JP2005332913A - Method for forming silicon film for solar battery, and solar battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for easily forming a silicon film having performance appropriate as a semiconductor layer used for a solar battery, and a solar battery using the silicon film. <P>SOLUTION: A method for forming a silicon film for a solar battery includes the steps of coating a substrate with a composition containing silicon particles and high-order silane compound; and heating resultant coating under pressure lower than that of the coating process, and a solar battery including at least one layer of silicon films formed by the method inside a cell. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming a silicon film suitably used for a solar cell and a solar cell having the silicon film.

In recent years, solar cells using an amorphous silicon film or a polycrystalline silicon film are becoming popular from the viewpoint of energy saving. Conventionally, a thermal CVD (Chemical Vapor Deposition) method, a plasma CVD method, a photo CVD method, or the like is used as a method for forming a silicon film used in such a solar cell. (See Non-Patent Documents 1 and 2)
However, the formation of silicon films by these CVD methods is (1) difficult to handle the source gas, (2) contamination of the device and generation of foreign matter due to by-product of silicon powder, and (3) irregularities on the surface. It is difficult to obtain a uniform film thickness on a certain substrate, (4) the generation rate of a silicon film is slow, (5) an expensive and complicated device is required, and (6) a large amount of energy is consumed. Have a problem.

  On the other hand, a method of applying low molecular weight liquid silicon hydride without using a vacuum system has been proposed (see Patent Documents 1 and 2). However, these techniques have the disadvantages that a complicated apparatus is required for handling the raw material silicon hydride, and it is difficult to control the film thickness.

In recent years, a method for forming a silicon film using a liquid composition containing silicon particles, a higher order silane compound and a silane oligomer has been disclosed (see Patent Document 3). This technique is an excellent technique in which a high-quality silicon film can be easily obtained by using a liquid composition that is easy to handle as a raw material, coating the composition on a substrate, and then subjecting it to heat and / or light treatment. However, when this is applied to a solar cell, the relationship between the composition of the composition, the film formation conditions of the silicon film, and the characteristics of the obtained solar cell has not been sufficiently studied.
J. et al. Vac. Sci. Technology. 14: 1082 (1977) Solid State Com. 17: 1193 (1975) JP-A-1-29661 JP-A-7-267621 JP 2003-171556 A

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for easily forming a silicon film having suitable performance as a semiconductor layer used in a solar cell, and a solar cell using the silicon film. It is in.

  According to the present invention, the above-mentioned problems of the present invention are, firstly, a step of applying a composition containing silicon particles and a higher silane compound on a substrate, and an obtained coating film than the application step. It is achieved by a method for forming a silicon film for a solar cell, comprising a step of heating under a low pressure.

  Secondly, the above object of the present invention is achieved by a solar cell comprising at least one silicon film formed by the above method in a cell.

  ADVANTAGE OF THE INVENTION According to this invention, the high performance solar cell using the method of forming easily the silicon film which has a suitable performance as a semiconductor layer used for a solar cell, and this silicon film is provided.

  The method for forming a silicon film for a solar cell of the present invention uses a composition containing silicon particles and a higher silane compound as raw materials.

  Any silicon particles can be used as long as they are silicon particles, but it is preferably polycrystalline or single crystal and highly pure. Such silicon particles can be produced, for example, by pulverizing a polycrystal or single crystal silicon lump, and can also be formed by collecting powder waste generated during the formation of a silicon film. The silicon lump that can be used here or the powder waste generated when forming the silicon film includes high-purity i-type polycrystal or single-crystal silicon, n-type polycrystal or single-crystal silicon, and p-type polycrystal or single crystal. Silicon can be mentioned.

  The i-type polycrystal or single crystal silicon lump is preferably highly pure, for example, having a purity of 99.99% or more, more preferably 99.9999% or more.

The n-type polycrystal or single crystal silicon block can be doped with, for example, a nitrogen atom, a phosphorus atom, an arsenic atom, or an antimony atom. Of these doped atoms, phosphorus atoms are preferred. The doping amount is preferably about 10 ¹⁰ to 10 ²¹ atoms / cm ³ , more preferably 10 ¹⁵ to 10 ²⁰ atoms / cm ³ . By setting the doping amount within this range, the formed silicon film can be an n-type semiconductor film exhibiting suitable electrical characteristics.

