Tandem solar cell and method for manufacturing tandem solar cell

Abstract

The present invention provides a tandem solar cell in which a reduction in power generation efficiency can be mitigated. A solar cell 2 is a two-terminal tandem solar cell comprising: a first photoelectric conversion part 10 that includes a crystalline silicon substrate 11; a second photoelectric conversion part 20 which is disposed farther to a light-receiving surface side than the first photoelectric conversion part 10 and which includes a perovskite thin film 21; a first electrode 31 disposed on the light-receiving surface side of the second photoelectric conversion part 20; and a second electrode 32 disposed on a back surface side of the first photoelectric conversion part 10, wherein the portion of the perovskite thin film 21 that corresponds to the first electrode 31 and an interconnect member 6 connected to the first electrode 31 has a higher resistance than other portions of the perovskite thin film 21.

Description

Tandem solar cell and method for manufacturing the tandem solar cell

[0001] The present invention relates to a tandem solar cell and a method for manufacturing a tandem solar cell.

[0002] Solar cell modules in which multiple solar cells are connected by wiring members such as tabs are known. Known solar cell types include crystalline silicon solar cells that use a crystalline silicon substrate as a photoelectric conversion layer, and thin-film solar cells that use an inorganic thin film such as an amorphous silicon thin film as a photoelectric conversion layer. Also known thin-film solar cells include perovskite thin-film solar cells that use a perovskite thin film, which is an organic thin film (more specifically, an organic / inorganic hybrid thin film), as a photoelectric conversion layer.

[0003] Furthermore, in recent years, multi-junction (tandem) solar cells have become known in which two photoelectric conversion units including photoelectric conversion layers with different bandgaps are stacked together, with the aim of effectively utilizing light in a wide wavelength range to increase the conversion efficiency of the solar cell. For example, Patent Document 1 discloses a tandem solar cell including a bottom cell (first photoelectric conversion unit) including a crystalline silicon substrate as the photoelectric conversion layer, and a top cell (second photoelectric conversion unit) including a perovskite thin film as the photoelectric conversion layer.

[0004] Tandem solar cells include two-terminal types in which a top cell and a bottom cell are connected in series, and four-terminal types in which electricity is extracted separately from the top cell and the bottom cell. Furthermore, a three-terminal tandem solar cell has been devised that can utilize the advantages of the two-terminal and four-terminal types and has the potential to further improve photoelectric conversion efficiency (see, for example, Patent Document 2).

[0005] JP 2018-11058 A International Publication No. 2020 / 196288

[0006] In such a tandem solar cell, for example, a slit-shaped electrode is arranged on the light-receiving surface side, and a strip-shaped wiring member is connected to this electrode.

[0007] Because the electrodes on the light-receiving surface side and the wiring members connected to the electrodes are in shadow, dark current leakage can occur in the parts of the perovskite thin film that correspond to the electrodes and the wiring members connected to the electrodes, reducing power generation efficiency.

[0008] An object of the present invention is to provide a tandem solar cell that can suppress a decrease in power generation efficiency, and a method for manufacturing a tandem solar cell.

[0009] The tandem solar cell of the present invention is a two-terminal tandem solar cell comprising a first photoelectric conversion unit including a crystalline silicon substrate, a second photoelectric conversion unit arranged on the light-receiving surface side of the first photoelectric conversion unit and including a perovskite thin film, a first electrode arranged on the light-receiving surface side of the second photoelectric conversion unit, and a second electrode arranged on the back surface side of the first photoelectric conversion unit, and the portion of the perovskite thin film corresponding to the first electrode and a wiring member connected to the first electrode has a higher resistance than other portions of the perovskite thin film.

[0010] The method for manufacturing a tandem solar cell according to the present invention is a method for manufacturing the above-mentioned tandem solar cell, in which the resistance of the perovskite thin film is increased by locally heating the portions of the perovskite thin film corresponding to the first electrode and the wiring member connected to the first electrode.

[0011] According to the present invention, it is possible to suppress a decrease in power generation efficiency in a tandem solar cell.

