WO2023048117A1

WO2023048117A1 - Solar cell

Info

Publication number: WO2023048117A1
Application number: PCT/JP2022/034907
Authority: WO
Inventors: 暢入江; 良太三島
Original assignee: 株式会社カネカ
Priority date: 2021-09-22
Filing date: 2022-09-20
Publication date: 2023-03-30

Abstract

A solar cell 1 according to an aspect of the present invention has high production efficiency and receives light on a side opposite to a base material. The solar cell 1 comprises, in the following order, a base material 10, a first electrode layer 21, a first charge transport layer 22, a photoelectric conversion layer 23 including a perovskite compound, a second charge transport layer 24, a buffer layer 25 made of an organic material, a contact layer 26 made of a polycrystal ITO, and a second electrode layer 27 made of an amorphous ITO.

Description

solar cell

The present invention relates to solar cells.

The use of solar cells is expanding as an energy source with a low environmental impact. When arranging solar cells in various devices, vehicles, buildings, etc., the photoelectric conversion efficiency of the solar cells can be important because the installation area is limited. Perovskite solar cells using organic materials have been studied as solar cells with high photoelectric conversion efficiency. A basic perovskite solar cell consists of a substrate, a first electrode (anode or cathode), a first charge transport layer (hole transport layer or electron transport layer), a photoelectric conversion layer (perovskite layer), a second charge transport layer. (electron transport layer or hole transport layer) and a second electrode (cathode or anode) are laminated in this order. Furthermore, by providing a first buffer layer between the first electrode and the first charge transport layer, or providing a second buffer layer between the second charge transport layer and the second electrode, the photoelectric conversion efficiency can be improved. It is also known that it can be improved.

In order to allow light to enter the photoelectric conversion layer, at least one of the first and second electrodes of the perovskite solar cell is a transparent electrode that can be made of metal oxide such as ITO. Such a transparent electrode can be formed, for example, by a physical vapor deposition method such as sputtering. However, when a material is laminated on a layer containing an organic substance by a physical vapor deposition method, the organic substance may be damaged and the performance of the solar cell may be deteriorated. . For this reason, in a general perovskite solar cell, a transparent electrode is laminated as a first electrode on a transparent base material, a layer that can contain an organic substance such as a photoelectric conversion layer is laminated, and finally a second electrode is laminated with silver. It is formed of paste or the like, and is often configured to receive light from the substrate side.

However, there are also perovskite solar cells that receive light from the opposite side of the substrate. By way of example, US Pat. No. 6,300,001 describes a tandem solar cell using a crystalline silicon solar cell as the substrate. The tandem solar cell utilizes the fact that the wavelengths of light photoelectrically converted by the perovskite solar cell and the crystalline silicon solar cell are different. A crystalline silicon solar cell photoelectrically converts the light of the wavelength. In this case, both the first electrode and the second electrode of the perovskite solar cell need to be transparent electrodes.

JP 2018-163959 A

When the second electrode on the opposite side of the substrate of the perovskite solar cell is a transparent electrode, a thin film such as SnO ₂ is deposited as the second buffer layer by atomic layer deposition (ALD: Atomic Layer Deposition) can suppress a decrease in photoelectric conversion efficiency. However, since atomic layer deposition takes a long process time, it is difficult to improve production efficiency.

An object of the present invention is to provide a solar cell that has high production efficiency and receives light on the side opposite to the substrate.

A solar cell according to an aspect of the present invention includes a substrate, a first electrode layer, a first charge transport layer, a photoelectric conversion layer containing a perovskite compound, a second charge transport layer, and an organic material. A buffer layer, a contact layer made of polycrystalline ITO, and a second electrode layer made of amorphous ITO are provided in this order.

In the solar cell described above, the doping amount of tin oxide in the second electrode layer may be larger than the doping amount of tin oxide in the contact layer.

In the solar cell described above, the second charge transport layer may contain fullerene.

