EP2529411A1 - Solar cell and method for manufacturing the same - Google Patents

Solar cell and method for manufacturing the same

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Publication number
EP2529411A1
EP2529411A1 EP20110857332 EP11857332A EP2529411A1 EP 2529411 A1 EP2529411 A1 EP 2529411A1 EP 20110857332 EP20110857332 EP 20110857332 EP 11857332 A EP11857332 A EP 11857332A EP 2529411 A1 EP2529411 A1 EP 2529411A1
Authority
EP
Grant status
Application
Patent type
Prior art keywords
layer
back
electrode
substrate
holes
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP20110857332
Other languages
German (de)
French (fr)
Other versions
EP2529411A4 (en )
Inventor
Do Won Bae
Young Sam Yu
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
LG Innotek Co Ltd
Original Assignee
LG Innotek Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L31/00Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and 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 peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and 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 peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and 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 peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by at least one potential-jump barrier or surface barrier
    • H01L31/072Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and 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 peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by at least one potential-jump barrier or surface barrier the potential barriers being only of the PN heterojunction type
    • H01L31/0749Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and 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 peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by at least one potential-jump barrier or surface barrier the potential barriers being only of the PN heterojunction type including a AIBIIICVI compound, e.g. CdS/CulnSe2 [CIS] heterojunction solar cells
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L31/00Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and 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 peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02Details
    • H01L31/0224Electrodes
    • H01L31/022408Electrodes for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/022425Electrodes for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L31/00Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and 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 peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02Details
    • H01L31/0236Special surface textures
    • H01L31/02366Special surface textures of the substrate or of a layer on the substrate, e.g. textured ITO/glass substrate or superstrate, textured polymer layer on glass substrate
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L31/00Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and 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 peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and 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 peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042PV modules or arrays of single PV cells
    • H01L31/0445PV modules or arrays of single PV cells including thin film solar cells, e.g. single thin film a-Si, CIS or CdTe solar cells
    • H01L31/046PV modules composed of a plurality of thin film solar cells deposited on the same substrate
    • H01L31/0463PV modules composed of a plurality of thin film solar cells deposited on the same substrate characterised by special patterning methods to connect the PV cells in a module, e.g. laser cutting of the conductive or active layers
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/50Photovoltaic [PV] energy
    • Y02E10/54Material technologies
    • Y02E10/541CuInSe2 material PV cells
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50Manufacturing or production processes characterised by the final manufactured product
    • Y02P70/52Manufacturing of products or systems for producing renewable energy
    • Y02P70/521Photovoltaic generators

Abstract

Disclosed are a solar cell and a method for manufacturing the same. The solar cell includes a substrate, a back electrode layer on the substrate, a light absorbing layer on the back electrode layer, a buffer layer on the light absorbing layer, and a window layer on the buffer layer. The lateral surfaces of the first through holes are inclined with respect to the top surface of the substrate.

Description

    SOLAR CELL AND METHOD FOR MANUFACTURING THE SAME
  • [01]
    The embodiment relates to a solar cell and a method for manufacturing the same.
  • [02]
    Recently, as energy consumption is increased, the development on a solar cell to convert solar energy into electrical energy has been performed.
  • [03]
    In particular, a CIGS-based solar cell has been extensively used, in which the CIGS-based solar cell is a PN hetero junction device having a support substrate structure including a glass support substrate, a metallic back electrode layer, a P type CIGS-based light absorbing layer, a buffer layer, and an N type transparent electrode layer.
  • [04]
    In addition, in order to increase the efficiency of the solar cell, various studies have been performed.
  • [05]
    The embodiment provides a solar cell having improved reliability and a method for manufacturing the same.
  • [06]
    According to the embodiment, a solar cell includes a substrate, a back electrode layer on the substrate, a light absorbing layer on the back electrode layer, a buffer layer on the light absorbing layer, and a window layer on the buffer layer. The lateral surfaces of the first through holes are inclined with respect to the top surface of the substrate.
