CN118648122A - Impurity diffusion composition and method for manufacturing solar cell using the same - Google Patents

Abstract

The present invention provides an impurity diffusion composition which stably forms a p++ high concentration impurity diffusion layer by a laser irradiation method and has little reduction in carrier lifetime, and a method for manufacturing a solar cell by using the composition. An impurity diffusion composition comprising (a-1) a compound represented by the general formula (1) and/or polyvinyl alcohol, (a-2) particles having an average particle diameter of 200nm or less and (a-3) a boron compound, wherein, based on 100 parts by mass of the (a-3) boron compound, 5 to 50 parts by mass of the (a-2) particles are contained (in the general formula (1), R ¹～R⁴ may be the same or different, each represents a 1-valent organic group having 1 to 3 carbon atoms, X ¹ represents a single bond or at least one organic group selected from methylene groups having 1 to 3 carbon atoms, -CH ₂OCH₂ -, n ₁ is an integer of 2 to 4, n ₂～n₄ may be the same or different, each represents an integer of 0 to 2, and n ₁+n₂+n₃+n₄＝4;m₁ is an integer of 1 to 3, m ₂～m₃ may be the same or different, each represents an integer of 0 to 2, and m ₁+m₂+m₃ = 3.

Description

Impurity diffusion composition and method for manufacturing solar cell using the same

Technical Field

The present invention relates to an impurity diffusion composition and a method for manufacturing a solar cell using the composition.

Background Art

Conventionally, in the manufacture of a solar cell having a pn junction, a p-type impurity is diffused on an n-type semiconductor substrate such as silicon to form a p-type diffusion layer, thereby forming a pn junction.

In recent years, solar cells with a selective emitter structure proposed to reduce the contact resistance with the electrode and suppress the recombination of carriers have been disclosed (Non-Patent Document 1). For example, in a solar cell with a selective emitter structure using an n-type silicon substrate as the base, in the p-type diffusion layer on the light-receiving surface side, a high-concentration p-type diffusion layer (p++ layer) is formed just below the electrode, and a low-concentration to medium-concentration p-type diffusion layer (p+ layer) is formed on the light-receiving surface other than just below the electrode. It is known that in order to form a selective emitter structure, a complex process combining multiple diffusions and partial etching by masking is required (Patent Document 1). In recent years, in order to simplify the process, a method has been proposed in which an impurity diffusion composition is applied to a substrate by screen printing or the like, and a high-concentration diffusion layer is selectively formed by treatment with a heating furnace or laser irradiation (Patent Documents 2 to 4). In particular, laser irradiation can apply energy uniformly within the substrate surface, and is therefore highly expected as a useful method (Patent Document 5).

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application Publication No. 2004-193350

Patent Document 2: International Publication No. 2015/2132

Patent Document 3: Japanese Patent Application Publication No. 2013-77804

Patent Document 4: Japanese Patent Application No. 2010-514585

Patent Document 5: Japanese Patent Application No. 2018-508976

Non-patent literature

Non-patent document 1: E.Lee et.al., "Exceeding 19% efficient 6inch screenprinted crystalline silicon solar cells with selective emitter", RenewableEnergy, Volume 42 (June 2012), p.95-99

Summary of the invention

Problems to be solved by the invention

However, since high energy is required to form a p-type diffusion layer, when laser irradiation is performed on a layer formed by coating an impurity diffusion composition on a substrate surface, if the output power is low, diffusion of impurities does not proceed, and if the output power is high, the silicon substrate is damaged, the defect density increases, the carrier lifetime decreases, and a high-concentration p++ layer cannot be stably formed. In addition, there is a problem that a small amount of inorganic particles contained in the impurity diffusion composition and organic matter that becomes carbide by laser irradiation remain even after the stripping process after irradiation, resulting in a decrease in carrier lifetime.

The present invention has been completed in view of the above-mentioned previous problems, and its purpose is to provide an impurity diffusion composition that can stably form a high-concentration impurity diffusion layer of p++ by using a laser irradiation method, with little reduction in carrier lifetime, and a method for manufacturing a solar cell using the composition.

Solution

In order to solve the aforementioned problems, the impurity-diffusing composition of the present invention has the following structure.

[1]. An impurity diffusion composition comprising:

(a-1) a compound represented by the general formula (1) and/or polyvinyl alcohol,

(a-2) particles having an average particle size of 200 nm or less and containing an inorganic oxide as a main component, and

(a-3) a boron compound,

Furthermore, the (a-2) particles are contained in an amount of 5 to 50 parts by mass relative to 100 parts by mass of the (a-3) boron compound.

In the general formula (1), R ¹ to R ⁴ may be the same or different and represent a monovalent organic group having 1 to 3 carbon atoms, X ¹ represents a single bond, or at least one organic group selected from a methylene group having 1 to 3 carbon atoms and a -CH ₂ OCH ₂ - group; n ₁ is an integer of 2 to 4, n ₂ to n ₄ may be the same or different and represent an integer of 0 to 2, and n ₁ + n ₂ + n ₃ + n ₄ = 4; m ₁ is an integer of 1 to 3, m ₂ to m ₃ may be the same or different and represent an integer of 0 to 2, and m ₁ + m ₂ + m ₃ = 3.

[2] The impurity-diffusing composition according to [1], comprising a trimethylol compound as the compound represented by the general formula (1).

[3] In the impurity diffusion composition described in [1] or [2], the inorganic oxide is silicon oxide.

[4] The impurity-diffusing composition according to any one of [1] to [3], wherein the (a-1) contains polyvinyl alcohol, and the degree of saponification of the polyvinyl alcohol is 30 to 70%.

[5] The impurity-diffusing composition according to [2], wherein the trimethylol compound comprises trimethylolpropane, trimethylolethane and/or di(trimethylolpropane).

[6]. The impurity-diffusing composition according to any one of claims [1] to [5], wherein the (a-2) particles have a particle surface treated to be hydrophobic.

[7] The impurity-diffusing composition according to any one of claims [1] to [6], which does not contain an alkoxysilane compound, a silanol compound, and a siloxane resin, or contains these compounds in an amount of 10% by mass or less.