[0012] 1 is a cross-sectional view of a solar cell module and a solar cell device according to an embodiment of the present invention;

[0013] An example of an embodiment of the present invention will be described below with reference to the accompanying drawings. The same or equivalent parts in each drawing are designated by the same reference numerals. For convenience, hatching and reference numerals may be omitted. In such cases, reference should be made to other drawings.

[0014] (Solar Cell Module and Solar Cell Device) Fig. 1 is a cross-sectional view of a solar cell module and a solar cell device according to this embodiment. An XY Cartesian coordinate system is shown in Fig. 1 and in the drawings described below. The XY plane is a plane along the light-receiving surface and back surface of the solar cell module and solar cell device, as well as the solar cell cells described below. As shown in Fig. 1, the solar cell module 100 includes one or more solar cell devices 1, and the solar cell device 1 includes a plurality of solar cell cells 2.

[0015] The solar cell device 1 is sandwiched between a light-receiving-side protection member 3 and a back-side protection member 4. A liquid or solid sealing material 5 is filled between the light-receiving-side protection member 3 and the back-side protection member 4, thereby sealing the solar cell device 1.

[0016] The encapsulant 5 encapsulates and protects the solar cell device 1, i.e., the solar cell 2, and is interposed between the light-receiving side surface of the solar cell 2 and the light-receiving-side protection member 3, and between the back side surface of the solar cell 2 and the back-side protection member 4. The shape of the encapsulant 5 is not particularly limited, and may be, for example, a sheet. This is because a sheet shape makes it easy to cover the front and back surfaces of the planar solar cell 2.

[0017] The material for the encapsulant 5 is not particularly limited, but preferably has the property of transmitting light (translucency). Furthermore, the material for the encapsulant 5 preferably has adhesive properties that allow it to bond the solar cell 2, the light-receiving-side protection member 3, and the back-side protection member 4 together. Examples of such materials include translucent resins such as ethylene / vinyl acetate copolymer (EVA), ethylene / α-olefin copolymer, ethylene / vinyl acetate / triallyl isocyanurate (EVAT), polyvinyl butyrate (PVB), acrylic resin, urethane resin, and silicone resin.

[0018] The light-receiving-side protection member 3 covers the surfaces (light-receiving surfaces) of the solar cell device 1, i.e., the solar cells 2, via the sealing material 5, to protect the solar cells 2. The shape of the light-receiving-side protection member 3 is not particularly limited, but a plate or sheet shape is preferred in order to indirectly cover the planar light-receiving surface.

[0019] The material for the light-receiving-side protective member 3 is not particularly limited, but, like the encapsulant 5, a material that is translucent and resistant to ultraviolet light is preferred, for example, glass or a transparent resin such as an acrylic resin or a polycarbonate resin. The surface of the light-receiving-side protective member 3 may be textured or may be coated with an anti-reflection coating layer. In this way, the light-receiving-side protective member 3 makes it difficult for the received light to be reflected, allowing more light to be guided to the solar cell device 1.

[0020] The backside protection member 4 covers the backside of the solar cell device 1, i.e., the solar cells 2, via the sealing material 5, to protect the solar cells 2. The shape of the backside protection member 4 is not particularly limited, but similar to the light-receiving-side protection member 3, a plate or sheet shape is preferable in order to indirectly cover the planar backside.

[0021] The material for the back protection member 4 is not particularly limited, but is preferably a material that prevents the intrusion of water, etc. (highly water-proof material.) Examples include resin films such as polyethylene terephthalate (PET), polyethylene (PE), olefin-based resins, fluorine-containing resins, and silicone-containing resins, or laminates of a translucent plate-shaped resin member such as glass, polycarbonate, or acrylic with a metal foil such as aluminum foil.

[0022] The above-described materials for the light-receiving-side protection member 3 and the sealing material 5 provide light transmission for the light-receiving-side protection member 3 and the sealing material 5. Furthermore, if the back-side protection member 4 is also made of one of the above-described materials, the back-side protection member 4 also has light transmission, which is preferable. This allows light to be incident not only from the light-receiving surface side but also from the back surface side, thereby improving photoelectric conversion efficiency.

