JP2015159266A - Heterojunction solar cell and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heterojunction solar cell capable of exerting more excellent photoelectric conversion efficiency in a non-vacuum process.SOLUTION: The heterojunction solar cell includes: a layer containing silicon; and a layer containing anatase type titania particles. In an X-ray diffraction spectrum for the layer containing anatase type titania particles, a half value width of a diffraction peak appearing at a diffraction angle of 2θ=24 to 26° is equal to or more than 0.2° and equal to or less than 5.0°.

Description

  The present invention relates to a heterojunction solar cell (particularly a silicon-based solar cell) and a method for manufacturing the same.

  In the field of solar cells, heterojunction solar cells including a metal oxide layer on a silicon substrate are known as existing technologies. As a method for manufacturing such a solar cell, a vacuum process such as a plasma CVD method, a sputtering method, or a vapor deposition method is used. For example, Patent Document 1 discloses a solar cell in which a metal oxide containing indium is formed into a film by a sputtering method and the film is provided as a semiconductor layer. In contrast, non-vacuum processes have been actively studied. A method of forming a layer made of metal oxide particles on a silicon substrate by a coating method, which is a non-vacuum process, has been actively developed because of its excellent workability and easy cost reduction. Yes.

JP 2011-86770 A

  However, in the solar cell as shown in Patent Document 1, the point of using the sputtering method, which is a vacuum process, is a high cost, which is a problem. On the other hand, although a non-vacuum process such as a coating method is a relatively low cost method, it cannot be said that the photoelectric conversion efficiency of the obtained solar cell is still sufficient.

  Then, an object of this invention is to provide the heterojunction solar cell which can express the more excellent photoelectric conversion efficiency in a non-vacuum system process, and the manufacturing method of the said solar cell.

  As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.

  That is, the present invention includes a layer containing silicon and a layer containing titanium oxide particles, and a diffraction that appears at a diffraction angle 2θ = 24 to 26 ° in an X-ray diffraction spectrum for a layer containing anatase-type titanium oxide particles. The present invention relates to a heterojunction solar cell having a peak half-value width of 0.2 ° to 5.0 °.

In the present invention, the layer density of the layer containing titanium oxide particles is preferably 0.4 g / cm ³ or more and 3.0 g / cm ³ or less.

  In this invention, it is preferable that the average particle diameter of a titanium oxide particle is 0.5 to 50 nm.

  The present invention also provides an application step of applying a dispersion liquid having a pH of 0.5 to 10.0 and dispersed titanium oxide particles on an electrode or a silicon substrate, and the electrode or silicon substrate coated with the dispersion liquid. In a X-ray diffraction spectrum for a layer containing titanium oxide particles, and a treatment step of forming a layer containing titanium oxide particles on an electrode or a silicon substrate. Further, the present invention relates to a method for manufacturing a heterojunction solar cell, wherein the half-value width of a diffraction peak appearing at a diffraction angle 2θ = 24 to 26 ° is 0.2 ° or more and 5.0 ° or less.

  In the present invention, the treatment step may be performed by leaving the electrode or silicon substrate coated with the dispersion at a temperature of 10 ° C. or higher and 30 ° C. or lower.

  In the production method of the present invention, the average particle diameter of the titanium oxide particles is preferably 0.5 nm or more and 50 nm or less.

  ADVANTAGE OF THE INVENTION According to this invention, the heterojunction solar cell which can express the more superior photoelectric conversion efficiency in a non-vacuum system process can be provided. In addition, since the present invention can be manufactured by a low temperature process, it is possible to provide a low cost method for manufacturing a heterojunction solar cell.

It is sectional drawing which shows one Embodiment of the solar cell of this invention. It is a figure which shows the specific preparation method of the sample for solar cell evaluation in an Example.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiment, and can be implemented with various modifications within the scope of the gist.

  The solar cell of this embodiment includes a layer containing silicon and a layer containing titanium oxide particles. Note that the solar cell may include other materials between the layer containing silicon and the layer containing titanium oxide particles.

<Layer containing silicon>
The layer containing silicon is formed of a semiconductor containing silicon. Specifically, examples of the layer containing silicon include a monocrystalline or polycrystalline silicon wafer, amorphous silicon, and a layer containing silicon particles.

  Silicon is roughly classified into p-type and n-type. Here, p-type refers to the case where the charge transferer in the semiconductor is holes. The n-type refers to the case where conduction electrons are responsible for charge movement in a semiconductor. These holes and conduction electrons are collectively referred to as carriers.

In the case of a p-type silicon wafer, for example, a silicon wafer doped with boron, gallium or the like as an additive is used. In the case of an n-type silicon wafer, a silicon wafer doped with phosphorus, nitrogen, arsenic or the like as an additive is used. The concentration of these additives contained in the silicon wafer is preferably 10 ¹² atoms / cm ³ or more, and more preferably 10 ¹³ atoms / cm ³ or more. Furthermore, the additive concentration is ^preferably 10 21 atom / cm ³ or ^less, more preferably 10 20 atom / cm ³ or less.

  The resistivity of the silicon wafer is preferably 0.0001 Ωcm or more, and more preferably 0.001 Ωcm or more, from the viewpoint of charge transfer and depletion layer spreading in the semiconductor. The resistivity is preferably 1000 Ωcm or less, more preferably 100 Ωcm or less.

Next, amorphous silicon will be described. Amorphous silicon can be produced by a glow discharge method, a reactive sputtering method, a chemical vapor deposition method (CVD method), or the like. The glow discharge method is a method for decomposing SiH ₄ in plasma generated by glow discharge. In the reactive sputtering method, electric power is applied between electrodes placed in a low-pressure argon gas to cause a discharge, a crystalline silicon substrate (target) is placed on one electrode, and sputtering is performed. This is a method of forming a film on a substrate placed on the substrate. The chemical vapor deposition method is a method for producing amorphous silicon by thermally decomposing SiH ₄ at 400 ° C. to 700 ° C. and subsequently performing hydrogen plasma treatment.

  In the case of p-type amorphous silicon, amorphous silicon doped with boron, gallium or the like as an additive is used. In the case of n-type amorphous silicon, amorphous silicon doped with phosphorus, nitrogen, arsenic or the like as an additive is used. In the case of amorphous silicon, the conductivity type can be controlled by diluting and introducing each dopant into hydrogen gas.

  Next, the layer containing silicon particles will be described. The layer containing silicon particles is a layer containing silicon particles alone or a layer containing silicon particles and other compounds such as a solvent, a binder component, and a semiconductor component other than silicon particles. In addition, it is preferable that it is 10 mass%-100 mass%, and, as for content of the silicon particle contained in the layer containing a silicon particle, it is more preferable that it is 30 mass%-100 mass%. When the content is at least 10% by mass or more, the function as a semiconductor layer is sufficiently exhibited.

