US20110318862A1

US20110318862A1 - System and method for creating electric isolation between layers comprising solar cells

Info

Publication number: US20110318862A1
Application number: US12/885,532
Authority: US
Inventors: Erel Milshtein; Benyamin Buller
Original assignee: Solyndra Inc
Current assignee: Solyndra Inc
Priority date: 2006-08-04
Filing date: 2010-09-19
Publication date: 2011-12-29
Also published as: WO2008019073A2; US7879685B2; US20080029154A1; WO2008019073A3

Abstract

Methods for forming a patterned layer from common layer in a photovoltaic application are provided. The patterned layer is configured to form one or more portions of one or more solar cells on a rigid substrate. A first pass is made with a first laser beam over an area on the common layer. A second pass is made with a second laser beam over approximately the same area on the common layer. The first pass provides a first level of electrical isolation between a first portion and a second portion of the common layer. The second pass provides a second level of electrical isolation between the first portion and the second portion of the common layer. The second level of electrical isolation is greater than the first level of electrical isolation.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. §119(e), of U.S. Provisional Patent Application No. 60/835,724, filed on Aug. 4, 2006, which is hereby incorporated by reference herein in its entirety. Furthermore, this application is a Continuation-In-Part of U.S. patent application Ser. No. 11/499,608, filed Aug. 4, 2006, which is hereby incorporated by reference herein in its entirety. Furthermore, this Application is a Continuation of U.S. patent application Ser. No. 11/881,000, filed Jul. 25, 2007, which is hereby incorporated by reference herein in its entirety.

FIELD

This application is directed to the laser scribing of layers in solar cells. In particular, it is directed to delineating devices and functions within the solar cell using multiple passes of a laser.

DESCRIPTION OF THE FIGURES

The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the present invention and, together with the detailed description, serve to explain the principles and implementations of the invention.

FIGS. 1A-1C are side views detailing an exemplary generation of a solar cell.

FIGS. 2A-2B detail the method being applied to a layer disposed upon another layer within a solar cell.

FIGS. 3A-3B detail the method being applied to multiple layers disposed upon a rigid substrate within a solar cell.

FIGS. 4A-4M illustrate processing steps for forming a monolithically integrated solar cell unit in accordance with embodiments of the present application.

DETAILED DESCRIPTION

Embodiments of the present invention are described herein in the context of a system and method for creating electric isolation between layers comprising solar cells. Those of ordinary skill in the art will realize that the following detailed description of the present invention is illustrative only and is not intended to be in any way limiting. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations of the present invention as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts.
In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals, such as compliance with application- and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.
FIGS. 1A-1C are side views detailing an exemplary generation of a solar cell. FIG. 1A is a side view of a solar cell showing the preliminary composition of a generic solar cell. A solar cell 10 has a rigid substrate 12, upon which a layer of material 14 has been placed. This layer 14 can be placed on the rigid substrate 12 using various means of manufacture, including many semiconductor fabrication techniques. Layer 14 can be of various thicknesses, depending upon the manner in which the layer has been placed upon the rigid substrate.
In practice, layer 14 is typically a conductive layer in a solar cell, which serves as one electrode in the makeup of the solar cell. However, in this application, the particular layer that layer 14 represents is demonstrative in nature. Accordingly, for the purposes of this application, layer 14 can be a conductive layer, an intrinsic layer, a semiconductor layer, or any other type of layer that could be formed on a rigid substrate using semiconductor manufacturing methods.
Rigid substrate 12 in this example is glass, but again this is demonstrative in nature. For the purposes of this application, rigid substrate 12 can be any material that is used, or will be used in the future, as a rigid substrate in a semiconductor manufacturing process.
In FIG. 1B, a first pass has been made with a laser beam over an area of layer 14. In many uses, the laser beam can be applied to the top layer, which will cause the material in layer 14 to be rejected from the main mass of solar cell 10. The energy imparted to layer 14 can cause the material in the layer 14 to boil, vaporize, or explode away from the main mass of solar cell 10. This expulsion of material from layer 14 forms a groove or trench 16 in layer 14. In terms of conductive or semiconductor materials, this removal of material also results in an electrical isolation between portions of the material, in this diagram portions 14 a and 14 b, respectively.
However, the cut in the material may not prove to be effective to produce as good an electrical isolation as needed between portions 14 a and 14 b. For example, portions of the material may absorb the energy of the laser beam in the first pass and liquefy without vaporizing. In this case, the molten material may reform at the bottom of the trench 16. Or, molten material from the sides of the layer 14 may flow into the trench 16. Or, the laser pass may involve multiple pulses at differing points on the solar cell 10. In this case, the pulses could produce crater-like results in layer 14, which effectively act as a first rough electrical isolation step between portions 14 a and 14 b.
In one case, the first laser pass can be applied from the underside of rigid substrate 12. In this case, layer 14 melts and forms a pool of molten material underneath the top surface of material 14. After sufficient application of the first laser beam pass, molten material 14 explodes through the surface of layer 14. In this case, both solid and molten ejecta could fall back into the now-cleaved trench.
In short, the first laser beam pass produces trench 16, but remnants of layer 14 may pollute the trench 16 created in the material. Or, the laser process could be somewhat incomplete, again leaving remnants of material 14 in trench 16. These remnants of material 14 could create electrical pathways through the trench 16, thus resulting in a lower overall electrical resistance or higher conductance through the trench 14.
In FIG. 1C, a second laser beam pass has been made. In this case, the second laser beam pass has removed a portion of the detritus and ejecta produced by the first laser beam pass. In this manner, the remains of the first laser beam pass are removed by the laser beam pass, thus increasing the level of electrical isolation between portions 14 a and 14 b.
FIGS. 2A-2B detail the method being applied to a layer disposed upon another layer within a solar cell. As can be gleaned, embodiments could be applied to more than one layer, or a layer sitting on top of another layer as well. FIGS. 2A-2B show a trench on a topmost layer 24 on a solar cell 20 after being cut through by a first laser beam pass and after a subsequent laser beam pass. The cutting process can either leave remnants of the topmost layer 24, remnants of the relatively untouched bottom layer 22, or both, within trench 26. This is shown in FIG. 2A. In FIG. 2B, a second laser beam pass has removed a portion of the remnants, thus increasing the electrical isolation between portions 24 a and 24 b.
FIGS. 3A-3B detail the method being applied to multiple layers disposed upon a rigid substrate within a solar cell. In this case, a trench can be cut through a first layer 34 and a second layer 32 on a solar cell 30. The cutting process can either leave remnants of the topmost layer 34, remnants of bottom layer 32, or both, within the trench 36. This is shown in FIG. 3A. In FIG. 3B, a second laser beam pass has removed a portion of the remnants, thus increasing the electrical isolation between portions 34 a and 34 b, and/or portions 32 a and 32 b of layer 34.
The laser used in the first laser beam pass or the second laser beam pass can be of any variety used to created isolative trenches in semiconductor materials, and can be of the pulse-variety as well. The second pass may be carried out by the same laser that was applied with the first path at the same or with different energies and/or beam properties. Or, the laser used in the second pass can be another laser with completely differing, similar, or identical characteristics to the first laser. The energies applied to the materials can be of any variety used to created isolative trenches in semiconductor materials. The number of subsequent passes can be of any number, although only one is detailed in this application. Further, any of the first pass or the subsequent passes can be made from the top or the bottom of the mass of material.
In some embodiments, the substrate on which the one or more layers to be patterned is rigid. Rigidity of a material can be measured using several different metrics including, but not limited to, Young's modulus. In solid mechanics, Young's Modulus (E) (also known as the Young Modulus, modulus of elasticity, elastic modulus or tensile modulus) is a measure of the stiffness of a given material. It is defined as the ratio, for small strains, of the rate of change of stress with strain. This can be experimentally determined from the slope of a stress-strain curve created during tensile tests conducted on a sample of the material. Young's modulus for various materials is given in the following table.