  • [07]
    According to the embodiment, a method for manufacturing a solar cell includes forming a back electrode layer on a substrate, etching a portion of the back electrode layer to expose a top surface of the substrate; and forming a light absorbing layer, a buffer layer, and a window layer on the back electrode layer. A laser beam is irradiated onto the substrate while being inclined with respect to the top surface of the substrate when the portion of the back electrode layer is etched.
  • [08]
    As described above, according to the embodiment, the lateral surfaces of the back electrode layer divided into a plurality of back electrode layers by the first through holes can be inclined with respect to the substrate. Accordingly, the burr cannot be prevented from occurring due to the thermal shock caused by the laser beams when the first through holes are formed.
  • [09]
    In addition, coverage failures can be prevented by the first through holes having inclined surfaces with respect to the support substrate, so that the reliability of the solar cell can be improved.
  • [10]
    FIG. 1 is a plan view showing a solar power generator according to the embodiment;
  • [11]
    FIG. 2 is a sectional view taken along line A-A'of FIG. 1;
  • [12]
    FIG. 3 is an enlarged sectional view of B of FIG. 2; and
  • [13]
    FIGS. 4 to 7 are sectional views showing a method for manufacturing a solar cell according to the embodiment.
  • [14]
    In the description of the embodiments, it will be understood that, when a layer (or film), a region, a pattern, or a structure is referred to as being 'on' or 'under' another substrate, another layer (or film), another region, another pad, or another pattern, it can be directly or indirectly on the other substrate, layer (or film), region, pad, or pattern, or one or more intervening layers may also be present. Such a position of the layer has been described with reference to the drawings.
  • [15]
    The thickness and size of each layer shown in the drawings may be exaggerated, omitted or schematically drawn for the purpose of convenience or clarity. In addition, the size of elements does not utterly reflect an actual size.
  • [16]
    FIG. 1 is a plan view showing a solar power generator according to the embodiment, and FIG. 2 is a sectional view taken along line A-A'of FIG. 1
  • [17]
    Referring to FIG. 2, the solar cell according to the embodiment includes a support substrate 100, an back electrode layer 200 on the support substrate 100, a light absorbing layer 300 on the back electrode layer 200, a buffer layer 400 and a high resistance buffer layer 500 on the light absorbing layer 300, and a window layer 600 on the high resistance buffer layer 500
  • [18]
    The support substrate 100 has a plate shape and supports the back electrode layer 200, the light absorbing layer 300, the buffer layer 400, the high resistance buffer layer 500, and the window layer 600. The support substrate 100 may include an insulator. The support substrate 100 may include a glass substrate, a plastic substrate, or a metallic substrate. In more detail, the support substrate 100 may include a soda lime glass substrate.
  • [19]
    If the support substrate 100 includes soda lime glass, sodium (Na) contained in the soda lime glass may be diffused into the light absorbing layer 300 including CIGS when manufacturing the solar cell. Accordingly, the concentration of charges of the light absorbing layer 300 may be increased. Therefore, the photoelectric conversion efficiency can be increased.
  • [20]
    In addition, the support substrate 100 may include a ceramic substrate including alumina, stainless steel, or polymer having flexibility. Therefore, the support substrate 100 may be transparent, rigid, or flexible.
  • [21]
    The back electrode layer 200 is provided on the support substrate 100. The back electrode layer 200 is a conductive layer. The back electrode layer 200 moves charges generated from the light absorbing layer 300 of the solar cell so that current can flow to the outside of the solar cell.
  • [22]
    The back electrode layer 200 must represent high electrical conductivity or low resistivity to perform the functions.
  • [23]
    In addition, since the back electrode layer 200 makes contact with a CIGS compound constituting the light absorbing layer 300, the back electrode layer 200 must make ohmic contact with the light absorbing layer 300 so that a low contact resistance value can be obtained.
  • [24]
    The back electrode layer 200 must maintain stability in the high-temperature condition when the heat treatment process is performed under sulfur (S) or selenium (Se) atmosphere as a CIGS compound is formed. In addition, the back electrode layer 200 must represent a superior adhesive property with respect to the support substrate 100 such that the back electrode layer 200 is not delaminated from the support substrate 100 due to the difference in the thermal expansion coefficient between the back electrode layer 200 and the support substrate 100.