In the solar cell described above, the contact layer may have a thickness of 3 nm or more and 20 nm or less, and the second electrode layer may have a thickness of 10 nm or more and 200 nm or less.

In the solar cell described above, the substrate may be a crystalline silicon solar cell.

According to the present invention, it is possible to provide a solar cell that has high production efficiency and receives light on the side opposite to the substrate.

1 is a schematic cross-sectional view showing a layer structure of a solar cell according to one embodiment of the present invention; FIG. 4 is a graph showing output characteristics of an example of the present invention;

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the layer structure of a solar cell 1 according to one embodiment of the invention.

The solar cell 1 includes a base material 10, a perovskite solar cell part 20 laminated on the surface of the base material 10, a back surface collection electrode 31 laminated on the back surface of the base material 10, and a part on the surface of the perovskite solar cell part 20. and an antireflection layer 33 covering the surface of the perovskite solar cell section 20 and the surface collector electrode 32 . Light enters the solar cell 1 through the antireflection layer 33 and performs photoelectric conversion in the perovskite solar cell section 20 .

The base material 10 is a structure that supports the perovskite solar cell part 20, and may have a photoelectric conversion function. Specifically, the substrate 10 may be, for example, a glass substrate, a resin sheet, or the like, but in the solar cell 1 of this embodiment, the substrate 10 is a crystalline silicon solar cell. In the solar cell 1 , light incident through the antireflection layer 33 is first photoelectrically converted by the perovskite solar cell section 20 , and light having a wavelength transmitted through the perovskite solar cell section 20 is photoelectrically converted by the crystalline silicon solar cell 10 . Since the crystalline silicon solar cell has sufficient strength, it can function as the base material 10 that supports the perovskite solar cell portion 20, and converts the light that has passed through the perovskite solar cell portion 20 into electricity. Conversion efficiency can be improved. In the solar cell 1, the crystalline silicon solar cell and the perovskite solar cell portion 20 are connected in series by laminating the perovskite solar cell portion 20 on the crystalline silicon solar cell serving as the substrate 10.

The base material 10 of the present embodiment includes a semiconductor substrate 11, a first semiconductor layer 12 laminated on the front surface side of the semiconductor substrate 11, and a second semiconductor layer 13 laminated on the back surface side of the semiconductor substrate 11.

The perovskite solar cell section 20 includes, from the substrate 10 side, a first electrode layer 21, a first charge transport layer 22, a photoelectric conversion layer 23, a second charge transport layer 24, a buffer layer 25, and a contact layer 26. , and the second electrode layer 27 are provided in this order.

The first electrode layer 21 is one electrode of the perovskite solar cell section 20, and is a positive electrode in this embodiment. The first electrode layer 21 can be formed of a transparent conductive oxide (TCO) having electrical conductivity and optical transparency, a thin semiconductor layer, or the like. As the transparent conductive oxide forming the first electrode layer 21, for example, indium oxide, tin oxide, zinc oxide, titanium oxide, composite oxides thereof, and the like can be used. Among these, an indium-based composite oxide containing indium oxide as a main component is preferable. Indium oxide is particularly preferred from the viewpoint of high electrical conductivity and transparency. Additionally, it is preferable to add dopants to the indium oxide to ensure reliability or higher conductivity. Examples of dopants include Sn, W, Zn, Ti, Ce, Zr, Mo, Al, Ga, Ge, As, Si, S and the like. For example, ITO (Indium Tin Oxide), in which tin is added to indium oxide, is widely known.

The first electrode layer 21 can be laminated on the substrate 10 by a method such as sputtering or vacuum deposition. The thickness of the first electrode layer can be, for example, 1 nm or more and 200 nm or less when electric power is output from the perovskite solar cell section 20 to the base material 10 (when current flows in the thickness direction).

