in the glass and bonding layer (e.g., PVB layer) are more controlled to prevent future failures of the hermetic seal or failure of the glass due to the stress induced during the bonding process. Typically, it may be desirable to heat the solar cell composite structure to a temperature that causes stress relaxation in one or more of the components therein.

[0008] Thus, between the special handling requirements, the expensive raw material cost and the need for autoclaving (an autoclave tool cost, energy cost and time required to autoclave), the use of PVB encapsulation poses a significant cost component for both the price of the solar cell devices and the equipment utilized to fabricate the same.

[0009] With high traditional energy source prices, a need exists for a low cost method of producing electricity using a low cost solar cell device, to help drive down the cost per watt in solar module manufacturing. Therefore, there is a need for bonding materials with advantages of low cost, good moisture resistance and without an expensive autoclaving process requirement, to reduce cost and improve device yield in solar module manufacturing. SUMMARY OF THE INVENTION

[0010] The present invention generally relates to a method and apparatus for bonding a composite solar cell structure. More particularly, the invention provides a method and apparatus for bonding a composite solar cell structure using an asphalt-based and/or tar-based bonding material.

[0011] One aspect of the invention generally provides an apparatus for bonding a composite solar cell structure.

[0012] In one embodiment, an apparatus for bonding a solar cell structure includes a preparation module and a bonding module. The preparation module is configured to prepare the composite solar cell structure by placing a bonding material over a device substrate having solar cell devices formed thereon and placing a back substrate over the bonding material and the device substrate, wherein the bonding material is an asphalt-based and/or tar-based material. The bonding module is configured to apply heat and pressure to the composite solar cell structure to bond the back substrate to the device substrate.

[0013] Another aspect of the invention generally provides a method for bonding a composite solar cell structure.

[0014] In one embodiment, a method for bonding a composite solar cell structure includes preparing the composite solar cell structure and applying heat and pressure to the composite solar cell structure to bond the back substrate to the device substrate. Preparing the composite solar cell structure includes preparing a device substrate having solar cell devices formed thereon, placing a bonding material over the device substrate wherein the bonding material is an asphalt-based and/or tar-based material and placing a back substrate over the bonding material and the device substrate.

[0015] Another aspect of the invention generally provides a composite solar cell structure. In one embodiment of the invention, the composite solar cell structure includes a device substrate having solar cell devices formed thereon, a bonding material formed over the device substrate wherein the bonding material is an asphalt-based and/or tar-based material, and a back substrate formed over the bonding material and the device substrate, wherein the back substrate is bonded to the device substrate using the bonding material.

[0016] In summary, the method and apparatus according to the invention is used for bonding a composite solar cell structure. More particularly, the method and apparatus according to the invention bonds the composite solar cell structure using an asphalt-based and/or tar-based bonding material. Compared with typically used bonding materials such as PVB or EVA, the asphalt-based and/or tar-based bonding material is less expensive and has good moisture resistance, thus it costs less and the device yield is improved.

[0017] Moreover, since the bonding established in the bonding module provides sufficient encapsulation to the composite solar cell structure, separate autoclaving process is no longer needed and the cost regarding autoclaving (e.g., autoclave tool cost, energy cost and time consumption) is significantly reduced.

BRIEF DESCRIPTION OF THE APPENDED DRAWINGS

[0018] The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:

[0019] FIG. 1 is a plan view of an apparatus for bonding a composite solar cell structure according to an embodiment of the invention.

[0020] FIG. 2 is a simplified schematic diagram of a solar cell device formed by a solar cell production system.

[0021] FIG. 3 is a plan view that schematically illustrates an example of the rear surface of the formed solar cell.

[0022] FIG. 4 is a flow diagram depicting a method for bonding a composite solar cell structure according to a preferred embodiment of the invention.

[0023] FIG. 5 is a flow diagram depicting sub-steps of the preparing step in FIG. 4.

[0024] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.

DETAILED DESCRIPTION

[0025] Embodiments of the invention generally provide a method and apparatus for bonding a composite solar cell structure using an asphalt-based and/or tar-based bonding material, which has the advantage of lowering the cost and increasing device yield without an expensive autoclaving process requirement.

