JP6434310B2 - Passivation film, coating type material, solar cell element, and silicon substrate with passivation film - Google Patents

Description

  The present invention relates to a passivation film, a coating material, a solar cell element, and a silicon substrate with a passivation film.

  The solar cell element is a photoelectric conversion element that converts solar energy into electric energy, and is expected to be further spread in the future as one of pollution-free and infinite renewable energy.

  A solar cell element usually includes a p-type semiconductor and an n-type semiconductor, and generates electron-hole pairs inside the semiconductor by absorbing solar energy. Here, the generated electrons are transferred to the n-type semiconductor and the holes (holes) are transferred to the p-type semiconductor, and these are collected by the electrodes, whereby electric energy can be used outside.

  On the other hand, in a solar cell element, it is important to increase efficiency so that sunlight energy can be converted into as much electrical energy as possible and output. In order to increase the efficiency of such a solar cell element, it is important to generate as many electron-hole pairs as possible inside the semiconductor. In addition, it is important to take out the generated charge while suppressing loss of the generated charge.

  Charge loss can occur for a variety of reasons. In particular, the generated electrons and holes are recombined, and the charge is lost.

As shown in FIG. 1, a crystalline silicon solar cell element that is currently mainstream uses a p-type silicon substrate 11 having a pyramid structure portion (not shown) for preventing reflection, which is called a texture. The n layer 12 is formed on the back surface, and the p ⁺ layer 14 is formed on the back surface. Further, a silicon nitride (SiN) film 13 is provided as a light-receiving surface passivation film on the light-receiving surface side, and a silver collector electrode called a finger electrode 15 is formed. On the back surface side, an aluminum electrode 16 that also serves to suppress light transmission on the back surface is formed on the entire surface.

The silicon n layer 12 is generally formed by diffusing phosphorus into the silicon substrate 11 from a gas phase or a solid phase. The p ⁺ layer 14 on the back surface is formed by applying heat of 700 ° C. or more at the contact portion between the aluminum and the p-type silicon substrate 11 when forming the aluminum electrode 16 on the back surface. Through this step, aluminum diffuses into the silicon substrate 11 to form an alloy, and the p ⁺ layer 14 is formed.

An electric field derived from a potential difference is formed at the interface between the p-type silicon substrate 11 and the p ⁺ layer 14. This electric field generated by the p ⁺ layer 14 is mainly generated in the p-type silicon substrate 11, and of the holes and electrons diffused on the back surface, the electrons are reflected inside the p-type silicon substrate 11, and holes are formed. Is selectively passed through the p ⁺ layer 14. That is, this action brings about an effect of eliminating electrons and reducing recombination of holes and electrons at the back surface interface of the solar cell element. A conventional solar cell element having such an aluminum alloy layer on the back surface is widely used as a structure of a solar cell element suitable for mass production because it is relatively easy to manufacture.

However, in the conventional solar cell element having the p ⁺ layer 14 on the back surface as described above, an inactivation process is performed on the interface between the p ⁺ layer 14 and the back electrode 16 to reduce the interface recombination rate. Not. In addition, since the aluminum itself highly doped in the p ⁺ layer 14, that is, an alloy of aluminum silicon, forms a recombination center, the existence density of the recombination center is high, and the quality as a semiconductor is higher than that of other regions. Is also low.

In order to solve this problem, the development of a back-side passivation type solar cell element is underway for the future replacement of the conventional solar cell element. Unlike the conventional solar cell elements described above, the back surface passivation type solar cell element is inherently present at the interface between the silicon substrate and the passivation film by covering the back surface of the solar cell element with a passivation film. The dangling bond can be terminated. That is, the back surface passivation type solar cell element does not attempt to reduce the carrier recombination rate due to the electric field generated at the p / p ⁺ interface, but reduces the density of recombination centers on the back surface itself, and the carrier (hole and hole). To recombine electrons). On the other hand, a passivation film that suppresses the carrier recombination rate by lowering the carrier concentration by an electric field generated by a fixed charge in the passivation film is called a field effect passivation film. In particular, when the density of recombination centers on the back surface is large, a field-effect passivation film that can move carriers away from the recombination centers by an electric field is effective.

  As a field effect passivation film, an aluminum oxide film formed by ALD-CVD (Atomic Layer Deposition-Chemical Vapor Deposition) is known. Further, in order to reduce the film formation cost, a technique using an aluminum oxide sol-gel coating film as a passivation film is known (for example, International Publication No. 2008/137174 pamphlet, Japanese Patent Application Laid-Open No. 2009-194120 and B). Hoex, J. Schmidt, P. Pohl, MCM van de Sanden, WMM Kesseles, “Silicon surface passivation by atomic layer deposited Al2O3”, J Appl. Phys, 104, p.44903 (2008)). In addition, a technique using other materials such as a dielectric coating material containing titanium and phosphorus and a polyimide resin as a coating-type back surface passivation material is also known (for example, International Publication No. 2009/052227 pamphlet and Japanese Patent Laid-Open No. 2012). -65992).

  However, in general, the ALD method has a problem that it is difficult to reduce the cost because the deposition rate is low and high throughput cannot be obtained. Furthermore, after forming the aluminum oxide film, a through hole for making contact with the electrode on the back surface is necessary, and some patterning technique is required.

  In addition, in order to reduce the cost of forming an aluminum oxide film, a technique using a coating film such as a sol-gel of aluminum oxide as a passivation film is known.

However, since the negative fixed charge is unstable in the aluminum oxide coating film, it tends to be difficult to obtain the negative fixed charge by the CV (Capacitance Voltage) method.
In view of the above problems, the first problem to be solved by the present invention is to realize a passivation film having a long carrier lifetime and a negative fixed charge at a low cost. A second problem is to provide a coating type material for realizing the formation of the passivation film. A third problem is to realize a low-cost and highly efficient solar cell element using the passivation film at a low cost. A fourth problem is to realize a silicon substrate with a passivation film that extends the carrier lifetime of the silicon substrate and has a negative fixed charge at low cost.

  The above and other problems and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

Means for solving the above problems include the following aspects.
<1> A passivation film for use in a solar cell element having a silicon substrate, comprising aluminum oxide and at least one oxide of vanadium group element selected from the group consisting of vanadium oxide and tantalum oxide.
By including aluminum oxide and an oxide of at least one vanadium group element selected from the group consisting of vanadium oxide and tantalum oxide, the carrier lifetime of the silicon substrate is increased and negative fixed charge is provided. Can do. The reason why the carrier lifetime becomes long is not clear, but one of the reasons may be termination of dangling bonds.

<2> The passivation film according to <1>, wherein a mass ratio of the vanadium group element oxide to the aluminum oxide (vanadium group element oxide / aluminum oxide) is 30/70 to 90/10.
This can have a large stable negative fixed charge.

  <3> The passivation film according to <1> or <2>, in which a total content of the oxide of the vanadium group element and the aluminum oxide is 90% or more.

  <4> The oxide of the vanadium group element includes any of oxides of two or three vanadium group elements selected from the group consisting of vanadium oxide, niobium oxide, and tantalum oxide. Any of <1> to <3> The passivation film according to claim 1.

  <5> Heat treatment of a coating-type material comprising: a precursor of aluminum oxide; and a precursor of an oxide of at least one vanadium group element selected from the group consisting of a precursor of vanadium oxide and a precursor of tantalum oxide. The passivation film according to any one of <1> to <4>, which is a product.

The coating type material of the present invention for solving the second problem is as follows.
<6> an aluminum oxide precursor, and at least one vanadium group element oxide precursor selected from the group consisting of a vanadium oxide precursor and a tantalum oxide precursor, and having a silicon substrate A coating type material used for forming a passivation film of a solar cell element.

The solar cell element of the present invention for solving the third problem is as follows.
<7> a p-type silicon substrate;
An n-type impurity diffusion layer formed on the first surface side which is the light-receiving surface side of the silicon substrate;
A first electrode formed on the impurity diffusion layer;
A passivation film formed on the second surface side opposite to the light receiving surface side of the silicon substrate and having an opening;
A second electrode formed on the second surface side of the silicon substrate and electrically connected to the second surface side of the silicon substrate through the opening of the passivation film;
The said passivation film is a solar cell element containing aluminum oxide and the oxide of the at least 1 sort (s) of vanadium group element selected from the group which consists of vanadium oxide and a tantalum oxide.

