TWI599064B - Passivation film, coating material, solar cell component, and germanium substrate with passivation film - Google Patents

Description

Passivation film, coating material, solar cell component and with passivation film 矽 substrate

The present invention relates to a passivation film, a coating type material, a solar cell element, and a tantalum 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 become more popular in the future as one of the energy that is pollution-free and infinitely reproducible.

Solar cell elements typically contain a p-type semiconductor and an n-type semiconductor, and an electron-hole pair is generated inside the semiconductor by absorbing solar energy. Here, the generated electrons are moved to the n-type semiconductor, the holes are moved to the p-type semiconductor, and the carriers are collected by the electrodes, whereby the electric energy can be utilized externally.

On the other hand, for solar cell elements, it is important to increase the efficiency by converting solar energy into as much electric energy as possible and outputting it. In order to increase the efficiency of such solar cell elements, it is important to generate as many electron-hole pairs as possible inside the semiconductor. Further, it is also important to suppress the loss of the generated charges and take out the charges to the outside.

The loss of charge is generated for various reasons. Especially generated electrons and electricity The holes recombine and the charge disappears, thereby causing a loss of charge.

In the crystallization solar cell element which is currently in the mainstream, as shown in FIG. 1, a p-type ruthenium substrate 11 having a pyramid for anti-reflection called texture is provided. The structure portion (not shown) forms an n layer 12 on the light receiving surface and a p ⁺ layer 14 on the back surface. Further, a tantalum nitride (SiN) film 13 is provided as a light-receiving surface passivation film on the light-receiving surface side, and a collector of silver called a finger electrode 15 is formed. On the back side, an aluminum electrode 16 which suppresses light transmission on the back surface is formed on the entire surface.

The n-layer 12 of the above-described germanium is usually formed by diffusing phosphorus into the germanium 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 to the contact portion between the aluminum and the p-type germanium substrate 11 when the aluminum electrode 16 on the back surface is formed. By this step, aluminum is diffused into the ruthenium substrate 11 to form an alloy, and the p ⁺ layer 14 is formed.

An electric field due to a potential difference is formed at the interface between the p-type germanium substrate 11 and the p ⁺ layer 14. The electric field formed by the p ⁺ layer 14 has a function of reflecting electrons generated in the p-type germanium substrate 11 and diffused toward the back surface and electrons in the electrons to the inside of the p-type germanium substrate 11 to make a hole Optionally pass to the p ⁺ layer 14. That is, this effect brings about the effect of repelling electrons and reducing the recombination of holes and electrons on the back interface of the solar cell element. Such a solar cell element of the prior art having an alloy layer of aluminum on the back surface can be widely used as a structure suitable for mass production of solar cell elements because it is relatively simple to manufacture.

However, in the solar cell element of the prior art having the p ⁺ layer 14 on the back surface as described above, the inerting treatment for lowering the recombination speed of the interface is not performed at the interface between the p ⁺ layer 14 and the electrode 16 on the back surface. Further, since the high-concentration-doped aluminum of the p ⁺ layer 14 itself, that is, the alloy of aluminum bismuth, forms a recombination center, the density of the recombination center is high, and the quality as a semiconductor is lower than that of other regions.

In order to solve this problem, development of a back passivation type solar cell element is being advanced in order to replace the solar cell element of the above-described conventional method. The back passivation type solar cell element is different from the above-described conventional solar cell element in that, by covering the back surface of the solar cell element with a passivation film, the unbonded key which is originally present at the interface between the tantalum substrate and the passivation film causes recombination ( Dangling bond). That is, the back passivation type solar cell element does not reduce the carrier recombination speed by the electric field generated at the p/p ⁺ interface, but reduces the density of the recombination center in the back surface itself to reduce the carrier (electricity Recombination of holes and electronics). On the other hand, a passivation film which lowers the carrier concentration by the electric field generated by the fixed charge in the passivation film and suppresses the recombination speed of the carrier is referred to as a field effect passivation film. Especially in the case where the density of the recombination center of the back surface is large, the electric field effect passivation film which can move the carrier away from the recombination center by the electric field is effective.

An electric field effect passivation film is known as an aluminum oxide film obtained by film formation by Atomic Layer Deposition-Chemical Vapor Deposition (ALD-CVD). In addition, in order to reduce the cost of film formation, a coating film using a sol-gel of alumina is used as a passivation film (for example, International Publication No. 2008/137174, Japanese Patent Laid-Open No. 2009-194120, and B. Hoex, J. Schmidt, P. Pohl, MCMvan de Sanden, WMM Kesseles, "Surface surface passivation from atomic layer deposition of Al2O3" (Silicon surface Passivation by atomic layer deposited Al2O3), J Appl. Phys, 104, p. 44903 (2008)). Further, there is also known a technique of using a dielectric coating material containing titanium or phosphorus or another material such as a polyimide resin as a coating type back surface passivation material (for example, International Publication No. 2009/052227 manual and Japanese patent) JP-A-2012-69592).

However, in general, the ALD method has a problem that the deposition speed is slow and a high throughput cannot be obtained, so that it is difficult to achieve cost reduction. Further, after the formation of the aluminum oxide film, a through hole for achieving contact by the electrode on the back surface is required, and some patterning technique is required.

In addition, in order to reduce the cost of film formation of an aluminum oxide film, a technique of using a sol-gel-coated film of alumina as a passivation film has been known.

However, since the coating film of alumina is unstable due to a negative fixed charge, it is difficult to obtain a negative fixed charge in a capacitance-voltage (CV) method.

In view of the above problems, the first object to be solved by the present invention is to realize a passivation film having a negative fixed charge by extending the carrier life of the ruthenium substrate at low cost. A second object is to provide a coating material for realizing formation of the above-described passivation film. A third problem is to realize a low-cost and highly efficient solar cell element using the above-described passivation film at low cost. A fourth object is to realize a germanium substrate with a passivation film having a negative fixed charge and a negative fixed charge at a low cost.

The above problems and other problems and novel features of the present invention are claimed by the present application. The description of the case description and the accompanying drawings indicate.

Means for solving the above problems include the following aspects.

<1> A passivation film containing an oxide of at least one vanadium element selected from the group consisting of vanadium oxide and cerium oxide, and used in a solar cell element having a ruthenium substrate.

By containing an oxide of at least one vanadium element selected from the group consisting of alumina and vanadium oxide and cerium oxide, the carrier life of the ruthenium substrate can be extended and a negative fixed charge can be obtained. Although the reason why the carrier lifetime becomes long is not clear, it can be considered that the end of the dangling bond is one of the causes.

<2> The passivation film according to <1>, wherein the mass ratio of the oxide of the vanadium group element to the aluminum oxide (the oxide of the vanadium group element/alumina) is 30/70 to 90/10.

Thereby it is possible to have a large and stable negative fixed charge.

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

The passivation film according to any one of <1> to <3> containing an oxide of two or three kinds of vanadium elements selected from the group consisting of vanadium oxide, cerium oxide and cerium oxide. It is an oxide of the above-mentioned vanadium group element.

The passivation film according to any one of <1> to <4> which is a heat-treated material of a coating material containing a precursor of alumina and a precursor selected from vanadium oxide. A precursor of an oxide of at least one vanadium element in the group consisting of precursors of cerium oxide and cerium oxide.

The coating material of the present invention for solving the second problem is as follows.

<6> a coating type material comprising a precursor of an alumina, a precursor of an oxide of at least one vanadium element selected from the group consisting of a precursor of vanadium oxide and a precursor of cerium oxide, and A passivation film for forming a solar cell element having a germanium substrate.

The solar cell element of the present invention for solving the third problem is as follows.

<7> A solar cell element comprising: a p-type germanium substrate; an n-type impurity diffusion layer formed on a first surface side of the germanium substrate as a light-receiving surface; a first electrode formed on the impurity diffusion layer; and passivation a film formed on the second surface side opposite to the light-receiving surface side of the ruthenium substrate and having an opening; and a second electrode formed on the second surface side of the ruthenium substrate and having the opening through the passivation film The second surface side of the germanium substrate is electrically connected; and the passivation film contains an oxide of at least one vanadium group element selected from the group consisting of vanadium oxide and cerium oxide.