[8] A method for manufacturing a solar cell, wherein an impurity diffusion layer (c) is formed on a semiconductor substrate, comprising the following steps:

a step of applying the impurity-diffusing composition (a) according to any one of [1] to [7] on the semiconductor substrate to form an impurity-diffusing composition film (b); and

A step of irradiating the impurity-diffusing composition film (b) with laser light to form the impurity-diffusing layer (c).

Effects of the Invention

According to the present invention, it is possible to provide an impurity diffusion composition that can stably form a p++ high-concentration impurity diffusion layer by laser irradiation and that has little reduction in carrier lifetime, and a method for manufacturing a solar cell using the composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a process of an example of a method for producing a solar cell of the present invention.

FIG. 2 is a cross-sectional view showing another example of the method for producing a solar cell according to the present invention.

FIG. 3 is a diagram showing a screen printing pattern used in the embodiment of the present invention.

FIG. 4 is an enlarged view of a pattern portion within the substrate surface of FIG. 3 .

DETAILED DESCRIPTION

Hereinafter, the method for manufacturing a solar cell of the present invention will be described with reference to the accompanying drawings. Note that the following embodiments are examples, and the present invention is not limited to these embodiments.

<Impurity-diffusing composition (a)>

The impurity-diffusing composition (a) comprises:

(a-1) A compound represented by the general formula (1) and/or polyvinyl alcohol (hereinafter referred to as "(a-1) compound" in some cases)

(a-2) particles having an inorganic oxide as a main component and an average particle size of 200 nm or less (hereinafter referred to as "(a-2) particles" in some cases) and

(a-3) Boron compounds.

[(a-1) Compound]

In the general formula (1), ^R1 to ^R4 may be the same or different and represent a monovalent organic group having 1 to 3 carbon atoms. From the viewpoint of forming a stable complex with a boron compound, preferred organic groups include saturated hydrocarbon groups such as methyl, ethyl, propyl and isopropyl.

^X1 represents a single bond, or at least one organic group selected from a methylene group having 1 to 3 carbon atoms and _{a -CH2OCH2-} group. From the viewpoint of forming a stable complex with a _boron compound, ^X1 is preferably at least one organic group selected from a single bond and a _-CH2OCH2- group.

_n1 is an integer of 2 to 4, and _n2 to _n4 may be the same or different and represent an integer of 0 to 2. Herein, _n1 + _n2 + _n3 + _n4 = 4. From the viewpoint of forming a stable complex with a boron compound, _n1 is preferably an integer of 2 to 4, and more preferably an integer of 3 to 4. _m1 is an integer of 1 to 3, and _m2 to _m3 may be the same or different and represent an integer of 0 to 2. Herein, _m1 + _m2 + _m3 = 3. From the viewpoint of forming a stable complex with a boron compound, _m1 is preferably 2 to 3, and more preferably 3.

Preferred specific examples of the general formula (1) include dimethylol compounds such as dimethylolethane, dimethylolpropane, and dimethylolbutane, trimethylol compounds such as trimethylolmethane, trimethylolbutane, trimethylolpentane, trimethylolpropane, trimethylolethane, and di(trimethylolpropane), and tetramethylol compounds such as pentaerythritol. Among them, from the viewpoint of being able to easily form a higher concentration impurity region and further suppressing the reduction of carrier lifetime, it is more preferred to contain a trimethylol compound, further preferably to contain trimethylolpropane, trimethylolethane and/or di(trimethylolpropane), and most preferably to contain trimethylolethane.

In addition, from the viewpoint of being able to easily form a higher concentration impurity region and further suppressing the reduction of carrier lifetime, the saponification degree of the polyvinyl alcohol (hereinafter sometimes referred to as "PVA") is preferably 30 to 70%. By having a saponification degree of 30% or more, a strong complex is formed with a boron compound, and a higher concentration impurity region can be easily formed, which can further suppress the reduction of carrier lifetime. The saponification degree is more preferably 40% or more. On the other hand, by having a saponification degree of 70% or less, the complex formed with the boron compound is stabilized in the solvent, and a higher concentration impurity region can be easily formed, which can further suppress the reduction of carrier lifetime. The saponification degree is more preferably 50% or less.

The average polymerization degree of PVA is preferably 150 to 1000 in terms of solubility and complex stability. In the present invention, the average polymerization degree and saponification degree are values measured according to JIS K6726 (1994). The saponification degree is a value measured by a back titration method in the method described in the JIS.

The compound represented by the general formula (1) and/or PVA, the 1,3-diol part contained in the structure forms a stable complex with the (a-3) boron compound to form a good impurity diffusion layer. Thus, a high-concentration impurity diffusion layer with high stability of the complex during laser irradiation can be formed, and residues can be effectively removed in the stripping process, which can suppress the reduction of carrier lifetime.

From the viewpoint of being able to easily form a higher concentration impurity region and further suppressing the reduction of carrier lifetime, the (a-1) compound is preferably 1 to 30% by mass in the impurity diffusion composition. By making the content of the (a-1) compound 1% or more by mass, a higher concentration impurity region can be easily formed. The content of the (a-1) compound is more preferably 5% or more by mass. On the other hand, by making the content of the (a-1) compound 30% or less by mass, the reduction of carrier lifetime can be further suppressed. The content of the (a-1) compound is more preferably 20% or less by mass.

Regarding the carrier lifetime, after manufacturing the solar cell unit, a solar simulator with a spectral distribution of AM1.5 is used to irradiate simulated sunlight at an energy density of 100mW/ ^cm2 at 25°C, and the open circuit voltage _VOC (VoltageOpen Circuit) is measured to estimate the carrier lifetime. The higher _{the VOC} , the longer the carrier lifetime.

[(a-2) Particles]

The average particle size of the (a-2) particles is 200 nm or less. When the average particle size is 200 nm or less, the diffusion of boron from the (a-3) boron compound can be promoted by laser irradiation, and a high-concentration impurity diffusion layer (c) can be stably formed. The average particle size of the (a-2) particles is preferably 50 nm or less.

The average particle size of the particles is the median diameter (d50) in the particle size distribution, and can be estimated by subjecting the particles to ultrasonic treatment with an aqueous solution or the like for 10 to 30 minutes to loosen agglomerates and then using a laser diffraction/scattering particle size distribution analyzer.