  Examples of the solvent include water, pentane, hexane, peptane, octane, nonane, decane, 2-methylhexane, decalin, tetralin, methanol, ethanol, n-propanol, 2-propanol, n-butanol, t-butanol, and ethylene glycol. , Diethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, ethylene glycol mono 2-ethylhexyl ether, propylene glycol n-butyl ether, dipropylene glycol n- Butyl ether, tripropylene glycol n-butyl ether, dipro Ketones such as lenglycol methyl ether, tripropylene glycol methyl ether, glycerin acetone, methyl ethyl ketone, aromatics such as benzene, xylene, toluene, phenol, aniline, diphenyl ether, dimethyl sulfoxide, dimethylformamide, acetonitrile, methyl acetate, tetrahydrofuran, Examples include butyl lactate and N-methylpyrrolidone. It is also possible to use a mixture of these.

  Examples of the binder component include general versatile resins and surfactants. Specifically, general-purpose resins include epoxy resin, acrylic resin, phenol resin, melamine resin, urea resin, unsaturated polyester resin, alkyd resin, polyurethane, polyimide, polyethylene, polypropylene, polyvinyl chloride, polystyrene, and polyacetic acid. Examples thereof include vinyl, polytetrafluoroethylene, acrylonitrile-butadiene-styrene resin (ABS resin), polyamide, polyacetal, polycarbonate, polyester, cyclic polyolefin, and polysulfone.

  Examples of the surfactant include an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant. Specifically, examples of the anionic surfactant include fatty acid sodium, monoalkyl sulfate, alkyl benzene sulfonate, and monoalkyl phosphate. Examples of the cationic surfactant include alkyltrimethylammonium salts, dialkyldimethylammonium salts, and alkylbenzylmethylammonium salts. Examples of amphoteric surfactants include alkyl dimethylamine oxide and alkyl carboxybetaine. Examples of the nonionic surfactant include polyoxyethylene alkyl ether, fatty acid sorbitan ester, alkyl polyglycoside, fatty acid ethanolamide, and alkyl monoglyceryl ether.

  The silicon particle production method is not particularly limited. For example, a method using a highly crystalline semiconductor microparticle production apparatus using a pulse pressure applied orifice injection method, a polycrystalline or single crystal silicon ingot or wafer is used. It can be produced by a grinding method or the like. Further, chips at the time of wafer fabrication can be used as silicon particles. As a method of pulverizing the ingot or wafer, either dry pulverization or wet pulverization may be used, or both methods may be used. For the dry pulverization, a Hammar crusher or the like can be used. For wet grinding, a ball mill, a planetary ball mill, a bead mill, a homogenizer, or the like can be used. The following are mentioned as a solvent at the time of wet grinding.

  Specifically, as a solvent, water, pentane, hexane, peptane, octane, nonane, decane, 2-methylhexane, decalin, tetralin, methanol, ethanol, n-propanol, 2-propanol, n-butanol, t- Butanol, ethylene glycol, diethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, ethylene glycol mono 2-ethylhexyl ether, propylene glycol n-butyl ether, di Propylene glycol n-butyl ether, tripropylene glycol n-butyl ether Ketones such as dipropylene glycol methyl ether, tripropylene glycol methyl ether, glycerin acetone, methyl ethyl ketone, aromatics such as benzene, xylene, toluene, phenol, aniline, diphenyl ether, dimethyl sulfoxide, dimethylformamide, acetonitrile, methyl acetate, tetrahydrofuran , Butyl lactate, N-methylpyrrolidone and the like. It is also possible to use a mixture of these. In addition to the solvent described above, a surfactant or the like may be added.

As the p-type silicon particles, for example, silicon particles doped with boron, gallium or the like as an additive are used. As the n-type silicon particles, silicon particles doped with phosphorus, nitrogen, arsenic or the like as an additive are used. The concentration of these additives contained in the silicon particles is preferably 10 ¹² atoms / cm ³ or more, and more preferably 10 ¹³ atoms / cm ³ or more. Furthermore, the additive concentration is ^preferably 10 21 atom / cm ³ or ^less, more preferably 10 20 atom / cm ³ or less.

  The resistivity of the silicon particles is preferably 0.0001 Ωcm or more, and more preferably 0.001 Ωcm or more, from the viewpoint of charge transfer in the semiconductor and the spread of the depletion layer. The resistivity is preferably 1000 Ωcm or less, more preferably 100 Ωcm or less.

  The average particle diameter of the silicon particles is preferably 400 μm or less, more preferably 200 μm or less, further preferably 100 μm or less, and extremely preferably 70 μm or less from the viewpoint of reducing the contact resistance between the particles. Further, from the viewpoint of reducing the contact resistance between the particles and the electrode and the diffusion length, 0.001 μm or more is preferable, 0.01 μm or more is more preferable, and 1 μm or more is more preferable.

  In this embodiment, the average particle diameter of particles such as silicon particles is measured by an image processing method using a microscope.

  In addition, as a method for forming a film-like semiconductor layer from silicon particles, a method using a vacuum system such as a vapor deposition method, a sputtering method, a CVD method, a printing method such as screen printing, gravure printing, letterpress printing, blade coating, etc. And non-vacuum methods such as a wet coating method such as a spin coating method. Moreover, the layer which consists of multiple types of inorganic semiconductor particles containing a silicon particle can also be employ | adopted as a layer containing silicon. As a method of forming a film-like semiconductor layer from these plural types of inorganic semiconductor particles, for example, a method of co-evaporating a plurality of materials and depositing on a substrate with an electrode, a single coating solution containing a plurality of materials The method of preparing and producing a semiconductor layer by various printing methods using the coating liquid is mentioned.

  The layer containing silicon is preferably a single crystal or polycrystalline silicon wafer, or a layer made of silicon particles (that is, a layer made of silicon) from the viewpoint of carrier movement and cost.

  When the layer containing silicon is a silicon wafer, the thickness is preferably 50 μm or more. The thickness is preferably 1000 μm or less, more preferably 700 μm or less, and even more preferably 300 μm or less. In the case of a layer in which silicon particles are hardened (layer made of silicon particles), the thickness is preferably 0.5 μm or more. The thickness is preferably 500 μm or less, and more preferably 300 μm or less.

  Further, when a semiconductor layer formed from a plurality of inorganic semiconductor particles including silicon particles is employed as a layer containing silicon, that is, when a film-shaped semiconductor layer is formed from a plurality of inorganic semiconductor particles, the thickness is From the relationship between light absorption ability and carrier transport, 0.01 μm or more is preferable, 1000 μm or less is preferable, 600 μm or less is more preferable, and 300 μm or less is more preferable.

<Layer containing titanium oxide particles>
The layer containing titanium oxide particles is a layer containing titanium oxide particles alone, or a layer containing titanium oxide particles and a semiconductor or an insulator other than the binder component and titanium oxide particles. Here, examples of the binder component include general-purpose resins and surfactants. In addition, it is preferable that it is 10 mass%-100 mass%, and, as for content of the titanium oxide particle contained in the layer containing a titanium oxide particle, it is more preferable that it is 30 mass%-100 mass%. When the content is at least 10% by mass or more, the function as a semiconductor layer is sufficiently exhibited.