  • [25]
    The back electrode layer 200 may include one selected from the group consisting of molybdenum (Mo), gold (Au), aluminum (Al), chrome (Cr), tungsten (W), and copper (Cu). Among them, the Mo represents the low thermal expansion coefficient difference with the support substrate 100 as compared with other elements. Accordingly, the Mo represents a superior adhesive property with respect to the support substrate 100, so that delamination from the support substrate 100 can be prevented. In addition, the Mo satisfies the characteristics required for the back electrode layer 200.
  • [26]
    The back electrode layer 200 may include at least two layers. In this case, the layers include the same metal, or different metals.
  • [27]
    First through holes TH1 are formed in the back electrode layer 200. The first through holes TH1 are open regions to expose portions of the top surface of the support substrate 100. The first through holes TH1 may extend in one direction when viewed in a plan view.
  • [28]
    The width of the support substrate 100 exposed through the first through hole TH1 is in the range of about 20㎛ to about 150㎛.
  • [29]
    The back electrode layer 200 is divided into a plurality of back electrodes by the first through holes TH1. In other words, the back electrodes are defined by the first through holes TH1.
  • [30]
    The back electrodes are arranged in the shape of a stripe. In addition, the back electrodes may be arranged in the form of a matrix. In this case, the first through holes TH1 may be formed in the form of a lattice when viewed in a plan view.
  • [31]
    The first through holes TH1 are patterned by using a laser. When a conventional laser-based patterning process is performed by irradiating a laser beam perpendicularly to the support substrate 100 in order to form the first through holes TH1, burr may occur in the back electrode layer 200 due to thermal expansion and thermal shock in the region into which the laser beam is irradiated.
  • [32]
    The burr refers to a process trace which occurs at the edge of the first through hole TH1 because a tip of the edge is thinly rolled when the back electrode layer 200 is patterned.
  • [33]
    In the case of a large-area solar cell, the back electrode layer 200 grown from the support substrate 100 may include a plurality of layers having different densities. In this case, a lower back electrode layer 200 in the contact with the support substrate 200 may have a low density in order to improve the adhesive property with respect to the support substrate 100. An upper back electrode layer in the contact with the light absorbing layer 300 may have a higher density based on electrical conductivity.
  • [34]
    When a plurality of layers having different densities are grown, the thermal expansion coefficient of the lower back electrode layer having the lower density may have a greater value due to thermal shock caused by the laser beam when performing the patterning process to form the first through holes TH1.
  • [35]
    Accordingly, since the lower back electrode layer is more expanded than the upper back electrode layer, the edges of the back electrode layer in which the first through holes TH1 are formed are curved upward.
  • [36]
    In addition, when the first through holes TH1 are formed in the back electrode layers 200 by vertically irradiating a laser beam, the light absorbing layer 300 may be not uniformly grown, but have the shape in which grains are combined with each other. Accordingly, coverage failures may occur.
  • [37]
    Therefore, current loss may occur at the interface between the grains. In addition, since the grains may be spaced away from the substrate 100 by a predetermined distance, the reliability of the device may be improved.
  • [38]
    FIG. 3 is an enlarged view of B of FIG. 2. According to the embodiment, lateral surfaces 210 and 220 of the first through holes TH1 are inclined at a predetermined angle θ with respect to a normal line to the support substrate 100.
  • [39]
    If the predetermined angle θ exceeds about 80° the distance between adjacent back electrodes is increased. Accordingly, a solar generation region is increased. If the predetermined angle θ is less than 30° the distance between adjacent back electrodes is narrowed, so that short may occur between adjacent solar cells. Accordingly, the angle θ may be formed in the range of 10°〈θ≤80° preferably, in the range of 30°≤θ≤80°
  • [40]
    The lateral surfaces 210 and 220 of the first through holes TH1 may be formed at the same angle, or may be formed at different angles within the angular range.