The first charge transport layer 22 is a layer that allows passage of charges of the first polarity generated in the photoelectric conversion layer 23, and in this embodiment, a hole transport layer (HTL) that transmits holes to the first electrode layer 21. is. As the main material of the first charge transport layer 22 which is a hole transport layer, metal oxides such as nickel oxide (NiO) and copper oxide (Cu ₂ O), for example, PTAA (Poly(bis(4-phenyl)( 2,4,6-trimethylphenyl)amine)) and Spiro-MeOTAD. Further, the first charge transport layer 22 includes, for example, 2PACz ([2-(9H-Carbazol-9-yl)ethyl]phosphonic Acid), MeO-2PACz ([2-(3,6-Dimethoxy-9H-carbazol-9 SAM: Self-Assembled Monolayers). Also, the first charge transport layer 22 may have a multilayer structure.

The first charge transport layer 22 can be formed by a method such as sputtering or vacuum deposition. Also, the first charge transport layer 22 containing an organic substance can be formed by a method such as applying a solution of an organic substance and drying it. The thickness of the first charge transport layer 22 may vary greatly depending on the material, the structure of adjacent layers, etc., but can be, for example, 1 nm or more and 200 nm or less. thickness.

Photoelectric conversion layer 23 contains a perovskite compound. As the perovskite compound, an organic atom A containing at least one of monovalent organic ammonium ions and amidinium ions, a metal atom B that generates a divalent metal ion, an iodide ion I, a bromide ion Br, and a chloride A compound represented by ABX ₃ containing a halogen atom X containing at least one of a compound ion Cl and a fluoride ion F can be used. Among them, when the photoelectric conversion layer 23 is formed by a vapor deposition method (dry process), the organic atom A is preferably methylammonium MA(CH ₃ NH ₃ ), the metal atom B is preferably lead Pb, and the halogen atom X is preferably At least one of iodide I, bromide ion Br and chloride ion Cl is preferred.

Specifically, preferred perovskite compounds include methylammonium lead halide MAPbX ₃ (CH ₃ NH ₃ PbX ₃ ), MAPbI ₃ , MAPbBr ₃ and MAPbCl ₃ . In addition, as the halogen atom X, multiple types may be included. Examples of perovskite compounds containing iodide I and other halogen atoms X include methylammonium lead iodide MAPbI _y X _(3-y) (CH ₃ NH ₃ PbI _y X _(3-y) ), MAPbI _y Br _{( 3-y)} , MAPbI _y Cl _(3-y) , etc. (y is any positive integer).

When the perovskite compound is methylammonium lead halide (MAPbX ₃ (CH ₃ NH ₃ PbX ₃ )), the photoelectric conversion layer 23 is made of lead halide (PbX ₂ ) material and methylammonium halide (MAX) material in order. can be formed by coating and reacting thin films of these materials at reaction temperatures. For example, when the perovskite compound is methylammonium lead iodide (MAPbI _y X _(3-y) (CH ₃ NH ₃ PbI _y X _(3-y) )), the photoelectric conversion layer 23 is, for example, a lead halide (PbX2 ) material and a methylammonium iodide (MAI) material, and reacting thin films of these materials at the reaction temperature. The photoelectric conversion layer 23 can also be formed by a method such as a sol-gel method for synthesizing a perovskite compound in a liquid-phase coating film, or a coating method for applying a solution containing a pre-synthesized perovskite compound.

The thickness of the photoelectric conversion layer 23 is preferably 100 nm or more and 1000 nm or less in order to increase the light absorptivity and reduce the travel distance of the generated charges, although it depends on the forming material.

The second charge transport layer 24 is a layer that allows passage of charges of the second polarity generated in the photoelectric conversion layer 23. In this embodiment, the second charge transport layer 24 transfers electrons to the second electrode layer 27 through the buffer layer 25 and the contact layer 26. An electron transport layer (ETL). Examples of the main material of the second charge transport layer 24, which is an electron transport layer, include fullerene. Examples of fullerenes include C60, C70, their hydrides, oxides, metal complexes, alkyl group-added derivatives such as PCBM ([6,6]-Phenyl-C61-Butyric Acid Methyl Ester). be done. By forming the second charge transport layer 24 from a material containing fullerene in which lithium Li is included, the electron transport efficiency can be improved.

