JP7792266B2 - Solar cell and solar cell manufacturing method - Google Patents

Description

The present invention relates to a solar cell and a solar cell manufacturing method.

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

Patent Document 1 also describes a solar cell in which a monomolecular film is formed on the surface of a first electrode laminated on a substrate, a photoelectric conversion layer is laminated directly on the monomolecular film, and an electron transport layer and a transparent electrode are further laminated.

JP 2010-141165 A

Patent Document 1 recommends adding a hole transport layer between the monolayer and the photoelectric conversion layer to enable more efficient extraction of charges. The hole transport layer improves photoelectric conversion efficiency by blocking electrons and selectively allowing holes to reach the electrode, but it also limits photoelectric conversion efficiency by increasing the distance the holes travel. In other words, the solar cell described in Patent Document 1 does not have sufficient hole selection (electron blocking) function of the monolayer, so the benefits of improving the electron blocking effect obtained by adding a hole transport layer outweigh the disadvantages of increasing the distance the holes travel. Conversely, if a monolayer with high hole selectivity can be formed, it will function sufficiently as a hole transport layer, making it possible to manufacture solar cells with higher photoelectric conversion efficiency.

The objective of the present invention is to provide a solar cell with high photoelectric conversion efficiency and a method for manufacturing the same.

A solar cell according to one embodiment of the present invention comprises, in this order, an anode layer, a hole transport layer, a perovskite compound, a photoelectric conversion layer in contact with the hole transport layer, an electron transport layer, and a cathode layer, and the hole transport layer is a monolayer formed from two types of carbazole compound molecules, and the two types of carbazole compound molecules have the same carbon chain bonded to the carbazole nitrogen atom and differ only in the substituents on the benzene ring.

In the above-mentioned solar cell, the two types of carbazole compound molecules may be 2PACz and MeO-2PACz.

In the above-mentioned solar cell, the mass ratio of the 2PACz to the MeO-2PACz in the hole transport layer may be 1:99 or more and 60:40 or less.

In the above-mentioned solar cell, the ratio of the area ratio of the 2PACz to the MeO-2PACz in the hole transport layer may be 1:99 or more and 50:50 or less.

A solar cell manufacturing method according to another aspect of the present invention includes the steps of: laminating a conductive material on a substrate; applying a monolayer-forming material solution containing two types of self-assembled monolayer-forming molecules to the conductive material layer; drying the coating of the monolayer-forming material solution; and applying a photoelectric conversion layer-forming material solution to the dried coating of the monolayer-forming material solution, wherein the two types of carbazole compound molecules have the same carbon chain bonded to the nitrogen atom of the carbazole and differ only in the substituents on the benzene ring.

In the solar cell manufacturing method described above, the two types of carbazole compound molecules may be 2PACz and MeO-2PACz, and the mass ratio of the 2PACz to the MeO-2PACz in the photoelectric conversion layer-forming material solution may be 1:99 or more and 70:30 or less.

In the solar cell manufacturing method described above, the application of the photoelectric conversion layer forming material solution may be performed by spin coating.

The present invention provides solar cells with high photoelectric conversion efficiency.

1 is a schematic cross-sectional view showing a layer structure of a solar cell according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing the configuration of a hole transport layer in the solar cell of FIG. 1. 2 is a flowchart showing the steps of a method for manufacturing the solar cell of FIG. 1 .

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

The solar cell 1 comprises a substrate 10, a perovskite solar cell section 20 laminated on the surface of the substrate 10, a back collector electrode 31 laminated on the back surface of the substrate 10, a front collector electrode 32 partially laminated on the surface of the perovskite solar cell section 20, and an anti-reflection layer 33 covering the surfaces of the perovskite solar cell section 20 and the front collector electrode 32. Light enters the solar cell 1 through the anti-reflection layer 33, and photoelectric conversion occurs in the perovskite solar cell section 20.