  As the titanium oxide particles, for example, one kind or a combination of two or more kinds of particles made of titanium dioxide, titanium monoxide, dititanium trioxide and the like can be used. Among these, as titanium oxide particles, Those composed mainly of titanium dioxide are preferred. Titanium dioxide is highly sensitive to light, and electrons are excited more easily and reliably. For this reason, the titanium oxide layer mainly using titanium dioxide particles as titanium oxide particles can generate electrons more reliably (hereinafter, “titanium oxide” indicates titanium dioxide).

  The average particle size of the titanium oxide particles used in the present embodiment is preferably 0.5 nm or more, more preferably 1 nm or more, further preferably 3 nm or more, and further preferably 10 nm or more from the viewpoint of film formability. In addition, since the layer containing titanium oxide particles is densely packed to suppress leakage and improve carrier transport, the average particle size is preferably 50 nm or less, more preferably 30 nm or less, and further preferably 20 nm or less. Preferably, 15 nm or less is very preferable.

  The titanium oxide particles used in the present embodiment preferably have a relative standard deviation σ of the particle size distribution of 0.1 nm to 5.0 nm. In addition, from the viewpoint of reducing resistance, the upper limit of the relative standard deviation σ is more preferably 3.0 nm or less, and further preferably 2.0 nm or less.

  As types of titanium oxide particles that can be used, ST-01 (manufactured by Ishihara Sangyo Co., Ltd.), ST-21 (manufactured by Ishihara Sangyo Co., Ltd.), ST-31 (manufactured by Ishihara Sangyo Co., Ltd.), ST-41 (manufactured by Ishihara Sangyo Co., Ltd.), ST-30L (manufactured by Ishihara Sangyo), STS-01 (manufactured by Ishihara Sangyo), STS-02 (manufactured by Ishihara Sangyo), STS-21 (manufactured by Ishihara Sangyo), STS-100 (manufactured by Ishihara Sangyo) ST-K211 (Ishihara Sangyo Co., Ltd.), ST-K101 (Ishihara Sangyo Co., Ltd.), ST-K102a (Ishihara Sangyo Co., Ltd.), ST-K102b (Ishihara Sangyo Co., Ltd.), ST-K300 (Ishihara Sangyo Co., Ltd.), ST-K211 (made by Ishihara Sangyo), ST-K102 (made by Ishihara Sangyo), PT-301 (made by Ishihara Sangyo), PT-401M (made by Ishihara Sangyo), PT-401L (made by Ishihara Sangyo) CR-EL (made by Ishihara Sangyo Co., Ltd.), PT-501R Ishihara Sangyo), PT501A (Ishihara Sangyo), MC-50 (Ishihara Sangyo), MC-90 (Ishihara Sangyo), MC-150 (Ishihara Sangyo), FTL-100 (Ishihara Sangyo) FTL-110 (Ishihara Sangyo), FTL-200 (Ishihara Sangyo), FTL-300 (Ishihara Sangyo), R-820 (Ishihara Sangyo), R-830 (Ishihara Sangyo) R-930 (Ishihara Sangyo Co., Ltd.), R-980 (Ishihara Sangyo Co., Ltd.), CR-Super70 (Ishihara Sangyo Co., Ltd.), CR-80 (Ishihara Sangyo Co., Ltd.), CR-90 (Ishihara Sangyo Co., Ltd.) CR-90-2 (Ishihara Sangyo), CR-93 (Ishihara Sangyo), CR-95 (Ishihara Sangyo), CR-97 (Ishihara Sangyo), UT771 (Ishihara Sangyo) R-630 (Ishihara Sangyo), CR-50 (Ishihara Sangyo), CR-50-2 (Ishihara Sangyo Co., Ltd.), CR-57 (Ishihara Sangyo Co., Ltd.), CR-953 (Ishihara Sangyo Co., Ltd.), R-630 (Ishihara Sangyo Co., Ltd.), CR-58 (Ishihara Sangyo Co., Ltd.) ), R-780 (Ishihara Sangyo Co., Ltd.), CR-58-2 (Ishihara Sangyo Co., Ltd.), R-780-2 (Ishihara Sangyo Co., Ltd.), PF-736 (Ishihara Sangyo Co., Ltd.), CR-63 ( Ishihara Sangyo), PF-742 (Ishihara Sangyo), CR-60-2 (Ishihara Sangyo), R-550 (Ishihara Sangyo), PF-690 (Ishihara Sangyo), PF- 691 (made by Ishihara Sangyo), PF-737 (made by Ishihara Sangyo), PF-711 (made by Ishihara Sangyo), R-680 (made by Ishihara Sangyo), PF-739 (made by Ishihara Sangyo), PC- 3 (made by Ishihara Sangyo), W-10 (made by Ishihara Sangyo), A-220 (made by Ishihara Sangyo), TTO-51 (A) (stone Industrial company), TTO-51 (C) (Ishihara Sangyo), TTO-55 (A) (Ishihara Sangyo), TTO-55 (B) (Ishihara Sangyo), TTO-55 (C) (Ishihara Sangyo Co., Ltd.), TTO-55 (D) (Ishihara Sangyo Co., Ltd.), TTO-S-1 (Ishihara Sangyo Co., Ltd.), TTO-S-2 (Ishihara Sangyo Co., Ltd.), TTO-S-3 ( Ishihara Sangyo), TTO-S-4 (Ishihara Sangyo), MPT-136 (Ishihara Sangyo), TTO-V-3 (Ishihara Sangyo), TTO-V-4 (Ishihara Sangyo) ), TTO-F-2 (Ishihara Sangyo Co., Ltd.), TTO-F-6 (Ishihara Sangyo Co., Ltd.), TTO-W-5 (Ishihara Sangyo Co., Ltd.), P25 (Nihon Aerosil Co., Ltd.), PF2 (Nippon Aerosil Co., Ltd.) P90 (made by Nippon Aerosil Co., Ltd.), T805 (made by Nippon Aerosil Co., Ltd.), NKT90 (made by Nippon Aerosil Co., Ltd.) , JR-301 (manufactured by Teica), JR-403 (manufactured by Teica), JR-405 (manufactured by Teica), JR-600A (manufactured by Teica), JR-605 (manufactured by Teica), JR-600E ( (Taika), JR-603 (Taika), JR-701 (Taika), JRNC (Taika), JR-800 (Taika), JR-805 (Taika), JR- 806 (manufactured by Teica), JR (manufactured by Teica), JA-1 (manufactured by Teica), JA-3 (manufactured by Teica), JA-C (manufactured by Teica), MT-01 (manufactured by Teica), MT-10EX (manufactured by Teica), MT-05 (manufactured by Teica), MT-100TV (manufactured by Teica), MT-100Z (manufactured by Teica), MT-150A (manufactured by Teica), MT-150EX (Taika) ), MT-150W (Taika), MT-100AQ (manufactured by Teica), MT-100WP (manufactured by Teica), MT-100SA (manufactured by Teica), MT-100HD (manufactured by Teica), MT-500B (manufactured by Teica), MT-500SA (Taika) ), MT-600B (manufactured by Teica), MT-700B (manufactured by Teica), MTY-02 (manufactured by Teica), MTY-110M3S (manufactured by Teica), MT-500 SAS (manufactured by Teica), MTY -700BS (manufactured by Teica), MT-300HD (manufactured by Teica), MT-500HD (manufactured by Teica), MT-600SA (manufactured by Teica), MT-700HD (manufactured by Teica), JMT-150IB (Taika) Manufactured), JMT-150AO (manufactured by Teica), JMT-150FI (manufactured by Teica), JMT-150ANO (manufactured by Teica), AMT-100 (manufactured by TECA) Manufactured by Kay), AMT-400 (manufactured by Teika), AMT-600 (manufactured by Teika), TITANIX JA-1 (manufactured by Teica), TKP-101 (manufactured by Teika), TKP-102 (manufactured by Teica) , TKS-201 (manufactured by Teica), TKS-202 (manufactured by Teica), TKS-203 (manufactured by Teica), TKD-701 (manufactured by Teica), TKD-702 (manufactured by Teica), TKD-801 ( (Taika), TKD-802 (Taika), TKC-303 (Taika), TKC-304 (Taika), TKC-305 (Taika), JR-1000 (Taika), etc. Is mentioned.