<8> A p-type impurity diffusion layer formed on part or all of the second surface side of the silicon substrate and doped with an impurity at a higher concentration than the silicon substrate,
The solar cell element according to <7>, wherein the second electrode is electrically connected to the p-type impurity diffusion layer through an opening of the passivation film.

<9> an n-type silicon substrate;
A p-type impurity diffusion layer formed on the first surface which is the light-receiving surface side of the silicon substrate;
A first electrode formed on the impurity diffusion layer;
A passivation film formed on the second surface side opposite to the light receiving surface side of the silicon substrate and having an opening;
A second electrode formed on the second surface side of the silicon substrate and electrically connected to the second surface side of the silicon substrate through the opening of the passivation film;
The said passivation film is a solar cell element containing aluminum oxide and the oxide of the at least 1 sort (s) of vanadium group element selected from the group which consists of vanadium oxide and a tantalum oxide.

<10> An n-type impurity diffusion layer formed on a part or all of the second surface side of the silicon substrate and doped with impurities at a higher concentration than the silicon substrate,
The solar cell element according to <9>, wherein the second electrode is electrically connected to the n-type impurity diffusion layer through an opening of the passivation film.

  <11> The solar cell element according to any one of <7> to <10>, wherein a mass ratio of the oxide of the vanadium group element and the aluminum oxide in the passivation film is 30/70 to 90/10. .

  <12> The solar cell element according to any one of <7> to <11>, wherein a total content of the oxide of the vanadium group element and the aluminum oxide in the passivation film is 90% or more.

  <13> The oxide of the vanadium group element includes oxides of two or three vanadium group elements selected from the group consisting of vanadium oxide, niobium oxide, and tantalum oxide, <7> to <12> The solar cell element according to any one of the above.

The silicon substrate with a passivation film of the present invention for solving the fourth problem is as follows.
<14> a silicon substrate;
The passivation film for solar cell elements according to any one of <1> to <5>, provided on the entire surface or a part of the silicon substrate,
A silicon substrate with a passivation film.

  According to the present invention, a passivation film having a long carrier lifetime of a silicon substrate and having a negative fixed charge can be realized at low cost. In addition, a coating type material for realizing the formation of the passivation film can be provided. In addition, a low-cost and highly efficient solar cell element using the passivation film can be realized. In addition, a silicon substrate with a passivation film having a long carrier lifetime and a negative fixed charge can be realized at low cost.

It is sectional drawing which showed the structure of the conventional double-sided electrode type solar cell element. It is sectional drawing which shows the 1st structural example of the solar cell element which used the passivation film for the back surface. It is sectional drawing which shows the 2nd structural example of the solar cell element which used the passivation film for the back surface. It is sectional drawing which shows the 3rd structural example of the solar cell element which used the passivation film for the back surface. It is sectional drawing which shows the 4th structural example of the solar cell element which used the passivation film for the back surface. It is sectional drawing which shows the structural example of the solar cell element which used the passivation film for the light-receiving surface.

  In this specification, the term “process” is not limited to an independent process, and is included in this term if the purpose of the process is achieved even when it cannot be clearly distinguished from other processes. In the present specification, a numerical range indicated by using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively. Further, in the present specification, the content of each component in the composition is the total amount of the plurality of substances present in the composition unless there is a specific notice when there are a plurality of substances corresponding to each component in the composition. Means. In addition, in the present specification, the term “layer” includes a configuration of a shape formed in part in addition to a configuration of a shape formed on the entire surface when observed as a plan view.

(Embodiment 1)
The passivation film of the present embodiment is a passivation film used for a silicon solar cell element, and includes aluminum oxide and an oxide of at least one vanadium group element selected from the group consisting of vanadium oxide and tantalum oxide. It is what was included.

  The passivation film includes aluminum oxide and an oxide of at least one vanadium group element selected from the group consisting of vanadium oxide and tantalum oxide, thereby extending the carrier lifetime of the silicon substrate and negative fixed charge. Can have. Therefore, the passivation film of the present invention can improve the photoelectric conversion efficiency of the silicon solar cell element. Furthermore, since the passivation film of the present invention can be formed using a coating method or a printing method, the film formation process is simple and the film formation throughput is high. As a result, pattern formation is easy and cost reduction can be achieved.

  In this embodiment mode, the amount of fixed charges included in the passivation film can be controlled by changing the composition of the passivation film. Here, the vanadium group element is a Group 5 element in the periodic table, and is an element selected from vanadium, niobium, and tantalum.

  The functions of a general passivation film include [1] termination of dangling bonds and [2] band bending due to fixed charges in the film. Of these, the passivation film having the function of band bending by the fixed charge in the film [2] is called a field effect passivation film, and it works to prevent recombination by chasing either holes or electrons with the charge. There is. In a solar cell element using a normal p-type silicon substrate, electrons are extracted from the light-receiving surface side and holes are extracted from the back surface side among the generated carriers. Therefore, as a passivation film on the back surface side of the p-type silicon substrate, a field-effect passivation film having a negative fixed charge is required in order to drive electrons back to the light receiving surface side (for example, Japanese Patent Application Laid-Open No. 2012-33759). Publication).

  On the other hand, in this embodiment, the fixed charge of the passivation film can be made negative by using the oxide of the vanadium group element and aluminum oxide in combination, and further, the oxide of the vanadium group element and the aluminum oxide By adjusting the mass ratio [oxide of vanadium group element / aluminum oxide], the fixed charge of the passivation film can be stably made negative. Specifically, the mass ratio of the oxide of vanadium group element to aluminum oxide [the oxide of vanadium group element / aluminum oxide] is 30/70 to 90/10, so that a large stabilized negative fixed charge can be obtained. Tend to be achieved. As described above, since the passivation film of the present invention can be formed using a coating method or a printing method, the film formation process is simple and the film formation throughput is high. As a result, in the present embodiment, pattern formation is easy and cost reduction can be achieved.

  The mass ratio of the vanadium group element oxide to aluminum oxide is more preferably 35/65 to 90/10, from the viewpoint that the negative fixed charge can be stabilized, and is 50/50 to 90/10. More preferably.

  The mass ratio of vanadium group element oxide and aluminum oxide in the passivation film is determined by energy dispersive X-ray spectroscopy (EDX), secondary ion mass spectrometry (SIMS), and high frequency inductively coupled plasma mass spectrometry (ICP-MS). ) Can be measured. Specific measurement conditions are as follows in the case of ICP-MS, for example. Dissolving the passivation film in acid or alkaline aqueous solution, atomizing this solution and introducing it into Ar plasma, measuring the wavelength and intensity by spectroscopically analyzing the light emitted when the excited element returns to the ground state, Element qualification is performed from the obtained wavelength, and quantification is performed from the obtained intensity.

  The total content of vanadium group oxide and aluminum oxide in the passivation film is preferably 80% by mass or more, and more preferably 90% by mass or more from the viewpoint of maintaining good characteristics. When the components other than the oxide of vanadium group elements and aluminum oxide in the passivation film increase, the effect of negative fixed charges increases.

  Further, in the passivation film, components other than the oxide of vanadium group element and aluminum oxide may be contained as an organic component from the viewpoint of improving the film quality and adjusting the elastic modulus. The presence of the organic component in the passivation film can be confirmed by elemental analysis and measurement of the FT-IR of the film.

As the oxide of the vanadium group element, it is preferable to select vanadium oxide (V ₂ O ₅ ) from the viewpoint of obtaining a larger negative fixed charge. Since vanadium oxide has a negative fixed charge larger than that of tantalum oxide, carrier recombination can be more effectively prevented.

  The passivation film may include an oxide of a vanadium group element selected from the group consisting of vanadium oxide, niobium oxide, and tantalum oxide as an oxide of a vanadium group element.

  The passivation film is preferably obtained by heat-treating a coating-type material, and can be obtained by forming a coating-type material using a coating method or a printing method, and then removing organic components by heat treatment. More preferred. That is, the passivation film may be obtained as a heat-treated product of a coating type material containing an aluminum oxide precursor and a vanadium group element oxide precursor. Details of the coating type material will be described later.

(Embodiment 2)
The coating type material of the present embodiment is a coating type material used for a passivation film for a solar cell element having a silicon substrate, and includes a precursor of aluminum oxide, a precursor of vanadium oxide, and a precursor of tantalum oxide. And a precursor of an oxide of at least one vanadium group element selected from the group. As a precursor of the oxide of the vanadium group element contained in the coating material, a precursor of vanadium oxide (V ₂ O ₅ ) is selected from the viewpoint of the negative fixed charge of the passivation film formed from the coating material. It is preferable. The coating type material is composed of two or three vanadium group elements selected from the group consisting of vanadium oxide precursors, niobium oxide precursors and tantalum oxide precursors as vanadium group oxide precursors. An oxide precursor may also be included.