	Young's	Young's
	modulus	modulus
Material	(E) in GPa	(E) in lbf/in²(psi)

Rubber (small strain)	0.01-0.1	1,500-15,000
Low density polyethylene	0.2	30,000
Polypropylene	1.5-2	217,000-290,000
Polyethylene terephthalate	2-2.5	290,000-360,000
Polystyrene	3-3.5	435,000-505,000
Nylon	3-7	290,000-580,000
Aluminum alloy	69	10,000,000
Glass (all types)	72	10,400,000
Brass and bronze	103-124	17,000,000
Titanium (Ti)	105-120	15,000,000-17,500,000
Carbon fiber reinforced plastic	150	21,800,000
(unidirectional, along grain)
Wrought iron and steel	190-210	30,000,000
Tungsten (W)	400-410	58,000,000-59,500,000
Silicon carbide (SiC)	450	65,000,000
Tungsten carbide (WC)	450-650	65,000,000-94,000,000
Single Carbon nanotube	1,000+	145,000,000
Diamond (C)	1,050-1,200	150,000,000-175,000,000

In some embodiments of the present application, a material (e.g., a substrate) is deemed to be rigid when it is made of a material that has a Young's modulus of 20 GPa or greater, 30 GPa or greater, 40 GPa or greater, 50 GPa or greater, 60 GPa or greater, or 70 GPa or greater. In some embodiments of the present application a material (e.g., the substrate) is deemed to be rigid when the Young's modulus for the material is a constant over a range of strains. Such materials are called linear, and are said to obey Hooke's law. Thus, in some embodiments, the substrate is made out of a linear material that obeys Hooke's law. Examples of linear materials include, but are not limited to, steel, carbon fiber, and glass. Rubber and soil (except at very low strains) are non-linear materials.
The present application is not limited to substrates that have rigid cylindrical shapes or are solid rods, or are flat planar. All or a portion of the substrate can be characterized by a cross-section bounded by any one of a number of shapes other than circular. The bounding shape can be any one of circular, ovoid, or any shape characterized by one or more smooth curved surfaces, or any splice of smooth curved surfaces. The bounding shape can be an n-gon, where n is 3, 5, or greater than 5. The bounding shape can also be linear in nature, including triangular, rectangular, pentangular, hexagonal, or having any number of linear segmented surfaces. Or, the cross-section can be bounded by any combination of linear surfaces, arcuate surfaces, or curved surfaces. As described herein, for ease of discussion only, an omnifacial circular cross-section is illustrated to represent nonplanar embodiments of the photovoltaic device. However, it should be noted that any cross-sectional geometry may be used in a photovoltaic device 10 that is nonplanar in practice.
In some embodiments, a first portion of the substrate is characterized by a first cross-sectional shape and a second portion of the substrate is characterized by a second cross-sectional shape, where the first and second cross-sectional shapes are the same or different. In some embodiments, at least ten percent, at least twenty percent, at least thirty percent, at least forty percent, at least fifty percent, at least sixty percent, at least seventy percent, at least eighty percent, at least ninety percent or all of the length of the substrate 102 is characterized by the first cross-sectional shape. In some embodiments, the first cross-sectional shape is planar (e.g., has no arcuate side) and the second cross-sectional shape has at least one arcuate side.
In some embodiments, the substrate is made of a rigid plastic, metal, metal alloy, or glass. In some embodiments, the substrate is made of a urethane polymer, an acrylic polymer, a fluoropolymer, polybenzamidazole, polymide, polytetrafluoroethylene, polyetheretherketone, polyamide-imide, glass-based phenolic, polystyrene, cross-linked polystyrene, polyester, polycarbonate, polyethylene, polyethylene, acrylonitrile-butadiene-styrene, polytetrafluoro-ethylene, polymethacrylate, nylon 6,6, cellulose acetate butyrate, cellulose acetate, rigid vinyl, plasticized vinyl, or polypropylene. In some embodiments, the substrate 102 is made of aluminosilicate glass, borosilicate glass, dichroic glass, germanium/semiconductor glass, glass ceramic, silicate/fused silica glass, soda lime glass, quartz glass, chalcogenide/sulphide glass, fluoride glass, a glass-based phenolic, flint glass, or cereated glass.
In some embodiments, the substrate is made of a material such as polybenzamidazole (e.g., CELAZOLE®, available from Boedeker Plastics, Inc., Shiner, Tex.). In some embodiments, the substrate 102 is made of polymide (e.g., DUPONT™ VESPEL®, or DUPONT™ KAPTON®, Wilmington, Del.). In some embodiments, the substrate is made of polytetrafluoroethylene (PTFE) or polyetheretherketone (PEEK), each of which is available from Boedeker Plastics, Inc. In some embodiments, the substrate is made of polyamide-imide (e.g., TORLON® PAI, Solvay Advanced Polymers, Alpharetta, Ga.).
In some embodiments, the substrate is made of a glass-based phenolic. Phenolic laminates are made by applying heat and pressure to layers of paper, canvas, linen or glass cloth impregnated with synthetic thermosetting resins. When heat and pressure are applied to the layers, a chemical reaction (polymerization) transforms the separate layers into a single laminated material with a “set” shape that cannot be softened again. Therefore, these materials are called “thermosets.” A variety of resin types and cloth materials can be used to manufacture thermoset laminates with a range of mechanical, thermal, and electrical properties. In some embodiments, the substrate 102 is a phenoloic laminate having a NEMA grade of G-3, G-5, G-7, G-9, G-10 or G-11. Exemplary phenolic laminates are available from Boedeker Plastics, Inc.
In some embodiments, the substrate is made of polystyrene. Examples of polystyrene include general purpose polystyrene and high impact polystyrene as detailed in Marks' Standard Handbook for Mechanical Engineers, ninth edition, 1987, McGraw-Hill, Inc., p. 6-174, which is hereby incorporated by reference herein in its entirety. In still other embodiments, the substrate 102 is made of cross-linked polystyrene. One example of cross-linked polystyrene is REXOLITE® (available from San Diego Plastics Inc., National City, Calif.). REXOLITE is a thermoset, in particular a rigid and translucent plastic produced by cross linking polystyrene with divinylbenzene.
In still other embodiments, the substrate is made of polycarbonate. Such polycarbonates can have varying amounts of glass fibers (e.g., 10%, 20%, 30%, or 40%) in order to adjust tensile strength, stiffness, compressive strength, as well as the thermal expansion coefficient of the material. Exemplary polycarbonates are ZELUX® M and ZELUX® W, which are available from Boedeker Plastics, Inc.