[0026] FIG. 1 is a plan view of an apparatus 100 for bonding a composite solar cell structure according to an embodiment of the invention. In one embodiment, the apparatus 100 for bonding a composite solar cell structure is a portion (for example, a lamination module) of a solar cell production system (not shown) which is used for forming a solar cell device. One example of a system which may be adapted to benefit from the invention is described in U.S. Patent Publication No. 2009/0188603 filed January 23, 2009, which is incorporated by reference in its entirety. Details of the apparatus 100 are described further below.

[0027] FIG. 2 is a simplified schematic diagram of a solar cell device 300 that can be formed by aforesaid solar cell production system. As shown in FIG. 2, the solar cell 300 may include a substrate 302, such as a glass substrate, polymer substrate, metal substrate, or other suitable substrate, with thin films formed thereover. While a single junction type solar cell is illustrated in FIG. 2 this configuration is not intended to limit the scope of the invention described herein.

[0028] The solar cell 300 further includes a first transparent conducting oxide (TCO) layer 310 (e.g., zinc oxide (ZnO), tin oxide (SnO)) formed over the substrate 302, a p-i-n junction 320 formed over the first TCO layer 310, a second TCO layer 340 formed over the first p-i-n junction 320, and a back contact layer 350 formed over the second TCO layer 340. In one configuration, the first p-i-n junction 320 may comprise a p-type amorphous silicon layer 322 , an intrinsic type amorphous silicon layer 324 formed over the p-type amorphous silicon layer 322 , and an n-type microcrystalline silicon layer 326 formed over the intrinsic type amorphous silicon layer 324. Referring additionally to a plan view of FIG. 3 that schematically illustrates an example of the rear surface of the formed solar cell 300, the solar cell 300 includes the substrate 302, the solar cell device elements (e.g., reference numerals 310 - 350), one or more internal electrical connections (e.g., side buss 355, cross-buss 356), a layer of bonding material 360, a back substrate 361, and a junction box 370.

[0029] The junction box 370 may generally contain two junction box terminals 371, 372 that are electrically connected to portions of the solar cell 300 through the side buss 355 and the cross-buss 356, which are in electrical communication with the back contact layer 350 and active regions of the solar cell 300.

[0030] To avoid confusion relating to the actions specifically performed on the substrates 302 in the discussion below, a substrate 302 having one or more of the deposited layers (e.g., reference numerals 310 - 350) and/or one or more internal electrical connections (e.g., side buss 355 , cross-buss 356) disposed thereon is generally referred to as a device substrate 303. Similarly, the device substrate 303 that has been bonded to a back substrate 361 using a bonding material 360 is referred to as a composite solar cell structure 304.

[0031] In one embodiment of the invention, the bonding material 360 formed over the device substrate 303 is an asphalt-based and/or tar-based material, such as a Styrene-Butyl-Styrene material. Additionally, the back substrate 361 is bonded to the device substrate 303 using the bonding material 360, in one embodiment, using apparatus and method described below.

[0032] Referring back to FIG. 1, the apparatus 100 for bonding the composite solar cell structure 304 includes a preparation module 102 and a bonding module 104. In an embodiment, the apparatus 100 is used for bonding the back substrate 361 onto the device substrate 303. In one embodiment, the device substrate 303 is formed by other processing modules of the solar cell production system and is transported to the preparation module 102 of the apparatus 100. In the bonding process, the bonding material 360 is prepared to be placed between the back substrate 361 and the deposited layers on the device substrate 303 to form a hermetic seal to prevent the environment from attacking the solar cell during its life.

[0033] In an embodiment, the preparation module 102 is configured to prepare the composite solar cell structure 304. As shown in FIG. 1, the preparation module 102 includes a material preparation module 102 A, a glass loading module 102B, and a glass cleaning module 102C. ¾.

[0034] The bonding material 360 is prepared in the material preparation module 102 A and placed over the device substrate 303. The back substrate 361 is loaded into the loading module 102B and washed by the cleaning module 102C, and the back substrate 361 is then placed over the bonding material 360 and the device substrate 303.