The aluminum oxide precursor can be used without particular limitation as long as it produces aluminum oxide. As the aluminum oxide precursor, it is preferable to use an organic aluminum oxide precursor from the viewpoint of uniformly dispersing aluminum oxide on the silicon substrate and a chemically stable viewpoint. Examples of the organic aluminum oxide precursor include aluminum triisopropoxide (structural formula: Al (OCH (CH ₃ ) ₂ ) ₃ , Kojundo Chemical Laboratory, SYM-AL04.

  The precursor of the oxide of the vanadium group element can be used without particular limitation as long as it generates an oxide of the vanadium group element. The vanadium group element oxide precursor is preferably an organic vanadium group oxide oxide precursor from the viewpoint of uniformly dispersing aluminum oxide on the silicon substrate and chemically stable. .

Examples of organic vanadium oxide precursors include vanadium (V) oxytriethoxide (structural formula: VO (OC ₂ H ₅ ) ₃ , molecular weight: 202.13), High Purity Chemical Laboratory, V-02 can be mentioned. Examples of organic tantalum oxide precursors include tantalum (V) methoxide (structural formula: Ta (OCH ₃ ) ₅ , molecular weight: 336.12), Kojundo Chemical Laboratory, Ta-10-P Can be mentioned. Examples of organic niobium oxide precursors include niobium (V) ethoxide (structural formula: Nb (OC ₂ H ₅ ) ₅ , molecular weight: 318.21), High Purity Chemical Laboratory, Nb-05. Can be mentioned.

  By forming a coating type material containing an organic vanadium group oxide precursor and an organic aluminum oxide precursor using a coating method or a printing method, and then removing the organic components by a heat treatment, A passivation film can be obtained. Therefore, as a result, a passivation film containing an organic component may be used. The content of the organic component in the passivation film is more preferably less than 10% by mass, still more preferably 5% by mass or less, and particularly preferably 1% by mass or less.

(Embodiment 3)
The solar cell element (photoelectric conversion device) of the present embodiment has a passivation film (insulating film, protective insulating film) described in the first embodiment in the vicinity of the photoelectric conversion interface of the silicon substrate, that is, aluminum oxide and oxidized It has a film containing at least one oxide of a vanadium group element selected from the group consisting of vanadium and tantalum oxide. By containing aluminum oxide and an oxide of at least one vanadium group element selected from the group consisting of vanadium oxide and tantalum oxide, the carrier lifetime of the silicon substrate can be extended and negative fixed charges can be obtained. And the characteristics (photoelectric conversion efficiency) of the solar cell element can be improved.

<Description of structure>
First, the structure of the solar cell element of the present embodiment will be described with reference to FIGS. 2-5 is sectional drawing which shows the 1st-4th structural example of the solar cell element which used the passivation film for the back surface of this Embodiment.

  As a silicon substrate (a crystalline silicon substrate or a semiconductor substrate) used in this embodiment mode, either single crystal silicon or polycrystalline silicon may be used. Further, either a p-type crystalline silicon substrate or an n-type crystalline silicon substrate may be used. As the silicon substrate 1, either p-type crystalline silicon or n-type crystalline silicon may be used. From the viewpoint of further exerting the effects of the present invention, p-type crystalline silicon is more suitable.

  In the following FIGS. 2 to 5, an example in which p-type single crystal silicon is used as the silicon substrate 1 will be described. The single crystal silicon or polycrystalline silicon used for the silicon substrate 1 may be arbitrary, but single crystal silicon or polycrystalline silicon having a resistivity of 0.5 Ω · cm to 10 Ω · cm is preferable.

  As shown in FIG. 2 (first configuration example), n is obtained by doping (adding) a group V element such as phosphorus on the light-receiving surface side (upper side, first surface, surface in the figure) of the p-type silicon substrate 1. A mold diffusion layer 2 is formed. A pn junction is formed between the silicon substrate 1 and the diffusion layer 2. On the surface of the diffusion layer 2, a light receiving surface antireflection film 3 such as a silicon nitride (SiN) film, and a first electrode 5 (light receiving surface side electrode, first surface electrode, upper surface electrode) using silver (Ag) or the like. , Surface electrode) is formed. The light receiving surface antireflection film 3 may also have a function as a light receiving surface passivation film. By using the SiN film, both functions of the light receiving surface antireflection film and the light receiving surface passivation film can be provided.

  Note that the solar cell element of the present invention may or may not have the light-receiving surface antireflection film 3. The light receiving surface of the solar cell element is preferably formed with a concavo-convex structure (texture structure) in order to reduce the reflectance on the surface, but the solar cell element of the present invention has a texture structure. Even if it does not have.

  On the other hand, a BSF (Back Surface Field) layer 4, which is a layer doped with a group III element such as aluminum or boron, is formed on the back surface side (lower side, second surface, back surface in the figure) of the silicon substrate 1. . However, the solar cell element of the present invention may or may not have the BSF layer 4.

  On the back side of the silicon substrate 1, a second layer made of aluminum or the like is used to make contact (electrical connection) with the BSF layer 4 (or the surface on the back side of the silicon substrate 1 when there is no BSF layer 4). Electrodes 6 (back surface side electrode, second surface electrode, back surface electrode) are formed.

  Further, in FIG. 2 (first configuration example), the contact region (the surface on the back surface side of the silicon substrate 1 when the BSF layer 4 is not provided) and the second electrode 6 are electrically connected. A passivation film 7 (passivation layer) containing aluminum oxide and an oxide of at least one vanadium group element selected from the group consisting of vanadium oxide and tantalum oxide is provided in a portion excluding the opening OA). Is formed. As described in detail in Embodiment 1, the passivation film 7 of the present invention can have a negative fixed charge. Due to this fixed charge, electrons which are minority carriers among the carriers generated in the silicon substrate 1 by light rebound to the surface side. For this reason, a short circuit current increases and it is anticipated that photoelectric conversion efficiency will improve.

  Next, a second configuration example shown in FIG. 3 will be described. In FIG. 2 (first configuration example), the second electrode 6 is formed on the entire surface of the contact region (opening OA) and the passivation film 7. In FIG. The second electrode 6 is formed only in the region (opening OA). The second electrode 6 may be formed only on the contact region (opening OA) and part of the passivation film 7. Even with the solar cell element having the configuration shown in FIG. 3, the same effect as that of FIG. 2 (first configuration example) can be obtained.

  Next, a third configuration example shown in FIG. 4 will be described. In the third configuration example shown in FIG. 4, the BSF layer 4 is formed only on a part of the back side including the contact region (opening OA portion) with the second electrode 6, and FIG. 2 (first configuration example). Thus, it is not formed on the entire back surface side. Even with the solar cell element having such a configuration (FIG. 4), the same effect as that of FIG. 2 (first configuration example) can be obtained. Further, according to the solar cell element of the third configuration example of FIG. 4, the BSF layer 4, that is, the impurity is doped at a higher concentration than the silicon substrate 1 by doping a group III element such as aluminum or boron. Since the area is small, it is possible to obtain higher photoelectric conversion efficiency than that in FIG. 2 (first configuration example).

  Next, a fourth configuration example shown in FIG. 5 will be described. In FIG. 4 (third configuration example), the second electrode 6 is formed on the entire surface of the contact region (opening OA) and the passivation film 7, but in FIG. 5 (fourth configuration example), the contact The second electrode 6 is formed only in the region (opening OA). The second electrode 6 may be formed only on the contact region (opening OA) and part of the passivation film 7. Even with the solar cell element having the configuration shown in FIG. 5, the same effect as that of FIG. 4 (third configuration example) can be obtained.

  In addition, when the second electrode 6 is applied by a printing method and baked at a high temperature to form the entire surface on the back side, a convex warpage tends to occur in the temperature lowering process. Such warpage may cause damage to the solar cell element, which may reduce the yield. Further, the problem of warpage increases as the silicon substrate becomes thinner. The cause of this warp is that stress is generated because the second electrode 6 made of metal (for example, aluminum) has a larger thermal expansion coefficient than the silicon substrate, and the shrinkage in the temperature lowering process is correspondingly large.

  From the above, when the second electrode 6 is not formed on the entire back surface side as shown in FIG. 3 (second configuration example) and FIG. 5 (fourth configuration example), the electrode structure tends to be symmetrical vertically. This is preferable because stress due to the difference in thermal expansion coefficient is unlikely to occur. However, in that case, it is preferable to provide a separate reflective layer.