The p-type polycrystal or single crystal silicon lump can be doped with, for example, boron atoms, aluminum atoms, or gallium atoms. Of these doped atoms, boron atoms are preferred. The doping amount is preferably about 10 ¹⁰ to 10 ²¹ atoms / cm ³ , more preferably 10 ¹⁵ to 10 ²⁰ atoms / cm ³ . By setting the doping amount within this range, the formed silicon film can be a p-type semiconductor film having suitable electrical characteristics.

  When the polycrystalline or single crystal silicon lump as described above is pulverized, either dry pulverization or wet pulverization may be employed. After pre-pulverization to an appropriate size by dry pulverization, and further wet pulverization using the dispersion medium to be contained in the composition for forming a silicon film of the present invention, the silicon of the present invention is directly used after the pulverization treatment. It can be used for the production of a film-forming composition and is convenient.

  The dry pulverization can be performed by a known method using, for example, a chip crusher, a hammer crusher, a cutter mill or the like. Moreover, the temperature at the time of grinding | pulverization does not have a restriction | limiting in particular, For example, it can carry out in the range of -200 degreeC-500 degreeC. Grinding in liquid nitrogen is preferable in that the surface state can be uniformly ground and the dangling bond density of the resulting silicon fine particles is reduced.

  The wet pulverization can be performed by a known method using, for example, a bead mill, a ball mill, a high-pressure liquid-liquid collision type mill, or the like. As a medium used in wet pulverization, a dispersion medium to be contained in the composition of the present invention described later can be used. In addition, the particle size of a silicon particle can be adjusted to a preferable particle size to contain in the composition for silicon film formation of this invention. Moreover, it does not specifically limit as a shape of a silicon particle, Arbitrary shapes, such as spherical shape, scale shape, cubic shape, and indefinite shape, can be mentioned.

After the wet milling or synthesis, the particles are subjected to an appropriate treatment so that the surface of the particles is treated with SiX _l (X is a hydrogen atom or a halogen atom, preferably a hydrogen atom, and l is 1 to 3). can do. As a treatment method, for example, a hydrogen fluoride treatment method under an electrical, chemical or photochemical condition using an aqueous solution of hydrogen fluoride or an aqueous solution of ammonium fluoride, or an RCA cleaning method (RCA Review, 1970 (Jun)). , P187) and a washing method using an appropriate washing agent such as aqua regia or nitric acid. These washing methods can also be used in combination. By performing the washing step, the silicon oxide layer formed on the surface of the silicon particles generated during pulverization can be removed. As a result, the silicon particles contained in the composition of the present invention can have higher purity, and dangling bonds that degrade the solar cell characteristics can be reduced. In addition, the particle size of a silicon particle can be adjusted to a preferable particle size to contain in the composition for silicon film formation of this invention.

By the way, it is generally said that if the dangling bond density of the silicon film remains high, the recombination of carriers is large and it is not suitable for solar cell applications. Further, according to the study by the present inventors, it was found that the dangling bond density is preferably 1 × 10 ¹⁷ pieces / cm ³ or less for solar cell applications.

As described above, the silicon particles contained in the raw material composition used in the method of the present invention can be obtained by pulverizing a silicon lump. However, when silicon is pulverized, dangling bonds increase and the particle diameter is 10 μm or less. It is known that when pulverization is performed, the dangling bond density is 1 × 10 ¹⁸ pieces / cm ³ or more, and when it is large, it is 1 × 10 ¹⁹ pieces / cm ³ or more. Furthermore, it has been found that dangling bonds of silicon particles generated during pulverization are not only present on the surface of the particles but are also present in the vicinity of the particle surface. It has been found that it is effective to remove the particle surface by the method described above in order to reduce the dangling bonds to the desired value. For example, by performing a treatment using a mixed aqueous solution of hydrofluoric acid and nitric acid, a layer containing dangling bonds on the surface can be efficiently removed. As a result, 1 × 10 ¹⁷ dangling bonds of silicon particles are obtained. / Cm ³ or less. The removal rate and efficiency of the silicon surface can be controlled by adjusting the acid concentration. The concentration of hydrofluoric acid is, for example, 0.001 to 40% by weight, preferably 0.01 to 10% by weight, and more preferably 0.01 to 5% by weight. The concentration of nitric acid is, for example, 0.001 to 70% by weight, preferably 0.01 to 30% by weight, and more preferably 0.01 to 15% by weight. When the concentration of the acid exceeds this range, the particles to be washed are eroded too early, which is not preferable. Moreover, when it exceeds this range and it is thin, since surface treatment takes time too much, it is unpreferable.