The (a-2) particles have an inorganic oxide as a main component. Preferred specific examples include oxides of silicon, titanium, zirconium, aluminum, germanium, gallium, bismuth, and barium, but are not limited thereto.

From the viewpoint of further suppressing the reduction of carrier lifetime, the (a-2) particles preferably have silicon oxide as the main component. Here, the main component refers to a component containing 70 parts by mass or more when the entire particle is set to 100 parts by mass. The content of silicon oxide as the main component in the (a-2) particles is preferably 80 parts by mass or more, more preferably 90 parts by mass or more.

The content of silicon oxide in the particles can be differentiated by subjecting the particles to a stepwise acid dissolution treatment and estimated using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy).

In order to suppress the influence of trace residues after the lift-off step and further suppress the reduction of carrier lifetime, it is preferred that the (a-2) particles themselves do not contain a boron component.

The (a-2) particles preferably have a particle surface that has been treated with hydrophobicity. By having a particle surface that has been treated with hydrophobicity, the promotion of boron diffusion during laser irradiation that is hindered by the (a-2) particles combining with each other to form granules can be suppressed, and a higher concentration of impurity diffusion layer can be formed. Here, the so-called "hydrophobic treatment" refers to a treatment that reduces the concentration of hydrophilic functional groups on the particle surface by using a silane coupling agent such as trimethylsilane and hexamethylenedisilazane to form a covalent bond on the surface, or using a fluoroalkylamine such as nonafluorobutylamine to form an ionic bond. Whether the (a-2) particles have a particle surface that has been treated with hydrophobicity can be determined by adding the (a-2) particles to water at a concentration of 4% by mass and whether they disperse after stirring.

The (a-2) particles are 5 to 50 parts by mass relative to 100 parts by mass of the (a-3) boron compound. By making the (a-2) particles 5 parts by mass or more, a higher concentration impurity region can be easily formed. The (a-2) particles are more preferably 10 parts by mass or more, and further preferably 20 parts by mass or more. On the other hand, by making the (a-2) particles 50 parts by mass or less, the reduction in carrier lifetime can be further suppressed. The (a-2) particles are more preferably 30 parts by mass or less.

[(a-3) Boron compounds]

(a-3) The boron compound is a component for forming a p-type impurity diffusion layer in a semiconductor substrate.

Examples of the boron compound include boric acid, boron trioxide, methylboric acid, phenylboric acid, trimethyl borate, triethyl borate, tripropyl borate, tributyl borate, trioctyl borate, triphenyl borate, etc. Among them, boric acid and boron trioxide are more preferred from the viewpoint of doping properties.

From the viewpoint of stabilization of the complex during laser irradiation, the amount of the (a-3) boron compound contained in the impurity-diffusing composition is preferably 1 to 30% by mass based on 100% by mass of the entire impurity-diffusing composition.

From the viewpoint of diffusion uniformity, the mass ratio of the (a-1) compound to the (a-3) boron compound is preferably 1:1 to 20:1, more preferably 1:1 to 10:1.

[Alkoxysilane compound, silanol compound and siloxane resin]

In the impurity diffusion composition, it is preferred that alkoxysilane compounds, silanol compounds and siloxane resins are not contained, or their content is 10% by mass or less. By making the content of alkoxysilane compounds, silanol compounds and siloxane resins less than 10% by mass, it is possible to suppress the situation where the promotion of boron diffusion during laser irradiation is hindered by the bonding granulation between particles, thereby forming an impurity diffusion layer with a higher concentration. The less the content of alkoxysilane compounds, silanol compounds and siloxane resins, the better, more preferably less than 5% by mass, further preferably less than 1% by mass, and most preferably less than 0.1% by mass. Here, the content of alkoxysilane compounds, silanol compounds and siloxane resins in the impurity diffusion composition refers to their mass fraction relative to the total mass of the impurity diffusion composition. When any one of the alkoxysilane compounds, silanol compounds or siloxane resins is contained, it is called its content, and when two or more are contained, it is called its total content.

The concentration of the impurity diffusion layer can be estimated by measuring the surface resistance of the semiconductor substrate after the impurity diffusion using a four-probe surface resistance measuring apparatus RT-70V (manufactured by Napson Corporation). The lower the resistance value, the higher the diffusion concentration.

[Solvent]

The impurity-diffusing composition preferably further contains a solvent. In particular, from the viewpoint of further improving printability when using a screen printing method or a spin coating printing method, a solvent having a boiling point of 100° C. or higher is preferred. When the boiling point is 100° C. or higher, when the impurity-diffusing composition is printed on a printing plate used in a screen printing method, for example, it is easy to suppress the impurity-diffusing composition from drying and fixing on the printing plate.

The content of the solvent having a boiling point of 100° C. or higher is preferably 20% by mass or more relative to the total amount of the solvent. Examples of the solvent having a boiling point of 100° C. or higher include ethyl lactate (boiling point 155° C.), diacetone alcohol (boiling point 169° C.), propylene glycol monomethyl ether acetate (boiling point 145° C.), propylene glycol monomethyl ether (boiling point 120° C.), 3-methoxy-3-methyl-1-butanol (boiling point 174° C.), γ-butyrolactone (boiling point 204° C.), N-methyl-2-pyrrolidone (boiling point 204° C.), N,N-dimethylimidazolidinone (boiling point 226° C.), terpineol (boiling point 219° C.), and 1,3-propylene glycol (boiling point 214° C.).

As a preferred solvent, 1,3-propylene glycol is more preferably contained. By containing 1,3-propylene glycol, the stability of the complex of the (a-1) compound and the (a-3) boron compound is further improved, and it contributes to the formation of a higher concentration impurity region during laser irradiation.

[Surfactant]

The impurity diffusion composition may contain a surfactant. By containing a surfactant, coating unevenness can be improved and a uniform coating film can be obtained. As the surfactant, a fluorine-based surfactant or a silicone-based surfactant is preferably used.

When the surfactant is contained, the content is preferably 0.0001 to 1 mass % in the impurity-diffusing composition.

[Thickener]

The impurity-diffusing composition may contain a thickener to adjust the viscosity, thereby enabling application in a more precise pattern by a printing method such as screen printing.

