US20150287851A1 - Solar cell and solar cell module - Google Patents

Solar cell and solar cell module Download PDF

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US20150287851A1
US20150287851A1 US14/439,344 US201314439344A US2015287851A1 US 20150287851 A1 US20150287851 A1 US 20150287851A1 US 201314439344 A US201314439344 A US 201314439344A US 2015287851 A1 US2015287851 A1 US 2015287851A1
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solar cell
electrodes
electrode
bus bar
finger electrodes
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Yoko Endo
Hiroyuki Otsuka
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Shin Etsu Chemical Co Ltd
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Shin Etsu Chemical Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/02002—Arrangements for conducting electric current to or from the device in operations
    • H01L31/02005—Arrangements for conducting electric current to or from the device in operations for device characterised by at least one potential jump barrier or surface barrier
    • H01L31/02008—Arrangements for conducting electric current to or from the device in operations for device characterised by at least one potential jump barrier or surface barrier for solar cells or solar cell modules
    • H01L31/0201—Arrangements for conducting electric current to or from the device in operations for device characterised by at least one potential jump barrier or surface barrier for solar cells or solar cell modules comprising specially adapted module bus-bar structures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0224—Electrodes
    • H01L31/022408—Electrodes for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/022425—Electrodes for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • H01L31/022433—Particular geometry of the grid contacts
    • H—ELECTRICITY
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    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0216—Coatings
    • H01L31/02161—Coatings for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/02167—Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • H01L31/02168—Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells the coatings being antireflective or having enhancing optical properties for the solar cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0236—Special surface textures
    • H01L31/02363—Special surface textures of the semiconductor body itself, e.g. textured active layers
    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/028—Inorganic materials including, apart from doping material or other impurities, only elements of Group IV of the Periodic Table
    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042—PV modules or arrays of single PV cells
    • H01L31/048—Encapsulation of modules
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042—PV modules or arrays of single PV cells
    • H01L31/05—Electrical interconnection means between PV cells inside the PV module, e.g. series connection of PV cells
    • H01L31/0504—Electrical interconnection means between PV cells inside the PV module, e.g. series connection of PV cells specially adapted for series or parallel connection of solar cells in a module
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042—PV modules or arrays of single PV cells
    • H01L31/05—Electrical interconnection means between PV cells inside the PV module, e.g. series connection of PV cells
    • H01L31/0504—Electrical interconnection means between PV cells inside the PV module, e.g. series connection of PV cells specially adapted for series or parallel connection of solar cells in a module
    • H01L31/0508—Electrical interconnection means between PV cells inside the PV module, e.g. series connection of PV cells specially adapted for series or parallel connection of solar cells in a module the interconnection means having a particular shape
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/068—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/547—Monocrystalline silicon PV cells

Definitions

  • This invention relates to a solar cell which has long-term reliability and high conversion efficiency and maintains high output, and a solar cell module comprising solar cells arranged in series.
  • a solar cell is generally manufactured as shown in FIGS. 1 to 3 .
  • a p-type semiconductor substrate 100 b of silicon or the like an n-type dopant is diffused to form an n-type diffusion layer 101 to define a pn junction.
  • an antireflection coating layer 102 such as SiNx film is formed on the n-type diffusion layer 101 .
  • aluminum paste is printed over substantially the entire surface and alloyed into silicon to form a back surface field (BSF) layer 103 and an aluminum electrode 104 by firing.
  • BSF back surface field
  • a conductive paste containing silver or the like is printed and fired to form a thick electrode 106 which is known as bus bar electrode.
  • a conductive paste containing silver or the like is printed and fired to form a thick electrode 106 which is known as bus bar electrode.
  • finger electrodes 107 for current collection and thick electrodes formed for collecting current from the finger electrodes known as bus bar electrodes 105 are arranged in comb-grid shape so that they intersect substantially at right angles.