Typical methods for producing titanium oxide particles include a chlorine method and a sulfuric acid method. In the chlorine method, raw materials (ilmenite ore) are reacted with coke and chlorine to form gaseous titanium tetrachloride. Titanium oxide particles are obtained by cooling gaseous titanium tetrachloride to a liquid state and then reacting with oxygen at a high temperature to separate chlorine gas. For example, the above-described titanium oxide P90 (manufactured by Nippon Aerosil Co., Ltd.) and P25 (manufactured by Nippon Aerosil Co., Ltd.) can be produced by the chlorine method. On the other hand, in the sulfuric acid method, a raw material (ilmenite ore) is dissolved in concentrated sulfuric acid, and iron as an impurity is separated as iron sulfate (FeSO ₄ ), and once converted to titanium oxysulfate (TiOSO ₄ ). When this is hydrolyzed, it becomes titanium oxyhydroxide (TiO (OH) ₂ ) and precipitates. The precipitate is washed, dried and fired to obtain titanium oxide particles. For example, the above-described titanium oxide ST-01 (manufactured by Ishihara Sangyo Co., Ltd.) can be produced by a sulfuric acid method.

  Crystal forms of titanium oxide include anatase type, rutile type, and brookite type. The crystal form of titanium oxide can be identified by X-ray diffraction measurement because the lattice constant, strength, and plane index differ depending on the anatase type, rutile type, and brookite type.

  The titanium oxide particles of this embodiment are preferably anatase type and include anatase type titanium oxide particles. Of the titanium oxide particles in the layer containing titanium oxide particles, anatase-type titanium oxide particles that easily generate electrons are preferably contained in an amount of 30% by mass or more, more preferably 60% by mass or more, and more preferably 80% by mass. More preferably, it is contained more than 90% by mass, most preferably 100% by mass.

  In the X-ray diffraction spectrum for the layer containing titanium oxide particles, the half width of the main peak is a measure representing the crystallinity of the same layer. When X-ray diffraction measurement is performed on a layer containing titanium oxide particles, if anatase-type titanium oxide particles are used, a diffraction peak of (101) plane which is a main peak of anatase at a diffraction angle 2θ = 24 to 26 °. Appears. The full width at half maximum can be measured from the main peak. The half width obtained from X-ray diffraction showing the crystallinity of titanium oxide is preferably 5.0 ° or less, more preferably 2.0 ° or less, and more preferably 1.5 ° or less from the viewpoint of carrier transport in the titanium oxide particles. Further preferred. Moreover, since the photoelectric conversion characteristics are deteriorated because the crystallinity of the film containing titanium oxide is too high, the half width is preferably 0.2 ° or more, more preferably 0.3 ° or more, and 0.4 ° or more. More preferably, 0.5 ° or more is very preferable, and 0.6 ° or more is particularly preferable.

  The layer containing titanium oxide may be mixed with one or more materials in addition to the titanium oxide particles alone. Specifically, a semiconductor or an insulator can be given.

  Specifically, general-purpose resins include epoxy resin, acrylic resin, phenol resin, melamine resin, urea resin, unsaturated polyester resin, alkyd resin, polyurethane, polyimide, polyethylene, polypropylene, polyvinyl chloride, polystyrene, and polyacetic acid. Examples thereof include vinyl, polytetrafluoroethylene, acrylonitrile-butadiene-styrene resin (ABS resin), polyamide, polyacetal, polycarbonate, polyester, cyclic polyolefin, and polysulfone.

  Examples of the surfactant include an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant. Specifically, examples of the anionic surfactant include fatty acid sodium, monoalkyl sulfate, alkyl benzene sulfonate, and monoalkyl phosphate. Examples of the cationic surfactant include alkyltrimethylammonium salts, dialkyldimethylammonium salts, and alkylbenzylmethylammonium salts. Examples of amphoteric surfactants include alkyl dimethylamine oxide and alkyl carboxybetaine. Examples of the nonionic surfactant include polyoxyethylene alkyl ether, fatty acid sorbitan ester, alkyl polyglycoside, fatty acid ethanolamide, and alkyl monoglyceryl ether.

Examples of the semiconductor include an n-type semiconductor. Specifically, for example, metal oxide such as amorphous silicon, zinc oxide, indium oxide, tin oxide, indium tin oxide (ITO), indium / gallium / zinc oxide (IGZO), etc. Examples thereof include a layer made of a material, a layer made of silicon particles, titanium oxide particles, zinc oxide particles, indium tin oxide (ITO), metal oxide particles such as indium oxide, tin oxide, and IGZO, and an n-type organic semiconductor. Examples of the n-type organic semiconductor include fluorinated acene compounds, fullerenes, fullerenes such as 60 PCBM ([6,6] -phenylC ₆₁ methyl acid methyl ester), 70 PCBM ([6,6] -phenyl C ₇₁ methyl acid ester). Examples thereof include compounds, naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, pyrene derivatives, perylene derivatives, perylene tetracarboxylic acid diimide derivatives, oxadiazole derivatives, triazole derivatives, triazine derivatives, quinoline derivatives, and the like. As the n-type semiconductor, a metal oxide is preferable from the viewpoint of transparency and mobility.

Insulators include calcium silicate, barium titanate, bismuth silicate, bakelite, pyrex (registered trademark), petrolatum, mica, copper chloride, copper oxide, copper sulfate, iron oxide, potassium chlorate, potassium bromide, fluoride Examples thereof include lithium, silicon oxide, magnesium oxide, calcium fluoride, zinc sulfide, NaI, NaF, NaClO ₃ and NaSO ₄ .