The substrate 10 is a structure that supports the perovskite solar cell unit 20 and may have a photoelectric conversion function. Specifically, the substrate 10 may be, for example, a glass substrate or a resin sheet. However, 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 anti-reflection layer 33 is first photoelectrically converted by the perovskite solar cell unit 20, and light of a wavelength that passes through the perovskite solar cell unit 20 is photoelectrically converted by the crystalline silicon solar cell 10. Because the crystalline silicon solar cell has sufficient strength, it can function as the substrate 10 that supports the perovskite solar cell unit 20 and can improve photoelectric conversion efficiency by converting light that passes through the perovskite solar cell unit 20 into electricity. In the solar cell 1, the perovskite solar cell unit 20 is stacked on the crystalline silicon solar cell that serves as the substrate 10, thereby connecting the crystalline silicon solar cell and the perovskite solar cell unit 20 in series.

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

The perovskite solar cell section 20 comprises, in this order from the substrate 10 side, an anode layer 21, a hole transport layer 22, a photoelectric conversion layer 23, an electron transport layer 24, a buffer layer 25, and a cathode layer 26.

The anode layer 21 is one of the electrodes of the perovskite solar cell unit 20. The anode layer 21 can be formed from a transparent conductive oxide (TCO) that is conductive and optically transparent. Examples of transparent conductive oxides that can be used to form the anode layer 21 include indium oxide, tin oxide, zinc oxide, titanium oxide, and composite oxides thereof. Among these, indium-based composite oxides containing indium oxide as the main component are preferred. Indium oxide is particularly preferred from the standpoint of high conductivity and transparency. Furthermore, to ensure reliability or higher conductivity, it is preferable to add a dopant to indium oxide. Examples of dopants include Sn, W, Zn, Ti, Ce, Zr, Mo, Al, Ga, Ge, As, Si, and S. For example, ITO (indium tin oxide), in which tin is added to indium oxide, is widely known.

The anode layer 21 can be layered on the substrate 10 by, for example, sputtering or vacuum deposition. The thickness of the anode layer can be, for example, 5 nm to 100 nm when power is output from the perovskite solar cell unit 20 to the substrate 10 on its surface (when current flows in the thickness direction), and can be, for example, 500 nm to 1000 nm when power is output to wiring connected to the anode layer (when current flows in the surface direction).

The hole transport layer (HTL) 22 selectively transports holes generated in the photoelectric conversion layer 23 to the anode layer 21. The hole transport layer 22 is a self-assembled monolayer (SAM) formed from two types of carbazole compound molecules. The two types of carbazole compound molecules forming the hole transport layer 22 have the same carbon chain bonded to the nitrogen atom of the carbazole, and differ only in the substituents on the benzene ring (one of which may be hydrogen). The two types of carbazole compound molecules are preferably 2PACz ([2-(9H-Carbazol-9-yl)ethyl]phosphonic Acid) and MeO-2PACz ([2-(3,6-Dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic Acid). Self-assembled monolayers formed from two types of carbazole compound molecules, particularly 2PACz and MeO-2PACz, in which the same carbon chain is bonded to the carbazole nitrogen atom and only the substituents on the benzene ring differ, have sufficient hole-selective function, making it possible to efficiently extract holes while blocking electrons even when a photoelectric conversion layer 23 is directly laminated on top of them.

The hole transport layer 22 can be formed by coating and drying a monolayer-forming material solution prepared by dissolving 2PACz and MeO-2PACz in an organic solvent such as ethanol or isopropanol. The total concentration of 2PACz and MeO-2PACz in the monolayer-forming material solution is approximately 0.3 mg/mL.

Considering only the wettability of the photoelectric conversion layer-forming material that forms the photoelectric conversion layer 23 and the hole selectivity with the perovskite layer due to the methoxy group, MeO-2PACz is considered to be advantageous. However, a monolayer-forming material solution containing only MeO-2PACz creates pinholes between the individual domains of the MeO-2PACz monolayer, which grow separately like crystal grains, preventing complete coverage of the surface of the anode layer 21. Therefore, by using a monolayer-forming material solution that contains 2PACz in addition to MeO-2PACz, individual domains of 2PACz monolayer, which have a high degree of freedom in the shape of the individual domains, can be formed between the individual domains of the MeO-2PACz monolayer, as shown schematically in Figure 2, and pinholes in the hole transport layer 22 can be reduced. In a monolayer-forming material solution containing 2PACz and MeO-2PACz, the growth of the MeO-2PACz monolayer is dominant, so the ratio of the area ratio of 2PACz to the area ratio of MeO-2PACz in the formed hole transport layer 22 is smaller than the ratio of the 2PACz content to the MeO-2PACz content in the monolayer-forming material solution.