From the viewpoint of dense film formation and residue reduction, the 90% thermal decomposition temperature of the thickener is preferably below 400°C. Specifically, polyethylene glycol, polyethylene oxide, polypropylene glycol, polypropylene oxide, and various acrylate resins are preferred, among which polyethylene oxide, polypropylene oxide, or acrylate resins are preferred. From the viewpoint of storage stability, acrylate resins are particularly preferred. Here, the 90% thermal decomposition temperature refers to the temperature at which the weight of the thickener is reduced by 90% due to thermal decomposition. The 90% thermal decomposition temperature can be measured using a thermogravimetric analyzer (TGA) or the like.

〔Thixotropic agent〕

From the viewpoint of screen printability, the impurity diffusion composition may contain a thixotropic agent that imparts thixotropy. Here, the so-called imparting thixotropy refers to increasing the ratio (η1/η2) of the viscosity (η2) at low shear stress to the viscosity (η1) at high shear stress. By containing a thixotropic agent, the pattern accuracy of screen printing can be improved. It can be inferred that this is due to the following reasons. That is, it is inferred that the impurity diffusion composition (a) containing a thixotropic agent has a low viscosity at high shear stress, so it is not easy to block the screen during screen printing, and since the viscosity is high at low shear stress, it is difficult to cause bleeding and thickening of the pattern line width when printing is just completed.

As the thixotropic agent, specifically, cellulose derivatives, polysaccharides, hydrogenated castor oil-based polyethylene oxide-based, fatty acid-based polycarboxylic acids, phosphate-based surfactants, etc. can be exemplified. The thixotropic agent can be used alone, but two or more thixotropic agents can also be combined. In addition, it is more preferably used in combination with the thickener, so that a higher effect can be obtained.

There is no particular restriction on the solid content concentration of the impurity diffusion composition, but it is preferably in the range of 1 mass % to 90 mass %. If it is lower than this concentration range, the coating film thickness sometimes becomes too thin, making it difficult to obtain the desired doping and masking properties, and if it is higher than this concentration range, the storage stability sometimes decreases.

<Method for manufacturing solar cell>

The method for manufacturing a solar cell of the present invention is a method for manufacturing a solar cell in which an impurity diffusion layer (c) is formed on a semiconductor substrate, comprising: a step of coating an impurity diffusion composition (a) on the semiconductor substrate to form an impurity diffusion composition film (b), and a step of irradiating the impurity diffusion composition film (b) with a laser to form the impurity diffusion layer (c).

Examples of the semiconductor substrate include n-type substrates, and specifically single crystal silicon, polycrystalline silicon, and crystalline silicon substrates mixed with other elements such as germanium and carbon having an impurity concentration of 10 ¹⁵ to 10 ¹⁶ atoms/cm ³ .

The semiconductor substrate is preferably 50 to 300 μm thick and has a roughly quadrilateral shape with a side of 100 to 250 mm. In addition, in order to remove the slice damage or the natural oxide film, it is preferred to etch the surface of the semiconductor substrate in advance with a hydrofluoric acid solution or an alkaline solution. At this time, countless concave and convex texture shapes with a typical width of 40 to 100 μm and a depth of about 3 to 4 μm are formed on the surface of the semiconductor substrate.

In the case of forming a selective emitter structure, an impurity diffusion layer is formed with two or more levels of different impurity concentrations, namely, a high-concentration p-type diffusion layer (p++ layer) and a low-concentration to medium-concentration p-type diffusion layer (p+ layer). The different impurity concentrations mentioned here refer to an impurity concentration difference of 1×10 ¹⁷ atoms/cm ³ or more, and a difference in sheet resistance value of the substrate surface of the portion where the impurity diffusion layer is formed is 10Ω/□ or more.

<Step of Forming the Impurity-Diffusing Composition Film (b)>

First, as shown in Fig. 1(i), an impurity-diffusing composition (a) is applied on a semiconductor substrate 1 to form an impurity-diffusing composition film (b). Fig. 1 shows a state where a pattern 2 of the impurity-diffusing composition film (b) is formed by a method described later.

Examples of the coating method of the impurity-diffusing composition (a) include spin coating, screen printing, inkjet printing, slit coating, spray coating, relief printing, gravure printing, etc. When the impurity-diffusing composition film (b) is to be patterned, for example, it can be patterned by a method of screen printing or spray coating through a mask having openings in a desired pattern, a method of directly drawing a pattern by inkjet printing while moving a nozzle according to a pattern layout, a method of forming a film on the entire surface of a substrate by spin coating, then forming a pattern with a photoresist, etching the openings, and then peeling off the photoresist pattern to leave the portion covered by the resist as a pattern, etc.

Preferably, after applying the impurity diffusion composition (a) by these methods, the semiconductor substrate 1 coated with the impurity diffusion composition (a) is dried using a hot plate, an oven, etc. at a temperature in the range of 50 to 300° C. for 30 seconds to 30 minutes to form a pattern 2 of the impurity diffusion composition film (b).

The film thickness of the impurity-diffusing composition film (b) after drying is preferably 100 nm or more from the viewpoint of diffusibility of impurities, and is preferably 10 μm or less from the viewpoint of residues after etching.

＜Laser irradiation process＞

Next, as shown in FIG. 1( ii ), laser irradiation is performed on the pattern 2 of the impurity-diffusing composition film (b) to form an impurity diffusion layer (c).

There is no particular limitation on laser irradiation, and known lasers can be used. For example, as lasers, the fundamental wave (1064 [nm]), double wave (532 [nm]), triple wave (355 [nm]) of Nd:YAG laser or Nd:YVO ₄ laser, or XeCl excimer laser (308 [nm]), KrF excimer laser (248 [nm]), ArF excimer laser (198 [nm]) and the like can be used. They are irradiated at an oscillation frequency of 5 to 100 kHz and a pulse width of 10 to 200 nsec, and heated so that the temperature within the beam diameter is 800 to 1000°C, thereby forming a diffusion layer with a surface impurity concentration of 10 ¹⁹ to 10 ²¹ atoms/cm ³ .

When the impurity-diffusing composition film (b) is not patterned, the impurity diffusion layer (c) having a desired pattern shape can be formed by irradiating the impurity-diffusing composition film (b) with laser light in a desired pattern from above.