The second charge transport layer 24 can be formed, for example, by a sol-gel method, a coating method, or the like. The thickness of the second charge transport layer 24 may be, for example, 3 nm or more and 30 nm or less.

The buffer layer 25 prevents recombination of the first charge and the second charge by blocking passage of charges of the first polarity, and blocking holes in this embodiment. In addition, the buffer layer 25 prevents the metals of the contact layer 26 and the second electrode layer 27 from diffusing into the second charge transport layer 24 and thus from recombination of charges. Further, the buffer layer 25 also functions as a buffer layer for preventing damage to the second charge transport layer 24 when the contact layer 26 and the second electrode layer 27 are formed by sputtering or the like.

The buffer layer 25 is made of an organic material that blocks charges of the first polarity, for example, an organic material that has a hole blocking function due to its HOMO (valence band) having a lower energy level than the HOMO of the second charge transport layer 24 . can be formed from In addition, good characteristics tend to be obtained by using a material having a wide HOMO-LUMO (band) gap and high insulating properties as a material for forming the buffer layer 25 . Specific organic materials for forming the buffer layer 25 include, for example, bathocuproine (2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline) and Bphen (4,7-Diphenyl-1,10-phenanthroline). , TPBi (1,3,5-Tris(1-phenyl-1Hbenzimidazol-2-yl)benzene), TMPyPB (1,3,5-Tris(3-pyridyl-3-phenyl)benzene), FPI (fluorinated polyimide ) and the like. In particular, by laminating the buffer layer 25 made of bathocuproine on the second charge transport layer 24 containing fullerene, the effect of improving the efficiency of extracting electrons from the photoelectric conversion layer 23 to the second electrode layer 27 becomes remarkable.

The buffer layer 25 can be formed by a method such as vacuum deposition. The thickness of the buffer layer 25 can be, for example, 3 nm or more and 30 nm or less, preferably 10 nm or less. By making the thickness of the buffer layer 25 equal to or greater than the lower limit, pinholes in the buffer layer 25 can be prevented. Further, by setting the thickness of the buffer layer 25 to be equal to or less than the upper limit, the carrier transmission efficiency can be improved.

The contact layer 26 is provided to improve adhesion between the buffer layer 25 and the second electrode layer 27 . Contact layer 26 is formed from polycrystalline ITO. Polycrystalline ITO produces a single peak between 30 and 31° in the in-plane XRD measurement, which does not occur with amorphous ITO. Such polycrystalline ITO can exhibit sufficient adhesion to the buffer layer 25 made of bathocuproine.

The contact layer 26 can be formed by a sputtering method. In other words, it is possible to control whether the ITO is polycrystalline or amorphous depending on the sputtering conditions. Specifically, ITO can be polycrystallized by setting the back pressure of the process chamber to be low. Also, the smaller the amount of tin oxide doped into ITO, the easier it is to crystallize ITO. The doping amount of tin oxide in the contact layer 26 can be, for example, 2% by mass or more and 4% by mass or less. In addition, crystallization of ITO can be promoted by increasing the output of the sputtering apparatus. However, if the output of the sputtering device is increased too much, there is a risk of damaging the layers containing organic matter such as the second charge transport layer 24 . Furthermore, the crystallization of ITO can be promoted by setting the flow rate of oxygen during sputtering to be less than the amount of oxygen (bottom oxygen amount) at which the sheet resistance of ITO becomes the lowest. In addition, if the contact layer 26 is formed in a plurality of steps, the crystallization of ITO is inhibited. Therefore, it is preferable to form the contact layer 26 at one time.