  • [41]
    The back electrode layer 200 may be formed in the shape of a trapezoid representing that the back electrode layers 200 have etch areas different from each other in the upper and lower portions thereof by the angle θ. In other words, laser beams are incident in a plurality of directions in order to form the first through holes TH1 while being inclined with respect to the normal surface to the support substrate 100, so that the etch areas of the first through holes TH1 are enlarged upward.
  • [42]
    Since a plurality of laser beams are incident while being inclined to each other to form the first through holes TH1 as described above, the lateral surface of the back electrode layer 200 is inclined with respect to the support substrate 100.
  • [43]
    In other words, since the etch area is increased upward from the support substrate 100, the width of the first through holes TH1 may be increased upward. Accordingly, the probability of generating the burr due to the difference in thermal expansion coefficient between the upper and lower portions of the back electrode layer 200 is reduced, so that the reliability of the device can be improved.
  • [44]
    The light absorbing layer 300 may be formed on the back electrode layer 200. The light absorbing layer 300 includes a P type semiconductor compound. In more detail, the light absorbing layer 300 includes group I-III-V compounds. For example, the light absorbing layer 300 may have a Cu-In-Ga-Se-based crystal structure (Cu(In,Ga)Se2;CIGS), a Cu-In-Se-based crystal structure, a Cu-Ga-Se based crystal structure, or a Cu-Zn-Sn- Se-based crystal structure.
  • [45]
    The buffer layer 400 and the high resistance buffer layer 500 may be formed on the light absorbing layer 300. In a solar cell including a CIGS compound constituting the light absorbing layer 300, PN junction is formed between a CIGS compound thin film including a P type semiconductor and the window layer 600 including an N type semiconductor.
  • [46]
    However, since two above materials represent great difference in a lattice constant and bandgap energy, a buffer layer having intermediate band gap between the band gaps of the two materials is required in order to form superior junction.
  • [47]
    The buffer layer 400 includes group II-VI materials such as CdS or ZnS, and the CdS represents more improved generating efficiency of the solar cell.
  • [48]
    The high-resistance buffer layer 500 includes i-ZnO that is not doped with impurities. The energy band gap of the high-resistance buffer layer 500 is in the range of about 3.1eV to about 3.3eV.
  • [49]
    The window layer 600 is formed on the high-resistance buffer layer 500. The window layer 600 is a transparent conductive layer. In addition, the resistance of the window layer 600 is higher than the resistance of the back electrode layer 200.
  • [50]
    The window layer 600 includes an oxide. For example, the window layer 600 may include zinc oxide, indium tin oxide (ITO), or indium zinc oxide (IZO).
  • [51]
    In addition the oxide may include conductive impurities such as aluminum (Al), alumina (Al2O3), magnesium (Mg), or gallium (Ga). In more detail, the window layer 600 may include Al doped zinc oxide (AZO) or Ga doped zinc oxide (GZO).
  • [52]
    As described above, since the first through holes TH1 have inclined surfaces with respect to a normal line to the support substrate 100, the burr can be prevented from occurring due to the thermal shock caused by the laser beams when the first through holes TH1 are formed.
  • [53]
    In addition, since coverage failures can be prevented by the first through holes TH1 having inclined surfaces with respect to the support substrate 100, the reliability of the solar cell can be improved.
  • [54]
    FIGS. 4 to 7 are sectional views showing a method for manufacturing the solar power generator according to the embodiment. The details of the method for manufacturing the solar cell apparatus will be given based on the description about the solar cell apparatus that has been described.
  • [55]
    Referring to FIG. 4, after forming the back electrode layer 200 on the support substrate 100, the back electrode layer 200 is patterned, thereby forming the first through holes TH1. Accordingly, a plurality of back electrodes are formed on the support substrate 100. The back electrode layer 200 is patterned by using a laser.
  • [56]
    The first through holes TH1 expose the top surface of the support substrate 100, and may have a width in the range of about 80㎛ to about 200㎛.
  • [57]
    In addition, an additional layer such as an anti-diffusion layer may be interposed between the support substrate 100 and the back electrode layer 200. In this case, the first through holes TH1 expose the top surface of the additional layer.