  • the contact resistance between the front finger electrodes 107 and the semiconductor substrate 100 b and the line resistance of electrodes have a large impact on the conversion efficiency of the solar cell.
  • screen printing method is often employed as the electrode forming method for solar cells.
  • the screen printing method has advantages including ease of formation of printed pattern, an ability to adjust printing pressure to minimize substrate damage, a high working speed per cell, low cost and high productivity. If a conductive paste which is so thixotropic that the profile may be maintained even after transfer is used, electrodes having a high aspect ratio can be formed.
  • finger electrodes 107 , 107 connected to bus bar electrodes 105 , 105 are shortened such that distal ends of finger electrodes 107 , 107 are spaced apart, thereby reducing warpage. This, however, induce disconnection of the finger electrodes 107 between bus bar electrodes 105 , 105 . Since the number of distal ends of finger electrodes is doubled as compared with the finger electrodes in FIG. 1 , a peeling failure rate of distal ends may increase. It is also proposed in JP-A 2006-324504 to enlarge the width (or area) of the distal portions of finger electrode to increase the adhesive area, for thereby increasing the adhesive strength.
  • the finger electrodes are typically designed to a line width of about 60 to 120 ⁇ m. They are printed and formed by the screen printing method as mentioned above. Such reduced line width may induce problems like skipping, further narrowing of line width, and breakage. Such failure, if any, may lead to the problem of interfering with electric conduction from the finger electrode at the failed site to the bus bar electrode.
  • Patent Document 1 JP-A 2006-324504
  • An object of the invention which has been made under the above-mentioned circumstances, is to provide a solar cell and a solar cell module, featuring mitigated warpage of a solar cell substrate against high adhesive strength of distal portions of finger electrodes and possible electric conduction of a finger electrode to a bus bar electrode even if the electrodes are locally cut or broken, eventually having long-term reliability and high conversion efficiency, and maintaining high output.
  • the invention provides a solar cell and solar cell module as defined below.
  • a solar cell comprising a semiconductor substrate having at least a pn junction formed therein, a multiplicity of finger electrodes which are formed in comb shape on at least one surface of the semiconductor substrate, and a plurality of bus bar electrodes which extend orthogonal to the longitudinal direction of the finger electrodes and are connected to the finger electrodes, wherein
  • first finger electrodes which are connected to a first bus bar electrode are spaced apart from second finger electrodes which are connected to a second bus bar electrode extending parallel with the first bus bar electrode, and longitudinal ends of adjacent two or more of the finger electrodes connected to each bus bar electrode are electrically connected together by an auxiliary electrode.
  • the solar cell of the invention eliminates drawbacks associated with breaks of finger electrodes and offers a high fill factor, high conversion efficiency, mitigated cell warpage, improved manufacture yield, least cost increase, and long-term reliability.
  • the solar cell module comprising such solar cells has a high percent output retention.
  • FIG. 1 is a cross-sectional view showing the construction of a conventional solar cell.
  • FIG. 2 is a plane view showing an electrode pattern on the front surface of the conventional solar cell.
  • FIG. 3 is a plane view showing an electrode pattern on the back surface of the conventional solar cell.
  • FIG. 4 is a plane view showing an electrode pattern on the front surface of a prior art solar cell.
  • FIG. 5 is a plane view showing an electrode pattern on the front surface of a solar cell in one embodiment of the invention.
  • FIG. 6 is a plane view showing an electrode pattern on the front surface of a solar cell in another embodiment of the invention.
  • FIG. 7 is a plane view showing a modified example (1) of the electrode pattern on the front surface of the solar cell of FIG. 5 .
  • FIG. 8 is a plane view showing a modified example (2) of the electrode pattern on the front surface of the solar cell of FIG. 5 .
  • FIG. 9 is a schematic cross-sectional view showing the basic construction of a conventional solar cell module.
  • FIG. 10 illustrates how to evaluate warpage of a solar cell.
  • FIG. 11 is a diagram showing short circuit current density and fill factor in Example 3.