The lower limit of the thickness of the contact layer 26 is preferably 3 nm, more preferably 5 nm. On the other hand, the upper limit of the thickness of the contact layer 26 is preferably 25 nm, more preferably 20 nm. By setting the thickness of the contact layer 26 to be equal to or greater than the lower limit, the entire surface of the buffer layer 25 can be covered and the adhesion to the second electrode layer 27 can be reliably improved. Further, by setting the thickness of the contact layer 26 to be equal to or less than the upper limit, it is possible to suppress the reduction in the output of the perovskite solar cell section 20 due to the electrical resistance of the contact layer 26 .

The second electrode layer 27 is an electrode paired with the first electrode layer 21 of the perovskite solar cell section 20, and is a negative electrode in this embodiment. The second electrode layer 27 is a transparent electrode that transmits incident light through the antireflection layer 33, and is made of amorphous ITO.

The second electrode layer 27 can be formed by a sputtering method. More specifically, the second electrode layer 27 is formed by using the same sputtering apparatus as the sputtering for forming the contact layer 26, and the conditions such as the back pressure of the process chamber, the doping amount of tin oxide, the output of the sputtering apparatus, and the oxygen flow rate are different. can be formed by A plurality of conditions may be different between the formation of the second electrode layer 27 and the formation of the contact layer 26 . By doing so, it becomes easy to polycrystallize the ITO forming the contact layer 26 and to make the ITO forming the second electrode layer 27 amorphous.

The lower limit of the thickness of the second electrode layer 27 is preferably 10 nm, more preferably 20 nm. On the other hand, the upper limit of the thickness of the second electrode layer 27 is preferably 200 nm, more preferably 100 nm. By making the thickness of the second electrode layer 27 equal to or greater than the lower limit, the electrical resistance up to the surface collector electrode 32 (the internal resistance of the perovskite solar cell section 20) can be made sufficiently small. Moreover, by making the thickness of the second electrode layer 27 equal to or less than the upper limit, the light transmittance of the second electrode layer 27 can be increased, and the photoelectric conversion efficiency of the solar cell 1 as a whole can be improved.

The back collector electrode 31 and the front collector electrode 32 are electrode pairs for extracting electric power from the laminate of the crystalline silicon solar cell and the perovskite solar cell and outputting it to the outside. The back collector electrode 31 may be laminated over the entire surface, while the front collector electrode 32 is composed of a plurality of linear portions arranged at intervals to allow light to enter the perovskite solar cell portion 20 . , so-called finger electrodes.

The back collector electrode 31 and the front collector electrode 32 are made of a conductive material. As a method for forming the back surface collection electrode 31 and the front surface collection electrode 32, for example, a known method such as sputtering or plating can be used. As a method for forming the pattern, it is preferable to form by printing and baking a conductive paste such as a silver paste. The thickness of the back collector electrode 31 and the front collector electrode 32 can be, for example, 100 nm or more and 300 nm or less.

Antireflection layer 33 reduces reflection of light on the light receiving surface of solar cell 1 . The antireflection layer 33 can be made of a low refractive index material such as magnesium fluoride (MgF ₂ ), silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), cerium fluoride (CeF ₂ ), or the like. can. Also, the antireflection layer 33 may be a multilayer film in which a low refractive index material and a high refractive index material are alternately laminated. The thickness of the antireflection layer 33 can be, for example, 50 nm or more and 200 nm or less.

In the solar cell 1 having the above configuration, the second electrode layer 27 formed of transparent amorphous ITO is provided on the side of the perovskite solar cell portion 20 opposite to the substrate 10, and the second electrode layer 27 side receives light to generate photoelectric conversion. Transformation can be done. Also, in the solar cell 1, between the buffer layer 25 made of bathocuproine and the second electrode layer 27 made of amorphous ITO, relatively high adhesion to both the buffer layer 25 and the second electrode layer 27 is achieved. Since the contact layer 26 made of polycrystalline ITO that can exert force is interposed, the peeling of the second electrode layer 27 can be prevented. Further, the buffer layer 25 made of bathocuproine, the contact layer 26 made of polycrystalline ITO, and the second electrode layer 27 made of amorphous ITO can be formed by a general film forming apparatus. The solar cell 1 has high production efficiency.