  The particle size of the silicon particles contained in the raw material composition used in the method of the present invention is equal to or less than the target film thickness in order to form a silicon film having no uniform voids. / 10 or less. For example, it is 0.01 to 500 μm, more preferably 0.1 to 100 μm, and most preferably 0.1 to 10 μm. When the particle diameter is larger than this range, it is not preferable because a uniform silicon film cannot be formed. When it is smaller than this range, recombination at the grain boundaries increases, and it becomes difficult to carry out the subsequent treatment, which is not preferable.

  Further, the silicon particles having a particle size of 0.35 to 2.0 μm having the same size as the wavelength of sunlight may contain at least 5% by weight, preferably 20% by weight or more, and most preferably 40% by weight or more. desirable. If content is in this range, the light confinement effect by scattering of sunlight can be made high, and it is preferable.

  The higher order silane compound contained in the raw material composition used in the method of the present invention is represented, for example, by the following formula (1).

Si _n X _m (1)

Here, X is a hydrogen atom or a halogen atom, n is an integer of 11 or more, and m is an integer of (2n-2), 2n, or (2n + 2).

  Examples of the halogen atom of X in the above formula (1) include fluorine, chlorine and bromine.

The higher order silane compound is, for example, the following formula (1) -1
Si _i X _{2i + 2} (1) -1

Here, X is a hydrogen atom or a halogen atom and i is an integer of 2 to 10,
A linear silane compound represented by the following formula (1) -2
Si _j X _2j (1) -2

Here, X is a hydrogen atom or a halogen atom, and j is an integer of 3 to 10,
And a cyclic silane compound represented by the following formula (1) -3
Si _k X _k (1) -3

Where X is a hydrogen atom or a halogen atom and k is 6, 8 or 10.
It is obtained by irradiating at least one silane compound selected from the group consisting of a cage silane compound represented by the formula (1) with radiation containing light having a wavelength of 150 to 450 nm.

  The “cage shape” means a structure including a Prisman skeleton, a Cuban skeleton, a pentagonal skeleton, and the like.

  As such a silane compound, for example, at least one compound selected from the group consisting of cyclopentasilane, cyclohexasilane, and silylcyclopentasilane is particularly preferable.

  These silane compounds can be produced via decaphenylcyclopentasilane and dodecaphenylcyclopentasilane produced from diphenyldichlorosilane.

  These silane compounds can be used alone or as a mixture of two or more.

  Examples of the radiation applied to the silane compound as described above include low-pressure mercury lamp, high-pressure mercury lamp, rare gas discharge light such as argon, krypton, xenon, YAG laser, argon laser, carbon dioxide laser, XeF, XeCl, XeBr, It can be carried out by light irradiation using an excimer laser such as KrF, KrCl, ArF, ArCl or the like as a light source. As these light sources, those having an output of 10 to 5,000 W are preferably used. Usually 100 to 1,000 W is sufficient.

  The raw material composition used in the method of the present invention only needs to contain the higher order silane compound synthesized as described above together with the silicon particles, and is used as a raw material for synthesizing the higher order silane compound. The used silane compound having 2 to 10 silicon atoms may remain in the raw material composition.

  The raw material composition used in the method of the present invention is preferably used in a state of being dispersed and dissolved in an appropriate dispersion medium.