  • FIG. 12 is a diagram showing conversion efficiency in Example 3.
  • the solar cell and solar cell module according to the invention are described. Understandably, the invention is not limited to the solar cells of the illustrated embodiments.
  • the solar cell of the invention is illustrated as comprising a semiconductor substrate having at least a pn junction formed therein, a multiplicity of finger electrodes 107 a , 107 b which are formed in comb shape on at least one surface of the semiconductor substrate, and a plurality of (two in FIGS. 5 to 8 ) bus bar electrodes 105 a , 105 b which extend orthogonal to the longitudinal direction of the finger electrodes 107 a , 107 b and are connected to the finger electrodes 107 a , 107 b .
  • first finger electrodes 107 a which are connected to a first bus bar electrode 105 a are spaced apart from second finger electrodes 107 b which are connected to a second bus bar electrode 105 b extending parallel with the first bus bar electrode 105 a , and longitudinal ends (also referred to as distal portions, hereinafter) of adjacent two or more electrodes of the finger electrodes connected to each bus bar electrode are electrically connected together by an auxiliary electrode 108 .
  • the solar cell of the invention is characterized by the front surface electrode pattern while the remaining construction may be as shown in FIG. 1 , for example.
  • all adjacent distal portions of the finger electrodes 107 a , 107 b connected to each of the bus bar electrodes 105 a , 105 b are connected together by the auxiliary electrode 108 .
  • two adjacent distal portions are connected by the auxiliary electrode 108 .
  • the mode of connecting adjacent distal portions by the auxiliary electrode 108 is not limited to these embodiments.
  • the finger electrodes 107 a , 107 b project from the bus bar electrodes 105 a , 105 b to which they are connected, in opposite directions orthogonal to the bus bar electrodes 105 a , 105 b .
  • auxiliary electrode 108 Preferably at each of opposite ends of finger electrodes 107 a (or 107 b ) projecting from the bus bar electrode 105 a (or 105 b ), longitudinal ends of adjacent finger electrodes 107 a (or 107 b ) are electrically connected together by the auxiliary electrode 108 .
  • auxiliary electrode 108 which extends orthogonal to the longitudinal direction of the finger electrodes 107 a (or 107 b ).
  • the number of additional auxiliary electrodes 108 is preferably 1 to 10.
  • FIGS. 7 and 8 shows the embodiments wherein additional auxiliary electrodes 108 are provided at positions other than the longitudinal end (or distal portion) of the finger electrodes 107 a , 107 b , in the electrode pattern of FIG. 5 .
  • auxiliary electrodes 108 extending orthogonal to the longitudinal direction of finger electrodes 107 a are provided on each side such that they are equally spaced between the distal portions of finger electrodes 107 a and the bus bar electrode 105 a , for connecting the finger electrodes 107 a all together; and three auxiliary electrodes 108 extending orthogonal to the longitudinal direction of finger electrodes 107 b are provided on each side such that they are equally spaced between the distal portions of finger electrodes 107 b and the bus bar electrode 105 b , for connecting the finger electrodes 107 b all together.
  • This embodiment reduces the conductive paste necessary to form auxiliary electrodes to the requisite minimum and is effective for suppressing any reduction of the solar cell fill factor even if by any chance finger electrodes are broken.
  • the embodiment of FIG. 7 also has the advantage that if a finger electrode is broken at any position, the distance from the broken site to the auxiliary electrode is so short that the reduction of fill factor is minimized.
  • auxiliary electrodes 108 in addition to the auxiliary electrodes 108 provided at the distal portions of finger electrodes 107 a , 107 b , two auxiliary electrodes 108 extending orthogonal to the longitudinal direction of finger electrodes 107 a , 107 b are provided in proximity to the distal portions of finger electrodes 107 a , 107 b , for connecting the finger electrodes 107 a all together and connecting the finger electrodes 107 b all together.
