JP6661891B2 - Method of manufacturing solar cell element and solar cell element - Google Patents

Description

  The present invention relates to a method for manufacturing a solar cell element and a solar cell element.

First, a manufacturing process of a conventional solar cell element will be described.
Irregularities (texture structure) are formed on the surface serving as a light receiving surface of a semiconductor substrate cut out from a crystal ingot of a p-type silicon crystal or the like, which is widely used as a solar cell substrate, to a thickness of about several hundred μm. By forming the texture structure, the obtained solar cell element can efficiently absorb light. Subsequently, in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen, a heat treatment of several tens of minutes is performed at 700 ° C. to 900 ° C. to form an n-type diffusion layer uniformly on the surface of the p-type semiconductor substrate. . As a result, a pn junction is formed on the p-type semiconductor substrate. After phosphorus is diffused using the mixed gas, an extra n-type diffusion layer on the back surface of the p-type semiconductor substrate is etched. A film such as SiO ₂ , Al ₂ O ₃ , silicon nitride (SiN _x ) or the like is formed on the phosphorus diffusion layer on the surface serving as the light receiving surface to prevent surface recombination and increase the light collection rate. Finally, an electrode composition containing Ag as a main component is applied on the front surface, and an electrode composition containing Al as a main component is applied on the back surface, and heat treatment (firing) is performed to obtain an ohmic contact. At this time, a high-concentration p-type diffusion layer is formed of Al on the back surface of the p-type semiconductor substrate. This layer has the effect of enhancing solar cell characteristics.

It is known that a solar cell element using an n-type semiconductor substrate has higher power generation efficiency than a solar cell element using a p-type semiconductor substrate. This is because an n-type semiconductor substrate has a longer carrier lifetime and a smaller number of oxygen defects than a p-type semiconductor substrate, so that high power generation efficiency can be easily obtained. When a solar cell element is manufactured using an n-type semiconductor substrate, a step of diffusing an acceptor element such as boron to form a pn junction may be included. Known methods for diffusing boron as an acceptor element include a method using boron tribromide (BBr ₃ ) gas, a method using a coating material containing boron, and an ion implantation method.

As a solar cell element using an n-type semiconductor substrate, a double-sided light receiving solar cell element is known. In general, a dual-sided solar cell element has a p-type diffusion layer formed on one side of a substrate using an acceptor element, and has a slightly higher concentration than the substrate using a donor element such as phosphorus on the other side. An n-type diffusion layer is formed. Then, an electrode is formed using an electrode composition containing Ag as a main component so that light is efficiently absorbed on both surfaces and electricity is efficiently transmitted. At present, a double-sided solar cell element is required to form a p-type diffusion layer as uniformly as possible over the entire surface of one surface of a substrate. Therefore, when a p-type diffusion layer is formed using boron as an acceptor element, boron tribromide (BBr ₃ ) gas or a coating material is often used.

  By the way, as a structure of the solar cell element for the purpose of increasing the power generation efficiency of the double-sided light receiving solar cell element described above, as compared with the concentration of the diffusion layer in the area immediately below the electrode, the area other than immediately below the electrode (light receiving area) 2), a selective emitter structure in which the diffusion concentration is lowered is known. In this structure, a region having a high diffusion concentration (hereinafter, this region is also referred to as a “selective emitter”) is formed immediately below the electrode, so that the contact resistance between the electrode and the semiconductor can be reduced. Further, since the diffusion concentration is relatively low in the region other than the region where the electrode is formed, the carrier lifetime is further increased, and the power generation efficiency of the solar cell element can be improved.

The selective emitter structure of the double-sided light receiving solar cell element is based on the fact that high power generation efficiency can be obtained when the phosphorus diffused layer in the structure of the conventional solar cell element using the p-type semiconductor substrate is used as the selective emitter structure. . It has been reported that high voltage characteristics can be obtained by forming the phosphorus diffusion layer on the back surface of the double-sided light receiving type solar cell element into a selective emitter structure (for example, see Non-Patent Document 1). As a technique for forming a selective emitter structure of a phosphorus diffusion layer, a low-concentration diffusion layer is formed over the entire surface of a semiconductor substrate by the gas diffusion method using POCl ₃ described above, and then a high-concentration diffusion layer is formed immediately below an electrode using a coating material. A method of forming a high-concentration diffusion region in a pattern just below an electrode using a laser, a method of forming a high-concentration diffusion layer using a POCl ₃ gas, and then selectively. There is known an etch-back method or the like in which an excessive surface layer of a high concentration diffusion layer is thermally oxidized and removed by etching.

  In the double-sided light receiving solar cell element, the power generation efficiency can be further improved by forming the surface on the side where the p-type diffusion layer is formed with the selective emitter structure. The p-type diffusion layer having the selective emitter structure can also be formed by a method using the above-described coating material, a method using a laser, an etch-back method, or the like.

Yvonne Schiele et al. Energy Prcedia 55 (2014) 295-301

  In order to form the selective emitter structure by any of the above methods, the formation of the diffusion layer in the light receiving region and the formation of the diffusion layer immediately below the electrode must be performed separately. Also increased.

  The present invention has been made in view of the above problems, and provides a method for manufacturing a solar cell element that can be implemented by a simple method, and a solar cell element manufactured by the method.

Means for solving the above problems are as follows.
<1> a step of applying a p-type diffusion layer forming composition containing a glass compound containing an acceptor element to at least a partial region of at least one surface of the semiconductor substrate;
The semiconductor substrate is subjected to a thermal diffusion process in an atmosphere having an oxygen concentration of 5% by volume or less, and a first p-type diffusion layer is formed in a region of the semiconductor substrate provided with the p-type diffusion layer forming composition. Forming a second p-type diffusion layer having a lower acceptor element concentration than the first p-type diffusion layer in at least a part of a region to which the p-type diffusion layer forming composition has not been applied; When,
A method for manufacturing a solar cell element having:
<2> The concentration of the acceptor element in the first p-type diffusion layer is 1 × 10 ²⁰ atoms / cm ³ or more at a point at a distance of 0.05 μm from the surface of the semiconductor substrate, and the second p-type diffusion layer <1> The method for manufacturing a solar cell element according to <1>, wherein the concentration of the acceptor element in the layer is 5 × 10 ¹⁹ atoms / cm ³ or less at a point at a distance of 0.05 μm from the surface of the semiconductor substrate.
<3> When the glass compound containing the acceptor element is SiO ₂ , Al ₂ O _3, K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ The solar cell element according to <1> or <2>, comprising at least one glass component selected from O ₅ , SnO, MoO ₃ , GeO ₂ , Y ₂ O ₃ , CsO ₂ , TiO _2, and ZrO ₂ . Production method.
<4> The method for manufacturing a solar cell element according to any one of <1> to <3>, wherein the acceptor element includes at least one selected from the group consisting of B (boron) and Al (aluminum).
<5> The method for manufacturing a solar cell element according to any one of <1> to <4>, wherein the solar cell element is a double-sided light receiving type.
<6> A solar cell element manufactured by the method for manufacturing a solar cell element according to any one of <1> to <5>.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the solar cell element which can be implemented by a simple method and the solar cell element manufactured by it are provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing of the structure of the double-sided light receiving solar cell element concerning one Embodiment of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps and the like) are not essential unless otherwise specified, and unless it is deemed essential in principle. The same applies to numerical values and their ranges, and does not limit the present invention.