<8> The solar cell element according to <7>, which has a p-type impurity diffusion layer formed on a part or all of the second surface side of the tantalum substrate, and is larger than the tantalum substrate Impurities are added to a higher concentration, and the second electrode is electrically connected to the p-type impurity diffusion layer through an opening of the passivation film.

<9> A solar cell element comprising: an n-type germanium substrate; a p-type impurity diffusion layer formed on a first surface side of the germanium substrate as a light receiving surface side; a first electrode formed on the impurity diffusion layer; and passivation a film formed on the second surface side opposite to the light-receiving surface side of the ruthenium substrate and having an opening; and a second electrode formed on the second surface side of the ruthenium substrate and having the opening through the passivation film The second surface side of the germanium substrate is electrically connected; and the passivation film contains an oxide of at least one vanadium group element selected from the group consisting of vanadium oxide and cerium oxide.

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

The solar cell element according to any one of the above aspects, wherein the mass ratio of the oxide of the vanadium group element to the aluminum oxide in the passivation film is 30/70 to 90/10.

The solar cell element according to any one of the above aspects of the present invention, wherein the total content of the oxide of the vanadium group element and the aluminum oxide of the passivation film is 90% or more.

The solar cell element according to any one of <7> to <12> containing oxidation of two or three kinds of vanadium elements selected from the group consisting of vanadium oxide, cerium oxide and cerium oxide. The substance acts as an oxide of the above vanadium group element.

The tantalum substrate with a passivation film of the present invention for solving the fourth problem is as follows.

<14> A solar cell element according to any one of <1> to <5>, wherein: Passivation film.

According to the present invention, it is possible to realize a passivation film which has a carrier life of a ruthenium substrate and has a negative fixed charge at a low cost. In addition, a coating type material for realizing the formation of the above passivation film can be provided. In addition, a low-cost and highly efficient solar cell element using the above passivation film can be realized. In addition, a passivation film-attached germanium substrate having a negative carrier charge and a negative fixed charge can be realized at low cost.

1‧‧‧矽 substrate

2‧‧‧n type diffusion layer

3‧‧‧Lighted anti-reflection film

4‧‧‧BSF layer

5‧‧‧1st electrode

6‧‧‧2nd electrode

7‧‧‧passivation film

11‧‧‧p type copper substrate

12‧‧‧n layer

13‧‧‧ nitrided (SiN) film

14‧‧‧p ⁺ layer

15‧‧‧ finger electrode

16‧‧‧Aluminum electrode

OA‧‧‧ openings

Fig. 1 is a cross-sectional view showing the structure of a conventional double-sided electrode type solar cell element.

2 is a cross-sectional view showing a first configuration example of a solar cell element using a passivation film on the back surface.

3 is a view showing a second configuration of a solar cell element using a passivation film on the back surface A cross-sectional view of an example.

4 is a cross-sectional view showing a third configuration example of a solar cell element using a passivation film on the back surface.

Fig. 5 is a cross-sectional view showing a fourth configuration example of a solar cell element using a passivation film on the back surface.

6 is a cross-sectional view showing a configuration example of a solar cell element in which a passivation film is used on a light receiving surface.

In the present specification, the term "step" means not only an independent step, but even in the case where it cannot be clearly distinguished from other steps, it is included in the term as long as the purpose of the step can be achieved. In addition, in this specification, the numerical range represented by "~" is a range which contains the numerical value of the before and after "~" as a minimum and maximum. Further, in the present specification, when a plurality of substances corresponding to the respective components are present in the composition in the content of each component in the composition, unless otherwise specified, it means the plurality of substances present in the composition. Total measurement. In addition, in this specification, the term "layer" includes a configuration of a shape formed on a part of the entire surface, in addition to a configuration of a shape formed on the entire surface when viewed in a plan view.

(Embodiment 1)

The passivation film of the present embodiment is a passivation film used in a tantalum solar cell element, and contains an oxide of at least one vanadium group element selected from the group consisting of alumina oxide and cerium oxide.

By passivation film containing aluminum oxide, and selected from the group consisting of vanadium oxide and cerium oxide The oxide of at least one vanadium element in the resulting group can extend the carrier lifetime of the tantalum substrate and have a negative fixed charge. Therefore, the passivation film of the present invention can improve the photoelectric conversion efficiency of the tantalum solar cell element. Further, since the passivation film of the present invention can be formed by a coating method or a printing method, the film formation step is simple, and the film formation yield is high. As a result, pattern formation is also easy, and cost reduction can be achieved.

Further, in the present embodiment, the amount of the fixed charge which the passivation film has can be controlled by changing the composition of the passivation film. Here, the vanadium group element refers to a group 5 element of the periodic table of elements, and is an element selected from the group consisting of vanadium, niobium and tantalum.

The function of a typical passivation film is [1] the end of the dangling bond, and [2] the band bending caused by the fixed charge in the film. Among them, a passivation film having a function of [2] band bending due to a fixed charge in a film is called a field effect passivation film, and it is possible to prevent recombination by using any electric charge to drive out holes and electrons. Features. In a solar cell element using a p-type germanium substrate in general, electrons in the generated carrier are taken out from the light receiving surface side, and the holes are taken out from the back side. Therefore, as the passivation film on the back side of the p-type germanium substrate, in order to drive the electrons to the light-receiving surface side, it is necessary to have a field-effect passivation film having a negative fixed charge (for example, JP-A-2012-33759).

On the other hand, in the present embodiment, the fixed charge of the passivation film can be made negative by using the oxide of the vanadium group together with the aluminum oxide, and the mass ratio of the oxide of the vanadium element to the alumina can be adjusted. [Oxide/Alumina of Vanadium Group Element], the fixed charge of the passivation film can be stably negative. Specifically, by setting the mass ratio of the oxide of the vanadium element to the alumina [oxide/alumina of the vanadium element] 30/70~90/10, there is a tendency to achieve a large and stable negative fixed charge. Further, as described above, the passivation film of the present invention can be formed by a coating method or a printing method, so that the film formation step is simple and the film formation yield is high. As a result, in the present embodiment, pattern formation is also easy, and cost reduction can be achieved.

Further, from the viewpoint of stabilizing the negative fixed charge, the mass ratio of the oxide of the vanadium element to the alumina is preferably 35/65 to 90/10, and more preferably 50/50 to 90/10.

The mass ratio of the oxide of the vanadium group element to the aluminum oxide in the passivation film can be determined by Energy Dispersive X-ray spectroscope (EDX) or secondary ion mass spectrometry (Secondary Ion Mass Spectrometer, SIMS). And inductively coupled plasma-mass spectrometry (ICP-MS). Regarding specific measurement conditions, for example, the conditions in the case of ICP-MS are as follows. Dissolving the passivation film in an acid or alkaline aqueous solution, forming the solution into a mist and introducing it into the Ar plasma, and splitting the light emitted by the excited element back to the ground state to measure the wavelength and intensity, according to the obtained The wavelength is used to characterize the element, and the amount is quantified based on the obtained intensity.

The total content of the oxide of the vanadium group element and the 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 oxide of the vanadium group element and the components other than the alumina in the passivation film are increased, the effect of negatively fixing the charge becomes large.

Further, in the passivation film, in terms of improving the film quality and adjusting the elastic modulus, the oxide and the alumina of the vanadium element can be contained in the form of an organic component. Other ingredients. The presence of the organic component in the passivation film can be confirmed by elemental analysis and Fourier transform infrared spectroscopy (FT-IR) measurement of the film.

From the viewpoint of obtaining a larger negative fixed charge, the oxide of the above-mentioned vanadium element is preferably selected from vanadium oxide (V ₂ O ₅ ). Vanadium oxide has a larger negative fixed charge than ruthenium oxide, so that recombination of carriers can be more effectively prevented.

The passivation film may further contain an oxide of two or three kinds of vanadium elements selected from the group consisting of vanadium oxide, cerium oxide, and cerium oxide as an oxide of a vanadium group element.

The passivation film is preferably obtained by heat-treating a coating type material, and is more preferably obtained by forming a coating type material by a coating method or a printing method, and then subjecting the organic component to heat treatment by heat treatment. Remove. That is, the passivation film can also be obtained as a heat-treated product of a coating material containing a precursor of an oxide of an alumina precursor and an oxide of a vanadium group. The details of the coating material will be described later.

