JP2014090153A - Formation method of surface coating film and solar cell having the surface coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a formation method capable of reducing production cost of a final product such as a solar cell by forming with a simple formation method a surface coating film excellent in performances.SOLUTION: A surface coating film having two or more elements selected from elements Si, Ti, and Zr is formed by coating a compound component for surface coating film formation having two or more elements selected from elements Si, Ti, and Zr and a composition for surface coating film formation containing an organic solvent component on a base material to be coated to form a coating film and baking the coating film.

Description

  The present invention relates to a method for forming a surface coating film and a solar cell having a surface coating film formed by the method.

  A solar cell is a semiconductor element that converts light energy into electric power, and includes a pn junction type, a pin type, a Schottky type, and the pn junction type is widely used. In these silicon crystal solar cells, after the minority carriers generated by photoexcitation with sunlight incident light reach the pn junction surface, they are taken out as majority carriers from the electrodes attached to the light receiving surface and the back surface. It becomes electric energy.

  Solar cells are required to have high energy conversion efficiency, but carriers that can be taken out as current can be lost due to recombination via interface states existing on the substrate surface other than the electrode surface. Yes, leading to a decrease in conversion efficiency.

Therefore, in a high efficiency solar cell, a passivation film made of a silicon nitride (SiN _x : H) film or a silicon oxide (SiO ₂ ) film is formed on the surface of the silicon substrate except for a contact portion with the electrode, and the silicon substrate By suppressing carrier recombination at the interface between the passivation film and the passivation film, conversion efficiency is improved. In particular, a silicon nitride film is mainly used as a passivation film.

The silicon nitride film can also be used as an antireflection film that suppresses surface reflection for reducing the incidence loss of light of the solar cell. On the other hand, in the case of providing a passivation film made of a silicon oxide film, it is necessary to provide a film having a high refractive index such as a titanium oxide (TiO ₂ ) film on the outer side from the viewpoint of antireflection properties (Patent Document 1, Non-Patent Document 1). Patent Document 1).

JP 2011-159783 A

B. S. Richards, “Comparison of TiO2 and Other Dielectric Coatings for Burried-contact Solar Cells: a Review”, Prog. Photovolt: Res. Appl. 2004; 12: 253-281

  However, the silicon nitride film is formed by various CVD methods such as microwave plasma CVD method, RF plasma CVD method, photo CVD method, thermal CVD method, MOCVD method, or EB deposition, MBE, ion plating, ion beam. It is formed by using a vacuum apparatus such as various vapor deposition methods such as a sputtering method and a sputtering method. This led to an increase in the cost of the final product provided with a film.

  The present invention has been made in view of the above-described problems, and is a surface coating film capable of forming a surface coating film having excellent characteristics by a simple forming method and reducing the manufacturing cost of the final product. An object is to provide a forming method. Moreover, an object of this invention is to provide the solar cell which has the surface coating film formed by such a method.

  The present inventors have found that a surface coating film having two or more elements selected from Si, Ti, and Zr elements is effective as an antireflection film or a passivation film for solar cells, and has completed the present invention. It came to do. More specifically, the present invention provides the following.

  A first aspect of the present invention is a composition for forming a surface coating film comprising a compound component for forming a surface coating film having two or more elements selected from Si, Ti, and Zr and an organic solvent component A surface coating having two or more elements selected from Si, Ti, and Zr, each of which includes a coating process for coating a base material to be coated to form a coating film, and a firing process for firing the coating film. This is a method of forming a covering film.

  A second aspect of the present invention is a solar cell having a surface coating film formed by the method for forming a surface coating film according to the first aspect of the present invention.

  According to the present invention, a surface coating film having excellent characteristics can be formed by a simple forming method, and the manufacturing cost of a final product such as a solar cell can be reduced. Moreover, when the surface coating film is provided on the surface of the solar cell by the formation method of the present invention, a surface coating film serving as both a passivation film and an antireflection film can be obtained.

  Hereinafter, although embodiment of this invention is described, this invention is not limited to these.