  In addition to the above, lead zirconate titanate, barium titanate, strontium titanate, calcium titanate, barium strontium titanate, or the like, or a composite oxide thereof as a main component, and Ba site Perovskite-type composite oxides in which magnesium is substituted for Ti and tin and / or zirconium are substituted on the Ti site can also be used. Furthermore, what added 1 type, or 2 or more types of trace additive to the perovskite type complex oxide can also be used.

  The thickness of the titanium oxide-containing layer is preferably 0.01 μm or more and 10 μm or less, more preferably 0.03 μm or more and 7 μm or less, and more preferably 0.05 μm or more and 5 μm or less from the viewpoint of leakage prevention and carrier transport. Is more preferable.

  The layer thickness of the semiconductor layer (a layer containing silicon and a layer containing titanium oxide particles) is measured by TEM observation of a cross section.

In the present embodiment, the layer containing the titanium oxide particles has a layer density of 0.4 g / cm ³ from the viewpoint that the series resistance is reduced by dense packing of the titanium oxide particles. The above is preferable, 0.5 g / cm ³ or more is more preferable, 0.6 g / cm ³ or more is further preferable, 0.7 g / cm ³ or more is extremely preferable, and 0.8 g / cm ³ or more is particularly preferable. From the viewpoint of flexibility, the upper limit of the layer density is preferably 4.3 g / cm ³ or less, more preferably 3.0 g / cm ^3, more preferably 2.5 g / cm ³ or less, 2.0 g / A cm ³ or less is very preferable. Here, the layer density is a parameter indicating the degree of filling of the titanium oxide particles forming the semiconductor layer.

  The present embodiment is characterized in that in the step of forming the layer containing titanium oxide particles, the heat treatment temperature is low and the particles are not sintered. Thereby, since it becomes a film | membrane with a low layer density and the form of particle | grains hold | maintained, a softness | flexibility is provided. The process temperature is preferably 300 ° C. or less, more preferably 250 ° C. or less, further preferably 200 ° C. or less, extremely preferably 50 ° C. or less, and 30 ° C., because the titanium oxide particles are not sintered and lead to lower costs. The following are particularly preferred: Moreover, 10 degreeC or more is preferable from a viewpoint of the efficiency of drying, and 20 degreeC or more is more preferable.

  In this embodiment, since the layer containing silicon is responsible for light absorption, the layer containing titanium oxide particles preferably has high light transmittance, and the transmittance for light with a wavelength of 550 nm is 70% or more and less than 100%. Preferably, 75% or more and less than 100% are preferable, and 80% or more and less than 100% are more preferable. Here, the transmittance is a parameter indicating the degree of whether or not the layer containing titanium oxide particles can deliver light to silicon without hindering light transmission, and is measured using a spectrophotometer. be able to.

  As a method for forming a layer containing titanium oxide particles, a coating solution (for example, a surfactant obtained by dispersing titanium oxide particles in water or an organic solvent or hydrolyzing a metal alkoxide is added. There is a method of preparing a dispersion), applying it to a substrate, and drying by heating.

  In the method for producing a layer containing titanium oxide particles according to the present embodiment, the pH is adjusted to 0.5 to 10.0 and the titanium oxide particles are dispersed on a predetermined base material (electrode or silicon substrate). A coating step of coating the dispersion, a treatment step of treating the substrate coated with the dispersion at a temperature of 10 ° C. or more and 300 ° C. or less, and forming a layer containing titanium oxide particles on the substrate; It is characterized by not having a sintering process. By eliminating the firing step, flexibility can be imparted to the layer containing the titanium oxide particles, and when the treatment step is at a low temperature, a general-purpose resin can be used and a coating process can be employed.

  The amount of titanium oxide particles used in the dispersion is preferably 5 to 50% by mass, more preferably 10 to 40% by mass.

(Titanium oxide particle dispersion)
It is preferable that the titanium oxide particle dispersion liquid of this embodiment consists of the said titanium oxide particle and the dispersion medium adjusted to pH 0.5-10.0. Further, a surfactant or an additive can be added to the dispersion.

  As a dispersion medium, water, pentane, hexane, peptane, octane, nonane, decane, 2-methylhexane, decalin, tetralin, methanol, ethanol, n-propanol, 2-propanol, n-butanol, t-butanol, ethylene glycol , Diethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, ethylene glycol mono 2-ethylhexyl ether, propylene glycol n-butyl ether, dipropylene glycol n- Butyl ether, tripropylene glycol n-butyl ether, dipropy Ketones such as N-glycol methyl ether, tripropylene glycol methyl ether, glycerin acetone, methyl ethyl ketone, aromatics such as benzene, xylene, toluene, phenol, aniline, diphenyl ether, dimethyl sulfoxide, dimethylformamide, acetonitrile, methyl acetate, tetrahydrofuran, Examples include butyl lactate and N-methylpyrrolidone. It is also possible to use a mixture of these.

  Examples of the surfactant include an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant. Specifically, examples of the anionic surfactant include fatty acid sodium, monoalkyl sulfate, alkyl benzene sulfonate, and monoalkyl phosphate. Examples of the cationic surfactant include alkyltrimethylammonium salts, dialkyldimethylammonium salts, and alkylbenzylmethylammonium salts. Examples of amphoteric surfactants include alkyl dimethylamine oxide and alkyl carboxybetaine. Examples of the nonionic surfactant include polyoxyethylene alkyl ether, fatty acid sorbitan ester, alkyl polyglycoside, fatty acid ethanolamide, and alkyl monoglyceryl ether.

  As additives, acids such as hydrochloric acid, sulfuric acid and formic acid, and alkalis such as ammonia, sodium hydroxide and potassium hydroxide can be added.

  The average particle diameter of the titanium oxide particles used in the present embodiment is preferably 0.5 nm or more, more preferably 1 nm or more, and further preferably 3 nm or more from the viewpoint of film formability. In addition, since the layer containing titanium oxide particles is densely packed to suppress leakage and improve carrier transport, the average particle size is preferably 50 nm or less, more preferably 30 nm or less, and further preferably 20 nm or less. Preferably, 15 nm or less is very preferable.

<Solar cell>
The solar cell of this embodiment includes the layer containing silicon, the layer containing titanium oxide, an electrode, and a substrate, and generates electricity by light. The junction between the silicon-containing layer and the titanium oxide-containing layer constituting the solar cell may be a pp junction or an nn junction, but is preferably a pn junction type. A different material may be added between the two types of semiconductor layers.

  As an example 1, a solar cell 100 shown in FIG. 1 includes an anode layer 120, a layer containing silicon (p-type semiconductor layer) 130, and a layer containing titanium oxide particles (n-type semiconductor layer) 140 on a substrate 110. , And a cathode layer 150. Each layer can be further subdivided to provide a plurality of layers. For example, a hole extraction layer (not shown) can be provided between the layer 130 and the layer 120. Further, an electron extraction layer (not shown) can be provided between the layer 140 and the layer 150. Further, a light absorption layer (not shown) can be provided between the layer 130 and the layer 140. Further, the layer 130 and the layer 140 may have a bulk heterostructure mixed with each other. It is preferable that either the layer 120 or the layer 150 is transparent. The substrate 110 may be on the layer 150 side, or may be on both the layer 120 side and the layer 150 side. The layer 150 is preferably transparent.