Alternatively, additional heat treatment may be performed after laser irradiation to further diffuse the impurities in the impurity diffusion layer (c).

The laser irradiation atmosphere is not particularly limited, and the irradiation may be performed in the air, or an inert gas such as nitrogen or argon may be used to appropriately control the amount of oxygen in the atmosphere.

When the impurity diffusion layer (c) is formed with two or more levels of different impurity concentrations, it is preferred to include a step of diffusing impurities into the portion where the impurity diffusion composition film (b) is not formed, using the impurity diffusion composition film (b) as a mask. Specifically, as shown in FIG1(iii), the impurity diffusion layer (d) having the same type of conductivity as the impurity diffusion layer (c) and a different impurity concentration is formed in the portion where the pattern is not formed, using the pattern 2 of the impurity diffusion composition film (b) as a mask.

The step of diffusing impurities into the unformed portion of the impurity diffusion composition film (b) using the impurity diffusion composition film (b) as a mask (the step of forming the impurity diffusion layer (d)) can be performed after the impurity diffusion composition film (b) is irradiated with a laser to diffuse the impurities into the semiconductor substrate 1 to form the impurity diffusion layer (c).

Specific examples of the method for diffusing impurities into the portion where the impurity-diffusing composition film (b) is not formed include: a method of injecting ions containing an impurity-diffusing component into the semiconductor substrate 1 having the pattern 2 of the impurity-diffusing composition film (b) and then annealing; a method of heating the semiconductor substrate 1 having the pattern 2 of the impurity-diffusing composition film (b) in an atmosphere containing the impurity-diffusing component; a method of applying another impurity-diffusing composition having the same type of conductivity and a different impurity concentration on the portion where the impurity-diffusing composition film (b) is not formed on the semiconductor substrate 1 having the pattern 2 of the impurity-diffusing composition film (b) to form an impurity-diffusing composition film and then performing electric heating, infrared heating, or microwave heating.

Among them, the step of diffusing the impurities into the portion where the impurity-diffusing composition film (b) is not formed is preferably a step of heating in an atmosphere containing an impurity-diffusing component.

When heating is performed in an atmosphere containing an impurity diffusion component, for example, in the case of a p-type, boron bromide (BBr ₃ ) can be bubbled and N ₂ can be flowed to form an atmosphere containing an impurity diffusion component, and the semiconductor substrate 1 with the pattern 2 of the impurity diffusion composition film (b) can be heated at 800 to 1000° C. in this atmosphere to form an impurity diffusion layer (d). By setting the gas pressure and heating conditions, the impurity concentration of the impurity diffusion layer (d) can be set to be different from the impurity concentration of the impurity diffusion layer (c).

Regarding the method of forming an impurity diffusion layer (c) with different impurity concentrations at two or more levels, as shown in FIG2 , an impurity diffusion layer (e) may be formed on the entire surface of one side of a semiconductor substrate, and an impurity diffusion layer (f) having a concentration different from that of (e) may be formed on the irradiated portion by laser irradiation. This embodiment is described in detail below.

First, as shown in FIG. 2( i ), an impurity diffusion layer (e) is formed on a semiconductor substrate 1 .

Examples of the formation method include a method of implanting ions containing an impurity diffusing component and then performing annealing, and a method of heating in an atmosphere containing an impurity diffusing component.

Among them, as a preferred formation method, for example, in the case of a p-type, boron bromide (BBr ₃ ) is bubbled, N ₂ is flowed to create an atmosphere containing an impurity diffusion component, and the semiconductor substrate is heated at 800 to 1000° C. in the atmosphere.

Next, as shown in Fig. 2(ii), the impurity diffusion composition (a) is coated on the impurity diffusion layer (e) to form a pattern 2 of the impurity diffusion composition film (b). The method for coating the impurity diffusion composition (a) and the method for forming the pattern 2 of the impurity diffusion composition film (b) are as described above.

Next, as shown in Fig. 2(iii), laser irradiation is performed on the pattern 2 to form an impurity diffusion layer (f). The laser irradiation method is as described above.

＜Peeling process＞

In this way, after the step of forming the impurity diffusion layer with two or more levels of different impurity concentrations, the pattern 2 of the impurity-diffusing composition film (b) is removed as shown in FIG. 1 (iV) and FIG. 2 (iV).

The pattern 2 of the impurity diffusion composition film (b) can be removed by a known etching method. The material used for etching is not particularly limited, and for example, as an etching component, it is preferred to contain at least one of hydrogen fluoride, ammonium, phosphoric acid, sulfuric acid, and nitric acid, and as other components, it is preferred to contain water, an organic solvent, etc.

<Back surface forming process>

The method for producing a solar cell of the present invention may include a back surface forming step.

For example, when a p-type impurity diffusion layer is formed on the surface of a semiconductor substrate with two or more levels of different impurity concentrations, and an n-type impurity diffusion layer is formed on the back side, the surface is protected by a _SiO2 film or the like to prevent n-type impurities from entering the surface. The preferred film thickness for obtaining the protective effect is 100 to 1000 nm, and in order to suppress the influence on the p-type diffusion layer on the surface of the semiconductor substrate, it is preferably formed by plasma CVD with a fast film forming speed at low temperature. More specifically, it is formed under the conditions of a mixed gas flow ratio _SiH4 / _N2O of 0.01 to 5.0, a pressure in the reaction chamber of 0.1 to 4 Torr, and a temperature during film formation of 300°C to 550°C.

Then, phosphorus oxychloride (POCl ₃ ) is bubbled on the back surface, and N ₂ is flowed to form an atmosphere containing an impurity diffusion component, and the semiconductor substrate is heated at 800-900° C. In this atmosphere, an n-type impurity diffusion layer is formed on the back surface of the semiconductor substrate, and a layer containing silicon oxide such as a phosphosilicate glass layer is formed on the outermost portion of the back surface by oxidation.

Next, the inorganic film on the surface of the semiconductor substrate and the layer containing silicon oxide on the back surface are removed by etching. A specific example of a preferred etching is the same as that in the case of forming an impurity diffusion layer with two or more levels of different impurity concentrations.