In some embodiments, the substrate is made of polyethylene. In some embodiments, the substrate is made of low density polyethylene (LDPE), high density polyethylene (HDPE), or ultra high molecular weight polyethylene (UHMW PE). Chemical properties of HDPE are described in Marks' Standard Handbook for Mechanical Engineers, ninth edition, 1987, McGraw-Hill, Inc., p. 6-173, which is hereby incorporated by reference herein in its entirety. In some embodiments, the substrate is made of acrylonitrile-butadiene-styrene, polytetrfluoro-ethylene (Teflon), polymethacrylate (lucite or plexiglass), nylon 6,6, cellulose acetate butyrate, cellulose acetate, rigid vinyl, plasticized vinyl, or polypropylene. Chemical properties of these materials are described in Marks' Standard Handbook for Mechanical Engineers, ninth edition, 1987, McGraw-Hill, Inc., pp. 6-172 through 6-175, which is hereby incorporated by reference in its entirety.
Additional exemplary materials that can be used to form the substrate are found in Modern Plastics Encyclopedia, McGraw-Hill; Reinhold Plastics Applications Series, Reinhold Roff, Fibres, Plastics and Rubbers, Butterworth; Lee and Neville, Epoxy Resins, McGraw-Hill; Bilmetyer, Textbook of Polymer Science, Interscience; Schmidt and Marlies, Principles of high polymer theory and practice, McGraw-Hill; Beadle (ed.), Plastics, Morgan-Grampiand, Ltd., 2 vols. 1970; Tobolsky and Mark (eds.), Polymer Science and Materials, Wiley, 1971; Glanville, The Plastics's Engineer's Data Book, Industrial Press, 1971; Mohr (editor and senior author), Oleesky, Shook, and Meyers, SPI Handbook of Technology and Engineering of Reinforced Plastics Composites, Van Nostrand Reinhold, 1973, each of which is hereby incorporated by reference herein in its entirety.
In some embodiments, a cross-section of the substrate is circumferential and has an outer diameter of between 3 mm and 100 mm, between 4 mm and 75 mm, between 5 mm and 50 mm, between 10 mm and 40 mm, or between 14 mm and 17 mm. In some embodiments, a cross-section of the substrate is circumferential and has an outer diameter of between 1 mm and 1000 mm.
In some embodiments, the substrate is a tube with a hollowed inner portion. In such embodiments, a cross-section of the substrate is characterized by an inner radius defining the hollowed interior and an outer radius. The difference between the inner radius and the outer radius is the thickness of the substrate. In some embodiments, the thickness of the substrate is between 0.1 mm and 20 mm, between 0.3 mm and 10 mm, between 0.5 mm and 5 mm, or between 1 mm and 2 mm. In some embodiments, the inner radius is between 1 mm and 100 mm, between 3 mm and 50 mm, or between 5 mm and 10 mm.
In some embodiments, the substrate has a length that is between 5 mm and 10,000 mm, between 50 mm and 5,000 mm, between 100 mm and 3000 mm, or between 500 mm and 1500 mm. In one embodiment, the substrate is a hollowed tube having an outer diameter of 15 mm and a thickness of 1.2 mm, and a length of 1040 mm. Although the substrate is a solid in some embodiments, it will be appreciated that in many embodiments, the substrate will have a hollow core and will adopt a rigid tubular structure such as that formed by a glass tube.
One aspect of the present application provides a method for forming a patterned layer from common layer in a photovoltaic application, wherein the patterned layer is configured to form one or more portions of one or more solar cells on a rigid substrate. For example, in FIG. 1C, common layer 14 is patterned to form portions 14 a and 14 b. Portions 14 a and 14 b are configured to form one or more portions of one or more solar cells. For example, portions 14 a and 14 b could respectively be the back-electrode of a first and second solar cell that is monolithically integrated onto substrate 12. In another example, turning to FIG. 2B, portions 24 a and 24 b could respectively be the semiconductor junction of a first and second solar cell that is monolithically integrated onto a substrate that is not shown. In still another example, referring to FIG. 2B, portions 24 a and 24 b could respectively be the transparent conducting layer (e.g., transparent conducting oxide) of a first and second solar cell that is monolithically integrated onto a substrate that is not shown. In the exemplary method, a first pass with a first laser beam is made over an area on the common layer. Then, a second pass is made with a second laser beam over approximately the same area on the common layer. The first pass provides a first level of electrical isolation between a first portion and a second portion of the common layer. The second pass provides a second level of electrical isolation between the first portion and the second portion of the common layer, the second level of electrical isolation being greater than the first level of electrical isolation.
In some embodiments the second pass comprises a plurality of laser beam passes. In some embodiments, the first laser beam and the second laser beam are generated by a common laser apparatus. In some embodiments, the first laser beam and the second laser beam are each generated by a different laser apparatus. In some embodiments, the first laser beam or the second laser beam is generated by a pulsed laser. In some embodiments, the pulsed laser has a pulse frequency in the range of 0.1 kilohertz (kHz) to 1,000 kHz during a portion of the first pass or a portion of the second pass. In some embodiments, a dose of radiant energy in a range from 0.01 Joules per square centimeters (J/cm²) to 50.0 J/cm²is delivered during a portion of the first pass or a portion of the second pass. In some embodiments, the common layer is a conductive layer. In some embodiments, the conductive layer comprises aluminum, molybdenum, tungsten, vanadium, rhodium, niobium, chromium, tantalum, titanium, steel, nickel, platinum, silver, gold, an alloy thereof, or any combination thereof. In some embodiments, the conductive layer comprises indium tin oxide, titanium nitride, tin oxide, fluorine doped tin oxide, doped zinc oxide, aluminum doped zinc oxide, gallium doped zinc oxide, boron dope zinc oxide indium-zinc oxide, a metal-carbon black-filled oxide, a graphite-carbon black-filled oxide, a carbon black-carbon black-filled oxide, a superconductive carbon black-filled oxide, an epoxy, a conductive glass, or a conductive plastic.