  The configuration of the solar cell of this embodiment may be a tandem structure in which two or more structures shown in FIG. 1 are stacked in series.

  As the substrate, any commonly used substrate such as a glass substrate, a plastic substrate such as PET (polyethylene terephthalate), PC (polycarbonate), PP (polypropylene), an aluminum substrate, a stainless steel (SUS) substrate, and a paper substrate can be used. .

  As cathode (layer), aluminum, SUS, gold, silver, alloy of indium and gallium, ITO (indium tin oxide), FTO (fluorine-doped tin oxide), IZO (indium zinc oxide), zinc oxide, aluminum-doped oxide Commonly used metals or metal oxides such as zinc can be used. Further, a conductive polymer, graphene, or the like can be used.

  As the anode (layer), aluminum, SUS, gold, silver, an alloy of indium and gallium, ITO (indium tin oxide), FTO (fluorine-doped tin oxide), IZO (indium zinc oxide), zinc oxide, aluminum-doped oxide Commonly used metals or metal oxides such as zinc can be used. Further, a conductive polymer, graphene, or the like can be used.

  The thickness of the substrate, the cathode layer, and the anode layer is not particularly limited, but the substrate can be 0.1 mm to 100 mm, the cathode layer can be 0.01 μm to 1000 μm, and the anode layer can be about 0.01 μm to 1000 μm. .

  In a solar cell further provided with an electrode (cathode layer in FIG. 1) on a layer containing titanium oxide particles, surface contact between the layer containing titanium oxide particles and the electrode from the viewpoint of efficiently extracting electrons. The rate is preferably 20% or more. Here, the surface contact rate can be determined, for example, by how much the layer containing the titanium oxide particles and the electrode are in two-dimensional contact by performing a TEM analysis of a cross section. Let the ratio obtained here be a surface contact rate. From the same viewpoint as described above, the surface contact ratio is more preferably 20% or more, and further preferably 30% or more. The upper limit of the surface contact rate is 100% or less.

<Method for producing solar cell including a layer containing titanium oxide>
An example of the manufacturing method of the solar cell provided with the layer containing the titanium oxide of this embodiment is shown below. The manufacturing method includes an application step of applying a dispersion liquid having a pH of 0.5 to 10.0 and titanium oxide particles dispersed on an electrode or a silicon substrate, and an electrode or silicon substrate coated with the dispersion liquid. Treatment at a temperature of 10 ° C. or higher and 300 ° C. or lower to form a layer containing titanium oxide particles on the electrode or silicon substrate. In the X-ray diffraction spectrum for the layer containing the formed titanium oxide particles, the half width of the diffraction peak appearing at the diffraction angle 2θ = 24 to 26 ° is 0.2 ° or more and 5.0 ° or less.

  As described above, the amount of titanium oxide particles used in the dispersion is preferably 5 to 50% by mass, more preferably 10 to 40% by mass. In this case, the titanium oxide particles are anatase type titanium oxide particles. It is preferable that the average particle diameter of the titanium oxide particles is 0.5 nm or more and 50 nm or less. Furthermore, the pH of the dispersion is preferably from 0.5 to 5.0, more preferably from 0.5 to 3.0, from the viewpoint of storage stability of the liquid. On the other hand, from the viewpoint of reducing impurities during layer formation as much as possible, the pH of the dispersion is preferably 5.0 to 10.0, more preferably 5.0 to 9.0, and 5.5. More preferably, it is -8.0.

  Then, a solar cell can be easily obtained by laminating or bonding the layer containing silicon and the layer containing titanium oxide particles obtained as described above. A different material may be added between the two types of semiconductor layers.

(Coating process)
The application process of this embodiment is a process of applying a dispersion having a pH of 0.5 to 10.0 and dispersed with titanium oxide particles on an electrode or a silicon substrate.

  In particular, the layer containing titanium oxide particles according to the present embodiment uses various dispersion methods such as dipping, doctor blade, spin coating, brush coating, spray coating, and roll coater, using a dispersion mainly containing titanium oxide particles. It is formed into a film shape (thick film shape and thin film shape) by such a method.

  According to the coating method, the operation is extremely simple and does not require a large-scale apparatus, which is advantageous in reducing the manufacturing cost and the manufacturing time of the titanium oxide film and the solar cell. Further, according to the coating method, a titanium oxide film having a desired pattern shape can be easily obtained by using, for example, masking.

(Processing process)
The treatment process (film-forming process) of the present invention is to apply a dispersion liquid and then heat it using an apparatus such as a hot plate or an oven (heat treatment) or leave it at a temperature of about room temperature for a predetermined time. This is a step of drying the dispersion to form a layer containing titanium oxide particles. The treatment temperature is preferably 300 ° C. or less, more preferably 250 ° C. or less, further preferably 200 ° C. or less, extremely preferably 50 ° C. or less, and particularly preferably 30 ° C. or less, from the viewpoint of cost reduction due to a decrease in process temperature. Moreover, 10 degreeC or more is preferable from a viewpoint of the efficiency of drying, and 20 degreeC or more is more preferable.

(Element formation process)
The method for manufacturing a solar cell according to the present embodiment includes, for example, a step of forming a layer containing silicon on a substrate including an electrode to obtain a substrate with a layer (semiconductor layer) including silicon, and a substrate including the electrode. Forming a layer containing titanium oxide particles on the substrate, obtaining a substrate with a layer (semiconductor layer) containing titanium oxide particles, and bonding these substrates so that the semiconductor layers face each other. Prepare. The above-mentioned bonded semiconductor layer is sandwiched with a jig as shown in FIG. 2 and fixed. Also preferred is a method of forming a transparent electrode such as ITO after applying a titanium oxide particle dispersion directly on a silicon wafer to form a titanium oxide particle layer. This manufacturing method does not require a heating step and can be a low-cost manufacturing method.

  In the present embodiment, a solar cell may be manufactured by forming a layer containing titanium oxide particles on a layer containing silicon and further forming an electrode thereon.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  Hereinafter, the present invention will be described in more detail with reference to specific examples.

[Evaluation method]
Hereinafter, unless otherwise specified, evaluation was performed under the conditions of 23 ° C. and humidity 45%. The evaluation results for each of the examples and comparative examples described later are shown together in Table 1.