[1] Composition for forming a surface coating film The composition for forming a surface coating film used in the forming method of the present invention is soluble in an organic solvent and changes into an oxide by heating, Si, Ti, Zr The compounds of these elements (referred to as silane compounds, titanium compounds, and zirconium compounds, respectively) are not particularly limited. Examples of such compounds include nitrates, chlorides, alcoholates and acetylacetonates of the respective elements, partial hydrolysates of alcoholates and acetylacetonates, and the like. Among these, it is preferable to employ alcoholates and acetylacetonates of the above elements and partial hydrolysates thereof.

As the alcoholate, for example, compounds represented by the following general formulas (1) to (3) can be used.
R ¹ _4-n SiX ¹ _n (1)
(N represents an integer of 2 to 4. R ¹ represents an organic group, and X ¹ represents an alkoxy group.)
R ² _4-n TiX ² _n (2)
(N represents an integer of 2 to 4. R ² represents an organic group, and X ² represents an alkoxy group.)
R ³ _4-n ZrX ³ _n (3)
(N represents an integer of 2 to 4. R ³ represents an organic group, and X ³ represents an alkoxy group.)

As the organic group for R ^{1 to} R ³ , those in a wide range can be used without any particular limitation, and examples thereof include those having a linear or branched alkyl group, alkenyl group, alkynyl group or hydrophilic group. . Examples of the alkyl group, alkenyl group and alkynyl group include the same groups as those described later for R ⁴ . Moreover, as an organic group which has a hydrophilic group, what is represented by the following general formula (4) can be illustrated, for example.
R ⁴ -ES-R ^5- (4)
Here, R ⁴ represents a linear or branched alkyl group, alkenyl group, or alkynyl group, ES represents an ester bond, and R ⁵ represents an alkylene group. The alkyl group, alkenyl group, and alkynyl group preferably have 1 to 10 carbon atoms, and more preferably have 2 to 6 carbon atoms. Also. The alkylene group preferably has 1 to 10 carbon atoms, and more preferably has 2 to 6 carbon atoms.

Examples of the hydrophilic group include a hydroxyl group, a carbonyl group, an ether group, and particularly an ester group (ester bond) among carbonyl groups. ^The number of carbon atoms of R 1 to R ³ is preferably 1 to 20, 1 to 6 is more preferable.

When two organic groups R ^{1 to} R ³ are present in each of the compounds represented by the general formulas (1) to (3), the organic groups may be the same as or different from each other.

X ^{1 to} X ³ are alkoxy groups, and an alkoxy group having 1 to 5 carbon atoms is particularly preferable. Examples of the alkoxy group having 1 to 5 carbon atoms include a methoxy group, an ethoxy group, an n-propoxy group, an i-propoxy group, an n-butoxy group, an i-butoxy group, a sec-butoxy group, and a t-butoxy group. A linear or branched alkoxy group can be mentioned. ^{When X} 1 to X ³ in the formula there are two or ^more, X 1 to X ³ may each be the same or different.

Examples of the silane compound represented by the general formula (1) include vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 2- (3 , 4-epoxycyclohexyl) ethyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldiethoxysilane, 3-mercaptopropyltri Methoxysilane, diallyldimethoxysilane, diallyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, allylaminotrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane , Tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetraisopropoxysilane, tetra-n-butoxysilane, tetraisobutoxysilane, diisopropoxydi-n-butoxysilane, di-t-butoxydi Examples include isopropoxysilane, tetra-t-butoxysilane, tetraisooctyloxysilane, and tetrastearyloxysilane.
Etc.

  Examples of the titanium compound represented by the general formula (2) include allyl trimethoxy titanium, allyl triethoxy titanium, diallyl dimethoxy titanium, diallyl diethoxy titanium, allyl amino trimethoxy titanium, tetramethoxy titanium, tetraethoxy titanium, tetra -N-propoxy titanium, tetraisopropoxy titanium, tetra-n-butoxy titanium, tetraisobutoxy titanium, diisopropoxy di-n-butoxy titanium, di-t-butoxy diisopropoxy titanium, tetra-t-butoxy titanium, Examples include tetraisooctyloxytitanium and tetrastearyloxytitanium.