  • [58]
    The first through holes TH1 may have an inclined lateral surface. To this end, a plurality of laser beams may be irradiated to the support substrate 100 at an inclined angle with respect to the normal line to the support substrate 100.
  • [59]
    The back electrode layer 200 may be formed in the shape of a trapezoid representing that the back electrode layer 200 has etch areas different from each other in the upper and lower portions thereof. In other words, a laser beam is incident in a plurality of directions in order to form the first through hole TH1 while being inclined with respect to the normal surface to the support substrate 100. Accordingly, the first through hole TH1 has an etch area enlarged upward.
  • [60]
    Preferably, the first through holes TH1 are formed by overlapping focuses of the laser beams with each other by about 5% to about 60%.
  • [61]
    For example, the first through holes TH1 may be formed by a laser beam having a wavelength in the range of about 500nm to about 1200nm.
  • [62]
    Referring to FIG. 5, the light absorbing layer 300, the buffer layer 400, and the high-resistance buffer layer 500 are formed on the back electrode layer 200.
  • [63]
    The light absorbing layer 300 may be formed through a sputtering process or an evaporation scheme. For example, the light absorbing layer 300 may be formed through various schemes such as a scheme of forming a Cu(In,Ga)Se2 (CIGS) based-light absorbing layer 300 by simultaneously or separately evaporating Cu, In, Ga, and Se and a scheme of performing a selenization process after a metallic precursor film has been formed.
  • [64]
    Regarding the details of the selenization process after the formation of the metallic precursor layer, the metallic precursor layer is formed on the back contact electrode 200 through a sputtering process employing a Cu target, an In target, or a Ga target.
  • [65]
    Thereafter, the metallic precursor layer is subject to the selenization process so that the Cu(In,Ga)Se2 (CIGS) based-light absorbing layer 300 is formed.
  • [66]
    Different from the above, the sputtering process and the selenization process employing the Cu target, the In target, and the Ga target may be simultaneously performed.
  • [67]
    In addition, a CIS or a CIG light absorbing layer 300 may be formed through a sputtering process and the selenization process employing only Cu and In targets or only Cu and Ga targets.
  • [68]
    Thereafter, the buffer layer 400 may be formed after depositing cadmium sulfide through a sputtering process or a CBD (chemical bath deposition) scheme.
  • [69]
    Next, a portion of the light absorbing layer 300, the buffer layer 400, and the high-resistance buffer layer 500 is removed, thereby forming second through holes TH2.
  • [70]
    The second through holes TH2 may be formed through a mechanical device such as a tip or a laser.
  • [71]
    For example, the light absorbing layer 300 and the buffer layer 400 may be patterned by the tip having a width of about 40㎛ to about 180㎛. In addition, the second through holes TH2 may be formed by the laser having the wavelength of about 200㎚ to about 600㎚ nanometers.
  • [72]
    The second through holes TH2 may have a width in the range of about 30㎛ to about 100㎛.
  • [73]
    In addition, the second through holes TH2 is formed to expose a portion of the top surface of the back electrode layer 200.
  • [74]
    Referring to FIG. 6, the window layer 600 is formed above the light absorbing layer 300 and at inner parts of the second through holes TH2. In other words, the window layer 600 is formed by depositing a transparent conductive material above the buffer layer 400 and at the inner parts of the second through holes TH2.
  • [75]
    In this case, the transparent conductive material is filled in the second through holes TH2, and the window layer 600 directly makes contact with the back electrode layer 200.
  • [76]
    In this case, the window layer 600 may be formed by depositing a transparent conductive material at an oxygen-free atmosphere. In more detail, the window layer 600 may be formed by depositing AZO under the atmosphere of inert gas that does not include oxygen.
  • [77]
    Next, portions of the buffer layer 400, the high-resistance buffer layer 500, and the window layer 600 are removed to form third through holes TH3. Accordingly, the window layer 600 is patterned, thereby defining a plurality of windows and a plurality of cells C1, C2, ... and CN. The width of each third through hole TH3 may be in the range of about 30㎛ to about 200㎛.