[0035] In one embodiment according to the invention, the bonding material 360 is an asphalt-based and/or tar-based material. For example, the bonding material 360 can be made of a Styrene-Butyl-Styrene material. Compared with conventional PVB or EVA bonding materials, the asphalt-based and/or tar-based bonding materials are significantly less expensive, and have good moisture resistance, and thus help drive down the cost of solar module manufacturing.

[0036] After the composite solar cell structure 304 is prepared, the composite solar cell structure 304 is transported to the bonding module 104. In an embodiment of the invention, the bonding module 104 is configured to apply heat and pressure to the composite solar cell structure 304 to bond the back substrate 361 to the device substrate 303. In the bonding module 104, the bonding material 360, such as Styrene-Butyl-Styrene (SBS), is sandwiched between the back substrate 361 and the device substrate 303. Heat and pressure are applied to the composite solar cell structure 304 to form a bonded and sealed device using various heating elements and other devices found in the bonding module 104.

[0037] In one embodiment, the bonding module 104 heats the composite solar cell structure 304 up to at least 100 degrees Celsius and holds the composite solar cell structure 304 at least about 100 degrees for at least about ten minutes. Thus, sufficient bonding of the composite solar cell structure 304 can be established using the Styrene-Butyl-Styrene (SBS) bonding material 360.

[0038] In one embodiment, in the bonding module 104, pressure may be applied forcing the back substrate 361 against the device substrate 303 utilizing mechanical means such as a press, piston or rollers. Alternatively, a vacuum may be established within the bonding module 104 to pull the back substrate 361 and device substrate 303 together. In one embodiment, the mechanical and/or vacuum develops a force of about 14.5 psi on the surface of the back substrate 361 to urge the back substrate 361 and device substrate 303 together.

[0039] In one embodiment, at least one hole formed in the back substrate 361 remains at least partially uncovered by the bonding material 360 to allow portions of the cross-buss 356 or the side buss 355 to remain exposed so that electrical connections of these regions of the solar cell structure 304 with the junction box 370 can be made in future processes. _*

[0040] It is worth noting that since the bonding established in the bonding module 104 using the asphalt-based and/or tar-based bonding material is sufficient for the composite solar cell structure 304, there is no need for separate autoclaving process, which was required when using conventional PVB or EVA as the bonding material. Accordingly, the cost regarding autoclaving (e.g., autoclave tool cost, energy cost and time consumption) is eliminated.

[0041] After the composite solar cell structure 304 is bonded in the bonding module 104, the composite solar cell structure 304 is transported to other processing modules of the solar cell production system for follow-up processes, so as to finish a complete solar cell device.

[0042] Referring to FIGS. 4 and 5, FIG. 4 is a flow diagram depicting a method for bonding a composite solar cell structure according to a preferred embodiment of the invention, while FIG. 5 is a flow diagram depicting sub-steps of the preparing step in FIG. 4. The method of the invention can be practiced, but not limited to, in the above-mentioned apparatus 100 for bonding the composite solar cell structure.

[0043] Please refer to FIG. 4 along with FIGS. 2 and 3. Firstly, step 500 is performed to prepare a composite solar cell structure 304. In one embodiment, step 500 further includes sub-steps 502, 504 and 506, as shown in FIG. 5. In sub-step 502, a device substrate 303 having solar cell devices formed thereon is provided. As mentioned above, the device substrate 303 may be prepared by other processing modules of the solar cell production system.

[0044] Then sub-step 504 is performed to place a bonding material 360 over the device substrate 303. In one embodiment of the invention, the bonding material 360 is an asphalt-based and/or tar-based material. For example, the bonding material 360 can be made of a Styrene-Butyl-Styrene material.

[0045] After sub-step 504 is complete, sub-step 506 is performed to place a back substrate 361 over the bonding material 360 and the device substrate 303. In practice, the preparation step 500 including sub-steps 502, 504 and 506, may be performed in the preparation module 102 mentioned above to prepare the composite solar cell structure 304.

[0046] After the composite solar cell structure 304 is prepared, step 510 is performed to apply heat and pressure to the composite solar cell structure 304 to bond the back substrate 361 to the device substrate 303. As mentioned above, in step 12, the bonding material 360, such as Styrene-Butyl-Styrene (SBS), is sandwiched between the back substrate 361 and the device substrate 303, and heat and pressure are applied to the composite solar cell structure 304 to form a bonded and sealed device using various heating elements and other devices found in the bonding module 104. The heating elements may be in the form of IR lights, resistive heaters, and the like.