(Embodiment 2)

The coating material of the present embodiment is a coating material for a passivation film for a solar cell element having a ruthenium substrate, and includes a precursor of alumina and a precursor selected from a precursor of vanadium oxide and ruthenium oxide. A precursor of an oxide of at least one vanadium element in the group formed. From the viewpoint of the negative fixed charge of the passivation film formed of the coating material, the precursor of the oxide of the vanadium element contained in the coating type material is preferably a precursor of selecting vanadium oxide (V ₂ O ₅ ). . The coating material may also contain a precursor of an oxide of two or three kinds of vanadium elements selected from the group consisting of a precursor of vanadium oxide, a precursor of cerium oxide, and a precursor of cerium oxide as a vanadium group. The precursor of the oxide of the element.

The alumina precursor can be used without particular limitation as long as it forms alumina. From the viewpoint of uniformly dispersing alumina on the ruthenium substrate and chemical stability, the alumina precursor preferably uses an organic alumina precursor. Examples of the organic alumina precursors include aluminum triisopropoxide (structural formula: Al(OCH(CH ₃ ) ₂ ) ₃ ), and SYM-AL04 of the Institute of High Purity Chemicals.

The precursor of the oxide of the vanadium group element can be used without particular limitation as long as it forms an oxide of a vanadium group element. The precursor of the oxide of the vanadium group element is preferably a precursor of an oxide of an organic vanadium group element from the viewpoint of uniformly dispersing alumina on the tantalum substrate and chemical stability.

Examples of the precursor of the organic vanadium oxide include vanadium oxyacetate (V) (structural formula: VO(OC ₂ H ₅ ) ₃ , molecular weight: 202.13), and V- of the High Purity Chemical Research Institute (share). 02. Examples of the precursor of the organic cerium oxide include methanol oxime (V) (structural formula: Ta(OCH ₃ ) ₅ , molecular weight: 336.12), and Ta-10-P of the High Purity Chemical Research Institute. Examples of the organic cerium oxide precursor include cerium (V) (structural formula: Nb(OC ₂ H ₅ ) ₅ , molecular weight: 318.21), and Nb-05 of the High Purity Chemical Research Institute.

A coating material containing an organic oxide-based vanadium element oxide precursor and an organic alumina precursor coating film is formed by a coating method or a printing method, and the organic component is removed by heat treatment thereafter. This gives a passivation film. Therefore, the passivation film can also be a passivation film containing an organic component. The content of organic components in the passivation film The yield is more preferably less than 10% by mass, further 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 the passivation film (insulating film, protective insulating film) described in the first embodiment in the vicinity of the photoelectric conversion interface of the ruthenium substrate, that is, contains alumina and is selected from vanadium oxide. And a film of an oxide of at least one vanadium element in the group consisting of cerium oxide. By using an oxide containing at least one vanadium element selected from the group consisting of alumina and vanadium oxide and cerium oxide, the carrier life of the ruthenium substrate can be extended and a negative fixed charge can be obtained, thereby improving solar cell elements. Characteristics (photoelectric conversion efficiency).

<Structure Description>

First, the structure of the solar cell element of the present embodiment will be described with reference to Figs. 2 to 5 . 2 to 5 are cross-sectional views showing a first configuration example to a fourth configuration example of a solar battery element using a passivation film on the back surface of the embodiment.

Any of a single crystal germanium or a polycrystalline germanium can be used as the germanium substrate (crystal germanium substrate or semiconductor substrate) used in the present embodiment. Further, any of a p-type crystalline germanium substrate or a n-type crystalline germanium substrate may be used. As the ruthenium substrate 1, any one of a p-type crystal yttrium or a n-type yttrium may be used. From the viewpoint of further exerting the effects of the present invention, a crystalline ruthenium of a p-type conductivity type is more suitable.

In the following FIGS. 2 to 5, an example in which a p-type single crystal germanium is used as the germanium substrate 1 will be described. In addition, the single crystal germanium or polycrystalline germanium used in the germanium substrate 1 may be For any one, it is preferred that the resistivity is 0.5 Ω. Cm~10Ω. Cm single crystal germanium or polycrystalline germanium.

As shown in FIG. 2 (the first configuration example), an n-type doped (added) with a group V element such as phosphorus is formed on the light-receiving surface side (upper side, first surface, and surface) of the p-type germanium substrate 1. Diffusion layer 2. Further, a pn junction is formed between the germanium substrate 1 and the diffusion layer 2. On the surface of the diffusion layer 2, a light-receiving surface anti-reflection film 3 such as a tantalum nitride (SiN) film or a first electrode 5 using silver (Ag) or the like (electrode on the light-receiving surface side, first surface electrode, and upper surface) is formed. Surface electrode, surface electrode). The light-receiving surface anti-reflection film 3 can also function as a light-receiving surface passivation film. By using the SiN film, both the function of the light-receiving surface anti-reflection film and the light-receiving surface passivation film can be achieved.

Further, the solar cell element of the present invention may have the light-receiving surface anti-reflection film 3 or may not have the light-receiving surface anti-reflection film 3. Further, in order to reduce the reflectance of the surface on the light-receiving surface of the solar cell element, it is preferable to form a textured structure (texture structure), and the solar cell element of the present invention may have a textured structure or may have no texture structure.

On the other hand, a back surface field (BSF) layer which is a layer doped with a group III element such as aluminum or boron is formed on the back surface side (the lower side, the second surface, and the back surface of the substrate). 4. Among them, the solar cell element of the present invention may have the BSF layer 4 or may not have the BSF layer 4.

In order to contact (electrically connect) the BSF layer 4 (the surface on the back side of the ruthenium substrate 1 when the BSF layer 4 is not present) on the back surface side of the ruthenium substrate 1, a second layer made of aluminum or the like is formed. Electrode 6 (electrode on the back side, second side electrode, back) Surface electrode).

Further, in FIG. 2 (the first configuration example), a contact region electrically connected to the second electrode 6 is provided in addition to the BSF layer 4 (the surface on the back side of the substrate 1 when the BSF layer 4 is not present). In a portion other than the opening portion OA), a passivation film 7 (passivation layer) containing at least one vanadium group selected from the group consisting of vanadium oxide and cerium oxide is formed. The oxide of the element. The passivation film 7 of the present invention may have a negative fixed charge as described in detail in the first embodiment. By the fixed electric charge, electrons, which are a minority carrier in the carrier generated in the crucible substrate 1 by light, are reflected back to the surface side. Therefore, the short-circuit current is increased, and the photoelectric conversion efficiency can be expected to be improved.

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, and in FIG. 3 (second configuration example), only contact The second electrode 6 is formed in the region (opening OA). The second electrode 6 may be formed on only a part of the contact region (opening OA) and the passivation film 7. Even in the solar cell element having the configuration shown in Fig. 3, the same effects as those in Fig. 2 (the 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 on only a part of the back surface side including the contact region (the opening portion OA portion) of the second electrode 6, instead of FIG. 2 (the first configuration) Example) is formed on the entire surface on the back side. Even in the solar cell element (FIG. 4) having such a configuration, the same effects as those of FIG. 2 (the first configuration example) can be obtained. In addition, According to the solar cell element of the third configuration example of FIG. 4, the BSF layer 4, that is, by doping a group III element such as aluminum or boron, has a region where impurities are doped at a higher concentration than the germanium substrate 1, and thus it is obtained. It is higher than the photoelectric conversion efficiency of FIG. 2 (the 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, and in FIG. 5 (fourth configuration example), only the contact is made. The second electrode 6 is formed in the region (opening OA). It is also possible to adopt a configuration in which the second electrode 6 is formed on only a part of the contact region (opening OA) and the passivation film 7. Even in the solar cell element having the configuration shown in FIG. 5, the same effects as those of FIG. 4 (the third configuration example) can be obtained.

In addition, when the second electrode 6 is applied by a printing method and formed on the entire surface on the back side by firing at a high temperature, warping of the upward convexity is likely to occur during the temperature lowering process. Such warpage sometimes causes damage to the solar cell components, and the yield may be lowered. In addition, the problem of warpage during the development of the thin film of the tantalum substrate becomes large. The reason for this warpage is that the second electrode 6 containing a metal (for example, aluminum) has a thermal expansion coefficient larger than that of the tantalum substrate, and thus the shrinkage during the cooling process is large, so that stress is generated.