  Examples of the zirconium compound represented by the general formula (3) include allyltrimethoxyzirconium, allyltriethoxyzirconium, diallyldimethoxyzirconium, diallyldiethoxyzirconium, allylaminotrimethoxyzirconium, tetramethoxyzirconium, tetraethoxyzirconium, tetra -N-propoxyzirconium, tetraisopropoxyzirconium, tetra-n-butoxyzirconium, tetraisobutoxyzirconium, diisopropoxydi-n-butoxyzirconium, di-t-butoxydiisopropoxyzirconium, tetra-t-butoxyzirconium, Examples thereof include tetraisooctyloxyzirconium and tetrastearyloxyzirconium.

  The composition for forming a surface coating film used in the present invention needs to use any two or more of elemental compounds of Si, Ti, and Zr. Of these, it is particularly preferable to use a silane compound and a titanium compound or a combination of a silane compound and a zirconium compound.

The ratio of the silane compound to the titanium compound is such that the mass ratio when each becomes an oxide, that is, the mass ratio in terms of SiO ₂ and TiO _{2 is} 1:99 to 97: 3. Preferably, it is set to 3:97 to 80:20, more preferably 5:95 to 75:25, still more preferably 10:90 to 60:40.
The ratio of the silane compound to the zirconium compound is 1:99 to 97: 3 in terms of the mass ratio when each becomes an oxide, that is, the mass ratio in terms of SiO ₂ and ZrO _2. Are preferably used, more preferably 3:97 to 97: 3, still more preferably 5:95 to 95: 5, and particularly preferably 10:90 to 80:20.

The hydrolysis product can be obtained by mixing Si, Ti and Zr element compounds and hydrolyzing them in the presence of water and an acid catalyst. As the acid catalyst, either an organic acid or an inorganic acid can be used.
In the present invention, a hydrolysis product having any one of Si, Ti, and Zr is used, and other metal compounds to which the above compounds other than the hydrolysis product are added are used. it can.

  As the inorganic acid, sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid and the like can be used, and among them, hydrochloric acid and nitric acid are preferable.

  As the organic acid, carboxylic acids such as formic acid, oxalic acid, fumaric acid, maleic acid, glacial acetic acid, acetic anhydride, propionic acid, n-butyric acid, and organic acids having a sulfur-containing acid residue are used. Examples of the organic acid having a sulfur-containing acid residue include organic sulfonic acids, and examples of esterified products thereof include organic sulfates and organic sulfites.

  What is necessary is just to prepare the quantity of the acid catalyst to be used, for example so that the density | concentration in the reaction system of a hydrolysis reaction may become the range of 1-1000 ppm, especially 5-800 ppm. By setting it as this range, precipitation of a hydrolysis product and a time-dependent change can be suppressed. Further, the amount of water added is preferably in the range of 0.2 to 4.0 moles per mole of the total of the silane compound, titanium compound, and / or zirconium compound to be hydrolyzed. The acid catalyst may be added after adding water, or may be added as an acid aqueous solution obtained by previously mixing the acid catalyst and water.

  This hydrolysis is performed by appropriately mixing a necessary amount of an organic solvent in addition to the silane compound, titanium compound and zirconium compound. As the organic solvent, alcohols such as ethyl alcohol described later can be used.

  Moreover, in order to adjust the solid content concentration in the composition for forming a surface coating film, it may be further diluted with a conventionally known organic solvent. Among them, for example, monohydric alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol, and ketones such as acetone, acetylacetone, methyl ethyl ketone, and methyl isoamyl ketone are preferable. The above organic solvents may be used alone or in combination of two or more.

  The solid content concentration of the silane compound, titanium compound, zirconium compound, and hydrolysis products thereof in the composition for forming a surface coating film (total of oxide equivalent masses of each of Si, Ti, and Zr element compounds) is: It is preferable to be 1 to 20% by mass, preferably 2 to 15% by mass.