  In the present specification, the term “step” is included in the term as well as an independent step, even if it cannot be clearly distinguished from other steps as long as the purpose of the step is achieved. Further, in this specification, a numerical range indicated by using “to” indicates a range including numerical values described before and after “to” as a minimum value and a maximum value, respectively. Further, in the present specification, the content of each component in the composition, when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, the plurality of substances present in the composition Means the total amount of In the present specification, the particle diameter of each component in the composition, when there are a plurality of types of particles corresponding to each component in the composition, unless otherwise specified, the plurality of types of particles present in the composition Mean the value for a mixture of Further, in this specification, the term “layer” includes, in a plan view, a configuration of a partly formed shape in addition to a configuration of a partly formed shape. The term "stacking" refers to stacking layers, where two or more layers may be joined or two or more layers may be removable. It will be apparent to one skilled in the art that the present invention may be practiced without some or all of the specific and detailed details described herein. In other instances, well-known points are not described or illustrated in detail to avoid obscuring aspects of the invention.

<Method of manufacturing solar cell element>
The method for manufacturing a solar cell element of the present invention includes:
A step of applying a p-type diffusion layer forming composition containing a glass compound containing an acceptor element to a partial region of at least one surface of the semiconductor substrate (an applying step);
The semiconductor substrate is subjected to a thermal diffusion process in an atmosphere having an oxygen concentration of 5% by volume or less, and a first p-type diffusion layer is formed in a region of the semiconductor substrate provided with the p-type diffusion layer forming composition. Forming a second p-type diffusion layer having a lower acceptor element concentration than the first p-type diffusion layer in at least a part of a region to which the p-type diffusion layer forming composition has not been applied; (Thermal diffusion step).

  According to the manufacturing method of the present invention, the formation of the p-type diffusion layer in the region immediately below the electrode and the formation of the p-type diffusion layer in the light receiving region of the solar cell element do not need to be performed separately, and can be performed collectively. it can. Therefore, a solar cell element having a selective emitter structure can be manufactured by a simple method.

  In the manufacturing method of the present invention, the reason why the second p-type diffusion layer is formed in at least a part of the region to which the p-type diffusion layer forming composition has not been applied is a phenomenon called out diffusion. Out diffusion refers to a phenomenon in which the acceptor element diffuses into a region other than the region where the p-type diffusion layer forming composition is applied. In the conventional method of forming a p-type diffusion layer, by allowing the acceptor element to be contained in the glass compound, volatilization of the acceptor element to the outside of the glass compound is suppressed, and out diffusion of the acceptor element is suppressed. In the present invention, a low-concentration p-type diffusion layer is formed in a region where the p-type diffusion layer forming composition is not provided by volatilizing the acceptor element to the outside of the glass compound to some extent and intentionally causing out diffusion. . As a result, two types of p-type diffusion layers having different acceptor element concentrations can be formed by a single thermal diffusion process.

The concentration of the acceptor element of the first p-type diffusion layer is preferably, for example, that the distance from the surface of the semiconductor substrate is ¹ × 1 19 atom / cm ³ or more at the point of 0.05μm, 1 × ¹⁰ 20 atom / Cm ³ or more. In addition, the concentration of the acceptor element in the first p-type diffusion layer is, for example, preferably 1 × 10 ²¹ atoms / cm ³ or less at a point at a distance of 0.05 μm from the surface of the semiconductor substrate, and 5 × 10 5 More preferably, it is ²⁰ atom / cm ³ or less. The concentration of the acceptor element can be measured by X-ray fluorescence analysis, secondary ion mass spectrometry, pseudo-steady state photoconductivity measurement (QSSPC), or the like.

The concentration of the acceptor element in the second p-type diffusion layer is, for example, preferably 1 × 10 ¹⁸ atom / cm ³ or more at a distance of 50 μm from the surface of the semiconductor substrate, and more preferably 5 × 10 ¹⁸ atom / cm 3. More preferably, it is ³ or more. The concentration of the acceptor element in the second p-type diffusion layer is, for example, preferably 1 × 10 ²⁰ atoms / cm ³ or less at a distance of 0.05 μm from the surface of the semiconductor substrate, and more preferably 5 × 10 ²⁰ atoms / cm ^3. More preferably, it is ¹⁹ atom / cm ³ or less.

  The places where the first p-type diffusion layer and the second p-type diffusion layer are formed are not particularly limited as long as desired characteristics of the solar cell element can be obtained. In one embodiment of the present invention, the first p-type diffusion layer is formed by applying the p-type diffusion layer forming composition to a region having an area of 50% or less of at least one surface of the semiconductor substrate. Here, even if the second p-type diffusion layer is formed on the entire surface of the surface of the semiconductor substrate on which the p-type diffusion layer is formed, except for the region where the p-type diffusion layer forming composition is applied, Only the second p-type diffusion layer may be formed.

(P-type diffusion layer forming composition)
The composition for forming a p-type diffusion layer contains a glass compound containing an acceptor element. The composition for forming a p-type diffusion layer is a composition which is applied to a semiconductor substrate and subjected to a thermal diffusion treatment, whereby an acceptor element is diffused into the semiconductor substrate to form a p-type diffusion layer. The p-type diffusion layer forming composition may contain components such as a dispersion medium as necessary.

  As described above, in the manufacturing method of the present invention, a low-concentration p-type diffusion layer is formed even in a region to which the p-type diffusion layer forming composition is not applied by out-diffusion of an acceptor element. Therefore, it is necessary to appropriately control out diffusion. Therefore, in the present invention, a glass compound containing an acceptor element is used. Since the acceptor element is contained in the glass compound, the degree of volatilization of the acceptor element to the outside of the glass compound can be appropriately controlled, and out diffusion can be appropriately controlled.

  An acceptor element is an element that forms a p-type diffusion layer by diffusing into a semiconductor substrate. Group 13 elements can be used as the acceptor elements. From the viewpoint of safety and the like, it is preferable to use at least one selected from the group consisting of B (boron) and Al (aluminum).

The glass compound containing the acceptor element is not particularly limited as long as the acceptor element can diffuse into the semiconductor substrate by thermal diffusion. For example, a glass compound formed including an oxide of an acceptor element and a glass component can be given. The oxide of the acceptor element is preferably at least one selected from the group consisting of B ₂ O ₃ and Al ₂ O ₃ .