(1) Average particle diameter The average particle diameter was measured using a transmission electron microscope (TEM) HF-2000 (manufactured by Hitachi, Ltd.). As a specific measurement method, a titanium oxide dispersion TKS201 (anatase type, manufactured by Teika Co., Ltd., solid content: 33% by mass) will be described as an example. First, the titanium oxide dispersion was diluted to 2000 times, this diluted dispersion was ultrasonically dispersed, and the soaked mesh was freeze-dried to obtain a sample for TEM measurement. This titanium oxide sample for TEM measurement was magnified up to 570000 times by TEM and observed. The Pixel number of the obtained particle image was calculated, and the diameter of each particle converted into a perfect circle was calculated from the Pixel number by the following formula.
Radius converted to perfect circle = (Pixel number / π) ²
Full circle equivalent diameter = true circle equivalent radius x 0.22 x 2

  The total circle equivalent diameter of 100 points (current number of points) of particles was measured by the above method, and the average value was defined as the average particle size.

(2) X-ray half width The half width by X-ray diffraction was measured using an X-ray diffractometer (XRD) RINT-2500 (manufactured by Rigaku Corporation) using CuKα rays as an X-ray source. The layer containing titanium oxide particles for measurement was prepared by applying to a substrate on a quartz substrate under the same conditions as those for device preparation. The full width at half maximum is obtained by X-ray diffraction measurement of a layer containing titanium oxide particles. The peak of the (101) plane of titanium oxide whose crystal type is anatase type (that is, 2θ = 24 to 26 ° (25 ° It was measured from the peak that appears in the vicinity).

(3) Evaluation of IV characteristics DC voltage / current source (6241A, manufactured by ADMT) controlled by a computer (Solar cell IV measurement software manufactured by System House Sunrise Co.) and a simple solar simulator (manufactured by Mitsunaga Electric Manufacturing Co., Ltd.) Photovoltaic characteristics were measured using XES-40S1), and IV characteristics were evaluated. A BS-500Si photodiode detector (for crystalline Si solar cell, manufactured by Spectrometer Co., Ltd., secondary reference solar cell) was used for the test of the light quantity (AM1.5G, 100 mW / cm ² ).

  The measurement was performed with the solar cell fixed. A specific method for preparing a measurement sample will be described with reference to FIG. First, the solar cell 4 is placed on a metal jig 5 coated with an insulating material. On top of that, a 2 mm thick silicone rubber sheet 3, a 3 mm thick quartz plate 2, and a metal jig 1 coated with an insulating treatment material (a light transmitting hole for transmitting light 10 at the center is provided. The metal jigs 1 and 5 are fixed with screws 9 at the four corners.

  In this evaluation, IV characteristics, Imax and Vmax were obtained. Note that Imax is a current when the output of the solar cell is maximized, and Vmax is a voltage when the output of the solar cell is maximized.

  And the short circuit current density, the open circuit voltage, FF, and the photoelectric conversion efficiency were computed from the graph of IV characteristic. The short-circuit current density (Jsc) is the current density when the voltage is 0, and the open circuit voltage (Voc) is the voltage when the current is 0.

FF can be obtained from the following equation.
FF = (Vmax · Imax) / (Voc · Jsc)
The photoelectric conversion efficiency η can be obtained from the following formula.
η = (output of solar cell) / 100 × 100
Output of solar cell = short circuit current density × open voltage × FF = Vmax · Imax

(4) Layer thickness The layer thickness of the layer containing silicon and the layer containing titanium oxide particles was measured by cross-sectional TEM. These semiconductor layers for measurement were prepared by coating on a substrate under the same conditions as in the device preparation. For these layers, the layer thickness was arbitrarily measured at five locations, and the average was calculated as the average layer thickness.

  The layer thickness of the layer made of silicon and the layer made of titanium oxide after producing the solar cell was measured by cross-sectional TEM observation. The measurement was performed after cutting the cross section of the solar cell by the FIB method.

  In the FIB method, Ga ions accelerated at 30 to 40 kV were focused to 0.01 to 0.1 μm and sputtered while scanning the cross section of the solar cell. A carbon film or a tungsten film was deposited as the protective film on the outermost surface of the sputtering. Further, cross-sectional TEM observation was performed at two locations, and the five-point layer thickness was measured at equal intervals per location. The average value of the layer thicknesses of a total of 10 points was calculated and taken as the average layer thickness.

(5) Layer density The layer density of the layer containing titanium oxide particles was measured as follows. First, the weight of the layer containing titanium oxide particles was measured. Next, the volume was calculated by measuring the area and film thickness of the layer. The layer density was measured by weight / volume. The layer thickness of the titanium oxide layer was measured by the method (4). The stratified area of the layer containing titanium oxide particles was measured with a ruler or a caliper.

Example 1 Production of Heterojunction Solar Cell Using Silicon Wafer Titanium oxide particle dispersion liquid (anatase type, Teika Co., Ltd.) having an average particle diameter of 6 nm on a PET film with ITO (manufactured by Aldrich, sheet resistance 60Ω / □) Manufactured by TKS201, solid content of 33% by mass, pH 1.0) by spin coating. In addition, the thickness of the layer which consists of a titanium oxide particle after drying for 10 minutes at 120 degreeC after spin coating was 1150 nm. On the other hand, a hydrofluoric acid treatment described later was performed on a p-type silicon crystal wafer having a thickness of 500 μm and a resistivity of 3 Ωcm. A laminated body was prepared by laminating a silicon crystal wafer and a PET film with ITO coated with a layer made of titanium oxide particles. A 35 μm-thick Kapton film (“Kapton” is a registered trademark) having a 4 mmφ hole at the time of bonding was sandwiched, and the silicon crystal wafer and the titanium oxide-containing thin film were in contact with each other only at the holed portion. Furthermore, it was set as the mask by sticking the aluminum vapor deposition film which opened the hole of 2 mmphi on the PET side. A solar cell was fabricated using this laminate. The solar cell was fixed with the jig shown in FIG.
“Hydrofluoric acid treatment”: The p-type silicon crystal wafer was washed with acetone to remove dirt on the wafer surface, immersed in a 5% hydrofluoric acid solution for 5 minutes, and washed with ultrapure water. Thereafter, it was washed with methanol. After cleaning, the wafer was dried at room temperature under vacuum for 1 hour.

[Example 2]: Production of heterojunction solar cell using silicon wafer Titanium oxide particle dispersion was changed to titanium oxide particle dispersion having an average particle size of 14 nm (anatase type, manufactured by Nippon Aerosil Co., Ltd., VP TiO ₂ P90, solid content 20) A solar cell was fabricated in the same manner as in Example 1 except that the mass was changed to 1.4% by mass.

[Example 3]: Production of heterojunction solar cell using silicon wafer Titanium oxide particle dispersion was converted to titanium oxide particle dispersion having an average particle diameter of 7 nm (anatase type, manufactured by Ishihara Sangyo Co., Ltd., ST01, solid content 20% by mass, A solar cell was produced in the same manner as in Example 1 except that the pH was changed to 1.1).