FIG. 4 illustrates exemplary processing steps for manufacturing a solar cell using techniques disclosed in the present application. Other manufacturing techniques for manufacturing cylindrical monolithically integrated solar cells, and other forms of monolithically integrated cylindrical solar cells are disclosed in U.S. patent application Ser. No. 11/158,178, filed Jun. 20, 2005; Ser. No. 11/248,789, filed Oct. 11, 2005; Ser. No. 11/315,523, filed Dec. 21, 2005; Ser. No. 11/329,296, filed Jan. 9, 2006; Ser. No. 11/378,835, filed Mar. 18, 2006; Ser. No. 11/378,847, filed Mar. 18, 2006; Ser. No. 11/396,069, filed Mar. 30, 2006; and U.S. patent application Ser. No. 11/437,928, filed May 19, 2006, each of which is hereby incorporated by reference herein in its entirety.
FIG. 4 shows the perspective view of a solar cell in various stages of manufacture. Below each view is a corresponding cross-sectional view of one hemisphere of the corresponding solar cell. In typical embodiments, the solar cell illustrated in FIG. 4 does not have an electrically conducting substrate 102. In the alternative, in embodiments where substrate 102 is electrically conducting, the substrate is circumferentially wrapped with an insulator layer so that back-electrodes 104 of individual photovoltaic cells 700 are electrically isolated from each other.
Referring to FIG. 4A, the process begins with substrate 102. Substrate 102 is solid cylindrical shaped or hollowed cylindrical shaped. In some embodiments, substrate 102 is either (i) tubular shaped or (ii) a rigid solid rod shaped. Next, in FIG. 4B, back-electrode 104 is circumferentially disposed on substrate 102. Back-electrode 104 may be deposited by a variety of techniques, including some of the techniques disclosed in U.S. patent application Ser. No. 11/378,835, filed Mar. 18, 2006, which is hereby incorporated by reference herein in its entirety. In some embodiments, back-electrode 104 is circumferentially disposed on substrate 102 by sputtering or electron beam evaporation. In some embodiments, substrate 102 is made of a conductive material. In such embodiments, it is possible to circumferentially dispose back-electrode 104 onto substrate 102 using electroplating. In some embodiments, substrate 102 is not electrically conducting but is wrapped with a metal foil such as a steal foil or a titanium foil. In these embodiments, it is possible to electroplate back-electrode 104 onto the metal foil using electroplating techniques. In still other embodiments, back-electrode 104 is circumferentially disposed on substrate 102 by hot dipping.
Referring to FIG. 4C, back-electrode 104 is patterned in order to create grooves 292. Grooves 292 run the full perimeter of back-electrode 104, thereby breaking the back-electrode 104 into discrete sections. Each section serves as the back-electrode 104 of a corresponding photovoltaic cells 700. The bottoms of grooves 292 expose the underlying substrate 102. In some embodiments, grooves 292 are scribed using a laser beam having a wavelength that is absorbed by back-electrode 104.
FIG. 4D provides a schematic illustration of a set-up in accordance with the present application. After a primary laser beam pass (e.g., laser beam 360 as depicted in FIG. 4D), groove 292 contains residual 352 scattered on its sides and bottom. One or more secondary laser beam passes further sweeps away, by evaporation or ablation, residual material 352. In some embodiments, laser beam 360 is further modified, for example, by lens 370. It is not necessary to fully remove all residual 352 from the sides or bottom of groove 292 so long as the groove is electrically isolating. Because layer 104 is conductive, at least a portion of groove 292 must fully penetrate layer 104 to ensure that the groove is electrically isolating.
Forming groove 292 using laser scribing is advantageous over traditional machine cutting methods. Laser cutting of metal materials can be divided into two main methods: vaporization cutting and melt-and-blow cutting. In vaporization cutting, the material is rapidly heated to vaporization temperature and removed spontaneously as vapor. The melt-and-blow method heats the material to melting temperature while a jet of gas blows the melt away from the surface. In some embodiments, an inert gas (e.g., Ar) is used. In other embodiments, a reactive gas is used to increase the heating of the material through exothermal reactions with the melt. The thin film materials processed by laser scribing techniques include the semiconductors (e.g., cadmium telluride, copper indium gallium diselenide, and silicon), the transparent conducting oxides (e.g., fluorinedoped tin oxide and aluminum-doped zinc oxide), and the metals (e.g., molybdenum and gold). Such laser systems are all commercially available and are chosen based on pulse durations and wavelength. Some exemplary laser systems that may be used to laser scribe include, but are not limited, to those disclosed in Section 4.2. Examples of laser systems include Q-switched Nd:YAG laser systems, a Nd:YAG laser systems, copper-vapor laser systems, a XeC1-excimer laser systems, a KrFexcimer laser systems, and diode-laser-pumped Nd: YAG systems. See Compaan et al., 1998, “Optimization of laser scribing for thin film PV module,” National Renewable Energy Laboratory final technical progress report April 1995-October 1997; Quercia et al., 1995, “Laser patterning of CuInSe₂/Mo/SLS structures for the fabrication of CuInSe₂sub modules,” in Semiconductor Processing and Characterization with Lasers: Application in Photovoltaics, First International Symposium, Issue 173/174, Number com P: 53-58; and Compaan, 2000, “Laser scribing creates monolithic thin film arrays,” Laser Focus World 36: 147-148, 150, and 152, each of which is hereby incorporated by reference herein in its entirety, for detailed laser scribing systems and methods that can be used in the present application. In some embodiments, grooves 292 are scribed using mechanical means. For example, a razor blade or other sharp instrument is dragged over back-electrode 104 thereby creating grooves 292. In some embodiments grooves 292 are formed using a lithographic etching method.