<Product description>
Next, an example of a method for manufacturing the solar cell element (FIGS. 2 to 5) of the present embodiment having the above-described configuration will be described. However, the present invention is not limited to the solar cell element produced by the method described below.

  First, a texture structure is formed on the surface of the silicon substrate 1 shown in FIG. The texture structure may be formed on both sides of the silicon substrate 1 or only on one side (light receiving side). In order to form a texture structure, first, the damaged layer of the silicon substrate 1 is removed by immersing the silicon substrate 1 in a heated potassium hydroxide or sodium hydroxide solution. Then, a texture structure is formed on both surfaces or one surface (light receiving surface side) of the silicon substrate 1 by immersing in a solution containing potassium hydroxide and isopropyl alcohol as main components. As described above, since the solar cell element of the present invention may or may not have a texture structure, this step may be omitted.

Subsequently, after cleaning the silicon substrate 1 with a solution such as hydrochloric acid or hydrofluoric acid, a phosphorus diffusion layer (n ⁺ layer) is formed as the diffusion layer 2 on the silicon substrate 1 by thermal diffusion of phosphorus oxychloride (POCl ₃ ) or the like. To do. The phosphorus diffusion layer can be formed, for example, by applying a coating-type doping material solution containing phosphorus to the silicon substrate 1 and performing heat treatment. After the heat treatment, the phosphorus glass layer formed on the surface is removed with an acid such as hydrofluoric acid, whereby a phosphorus diffusion layer (n ⁺ layer) is formed as the diffusion layer 2. The method for forming the phosphorus diffusion layer is not particularly limited. The phosphorus diffusion layer may be formed so that the depth from the surface of the silicon substrate 1 is in the range of 0.2 μm to 0.5 μm, and the sheet resistance is in the range of 40Ω / square (ohm / square) to 100Ω / □. preferable.

Thereafter, a BSF layer 4 on the back surface side is formed by applying a coating-type doping material solution containing boron, aluminum or the like to the back surface side of the silicon substrate 1 and performing heat treatment. For the application, methods such as screen printing, ink jet, dispensing, spin coating and the like can be used. After the heat treatment, the BSF layer 4 is formed by removing the layer of boron glass, aluminum or the like formed on the back surface with hydrofluoric acid, hydrochloric acid or the like. The method for forming the BSF layer 4 is not particularly limited. Preferably, the BSF layer 4 is preferably formed so that the concentration range of boron, aluminum, etc. is 10 ¹⁸ cm ⁻³ to 10 ²² cm ^−3, and the BSF layer 4 is formed in a dot shape or a line shape It is preferable to do. Since the solar cell element of the present invention may or may not have the BSF layer 4, this step may be omitted.

Further, when both the diffusion layer 2 on the light receiving surface and the BSF layer 4 on the back surface are formed using a coating-type doping material solution, the above-described doping material solution is applied to both surfaces of the silicon substrate 1 and diffused. The phosphorus diffusion layer (n ⁺ layer) and the BSF layer 4 as the layer 2 may be formed in a lump, and then the phosphorus glass, boron glass, etc. formed on the surface may be removed in a lump.

  Thereafter, a silicon nitride film that is the light-receiving surface antireflection film 3 is formed on the diffusion layer 2. The method for forming the light receiving surface antireflection film 3 is not particularly limited. The light-receiving surface antireflection film 3 is preferably formed to have a thickness in the range of 50 to 100 nm and a refractive index in the range of 1.9 to 2.2. The light-receiving surface antireflection film 3 is not limited to a silicon nitride film, and may be a silicon oxide film, an aluminum oxide film, a titanium oxide film, or the like. The surface antireflection film 3 such as a silicon nitride film can be produced by a method such as plasma CVD or thermal CVD, and is preferably produced by plasma CVD that can be formed in a temperature range of 350 ° C. to 500 ° C.

  Next, a passivation film 7 is formed. The passivation film 7 includes aluminum oxide and an oxide of at least one vanadium group element selected from the group consisting of vanadium oxide and tantalum oxide. For example, an organometallic decomposable coating material from which aluminum oxide can be obtained after firing. And a precursor represented by a commercially available organometallic decomposition coating material from which an oxide of at least one vanadium group element selected from the group consisting of vanadium oxide and tantalum oxide is obtained after firing. A material including a body (passivation material) is applied and heat-treated (fired) (see Embodiment 1).

  The formation of the passivation film 7 can be performed as follows, for example. A 725 μm-thick 8-inch (20.32 cm) p-type silicon substrate (8 Ω · cm to 12 Ω · cm) obtained by removing the natural oxide film in advance with hydrofluoric acid having a concentration of 0.49% by mass. It spin-coats on one side and performs prebaking for 3 minutes at 120 degreeC on a hotplate. Thereafter, heat treatment is performed at 650 ° C. for 1 hour in a nitrogen atmosphere. In this case, a passivation film 7 containing aluminum oxide and at least one vanadium group element oxide selected from the group consisting of vanadium oxide and tantalum oxide is obtained. The thickness of the passivation film 7 formed by the above method is usually about several tens of nanometers as measured by an ellipsometer.

  The coating type material is applied to a predetermined pattern including the contact region (opening OA) by a method such as screen printing, offset printing, inkjet printing, or dispenser printing. In addition, after apply | coating, after said application | coating type material pre-baked in the range of 80 to 180 degreeC and evaporating a solvent, it is 600 degreeC to 1000 degreeC in nitrogen atmosphere or in the air for 30 minutes to 3 hours. It is desirable to perform a degree of heat treatment (annealing) to form a passivation film 7 (oxide film).

  Furthermore, the opening (contact hole) OA is desirably formed in a dot shape or a line shape on the BSF layer 4.

  As described in detail in Embodiment 1, the passivation film 7 used in the solar cell element has a mass ratio of oxide of vanadium group element to aluminum oxide (oxide of vanadium group element / aluminum oxide) of 30. It is preferably within the range of / 70 to 90/10, more preferably within the range of 35/65 to 90/10, and even more preferably within the range of 50/50 to 90/10. Thereby, the negative fixed charge can be stabilized.

  Further, in the passivation film 7, the total content of vanadium group oxide and aluminum oxide is preferably 90% or more.

  Next, the first electrode 5 which is an electrode on the light receiving surface side is formed. The 1st electrode 5 is formed by forming the paste which has silver (Ag) as a main component on the light-receiving surface antireflection film 3 by screen printing, and performing heat processing (fire through). The shape of the 1st electrode 5 may be arbitrary shapes, for example, may be a well-known shape which consists of a finger electrode and a bus-bar electrode.

  And the 2nd electrode 6 which is an electrode of the back side is formed. The 2nd electrode 6 can be formed by apply | coating the paste which has aluminum as a main component using screen printing or a dispenser, and heat-processing it. The shape of the second electrode 6 is desirably the same shape as the shape of the BSF layer 4, a shape covering the entire back surface, a comb shape, a lattice shape, or the like. Note that the first electrode 5 and the second electrode 6 are printed by first printing pastes for forming the first electrode 5 and the second electrode 6 that are electrodes on the light receiving surface side, and then performing heat treatment (fire-through). The electrodes 6 may be formed together.

  Further, by using a paste mainly composed of aluminum (Al) for forming the second electrode 6, aluminum diffuses as a dopant, and the BSF layer 4 is formed in a contact portion between the second electrode 6 and the silicon substrate 1 in a self-alignment manner. Is formed. As described above, the BSF layer 4 may be separately formed by applying a coating-type doping material solution containing boron, aluminum or the like to the back side of the silicon substrate 1 and then heat-treating it. .

  In the above description, a structural example and a manufacturing method example using p-type silicon for the silicon substrate 1 are shown, but an n-type silicon substrate can also be used as the silicon substrate 1. In this case, the diffusion layer 2 is formed by a layer doped with a group III element such as boron, and the BSF layer 4 is formed by doping a group V element such as phosphorus. However, it should be noted that in this case, a leakage current flows through a portion where the inversion layer formed at the interface due to the negative fixed charge and the metal on the back surface are in contact with each other, and the conversion efficiency may be difficult to increase.

  When an n-type silicon substrate is used, a passivation film 7 including aluminum oxide and an oxide of at least one vanadium group element selected from the group consisting of vanadium oxide and tantalum oxide is shown in FIG. Thus, it can be used on the light receiving surface side. FIG. 6 is a cross-sectional view illustrating a configuration example of a solar cell element using the light-receiving surface passivation film of the present embodiment.