  The content of the oxide of the acceptor element in the glass particles containing the acceptor element varies depending on the situation where the desired effect can be obtained. For example, from the viewpoint of diffusibility of the acceptor element, the content is preferably 0.5% by mass to 100% by mass, and more preferably 2% by mass to 80% by mass.

When the glass compound containing the acceptor element is a glass compound formed containing an oxide of the acceptor element and a glass component, the glass component contained in addition to the oxide of the acceptor element may be a commonly used glass component Can be used. For example, SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, from the viewpoint of setting the glass softening point to a desired range and reducing the difference from the thermal expansion coefficient of the semiconductor substrate. _{BeO, ZnO, PbO, CdO,} V 2 O 5, SnO, ZrO 2, WO 3, MoO 3, Y 2 O 3, CsO 2, TiO 2, TeO 2, La 2 O 3, Nb 2 O 5, Ta 2 Use of at least one selected from the group consisting of O ₅ , GeO ₂ , Lu ₂ O _3, and MnO may be used.

In order to properly obtain the desired effect as a glass compound, SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ , MoO ₃ , GeO ₂ , Y ₂ O ₃ , CsO ₂ and at least one selected from the group consisting of TiO ₂ , and SiO ₂ , K ₂ O, Na ₂ O, Li It is more preferable to use at least one selected from the group consisting of ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ and MoO ₃ .

Specific examples of the glass compound containing both the oxide of the acceptor element and the glass component include B ₂ O ₃ —SiO ₂ (described in the order of oxide of the acceptor element—glass component, and the same applies hereinafter), B ₂ O ₃ -ZnO _system, B ₂ O 3 -PbO _system, a B 2 _{O 3} system or the like used as both the oxide and the glass component of the acceptor element, those containing _B 2 _{O 3} as an oxide of the acceptor element, and, Al Examples include a system containing Al ₂ O ₃ as an oxide of an acceptor element, such as a ₂ O ₃ —SiO ₂ system.
Although a glass compound containing one or two components has been illustrated above, glass particles containing three or more components such as B ₂ O ₃ —SiO ₂ —CaO may be used.

The glass compound may be a glass compound containing an oxide of two or more acceptor elements, such as an Al ₂ O ₃ —B ₂ O ₃ system. As a glass compound containing two or more kinds of acceptor elements, at least B ₂ O ₃ and Al ₂ O ₃ are used as oxides of the acceptor element from the viewpoint of the resistance of the formed impurity diffusion layer and the control of out diffusion. _{, SiO 2, K 2 O,} Na 2 O, Li 2 O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V 2 O 5, SnO, ZrO 2, WO 3, MoO 3, GeO 2 _{, Y 2 O 3, CsO 2} , TiO 2, TeO 2, La 2 O 3, Nb 2 O 5, Ta 2 O 5, GeO 2, Lu 2 O 3 and at least one selected from the group consisting of MnO A glass compound containing a glass component is preferred.

The glass compound containing the acceptor element includes at least one selected from the group consisting of B ₂ O ₃ and Al ₂ O ₃ as an oxide of the acceptor element, and SiO ₂ , K ₂ O, Na ₂ O, and Li as glass components. ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ , WO ₃ , MoO ₃ , GeO ₂ , Y ₂ O ₃ , CsO ₂ , TiO ₂ , TeO ₂ , a glass compound containing at least one selected from the group consisting of La ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , GeO ₂ , Lu ₂ O ₃ and MnO is preferable,
At least one selected from the group consisting of B ₂ O ₃ and Al ₂ O ₃ as the oxide of the acceptor element, and SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, At least one selected from the group consisting of MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ , MoO ₃ , GeO ₂ , Y ₂ O ₃ , CsO ₂ and TiO _2. Glass compound is more preferable,
At least one selected from the group consisting of B ₂ O ₃ and Al ₂ O ₃ as the oxide of the acceptor element, and SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, Glass compounds containing at least one selected from the group consisting of MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ and MoO ₃ are more preferable,
At least one selected from the group consisting of B ₂ O ₃ and Al ₂ O ₃ as the oxide of the acceptor element, and SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, Glass compounds containing at least one selected from the group consisting of MgO, BeO, ZnO and ZrO ₂ are particularly preferred,
At least one selected from the group consisting of B ₂ O ₃ and Al ₂ O ₃ as the oxide of the acceptor element, and selected from the group consisting of SiO ₂ , ZnO, CaO, Na ₂ O, Li ₂ O and BaO as the glass component Most preferred is a glass compound containing at least one of the above.

  By using a glass compound having an appropriate composition, a desired effect can be obtained. For example, it becomes easy to lower the resistance value of the formed p-type diffusion layer and to control out diffusion.

  The state of the glass compound containing the acceptor element is not particularly limited. Particles are preferable from the viewpoints of the imparting property of the composition for forming a p-type diffusion layer and the diffusibility of an acceptor element. When the glass compound is a particle, the particle diameter (D50%) when the volume integrated from the smaller diameter side is 50% in the particle size distribution is preferably 0.01 μm to 100 μm, for example, and 0.02 μm. The thickness is more preferably from 50 to 50 μm, and even more preferably from 0.05 to 30 μm.

  The composition for forming a p-type diffusion layer may contain a compound containing an acceptor element other than a glass compound containing an acceptor element as long as the effects of the present invention are not impaired. Such compounds include oxides, ester compounds, nitrides, oxo acids and the like.

Examples of the oxide containing the acceptor element include boron oxide (B ₂ O ₃ ) and aluminum oxide (Al ₂ O ₃ ).
Examples of the ester compound containing an acceptor element include borate esters such as trimethyl borate.
Examples of the nitride containing the acceptor element include boron nitride.
Examples of the oxo acid containing the acceptor element include boric acid.

Compounds containing acceptor elements other than those described above include boron, aluminum-doped silicon particles, calcium borate, boron-containing silicon oxide compounds, aluminum alkoxides, organoaluminum compounds such as alkylaluminum, and the temperature during thermal diffusion (for example, , 800 ° C. or higher), a compound which can be changed to an oxide containing an acceptor element such as B ₂ O ₃ or Al ₂ O ₃ .

  The content of a compound containing an acceptor element in the p-type diffusion layer forming composition (meaning a glass compound containing an acceptor element and a compound containing another acceptor element included as necessary, and the same applies to the following), It is determined in consideration of imparting property, diffusibility of the acceptor element, and the like. Generally, the content of the compound containing the acceptor element in the p-type diffusion layer forming composition is preferably from 0.1% by mass to 95% by mass in the p-type diffusion layer forming composition, and is preferably 1% by mass. The content is more preferably from 90 to 90% by mass, still more preferably from 1 to 80% by mass, particularly preferably from 2 to 50% by mass, and particularly preferably from 5 to 20% by mass. Very preferred.

  When the content of the compound containing the acceptor element in the composition for forming a p-type diffusion layer is 0.1% by mass or more, the p-type diffusion layer can be sufficiently formed. When the content of the compound containing the acceptor element is 95% by mass or less, the dispersibility of the compound containing the acceptor element in the composition for forming a p-type diffusion layer is improved, and the application property to the semiconductor substrate is improved.