FIGS. 4E & 4F illustrate the case in which semiconductor junction 410 comprises a single absorber layer 106 and a single window layer 108 that are disposed on back-electrode 104. However, the application is not so limited. For example, junction layer 410 can be a homojunction, a heterojunction, a heteroface junction, a buried homojunction, a p-i-n junction, or a tandem junction. Referring to FIG. 4E, absorber layer 106 is circumferentially disposed on back-electrode 104. In some embodiments, absorber layer 106 is circumferentially deposited onto back-electrode 104 by thermal evaporation. For example, in some embodiments, absorber layer 106 is CIGS that is deposited using techniques disclosed in Beck and Britt, Final Technical Report, January 2006, NREL/SR-520-39119; and Delahoy and Chen, August 2005, “Advanced CIGS Photovoltaic Technology,” subcontract report; Kapur et al., January 2005 subcontract report, NREL/SR-520-37284, “Lab to Large Scale Transition for Non-Vacuum Thin Film CIGS Solar Cells”; Simpson et al., October 2005 subcontract report, “Trajectory-Oriented and Fault-Tolerant-Based Intelligent Process Control for Flexible CIGS PV Module Manufacturing,” NREL/SR-520-38681; and Ramanathan et al., 31^stIEEE Photovoltaics Specialists Conference and Exhibition, Lake Buena Vista, Fla., Jan. 3-7, 2005, each of which is hereby incorporated by reference herein in its entirety. In some embodiments, absorber layer 106 is circumferentially deposited on back-electrode 104 by evaporation from elemental sources. For example, in some embodiments, absorber layer 106 is CIGS grown on a molybdenum back-electrode 104 by evaporation from elemental sources. One such evaporation process is a three stage process such as the one described in Ramanthan et al., 2003, “Properties of 19.2% Efficiency ZnO/CdS/CuInGaSe₂Thin-film Solar Cells,” Progress in Photovoltaics: Research and Applications 11, 225, which is hereby incorporated by reference herein in its entirety, or variations of the three stage process. In some embodiments, absorber layer 106 is circumferentially deposited onto back-electrode 104 using a single stage evaporation process or a two stage evaporation process. In some embodiments, absorber layer 106 is circumferentially deposited onto back-electrode 104 by sputtering. Typically, such sputtering requires a substrate 102 to be heated during deposition of the back-electrode.
In some embodiments, absorber layer 106 is circumferentially deposited onto back-electrode 104 as individual layers of component metals or metal alloys of the absorber layer 106 using electroplating. For example, consider the case where absorber layer 106 is copper-indium-gallium-diselenide (CIGS). The individual component layers of CIGS (e.g., copper layer, indium-gallium layer, selenium) can be electroplated layer by layer onto back-electrode 104. In some embodiments, the individual layers of the absorber layer are circumferentially deposited onto back-electrode 104 using sputtering. Regardless of whether the individual layers of absorber layer 106 are circumferentially deposited by sputtering or electroplating, or a combination thereof, in typical embodiments (e.g. where active layer 106 is CIGS), once component layers have been circumferentially deposited, the layers are rapidly heated up in a rapid thermal processing step so that they react with each other to form the absorber layer 106. In some embodiments, the selenium is not delivered by electroplating or sputtering. In such embodiments the selenium is delivered to the absorber layer 106 during a low pressure heating stage in the form of an elemental selenium gas, or hydrogen selenide gas during the low pressure heating stage. In some embodiments, copper-indium-gallium oxide is circumferentially deposited onto back-electrode 104 and then converted to copper-indium-gallium diselenide. In some embodiments, a vacuum process is used to deposit absorber layer 106. In some embodiments, a non-vacuum process is used to deposit absorber layer 106. In some embodiments, a room temperature process is used to deposit absorber layer 106. In still other embodiments, a high temperature process is used to deposit absorber layer 106. Those of skill in the art will appreciate that these processes are just exemplary and there are a wide range of other processes that can be used to deposit absorber layer 106. In some embodiments, absorber layer 106 is deposited using chemical vapor deposition.
Referring to FIG. 4F, window layer 108 is circumferentially disposed on absorber layer 106. In some embodiments, absorber layer 106 is circumferentially deposited onto absorber layer 108 using a chemical bath deposition process. For instance, in the case where window layer 108 is a buffer layer such as cadmium sulfide, the cadmium and sulfide can each be separately provided in solutions that, when reacted, results in cadmium sulfide precipitating out of the solution. In some embodiments, the window layer 108 is an n type buffer layer. In some embodiments, window layer 108 is sputtered onto absorber layer 106. In some embodiments, window layer 108 is evaporated onto absorber layer 106. In some embodiments, window layer 108 is circumferentially disposed onto absorber layer 106 using chemical vapor deposition.
Referring to FIGS. 4G and 4H, semiconductor junction 410 (e.g., layers 106 and 108) are patterned in order to create grooves 294. In some embodiments, grooves 294 run the full perimeter of semiconductor junction 410, thereby breaking the semiconductor junction 410 into discrete sections. In some embodiments, grooves 294 do not run the full perimeter of semiconductor junction 410. In fact, in some embodiments, each groove only extends a small percentage of the perimeter of semiconductor junction 410. In some embodiments, each photovoltaic cell 700 may have one, two, three, four or more, ten or more, or one hundred or more pockets arranged around the perimeter of semiconductor junction 410 instead of a given groove 294. In some embodiments, grooves 294 are scribed using a laser beam having a wavelength that is absorbed by semiconductor junction 410.
FIG. 4I depicts a schematic illustration of a set-up used to create groove 294, in accordance with the present application. After a primary laser beam pass, groove 294 is depicted with residual 354 scattered on its sides and bottom. One or more secondary laser beam passes further sweeps away, by evaporation/ablation, residual 354 that causes groove 294 to be electrically conductive. It is not necessary to fully remove all residual 354 from groove 294, so long as the groove is electrically isolating. In subsequent processing steps, groove 294 is to be filled with conductive material to provide a connection between back-electrode 104 and transparent conductor 110 from adjacent photovoltaic cells 700. Current does not flow directly from side 295-1 to side 295-2 once groove 294 is filled to form a via 280. In some embodiments, groove 294 is extended into back-electrode layer 104. Furthermore, no connection is formed between the back-electrode layer 104 and transparent conductor 110 in the same photovoltaic cell 700. Otherwise, the cell would short. As such, only one side of groove 294 needs to be completely electrically isolating. In the solar cell configuration illustrated in FIG. 4I, only side 295-2 needs to be electrically isolating. In other embodiments, solar cells may be configured such that side 295-1 needs to be electrically isolating.