[2] Method for forming surface coating film In order to form a surface coating film using the composition for forming a surface coating film of the present invention, the composition for forming a surface coating film of the present invention is formed on a base material to be coated. May be applied and fired. Since this surface coating film forming method does not require an expensive vacuum apparatus and can be easily performed, the cost of the final product can be reduced.

  Specifically, for example, a spin coating method, a spray method, an ink jet method, a screen printing method, and a transfer are performed on a base material to be coated so that the composition for forming a surface coating film of the present invention has a predetermined film thickness. A coating or printing method such as a printing method is used. At that time, the film thickness of the coating film is appropriately selected in consideration of the film thickness required after firing depending on the device to be applied.

  Next, the applied composition for forming a surface coating film is heated in a hot plate, a heating and drying furnace or the like to volatilize the solvent, and further baked in a baking furnace to remove organic groups and Si, Ti or Zr oxide is formed. The firing temperature at this time is, for example, 200 ° C. or higher, preferably about 250 to 1000 ° C. Usually, the time required for firing can be selected in a wide range of 1 second to 180 minutes, but in a process requiring mass productivity such as a solar cell, a range of 3 seconds to 30 minutes is desirable.

  Moreover, it is preferable to heat the said coating film in a vacuum or gas atmosphere in the case of baking. The gas to be used is not particularly limited, such as oxygen, nitrogen, hydrogen, argon, and a mixed atmosphere thereof, and can be used according to the purpose. It is preferable to use an inert gas such as nitrogen or argon because defects hardly occur in the surface coating film. In particular, when the surface coating film is provided as a semiconductor passivation film, firing in an inert gas is preferable because the characteristics of the film are improved. Moreover, in the case of a mixed atmosphere, it is preferable to mix the inert gas and an active gas such as hydrogen gas or oxygen gas, and it is preferable to mix the active gas in a range of 1 to 10% of the whole.

[3] Application destination of surface coating film As a base material to be coated, various materials such as resin, glass, and semiconductor can be used without particular limitation, and various end products are applied. The surface coating film can be used as an insulating film, an antireflection film, or a semiconductor passivation film, but is particularly effective when applied as an antireflection film or a passivation film for solar cells.

  The solar cell is composed of a silicon substrate and two or more elements selected from Si, Ti, and Zr elements formed on the light receiving surface of the silicon substrate (the surface on which sunlight is incident) or on the opposite surface. And a passivation film.

  By adopting such a configuration, it is possible to prevent carriers from being recombined and lost through the interface states existing on the silicon substrate surface, and to improve the maximum power of the solar cell. In addition, because of its high refractive index, when a composite film is provided on the light receiving surface of the silicon substrate, it can also function as an antireflection film, thus preventing reflection of sunlight and, as a result, of the solar cell. The maximum power can be further improved. Further, in order to improve the surface protection and antireflection ability, another film may be further provided outside the surface coating film provided by using the production method of the present invention.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

<Coating liquid synthesis example 1>
284 g of tetraisopropoxy titanium, 90 g of glacial acetic acid and 1795 g of ethyl alcohol were mixed at room temperature with stirring. Immediately after mixing, a slight exotherm occurs and the reaction proceeds. Stirring was continued for 3 hours, and then 480 g of acetylacetone was added, followed by further stirring and stirring for 3 hours. In this way, a coating solution for forming a titanium oxide film having a solid content concentration of 3% by mass was obtained.

<Coating liquid synthesis example 2>
208 g of tetraethoxysilane, 700 g of ethyl alcohol and 228 g of glacial acetic acid were mixed at room temperature with stirring. While stirring, 17 g of pure water and 1.7 g of concentrated hydrochloric acid were added, and stirring was continued, followed by stirring for 3 hours. After leaving at room temperature for 1 day, 1039 g of ethyl alcohol was further mixed with stirring. In this way, a coating solution for forming a silicon oxide film having a solid content concentration of 3% by mass was obtained.

<Coating liquid synthesis example 3>
A coating solution for forming a zirconium oxide film having a solid content concentration of 3% by mass was obtained in the same manner as in Coating solution synthesis example 1 except that tetra-n-butoxyzirconium was used instead of tetraisopropoxytitanium.