The lower limit of the mass ratio of 2PACz to MeO-2PACz (2PACz proportion) in the hole transport layer 22 is preferably 1:99, more preferably 10:90. Meanwhile, the upper limit of the mass ratio of 2PACz to MeO-2PACz is preferably 60:40, more preferably 55:45, even more preferably 50:50, and particularly preferably 30:70. By maintaining the mass ratio of 2PACz to MeO-2PACz within this range, pinholes in the hole transport layer 22 are reduced while the wettability with the photoelectric conversion layer-forming material solution used to form the photoelectric conversion layer 23 is appropriate, thereby enabling the photoelectric conversion layer 23 to be formed appropriately. This optimizes the generation of carriers (holes and electrons) by the photoelectric conversion layer 23 and the transfer of holes from the photoelectric conversion layer 23 to the hole transport layer 22, thereby improving the photoelectric conversion efficiency of the solar cell 1.

The lower limit of the mass ratio of 2PACz to MeO-2PACz in the hole transport layer 22 is preferably 1:99, more preferably 10:90. On the other hand, the upper limit of the area ratio of 2PACz to MeO-2PACz is preferably 50:50, more preferably 30:70. By keeping the area ratio of 2PACz to MeO-2PACz within this range, pinholes in the hole transport layer 22 are reduced while the wettability with the photoelectric conversion layer-forming material solution used to form the photoelectric conversion layer 23 is appropriate, allowing the photoelectric conversion layer 23 to be formed appropriately.

The lower limit of the mass ratio of 2PACz to MeO-2PACz in the monolayer-forming material solution is preferably 1:99, more preferably 30:70. Meanwhile, the upper limit of the mass ratio of 2PACz to MeO-2PACz is preferably 70:30, more preferably 60:40. By ensuring that the mass ratio of 2PACz to MeO-2PACz in the monolayer-forming material solution is equal to or greater than the lower limit, a monolayer of 2PACz can be formed between the monolayers of MeO-2PACz, thereby reducing pinholes in the hole transport layer 22. Furthermore, by ensuring that the mass ratio of 2PACz to MeO-2PACz in the monolayer-forming material solution is equal to or less than the upper limit, the 2PACz does not inhibit the growth of the monolayer of MeO-2PACz, ensuring the formation of the hole transport layer 22.

The photoelectric conversion layer 23 absorbs light and generates carriers. The photoelectric conversion layer 23 includes a perovskite compound and is formed in contact with the hole transport layer 22. As the perovskite compound, a compound represented by ABX3 can be used, which includes an organic atom 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. In particular, 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 an iodide I, a bromide ion Br, and a chloride ion Cl.

Specifically, preferred perovskite compounds include methylammonium lead halide MAPbX ₃ (CH ₃ NH ₃ PbX ₃ ), MAPbI ₃ , MAPbBr ₃ , and MAPbCl _3. Note that multiple types of halogen atoms X 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) , and MAPbI _y Cl _(3-y) (where 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 can be formed by sequentially depositing films of a lead halide (PbX ₂ ) material and a methylammonium halide (MAI) material, and reacting the thin films of these materials at a reaction temperature. 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 can be formed by sequentially depositing films of a lead halide (PbX ₂ ) material and a methylammonium iodide (MAI) material, and reacting the thin films of these materials at a reaction temperature. Alternatively, the photoelectric conversion layer 23 may be formed by mixing a lead halide (PbX2) material and a methylammonium iodide (MAI) material, dissolving the mixture in a solvent, forming the solution into a film, and reacting the mixture at a reaction temperature.

The material that forms the photoelectric conversion layer 23 is preferably deposited by spin coating a solution of the photoelectric conversion layer material dissolved in a polar solvent such as DMF (N,N-dimethylformamide) or DMSO (dimethyl sulfoxide), as this allows for the formation of a uniform thin film. Furthermore, when depositing the material by spin coating, the effect of optimizing the wettability of the hole transport layer 22 is significant. Therefore, by forming the photoelectric conversion layer 23 by layering a material on the hole transport layer 22 by spin coating, the photoelectric conversion efficiency of the solar cell 1 can be particularly improved.