＜Passivation process＞

The method for manufacturing a solar cell of the present invention preferably provides a passivation film for suppressing surface recombination and preventing light reflection on the surface and back of the semiconductor substrate after the stripping step or after the back forming step if there is a back forming step. For example, as a passivation film for a p-type diffusion layer, _SiO2 obtained by heat treatment in a high-temperature oxygen atmosphere at 700°C or above and a silicon nitride film for protecting the film can be provided. In addition, only a SiNx film can be formed. In this case, it can be formed by a plasma CVD method using a mixed gas of _SiH4 and _NH3 as a raw material. At this time, hydrogen diffuses into the crystal, and orbitals that do not contribute to the bonding of silicon atoms, i.e., dangling bonds, are combined with hydrogen to inactivate defects (hydrogen passivation). More specifically, it is formed under the conditions that the mixed gas flow ratio _NH3 / _SiH4 is 0.05 to 5.0, the pressure of the reaction chamber is 0.1 to 4 Torr, and the temperature during film formation is 300°C to 550°C.

<Electrode Formation Process>

Next, a metal paste is printed by screen printing from the passivation film to the high-concentration impurity diffusion layer in the two horizontal impurity diffusion layers, and the electrode is formed by drying. The metal paste for the electrode has metal particles and glass particles as essential components, and contains a resin binder, other additives, etc. as needed. The metal particles used at this time are preferably Ag and Al.

<Electrode sintering process>

The electrode is then heat treated (fired) to complete the solar cell. After heat treatment (firing) at a temperature of 600°C to 900°C for a few seconds to a few minutes, the anti-reflection film on the light-receiving side, which is an insulating film made of glass particles contained in the metal paste for the electrode, melts, and the silicon surface is also partially melted, and the metal particles (such as silver particles) in the paste form a contact with the semiconductor substrate and solidify. As a result, the light-receiving surface electrode is connected to the semiconductor substrate. This is called melt-through.

The light-receiving surface electrode is generally composed of a busbar electrode and a finger electrode intersecting the busbar electrode. Such a light-receiving surface electrode can be formed by screen printing of the metal paste, electroplating of the electrode material, or evaporation of the electrode material by electron beam heating in a high vacuum. The busbar electrode and the finger electrode can be formed by a known method.

Example

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

(Matching Example 1)

<Preparation of p-type impurity diffusion composition>

3.0 g of boric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 13.5 g of polyvinyl alcohol having a saponification degree of 49% (manufactured by Nippon Acid Bio-Polymer Co., Ltd.) (hereinafter referred to as polyvinyl alcohol (49)), 5.0 g of fine-particle silica Aerosil #200 (manufactured by Nippon Aerosil Co., Ltd.: average primary particle size <20 nm, hydrophilic due to untreated surface), 32.9 g of γ-butyrolactone (manufactured by Tokyo Chemical Industry Co., Ltd.), and 45.0 g of terpineol (manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed and stirred thoroughly to make the mixture uniform, thereby obtaining a p-type impurity diffusion composition A1.

(Matching Example 2)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A2 was obtained in the same manner as in Formulation Example 1 except that polyvinyl alcohol having a saponification degree of 80% (manufactured by Nippon Obi Poval Co., Ltd.) (hereinafter referred to as polyvinyl alcohol (80)) was used instead of polyvinyl alcohol (49).

(Matching Example 3)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A3 was obtained in the same manner as in Formulation Example 1 except that polyvinyl alcohol having a saponification degree of 10% (manufactured by Nippon Obi Poval Co., Ltd.) (hereinafter referred to as polyvinyl alcohol (10)) was used instead of polyvinyl alcohol (49).

(Matching Example 4)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A4 was obtained in the same manner as in Formulation Example 1 except that Aerosil VPNKC130 (manufactured by Aerosil Japan Co., Ltd.: average primary particle size <20 nm, surface hydrophobic treated product) was used instead of Aerosil #200.

(Matching Example 5)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A5 was obtained in the same manner as in Formulation Example 1 except that trimethylolpropane (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of polyvinyl alcohol (49).

(Matching Example 6)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A6 was obtained in the same manner as in Formulation Example 1 except that trimethylolpropane was used instead of polyvinyl alcohol (49) and Aerosil VPNKC 130 was used instead of Aerosil #200.

(Matching Example 7)

<Preparation of p-type impurity diffusion composition>

12.5 g of boric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 12.5 g of trimethylolpropane, 2.6 g of Aerosil VPNKC130, 25.0 g of 1,3-propylene glycol (manufactured by Tokyo Chemical Industry Co., Ltd.), and 45.0 g of terpineol (manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed and stirred thoroughly to obtain a p-type impurity diffusion composition A7.

(Matching Example 8)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A8 was obtained in the same manner as in Formulation Example 7 except that di(trimethylolpropane) was used instead of trimethylolpropane.

(Matching Example 9)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A9 was obtained in the same manner as in Formulation Example 7 except that trimethylolethane was used instead of trimethylolpropane.

(Matching Example 10)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A10 was obtained in the same manner as in Formulation Example 2 except that 15.0 g of methyltriethoxysilane (KBM-13 manufactured by Shin-Etsu Chemical Co., Ltd.) was added.

(Matching Example 11)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A11 was obtained in the same manner as in Formulation Example 2 except that nanosilicon (manufactured by Aldrich Corporation: average primary particle size 100 nm, hydrophilic due to untreated surface) was used instead of Aerosil #200.

(Matching Example 12)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A12 was obtained in the same manner as in Formulation Example 2 except that silicon oxide SO-E2 (manufactured by Adomatex Co., Ltd.: average primary particle size 400 nm, hydrophilic due to untreated surface) was used instead of Aerosil #200.

(Matching Example 13)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A13 was obtained in the same manner as in Formulation Example 2 except that polyvinyl alcohol (80) was not added.

(Matching Example 14)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A14 was obtained in the same manner as in Formulation Example 2 except that Aerosil #200 was not added.

(Matching Example 15)

<Preparation of p-type impurity diffusion composition>

7.1 g of boric acid, 13.5 g of polyvinyl alcohol (80), 5.0 g of Aerol #200, 32.9 g of γ-butyrolactone and 45.0 g of terpineol were mixed and stirred well to obtain a p-type impurity diffusion composition A15.