According to the above, when the second electrode 6 is not formed on the entire surface on the back side as shown in FIG. 3 (the second configuration example) and FIG. 5 (the fourth configuration example), the electrode structure is likely to be vertically symmetrical, which is difficult. It is preferable to generate stress due to the difference in thermal expansion coefficient. In this case, it is preferable to additionally provide a reflective layer.

<Method Description>

Next, an example of a method of manufacturing the solar cell element (Figs. 2 to 5) of the present embodiment having the above configuration will be described. However, the present invention is not limited to solar cell elements fabricated by the methods described below.

First, a texture structure is formed on the surface of the ruthenium substrate 1 shown in FIG. 2 and the like. The texture structure may be formed on both sides of the ruthenium substrate 1, or may be formed only on one side (the light-receiving surface side). In order to form a texture structure, the tantalum substrate 1 is first immersed in a solution of heated potassium hydroxide or sodium hydroxide to remove the damaged layer of the tantalum substrate 1. Thereafter, it is immersed in a solution containing potassium hydroxide and isopropyl alcohol as a main component, whereby a texture structure is formed on both surfaces or one side (light-receiving surface side) of the tantalum substrate 1. Further, as described above, the solar cell element of the present invention may have a textured structure or a textured structure, so this step may be omitted.

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

Thereafter, a solution containing a coating type doping material such as boron or aluminum is applied to the back surface side of the tantalum substrate 1 and heat-treated to form a BSF layer 4 on the back side. At the time of coating, a method such as screen printing, inkjet, dispensing, spin coating, or the like can be used. After the heat treatment, a layer such as borosilicate glass or aluminum formed on the back surface is removed by hydrofluoric acid, hydrochloric acid or the like to form the BSF layer 4. The method of forming the BSF layer 4 is not particularly limited. It is preferable that the BSF layer 4 is formed so that the concentration of boron, aluminum, or the like is in the range of 10 ¹⁸ cm ^-3 to 10 ²² cm ^-3 , and it is preferable to form the BSF layer 4 in a dot shape or a line shape. Further, the solar cell element of the present invention may have the BSF layer 4 or the BSF layer 4, and 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 solution of a coating-type dopant, the solution of the dopant may be applied to the substrate 1 respectively. On both sides, the phosphorus diffusion layer (n ⁺ layer) as the diffusion layer 2 and the BSF layer 4 are formed together, and then the phosphor glass, borosilicate, or the like formed on the surface is removed together.

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

Then, a passivation film 7 is formed. The passivation film 7 contains an oxide of at least one vanadium element selected from the group consisting of vanadium oxide and cerium oxide, For example, it is formed by applying the following material (passivation material) and performing heat treatment (calcination) (refer to Embodiment 1), and the above material (passivation material) is contained in an organometallic decomposition coating type material in which alumina is obtained after calcination. a representative of an alumina precursor, and a precursor of a commercially available organometallic decomposition coating material obtained by calcining an oxide of at least one vanadium element selected from the group consisting of vanadium oxide and cerium oxide Things.

The formation of the passivation film 7 can be performed, for example, as follows. The above-mentioned coating type material was spin-coated on a 8 吋 (20.32 cm) p-type ruthenium substrate (8 Ω·cm - 12 Ω·cm) having a thickness of 725 μm of a natural oxide film removed by using hydrofluoric acid having a concentration of 0.49% by mass in advance. On one side, prebaking was carried out on a hot plate at 120 ° C for 3 minutes. Thereafter, heat treatment was performed at 650 ° C for 1 hour in a nitrogen atmosphere. In this case, a passivation film 7 containing aluminum oxide and an oxide of at least one vanadium group element selected from the group consisting of vanadium oxide and cerium oxide can be obtained. The film thickness of the passivation film 7 formed by the method described above by an ellipsometer is usually about several tens of nanometers (nm).

The coating type material is applied to a predetermined pattern including a contact region (opening OA) by a method such as screen printing, pattern printing, inkjet printing, or printing by a dispenser. Further, it is preferable that the coating type material is prebaked in a range of from 80 ° C to 180 ° C after application to evaporate the solvent, and then subjected to a nitrogen atmosphere or air at 600 ° C to 1000 ° C for 30 minutes. Heat treatment (annealing) for about 3 hours to form a passivation film 7 (film of an oxide).

Further, the opening portion (hole for contact) OA is desirably a dot or a line Formed on the BSF layer 4.

The passivation film 7 used in the above solar cell element is preferably 30/70 of the mass ratio of the oxide of the vanadium element to the alumina (the oxide of the vanadium element/alumina) as described in detail in the first embodiment. In the range of 90/10, it is more preferably in the range of 35/65 to 90/10, and further preferably in 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 the oxide of the vanadium group element and the alumina is preferably 90% or more.

Then, the first electrode 5 which is an electrode on the light-receiving surface side is formed. The first electrode 5 is formed by forming a paste containing silver (Ag) as a main component on the light-receiving surface anti-reflection film 3 by screen printing, and performing heat treatment (burn-through). The shape of the first electrode 5 may be any shape, and may be, for example, a well-known shape including a finger electrode and a bus bar electrode.

Then, the second electrode 6 as an electrode on the back side is formed. The second electrode 6 is formed by coating a paste containing aluminum as a main component using a screen printing or a dispenser, and heat-treating it. Further, the shape of the second electrode 6 is preferably the same shape as that of the BSF layer 4, the shape of the entire surface covering the back surface side, a comb shape, a lattice shape, or the like. In addition, printing of the paste for forming the first electrode 5 and the second electrode 6 as electrodes on the light-receiving surface side may be performed first, and then heat treatment (burn-through) may be performed to form the first electrode 5 and the second electrode together. Electrode 6.

Further, when the second electrode 6 is formed, aluminum is diffused as a dopant by using a paste containing aluminum (Al) as a main component, and is self-aligned to the second electrode 6 The BSF layer 4 is formed at a contact portion with the tantalum substrate 1. Further, as described above, a solution containing a coating type doping material such as boron or aluminum may be applied to the back surface side of the tantalum substrate 1 and heat-treated to form the BSF layer 4 separately.

Further, the above shows a configuration example and a manufacturing example in which a p-type germanium is used for the germanium substrate 1, and an n-type germanium substrate can be used as the germanium substrate 1. In this case, the diffusion layer 2 is formed by doping a layer of a group III element such as boron, and the BSF layer 4 is formed by doping a group V element such as phosphorus. In this case, it is necessary to pay attention to the fact that the negative electrode formed on the interface and the portion in contact with the metal on the back side are connected to each other to flow a leakage current, and the conversion efficiency is hard to be improved.

Further, in the case of using an n-type germanium substrate, a passivation film containing an oxide of at least one vanadium element selected from the group consisting of vanadium oxide and cerium oxide may be used as shown in FIG. 7 is used on the side of the light receiving surface. FIG. 6 is a cross-sectional view showing a configuration example of a solar cell element using the light-receiving surface passivation film of the embodiment.

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

Further, an anti-reflection film made of SiN or the like may be formed on the passivation film 7 by CVD or the like.

(Embodiment 4)

The tantalum substrate with a passivation film according to the present embodiment has a tantalum substrate and a passivation film described in the first embodiment, which is provided on the entire surface or a part of the tantalum substrate, that is, contains aluminum oxide and is selected from vanadium oxide and tantalum oxide. At least one of the group consisting of A film of an oxide of a vanadium group element. By the passivation film containing aluminum oxide and an oxide of at least one vanadium element selected from the group consisting of vanadium oxide and cerium oxide, the carrier life of the ruthenium substrate can be prolonged and a negative fixed charge can be obtained, thereby improving the sun. Characteristics of battery components (photoelectric conversion efficiency).

[Examples]

Hereinafter, the details will be described in detail with reference to the examples and comparative examples.

<Case of using vanadium oxide as an oxide of a vanadium group element>

[Example 1]

A commercially available organometallic thin film coating type material which can obtain alumina (Al ₂ O ₃ ) by heat treatment (calcination) [High Purity Chemical Research Institute, SYM-AL04, concentration: 2.3% by mass] 3.0 g, a commercially available organometallic thin film coating type material capable of obtaining vanadium oxide (V ₂ O ₅ ) by heat treatment (calcination) [High Purity Chemical Research Institute, V-02, concentration 2% by mass ] 6.0 g of a mixture was used to prepare a passivation material (a-1) as a coating type material.