Referring to FIG. 4J, transparent conductor 110 is circumferentially disposed on semiconductor junction 410. In some embodiments, transparent conductor 110 is circumferentially disposed onto back-electrode 104 by sputtering. In some embodiments, the sputtering is reactive sputtering. For example, in some embodiments a zinc target is used in the presence of oxygen gas to produce a transparent conductor 110 comprising zinc oxide. In another reactive sputtering example, an indium tin target is used in the presence of oxygen gas to produce a transparent conductor 110 comprising indium tin oxide. In another reactive sputtering example, a tin target is used in the presence of oxygen gas to produce a transparent conductor 110 comprising tin oxide. In general, any wide band gap conductive transparent material can be used as transparent conductor 110. As used herein, the term “transparent” means a material that is considered transparent in the wavelength range from about 300 nanometers to about 1500 nanometers. However, components that are not transparent across this full wavelength range can also serve as a transparent conductor 110, particularly if they have other properties such as high conductivity such that very thin layers of such materials can be used. In some embodiments, transparent conductor 110 is any transparent conductive oxide that is conductive and can be deposited by sputtering, either reactively or using ceramic targets.
In some embodiments, transparent conductor 110 is deposited using direct current (DC) diode sputtering, radio frequency (RF) diode sputtering, triode sputtering, DC magnetron sputtering or RF magnetron sputtering. In some embodiments, transparent conductor 110 is deposited using atomic layer deposition. In some embodiments, transparent conductor 110 is deposited using chemical vapor deposition.
Referring to FIG. 4K, transparent conductor 110 is patterned in order to create grooves 296. Grooves 296 run the full perimeter of transparent conductor 110 thereby breaking the transparent conductor 110 into discrete sections. The bottoms of grooves 296 expose underlying semiconductor junction 410. In some embodiments, a groove 298 is patterned at an end of solar cell unit 300 in order to connect the back-electrode 104 exposed by groove 296 to an electrode or other electronic circuitry. In some embodiments, grooves 296 are scribed using a laser beam having a wavelength that is absorbed by transparent conductor 110.
FIG. 4L provides a schematic illustration of a set-up in accordance with the present application. After a primary laser beam pass, groove 296 is depicted with residual 356 scattered on its sides and bottom. One or more secondary laser beam passes further sweep away residual 356, by evaporation/ablation, causing groove 296 to become electrically isolating. It is not necessary to fully remove all residual 356 material from the sides or bottom of groove 296 so long as the groove become electrically isolating. Because transparent conductor 110 is conductive, at least a portion of groove 296 must fully penetrate layer 110 to ensure electrical isolation.
Referring to FIG. 4M, optional antireflective coating 112 is circumferentially disposed on transparent conductor 110 using conventional deposition techniques. In some embodiments, solar cell units 300 are encased in a transparent tubular casing 310. More details on how elongated solar cells such as solar cell unit 300 can be encased in a transparent tubular case are described in U.S. patent application Ser. No. 11/378,847, filed Mar. 18, 2006, which is hereby incorporated by reference herein in its entirety. In some embodiments, an optional filler layer 330 is used to ensure that there are no pockets of air between the outer layers of solar cell unit 270 and the transparent tubular casing 310.
In some embodiments, counter-electrodes 420 are deposited on transparent conductor 110 using, for example, ink jet printing. Examples of conductive ink that can be used for such counter-electrodes include, but are not limited to silver loaded or nickel loaded conductive ink. In some embodiments epoxies as well as anisotropic conductive adhesives can be used to construct counter-electrodes 420. In typical embodiments such inks or epoxies are thermally cured in order to form counter-electrodes 420. In some embodiments, such counter-electrodes are not present in solar cell unit 300. In fact, in monolithic integrated designs, voltage across the length of the solar cell unit 300 is increased because of the presences of independent photovoltaic cell 700. Thus, current is decreased, thereby reducing the current requirements of individual photovoltaic cells 700. As a result, in many embodiments, there is no need for counter-electrodes 420.
In some embodiments, grooves 292, 294, and 296 are not concentric as illustrated in FIG. 4. Rather, in some embodiments, such grooves are spiraled down the tubular (long) axis of substrate 102. In some embodiments, optional filler layer 330 is circumferentially disposed onto transparent conductor 110 or antireflective layer 112. Depending on the embodiments, transparent tubular casing 310 is circumferentially fitted onto optional filler layer 330 (if present), or antireflective layer 112 (if present and if optional filler layer 330 is not present) or transparent conductor 110 (if optional filler layer 330 and antireflective layer 112 are not present). The methods and systems disclosed in the present application may be applied to create an electrically isolating groove (e.g., 292, 294, or 296) in any layer of a solar cell.
Thus, systems and methods for creating electric isolation between layers comprising solar cells is described and illustrated. Those skilled in the art will recognize that many modifications and variations of the present invention are possible without departing from the invention. Additionally, it is understood that the method could be applied to production of semiconductors in general. Of course, the various features depicted in each of the Figures and the accompanying text may be combined together. Accordingly, it should be clearly understood that the present invention is not intended to be limited by the particular features specifically described and illustrated in the drawings, but the concept of the present invention is to be measured by the scope of the appended claims. It should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention as described by the appended claims that follow.