The evaluation conditions of the minority carrier lifetime and surface recombination velocity in the following examples and comparative examples are described.
(lifetime)
The lifetime was measured by a quasi-steady state photoconductive method (QSSPC method). A measuring instrument manufactured by Sinton was used as the measuring instrument. In addition, the lifetime in an Example and a comparative example is a value in which excess carrier density is 10 ^{< 15} > cm ^<-3> .
(Surface recombination speed)
Based on the value measured in the above (lifetime measurement), the surface recombination velocity S was determined according to the following equation. In the equation, W represents the wafer thickness, τ _eff represents the effective lifetime, and τ _bulk represents the bulk lifetime. Note that the surface recombination velocity S decreases as the effective lifetime increases.

Example 1
The coating liquid 800 g obtained in the coating liquid synthesis example 1 and the coating liquid 200 g obtained in the coating liquid synthesis example 2 are mixed with stirring, and the coating is 8: 2 (mass ratio) in terms of titanium dioxide and silicon dioxide. A liquid was obtained.

  The coating solution of Example 1 thus obtained was applied to both sides of a p-type silicon wafer at 4000 rpm with a spin coater, dried on a hot plate at 140 ° C. for 1 minute, and then in a nitrogen atmosphere in a heating furnace. And baking at 600 ° C. for 15 minutes. As a result, a composite coating of titanium oxide and silicon oxide having a film thickness of 48 nm and a refractive index of 2.07 was obtained. It was 312 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. Moreover, the surface recombination velocity S was 99 cm / s.

  Further, the coating liquid of Example 1 was applied to both surfaces of an n-type silicon wafer at 4000 rpm with a spin coater, dried on a hot plate at 140 ° C. for 1 minute, and 600 ° C., 15 in a heating furnace under a nitrogen atmosphere. Baked for minutes. As a result, a composite coating of titanium oxide and silicon oxide having a film thickness of 49 nm and a refractive index of 2.08 was obtained. It was 1030 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. Further, the surface recombination speed S was 30 cm / s.

(Example 2)
5: 5 in terms of titanium dioxide and silicon dioxide in the same manner as in Example 1 except that 500 g of the coating liquid obtained in Synthesis Example 1 of the coating solution and 500 g of the coating solution obtained in Synthesis Example 2 of the coating solution were mixed. (Mass ratio) coating solution was obtained.

  Subsequently, the coating liquid of Example 2 was applied to both sides of the p-type silicon wafer in the same manner as in Example 1, and then baked to form a composite of titanium oxide and silicon oxide having a film thickness of 52 nm and a refractive index of 1.74. A coating was obtained. It was 267 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. Further, the surface recombination velocity S was 116 cm / s.

  In addition, the coating liquid of Example 2 was applied to both surfaces of an n-type silicon wafer in the same manner as in Example 1, and then baked to form a composite film of titanium oxide and silicon oxide having a film thickness of 51 nm and a refractive index of 1.73. Got. It was 852 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. The surface recombination velocity S was 36 cm / s.

(Example 3)
9: 1 (in terms of titanium dioxide and silicon dioxide) in the same manner as in Example 1 except that 900 g of the coating solution obtained in Coating Solution Synthesis Example 1 and 100 g of the coating solution obtained in Coating Solution Synthesis Example 2 were mixed. (Mass ratio) coating solution was obtained.

  Subsequently, the coating liquid of Example 3 was applied to both sides of the p-type silicon wafer in the same manner as in Example 1, and then baked to form a composite of titanium oxide and silicon oxide having a film thickness of 48 nm and a refractive index of 2.18. A coating was obtained. It was 245 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. Further, the surface recombination velocity S was 127 cm / s.

  In addition, the coating liquid of Example 3 was applied to both surfaces of an n-type silicon wafer in the same manner as in Example 1, and then baked to form a composite film of titanium oxide and silicon oxide having a film thickness of 49 nm and a refractive index of 2.17. Got. It was 897 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. Further, the surface recombination velocity S was 34 cm / s.