  In this case, the diffusion layer 2 on the light receiving surface side is p-type doped with boron, and collects holes on the light receiving surface side and electrons on the back surface side of the generated carriers. Therefore, it is preferable that the passivation film 7 having a negative fixed charge is on the light receiving surface side.

  An antireflection film made of SiN or the like may be further formed on the passivation film 7 by CVD or the like.

(Embodiment 4)
The silicon substrate with a passivation film of the present embodiment is composed of a silicon substrate and the passivation film described in the first embodiment provided on the entire surface or part of the silicon substrate, that is, aluminum oxide, vanadium oxide, and tantalum oxide. And a film containing at least one oxide of a vanadium group element selected from the group consisting of: The passivation film includes aluminum oxide and an oxide of at least one vanadium group element selected from the group consisting of vanadium oxide and tantalum oxide, thereby extending the carrier lifetime of the silicon substrate and negative fixed charge. The characteristics (photoelectric conversion efficiency) of the solar cell element can be improved.

  Details will be described below with reference to Examples and Comparative Examples.

<When vanadium oxide is used as the oxide of vanadium group element>
[Example 1]
3.0 g of a commercially available organometallic thin film coating type material [High purity chemical research laboratory, SYM-AL04, concentration 2.3 mass%] from which aluminum oxide (Al ₂ O ₃ ) can be obtained by heat treatment (firing) And 6.0 g of a commercially available organometallic thin film coating material [Vitamin Purity Laboratory, V-02, concentration 2 mass%] from which vanadium oxide (V ₂ O ₅ ) can be obtained by heat treatment (firing). By mixing, a passivation material (a-1) which is a coating type material was prepared.

Passivation of passivation material (a-1) on one side of a 725 μm thick 8-inch p-type silicon substrate (8Ω · cm to 12Ω · cm) from which a natural oxide film was previously removed with hydrofluoric acid having a concentration of 0.49% by mass It was applied and placed on a hot plate and prebaked at 120 ° C. for 3 minutes. Thereafter, a heat treatment (firing) was performed at 700 ° C. for 30 minutes in a nitrogen atmosphere to obtain a passivation film containing vanadium oxide and vanadium oxide [vanadium oxide / aluminum oxide = 63/37 (mass%)]. It was 51 nm when the film thickness was measured with the ellipsometer. When the FT-IR of the passivation film was measured, a peak due to a very few alkyl groups was observed in the vicinity of 1200 cm ⁻¹ .

Next, a plurality of aluminum electrodes having a diameter of 1 mm were formed on the above-described passivation film by vapor deposition through a metal mask, thereby manufacturing a capacitor having a MIS (metal-insulator-semiconductor) structure. . The voltage dependence (CV characteristics) of the capacitance of this capacitor was measured with a commercially available prober and LCR meter (HP, 4275A). As a result, it was found that the flat band voltage (Vfb) shifted from an ideal value of −0.81 V to +0.02 V. From this shift amount, it was found that the passivation film obtained from the passivation material (a-1) showed a negative fixed charge with a fixed charge density (Nf) of −5.2 × 10 ¹¹ cm ⁻² .

  In the same manner as described above, the passivation material (a-1) was applied to both sides of an 8-inch p-type silicon substrate, pre-baked, and subjected to heat treatment (baking) at 650 ° C. for 1 hour in a nitrogen atmosphere. A sample in which both surfaces of the substrate were covered with a passivation film was produced. The carrier lifetime of this sample was measured with a lifetime measuring device (Kobelco Research Institute, RTA-540). As a result, the carrier lifetime was 400 μs. For comparison, the same 8-inch p-type silicon substrate was measured by passivation using the iodine passivation method, and the carrier lifetime was 1100 μs. Further, when the carrier lifetime was measured again 14 days after the preparation of the sample, the carrier lifetime was 380 μs. Thereby, it was found that the decrease in carrier lifetime (from 400 μs to 380 μs) was within −10%, and the decrease in carrier lifetime was small.

  From the above, it was found that the passivation film obtained by heat-treating (sintering) the passivation material (a-1) exhibits a certain degree of passivation performance and a negative fixed charge.

[Example 2]
Similar to Example 1, a commercially available organometallic thin film coating material from which aluminum oxide (Al ₂ O ₃ ) can be obtained by heat treatment (calcination) [High Purity Chemical Laboratory, SYM-AL04, concentration 2.3 mass] %] And a commercially available organometallic thin film coating material [Vitamin Purity Laboratory, V-02, concentration 2 mass%] from which vanadium oxide (V ₂ O ₅ ) can be obtained by heat treatment are changed in ratio. Then, the passivation materials (a-2) to (a-7) shown in Table 1 were prepared.

  In the same manner as in Example 1, each of the passivation materials (a-2) to (a-7) was applied to one side of a p-type silicon substrate and heat-treated (fired) to produce a passivation film. The voltage dependence of the capacitance of the obtained passivation film was measured, and the fixed charge density was calculated therefrom.

  Further, in the same manner as in Example 1, the carrier lifetime was measured using a sample obtained by applying a passivation material to both surfaces of a p-type silicon substrate and performing heat treatment (firing).

  The results obtained are summarized in Table 1. Further, when the carrier lifetime was measured again 14 days after the preparation of the sample, the decrease in the carrier lifetime was found in any of the passivation films using the passivation materials (a-2) to (a-7) shown in Table 1. It was within -10%, and it was found that the decrease in carrier lifetime was small.

  Although the results are different depending on the ratio (mass ratio) of vanadium oxide / aluminum oxide after the heat treatment (firing), the passivation materials (a-2) to (a-7) are all negative after the heat treatment (firing). Since it showed a fixed charge and a certain carrier lifetime, it was suggested that it functions as a passivation film. It was found that the passivation films obtained from the passivation materials (a-2) to (a-7) all stably show negative fixed charges and can be suitably used as a passivation for a p-type silicon substrate. .

[Example 3]
As a compound for obtaining vanadium oxide (V ₂ O ₅ ) by heat treatment (firing), commercially available vanadium (V) oxytriethoxide (structural formula: VO (OC ₂ H ₅ ) ₃ , molecular weight: 202.13) is 1 0.02 g (0.010 mol) and a compound obtained from aluminum oxide (Al ₂ O ₃ ) by heat treatment (calcination), commercially available aluminum triisopropoxide (structure: Al (OCH (CH ₃ ) ₂ ) ₃ , A passivation material (b-1) having a concentration of 5% by mass was prepared by dissolving 2.04 g (0.010 mol) of molecular weight: 204.25) in 60 g of cyclohexane.

Passivation of passivation material (b-1) to one side of a 725 μm thick 8-inch p-type silicon substrate (8Ω · cm to 12Ω · cm) from which a natural oxide film was previously removed with hydrofluoric acid having a concentration of 0.49% by mass This was applied and prebaked at 120 ° C. for 3 minutes on a hot plate. Thereafter, a heat treatment (firing) was performed at 650 ° C. for 1 hour in a nitrogen atmosphere to obtain a passivation film containing aluminum oxide and vanadium oxide. When the film thickness was measured with an ellipsometer, it was 60 nm. As a result of elemental analysis, it was found that V / Al / C = 64/33/3 (mass%). When the FT-IR of the passivation film was measured, a peak due to a very few alkyl groups was observed in the vicinity of 1200 cm ⁻¹ .

Next, a plurality of aluminum electrodes having a diameter of 1 mm were formed on the above-described passivation film by vapor deposition through a metal mask, thereby manufacturing a capacitor having a MIS (metal-insulator-semiconductor) structure. . The voltage dependence (CV characteristics) of the capacitance of this capacitor was measured with a commercially available prober and LCR meter (HP, 4275A). As a result, it was found that the flat band voltage (Vfb) shifted from an ideal value of −0.81 V to +0.10 V. From this shift amount, it was found that the passivation film obtained from the passivation material (b-1) showed a negative fixed charge with a fixed charge density (Nf) of −6.2 × 10 ¹¹ cm ⁻² .

  In the same manner as described above, the passivation material (b-1) was applied to both sides of an 8-inch p-type silicon substrate, pre-baked, and subjected to heat treatment (baking) at 600 ° C. for 1 hour in a nitrogen atmosphere to obtain silicon. A sample in which both surfaces of the substrate were covered with a passivation film was produced. The carrier lifetime of this sample was measured by a lifetime measuring device (Kobelco Research Institute, RTA-540). As a result, the carrier lifetime was 400 μs. For comparison, the same 8-inch p-type silicon substrate was measured by passivation using the iodine passivation method, and the carrier lifetime was 1100 μs.