Claims

1. A method for forming a patterned layer from a common layer in a photovoltaic application, wherein the patterned layer is configured to form one or more portions of one or more solar cells on a rigid substrate, the method comprising:

making a first pass with a first laser beam over an area on the common layer; and

making a second pass with a second laser beam over approximately the same area on the common layer, wherein

the first pass provides a first level of electrical isolation between a first portion and a second portion of the common layer;

the second pass provides a second level of electrical isolation between the first portion and the second portion of the common layer, the second level of electrical isolation being greater than the first level of electrical isolation; and

the first pass has a first trajectory and the second pass has a second trajectory that corresponds to the first trajectory.

2. The method of claim 1, wherein the second pass comprises a plurality of laser beam passes.

3. The method of claim 1, wherein the first laser beam and the second laser beam are generated by a common laser apparatus.

4. The method of claim 1, wherein the first laser beam and the second laser beam are each generated by a different laser apparatus.

5. The method of claim 1, wherein the first laser beam or the second laser beam is generated by a pulsed laser.

6. The method of claim 5, wherein the pulsed laser has a pulse frequency in the range of 0.1 kilohertz (kHz) to 1,000 kHz during a portion of the first pass or a portion of the second pass.

7. The method of claim 1, wherein a dose of radiant energy in a range from 0.01 Joules per square centimeters (J/cm²) to 50.0 J/cm²is delivered during a portion of the first pass or a portion of the second pass.

8. The method of claim 1, wherein the common layer is a conductive layer.

9. The method of claim 8, wherein the conductive layer comprises aluminum, molybdenum, tungsten, vanadium, rhodium, niobium, chromium, tantalum, titanium, steel, nickel, platinum, silver, gold, an alloy thereof, or any combination thereof.