(Example 4)
Except for mixing 600 g of the coating liquid obtained in the coating liquid synthesis example 1 and 400 g of the coating liquid obtained in the coating liquid synthesis example 2, 6: 4 (in terms of titanium dioxide and silicon dioxide) in the same manner as in Example 1. (Mass ratio) coating solution was obtained.

  Subsequently, the coating liquid of Example 4 was applied to both sides of the p-type silicon wafer in the same manner as in Example 1, and then baked to form a composite of titanium oxide and silicon oxide having a film thickness of 48 nm and a refractive index of 1.83. A coating was obtained. It was 296 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. Further, the surface recombination velocity S was 105 cm / s.

  In addition, the coating solution of Example 4 was applied to both sides of an n-type silicon wafer in the same manner as in Example 1, and then baked to form a composite film of titanium oxide and silicon oxide having a film thickness of 48 nm and a refractive index of 1.83. Got. It was 1090 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. Further, the surface recombination velocity S was 27 cm / s.

(Example 5)
4: 6 (in terms of titanium dioxide and silicon dioxide) in the same manner as in Example 1, except that 400 g of the coating liquid obtained in Coating Solution Synthesis Example 1 and 600 g of the coating solution obtained in Coating Solution Synthesis Example 2 were mixed. (Mass ratio) coating solution was obtained.

  Subsequently, the coating solution of Example 5 was applied to both sides of the p-type silicon wafer in the same manner as in Example 1, and then baked to form a composite of titanium oxide and silicon oxide having a film thickness of 62 nm and a refractive index of 1.66. A coating was obtained. It was 203 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. Further, the surface recombination velocity S was 153 cm / s.

  Further, the coating liquid of Example 5 was applied to both surfaces of an n-type silicon wafer in the same manner as in Example 1, and then baked to form a composite film of titanium oxide and silicon oxide having a film thickness of 60 nm and a refractive index of 1.66. Got. It was 688 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. Further, the surface recombination velocity S was 45 cm / s.

(Comparative Example 1)
The coating solution obtained in Coating Solution Synthesis Example 1 was applied to both sides of a p-type silicon wafer in the same manner as in Example 1, and then baked to form titanium oxide (TiO ₂ having a thickness of 50 nm and a refractive index of 2.19). (100%)) A coating was obtained. It was 42 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. Further, the surface recombination velocity S was 743 cm / s.

In addition, the coating liquid obtained in the coating liquid synthesis example 1 was applied to both surfaces of an n-type silicon wafer in the same manner as in Example 1, and then baked to form a titanium oxide having a film thickness of 49 nm and a refractive index of 2.19 ( A TiO ₂ (100%)) coating was obtained. It was 61 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. Further, the surface recombination velocity S was 509 cm / s.

(Comparative Example 2)
The coating liquid obtained in coating liquid synthesis example 2 was applied to both sides of a p-type silicon wafer in the same manner as in Example 1, and then baked to form silicon oxide (SiO ₂ having a film thickness of 74 nm and a refractive index of 1.43. (100%)) A coating was obtained. It was 10 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. The surface recombination speed S was 3124 cm / s.

In addition, the coating liquid obtained in the coating liquid synthesis example 2 was applied to both surfaces of the n-type silicon wafer in the same manner as in Example 1, and then baked to form silicon oxide having a film thickness of 71 nm and a refractive index of 1.42 ( It was obtained SiO ₂ (100%)) coating. It was 34 microseconds when the lifetime was measured using the silicon wafer after surface coating film formation. Further, the surface recombination velocity S was 910 cm / s.

  The above results are summarized in Tables 1 and 2.