  Examples of such a dispersion medium include n-pentane, n-hexane, n-heptane, n-octane, decane, dicyclopentane, benzene, toluene, xylene, durene, indene, tetrahydronaphthalene, decahydronaphthalene, squalane and the like. Hydrocarbon solvents of: diethyl ether, dipropyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, tetrahydrofuran tetrahydropyran, bis (2-methoxyethyl) ) Ether solvents such as ether, p-dioxane, tetrahydrofuran; and propylene carbonate , .Gamma.-butyrolactone, N- methyl-2-pyrrolidone, dimethyl formamide, may be mentioned polar solvents such as acetonitrile. Of these, hydrocarbon solvents are preferred from the viewpoint of the stability of the solution. These solvents can be used alone or as a mixture of two or more.

  A surfactant can be further added to the raw material composition used in the method of the present invention as necessary within a range not impairing the object and function of the present invention. Such surfactants can be cationic, anionic, amphoteric or nonionic. Among these, nonionic surfactants improve the wettability of the composition to the object to be coated, improve the leveling of the applied film, and prevent the occurrence of coating crushing and distortion skin. It can be preferably used in terms of usefulness.

  The raw material composition according to the present invention is composed of high-order silane, silicon particles and dispersion medium, based on the total thereof, preferably high-order silane, 1 to 50% by weight, more preferably 1 to 30% by weight, silicon particles. Preferably it contains 1 to 60% by weight, more preferably 5 to 40% by weight and the dispersion medium preferably 10 to 90% by weight, more preferably 40 to 90% by weight.

  Next, the method for forming the silicon film for solar cell of the present invention will be described.

As a method for forming the silicon film for solar cell of the present invention, the following method can be preferably mentioned.
(A) A method in which the composition containing the silicon particles and the higher order silane compound is applied onto a substrate, and then the resulting coating film is heated under a pressure lower than that in the application step.
(B) After apply | coating the composition containing the said silicon particle and a higher order silane compound on a base | substrate, the composition containing a higher order silane compound is apply | coated further, Then, the obtained coating film is applied from the said application | coating process. A method of heating under a low pressure.
(C) A method of repeating the above method (A) or method (B) a plurality of times.

  In the method (A), specific examples of the base material that can be used include glass, metal, plastic, and ceramics. Examples of the glass that can be used include quartz glass, borosilicate glass, soda glass, lead glass, and lanthanum glass. Examples of metals that can be used include gold, silver, copper, nickel, silicon, aluminum, iron, and stainless steel. As the plastic, for example, polyimide, polyethersulfone, norbornene-based ring-opening polymer and hydrogenated product thereof can be used. Furthermore, the shape of these substrates is not particularly limited by a lump shape, a plate shape, a film shape, or the like.

  In order to form a coating film of a composition containing silicon particles and a higher-order silane compound on the substrate as described above, for example, spraying, roll coating, curtain coating, spin coating, wire coating, screen printing It is possible to remove the dispersion medium after coating by an appropriate method such as a method, an offset printing method, or an ink jet method.

  The coating film formation is preferably carried out in a non-oxidizing atmosphere. In order to realize such an atmosphere, an atmosphere substantially free of oxidizing substances such as oxygen and carbon dioxide may be used. Specifically, nitrogen, hydrogen, a rare gas, and a mixed gas thereof may be used. An atmosphere can be preferably used.

  The dispersion medium can be removed by standing at room temperature until the dispersion medium naturally evaporates, but can be more effectively performed by heating. Heating for removing the dispersion medium is usually performed at a temperature of about 100 to 300 ° C. for about 1 to 120 minutes using an appropriate heating tool such as an oven or a hot plate.

  Although the film thickness of a coating film changes with the particle sizes of the silicon particle contained in a raw material composition, it can be 0.001-10 micrometers, for example, Preferably it is about 0.01-5 micrometers. In addition, the said film thickness should be understood as a film thickness after dispersion medium removal.

  The coating film formed as described above can then be made into a silicon film for solar cells by heating under a pressure lower than that in the coating step.

  Here, the pressure for performing the heat treatment is preferably 1.5 to 95%, more preferably 5 to 90%, more preferably 15 to 85%, and particularly preferably 25 to 85% of the pressure in the coating step. 75%. For example, when the coating process is performed at 1 atm, the pressure of the heat treatment process is preferably 0.015 to 0.95 atm, more preferably 0.05 to 0.9 atm, and more preferably 0. .15 to 0.85 atm, particularly preferably 0.25 to 0.75 atm.