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. By way of example, solar cells according to the invention may include layers that prevent undesired inter-layer migration of charges or materials (e.g. a buffer layer that may be provided between the first electrode layer and the first charge transport layer, a substrate and a second layer). an intermediate layer that may be provided between one electrode layer), a layer for providing a dopant to a particular layer (e.g. a thin lithium fluoride layer that may be provided for providing lithium fluoride to an electron-transporting layer comprising fullerenes). ) and the like.

The present invention will be specifically described below based on examples, but the present invention is not limited to the following examples.

(Example 1)
A first electrode layer made of ITO, a first charge transport layer made of a self-assembled monolayer containing 2PACz, a photoelectric conversion layer containing a perovskite compound, a second charge transport layer containing fullerene, and bathocuproine on a glass substrate. A buffer layer made of polycrystalline ITO, a contact layer made of polycrystalline ITO, a second electrode layer made of amorphous ITO, and a surface collection electrode made of a sintered silver paste are laminated in this order, Example 1 of a solar cell was produced as a trial.

(Comparative example 1)
A first electrode layer made of ITO, a first charge transport layer made of a self-assembled monolayer containing 2PACz, a photoelectric conversion layer containing a perovskite compound, a second charge transport layer containing fullerene, and atoms on a glass substrate A comparative example of a solar cell was obtained by laminating in this order a buffer layer formed of layer-deposited tin oxide, a second electrode layer formed of amorphous ITO, and a surface collection electrode formed of a sintered body of silver paste. 1 was prototyped.

(Comparative example 2)
A first electrode layer made of ITO, a first charge transport layer made of a self-assembled monolayer containing 2PACz, a photoelectric conversion layer containing a perovskite compound, a second charge transport layer containing fullerene, and bathocuproine on a glass substrate. Comparative Example 2 of a solar cell was fabricated by laminating in this order a buffer layer formed of , a second electrode layer formed of amorphous ITO, and a surface collection electrode formed of a sintered body of silver paste.

For Example 1, Comparative Example 2, and Comparative Example 3 of the solar cell, light was irradiated from the surface collecting electrode side, and the output characteristics between the first electrode layer and the surface collecting electrode were measured. This result is shown in FIG. As shown in the figure, in Example 1 in which a contact layer made of polycrystalline ITO was formed between the buffer layer and the second electrode layer, the buffer layer formed from bathocuproine was damaged during lamination of the second electrode layer. Not only was a photoelectric conversion efficiency higher than that of Comparative Example 2 conceivable, but even compared to Comparative Example 1 having a buffer layer formed by atomic layer deposition, a photoelectric conversion efficiency higher than the maximum efficiency by 9.3% was obtained. was taken.

Reference Signs List 1 solar cell 10 substrate 11 semiconductor substrate 12 first semiconductor layer 13 second semiconductor layer 20 perovskite solar cell portion 21 first electrode layer 22 first charge transport layer 23 photoelectric conversion layer 24 second charge transport layer 25 buffer layer 26 contact Layer 27 Second electrode layer 31 Back collector electrode 32 Front collector electrode 33 Antireflection layer

Claims

A substrate, a first electrode layer, a first charge transport layer, a photoelectric conversion layer containing a perovskite compound, a second charge transport layer, a buffer layer made of an organic material, and a polycrystalline ITO. A solar cell comprising, in that order, a contact layer and a second electrode layer formed of amorphous ITO.
2. The solar cell according to claim 1, wherein the doping amount of tin oxide in the second electrode layer is larger than the doping amount of tin oxide in the contact layer.
The solar cell according to claim 1 or 2, wherein the second charge transport layer contains fullerene.
The contact layer has a thickness of 3 nm or more and 25 nm or less,
The solar cell according to any one of claims 1 to 3, wherein the second electrode layer has a thickness of 10 nm or more and 200 nm or less.
The solar cell according to any one of claims 1 to 4, wherein the substrate is a crystalline silicon solar cell.