The passivation material (a-1) was spin-coated on a 8-inch p-type tantalum substrate (8 Ω.cm to 12 Ω.cm) having a thickness of 725 μm of a natural oxide film removed by using hydrofluoric acid having a concentration of 0.49% by mass in advance. On one side, it was placed on a hot plate and prebaked at 120 ° C for 3 minutes. Thereafter, heat treatment (calcination) was performed at 700 ° C for 30 minutes in a nitrogen atmosphere to obtain a passivation film containing alumina and vanadium oxide [vanadium oxide / alumina = 63 / 37 (% by mass)]. The film thickness was measured by an ellipsometer and found to be 51 nm. The FT-IR of the passivation film was measured, and as a result, a very weak peak derived from an alkyl group was observed in the vicinity of 1200 cm ^-1 .

Then, on the passivation film, a plurality of aluminum electrodes having a diameter of 1 mm were formed by vapor deposition to form a capacitor of a metal-insulator-semiconductor (MIS) structure. The voltage dependence (CV characteristic) of the capacitance of the capacitor was measured by a commercially available prober and an inductance-capacitance resistance (LCR) meter (HP company, 4275A). The results show that the flat band voltage (Vfb) is shifted from the ideal value of -0.81V to +0.02V. From the amount of movement, it was found that the passivation film obtained from the passivation material (a-1) exhibited a fixed charge having a fixed charge density (Nf) of -5.2 × 10 ¹¹ cm ^-2 and a negative value.

The passivation material (a-1) was applied to both surfaces of a 8 Å p-type ruthenium substrate in the same manner as described above, prebaked, and heat-treated (calcined) at 650 ° C for 1 hour in a nitrogen atmosphere to prepare a ruthenium substrate. A sample covered by a passivation film on both sides. The carrier life of the sample was determined by a life measuring device (Kobelco Research Institute, RTA-540). The resulting carrier lifetime was 400 μs. For comparison, the same 8-inch p-type ruthenium substrate was passivated and measured by iodine passivation, and the carrier lifetime was 1100 μs. Further, after 14 days from the preparation of the sample, the carrier life was measured again, and as a result, the carrier lifetime was 380 μs. From this, it was found that the decrease in carrier lifetime (400 μs to 380 μs) was within -10%, and the decrease in carrier lifetime was small.

From the above, it is known that the passivation film obtained by subjecting the passivation material (a-1) to heat treatment (calcination) exhibits a certain degree of passivation performance and exhibits a negative fixed charge.

[Embodiment 2]

In the same manner as in Example 1, a commercially available organometallic thin film coating type material (High Purity Chemical Research Institute, SYM-AL04, which can obtain alumina (Al ₂ O ₃ ) by heat treatment (calcination), A commercially available organometallic thin film coating type material having a concentration of 2.3% by mass] and a vanadium oxide (V ₂ O ₅ ) which can be obtained by heat treatment [High Purity Chemical Research Institute, V-02, concentration 2 The mass%] was mixed and changed, and the passivation material (a-2) to passivation material (a-7) shown in Table 1 was prepared.

In the same manner as in the first embodiment, the passivation material (a-2) to the passivation material (a-7) were applied to one surface of a p-type germanium substrate, and heat-treated (calcined) to prepare a passivation film. The voltage dependence of the capacitance of the obtained passivation film was measured, and the fixed charge density was calculated based on this.

Further, in the same manner as in Example 1, a passivation material was applied to both surfaces of a p-type ruthenium substrate, and heat treatment (calcination) was carried out, and the carrier life was measured using the obtained sample.

The results obtained are summarized in Table 1. Further, after 14 days from the preparation of the sample, the carrier lifetime was measured again, and as a result, the carrier lifetime reduction of the passivation film using the passivation material (a-2) to the passivation material (a-7) shown in Table 1 was - Within 10%, it is known that the decrease in carrier life is small.

Depending on the ratio (mass ratio) of vanadium oxide/alumina after heat treatment (calcination), the passivation material (a-2) to passivation material (a-7) showed a negative fixed charge after heat treatment (calcination). The carrier lifetime also shows a certain degree of value, so it is suggested to function as a passivation film. It is known that the passivation film obtained from the passivation material (a-2) to the passivation material (a-7) stably exhibits a negative fixed charge, and can be preferably used as a passivation of a p-type germanium substrate.

[Example 3]

Commercially available vanadium oxyacetate (V) as a compound which can be obtained by heat treatment (calcination) to obtain vanadium oxide (V ₂ O ₅ ) (structural formula: VO(OC ₂ H ₅ ) ₃ , molecular weight: 202.13) 1.02 g (0.010 mol), and commercially available aluminum triisopropoxide as a compound which can be obtained by heat treatment (calcination) to obtain alumina (Al ₂ O ₃ ) (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 (b-1) having a concentration of 5 mass%.

The passivation material (b-1) was spin-coated on a 8-inch p-type tantalum substrate (8 Ω.cm to 12 Ω.cm) having a thickness of 725 μm of a natural oxide film removed by using hydrofluoric acid having a concentration of 0.49% by mass in advance. On one side, prebaking was carried out on a hot plate at 120 ° C for 3 minutes. Thereafter, heat treatment (calcination) was performed at 650 ° C for 1 hour in a nitrogen atmosphere to obtain a passivation film containing aluminum oxide and vanadium oxide. The film thickness was measured by an ellipsometer and found to be 60 nm. As a result of elemental analysis, V/Al/C = 64/33/3 (% by mass) was obtained. The FT-IR of the passivation film was measured, and as a result, a very weak peak derived from an alkyl group was observed in the vicinity of 1200 cm ^-1 .

Then, on the passivation film, a plurality of aluminum electrodes having a diameter of 1 mm were formed by vapor deposition to form a capacitor of a metal-insulator-semiconductor (MIS) structure. The voltage dependence (CV characteristic) of the capacitance of the capacitor was measured by a commercially available prober and an LCR meter (HP company, 4275A). The results show that the flat band voltage (Vfb) is shifted from the ideal value of -0.81V to +0.10V. From the amount of movement, the passivation film obtained from the passivation material (b-1) showed a fixed charge having a fixed charge density (Nf) of -6.2 × 10 ¹¹ cm ^-2 and a negative value.

In the same manner as described above, the passivation material (b-1) was applied to both surfaces of a 8 Å p-type ruthenium substrate, prebaked, and heat-treated (calcined) at 600 ° C for 1 hour in a nitrogen atmosphere to prepare ruthenium. A sample covered by a passivation film on both sides of the substrate. The carrier lifetime of the sample was measured by a life measuring device (Kobe 1 Co Research Institute, RTA-540). The resulting carrier lifetime was 400 μs. For comparison, the same 8-inch p-type ruthenium substrate was passivated and measured by iodine passivation, and the carrier lifetime was 1100 μs.

From the above, it is known that the passivation film obtained by subjecting the passivation material (b-1) to heat treatment (calcination) exhibits a certain degree of passivation performance and exhibits a negative fixed charge.

[Example 4]

Commercially available vanadium oxyacetate (V) (structural formula: VO(OC ₂ H ₅ ) ₃ , molecular weight: 202.13) 1.52 g (0.0075 mol), commercially available aluminum triisopropoxide (structural formula: Al ( OCH(CH ₃ ) ₂ ) ₃ , molecular weight: 204.25) 1.02g (0.005mol), 10g of novolak resin was dissolved in 10g of diethylene glycol monobutyl ether acetate and 10g of cyclohexane to prepare passivation material (b- 2).

The passivation material (b-2) was spin-coated on a 8-inch p-type ruthenium substrate (8 Ω.cm to 12 Ω.cm) having a thickness of 725 μm of a natural oxide film removed by using hydrofluoric acid having a concentration of 0.49% by mass in advance. On one side, it was placed on a hot plate and prebaked at 120 ° C for 3 minutes. Thereafter, the film was heated at 650 ° C for 1 hour in a nitrogen atmosphere to obtain a passivation film containing aluminum oxide and vanadium oxide. The film thickness was measured by an ellipsometer and found to be 22 nm. As a result of elemental analysis, V/Al/C = 71/22/7 (% by mass) was obtained. The FT-IR of the passivation film was measured, and as a result, a very weak peak derived from an alkyl group was observed in the vicinity of 1200 cm ^-1 .