  The pressure is preferably realized by a non-oxidizing gas, and more preferably performed in an atmosphere of nitrogen, argon, argon containing hydrogen, or nitrogen containing hydrogen.

  The concentration of the heat treatment is preferably 100 to 1,000 ° C, more preferably 200 to 850 ° C, still more preferably 250 ° C to 500 ° C, and most preferably 250 to 350 ° C. The heating time of the heat treatment is preferably 10 to 120 minutes, more preferably 15 to 60 minutes.

  In the method (B), the step of applying the composition containing the silicon particles and the higher silane compound on the substrate can be carried out in the same manner as in the method (A).

  In the method (B), the composition used in the step of applying the composition containing the higher silane compound is obtained by removing the silicon particles from the composition containing the silicon particles and the higher silane compound. That is, it can be a composition that does not contain silicon particles. The application method is the same as the case of applying a composition containing silicon particles and a higher order silane compound.

  The method of the present invention as described above has an advantage that a uniform thick film can be obtained by an inexpensive and easy method, and therefore can be suitably used as a method for forming a silicon film for solar cells.

  Next, the solar cell of the present invention will be described.

  The solar cell of the present invention includes at least one layer of the silicon film formed as described above.

  The substrate that can be used in the solar cell of the present invention is not particularly limited as long as it supports and reinforces the entire solar cell. For example, transparent materials such as glass and plastic can be used for super straight type solar cells, and metals, ceramics and the like can be used for substrate type solar cells. Further, metals such as stainless steel (SUS) and aluminum, ceramics, and the like can be used alone or in a laminated structure. Moreover, according to the utilization aspect of a board | substrate, it may have an unevenness | corrugation on the surface, Furthermore, an insulating film, a electrically conductive film, a buffer layer, etc., or these may be formed in combination.

In the super straight type solar cell, the transparent conductive layer formed on the transparent substrate is not particularly limited. For example, a single layer or a laminated layer of a transparent conductive material such as SnO ₂ , InO ₃ , ZnO, or ITO It can be formed by layers. The transparent conductive layer may contain impurities from the viewpoint of reducing the resistivity, and may be provided with irregularities to scatter light. Examples of impurities in this case include group III elements such as gallium and aluminum. The concentration is, for example, 5 × 10 ^{20 to} 5 × 10 ²¹ pieces / cm ³ , and the unevenness height is about 0.01 to 1 μm. As for the film thickness of a transparent conductive layer, 0.1-2 micrometers is mentioned. This can be formed on a substrate by sputtering, vacuum deposition, EB deposition, atmospheric pressure CVD, reduced pressure CVD, sol-gel, electrodeposition, or the like. Among these, the sputtering method is preferable because the transmittance and resistivity of the transparent conductive layer can be easily controlled to those suitable for polycrystalline silicon solar cells.

  Next, the photoelectric conversion layer formed on the transparent conductive layer is formed by a pin junction or a pn junction of a silicon film. Here, in the case of pin junction, the p layer is preferably 0.01 to 0.5 μm, more preferably 0.05 to 0.3 μm, and the i layer is preferably 0.1 to 50 μm, more preferably 1 to 50 μm. The 5 μm and n layers are preferably laminated to a thickness of 0.01 to 0.5 μm, more preferably 0.05 to 0.3 μm.

  In the case of a pn junction, the p layer or n layer used as the power generation layer of the solar cell is preferably 0.1 μm to 50 μm, more preferably 1 to 5 μm, and the p layer or n layer not used as the power generation layer is preferably The layers are laminated so as to have a thickness of 0.01 μm to 0.5 μm, more preferably 0.05 to 0.3 μm.

  The p layer, the i layer, and the n layer may be formed by using the above-described polycrystalline silicon film forming method, or any one of the layers may be formed by impurity diffusion or plasma CVD. Further, the p layer and the n layer formed by the plasma CVD method are not limited to the polycrystalline silicon film, but may be formed of an amorphous silicon film and a microcrystalline silicon film, and a buffer layer is inserted at the interface between the layers. May be. Note that the impurity diffusion and plasma impurity CVD process can be appropriately set by combining materials and conditions known in the art.