(Dispersion medium)
The composition for forming a p-type diffusion layer may include a dispersion medium. The dispersion medium is a medium for dispersing the compound containing the acceptor element in the composition for forming a p-type diffusion layer, and plays a role of adjusting the viscosity of the composition for forming a p-type diffusion layer. The type of the dispersion medium is not particularly limited, and a commonly used solvent or the like can be used.

  Examples of the dispersion medium include acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl isopropyl ketone, methyl-n-butyl ketone, methyl isobutyl ketone, methyl-n-pentyl ketone, methyl-n-hexyl ketone, diethyl ketone, Ketone solvents such as propyl ketone, diisobutyl ketone, trimethylnonanone, cyclohexanone, cyclopentanone, methylcyclohexanone, 2,4-pentanedione, and acetonylacetone; diethyl ether, methyl ethyl ether, methyl-n-propyl ether, diisopropyl ether , Tetrahydrofuran, methyltetrahydrofuran, dioxane, dimethyldioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol Di-n-propyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl-n-propyl ether, diethylene glycol methyl-n-butyl ether, diethylene glycol di-n-propyl ether, diethylene glycol di- n-butyl ether, diethylene glycol methyl-n-hexyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, triethylene glycol methyl-n-butyl ether, triethylene glycol di-n-butyl ether, triethylene Glycol glycol -N-hexyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, tetraethylene glycol methyl-n-butyl ether, diethylene glycol di-n-butyl ether, tetraethylene glycol methyl-n-hexyl ether, Tetraethylene glycol di-n-butyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether, propylene glycol dibutyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol methyl ethyl ether, Dipropylene glycol methyl- n-butyl ether, dipropylene glycol di-n-propyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol methyl-n-hexyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene glycol methyl ethyl ether , Tripropylene glycol methyl-n-butyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol methyl-n-hexyl ether, tetrapropylene glycol dimethyl ether, tetrapropylene glycol diethyl ether, tetrapropylene glycol methyl ethyl ether, tetrapropylene glycol Methyl-n-butyl ether, tetrapropylene glycol Ether solvents such as -n-butyl ether, tetrapropylene glycol methyl-n-hexyl ether, tetrapropylene glycol di-n-butyl ether; methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate; Sec-butyl acetate, n-pentyl acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, 2- (2-butoxyethoxy) ethyl acetate, benzyl acetate, acetic acid Cyclohexyl, methylcyclohexyl acetate, nonyl acetate, methyl acetoacetate, ethyl acetoacetate, diethylene glycol methyl ether acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol methyl ether acetate, acetic acid Propylene glycol ethyl ether, glycol diacetate, methoxytriethylene glycol acetate, ethyl propionate, n-butyl propionate, i-amyl propionate, diethyl oxalate, di-n-butyl oxalate, methyl lactate, ethyl lactate, lactic acid n-butyl, n-amyl lactate, ethylene glycol methyl ether propionate, ethylene glycol ethyl ether propionate, ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene Ester solvents such as glycol propyl ether acetate, γ-butyrolactone, γ-valerolactone; acetonitrile, N-methylpyro Aprotic polar solvents such as dinone, N-ethylpyrrolidinone, N-propylpyrrolidinone, N-butylpyrrolidinone, N-hexylpyrrolidinone, N-cyclohexylpyrrolidinone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide and the like Methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, 2-butanol, t-butanol, n-pentanol, isopentanol, 2-methylbutanol, sec-pentanol, t-pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol, 2-hexanol, 2-ethylbutanol, 2-heptanol, n-octanol, 2-ethylhexanol, 2-octanol, n-nonyl alcohol Cole, n-decanol, 2-undecanol, trimethylnonyl alcohol, 2-tetradecanol, 2-heptadecanol, phenol, cyclohexanol, methylcyclohexanol, benzyl alcohol, ethylene glycol, 1,2-propylene glycol, 1, Alcohol solvents such as 3-butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and tripropylene glycol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol Mono-n-butyl ether, diethylene glycol mono-n-hexyl Glycol monoether solvents such as ether, ethoxytriglycol, tetraethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether; terpinene, terpineol, myrcene And terpene solvents such as allocymene, limonene, dipentene, pinene, carvone, ocimene, and phenandrene; and water. These dispersion media are used alone or in combination of two or more. The content of the dispersion medium in the composition for forming a p-type diffusion layer is determined in consideration of applicability, viscosity and the like.

  From the viewpoint of applicability to a semiconductor substrate, the dispersion medium is preferably water, an alcohol solvent, a glycol monoether solvent, or a terpene solvent, and is water, alcohol, cellosolve, α-terpineol, diethylene glycol mono-n-butyl ether, or acetic acid. Diethylene glycol mono-n-butyl ether is preferred, and water, alcohol, α-terpineol or cellosolve is more preferred.

  When the p-type diffusion layer forming composition contains a dispersion medium, the content of the dispersion medium is not particularly limited, but the content of the dispersion medium in the p-type diffusion layer formation composition is 5% by mass or more and 99% by mass or less. Is preferably 20% by mass or more and 95% by mass or less, and further preferably 40% by mass or more and 90% by mass or less.

(High viscosity solvent)
The composition for forming a p-type diffusion layer may contain a high-viscosity solvent. Examples of the high-viscosity solvent include isobornylcyclohexanol, isobornylphenol, 1-isopropyl-4-methyl-bicyclo [2.2.2] oct-5-ene-2,3-dicarboxylic anhydride and It may include at least one selected from the group consisting of p-menthenylphenol, and preferably contains at least one selected from the group consisting of isobornylcyclohexanol and isobornylphenol. These compounds decompose or volatilize at low temperatures (for example, 400 ° C. or lower), and have a high viscosity due to a bulky structure. Therefore, it can be used as a substitute for a binder resin such as ethyl cellulose which has been conventionally used.

  In particular, when the composition for forming a p-type diffusion layer is applied to a semiconductor substrate by a screen printing method, it is necessary to increase the viscosity. In this case, when the content of the binder resin is increased (for example, 5% by mass in the composition for forming a p-type diffusion layer), the binder resin remains after the drying and heat diffusion steps, and this residue becomes a resistor. The power generation characteristics of the solar cell element may be adversely affected. Thus, by using a high-viscosity solvent, the amount of the resin binder can be reduced, and the amount of the resin binder can be reduced to a level that does not cause a problem.

  When the p-type diffusion layer forming composition contains a high-viscosity solvent, the content of the compound containing the acceptor element and the content of the high-viscosity solvent are not particularly limited. It is preferable that each of the p-type diffusion layer forming composition contains a compound containing an acceptor element in an amount of 5% to 40% by mass. It is more preferable to include a high-viscosity solvent in the range of 5% by mass to 95% by mass, respectively.