Then, on the passivation film, a plurality of aluminum electrodes having a diameter of 1 mm were formed by vapor deposition to form a capacitor of a metal-insulator-semiconductor (MIS) structure. The voltage dependence (CV characteristic) of the capacitance of the capacitor was measured by a commercially available prober and an LCR meter (HP company, 4275A). The results show that the flat band voltage (Vfb) is shifted from the ideal value of -0.81V to +0.03V. From the amount of movement, it was found that the passivation film obtained from the passivation material (b-2) showed a fixed charge having a fixed charge density (Nf) of -2.0 × 10 ¹¹ cm ^-2 and a negative value.

In the same manner as described above, the passivation material (b-2) was applied to both surfaces of a 8 Å p-type ruthenium substrate, prebaked, and heat-treated (calcined) at 600 ° C for 1 hour in a nitrogen atmosphere to prepare ruthenium. A sample covered by a passivation film on both sides of the substrate. borrow The carrier life of the sample was measured by a life measuring device (Kobelco Research Institute, RTA-540). The resulting carrier lifetime was 170 μs. For comparison, the same 8-inch p-type ruthenium substrate was passivated and measured by iodine passivation, and the carrier lifetime was 1100 μs.

From the above, it is known that the passivation film obtained by hardening the passivation material (b-2) exhibits a certain degree of passivation performance and exhibits a negative fixed charge.

<Case of using cerium oxide as an oxide of a vanadium group element>

[Example 5]

A commercially available organometallic thin film coating type material (high purity chemical research institute, SYM-AL04, concentration: 2.3% by mass) which can obtain alumina (Al ₂ O ₃ ) by heat treatment (calcination), A ratio of change in a commercially available organometallic thin film coating type material (high purity chemical research institute, Ta-10-P, concentration: 10% by mass) which can be obtained by heat treatment to obtain cerium oxide (Ta ₂ O ₅ ) While mixing, the passivation material (c-1) to the passivation material (c-6) shown in Table 2 were prepared.

The passivation material (c-1) to the passivation material (c-6) were respectively spin-coated on the 8-inch p-type germanium substrate having a thickness of 725 μm in which the natural oxide film was removed by using hydrofluoric acid having a concentration of 0.49% by mass. One side of 8 Ω.cm~12 Ω.cm) was placed on a hot plate and pre-baked at 120 ° C for 3 minutes. Thereafter, heat treatment (calcination) was performed at 700 ° C for 30 minutes in a nitrogen atmosphere to obtain a passivation film containing aluminum oxide and cerium oxide. The passivation film was used to measure the voltage dependence of the electrostatic capacitance, and the fixed charge density was calculated based on this.

Then, the passivation material (c-1) to the passivation material (c-6) are respectively coated On both sides of a p-type ruthenium substrate of 8 Å, prebaking was performed, and heat treatment (calcination) was performed at 650 ° C for 1 hour in a nitrogen atmosphere to prepare a sample covered with a passivation film on both sides of the ruthenium substrate. The carrier life of the sample was measured by a life measuring device (Kobelco Research Institute, RTA-540).

The results obtained are summarized in Table 2. Further, 14 days after the preparation of the sample, the carrier life was measured again, and as a result, the carrier lifetime of the passivation film using the passivation material (c-1) to passivation material (c-6) shown in Table 2 was reduced to -10. Within %, it is known that the decrease in carrier lifetime is small.

Depending on the ratio (mass ratio) of cerium oxide/alumina after heat treatment (calcination), the results are different, but the passivation material (c-1) to passivation material (c-6) show a negative fixation after heat treatment (calcination). The charge and carrier lifetime also show a certain degree of value, so it is suggested to function as a passivation film.

[Embodiment 6]

A commercially available methanol oxime (V) (structure: Ta(OCH ₃ ) ₅ , molecular weight: 336.12) 1.18 g (0.0025 mol) which is a compound which can obtain yttrium oxide (Ta ₂ O ₅ ) by heat treatment (calcination) And commercially available aluminum triisopropoxide as a compound which can be obtained by heat treatment (calcination) to obtain alumina (Al ₂ O ₃ ) (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 mass%.

The passivation material (d-1) was spin-coated on a 8-inch p-type tantalum substrate (8 Ω.cm to 12 Ω.cm) having a thickness of 725 μm of a natural oxide film removed by using hydrofluoric acid having a concentration of 0.49% by mass in advance. On one side, it was placed on a hot plate and prebaked at 120 ° C for 3 minutes. Thereafter, the film was heated at 700 ° C for 1 hour in a nitrogen atmosphere to obtain a passivation film containing aluminum oxide and cerium oxide. The film thickness was measured by an ellipsometer and found to be 40 nm. As a result of elemental analysis, Ta/Al/C = 75/22/3 (wt%) was obtained. The FT-IR of the passivation film was measured, and as a result, a very weak peak derived from an alkyl group was observed in the vicinity of 1200 cm ^-1 .

Then, on the passivation film, a plurality of aluminum electrodes having a diameter of 1 mm were formed by vapor deposition to form a capacitor of a metal-insulator-semiconductor (MIS) structure. The voltage dependence (CV characteristic) of the capacitance of the capacitor was measured by a commercially available prober and an LCR meter (HP company, 4275A). The results show that the flat band voltage (Vfb) is shifted from the ideal value of -0.81V to -0.30V. From the amount of movement, it was found that the passivation film obtained from the passivation material (d-1) showed a fixed charge having a fixed charge density (Nf) of -6.2 × 10 ¹⁰ cm ^-2 and a negative value.

In the same manner as described above, the passivation material (d-1) was applied to both surfaces of a 8 Å p-type ruthenium substrate, prebaked, and heat-treated (calcined) at 600 ° C for 1 hour in a nitrogen atmosphere to prepare ruthenium. A sample covered by a passivation film on both sides of the substrate. The carrier life of the sample was measured by a life measuring device (Kobelco Research Institute, RTA-540). The resulting carrier lifetime was 610 μs. For comparison, the same 8-inch p-type ruthenium substrate was passivated and measured by iodine passivation, and the carrier lifetime was 1100 μs.

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

[Embodiment 7]

Commercially available methanol oxime (V) (structure: Ta(OCH ₃ ) ₅ , molecular weight: 336.12) 1.18 g (0.005 mol) as a compound capable of obtaining cerium oxide (Ta ₂ O ₅ ) by heat treatment (calcination) , commercially available aluminum triisopropoxide as a compound which can be obtained by heat treatment (calcination) to obtain alumina (Al ₂ O ₃ ) (structural formula: Al(OCH(CH ₃ ) ₂ ) ₃ , molecular weight: 204.25) 1.02 g (0.005 mol) and 10 g of a 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).

The passivation material (d-2) was spin-coated on a 8-inch p-type tantalum substrate (8 Ω.cm to 12 Ω.cm) having a thickness of 725 μm of a natural oxide film removed by using hydrofluoric acid having a concentration of 0.49% by mass in advance. On one side, prebaking was carried out on a hot plate at 120 ° C for 3 minutes. Thereafter, the film was heated at 650 ° C for 1 hour in a nitrogen atmosphere to obtain a passivation film containing aluminum oxide and cerium oxide. The film thickness was measured by an ellipsometer and found to be 18 nm. The results of elemental analysis revealed that Ta/Al/C = 72/20/8 (wt%). The FT-IR of the passivation film was measured, and as a result, a very weak peak derived from an alkyl group was observed in the vicinity of 1200 cm ^-1 .

Then, on the passivation film, a plurality of aluminum electrodes having a diameter of 1 mm were formed by vapor deposition to form a capacitor of a metal-insulator-semiconductor (MIS) structure. The voltage dependence (CV characteristic) of the capacitance of the capacitor was measured by a commercially available prober and an LCR meter (HP company, 4275A). The results show that the flat band voltage (Vfb) is shifted from the ideal value of -0.81V to -0.43V. From the amount of movement, it was found that the passivation film obtained from the passivation material (d-2) showed a fixed charge having a fixed charge density (Nf) of -5.5 × 10 ¹⁰ cm ^-2 and a negative value.