At this time, the doping amount of impurities contained in the i layer and the p layer or the n layer used as the power generation layer is preferably about 10 ¹⁰ to 10 ¹⁸ atoms / cm ³ , more preferably 10 ¹⁰ to 10 ¹⁷ atoms / cm ^3. cm ³ .

The doping amount of impurities contained in the p layer and n layer that are not used as the power generation layer is preferably about 10 ¹⁹ to 10 ²¹ atoms / cm ³ , more preferably 10 ²⁰ to 10 ²¹ atoms / cm ³ .

  Finally, the back electrode is formed by a sputtering method or a vacuum deposition method using a material such as Ag, Al, Cu, Au, Ni, Cr, W, Ti, Pt, Fe, or Mo, and preferably has a thickness of several hundred nm. A solar cell can be formed by laminating a single layer of a metal film of about ˜1 μm or a plurality of metal films.

  In the case of a substrate type solar cell, a photoelectric conversion layer is formed on a substrate on which a back surface reflection layer is formed in reverse to the solar cell formation procedure described above, and a transparent conductive layer and a collector electrode Ag are formed on the photoelectric conversion layer. It can form by laminating | stacking metal films, such as.

  The solar cell of the present invention has an advantage of high photoelectric conversion efficiency. This is because the solar cell silicon film formed by the method of the present invention has both a silicon portion derived from silicon particles, preferably a crystalline silicon portion and an amorphous silicon portion derived from a higher silane compound. This is thought to be due to the large effect of taking

Synthesis Example 1 (Synthesis of higher order silane)
After replacing the inside of a 3 L four-necked flask equipped with a thermometer, a cooling condenser, a dropping funnel and a stirrer with argon, 1 L of fully dried tetrahydrofuran and 18.3 g of lithium metal were charged and bubbled with argon gas. . While stirring this mixed liquid at 0 ° C., 333 g of diphenyldichlorosilane was added from a dropping funnel. After completion of the dropwise addition, stirring was continued for 12 hours until lithium metal completely disappeared at room temperature. The reaction mixture was poured into 5 L of ice water, the produced precipitate was filtered off, washed well with water, then washed with cyclohexane, and water and solvent were removed under reduced pressure to obtain 140 g of a white solid.

  100 g of this white solid and 1,000 mL of dried cyclohexane were charged into a 2 L flask, 4 g of aluminum chloride was added, and hydrogen chloride gas dried at room temperature was bubbled with stirring for 8 hours.

  After replacing a 3 L flask different from the above with argon, charge 40 g of lithium aluminum hydride and 400 mL of diethyl ether, add the above reaction mixture while stirring at 0 ° C. in an argon atmosphere, and stir at the same temperature for 1 hour. Thereafter, stirring was further continued at room temperature for 12 hours.

After removing by-products from the reaction mixture, distillation under reduced pressure at 70 ° C. and 10 mmHg yielded 10 g of a colorless and transparent liquid. This was found to be cyclopentasilane from the IR, ¹ H-NMR, ²⁹ Si-NMR, and GC-mass spectra.

Next, 10 g of the cyclopentasilane synthesized above was placed in a 100 mL flask and irradiated with a 500 W high pressure mercury lamp for 20 minutes while stirring in an argon atmosphere. Toluene 40g was added to this, and the toluene solution of the higher order silane compound was obtained by filtering.
Synthesis example 2 (synthesis of silicon particles)
Silicon particles with an average particle size of 8 mm obtained by dry pulverization of a silicon single crystal ingot (resistivity 2 × 10 ³ Ωcm) were charged into a stainless steel ball mill and further dry pulverized in a nitrogen atmosphere at room temperature for 8 hours to obtain an average particle size of 1 μm. Obtained silicon particles. The silicon particles thus obtained were first washed with a piranha solution and then with boiling nitric acid, and then the particle surface was etched with a mixed solution of 1 wt% hydrofluoric acid and 3 wt% nitric acid, and further washed with ultrapure water. Thereafter, the silicon particles were put in a quartz container and subjected to heat treatment at 900 ° C. for 5 hours in a nitrogen atmosphere to obtain silicon particles used in the method of the present invention. When the dangling bond concentration of this particle was measured by the ESR method, it was 1.0 × 10 ¹⁶ pieces / cm ³ .