(Binder resin)
The p-type diffusion layer forming composition is applied on a substrate to prevent scattering of a compound containing an acceptor element in a dry state, and from the viewpoint of appropriately adjusting the viscosity of the p-type diffusion layer forming composition. And a binder resin.

Examples of the binder resin include polyvinyl alcohol, polyacrylamides, polyvinylamides, polyvinylpyrrolidone, polyethylene oxides, polysulfonic acid, acrylamide alkylsulfonic acid, cellulose ethers, cellulose derivatives (carboxymethylcellulose, hydroxyethylcellulose, ethylcellulose, etc.), Gelatin, starch and starch derivatives, sodium alginate, xanthan, guar gum and guar gum derivatives, scleroglucan and scleroglucan derivatives, tragacanth and tragacanth derivatives, dextrin and dextrin derivatives, (meth) acrylic acid resins, (meth) acrylic acid esters Resin (for example, alkyl (meth) acrylate resin, dimethylaminoethyl (meth) acrylate Etc.), butadiene resins, styrene resins and copolymers thereof, siloxane resins, can such suitably selected metal alkoxide. Among these binders, it is preferable to use a cellulose derivative, a (meth) acrylate resin or a (meth) acrylate resin from the viewpoint that the viscosity and the thixotropy can be easily adjusted even in a small amount.
These binder resins are used alone or in combination of two or more. The molecular weight of the binder resin is not particularly limited, and it is desirable to appropriately adjust the molecular weight in consideration of the desired viscosity of the composition for forming a p-type diffusion layer.
The content of the binder resin in the p-type diffusion layer forming composition of the present invention is not particularly limited, but is preferably less than 10% by mass, more preferably less than 3% by mass, and more preferably less than 1% by mass. Is more preferred.

(Alkoxysilane)
The composition for forming a p-type diffusion layer may include an alkoxysilane. By containing the alkoxysilane, there is a tendency that the viscosity of the composition for forming a p-type diffusion layer during drying can be favorably maintained. The alkoxy group constituting the alkoxysilane is preferably a linear or branched alkyloxy group, more preferably a linear or branched alkyloxy group having 1 to 24 carbon atoms, and has 1 to 10 carbon atoms. Is more preferable, and a linear or branched alkyloxy group having 1 to 4 carbon atoms is particularly preferable.

  Specific examples of the alkyl group of the alkoxy group include methyl, ethyl, propyl, butyl, isopropyl, isobutyl, pentyl, hexyl, octyl, 2-ethylhexyl, t-octyl, and decyl. Groups, dodecyl, tetradecyl, 2-hexyldecyl, hexadecyl, octadecyl, cyclohexylmethyl, octylcyclohexyl, and the like.

  Specifically, it is preferable to use at least one selected from the group consisting of tetramethoxysilane, tetraethoxysilane, and tetraisopropoxysilane as the alkoxysilane.

(Method for producing p-type diffusion layer forming composition)
The method for producing the p-type diffusion layer forming composition used in the present invention is not particularly limited. For example, it can be obtained by mixing a compound containing an acceptor element and other components contained as necessary using a blender, a mixer, a mortar, a rotor, or the like. When mixing, heating may be performed as necessary. The temperature when heating at the time of mixing can be, for example, 30 ° C to 100 ° C.

  The types of components contained in the p-type diffusion layer forming composition and the content of each component may be determined, for example, by thermal analysis such as TG / DTA (Thermo Gravimetry Analyzer / Differential Thermal Analysis, simultaneous differential thermal-thermogravimetric method). NMR (Nuclear Magnetic Resonance, Nuclear Magnetic Resonance), HPLC (High Performance Liquid Chromatography, High Performance Liquid Chromatography), GPC (Gel Permeation Chromatography, Gel Permeation Chromatography, GC-Chromatography, Chromatography / Chromatography) Mass spectrometry), IR (Infrared) Pectroscopy, infrared spectroscopy) can be confirmed using MALDI-MS (Matrix Assisted Laser Desorption / Ionization, matrix-assisted laser desorption ionization) and the like.

  In the p-type diffusion layer forming composition used in the present invention, the total amount of the lifetime killer element is preferably 1,000 ppm or less, more preferably 500 ppm or less, still more preferably 100 pm or less, and even more preferably 50 ppm or less. Is particularly preferred. When the total amount of the lifetime killer element is 1000 ppm or less, the lifetime of the substrate tends to be improved.

  Examples of the lifetime killer element include Fe, Cu, Ni, Mn, Cr, W, and Au. The amounts of these elements can be analyzed using an ICP (Inductively Coupled Plasma, Inductively Coupled Plasma) mass spectrometer, an ICP emission spectrometer, an atomic absorption spectrometer, or the like. The carrier lifetime can be measured by a microwave photoconductive decay method (μ-PCD method). These elements have a high diffusion rate in the semiconductor substrate, reach everywhere in the bulk of the substrate, and act as recombination centers.

(Applying step)
In the applying step, a p-type diffusion layer forming composition including a glass compound containing an acceptor element is applied to at least a part of a surface of a semiconductor substrate.
The semiconductor substrate is not particularly limited, and a normal substrate used for a solar cell element can be applied. For example, silicon substrate, gallium phosphide substrate, gallium nitride substrate, diamond substrate, aluminum nitride substrate, indium nitride substrate, gallium arsenide substrate, germanium substrate, zinc selenide substrate, zinc telluride substrate, cadmium telluride substrate, cadmium sulfide Substrates, indium phosphide substrates, silicon carbide, silicon germanium substrates, copper indium selenium substrates, and the like. The semiconductor substrate may be single crystal or polycrystalline. In the present invention, it is preferable to use an n-type semiconductor substrate, and it is more preferable to use an n-type silicon substrate.

  It is preferable that at least one surface of the semiconductor substrate is etched using an alkaline solution to form a texture structure. Specifically, it is preferable to form a texture structure by etching a semiconductor substrate obtained by slicing the ingot with a mixture of 1% by mass of caustic soda and 10% by mass of isopropyl alcohol. By using the surface on which the texture structure is formed as the light receiving surface, the light confinement effect is promoted, and the efficiency as a solar cell element is improved.

  The method for applying the p-type diffusion layer forming composition on the semiconductor substrate is not particularly limited as long as the p-type diffusion layer forming composition can be applied to a desired region. From the viewpoint of versatility and performance in the manufacturing process of the solar cell element, it is preferable to use a screen printing technique.

  The viscosity of the p-type diffusion layer forming composition applied on the semiconductor substrate is determined in consideration of the application method and the pattern of the application area. For example, it is preferably from 10 mPa · s to 1,000,000 mPa · s, and more preferably from 50 mPa · s to 500,000 mPa · s. The viscosity of the composition for forming a p-type diffusion layer can be adjusted by the type and content of a dispersion medium, a high-viscosity solvent, and the like.