  From the above, it was found that the passivation film obtained by heat-treating (sintering) the passivation material (b-1) exhibits a certain degree of passivation performance and a negative fixed charge.

[Example 4]
1.52 g (0.0075 mol) of commercially available vanadium (V) oxytriethoxide (structural formula: VO (OC ₂ H ₅ ) ₃ , molecular weight: 202.13) and commercially available aluminum triisopropoxide (structural formula : Al (OCH (CH ₃ ) ₂ ) ₃ , molecular weight: 204.25), 1.02 g (0.005 mol) and 10 g of novolak resin were dissolved in 10 g of diethylene glycol monobutyl ether acetate and 10 g of cyclohexane to passivate. Material (b-2) was prepared.

Passivation of passivation material (b-2) on one side of a 725 μm thick 8-inch p-type silicon substrate (8 Ω · cm to 12 Ω · cm) with natural oxide film removed beforehand with hydrofluoric acid at a concentration of 0.49% by mass It was applied and placed on a hot plate and prebaked at 120 ° C. for 3 minutes. Thereafter, heating was performed at 650 ° C. for 1 hour in a nitrogen atmosphere to obtain a passivation film containing aluminum oxide and vanadium oxide. When the film thickness was measured with an ellipsometer, it was 22 nm. As a result of elemental analysis, it was found that V / Al / C = 71/22/7 (mass%). When the FT-IR of the passivation film was measured, a peak due to a very few alkyl groups was observed in the vicinity of 1200 cm ⁻¹ .

Next, a plurality of aluminum electrodes having a diameter of 1 mm were formed on the above-described passivation film by vapor deposition through a metal mask, thereby manufacturing a capacitor having a MIS (metal-insulator-semiconductor) structure. . The voltage dependence (CV characteristics) of the capacitance of this capacitor was measured with a commercially available prober and LCR meter (HP, 4275A). As a result, it was found that the flat band voltage (Vfb) shifted from the ideal value of −0.81 V to +0.03 V. From this shift amount, it was found that the passivation film obtained from the passivation material (b-2) had a fixed charge density (Nf) of −2.0 × 10 ¹¹ cm ⁻² and a negative fixed charge.

  In the same manner as described above, the passivation material (b-2) is applied to both sides of an 8-inch p-type silicon substrate, pre-baked, and subjected to heat treatment (baking) at 600 ° C. for 1 hour in a nitrogen atmosphere. A sample in which both surfaces of the substrate were covered with a passivation film was produced. The carrier lifetime of this sample was measured by a lifetime measuring device (Kobelco Research Institute, RTA-540). As a result, the carrier lifetime was 170 μs. For comparison, the same 8-inch p-type silicon substrate was measured by passivation using the iodine passivation method, and the carrier lifetime was 1100 μs.

  From the above, it was found that the passivation film obtained by curing the passivation material (b-2) exhibited a certain degree of passivation performance and a negative fixed charge.

<When tantalum oxide is used as the oxide of vanadium group element>
[Example 5]
Commercially available organometallic thin film coating type material [High Purity Chemical Laboratory, SYM-AL04, concentration 2.3 mass%] from which aluminum oxide (Al ₂ O ₃ ) can be obtained by heat treatment (firing) and oxidation by heat treatment A commercially available organometallic thin film coating type material [Tapuro Chemical Laboratory Co., Ltd., Ta-10-P, concentration 10% by mass] from which tantalum (Ta ₂ O ₅ ) can be obtained is mixed at different ratios. The passivation materials (c-1) to (c-6) shown in 2 were prepared.

  Each of the passivation materials (c-1) to (c-6) is a 725 μm-thick 8-inch p-type silicon substrate (8Ω · cm to 12Ω) from which a natural oxide film has been removed in advance with hydrofluoric acid having a concentration of 0.49% by mass. (Cm) was spin-coated on one side, placed on a hot plate, and pre-baked at 120 ° C. for 3 minutes. Thereafter, a heat treatment (firing) was performed at 700 ° C. for 30 minutes in a nitrogen atmosphere to obtain a passivation film containing aluminum oxide and tantalum oxide. Using this passivation film, the voltage dependence of the capacitance was measured, and the fixed charge density was calculated therefrom.

  Next, each of the passivation materials (c-1) to (c-6) was applied to both sides of an 8-inch p-type silicon substrate, pre-baked, and heat-treated (fired) at 650 ° C. for 1 hour in a nitrogen atmosphere. ) To prepare a sample in which both surfaces of the silicon substrate were covered with a passivation film. The carrier lifetime of this sample was measured by a lifetime measuring device (Kobelco Research Institute, RTA-540).

  The results obtained are summarized in Table 2. Further, when the carrier lifetime was measured again 14 days after the preparation of the sample, the decrease in the carrier lifetime was found in any of the passivation films using the passivation materials (c-1) to (c-6) shown in Table 2. It was within -10%, and it was found that the decrease in carrier lifetime was small.

  Although the results differ depending on the ratio (mass ratio) of tantalum oxide / aluminum oxide after heat treatment (firing), the passivation materials (c-1) to (c-6) are all negative after heat treatment (firing). Since it showed a fixed charge and a certain carrier lifetime, it was suggested that it functions as a passivation film.

[Example 6]
As a compound from which tantalum oxide (Ta ₂ O ₅ ) can be obtained by heat treatment (firing), 1.18 g (0.002) of commercially available tantalum (V) methoxide (structural formula: Ta (OCH ₃ ) ₅ , molecular weight: 336.12) is obtained. As a compound from which aluminum oxide (Al ₂ O ₃ ) can be obtained by heat treatment (firing), commercially available aluminum triisopropoxide (structural formula: Al (OCH (CH ₃ ) ₂ ) ₃ , molecular weight: 204.25 2.04 g (0.010 mol) was dissolved in 60 g of cyclohexane to prepare a passivation material (d-1) having a concentration of 5% by mass.

Passivation of passivation material (d-1) on one side of a 725 μm thick 8-inch p-type silicon substrate (8Ω · cm to 12Ω · cm) with natural oxide film removed beforehand with hydrofluoric acid at a concentration of 0.49% by mass It was applied and placed on a hot plate and prebaked at 120 ° C. for 3 minutes. Thereafter, heating was performed at 700 ° C. for 1 hour in a nitrogen atmosphere to obtain a passivation film containing aluminum oxide and tantalum oxide. When the film thickness was measured with an ellipsometer, it was 40 nm. As a result of elemental analysis, it was found that Ta / Al / C = 75/22/3 (wt%). When the FT-IR of the passivation film was measured, a peak due to a very few alkyl groups was observed in the vicinity of 1200 cm ⁻¹ .

Next, a plurality of aluminum electrodes having a diameter of 1 mm were formed on the above-described passivation film by vapor deposition through a metal mask, thereby manufacturing a capacitor having a MIS (metal-insulator-semiconductor) structure. . The voltage dependence (CV characteristics) of the capacitance of this capacitor was measured with a commercially available prober and LCR meter (HP, 4275A). As a result, it was found that the flat band voltage (Vfb) was shifted from an ideal value of −0.81 V to −0.30 V. From this shift amount, it was found that the passivation film obtained from the passivation material (d-1) had a fixed charge density (Nf) of −6.2 × 10 ¹⁰ cm ⁻² and a negative fixed charge.

  In the same manner as described above, the passivation material (d-1) was applied to both sides of an 8-inch p-type silicon substrate, pre-baked, and subjected to heat treatment (baking) at 600 ° C. for 1 hour in a nitrogen atmosphere. A sample in which both surfaces of the substrate were covered with a passivation film was produced. The carrier lifetime of this sample was measured by a lifetime measuring device (Kobelco Research Institute, RTA-540). As a result, the carrier lifetime was 610 μs. For comparison, the same 8-inch p-type silicon substrate was measured by passivation using the iodine passivation method, and the carrier lifetime was 1100 μs.

  From the above, it was found that the passivation film obtained by heat-treating the passivation material (d-1) exhibits a certain degree of passivation performance and a negative fixed charge.