The piranha solution was prepared by mixing 120 mL of distilled water, 224 mL of concentrated sulfuric acid, and 56 mL of 34.5 wt% hydrogen peroxide solution.
Example 1
In a nitrogen atmosphere, 2.4 mL of the toluene solution of the higher order silane compound obtained in Synthesis Example 1 and 0.6 g of the silicon particles obtained in Synthesis Example 2 are mixed to contain silicon particles and the higher order silane compound. A composition was prepared.

This composition was applied onto an N-type silicon wafer having a resistivity of 0.1 Ωcm using a bar coater under a nitrogen atmosphere at a pressure of 760 mmHg, and then the pressure was reduced to 380 mmHg. During this operation, it was assumed that the toluene solvent in the coating film was substantially evaporated. Next, the coating film was heated at 400 ° C. for 30 minutes under a nitrogen pressure of 380 mmHg to obtain a silicon film having a thickness of 4.6 μm. FIG. 1 shows a cross-section of this silicon film and an SEM photograph (magnification 5000 times) viewed from an oblique direction. Further, when the pore volume and pore mode diameter of this silicon film were measured using a porosimeter (manufactured by Shimadzu Corporation, model “Autopore IV9500”), they were 0.05 cm ³ / g and 0.028 μm, respectively. Met.

Next, a P-type silicon film having a thickness of 0.1 μm was laminated on the silicon film formed as described above by plasma CVD. Further, an ITO film as a transparent electrode and a comb-shaped Ag electrode were sequentially formed as a collector electrode, and a PIN solar cell having the structure shown in FIG. 2 was created. This cell was irradiated with artificial sunlight of AM (air mass) = 1.5, and the solar cell characteristics were evaluated according to JIS C8913. V _oc (open voltage) = 0.48V, I _sc (short circuit) Current) = 17.5 mA, FF (fill factor) = 0.45, and η (solar cell conversion efficiency) = 3.8%.

Example 2
A composition containing silicon particles and a higher order silane compound prepared in the same manner as in Example 1 was applied onto an N-type silicon wafer having a resistivity of 0.1 Ωcm by a bar coater under a nitrogen atmosphere at a pressure of 760 mmHg. Next, the toluene solution of the higher order silane compound obtained in Synthesis Example 1 was applied onto the silicon film by spin coating (rotation speed: 500 rpm). Thereafter, the pressure was reduced and the pressure of the nitrogen atmosphere was 380 mmHg. During this operation, it was assumed that the toluene solvent in the coating film was substantially evaporated. Next, the coating film was heated at 400 ° C. for 30 minutes under a nitrogen pressure of 380 mmHg to obtain a silicon film having a thickness of 5.0 μm. FIG. 1 shows a cross-section of this silicon film and an SEM photograph (magnification 5000 times) viewed from an oblique direction. Further, when the pore volume and pore mode diameter of this silicon film were measured in the same manner as in Example 1, they were 0.04 cm ³ / g and 0.024 μm, respectively.

Next, on the silicon film formed as described above, a PIN type solar cell was prepared and evaluated in the same manner as in Example 1. As a result, V _oc = 0.48V, I _sc = 17.7 mA, FF = 0. 47, η = 4.0%.

Comparative Example 1
In Example 1, a silicon film having a thickness of 4.0 μm was obtained in the same manner as in Example 1 except that the nitrogen pressure when heating the coating film was changed to 760 mmHg. FIG. 1 shows a cross-section of this silicon film and an SEM photograph (magnification 5000 times) viewed from an oblique direction. The pore volume and pore mode diameter of this silicon film were measured in the same manner as in Example 1. The results were 0.54 cm ³ / g and 0.288 μm, respectively.

Next, a PIN type solar cell was prepared and evaluated on the silicon film formed as described above in the same manner as in Example 1. As a result, V _oc = 0.45 V, I _sc = 16.0 mA, FF = 0. 24, η = 1.7%.