10. The method of claim 9, wherein the conductive layer comprises indium tin oxide, titanium nitride, tin oxide, fluorine doped tin oxide, doped zinc oxide, aluminum doped zinc oxide, gallium doped zinc oxide, boron dope zinc oxide indium-zinc oxide, a metal-carbon black-filled oxide, a graphite-carbon black-filled oxide, a carbon black-carbon black-filled oxide, a superconductive carbon black-filled oxide, an epoxy, a conductive glass, or a conductive plastic.

11. The method of claim 1, wherein said substrate has a Young's modulus of 20 GPa or greater.

12. The method of claim 1, wherein said substrate has a Young's modulus of 40 GPa or greater.

13. The method of claim 1, wherein said substrate has a Young's modulus of 70 GPa or greater.

14. The method of claim 1, wherein said substrate is made of a linear material.

15. The method of claim 1, wherein all or a portion of the substrate is a rigid tube or a rigid solid rod.

16. The method of claim 1, wherein all or a portion of the substrate is characterized by a circular cross-section, an ovoid cross-section, a triangular cross-section, a pentangular cross-section, a hexagonal cross-section, a cross-section having at least one arcuate portion, or a cross-section having at least one curved portion.

17. The method of claims 1, wherein a first portion of the substrate is characterized by a first cross-sectional shape and a second portion of the substrate is characterized by a second cross-sectional shape.

18. The method of claim 17, wherein the first cross-sectional shape and the second cross-sectional shape are the same.

19. The method of claim 17, wherein the first cross-sectional shape and the second cross-sectional shape are different.

20. The method of claim 17, wherein at least sixty percent of the length of the substrate is characterized by the first cross-sectional shape.

21. The method of claim 17, wherein the first cross-sectional shape is planar and the second cross-sectional shape has at least one arcuate side.

22. A method for forming a patterned layer from a common layer in a photovoltaic application, wherein the patterned layer is configured to form one or more electrically isolated layers of material on a substrate, the method comprising:

making a first laser beam pass with a first laser beam over a first area on the common layer;

based on the step of making a first pass, removing a first amount of the common layer;

making a second laser beam pass with a second laser beam over a second area on the common layer, wherein the second area on the common layer is approximately the same as the first area on the common layer,

based on the step of making a second pass, removing a second amount of the common layer, the second amount of the common layer comprising either: a) portions of the common layer left after the first pass, or b) remnants of the first amount that resettle within the area;

wherein the first pass provides a first level of electrical isolation between a first portion and a second portion of the common layer;

wherein the second pass provides a second level of electrical isolation between the first portion and the second portion of the common layer, the second level of electrical isolation being greater than the first level of electrical isolation; and.

wherein the first pass has a first trajectory and the second pass has a second trajectory that corresponds to the first trajectory.

23. The method of claim 22, wherein the second laser beam pass comprises a plurality of laser beam passes.

24. The method of claim 22, wherein the first laser beam and the second laser beam are generated by a common laser apparatus.

25. The method of claim 22, wherein the first laser beam and the second laser beam are each generated by a different laser apparatus.

26. The method of claim 22, wherein the first laser beam or the second laser beam is generated by a pulsed laser.

27. The method of claim 26, wherein the pulsed laser has a pulse frequency in the range of 0.1 kilohertz (kHz) to 1,000 kHz during a portion of the first pass or a portion of the second pass.

28. The method of claim 22, wherein a dose of radiant energy in a range from 0.01 Joules per square centimeters (J/cm²) to 50.0 J/cm²is delivered during a portion of the first laser beam pass or a portion of the second laser beam pass.

29. The method of claim 22, wherein the common layer is a conductive layer.

30. The method of claim 29, wherein the conductive layer comprises aluminum, molybdenum, tungsten, vanadium, rhodium, niobium, chromium, tantalum, titanium, steel, nickel, platinum, silver, gold, an alloy thereof, or any combination thereof.

31. The method of claim 29, wherein the conductive layer comprises indium tin oxide, titanium nitride, tin oxide, fluorine doped tin oxide, doped zinc oxide, aluminum doped zinc oxide, gallium doped zinc oxide, boron dope zinc oxide indium-zinc oxide, a metal-carbon black-filled oxide, a graphite-carbon black-filled oxide, a carbon black-carbon black-filled oxide, a superconductive carbon black-filled oxide, an epoxy, a conductive glass, or a conductive plastic.

32. The method of claim 22, wherein said substrate has a Young's modulus of 20 GPa or greater.

33. The method of claim 22, wherein said substrate has a Young's modulus of 40 GPa or greater.

34. The method of claim 22, wherein said substrate has a Young's modulus of 70 GPa or greater.

35. The method of claim 22, wherein said substrate is made of a linear material.

36. The method of claim 22, wherein all or a portion of the substrate is a rigid tube or a rigid solid rod.

37. The method of claim 22, wherein all or a portion of the substrate is characterized by a circular cross-section, an ovoid cross-section, a triangular cross-section, a pentangular cross-section, a hexagonal cross-section, a cross-section having at least one arcuate portion, or a cross-section having at least one curved portion.

38. The method of claims 22, wherein a first portion of the substrate is characterized by a first cross-sectional shape and a second portion of the substrate is characterized by a second cross-sectional shape.

39. The method of claim 38, wherein the first cross-sectional shape and the second cross-sectional shape are the same.

40. The method of claim 38, wherein the first cross-sectional shape and the second cross-sectional shape are different.

41. The method of claim 38, wherein at least sixty percent of the length of the substrate is characterized by the first cross-sectional shape.

42. The method of claim 38, wherein the first cross-sectional shape is planar and the second cross-sectional shape has at least one arcuate side.