[0023] The solar cell device 1 includes a plurality of solar cells 2 and a plurality of wiring members 6 .

[0024] The plurality of solar cells 2 are arranged, for example, in the Y direction. The wiring members 6 electrically connect adjacent solar cells 2. Specifically, one end of the wiring member 6 is connected to a first electrode on the light-receiving surface side of one solar cell 2, and the other end of the wiring member 6 is connected to a second electrode on the back surface side of the other solar cell 2. The plurality of solar cells 2 connected in this string-like manner is called a solar cell string (solar cell device).

[0025] A known interconnector such as a tab is used as the wiring member 6. Examples of the wiring member 6 include a ribbon wire made of a copper core material coated with a low-melting-point metal or solder, a conductive film formed of a thermosetting resin film containing low-melting-point metal particles or metal fine particles, or a member formed of a knitted or woven fabric made of a plurality of conductive wires (see, for example, JP 2016-219799 A or JP 2014-3161 A).

[0026] The wiring member 6 may be connected to the first electrode and the second electrode of the solar cell 2 via a conductive adhesive member. Examples of the conductive adhesive member that can be used include a conductive film formed of a thermosetting resin film containing low-melting-point metal particles or metal fine particles, a conductive adhesive formed of low-melting-point metal fine particles or metal fine particles and a binder, and a solder paste containing solder particles.

[0027] (Solar Cell) Fig. 2 is a cross-sectional view schematically showing a solar cell according to this embodiment. The solar cell 2 shown in Fig. 2 is a tandem (multi-junction) two-terminal solar cell including a first photoelectric conversion section 10 (also referred to as bottom cell B) and a second photoelectric conversion section 20 (also referred to as top cell T) stacked on the light-receiving surface side of the first photoelectric conversion section 10.

[0028] The first photoelectric conversion unit 10 (bottom cell B) includes a first semiconductor layer as a photoelectric conversion layer 11. The first semiconductor layer absorbs light and generates photocarriers. The first semiconductor layer as the photoelectric conversion layer 11 is a crystalline silicon substrate such as single crystal silicon or polycrystalline silicon.

[0029] When the first semiconductor layer as the photoelectric conversion layer 11 is a single crystal silicon substrate, examples of the first photoelectric conversion section 10 include a diffusion type cell in which a diffusion layer of a second conductivity type is provided on the light-receiving surface side of a first conductivity type single crystal silicon substrate, and a heterojunction cell in which a silicon-based thin film is provided on both sides of a first conductivity type single crystal silicon substrate.

[0030] In the case of a heterojunction cell in which the first semiconductor layer as the photoelectric conversion layer 11 is a single crystal silicon substrate and has silicon-based thin films on the front and back of the single crystal silicon substrate, the first photoelectric conversion section 10 has a conductive silicon-based thin film 14 formed on the light-receiving surface side of the photoelectric conversion layer 11 and a conductive silicon-based thin film 15 formed on the back side of the photoelectric conversion layer 11.

[0031] The single-crystal silicon substrate may be either p-type or n-type. Since electrons have a higher mobility than holes, the use of an n-type single-crystal silicon substrate provides particularly excellent conversion characteristics. The conductive silicon-based thin films 14 and 15 are p-type or n-type silicon-based thin films.

[0032] An intrinsic silicon-based thin film may be provided between the single crystal silicon substrate as the photoelectric conversion layer 11 and the conductive silicon-based thin films 14, 15. By providing an intrinsic silicon-based thin film on the surface of the single crystal silicon substrate, surface passivation can be effectively performed while suppressing the diffusion of impurities into the single crystal silicon substrate. By providing an intrinsic amorphous silicon thin film as an intrinsic silicon-based thin film on the surface of the single crystal silicon substrate, a high passivation effect can be obtained for the surface of the single crystal silicon substrate.