As a specific example, the photoelectric conversion layer-forming material solution can be prepared by weighing lead(II) iodide, formamidine hydroiodide, lead(II) bromide, and methylamine hydrobromide, dissolving them in DMF and DMSO, and mixing them with a separately prepared DMSO solution of cesium iodide. In this case, the molar concentration of lead(II) iodide relative to the molar concentration of formamidine hydroiodide is preferably 1 to 1.1 times, and the molar concentration of lead(II) bromide relative to the molar concentration of methylamine hydrobromide is preferably 1 to 1.1 times, and more preferably 1.06 to 1.09 times, respectively. The molar concentration ratio of lead(II) iodide to lead(II) bromide is preferably 72:28 to 79:21, and even more preferably 74:26 to 77:23. The total molar concentration of formamidine hydroiodide and methylamine hydrobromide is preferably 1.5 to 2.0 M, and more preferably 1.6 to 1.8 M. The ratio of DMF to DMSO as solvents for dissolving lead(II) iodide, formamidine hydroiodide, lead(II) bromide, and methylamine hydrobromide is preferably 3:1 to 5:1. When mixing a DMSO solution of cesium iodide to form a mixed solution, the molar concentration of cesium iodide relative to the molar concentration of formamidine hydroiodide is preferably 4 to 6%. This photoelectric conversion layer-forming material solution can be appropriately formed by spin coating on the hole transport layer 22 composed of the above-mentioned monolayer.

The thickness of the photoelectric conversion layer 23 depends on the type of material used to form the photoelectric conversion layer, but is preferably between 100 nm and 1000 nm inclusive in order to increase the light absorption rate while reducing the distance traveled by the generated charges.

The electron transport layer (ETL) 24 selectively transports electrons generated in the photoelectric conversion layer 23 to the cathode layer 26 through the buffer layer 25. Examples of primary materials for the electron transport layer 24 include PTAA (Poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine)), Spiro-MeOTAD, and fullerene. Examples of fullerenes include C60, C70, and their hydrides, oxides, metal complexes, and derivatives with alkyl groups added. Forming the electron transport layer 24 from a material containing fullerenes encapsulating lithium (Li) can improve electron transport efficiency.

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

The buffer layer 25 prevents the metal of the cathode layer 26 from diffusing into the electron transport layer 24, thereby preventing the resulting recombination of charges. The buffer layer 25 also functions as a buffer layer to prevent damage to the electron transport layer 24 when the cathode layer 26 is formed by sputtering or the like. The buffer layer 25 is made of a stable metal oxide such as tin oxide (SnO ₂ ) or zinc oxide (ZnO), or an organic material such as bathocuproine (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline).

The buffer layer 25 can be formed by methods such as vacuum deposition, sputtering, and atomic layer deposition. The thickness of the buffer layer 25 can be, for example, 3 nm or more and 30 nm or less.

The cathode layer 26 is an electrode that forms a pair with the anode layer 21 of the perovskite solar cell section 20. The cathode layer 26 is a transparent electrode that transmits light that is incident through the anti-reflection layer 33, and is made of amorphous ITO. Furthermore, the cathode layer 26 is preferably doped with tin oxide (SnO ₂ ).

The cathode layer 26 can be formed by sputtering. The lower limit of the thickness of the cathode layer 26 can be, for example, 10 nm or more and 200 nm or less.

The back surface collecting electrode 31 and the front surface collecting electrode 32 are a pair of electrodes that extract power from the laminate of crystalline silicon solar cells and perovskite solar cells and output it to the outside. The back surface collecting electrode 31 may be laminated over the entire surface, but the front surface collecting electrode 32 has multiple linear portions, or so-called finger electrodes, arranged at intervals to allow light to enter the perovskite solar cell section 20.

The back surface collecting electrode 31 and the front surface collecting electrode 32 are formed from a conductive material. The back surface collecting electrode 31 and the front surface collecting electrode 32 can be formed by known methods such as sputtering and plating, but the front surface collecting electrode 32 is preferably formed by, for example, silver vapor deposition, as this method can be used without damaging the perovskite solar cell section 20. The thickness of the back surface collecting electrode 31 and the front surface collecting electrode 32 can be, for example, 100 nm or more and 300 nm or less.