Comparative Example 2
In Example 2, a silicon film having a thickness of 4.3 μm was obtained in the same manner as in Example 2 except that the nitrogen pressure when heating the coating film was changed to 760 mmHg. FIG. 1 shows a cross-section of this silicon film and an SEM photograph (magnification 5000 times) viewed from an oblique direction. Further, when the pore volume and pore mode diameter of this silicon film were measured in the same manner as in Example 1, they were 0.21 cm ³ / g and 0.18 μm, respectively.

Next, a PIN type solar cell was prepared on the silicon film formed as described above and evaluated in the same manner as in Example 1. As a result, V _oc = 0.46 V, I _sc = 16.0 mA, FF = 0. 25, η = 1.8%.

Example 3
In Example 1, it carried out similarly to Example 1 except the nitrogen pressure at the time of heating a coating film having been 610 mmHg, and obtained the 4.6-micrometer-thick silicon film. On this silicon film, a PIN type solar cell was prepared and evaluated in the same manner as in Example 1. As a result, V _oc = 0.48 V, I _sc = 16.8 mA, FF = 0.44, η = 3. 7%.

Example 4
In Example 1, a silicon film having a thickness of 4.8 μm was obtained in the same manner as in Example 1 except that the nitrogen pressure when heating the coating film was changed to 700 mmHg. On this silicon film, a PIN solar cell was prepared and evaluated in the same manner as in Example 1. As a result, V _oc = 0.47 V, I _sc = 16.4 mA, FF = 0.41, η = 3. 3%.

Example 5
In the same manner as in Example 2, a 5.0 μm thick silicon film was formed on an N-type silicon wafer having a resistivity of 0.1 Ωcm. A circular aluminum electrode having a diameter of 1 mm was formed on the silicon film by a mask vapor deposition method. Aluminum was vapor-deposited on one side of the back surface of the N-type silicon wafer to form an electrode. Wiring was applied to each of these electrodes, and Schottky diode characteristics were evaluated. The results are shown in FIG.

Comparative Example 3
In the same manner as in Comparative Example 2, a 4.3 μm thick silicon film was formed on an N-type silicon wafer having a resistivity of 0.1 Ωcm. With respect to this silicon film, Schottky diode characteristics were evaluated in the same manner as in Example 5. The results are shown in FIG.

3 is a SEM photograph of the silicon film formed in Examples 1 and 2 and Comparative Examples 1 and 2. It is a schematic diagram of the PIN type solar cell manufactured for evaluation in an Example and a comparative example. Here, (a) is a top view and (b) is a cross-sectional view. 6 is a graph showing Schottky diode characteristics of silicon films formed in Example 5 and Comparative Example 3.

Explanation of symbols

1 N-type silicon wafer (N layer).
2 Silicon film (I layer) formed by the method of the present invention.
3 P-type silicon film (P layer).
4 Transparent electrode (ITO).
5 Comb Ag electrode.

Claims (5)

A step of applying a composition containing silicon particles and a high-order silane compound on a substrate, and a step of heating the obtained coating film under a pressure lower than that of the application step. A method for forming a silicon film for a battery. The method of claim 1, wherein the silicon particles are crystalline silicon. The method according to claim 2, wherein the dangling bond density of the silicon particles is 1 × 10 ¹⁷ pieces / cm ³ or less. Higher order silane compounds
Formula Si _i X _{2i + 2}
(Wherein X is a hydrogen atom or a halogen atom, and i is an integer of 2 to 10)
A chain silane compound represented by:
Formula Si _j X _2j
(Wherein X is a hydrogen atom or a halogen atom, and j is an integer of 3 to 10)
And a formula Si _k X _k
(Wherein X is a hydrogen atom or a halogen atom and k is 6, 8 or 10)
The method of Claim 1 obtained by irradiating the radiation containing the light of the wavelength of 150-450 nm to at least 1 sort (s) of silane compound chosen from the group which consists of a cage-like silane compound represented by these. A solar cell comprising at least one layer of a silicon film formed by the method according to any one of claims 1 to 4 in a cell.