[0033] The second photoelectric conversion section 20 (top cell T) includes a thin-film second semiconductor layer as the photoelectric conversion layer 21. The second semiconductor layer absorbs light and generates photocarriers. The second semiconductor layer has a band gap different from that of the first semiconductor layer described above. Therefore, the first and second semiconductor layers described above have spectral sensitivity characteristics in different wavelength ranges. Therefore, in a stacked photoelectric conversion section in which the first photoelectric conversion section 10 including the first semiconductor layer as the photoelectric conversion layer 11 and the second photoelectric conversion section 20 including the second semiconductor layer as the photoelectric conversion layer 21 are stacked, light with a wider wavelength range can be contributed to photoelectric conversion.

[0034] Specifically, the thin film constituting the second semiconductor layer may be an organic semiconductor thin film, more specifically, an organic-inorganic hybrid semiconductor thin film, such as a perovskite thin film containing a photosensitive material with a perovskite crystal structure.

[0035] The perovskite thin film includes a perovskite compound, and the perovskite compound is not particularly limited, but may include, for example, an organic atomic group A including at least one of a monovalent organic ammonium ion and an amidinium ion, a metal atom B that generates a divalent metal ion, and a halogen atom X including at least one of an iodide ion I, a bromide ion Br, a chloride ion Cl, and a fluoride ion F, and the structure is ABX. ３ It is also being considered to replace part or all of the organic atomic group A with an alkali metal Am, and such perovskite compounds are not excluded from the present invention.

[0036] Known methods for forming perovskite thin films include wet processes such as printing, coating, and solution methods, and dry processes such as vapor deposition.

[0037] When the photoelectric conversion layer 21 includes a perovskite semiconductor thin film, the second photoelectric conversion section 20 has charge transport layers 24 and 25. One of the charge transport layers 24 and 25 is a hole transport layer, and the other is an electron transport layer.

[0038] The material for the hole transport layer is not particularly limited, but examples thereof include polythiophene derivatives such as poly-3-hexylthiophene (P3HT) and poly(3,4-ethylenedioxythiophene) (PEDOT), fluorene derivatives such as 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD), carbazole derivatives such as polyvinylcarbazole, triphenylamine derivatives, diphenylamine derivatives, polysilane derivatives, and polyaniline derivatives.

[0039] The material for the electron transport layer is not particularly limited, but examples thereof include metal oxides such as titanium oxide, zinc oxide, niobium oxide, zirconium oxide, and aluminum oxide.

[0040] The first photoelectric conversion section 10 and the second photoelectric conversion section 20 are connected in series. Examples of combinations of charge transport layer 24 / charge transport layer 25 / conductive semiconductor layer 14 / conductive semiconductor layer 15 of the second photoelectric conversion section 20 (top cell T) and the first photoelectric conversion section 10 (bottom cell B) include the following combinations: Hole transport layer (HTM) / electron transport layer (ETM) / n-type amorphous silicon semiconductor layer (na-Si) / p-type amorphous silicon semiconductor layer (p-a-Si): pn-np junction type Electron transport layer (ETM) / hole transport layer (HTM) / n-type amorphous silicon semiconductor layer (na-Si) / p-type amorphous silicon semiconductor layer (p-a-Si): np-np junction type Hole transport layer (HTM) / electron transport layer (ETM) / p-type amorphous silicon semiconductor layer (p-a-Si) / n-type amorphous silicon semiconductor layer (na-Si): pn-pn junction type Electron transport layer (ETM) / hole transport layer (HTM) / p-type amorphous silicon semiconductor layer (p-a-Si) / n-type amorphous silicon semiconductor layer (na-Si): np-pn junction type

[0041] The conductive semiconductor layer 14 of the first photoelectric conversion section 10 does not necessarily have to be provided. Furthermore, a transparent electrode 35 may be provided between the first photoelectric conversion section 10 and the second photoelectric conversion section 20.