The passivation material (d-2) was applied to both surfaces of a 8 Å p-type ruthenium substrate in the same manner as described above, and prebaked, and heat-treated (calcined) at 600 ° C for 1 hour in a nitrogen atmosphere to prepare A sample covered by a passivation film on both sides of the substrate. The carrier life of the sample was measured by a life measuring device (Kobelco Research Institute, RTA-540). The resulting carrier lifetime was 250 μs. For comparison, the same 8-inch p-type ruthenium substrate was passivated and measured by iodine passivation, and the carrier lifetime was 1100 μs.

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

<Case of using two or more oxides of vanadium elements>

As shown in the above-described Embodiments 1 to 7, the passivation film containing aluminum oxide and vanadium oxide, and the passivation film containing aluminum oxide and cerium oxide exhibit a negative fixed charge, and the lifetime of the carrier obtained by passivation is improved. effect.

Further, the inventors of the present invention have found that a passivation film containing aluminum oxide and cerium oxide exhibits a negative fixed charge and has an effect of improving the life of a carrier obtained by passivation in the published application (Japanese Patent Application No. 2012-160336). .

Therefore, a passivation film of an oxide of two or three kinds of vanadium elements selected from the group consisting of alumina oxide and an oxide of a vanadium group element selected from the group consisting of vanadium oxide, cerium oxide and cerium oxide is as follows research.

[Embodiment 8]

A commercially available organometallic thin film coating type material (high purity chemical research institute, SYM-AL04, concentration: 2.3% by mass) which can obtain alumina (Al ₂ O ₃ ) by heat treatment (calcination), A commercially available organometallic thin film coating type material capable of obtaining vanadium oxide (V ₂ O ₅ ) by heat treatment (calcination) [High Purity Chemical Research Institute, V-02, concentration: 2% by mass], and A commercially available organometallic thin film coating type material obtained by heat treatment (calcination) of lanthanum oxide (Ta ₂ O ₅ ) [High Purity Chemical Research Institute, Ta-10-P, concentration: 10% by mass] The passivation material (e-1) as a coating type material was prepared by mixing (refer to Table 3).

A commercially available organometallic thin film coating type material (high purity chemical research institute, SYM-AL04, concentration: 2.3% by mass) which can obtain alumina (Al ₂ O ₃ ) by heat treatment (calcination), A commercially available organometallic thin film coating type material capable of obtaining vanadium oxide (V ₂ O ₅ ) by heat treatment (calcination) [High Purity Chemical Research Institute, V-02, concentration: 2% by mass], and A commercially available organometallic thin film coating type material (high purity chemical research institute, Nb-05, concentration: 5% by mass) which can obtain cerium oxide (Nb ₂ O ₅ ) by heat treatment (calcination), A passivation material (e-2) as a coating type material was prepared (refer to Table 3).

A commercially available organometallic thin film coating type material (high purity chemical research institute, SYM-AL04, concentration: 2.3% by mass) which can obtain alumina (Al ₂ O ₃ ) by heat treatment (calcination), A commercially available organometallic thin film coating type material obtained by heat treatment (calcination) of lanthanum oxide (Ta ₂ O ₅ ) [High Purity Chemical Research Institute, Ta-10-P, concentration: 10% by mass] And a commercially available organometallic thin film coating type material which can obtain cerium oxide (Nb ₂ O ₅ ) by heat treatment (calcination) [High Purity Chemical Research Institute, Nb-05, concentration: 5% by mass] The passivation material (e-3) as a coating type material was prepared by mixing (refer to Table 3).

A commercially available organometallic thin film coating type material (high purity chemical research institute, SYM-AL04, concentration: 2.3% by mass) which can obtain alumina (Al ₂ O ₃ ) by heat treatment (calcination), A commercially available organometallic thin film coating type material capable of obtaining vanadium oxide (V ₂ O ₅ ) by heat treatment (calcination) [High Purity Chemical Research Institute, V-02, concentration: 2% by mass], A commercially available organometallic thin film coating type material obtained by heat treatment (calcination) of lanthanum oxide (Ta ₂ O ₅ ) [High Purity Chemical Research Institute, Ta-10-P, concentration: 10% by mass], And a commercially available organometallic thin film coating type material (high purity chemical research institute, Nb-05, concentration: 5% by mass) which can obtain cerium oxide (Nb ₂ O ₅ ) by heat treatment (calcination) A passivation material (e-4) as a coating type material was prepared (refer to Table 3).

The passivation materials (e-1) to (e-4) were spin-coated in the same manner as in Example 1 except that hydrofluoric acid having a concentration of 0.49 mass% was used in advance to remove 8 吋 of the thickness of the natural oxide film of 725 μm. One side of the ruthenium substrate (8 Ω.cm~12 Ω.cm) was placed on a hot plate and prebaked at 120 ° C for 3 minutes. Thereafter, heat treatment (calcination) was performed at 650 ° C for 1 hour in a nitrogen atmosphere to obtain a passivation film containing an oxide of alumina and two or more kinds of vanadium group elements.

The voltage dependence of the electrostatic capacitance was measured using the passivation film obtained above, and the fixed charge density was calculated based on this.

Then, the passivation material (e-1) to the passivation material (e-4) were respectively applied to both sides of a 8 Å p-type ruthenium substrate, and prebaked, and performed at 650 ° C for 1 hour under a nitrogen atmosphere. The heat treatment (calcination) was performed to prepare a sample covered by a passivation film on both sides of the tantalum substrate. The carrier life of the sample was measured by a life measuring device (Kobelco Research Institute, RTA-540).

The results obtained are summarized in Table 3.

Depending on the ratio (mass ratio) of oxides of two or more kinds of vanadium elements after heat treatment (calcination), the results are different, but passivation using passivation material (e-1) to passivation material (e-4) The film showed a negative fixed charge after heat treatment (calcination), and the carrier lifetime also showed a certain value, so it was suggested to function as a passivation film.

[Embodiment 9]

In the same manner as in Example 1, a commercially available organometallic thin film coating type material (High Purity Chemical Research Institute, SYM-AL04, which can obtain alumina (Al ₂ O ₃ ) by heat treatment (calcination), A commercially available organometallic thin film coating type material having a concentration of 2.3% by mass] and a vanadium oxide (V ₂ O ₅ ) which can be obtained by heat treatment (calcination) [High Purity Chemical Research Institute, V-02, A commercially available organometallic thin film coating type material having a concentration of 2% by mass or a cerium oxide (Ta ₂ O ₅ ) which can be obtained by heat treatment (calcination) [High Purity Chemical Research Institute, Ta-10- P, a concentration of 10% by mass] was mixed, and a passivation material (f-1) to a passivation material (f-8) as a coating material was prepared (refer to Table 4).

Further, a passivation material (f-9) using alumina alone was prepared (refer to Table 4).

In the same manner as in the first embodiment, the passivation material (f-1) to the passivation material (f-9) were applied to one surface of the p-type germanium substrate, respectively, and then heat-treated (calcined) to prepare a passivation film, and the passivation was used. The film measures the voltage dependence of the electrostatic capacitance, and calculates the fixed charge density based on this.

Further, in the same manner as in the first embodiment, the passivation material (f-1) to the passivation material (f-9) were applied to both surfaces of the p-type germanium substrate, and heat treatment (calcination) was carried out, and the obtained sample was used to measure the load. Child life. The results obtained are summarized in Table 4.

As shown in Table 4, when the alumina/vanadium oxide or yttrium oxide in the passivation material is 90/10 and 80/20, the deviation of the value of the fixed charge density is large, and the negative fixed charge density cannot be stably obtained, but It was confirmed that a negative fixed charge density can be achieved by using aluminum oxide and cerium oxide. When a passivation material using alumina, vanadium oxide or yttrium oxide of 90/10 and 80/20 is measured by the CV method, it may become a passivation film which exhibits a positive fixed charge, and thus it is known that it is not stably displayed. A negative fixed charge. Further, a passivation film exhibiting a positive fixed charge can be used as a passivation film of an n-type germanium substrate.

On the other hand, the passivation material (f-9) in which the alumina reaches 100% by mass cannot obtain a negative fixed charge density.

<summary>

Based on 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 cerium oxide exhibit a negative fixed charge, and have an effect of improving the lifetime of a carrier obtained by passivation.