[Example 4]: Production of heterojunction solar cell using silicon wafer Titanium oxide particles having an average particle diameter of 15 nm (AMT400, anatase type, manufactured by Teica) were dispersed in 2 methoxyethanol, and a dispersion of 33% by mass was obtained. Produced. 1.0 g of the dispersion was taken, 1.58 g of 2 methoxyethanol was added thereto, and the mixture was stirred to obtain dispersion A (pH 5.6). The dispersion A was allowed to stand for 1 day and then stirred for 10 seconds immediately before spin coating. On the other hand, a p-type silicon crystal wafer having a thickness of 500 μm and a resistivity of 3 Ωcm was ultrasonically cleaned with acetone for 5 minutes. Further, it was immersed in a 5% hydrofluoric acid solution for 5 minutes and then washed with ultrapure water. Immediately after washing, the dispersion A was dropped on a silicon wafer, and a titanium oxide thin film was produced by spin coating (2000 rpm, 30 seconds). The production temperature was 20 ° C. The thickness of the titanium oxide thin film was 1900 nm.

  Next, a PET film with ITO (sheet resistance 30 Ω / □, manufactured by Geomatic Co., Ltd.) was washed with methanol, and then bonded so that the ITO surface was in contact with the titanium oxide-containing thin film side. A 35 μm-thick Kapton film having a 4 mmφ hole at the time of bonding was sandwiched so that ITO and the titanium oxide-containing thin film were in contact with each other only at the holed portion. Furthermore, it was set as the mask by sticking the aluminum vapor deposition film which opened the hole of 2 mmphi on the PET side. This produced a solar cell.

[Example 5]: Production of heterojunction solar cell using silicon wafer Titanium oxide particles having an average particle diameter of 30 nm (AMT600, anatase type, manufactured by Teica) were dispersed in 2 methoxyethanol, and 33% by mass of dispersion B Was made. 1.0 g of the dispersion was taken, 1.58 g of 2 methoxyethanol was added thereto, and the mixture was stirred to obtain dispersion B (pH 7.6). Dispersion B was allowed to stand for 1 day and then stirred for 10 seconds immediately before spin coating. On the other hand, a p-type silicon crystal wafer having a thickness of 500 μm and a resistivity of 3 Ωcm was ultrasonically cleaned with acetone for 5 minutes. Furthermore, after being immersed in a 20% aqueous ammonium fluoride solution for 20 minutes, it was washed with ultrapure water. The dispersion B stirred immediately after washing was dropped onto a silicon wafer, and a titanium oxide thin film was produced by spin coating (2000 rpm, 30 seconds). The production temperature was 20 ° C. The thickness of titanium oxide was 2000 nm.

  Next, a PET film with ITO (sheet resistance 30 Ω / □, manufactured by Geomatic Co., Ltd.) was washed with methanol, and then bonded so that the ITO surface was in contact with the titanium oxide-containing thin film side. A 35 μm-thick Kapton film having a 4 mmφ hole at the time of bonding was sandwiched so that ITO and the titanium oxide-containing thin film were in contact with each other only at the holed portion. Furthermore, it was set as the mask by sticking the aluminum vapor deposition film which opened the hole of 2 mmphi on the PET side. This produced a solar cell.

[Comparative Example 1]: Production of heterojunction solar cell using silicon wafer Titanium oxide particle dispersion was changed to a titanium oxide particle dispersion having an average particle size of 15 nm (rutile type, MT-150A, manufactured by Teica Co., Ltd., solid content of 20% by mass). A solar cell 4 was produced in the same manner as in Example 1 except that the pH was changed to 1.3).

[Comparative Example 2]: Fabrication of heterojunction solar cell using silicon wafer A layer made of titanium oxide was formed by sputtering on a p-type silicon crystal wafer having a thickness of 500 μm and a resistivity of 3 Ωcm and subjected to the hydrofluoric acid treatment (substrate temperature) 100 ° C.). The thickness of the layer made of titanium oxide was 100 nm. A laminate was prepared by sputtering ITO on the titanium oxide layer formed by sputtering. A 35 μm-thick Kapton film having a 4 mmφ hole at the time of bonding was sandwiched and bonded. The ITO and the titanium oxide-containing thin film were in contact with each other only at a portion where a 4 mmφ hole was formed. Furthermore, it was set as the mask by sticking the aluminum vapor deposition film which opened the hole of 2 mmphi as a mask on the PET side. A solar cell 4 was produced using this laminate.

[Solar cell characteristics evaluation]
Table 1 shows the evaluation results of the solar cells of Examples 1 to 5 and Comparative Examples 1 and 2. The cell structures of Examples 1 to 5 and Comparative Examples 1 and 2 are structures substantially corresponding to FIG. The IV characteristics of the solar cell were adjusted and measured so that the amount of light of 1 sun was applied to the solar cell. In both Examples and Comparative Examples, the conductive tape (silver tape or copper tape) and the silicon crystal wafer were bonded to the silicon crystal wafer side using indium and gallium alloy paste. Moreover, the conductive tape was joined to the ITO electrode side using the silver paste for the ITO electrode. The terminal at the time of IV measurement was taken from the conductive tape.

  As shown in Table 1, it was found that the system in which the crystallinity of the titanium oxide particles is within the range defined by the present invention has improved short-circuit current density and increased photoelectric conversion efficiency.

  According to the present invention, a solar cell excellent in photoelectric conversion efficiency that can be manufactured at low cost can be provided.

  DESCRIPTION OF SYMBOLS 1,5 ... Metal jig | tool; 2 ... Quartz plate; 3 ... Silicone rubber sheet; 9 ... Screw; 10 ... Light; 4,100 ... Solar cell; 110 ... Substrate; 120 ... Anode layer; Layer (p-type semiconductor layer); 140... Layer containing titanium oxide particles (n-type semiconductor layer); 150.

Claims (6)

Comprising a layer containing silicon and a layer containing anatase-type titanium oxide particles;
In the X-ray diffraction spectrum for the layer containing the anatase-type titanium oxide particles, the half width of the diffraction peak appearing at a diffraction angle 2θ = 24 to 26 ° is 0.2 ° or more and 5.0 ° or less. Solar cell. The solar cell according to claim 1, wherein a layer density of the layer containing the titanium oxide particles is 0.4 g / cm ³ or more and 3.0 g / cm ³ or less.   The solar cell of Claim 1 or 2 whose average particle diameter of the said titanium oxide particle is 0.5 nm or more and 50 nm or less. An application step of applying a dispersion having a pH of 0.5 to 10.0 and dispersed titanium oxide particles on an electrode or a silicon substrate;
Treating the electrode or the silicon substrate coated with the dispersion at a temperature of 10 ° C. or more and 300 ° C. or less, and forming a layer containing the titanium oxide particles on the electrode or the silicon substrate; With
In the X-ray diffraction spectrum for the layer containing the titanium oxide particles, a half-width of a diffraction peak appearing at a diffraction angle 2θ = 24 to 26 ° is 0.2 ° or more and 5.0 ° or less. Production method.   The manufacturing method according to claim 4, wherein the treatment step is performed by leaving the electrode or the silicon substrate coated with the dispersion liquid at a temperature of 10 ° C. or higher and 30 ° C. or lower. The manufacturing method of Claim 4 or 5 whose average particle diameter of the said titanium oxide particle is 0.5 nm or more and 50 nm or less.

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