(Matching Example 16)

<Preparation of p-type impurity diffusion composition>

3.7 g of boric acid, 12.5 g of trimethylolpropane, 2.6 g of Aerol #200, 25.0 g of γ-butyrolactone and 45.0 g of terpineol were mixed and stirred well to obtain a p-type impurity diffusion composition A16.

(Matching Example 17)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A17 was obtained in the same manner as in Formulation Example 15 except that 11.1 g of boric acid was used.

(Matching Example 18)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A18 was obtained in the same manner as in Formulation Example 15 except that 11.1 g of boric acid and 16.1 g of methyltriethoxysilane were added.

(Matching Example 19)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A19 was obtained in the same manner as in Formulation Example 15 except that 11.1 g of boric acid and 9.3 g of methyltriethoxysilane were added.

(Matching Example 20)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A20 was obtained in the same manner as in Formulation Example 15 except that 11.1 g of boric acid was used and polyvinyl alcohol (80) was replaced with polyvinyl alcohol (10).

(Matching Example 21)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A21 was obtained in the same manner as in Formulation Example 16 except that 5.8 g of boric acid was used, trimethylolpropane was changed to pentaerythritol, and Aerosil #200 was changed to Aerosil VPNKC130.

(Matching Example 22)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A22 was obtained in the same manner as in Formulation Example 15 except that 11.1 g of boric acid was used, polyvinyl alcohol (80) was used as polyvinyl alcohol (10), and Aerosil #200 was used as Aerosil VPNKC130.

(Matching Example 23)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A23 was obtained in the same manner as in Formulation Example 15 except that 11.1 g of boric acid was used, polyvinyl alcohol (80) was changed to polyvinyl alcohol (65), and Aerosil #200 was changed to Aerosil VPNKC130.

(Matching Example 24)

<Preparation of p-type impurity diffusion composition>

A p-type impurity diffusion composition A24 was obtained in the same manner as in Formulation Example 15 except that 11.1 g of boric acid was used, polyvinyl alcohol (80) was changed to polyvinyl alcohol (30), and Aerosil #200 was changed to Aerosil VPNKC130.

<Evaluation of the ability to form a high-concentration diffusion region (measurement of resistance value)>

In order to evaluate the high-concentration diffusion region forming ability of the solar cell obtained in the example and the comparative example, a substrate for evaluating the high-concentration diffusion region forming ability was prepared as follows.

As a substrate, a semiconductor substrate composed of n-type single crystal silicon with a side length of 156 mm was prepared, and both surfaces were alkali-etched to remove the slice damage and natural oxide. At this time, countless concave and convex textures with a typical width of 40 to 100 μm and a depth of about 3 to 4 μm were formed on both sides of the semiconductor substrate, which was used as a substrate.

Next, the p-type impurity diffusion composition A1 was printed on the entire surface of one side of the substrate by screen printing (screen printer (TM-750 model, Microtech Co., Ltd.), screen mask (manufactured by SUS Co., Ltd., 400 mesh, line diameter 23 μm)).

After screen printing the p-type impurity diffusion composition, the substrate was heated in air on a hot plate at 140° C. for 5 minutes and then heated in an oven at 230° C. for 30 minutes, thereby forming a pattern with a thickness of about 1.5 μm.

Next, the entire surface of one side of the substrate was irradiated with laser. The irradiation was performed using the second harmonic of Nd:YAG laser (532nm), with a pulse width of 100nsec, an oscillation frequency of 10kHz, an output of 5W, and a beam diameter of The irradiation was performed, and the time was appropriately adjusted so that the temperature of the irradiated portion reached 980°C.

The irradiated substrate was immersed in a 5% hydrofluoric acid solution for 5 minutes to remove the p-type impurity diffusion composition remaining on the surface, and then washed with water and dried to obtain a substrate for evaluating the ability to form a high-concentration diffusion region.

For the obtained substrate, a four-probe surface resistance measuring device RT-70V (manufactured by Napson Co., Ltd.) was used to measure the surface resistance of 15 points at equal intervals in the direction of one side including the center of the substrate, and the average value was calculated. Similarly, the p-type impurity diffusion compositions A2 to A24 were also evaluated. The lower the value, the higher the concentration of the impurity diffusion layer formed in the solar cell obtained in the embodiment and the comparative example.

<Evaluation of carrier lifetime (V _OC measurement)>

For the solar cell units (B1 to B24) obtained in the examples and comparative examples, simulated sunlight was irradiated at an energy density of 100 mW/cm ² at 25°C using a solar simulator having a spectrum distribution of AM1.5, and the open circuit voltage V _OC (Voltage Open Circuit) was measured. The higher the V _OC , the longer the carrier lifetime and the better the characteristics of the solar cell unit.

<Evaluation of Temporal Stability of Characteristics>

Solar cell units (B1 to B24) were similarly formed from the p-type impurity diffusion compositions (A1 to A24) after being placed at room temperature (23°C) for 14 days, and the resistance values of A1 to A24 and the V _OC of B1 to B24 were measured after being placed for 14 days in the same manner as described above.

(Example 1)

As a substrate, a semiconductor substrate made of n-type single crystal silicon with a side length of 156 mm was prepared, and a position alignment mark for alignment was laser processed. Then, in order to remove slice damage and natural oxides, both surfaces were alkali etched. At this time, countless concave and convex textures with a typical width of 40 to 100 μm and a depth of about 3 to 4 μm were formed on both sides of the semiconductor substrate, which was used as a substrate.

The substrate was placed in a diffusion furnace (manufactured by Koyo Semiconductor Co., Ltd.), and boron bromide (BBr ₃ ) was bubbled in at 0.06 L/min of nitrogen in an atmosphere of 19 L/min of nitrogen and 0.6 L/min of oxygen, thereby forming an atmosphere containing a p-type impurity diffusion component in the furnace. The temperature was maintained at 930° C. for 30 minutes, thereby forming an impurity diffusion layer on the entire surface of the substrate.