[0042] An intermediate layer (not shown) may be provided between the first photoelectric conversion section 10 and the second photoelectric conversion section 20. The intermediate layer is provided for purposes such as band gap adjustment between the two stacked photoelectric conversion sections, selective carrier movement, formation of a tunnel junction, and wavelength selective reflection. The configuration of the intermediate layer is selected depending on the type and combination of the photoelectric conversion sections 10 and 20. The intermediate layer can be omitted by having the conductive semiconductor layer 14 and charge transport layer 25 provided at the interface between the first photoelectric conversion section 10 and the second photoelectric conversion section 20 function as an intermediate layer.

[0043] A first electrode 31 for extracting photogenerated carriers is formed on the main surface of second photoelectric conversion section 20 opposite to first photoelectric conversion section 10, i.e., on the light-receiving surface side of solar cell 2. A second electrode 32 for extracting photogenerated carriers is formed on the main surface of first photoelectric conversion section 10 opposite to second photoelectric conversion section 20, i.e., on the back surface side of solar cell 2.

[0044] The first electrode 31 may include a transparent electrode 311 and a metal electrode 312. Similarly, the second electrode 32 may include a transparent electrode 321 and a metal electrode 322. Metal oxides such as ITO, zinc oxide, and tin oxide are preferably used as materials for the transparent electrodes 311 and 321 and the transparent electrode 35. Silver, copper, aluminum, etc. are preferably used as materials for the metal electrodes 312 and 322.

[0045] The metal electrode 312 of the first electrode 31 on the light-receiving surface side is a grid-shaped or slit-shaped electrode. It is also preferable that the metal electrode 322 of the second electrode 32 on the back surface side is a grid-shaped or slit-shaped electrode. This allows light to be incident not only from the light-receiving surface side but also from the back surface side, thereby improving photoelectric conversion efficiency.

[0046] The above-mentioned wiring member 6 is connected onto the metal electrode 312 of the first electrode 31 and the metal electrode 322 of the second electrode 32 .

[0047] The perovskite thin film (photoelectric conversion layer) 21 has a high resistance region R21 in a portion corresponding to the metal electrode 312 of the first electrode 31 and the wiring member 6 connected to the metal electrode 312 of the first electrode 31. The high resistance region R21 has a higher resistance than the other portions of the perovskite thin film 21 other than the high resistance region R21. Furthermore, the high resistance region R21 has a higher transparency than the other portions of the perovskite thin film 21 other than the high resistance region R21.

[0048] (Method of manufacturing solar cell) First, the first photoelectric conversion section 10 is formed. For example, a conductive semiconductor layer 14 is formed on the light-receiving surface side of the photoelectric conversion layer 11, and a conductive semiconductor layer 15 is formed on the back surface side of the photoelectric conversion layer 11. The conductive semiconductor layers 14 and 15 can be formed by known techniques such as CVD or PVD.

[0049] Next, the second photoelectric conversion section 20 is formed. For example, a transparent electrode 35, a charge transport layer 25, a photoelectric conversion layer 21, and a charge transport layer 24 are formed in this order on the conductive semiconductor layer 14 on the light-receiving surface side of the first photoelectric conversion section 10. The transparent electrode 35 can be formed using a known technique, such as a CVD method or a PVD method. The charge transport layer 25 and the charge transport layer 24 can be formed using a known technique, such as a CVD method or a PVD method, such as a printing method, a coating method, a solution method, or a vapor deposition method. The photoelectric conversion layer 21 can be formed using a known technique, such as a printing method, a coating method, a solution method, or a vapor deposition method.

[0050] Next, the transparent electrodes 311 and 321 are formed. Specifically, the transparent electrode 311 is formed on the light-receiving surface side of the second photoelectric conversion section 20, and the transparent electrode 321 is formed on the back surface side of the first photoelectric conversion section 10. The transparent electrodes 311 and 321 are formed by known techniques, such as CVD or PVD.

[0051] Next, a high resistance region R21 is formed in a portion of the perovskite thin film (photoelectric conversion layer) 21 that corresponds to the metal electrode 312 of the first electrode 31 and the wiring member 6 connected to the metal electrode 312 of the first electrode 31. There are no particular limitations on the method for forming the high resistance region R21, but one example is to heat the portion of the perovskite thin film 21 that corresponds to the metal electrode 312 of the first electrode 31 to destroy the perovskite crystals. Heating the perovskite thin film in this way increases its transparency.