  • the proximity to the distal portions of finger electrodes 107 a , 107 b indicates a region that is deviated from an intermediate point between the distal portion of finger electrode and the bus bar electrode toward the distal portion of finger electrode, preferably a region that extends within a distance of L/3 from the distal portion of finger electrode wherein L is the distance between the distal portion and the bus bar electrode, and more preferably a region that extends within a distance of L/4 from the distal portion of finger electrode wherein L is the distance defined above.
  • This embodiment reduces the conductive paste necessary to form auxiliary electrodes to the requisite minimum and is effective for suppressing any reduction of the solar cell fill factor even if by any chance finger electrodes are broken.
  • the invention relies on an electrode printing method of forming bus bar electrodes, finger electrodes, and auxiliary electrodes at a time by screen printing technique.
  • the printing direction is generally set parallel to the finger electrodes and orthogonal to the bus bar electrodes and auxiliary electrodes. This is because the screen printing technique is difficult to print lines orthogonal to the printing direction, with the risk that such lines may be thinned or broken.
  • auxiliary lines are closely arranged as shown in FIG. 8 , the resulting auxiliary electrodes can compensate for breakage or thinning. Thickened auxiliary electrodes, though possible to print, are undesirable because the light receiving area is reduced.
  • FIGS. 7 and 8 are shown as modified examples of FIG. 5 , they may be applied to the electrode pattern of FIG. 6 .
  • the auxiliary electrode is not limited to the linear connection orthogonal to the longitudinal direction of finger electrodes as shown in FIGS. 5 to 8 .
  • a connection method using a connector of a curved shape which is convex outward of the longitudinal direction of finger electrodes between two finger electrodes to be connected is acceptable.
  • the auxiliary electrode may be a connector of an arc shape (arch shape) or a mountain-type protrusion (pseudo-arcuate shape) consisting of short linear segments connecting between the ends of two adjacent or close finger electrodes, so that the connection angle between the auxiliary electrode and the finger electrode (angle formed between auxiliary electrode and finger electrode) is not orthogonal.
  • the bus bar electrode is preferably formed to a line width of 0.5 to 3.0 mm, more preferably 1.0 to 1.5 mm.
  • the finger electrode is preferably formed to a line width of 30 to 120 ⁇ m, more preferably 60 to 120 ⁇ m, and most preferably 70 to 100 ⁇ m.
  • the auxiliary electrode is preferably formed to a line width of 30 to 500 ⁇ m, more preferably 60 to 500 ⁇ m, even more preferably 60 to 360 ⁇ m, and most preferably 70 to 240 ⁇ m.
  • the spacing between bus bar electrodes is preferably 20 to 100 mm, more preferably 39 to 78 mm.
  • the spacing between finger electrodes is preferably 0.5 to 4.0 mm, more preferably 1.5 to 2.5 mm.
  • the ratio of the line width of auxiliary electrode to the line width of finger electrode is preferably from 0.5 to 8.0, more preferably from 0.5 to 2.5.
  • a ratio of less than 0.5 may invite difficult fabrication of a screen printing plate and a likelihood of breakage whereas a ratio in excess of 8.0 may cause a reduction in light receiving area and hence, a lowering of conversion efficiency.
  • the solar cell of the invention as shown in FIG. 1 may be manufactured by any well-known methods.
  • bus bar electrodes, finger electrodes and auxiliary electrodes may be formed by the screen printing method. Desirably these electrodes are simultaneously formed by the screen printing method. This gives advantages of reducing the manufacturing cost by a single printing step and improving the manufacture yield by the reduction in cracking or fissure due to the reduced number of steps capable of applying stress to the semiconductor substrate.
  • the invention is also applicable to a solar cell wherein finger electrodes and bus bar electrodes are formed on the rear side, that is, bifacial solar cell.