  The shape of the region where the composition for forming a p-type diffusion layer is applied on a semiconductor substrate is preferably the same pattern as the electrode formed on the p-type diffusion layer in a subsequent process. The resulting p-type diffusion layer has a sufficient acceptor concentration for electrical contact with the electrode. The shape of the electrode pattern is not particularly limited as long as it can efficiently absorb sunlight and efficiently collect electricity generated in the semiconductor substrate. As the electrode structure of a general solar cell element, there are a plurality of linear electrodes having a width of about several tens μm to several hundred μm called finger electrodes and a linear electrode having a width of about 1 mm to 2 mm called bus bar electrodes. And the combination of the above electrodes.

  The p-type diffusion layer forming composition may be applied to a region corresponding to the pattern of the finger electrode, or may be applied to a region corresponding to the pattern of the finger electrode and the bus bar electrode. Further, in order to ensure that the electrode is formed on the p-type diffusion layer, the width of the region where the composition for forming the p-type diffusion layer is applied may be slightly larger than the width of the electrode. This facilitates the formation of the electrode on the p-type diffusion layer even if the alignment is slightly shifted.

  Depending on the composition of the p-type diffusion layer forming composition, after the p-type diffusion layer forming composition is applied on the semiconductor substrate, before the heat diffusion treatment step described later, the solvent or the like contained in the p-type diffusion layer forming composition May be performed for drying. The drying step can be performed, for example, at a temperature of about 80 ° C. to 300 ° C., for about 1 minute to 10 minutes when using a hot plate, and for about 10 minutes to 30 minutes when using a drier or the like. The conditions of the drying step can be adjusted depending on the type and content of the solvent and the like contained in the composition for forming a p-type diffusion layer.

(Thermal diffusion process)
In the thermal diffusion treatment step, the semiconductor substrate to which the p-type diffusion layer forming composition has been applied is subjected to a thermal diffusion treatment in an atmosphere having an oxygen concentration of 5% by volume or less, so that the p-type diffusion layer forming composition of the semiconductor substrate becomes The first p-type diffusion layer is formed in the provided region, and the concentration of the acceptor element is higher than that of the first p-type diffusion layer in at least a part of the region where the p-type diffusion layer forming composition is not provided. A low second p-type diffusion layer is formed.

  The heat diffusion treatment is preferably performed at 600 ° C to 1200 ° C, and more preferably at 850 ° C to 1000 ° C. The thermal diffusion treatment can be performed by a known method, for example, using a heating furnace that can be controlled to have a predetermined temperature, uniform temperature, and an atmosphere. In a heat diffusion process for manufacturing a solar cell element, a horizontal cylinder-type heating furnace is generally used.

  The thermal diffusion treatment is performed in an atmosphere having an oxygen concentration of 5% by volume or less. Thereby, volatilization of the acceptor element from the glass compound containing the acceptor element is promoted, and out diffusion is likely to occur. Examples of components in an atmosphere having an oxygen concentration of 5% by volume or less include inert gases such as nitrogen, helium, argon, neon, and xenon. Oxygen acts to suppress out diffusion. Therefore, by adjusting the oxygen concentration, it is possible to control the out-diffusion so as to obtain a desired diffusion concentration. In one embodiment, the thermal diffusion treatment is preferably performed in an atmosphere having an oxygen concentration of 3% by volume or less, more preferably in an atmosphere having an oxygen concentration of 1% by volume or less, and is substantially free of oxygen. More preferably, it is performed in an atmosphere.

Thermal diffusion treatment, the concentration of the acceptor element of the first p-type diffusion layer, be carried out as the distance from the surface of the semiconductor substrate is 1 × 1 ¹⁹ atom / cm ³ or more at the point of 0.05μm preferably It is more preferable to perform the treatment so as to be 1 × 10 ²⁰ atoms / cm ³ or more. It is preferable that the concentration of the acceptor element in the first p-type diffusion layer be 1 × 10 ²¹ atom / cm ³ or less at a point at a distance of 0.05 μm from the surface of the semiconductor substrate, and preferably 5 × It is more preferable to perform the treatment so as to be 10 ²⁰ atom / cm ³ or less.

The thermal diffusion treatment is preferably performed such that the concentration of the acceptor element in the second p-type diffusion layer is 1 × 10 ¹⁸ atoms / cm ³ or more at a point at a distance of 0.05 μm from the surface of the semiconductor substrate. More preferably, the concentration is set to 5 × 10 ¹⁸ atoms / cm ³ or more. Further, the concentration is preferably set so that the concentration of the acceptor element in the second p-type diffusion layer is 1 × 10 ²⁰ atoms / cm ³ or less at a point at a distance of 0.05 μm from the surface of the semiconductor substrate, and preferably 5 × It is more preferable to perform the treatment so as to be 10 ¹⁹ atoms / cm ³ or less.

(Other processes)
After the p-type diffusion layer is formed by the thermal diffusion treatment, the surface of the region of the semiconductor substrate to which the p-type diffusion layer forming composition has been applied is a glass layer made of a heat-treated product (fired product) of the p-type diffusion layer forming composition. Are formed. Further, a silicide layer such as boron silicide is formed in a region other than the region where the p-type diffusion layer forming composition is applied. For this reason, after the thermal diffusion treatment, a step of treating the semiconductor substrate with an etchant to remove the glass layer and the silicide layer may be performed.

  Examples of the etchant include an aqueous solution of hydrogen fluoride, ammonium fluoride, ammonium hydrogen fluoride, and the like, and an aqueous solution of sodium hydroxide. The method of the etching treatment is not particularly limited, and a known method such as immersing the semiconductor substrate in an etching solution can be applied.

  In order to easily remove the silicide layer, a step of oxidizing the silicide layer may be performed. By removing the silicide layer, a lifetime killer element such as Fe contained therein can be removed, and the passivation effect of a passivation film formed subsequently can be maximized.

  Examples of the method of oxidizing the silicide layer include a thermal oxidation method using oxygen gas, a method using a mixed solution of nitric acid and a small amount of hydrofluoric nitric acid, and a method using a boiling nitric acid solution. In the thermal oxidation method, by oxidizing at 800 ° C. or lower, the diffusion of the lifetime killer element gettered in the silicide layer into the semiconductor substrate in the oxidation step can be suppressed.

The content of the lifetime killer element such as Fe in the semiconductor substrate of the solar cell element obtained by the manufacturing method of the present invention is preferably 1 × 10 ¹ to 1 × 10 ¹² atoms / cm ³ , and more preferably 1 × 10 1 atoms / cm ^3. It is more preferably from ¹ to 1 × 10 ¹¹ atoms / cm ³ , and still more preferably from 1 × 10 ^{1 to} 5 × 10 ¹¹ atoms / cm ³ . Note that the content of the lifetime killer element in the semiconductor substrate can be measured by a fluorescent X-ray analysis method, a secondary ion mass spectrometry method, or a quasi-steady state photoconductivity measurement (QSSPC) method.