As shown in Table 1, in the evaluation on the p-type silicon wafer, the lifetime of the titanium oxide single coating or the silicon oxide single coating was 50 μs or less. However, in the composite coating of titanium oxide and silicon oxide, the titanium dioxide: silicon dioxide In the range of 4: 6 to 9: 1 (in particular, 6: 4 to 8: 2), the lifetime was significantly improved. In particular, the ratio of titanium dioxide: silicon dioxide = 8: 2 shows a value exceeding 300 μs, and it has been found that the characteristics as a semiconductor passivation film are excellent.
Moreover, as shown in Table 2, in the evaluation on the n-type silicon wafer, it was found that the improvement of the lifetime was more remarkable, and the ratio of titanium dioxide: silicon dioxide was greatly increased in the range of 4: 6 to 9: 1. Lifetime improvement was observed, and a value exceeding 1000 μs was shown particularly in the range of 6: 4 to 8: 2.
Therefore, when this surface coating film is applied as a passivation film of a solar cell, it can be expected that the power generation efficiency can be improved.

(Examples 6-8, Comparative Examples 3-8)
Continuing, with respect to the above-mentioned Example 1 in which the lifetime measurement result was good in the evaluation on the p-type silicon wafer, the firing atmosphere was Ar gas, Ar + H ₂ (3%) mixed gas, N ₂ + O ₂ ( The lifetime was measured in the same manner except that the gas mixture was changed to 5%). For the coating films of Comparative Examples 1 and 2, the lifetime was measured by changing the firing atmosphere in the same manner. The results are shown in Table 3.

  From the above results, it was confirmed that even if the firing atmosphere was changed, the composite coating of titanium oxide and silicon oxide showed a significant improvement in lifetime.

(Examples 9-14, Comparative Examples 9-10)
Using the coating solution obtained in Coating Solution Synthesis Example 2 and the coating solution obtained in Coating Solution Synthesis Example 3, the mass ratios shown in Tables 4 to 5 were carried out in the same manner as in Examples 1 to 5 above. The coating liquid of Examples 9-14 was obtained. Further, as the comparative example 9, the coating liquid of the coating liquid synthesis example 3 was used, and as the comparative example 10, the coating liquid of the coating liquid synthesis example 2 was used. In addition, about mass ratio, it is set as zirconia dioxide and silicon dioxide conversion.

  Then, after apply | coating the coating liquid of each example to both surfaces of a p-type silicon wafer or an n-type silicon wafer like Example 1, it baked and formed the surface coating film. Tables 4 and 5 show the results of the film thickness, refractive index, lifetime, and surface recombination velocity S of the surface coating film.

As shown in Tables 4 and 5, it was confirmed that the lifetime was improved in the composite coating of zirconium oxide and silicon oxide as compared with the zirconium oxide single coating and the silicon oxide single coating. In particular, the ratio of zirconium dioxide: silicon dioxide is in the range of 8: 2 to 2: 8 in the case of p-type silicon wafers, and in the range of 9: 1 to 2: 8 in the case of n-type silicon wafers. The improvement was observed, and it was found that the characteristics as a semiconductor passivation film were excellent.
Therefore, when this surface coating film is applied as a passivation film of a solar cell, it can be expected that the power generation efficiency can be improved.

Claims (5)

  A composition for forming a surface coating film comprising a compound component for forming a surface coating film having two or more elements selected from the elements of Si, Ti, and Zr and an organic solvent component is applied to the base material to be coated A method for forming a surface coating film having two or more elements selected from Si, Ti, and Zr elements, comprising a coating process for forming a coating film and a firing process for firing the coating film.   The method for forming a surface coating film according to claim 1, wherein the surface coating film is a passivation film. The composition for forming a surface coating film includes a compound component for forming a surface coating film having elements of Si and Ti and an organic solvent component, and a mass ratio in terms of SiO ₂ and TiO ₂ is 1:99 to The method for forming a surface coating film according to claim 1 or 2, wherein the ratio is 97: 3. The composition for forming a surface coating film includes a compound component for forming a surface coating film having elements of Si and Zr and an organic solvent component, and a mass ratio in terms of SiO ₂ and ZrO ₂ is 1:99 to The method for forming a surface coating film according to claim 1 or 2, wherein the ratio is 97: 3.   The solar cell which has a surface coating film formed by the formation method of the surface coating film of any one of Claims 1-4.