  • auxiliary electrode since the auxiliary electrode is connected to the ends of finger electrodes, the contact area with the semiconductor substrate at the finger electrode end is enlarged, whereby the adhesive strength of the finger electrode end is improved to prevent the finger electrode from peeling during long-term service. Third, the same prevents the finger electrode end from peeling from the semiconductor substrate upon thermal shrinkage after firing. Fourth, the auxiliary electrodes serve to reduce the line resistance, leading to increased fill factor and improved conversion efficiency. Fifth, the provision of auxiliary electrodes maintains a high conversion efficiency in that a loss of short circuit current density (Jsc) associated with a reduction of light receiving area is offset by an increase of fill factor.
  • Jsc short circuit current density
  • the current-collection electrode When the solar cell is exposed to an outdoor environment, the current-collection electrode is damaged by the impact of temperature, humidity, pressure or the like, resulting in the decrease in the conversion efficiency.
  • dust and foreign particles which are not transmissive to light deposit on the light-receiving surface, they interfere with entry of sunlight, inviting the substantial decrease in conversion efficiency.
  • a laminate of the order of transparent front-side cover e.g., colorless strengthened glass plate
  • Solar cell/fill e.g., EVA
  • the electrodes are corroded with moisture and allow metal particles to be leached out in moisture, in some cases, and if so, they weaken their bond to the semiconductor substrate and eventually peel off.
  • the solar cell module of the invention is constructed using the solar cells of the invention. As shown in FIG. 9 , a plurality of solar cells are electrically connected by soldering conductors or interconnectors 201 to their bus bar electrodes. In the illustrated embodiment, interconnectors 201 are connected to front bus bar electrode 105 and rear bus bar electrode 106 on the solar cell 100 via solders 202 .
  • the solar cell module of the invention is obtained by arranging a plurality of solar cells 100 of the illustrated construction along the longitudinal direction of bus bar electrodes 105 , with their light-receiving surfaces faced in an identical direction, and connecting a front bus bar electrode 105 of one solar cell 100 to a rear bus bar electrode 106 of an adjacent solar cell 100 via an interconnector 201 .
  • the number of solar cells connected is typically 2 to 60.
  • a solar cell module product is thus constructed such that a plurality of solar cells with interconnectors 201 as illustrated above are sandwiched between a transparent substrate such as glass plate and a back cover such as a back-sheet.
  • a super-straight system is generally employed, for example, wherein a plurality of solar cells 100 with interconnectors 201 are sandwiched between the transparent substrate and the back cover, with their light-receiving surfaces facing the transparent substrate, and encapsulated with a transparent fill material such as polyvinyl butyrol (PVB) having a minimal loss of light transmittance or ethylene vinyl acetate (EVA) having improved moisture resistance, and external terminals are connected thereto.
  • PVB polyvinyl butyrol
  • EVA ethylene vinyl acetate
  • solar cells 100 as shown in FIGS. 2 , 4 , 5 and 6 were fabricated by processing 400 semiconductor substrates through the following steps.
  • boron-doped ⁇ 100 ⁇ p-type silicon substrates 100 b as sliced of 15 cm squares and 250 ⁇ m thick, having a resistivity of 2.0 ⁇ cm.
  • the substrate was treated with a conc. potassium hydroxide aqueous solution to remove the damaged layer, textured, heat treated in a phosphorus oxychloride atmosphere at 850° C. to form an n-type diffusion layer 101 , treated with hydrofluoric acid to remove phosphorus glass, cleaned, and dried.
  • SiNx was deposited as an antireflection coating layer 102 .
  • a paste obtained by mixing silver powder and glass frit with an organic binder was screen-printed in a bus bar pattern for rear bus bar electrode 106 . Thereafter, a paste obtained by mixing aluminum powder with an organic binder was screen-printed in a region except on the previously printed bus bar pattern, for aluminum electrode 104 . The organic solvent was dried off, yielding the semiconductor substrate having rear electrodes formed thereon.