[0052] The method for heating the perovskite thin film 21 is not particularly limited, and examples thereof include localized light irradiation or laser irradiation. For example, light irradiation or laser irradiation can be performed on a portion of the perovskite thin film 21 corresponding to the metal electrode 312 of the first electrode 31 from the light-receiving surface side. Alternatively, examples of a method for heating the perovskite thin film 21 include heating by friction, such as applying ultrasonic waves. Alternatively, examples of a method for heating the perovskite thin film 21 include heating by contacting it with a high-temperature substance.

[0053] The perovskite thin film 21 may be heated when the wiring member 6 is heat-pressed to the metal electrode 312 of the first electrode 31, which will be described later, after the metal electrode 312 is formed.

[0054] Next, metal electrodes 312 and 322 are formed. Specifically, metal electrode 312 is formed on the light-receiving surface side of second photoelectric conversion unit 20, and metal electrode 322 is formed on the back surface side of first photoelectric conversion unit 10. Known techniques, such as CVD, PVD, and printing, are used to form metal electrodes 312 and 322.

[0055] In this way, the solar cell 2 shown in FIGS. 1 and 2 is obtained.

[0056] Here, the metal electrode 312 of the first electrode 31 on the light-receiving surface side and the wiring member 6 connected to the metal electrode 312 of the first electrode 31 are in shadow, so dark current leakage may occur in the parts of the perovskite thin film 21 corresponding to the metal electrode 312 of the first electrode 31 and the wiring member 6 connected to the metal electrode 312 of the first electrode 31, which may reduce the power generation efficiency.

[0057] In this regard, according to the solar cell 2 of this embodiment, the portion of the perovskite thin film 21 that corresponds to the metal electrode 312 of the first electrode 31 and the wiring member 6 connected to the metal electrode 312 of the first electrode 31 (high resistance region R21) is high resistance. This disables the portion of the perovskite thin film 21 below the metal electrode 312 of the first electrode 31 and the wiring member 6 connected to the metal electrode 312 of the first electrode 31 as a photoelectric conversion layer, thereby suppressing dark current leakage and reducing power generation efficiency. This makes it possible to suppress performance degradation (reduction in power generation efficiency) of the solar cell 2.

[0058] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and various changes and modifications are possible.

[0059] DESCRIPTION OF SYMBOLS 1 Solar cell device 2 Solar cell 3 Light-receiving side protective member 4 Back side protective member 5 Sealant 6 Wiring member 10, B First photoelectric conversion section (bottom cell) 11 Photoelectric conversion layer (first semiconductor layer) 14, 15 Conductive semiconductor layer (conductive silicon-based thin film) 20, T Second photoelectric conversion section (top cell) 21 Photoelectric conversion layer (second semiconductor layer) R21 High resistance region 24, 25 Charge transport layer 31 First electrode 32 Second electrode 311, 321 Transparent electrode 312, 322 Metal electrode 100 Solar cell module

Claims

1. A two-terminal tandem solar cell comprising: a first photoelectric conversion unit including a crystalline silicon substrate; a second photoelectric conversion unit arranged on the light-receiving surface side of the first photoelectric conversion unit and including a perovskite thin film; a first electrode arranged on the light-receiving surface side of the second photoelectric conversion unit; and a second electrode arranged on the back surface side of the first photoelectric conversion unit, wherein portions of the perovskite thin film corresponding to the first electrode and a wiring member connected to the first electrode have a higher resistance than other portions of the perovskite thin film.

2. A tandem solar cell according to claim 1, wherein the portion of the perovskite thin film corresponding to the first electrode and the wiring member connected to the first electrode has higher transparency than other portions of the perovskite thin film.

3. A method for manufacturing a tandem solar cell according to claim 1 or 2, wherein the resistance of the perovskite thin film is increased by locally heating the portions of the perovskite thin film that correspond to the first electrode and the wiring member connected to the first electrode.

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