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

As is clear from the above description, one embodiment of the solar cell manufacturing method according to the present invention for manufacturing solar cell 1 includes, as shown in FIG. 3, a step of laminating a conductive material that forms an anode layer 21 on substrate 10 (step S1: anode conductive material lamination step), a step of applying a monolayer-forming material solution containing two types of carbazole compound molecules to the conductive material layer, i.e., anode layer 21 (step S2: monolayer-forming material solution application step), a step of drying the monolayer-forming material solution coating (step S3: coating drying step), and a step of forming a photoelectric conversion layer 23 on the dried monolayer-forming material solution coating, i.e., hole transport layer 22. The method includes a step of applying a semi-dry photoelectric conversion layer forming material solution containing the material (step S4: photoelectric conversion layer forming material solution application step), a step of forming a photoelectric conversion layer 23 by reacting the photoelectric conversion layer forming material by heating (step S5: reaction step), a step of laminating a material that forms an electron transport layer 24 on the photoelectric conversion layer 23 (step S6: electron transport layer forming material lamination step), a step of laminating a material that forms a buffer layer 25 on the electron transport layer 24 (step S7: buffer layer forming material lamination step), and a step of laminating a conductive material that forms a cathode layer 26 on the buffer layer 25 (step S8: cathode conductive material lamination step).

The solar cell 1 manufactured using this solar cell manufacturing method has a hole transport layer 22 that is a monolayer formed from two types of carbazole compound molecules. This gives the hole transport layer 22 sufficient hole selectivity, and allows the photoelectric conversion layer 23 to be properly formed, resulting in a relatively high photoelectric conversion efficiency.

While the present invention has been described above with reference to exemplary embodiments, it is not limited to these and various modifications and variations are possible. For example, a solar cell according to the present invention may use a transparent substrate and convert light incident from the substrate side into electricity. Furthermore, a solar cell according to the present invention may further include an intermediate layer interposed between layers to improve adhesion, a blocking layer to prevent undesirable interlayer movement of charge or material, a doped layer to provide a dopant to a specific layer (e.g., a thin lithium fluoride layer that may be provided to provide lithium fluoride to an electron transport layer containing fullerene), etc. For example, some layers, such as a buffer layer or anti-reflection layer, may be omitted, or multiple layers may be replaced with a single layer that combines these functions. Furthermore, processes for manufacturing a solar cell according to the present invention may be omitted, added, or modified depending on the configuration of the solar cell being manufactured.

REFERENCE SIGNS LIST 1 Solar cell 10 Base material 11 Semiconductor substrate 12 First semiconductor layer 13 Second semiconductor layer 20 Perovskite solar cell section 21 Anode layer 22 Hole transport layer 23 Photoelectric conversion layer 24 Electron transport layer 25 Buffer layer 26 Cathode layer 31 Rear surface collecting electrode 32 Front surface collecting electrode 33 Antireflection layer

Claims (6)

a cathode layer, an anode layer, a hole transport layer, a photoelectric conversion layer containing a perovskite compound and in contact with the hole transport layer, an electron transport layer, and a cathode layer, in this order;
the hole transport layer is a monomolecular film formed of two types of carbazole compound molecules,
The two types of carbazole compound molecules are 2PACz and MeO-2PACz . The solar cell described in claim 1, wherein the mass ratio of the 2PACz to the MeO-2PACz in the hole transport layer is 1:99 or more and 60:40 or less. The solar cell described in claim 1, wherein the area ratio of the 2PACz to the MeO-2PACz in the hole transport layer is 1:99 or more and 50:50 or less. Laminating a conductive material to a substrate;
applying a monomolecular film-forming material solution containing two types of carbazole compound molecules onto the conductive material layer;
a step of drying the coating film of the monolayer-forming material solution;
applying a photoelectric conversion layer forming material solution to the dried coating film of the monomolecular film forming material solution;
Equipped with
The method for manufacturing a solar cell, wherein the two types of carbazole compound molecules are 2PACz and MeO-2PACz . 5. The solar cell according to claim 4 , wherein the mass ratio of the 2PACz to the MeO-2PACz in the monolayer-forming material solution is 1:99 or more and 70:30 or less. 6. The method for manufacturing a solar cell according to claim 4, wherein the photoelectric conversion layer forming material solution is applied by spin coating.