  • [78]
    Connection parts 700 are provided in the second through holes TH2. The connection parts 700 extend downward from the window layer 600 to make contact with the back electrode layer 200. For example, the connection part 700 extends from the window of the first cell to make contact with the back electrode of the second cell.
  • [79]
    Accordingly, the connection parts 700 connect adjacent cells to each other. In more detail, the connection parts 700 connect windows and back electrodes, which are contained in the cells C1, C2, ... and CN adjacent to each other, to each other.
  • [80]
    The connection part 700 is integrated with the window layer 600. In other words, the connection part 700 includes the same material as that constituting the window layer 600.
  • [81]
    Referring to FIG. 7, the portions of the buffer layer 400, the high-resistance buffer layer 500, and the window layer 600 are removed to form the third through hole TH3. Accordingly, the window layer 600 is patterned, thereby defining a plurality of windows and a plurality of cells C1, C2, ... and CN.
  • [82]
    As descried above, according to the embodiment, burrs can be prevented from occurring due to the thermal shock caused by a laser beam when the first through holes are formed. Accordingly, the reliability of the solar cell can be improved.
  • [83]
    Any reference in this specification to one embodiment, an embodiment, example embodiment,etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effects such feature, structure, or characteristic in connection with other ones of the embodiments.
  • [84]
    Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure.  More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims.  In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.

Claims (11)

  1. A solar cell comprising:
    a substrate;
    a back electrode layer on the substrate;
    a light absorbing layer on the back electrode layer;
    a buffer layer on the light absorbing layer; and
    a window layer on the buffer layer,
    wherein the back electrode layer includes first through holes, and has a trapezoidal shape in which an upper area is different from a lower area.
  2. The solar cell of claim 1, wherein a lateral surface of the back electrode layer formed with the first through holes is inclined at an angle of about 30°to about 60°with respect to a normal line to the substrate.
  3. The solar cell of claim 1, wherein the back electrode layer includes a plurality of back electrode layers.
  4. The solar cell of claim 3, wherein an upper back electrode layer of the back electrode layers has a particle density higher than a particle density of a lower back electrode layer of the back electrode layers.
  5. The solar cell of claim 1, wherein each first through hole has a width of about 20㎛ to about 150㎛.
  6. The solar cell of claim 1, further comprising an intermediate layer doped with sodium (Na) and interposed between the substrate and the back electrode layer.
  7. A method for manufacturing a solar cell, the method comprising:
    forming a back electrode layer on a substrate;
    etching a portion of the back electrode layer to expose a top surface of the substrate; and
    forming a light absorbing layer, a buffer layer, and a window layer on the back electrode layer,
    wherein a laser beam is irradiated onto the substrate while being inclined with respect to the top surface of the substrate when the portion of the back electrode layer is etched.
  8. The method of claim 7, wherein the laser beam is irradiated several times such that laser beams are irradiated symmetrically to each other about a normal line of the substrate and each laser beam is inclined at an angle of about 30°to about 60°with respect to the normal line of the substrate.
  9. The method of claim 7, wherein the first through holes are formed by irradiating the laser beam having a wavelength of about 500nm to about 1200nm.
  10. The method of claim 7, wherein the forming of the back electrode layer comprises:
    forming a lower back electrode layer adjacent to the substrate; and
    forming an upper back electrode layer, which has a particle density higher than a particle density of the lower back electrode layer, on the lower back electrode layer.
  11. The method of claim 8, wherein the first through holes are formed by overlapping focuses of the laser beams with each other by about 5% to about 60%.
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KR101405113B1 (en) * 2013-03-12 2014-06-11 한국에너지기술연구원 Solar Cell with Back-Side Buffer Layer and its Fabrication Method.
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EP2169724A1 (en) * 2007-06-04 2010-03-31 Kaneka Corporation Integrated thin film solar cell and method for fabricating the same
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US20100035052A1 (en) * 2005-11-02 2010-02-11 John Farah Polyimide substrate bonded to other substrate
EP2169724A1 (en) * 2007-06-04 2010-03-31 Kaneka Corporation Integrated thin film solar cell and method for fabricating the same
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