Next, the p-type impurity diffusion composition A17 was printed on the substrate by screen printing. The printing pattern was aligned to the arrangement shown in FIG. 3 and FIG. 4 (a screen printer (Microtech TM-750 model)) with a screen mask (SUS Co., Ltd., 400 mesh, line diameter 23 μm) corresponding to the pattern.

After screen printing the p-type impurity diffusion composition, the substrate was heated in air on a hot plate at 140° C. for 5 minutes and then heated in an oven at 230° C. for 30 minutes, thereby forming a pattern with a thickness of about 1.5 μm.

Next, the substrate was irradiated with laser in a manner overlapping the pattern of the p-type impurity diffusion composition shown in Figures 3 and 4. The irradiation was performed using the second harmonic (532 nm) of Nd:YAG laser with a pulse width of 100 nsec, an oscillation frequency of 10 kHz, an output of 5 W, and a beam diameter of 40 μmφ, and the time was appropriately adjusted so that the temperature of the irradiated portion reached 980°C.

The irradiated substrate was immersed in a 5% hydrofluoric acid solution for 5 minutes to remove the p-type impurity diffusion composition remaining on the surface, and then washed with water and dried.

Next, in order to form an n-type impurity diffusion layer on the back surface, the substrate surface was placed in a plasma CVD apparatus, and a 500nm thick silicon oxide layer was formed on the p-type impurity diffusion layer at a substrate temperature of 400°C, an RF power of 180W, a gas flow rate of _SiH4 =35scc, _N2O =1500scc, and a pressure of 2.5torr.

Next, the substrate was placed in a diffusion furnace (manufactured by Koyo Semiconductor Co., Ltd.), and nitrogen gas 19 L/min, oxygen gas 0.6 L/min, and phosphorus oxychloride (POCl ₃ ) were bubbling at 0.06 L/min of nitrogen gas to form an atmosphere containing n-type impurity diffusion components in the furnace. The temperature was maintained at 850° C. for 20 minutes, and n-type impurity diffusion was performed on the side opposite to the p-type impurity diffusion surface. After the diffusion was completed, the substrate was immersed in a 5% hydrofluoric acid solution for 10 minutes to remove the silicon oxide-containing layers on both sides of the substrate, and then washed with water and dried.

Next, the substrate was placed in a plasma CVD apparatus, and a passivation film of 80 nm thick silicon nitride was formed on both surfaces at a substrate temperature of 400° C., an RF power of 180 W, a gas flow rate of N ₂ = 750 scc, SiH ₄ = 35 scc, and NH ₃ = 90 scc, and a pressure of 2.0 torr.

Next, a commercially available Ag electrode paste was printed on both sides of the substrate by screen printing, and alignment was performed using alignment marks so that the printed pattern of the electrode overlapped with the pattern of the p-type impurity diffusion composition film.

Next, the substrate with the electrode pattern was placed in a diffusion furnace (manufactured by Koyo Solar Systems Co., Ltd.) and treated at 750°C for 3 minutes in an atmosphere of 16 L/min nitrogen and 4 L/min oxygen to make the electrode and the p-type impurity diffusion layer conductive, thereby forming a solar cell unit B17.

(Examples 2 to 11, Comparative Examples 1 to 13)

Solar battery cells B1 to B16 and B18 to B24 were produced in the same manner as in Example 1 except that p-type impurity diffusion layer forming compositions A1 to A16 and A18 to A24 were used.

The evaluation results are shown in Table 1.

Description of the accompanying drawings

1Semiconductor substrate

2 Pattern of impurity diffusion composition film (b)

3 Laser irradiation

4 Gases containing impurity diffusion components

5. Outermost pattern of impurity diffusion layer

6. The pattern of the substrate surface of the impurity diffusion layer (5 vertical lines and 121 horizontal lines)

(c), (d), (e), (f) Impurity diffusion layer

(g) Patterned area within the substrate surface

(h) Width of impurity diffusion layer pattern

(j) Interval of impurity diffusion layer pattern

Claims (8)

1. An impurity diffusion composition, which is an impurity diffusion composition (a) containing the following components: (a-1) a compound represented by the general formula (1) and/or polyvinyl alcohol, (a-2) particles having an average particle size of 200 nm or less and containing an inorganic oxide as a main component, and (a-3) a boron compound, Furthermore, the (a-2) particles are contained in an amount of 5 to 50 parts by mass relative to 100 parts by mass of the (a-3) boron compound. In the general formula (1), R ¹ to R ⁴ may be the same or different and represent a monovalent organic group having 1 to 3 carbon atoms, X ¹ represents a single bond, or at least one organic group selected from a methylene group having 1 to 3 carbon atoms and a -CH ₂ OCH ₂ - group; n ₁ is an integer of 2 to 4, n ₂ to n ₄ may be the same or different and represent an integer of 0 to 2, and n ₁ + n ₂ + n ₃ + n ₄ = 4; m ₁ is an integer of 1 to 3, m ₂ to m ₃ may be the same or different and represent an integer of 0 to 2, and m ₁ + m ₂ + m ₃ = 3. 2 . The impurity-diffusing composition according to claim 1 , wherein the compound represented by the general formula (1) contains a trimethylol compound. The impurity-diffusing composition according to claim 1 or 2, wherein the inorganic oxide is silicon oxide. 4 . The impurity-diffusing composition according to claim 1 , wherein the (a-1) contains polyvinyl alcohol, and the degree of saponification of the polyvinyl alcohol is 30 to 70%. 5 . The impurity-diffusing composition according to claim 2 , wherein the trimethylol compound comprises trimethylolpropane, trimethylolethane and/or di(trimethylolpropane). 6 . The impurity-diffusing composition according to claim 1 , wherein the (a-2) particles have a particle surface treated to be hydrophobic. 7. The impurity-diffusing composition according to claim 1 or 2, which does not contain an alkoxysilane compound, a silanol compound and a siloxane resin, or contains them in an amount of 10 mass % or less. 8. A method for manufacturing a solar cell, wherein an impurity diffusion layer (c) is formed on a semiconductor substrate, comprising the following steps: a step of applying the impurity-diffusing composition (a) according to claim 1 or 2 on the semiconductor substrate to form an impurity-diffusing composition film (b); and A step of irradiating the impurity-diffusing composition film (b) with laser light to form the impurity-diffusing layer (c).