[Example 7]
As a compound for obtaining tantalum oxide (Ta ₂ O ₅ ) by heat treatment (firing), 1.18 g (0.005 mol) of commercially available tantalum (V) methoxide (structural formula: Ta (OCH ₃ ) ₅ , molecular weight: 336.12) ) And aluminum oxide (Al ₂ O ₃ ) obtained by heat treatment (firing), a commercially available aluminum triisopropoxide (structure: Al (OCH (CH ₃ ) ₂ ) ₃ , molecular weight: 204.25) 1.02 g (0.005 mol) and 10 g of novolak resin were dissolved in a mixture of 10 g of diethylene glycol monobutyl ether acetate and 10 g of cyclohexane to prepare a passivation material (d-2).

Passivation of passivation material (d-2) on one side of a 725 μm thick 8-inch p-type silicon substrate (8Ω · cm to 12Ω · cm) with natural oxide film removed beforehand with hydrofluoric acid at a concentration of 0.49% by mass This was applied and prebaked at 120 ° C. for 3 minutes on a hot plate. Thereafter, heating was performed at 650 ° C. for 1 hour in a nitrogen atmosphere to obtain a passivation film containing aluminum oxide and tantalum oxide. When the film thickness was measured with an ellipsometer, it was 18 nm. As a result of elemental analysis, it was found that Ta / Al / C = 72/20/8 (wt%). When the FT-IR of the passivation film was measured, a peak due to a very few alkyl groups was observed in the vicinity of 1200 cm ⁻¹ .

Next, a plurality of aluminum electrodes having a diameter of 1 mm were formed on the above-described passivation film by vapor deposition through a metal mask, thereby manufacturing a capacitor having a MIS (metal-insulator-semiconductor) structure. . The voltage dependence (CV characteristics) of the capacitance of this capacitor was measured with a commercially available prober and LCR meter (HP, 4275A). As a result, it was found that the flat band voltage (Vfb) shifted from an ideal value of −0.81 V to −0.43 V. From this shift amount, it was found that the passivation film obtained from the passivation material (d-2) had a fixed charge density (Nf) of −5.5 × 10 ¹⁰ cm ⁻² and a negative fixed charge.

  In the same manner as described above, the passivation material (d-2) was applied to both sides of an 8-inch p-type silicon substrate, pre-baked, and subjected to heat treatment (baking) at 600 ° C. for 1 hour in a nitrogen atmosphere to obtain silicon. A sample in which both surfaces of the substrate were covered with a passivation film was produced. The carrier lifetime of this sample was measured by a lifetime measuring device (Kobelco Research Institute, RTA-540). As a result, the carrier lifetime was 250 μs. For comparison, the same 8-inch p-type silicon substrate was measured by passivation using the iodine passivation method, and the carrier lifetime was 1100 μs.

  From the above, it was found that the passivation film obtained by heat-treating (firing) the passivation material (d-2) exhibits a certain degree of passivation performance and a negative fixed charge.

<When two or more vanadium group element oxides are used>
As shown in Examples 1 to 7, the passivation film containing aluminum oxide and vanadium oxide and the passivation film containing aluminum oxide and tantalum oxide exhibit a negative fixed charge and have an effect of improving the carrier lifetime due to the passivation. It has been found.

  In addition, the present inventors have found in a previously filed application (Japanese Patent Application No. 2012-160336) that a passivation film containing aluminum oxide and niobium oxide exhibits a negative fixed charge and has an effect of improving the carrier lifetime by the passivation. Yes.

  Accordingly, a passivation film containing aluminum oxide and two or three vanadium group oxides selected from the group consisting of vanadium oxide, niobium oxide and tantalum oxide as oxides of vanadium group elements is examined as follows. did.

[Example 8]
Commercially available organometallic thin film coating type material that can obtain aluminum oxide (Al ₂ O ₃ ) by heat treatment (firing) [High Purity Chemical Laboratory, SYM-AL04, concentration 2.3 mass%], heat treatment (firing) Commercially available organometallic thin film coating type material (VCO, Co., Ltd., V-02, concentration 2% by mass) from which vanadium oxide (V ₂ O ₅ ) can be obtained by heat treatment, and tantalum oxide (Ta ₂ O ₅ ), a commercially available organometallic thin film coating material [High Purity Chemical Laboratory Co., Ltd., Ta-10-P, concentration 10% by mass] is mixed to form a passivation material (e -1) was prepared (see Table 3).

By commercially available organometallic thin film coating type material [Coal Chemical Industries Ltd. SYM-AL04, concentration 2.3 mass%] from which aluminum oxide (Al ₂ O ₃ ) can be obtained by heat treatment (firing), heat treatment (firing) Niobium oxide (Nb ₂ O) by commercially available organometallic thin film coating type material (Vitamin Co., Ltd., V-02, concentration 2 mass%) from which vanadium oxide (V ₂ O ₅ ) is obtained, and heat treatment (firing) ₅ ) A commercially available organometallic thin film coating type material [High Purity Chemical Laboratory, Nb-05, concentration 5 mass%] obtained is mixed to obtain a passivation material (e-2) which is a coating type material. Prepared (see Table 3).

By commercially available organometallic thin film coating type material [Coal Chemical Industries Ltd. SYM-AL04, concentration 2.3 mass%] from which aluminum oxide (Al ₂ O ₃ ) can be obtained by heat treatment (firing), heat treatment (firing) Niobium oxide (Nb) by commercially available organometallic thin film coating material [Tapuro Chemical Laboratories Ta-10-P, concentration 10% by mass] from which tantalum oxide (Ta ₂ O ₅ ) can be obtained, and heat treatment (firing) ₂ O ₅ ), a commercially available organometallic thin film coating type material [High Purity Chemical Laboratory Nb-05, concentration 5 mass%] is mixed to form a passivation material (e-3) that is a coating type material Was prepared (see Table 3).

By commercially available organometallic thin film coating type material [Coal Chemical Industries Ltd. SYM-AL04, concentration 2.3 mass%] from which aluminum oxide (Al ₂ O ₃ ) can be obtained by heat treatment (firing), heat treatment (firing) Tantalum oxide (Ta ₂ O ₅ ) by commercially available organic metal thin film coating type material [Co., Ltd., Purity Chemical Laboratory V-02, concentration 2 mass%] from which vanadium oxide (V ₂ O ₅ ) is obtained, and heat treatment (firing) Niobium oxide (Nb ₂ O ₅ ) can be obtained by a commercially available organometallic thin film coating type material [High purity chemical research laboratory Ta-10-P, concentration 10% by mass] and heat treatment (firing). Commercially available organic metal thin film coating type material [High Purity Chemical Laboratory Nb-05, concentration 5 mass%] was mixed to prepare a passivation material (e-4) which is a coating type material (see Table 3). ).

  As in Example 1, each of the passivation materials (e-1) to (e-4) is a 725 μm-thick 8-inch p-type film in which the natural oxide film is previously removed with hydrofluoric acid having a concentration of 0.49% by mass. A silicon substrate (8Ω · cm to 12Ω · cm) was spin-coated on one side, placed on a hot plate, and pre-baked at 120 ° C. for 3 minutes. Thereafter, a heat treatment (firing) was performed at 650 ° C. for 1 hour in a nitrogen atmosphere to obtain a passivation film containing aluminum oxide and two or more vanadium group element oxides.

  Using the passivation film obtained above, the voltage dependence of the capacitance was measured, and the fixed charge density was calculated therefrom.

  Next, each of the passivation materials (e-1) to (e-4) is applied to both sides of an 8-inch p-type silicon substrate, pre-baked, and heat-treated (fired) at 650 ° C. for 1 hour in a nitrogen atmosphere. ) To prepare a sample in which both surfaces of the silicon substrate were covered with a passivation film. The carrier lifetime of this sample was measured by a lifetime measuring device (Kobelco Research Institute, RTA-540).

  The results obtained are summarized in Table 3.

  Passivation using passivation materials (e-1) to (e-4), depending on the ratio (mass ratio) of two or more vanadium group element oxides and aluminum oxide after heat treatment (firing). Regarding the films, all showed negative fixed charges after heat treatment (firing), and the carrier lifetime also showed a certain value, suggesting that it functions as a passivation film.

[Example 9]
Similar to Example 1, a commercially available organometallic thin film coating material from which aluminum oxide (Al ₂ O ₃ ) can be obtained by heat treatment (calcination) [High Purity Chemical Laboratory, SYM-AL04, concentration 2.3 mass] %] And a commercially available organometallic thin film coating type material [Vitamin Purity Laboratory, V-02, concentration 2 mass%] from which vanadium oxide (V ₂ O ₅ ) is obtained by heat treatment (firing), or heat treatment Commercially available organometallic thin film coating type material [Takara Chemical Lab., Ltd., Ta-10-P, concentration 10% by mass] obtained by calcination (tantalum oxide (Ta ₂ O ₅ )) is applied and mixed. Passivation materials (f-1) to (f-8) as mold materials were prepared (see Table 4).