(2) Regarding the mass ratio of vanadium oxide to aluminum oxide, it is preferable to consider the improvement of the carrier lifetime and the stable negative fixed charge, and it is preferably 30/70 to 90/10, and further preferably 35/65~ 90/10.

(3) Regarding the mass ratio of cerium oxide to aluminum oxide, it is preferable to consider the improvement of the carrier lifetime and the stable negative fixed charge, and it is preferably 30/70 to 90/10, and further preferably 35/65~ 90/10.

(4) According to the results of elemental analysis or FT-IR measurement of the film, it is known that the passivation film contains an oxide of a vanadium group element (here, vanadium oxide or cerium oxide) and an alumina in the form of an organic component. Other than the component, as long as the content (mass) of the oxide of the vanadium group element (here, vanadium oxide or cerium oxide) and the aluminum oxide in the passivation film is 90% or more, more preferably 95% or more, The tendency to maintain good characteristics as a passivation film is maintained.

(5) A passivation film containing an oxide of aluminum oxide and two or more kinds of vanadium group elements exhibits a negative fixed charge and has an effect of improving the lifetime of a carrier obtained by passivation.

[Embodiment 10]

A single crystal germanium substrate using boron as a dopant was used as the germanium substrate 1, and a solar cell element having the structure shown in Fig. 4 was produced. After the surface of the ruthenium substrate 1 is textured, the coated phosphorus diffusion material is applied only to the light-receiving surface side, and diffusion is formed by heat treatment. Layer 2 (phosphorus diffusion layer). Thereafter, the coated phosphorus diffusion material was removed using dilute hydrofluoric acid.

Then, on the light-receiving side, a SiN film is formed as a light-receiving surface anti-reflection film 3 by plasma CVD. Thereafter, the passivation material (a-1) prepared in Example 1 was applied on the back side of the tantalum substrate 1 in a region other than the contact region (opening portion OA) by an inkjet method. Thereafter, heat treatment is performed to form a passivation film 7 having an opening OA. Further, as the passivation film 7, a sample using the passivation material (c-1) prepared in Example 5 was also prepared.

Then, on the light-receiving surface anti-reflection film 3 (SiN film) formed on the light-receiving surface side of the ruthenium substrate 1, a paste containing silver as a main component is screen-printed in the shape of a predetermined finger electrode and a bus bar electrode. On the back side, a paste containing aluminum as a main component is printed on the entire surface. Thereafter, heat treatment (burn-through) was performed at 850 ° C to form electrodes (first electrode 5 and second electrode 6), and aluminum was diffused in a portion of the opening OA of the back surface to form BSF layer 4, and FIG. 4 was formed. The solar cell element of the structure shown.

Further, in the formation of the silver electrode on the light-receiving surface, a burn-through step in which the hole is not formed in the SiN film is described, and the opening portion OA may be formed by etching first in the SiN film, and then the silver electrode may be formed.

For the comparison, in the above-described production step, the formation of the passivation film 7 is not performed, and the aluminum paste is printed on the entire surface on the back side, and the p ⁺ layer 14 and the second electrode corresponding to the BSF layer 4 are formed on the entire surface. The corresponding electrode 16 forms the solar cell element of the structure of Fig. 1. The solar cell elements were evaluated for characteristics (short circuit current, open circuit voltage, curve factor, and conversion efficiency). The evaluation of the characteristics was carried out in accordance with Japanese Industrial Standards (JIS)-C-8913 (2005) and JIS-C-8914 (2005). The results are shown in Table 5.

It is shown in Table 5 that when the solar cell element having the passivation film of the present invention is compared with the solar electronic component having no passivation film, both the short-circuit current and the open circuit voltage are increased, and the conversion efficiency (photoelectric conversion efficiency) is increased by 0.6% at maximum. The effect of the present invention.

The inventions of the present invention have been described in detail with reference to the embodiments and examples thereof. However, the invention is not limited thereto, and various modifications may be made without departing from the spirit and scope of the invention.

All the contents disclosed in Japanese Patent Application No. 2012-160336, Japanese Patent Application No. 2012-218389, and Japanese Patent Application No. 2013-011934 are hereby incorporated by reference. All the documents, Japanese patent applications, and technical standards described in the present specification are incorporated herein by reference in the same manner as the following, which are specifically and separately described in the respective documents, Japanese Patent Applications, and The case where the standard is incorporated by reference.

1‧‧‧矽 substrate

2‧‧‧n type diffusion layer

3‧‧‧Lighted anti-reflection film

4‧‧‧BSF layer

5‧‧‧1st electrode

6‧‧‧2nd electrode

7‧‧‧passivation film

OA‧‧‧ openings

Claims (12)

A passivation film containing alumina, an oxide of at least one vanadium element selected from the group consisting of vanadium oxide and cerium oxide, and used in a solar cell element having a ruthenium substrate, wherein the above-mentioned vanadium element The mass ratio of the oxide to the above alumina (oxide of vanadium element/alumina) is 30/70 to 90/10. The passivation film according to claim 1, wherein the total content of the oxide of the vanadium group element and the aluminum oxide is 90% or more. The passivation film according to claim 1 or 2, comprising an oxide of two or three kinds of vanadium elements selected from the group consisting of vanadium oxide, cerium oxide and cerium oxide as the vanadium group The oxide of the element. The passivation film according to claim 1 or 2, which is a heat-treated product of a coating type material containing a precursor of alumina, a precursor selected from vanadium oxide, and cerium oxide. The precursor of the oxide of at least one vanadium element in the group consisting of precursors. A coating type material comprising a precursor of an alumina, a precursor of an oxide of at least one vanadium element selected from the group consisting of a precursor of vanadium oxide and a precursor of cerium oxide, and is used for forming A passivation film according to any one of claims 1 to 4, which is a solar cell element having a ruthenium substrate. A solar cell element comprising: a p-type germanium substrate; and an n-type impurity diffusion layer formed on a first surface side of the germanium substrate as a light-receiving surface side; a first electrode is formed on the impurity diffusion layer; a passivation film is formed on the second surface side opposite to the light-receiving surface side of the germanium substrate, and has an opening; and a second electrode is formed on the second substrate a surface side electrically connected to the second surface side of the germanium substrate via the opening of the passivation film; and the passivation film contains aluminum oxide and at least one vanadium selected from the group consisting of vanadium oxide and cerium oxide. The oxide of the group element in which the mass ratio of the oxide of the above vanadium group element to the above alumina (the oxide of the vanadium group element/alumina) is 30/70 to 90/10. The solar cell element according to claim 6, comprising a p-type impurity diffusion layer formed on a part or all of the second surface side of the germanium substrate, and being larger than the germanium substrate Impurities are added to a higher concentration, and the second electrode is electrically connected to the p-type impurity diffusion layer through an opening of the passivation film. A solar cell element comprising: an n-type germanium substrate; a p-type impurity diffusion layer formed on a first surface side of the germanium substrate as a light receiving surface side; a first electrode formed on the impurity diffusion layer; and a passivation film formed An opening portion on the second surface side of the tantalum substrate opposite to the light receiving surface side; The second electrode is formed on the second surface side of the tantalum substrate, and is electrically connected to the second surface side of the tantalum substrate via an opening of the passivation film; and the passivation film contains alumina and is selected from vanadium oxide and An oxide of at least one vanadium element in the group consisting of cerium oxide, wherein the mass ratio of the oxide of the above vanadium element to the above alumina (oxide/alumina of vanadium element) is 30/70 to 90 /10. The solar cell element according to claim 8 is characterized in that the n-type impurity diffusion layer is formed on a part or all of the second surface side of the tantalum substrate, and is larger than the tantalum substrate. The higher concentration is added with impurities, and the second electrode is electrically connected to the n-type impurity diffusion layer through the opening of the passivation film. The solar cell element according to any one of the sixth aspect, wherein the oxide film of the vanadium group element and the total content of the aluminum oxide of the passivation film are 90% or more. The solar cell element according to any one of claims 6 to 9, which contains an oxidation of two or three kinds of vanadium elements selected from the group consisting of vanadium oxide, cerium oxide and cerium oxide. The substance acts as an oxide of the above vanadium group element. A ruthenium substrate with a passivation film, comprising: a ruthenium substrate; and a solar cell element according to any one of claims 1 to 4, which is provided on the entire surface or a part of the ruthenium substrate. Passivation film.