  • a conductive paste containing silver powder, glass frit, organic vehicle and organic solvent as main components and metal oxide as additive was printed on the antireflection coating layer 102 on the semiconductor substrate through a screen under such conditions as squeezer rubber hardness 70°, squeezer angle 70°, printing pressure 0.3 MPa, and printing speed 50 mm/sec. After printing, the paste was dried in a clean oven at 150° C. to remove the organic solvent, and fired at 800° C. in an air atmosphere, yielding the solar cell 100 .
  • Two bus bar electrodes were formed with a spacing of 78 mm (in case of three bus bar electrodes, 52 mm) and a line width of 1.5 mm. Finger electrodes had a line width of 90 ⁇ m and a mutual spacing of 2.0 mm. Auxiliary electrodes had a line width of 120 ⁇ m.
  • Solar cell electric properties were evaluated by using a solar simulator (model YSS-160A by Yamashita Denso Corp.). I-V characteristics were measured by irradiating simulated sun light from the simulator to a solar cell sample (substrate temperature 25° C., irradiance 1 kW/m 2 , spectrum AM 1.5 global). From the data, fill factor, short-circuit current density and conversion efficiency were computed. The measurement was reported as an average of 100 solar cell samples for each Example.
  • Warpage of a solar cell was evaluated as shown in FIG. 10 .
  • a solar cell sample 100 was set on a platform 300 , and the distance “d” from the topmost of the sample to the platform 300 was measured.
  • Example 1 the electrode patterns of Examples 1 and 2 demonstrate that even when the electrode area is increased as in Example 1, the reduction in short circuit current is less and the fill factor increases remarkably. This leads to a 0.8% increase in conversion efficiency over Comparative Example 1.
  • a linear interconnector 201 of 2 mm wide and 0.2 mm thick was used. As shown in FIG. 9 , flux was previously applied to the region for connection between interconnector 201 and bus bar electrode 105 , and the interconnector 201 was solder-connected to the bus bar electrode 105 on the light-receiving surface of the solar cell. Likewise, an interconnector 201 was soldered to the rear bus bar electrode 106 of the solar cell. Next, components were stacked in the order of colorless strengthened glass/ethylene vinyl acetate (EVA)/interconnected solar cell 100 /EVA/polyethylene terephthalate (PET). By vacuuming the ambient atmosphere, heat/pressure bonding at a temperature of 150° C. for 10 minutes to make them a module. Furthermore, this module was post-annealed at 150° C. for 1 hour to completely cure. Herein 60 solar cells were connected to each other by interconnectors 201 and encapsulated.
  • EVA colorless strengthened glass/ethylene vinyl acetate
  • PET polyethylene ter
  • the solar cell modules were manufactured.
  • a thermal cycling test (JIS C8917) was performed on each of the solar cell modules manufactured using the solar cells of Examples 1 and 2 and Comparative Examples 1 and 2, comparing the output of the solar cell module before and after the test.
  • the thermal cycling test included 400 cycles under the conditions according to JIS C8917 standards. Specifically, the test includes heating from room temperature (25° C.) to 90° C. at a rate of up to 87° C./hr, holding at the temperature (90° C.) for 10 minutes, then cooling down to ⁇ 40° C. at a rate of up to 87° C./hr, holding at the temperature ( ⁇ 40° C.) for 10 minutes, and heating up to 25° C. at a rate of up to 87° C./hr.
  • the solar cell module using the solar cells of Comparative Example 1 showed an output drop to 77%. In the solar cell module using the solar cells of Comparative Example 2, the output dropped to 54%.
  • the solar cell module using the solar cells of Example 1 showed an output retention of 99%.
  • the solar cell module using the solar cells of Example 2 showed an output retention of 97%. No significant output drops could be found.

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US10861999B2 (en) 2015-04-21 2020-12-08 Sunpower Corporation Shingled solar cell module comprising hidden tap interconnects
US11038072B2 (en) 2014-05-27 2021-06-15 Sunpower Corporation Shingled solar cell module
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EP2916361A1 (en) 2015-09-09

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