  Moreover, the passivation material (f-9) which used aluminum oxide independently was prepared (refer Table 4).

  As in Example 1, each of the passivation materials (f-1) to (f-9) was applied to one side of a p-type silicon substrate, and then heat treatment (firing) was performed to produce a passivation film, Using this, the voltage dependence of the capacitance was measured, and the fixed charge density was calculated therefrom.

  Further, in the same manner as in Example 1, each of the passivation materials (f-1) to (f-9) was applied to both sides of a p-type silicon substrate, and a sample obtained by heat treatment (firing) was used. Career lifetime was measured. The results obtained are summarized in Table 4.

As shown in Table 4, when the aluminum oxide / vanadium oxide or tantalum oxide in the passivation material is 90/10 and 80/20, the fixed charge density varies greatly, and the negative fixed charge density is stable. However, it was confirmed that a negative fixed charge density can be realized by using aluminum oxide and niobium oxide. When measured by the CV method using a passivation material in which aluminum oxide / vanadium oxide or tantalum oxide is 90/10 and 80/20, a passivation film showing a positive fixed charge is obtained in some cases. It turns out that it has not reached to show stably. Note that a passivation film exhibiting a positive fixed charge can be used as a passivation film for an n-type silicon substrate.
On the other hand, a negative fixed charge density could not be obtained with the passivation material (f-9) containing 100% by mass of aluminum oxide.

<Summary>
From the above results, the following can be considered.

  (1) A passivation film containing aluminum oxide and vanadium oxide and a passivation film containing aluminum oxide and tantalum oxide exhibit a negative fixed charge, and have an effect of improving carrier lifetime due to passivation.

  (2) The mass ratio of vanadium oxide to aluminum oxide is 30/70 to 90/10, more preferably 35/65 to 90/10, which improves carrier lifetime and provides a stable negative fixed charge. It is more preferable from the viewpoint of achieving both.

  (3) The mass ratio of tantalum oxide to aluminum oxide is 30/70 to 90/10, more preferably 35/65 to 90/10, which improves carrier lifetime and provides stable negative fixed charge. It is more preferable from the viewpoint of achieving both.

  (4) In the passivation film, based on the results of elemental analysis and FT-IR measurement of the film, components other than the oxide of vanadium group elements (here, vanadium oxide or tantalum oxide) and aluminum oxide are included as organic components. It can be seen that the content (mass) of the vanadium group element oxide (here vanadium oxide or tantalum oxide) and aluminum oxide in the passivation film is 90% or more, more preferably 95% or more. Therefore, it tends to maintain better characteristics as a passivation film.

  (5) A passivation film containing aluminum oxide and two or more vanadium group element oxides exhibits a negative fixed charge, and has an effect of improving carrier lifetime due to passivation.

[Example 10]
Using a single crystal silicon substrate with boron as a dopant as the silicon substrate 1, a solar cell element having the structure shown in FIG. 4 was produced. After the surface of the silicon substrate 1 was textured, a coating type phosphorous diffusion material was applied only to the light receiving surface side, and a diffusion layer 2 (phosphorus diffusion layer) was formed by heat treatment. Thereafter, the coating type phosphorus diffusing material was removed with dilute hydrofluoric acid.

  Next, a SiN film was formed on the light receiving surface side by plasma CVD as the light receiving surface antireflection film 3. Thereafter, the passivation material (a-1) prepared in Example 1 was applied to the region excluding the contact region (opening OA) on the back surface side of the silicon substrate 1 by an inkjet method. Thereafter, heat treatment was performed to form a passivation film 7 having an opening OA. In addition, a sample using the passivation material (c-1) prepared in Example 5 was separately prepared as the passivation film 7.

  Next, on the light-receiving surface antireflection film 3 (SiN film) formed on the light-receiving surface side of the silicon substrate 1, a paste mainly composed of silver was screen-printed in the shape of predetermined finger electrodes and bus bar electrodes. On the back side, a paste mainly composed of aluminum was screen-printed on the entire surface. Thereafter, heat treatment (fire-through) is performed at 850 ° C. to form electrodes (first electrode 5 and second electrode 6), and aluminum is diffused into the opening OA on the back surface to form the BSF layer 4. Thus, a solar cell element having the structure shown in FIG. 4 was formed.

  In this case, regarding the formation of the silver electrode on the light receiving surface, the fire-through process in which the SiN film is not perforated is described. However, the opening OA is first formed in the SiN film by etching or the like, and then the silver electrode is formed. You can also

For comparison, the passivation film 7 is not formed in the above manufacturing process, an aluminum paste is printed on the entire back surface, the p ⁺ layer 14 corresponding to the BSF layer 4 and the electrode 16 corresponding to the second electrode. Was formed on the entire surface to form a solar cell element having the structure of FIG. About these solar cell elements, characteristic evaluation (a short circuit current, an open circuit voltage, a fill factor, and conversion efficiency) was performed. Characteristic evaluation was measured based on JIS-C-8913 (2005) and JIS-C-8914 (2005). The results are shown in Table 5.

  From Table 5, the solar cell element having the passivation film of the present invention has both the short-circuit current and the open-circuit voltage increased, and the conversion efficiency (photoelectric conversion efficiency) is maximum as compared with the solar electronic element not having the passivation film. It has been found that the effect of the present invention can be obtained with an improvement of 0.6%.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiments and examples. However, the present invention is not limited to the above-described embodiments and examples, and does not depart from the gist of the invention. Various changes can be made.

  The disclosures of Japanese Application Nos. 2012-160336, 2012-218389, and 2013-011934 are incorporated herein by reference in their entirety. All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated by reference, Incorporated herein by reference.

Claims (10)

  A heat-treated product of a coating-type material comprising: a precursor of aluminum oxide; and a precursor of an oxide of at least one vanadium group element selected from the group consisting of a precursor of vanadium oxide and a precursor of tantalum oxide. A passivation film used for a solar cell element having a silicon substrate.   The passivation film according to claim 1, wherein a total content of the oxide of the vanadium group element and the aluminum oxide is 90% by mass or more.   The passivation film according to claim 1, further comprising at least one selected from the group consisting of niobium oxide and tantalum oxide as the oxide of the vanadium group element.   A solar cell element having a silicon substrate, comprising: a precursor of aluminum oxide; and a precursor of an oxide of at least one vanadium group element selected from the group consisting of a precursor of vanadium oxide and a precursor of tantalum oxide Coating type material used to form a passivation film.   The coating type material according to claim 4, further comprising at least one selected from the group consisting of a niobium oxide precursor and a tantalum oxide precursor as the vanadium group element oxide precursor. a p-type silicon substrate;
An n-type impurity diffusion layer formed on the first surface side which is the light-receiving surface side of the silicon substrate;
A first electrode formed on the impurity diffusion layer;
A passivation film formed on the second surface side opposite to the light receiving surface side of the silicon substrate and having an opening;
A second electrode formed on the second surface side of the silicon substrate and electrically connected to the second surface side of the silicon substrate through the opening of the passivation film;
The said passivation film is a solar cell element containing the passivation film of any one of Claims 1-3 . A p-type impurity diffusion layer formed on a part or all of the second surface side of the silicon substrate and doped with impurities at a higher concentration than the silicon substrate;
The solar cell element according to claim 6, wherein the second electrode is electrically connected to the p-type impurity diffusion layer through an opening of the passivation film. an n-type silicon substrate;
A p-type impurity diffusion layer formed on the first surface which is the light-receiving surface side of the silicon substrate;
A first electrode formed on the impurity diffusion layer;
A passivation film formed on the second surface side opposite to the light receiving surface side of the silicon substrate and having an opening;
A second electrode formed on the second surface side of the silicon substrate and electrically connected to the second surface side of the silicon substrate through the opening of the passivation film;
The said passivation film is a solar cell element containing the passivation film of any one of Claims 1-3 . An n-type impurity diffusion layer formed on part or all of the second surface side of the silicon substrate and doped with impurities at a higher concentration than the silicon substrate;
The solar cell element according to claim 8, wherein the second electrode is electrically connected to the n-type impurity diffusion layer through an opening of the passivation film. A silicon substrate;
The passivation film according to any one of claims 1 to 3 , provided on the entire surface or a part of the silicon substrate,
A silicon substrate with a passivation film.