[0047] In one embodiment, in step 510, the composite solar cell structure 304 is heated up to at least 100 degrees Celsius and the composite solar cell structure 304 is held at least about 100 degrees for at least about ten minutes. Thus, sufficient bonding of the composite solar cell structure 304 can be established using the Styrene-Butyl-Styrene (SBS) bonding material 360.

[0048] In one embodiment, in step 510, pressure may be applied forcing the back substrate

361 against the device substrate 303 utilizing mechanical means such as a press, piston or rollers.

Alternatively, a vacuum may be established within the bonding module 104 to pull the back substrate 361 and device substrate 303 together. In one embodiment, the vacuum and/or mechanical means develops a force at least about 14.5 psi, on the surface of the back substrate 361 to urge the back substrate 361 against the device substrate 303.

[0049] It is to be emphasized that since the bonding established in step 510 using the asphalt-based and/or tar-based bonding material is sufficient for the composite solar cell structure 304, there is no need for a separate autoclaving process, which was required when using conventional PVB or EVA as the bonding material. Accordingly, the cost regarding autoclaving (e.g., autoclave tool cost, energy cost and time consumption) is eliminated.

[0050] After the composite solar cell structure 304 is bonded through steps 500 and 510, the composite solar cell structure 304 is transported to other processing modules of the solar cell production system for follow-up processes, so as to finish a complete solar cell device.

[0051] Conventionally, during PV solar cell manufacture, Polyvinyl Butyl (PVB) or Ethylene Vinyl Acetate (EVA) is widely used in an encapsulation as the bonding material. However, PVB or EVA materials are relatively expensive, and require special storage and process environment for controlling humidity and temperature owing to high water absorption property. Moreover, PVB also requires autoclaving to bond the back glass to the device substrate.

[0052] Compared with aforesaid prior art, the method and apparatus according to the invention bond the composite solar cell structure using an asphalt-based and/or tar-based bonding material. Since the asphalt-based and/or tar-based bonding material is less expensive and has good moisture resistance, the cost is lower and device yield is also improved. Additionally, bonding with the asphalt-based and/or tar-based bonding material in general requires lower process temperatures and shorter process time, thus further reducing the cost and power consumption required to fabricate a solar device.

[0053] Moreover, since the bonding established using the asphalt-based and/or tar-based bonding material provides sufficient encapsulation to the composite solar cell structure, a separate autoclaving process is no longer needed and the cost required for autoclaving and its associated equipment is significantly reduced.

[0054] With the example and explanations above, the features and spirits of the embodiments of the invention are described. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teaching of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

Claims

What is claimed is:

1. A composite solar cell structure, comprising:

a device substrate having solar cell devices formed thereon;

a bonding material formed over the device substrate, wherein the bonding material is an asphalt-based and/or tar-based material; and

a back substrate formed over the bonding material and the device substrate, wherein the back substrate is bonded to the device substrate using the bonding material.

2. The composite solar cell structure of claim 1, wherein the bonding material is a Styrene-Butyl-Styrene material.

3. The composite solar cell structure of claim 1, wherein the bonding material is an asphalt-based material.

4. The composite solar cell structure of claim 1, wherein the bonding material is a tar-based material.

5. A method for bonding a composite solar cell structure, comprising:

contacting a bonding material to a device substrate having solar cell devices formed thereon, wherein the bonding material is an asphalt-based and/or tar-based material; and

contacting a back substrate to the bonding material; and

applying heat and pressure to bond the back substrate to the device substrate.

6. The method of claim 5, wherein the bonding material is a Styrene-Butyl-Styrene material.

7. The method of claim 5, wherein applying heat and pressure holding the composite solar cell structure at least about 100 degrees Celsius for at least about ten minutes.

8. The method of claim 5, wherein the pressure is applied by mechanical means.

9. The method of claim 5, wherein the pressure is applied by establishing a vacuum.

10. The method of claim 9, wherein the pressure urging the back substrate against the device substrate is at least about 14.5 psi.