(Method of manufacturing double-sided light receiving solar cell element having selective emitter structure)
Next, a method for manufacturing a double-sided light receiving solar cell having a selective emitter structure will be described with reference to the drawings. In FIG. 1, reference numeral 10 denotes an n-type silicon substrate, reference numeral 20 denotes a p-type diffusion layer 1 (first p-type diffusion layer), reference numeral 21 denotes a p-type diffusion layer 2 (second p-type diffusion layer), and reference numeral 30 Denotes an electrode 1, reference numeral 40 denotes an n-type diffusion layer 1, reference numeral 41 denotes an n-type diffusion layer 2, and reference numeral 50 denotes an electrode 2. The size of each member in the drawing is conceptual, and the relative size relationship between members is not limited to this.

  First, a silicon substrate having a thickness of about 200 μm is sliced from an n-type silicon ingot, and a damaged layer on the surface generated when the silicon substrate is sliced is removed with 20% by mass of caustic soda. Then, etching is performed with a mixed solution of 1% by mass of caustic soda and 10% by mass of isopropyl alcohol to form a texture structure. By forming a texture structure on the light receiving surface of the solar cell element, a light confinement effect is promoted, and high efficiency is achieved.

  Next, a p-type diffusion layer forming composition is applied to the surface of the silicon substrate in the same pattern as the electrode pattern so that a selective emitter structure is formed on one surface of the n-type silicon substrate. The thermal diffusion treatment is performed at a temperature in an atmosphere having an oxygen concentration of 5% by volume or less. As shown in FIG. 1, the p-type diffusion layer 1 (first p-type diffusion layer) is formed in the region where the p-type diffusion layer forming composition has been applied by the thermal diffusion treatment. The concentration of the acceptor element in the p-type diffusion layer 1 is large enough for the electrode contact.

  Further, a p-type diffusion layer 2 (second p-type diffusion layer) is formed by out-diffusion also in a region to which the p-type diffusion layer forming composition is not applied, and a diffusion concentration sufficient for operating as a solar cell is obtained. can get. Carrier recombination can be suppressed by performing thermal diffusion processing under such a condition that the concentration of the acceptor element in the p-type diffusion layer 2 is lower than the concentration of the acceptor element in the p-type diffusion layer 1, and higher power generation can be achieved. Efficiency can be obtained. Further, since the p-type diffusion layer forming composition may be applied only directly below the electrode pattern, the amount of application can be reduced, and the manufacturing cost of the solar cell element can be reduced.

Although not shown in FIG. 1, it is preferable to provide a passivation film on the p-type diffusion layer 1 and the p-type diffusion layer 2 for suppressing surface recombination and preventing light reflection. As the passivation film, for example, a film of SiO ₂ obtained by performing a heat treatment in a high-temperature oxygen atmosphere at 700 ° C. or higher, a film of Al ₂ O ₃ by ALD (Atomic Layer Deposition, atomic layer deposition), or the like can be used. In order to protect the passivation film, a silicon nitride film may be provided thereon. The silicon nitride film can be formed by a plasma CVD method using a mixed gas of SiH ₄ and NH ₃ as a raw material. At this time, hydrogen diffuses into the crystal, and a trajectory that does not contribute to the bonding of silicon atoms, that is, a dangling bond and hydrogen are bonded to inactivate a defect (hydrogen passivation). More specifically, the mixed gas flow ratio (NH ₃ / SiH ₄ ) is 0.05 to 1.0, the pressure in the reaction chamber is 13.3 Pa to 266.6 Pa (0.1 Torr to 2 Torr), It is formed under the condition that the temperature is 300 ° C. to 550 ° C. and the frequency for plasma discharge is 100 kHz or more.

  Next, an n-type diffusion layer 1 and an n-type diffusion layer 2 having an impurity concentration lower than that of the n-type diffusion layer 1 are provided on a surface of the n-type silicon semiconductor substrate opposite to the surface on which the p-type diffusion layer is formed. To form By selectively forming the n-type diffusion layers 1 and 2 having different concentrations, high power generation efficiency can be easily obtained.

The n-type diffusion layers 1 and 2 can be formed by a known method. For example, a low-concentration n-type diffusion layer 2 is first formed by performing phosphorus diffusion using a gas such as POCl _{3 over} the entire surface of the n-type silicon semiconductor substrate, and then a high-concentration n-type diffusion layer is formed using a laser, a coating material, or the like. 1 may be formed. Alternatively, a high-concentration n-type diffusion layer 1 is first formed on the entire surface of an n-type silicon semiconductor substrate by performing phosphorus diffusion using a POCl ₃ gas, and then a low-concentration n-type diffusion layer 2 is formed by an etch-back method. Good. Alternatively, similarly to the method of forming the p-type diffusion layer 1 and the p-type diffusion layer 2 described above, an n-type diffusion layer forming composition containing a glass compound containing a donor element is applied only to a region below the electrode, and subjected to a thermal diffusion process. May be performed to form the n-type diffusion layer 1, and the n-type diffusion layer 2 may be formed by out-diffusion.

  Although not shown in FIG. 1, it is preferable to provide a passivation film on the n-type diffusion layer 1 and the n-type diffusion layer 2 for suppressing surface recombination and preventing light reflection. Further, a silicon nitride film may be provided thereon. The details of the passivation film and the silicon nitride film are the same as the details of the passivation and the silicon nitride film that may be provided on the p-type diffusion layers 1 and 2.

  Next, a metal paste is printed by a screen printing method on a region of the surface of the n-type silicon substrate where an electrode is to be formed, and dried. The metal paste contains metal particles and glass particles as essential components, and includes a resin binder and other additives as necessary. It is preferable to apply a metal paste suitable for forming an electrode on a p-type diffusion layer and a metal paste suitable for forming an electrode on an n-type diffusion layer.

  Then, heat treatment (firing) of the n-type silicon substrate is performed to form electrodes, thereby completing the solar cell element. The heat treatment (firing) is performed, for example, in a range of 600 ° C. to 900 ° C. for several seconds to several minutes. By performing the heat treatment (firing), the silicon nitride film serving as an insulating film is melted by the glass particles contained in the metal paste, and the surface of the silicon substrate is also partially melted, so that the metal particles (for example, silver) in the metal paste are melted. Particles) form a contact with the silicon substrate and solidify. Thereby, the formed electrode and the semiconductor substrate are conducted. This is called firethrough.

  The electrodes are generally composed of busbar electrodes and finger electrodes intersecting the busbar electrodes. The bus bar electrode and the finger electrode can be formed by a known method. For example, it can be formed by screen printing of a metal paste as described above, plating of an electrode material, vapor deposition of an electrode material by electron beam heating in a high vacuum, or the like.

  Hereinafter, examples of the present invention will be described more specifically, but the present invention is not limited to these examples. Unless otherwise specified, all chemicals used reagents. "%" Means "% by mass" unless otherwise specified.

[Example 1]
(Synthesis of glass particles)
B ₂ O ₃ , SiO ₂ , Al ₂ O _3, and CaO (all manufactured by Kojundo Chemical Laboratory Co., Ltd.) were weighed such that the composition molar ratios became 40 mol%, 40 mol%, 10 mol%, and 10 mol%, respectively. Mix in an agate mortar. The mixture was placed in a platinum crucible and kept at 1500 ° C. for 2 hours in a glass melting furnace. Then, it was quenched to obtain a glass lump. This was ground in an agate mortar and further ground in a planetary ball mill. Glass particles having a spherical particle shape, an average particle size (D50%) of 0.35 μm, and a softening temperature of about 800 ° C. were obtained. The glass particles, ethylcellulose and terpineol were mixed in amounts of 10 g, 6 g and 84 g, respectively, to form a paste, thereby preparing a composition for forming a p-type diffusion layer.

  Next, an n-type silicon substrate (thickness: 180 μm, specific resistance: 3.2 Ω · cm) having a texture structure formed on both surfaces is immersed in a 30% NaOH aqueous solution set at 85 ° C., and treated for 5 minutes to obtain a surface. Removed the damaged layer. The thickness of the substrate after the treatment was 160 μm.

  The composition for forming a p-type diffusion layer was applied to one surface of the n-type silicon substrate by screen printing using a mask having a line width of 150 μm, and dried at 150 ° C. for 1 minute.

Next, a boat containing an n-type silicon substrate was charged at 650 ° C. in a diffusion furnace (206A-M100, Koyo Thermo System Co., Ltd.) flowing N ₂ : 10 L / min. Thereafter, the temperature was raised to 950 ° C. at a temperature rising rate of 15 ° C./min, and thermal diffusion treatment was performed at 950 ° C. for 30 minutes to diffuse boron into the silicon substrate to form a p-type diffusion layer. Next, the temperature was lowered to 650 ° C. at 4 ° C./min, and when the temperature reached 650 ° C., the boat was taken out.

(Removal of glass layer)
The n-type silicon substrate after the thermal diffusion treatment was immersed in a 5% by mass HF aqueous solution for 5 minutes, and then washed three times with ultrapure water. Then, it was air-dried. Thus, the boron silicate glass layer formed in the region where the p-type diffusion layer forming composition was applied was removed.

(Oxidation and etching of silicide layer using oxygen gas)
Next, the n-type silicon substrate was placed in a 700 ° C. diffusion furnace in which N ₂ : ₂ L / min and O ₂ : 10 L / min were flown, and held for 30 minutes. Next, the n-type silicon substrate was taken out and allowed to cool. Then, it was immersed in a 5% by mass HF aqueous solution for 5 minutes, washed three times with ultrapure water, and air-dried. Thus, the silicide layer formed in the region other than the region where the p-type diffusion layer forming composition was applied was removed.

(Evaluation of sheet resistance)
The sheet resistance of the n-type semiconductor substrate subjected to the above treatment was measured using a low resistivity meter (Mitsubishi Chemical Corporation, Loresta MCP-T360). The sheet resistance of the region where the p-type diffusion layer forming composition was applied was 70 Ω / sq. It was found that a high concentration p-type diffusion layer was formed. The sheet resistance in a region other than the region where the p-type diffusion layer forming composition was applied was 150 Ω / sq. It was found that a low-concentration p-type diffusion layer was formed.

(Formation of n-type diffusion layer)
A high-concentration n-type diffusion layer and a low-concentration n-type diffusion layer were formed on a surface of the n-type semiconductor substrate on which the p-type diffusion layer was formed, opposite to the surface on which the p-type diffusion layer was formed, by an etch-back method. Specifically, first, a thermal diffusion process is performed at 850 ° C. for 20 minutes using a POCl ₃ gas in a diffusion furnace to diffuse phosphorus over the entire surface of the n-type semiconductor substrate, thereby forming a high-concentration n-type diffusion layer over the entire surface. did. Thereafter, using the SiN _x was formed on the high concentration plasma enhanced chemical vapor deposition with a barrier film line width 150μm for protecting a patterned by (PECVD), 20 minutes at 850 ° C. at a steam thermal oxidation furnace, phosphorus The layer was oxidized. Thereafter, the oxide film and the nitrogen silicon film were removed with a 5% by mass HF aqueous solution.

(Evaluation of sheet resistance)
The sheet resistance of the n-type semiconductor substrate subjected to the above treatment was measured using a low resistivity meter (Mitsubishi Chemical Corporation, Loresta MCP-T360). The sheet resistance of the area protected by the barrier film is 40Ω / sq. It was found that a high concentration n-type diffusion layer was formed. The sheet resistance of the region other than the region protected by the barrier film is 90 Ω / sq. It was found that a low-concentration n-type diffusion layer was formed.

  The n-type semiconductor substrate on which the p-type diffusion layer and the n-type diffusion layer were formed as described above was treated at 700 ° C. for 20 minutes in a thermal oxidation furnace flowing oxygen at 5 L / min to form passivation films on both surfaces. Thereafter, a nitrogen silicon film was formed on both sides by PECVD. Next, silver paste is applied to both sides of the n-type semiconductor substrate by screen printing in the form of an electrode having a width of 80 μm, and fired at 800 ° C. to secure electrical contact with the p-type diffusion layer or the n-type diffusion layer. The thus formed electrode was formed, and a double-sided light receiving type solar cell element was produced.

(IV measurement)
The power generation efficiency on the p-type diffusion layer side of the solar cell element was measured using an IV tracer (Hideki Seiki Co., Ltd., MP-180) under a light source set to AM1.5G. As a result, the power generation efficiency was 19.8%.

[Example 2]
A solar cell element was produced in the same manner as in Example 1, except that the application width of the p-type diffusion layer forming composition was 100 μm and the electrode width was 60 μm. The result of the power generation efficiency of the solar cell element measured in the same manner as in Example 1 was 19.7%.

[Example 3]
The sheet resistance is 70Ω / sq. over the entire surface without dividing the n-type diffusion layer into a high concentration region and a low concentration region. A solar cell element was produced in the same manner as in Example 1, except that phosphorus was diffused to form a solar cell element. The power generation efficiency of the solar cell element measured in the same manner as in Example 1 was 19.5%.

[Example 4]
The sheet resistance is 70Ω / sq. over the entire surface without dividing the n-type diffusion layer into a high concentration region and a low concentration region. A solar cell element was produced in the same manner as in Example 2 except that phosphorus was diffused to form a solar cell element. The power generation efficiency of the solar cell element measured in the same manner as in Example 1 was 19.4%.

[Comparative Example 1]
without dividing the p-type diffusion layer and the high concentration region and the low density region, a sheet resistance on one side of entire surface of the n-type silicon substrate with BBr ₃ gas 70 ohm / sq. A solar cell element was produced in the same manner as in Example 1 except that the solar cell element was formed as follows. The power generation efficiency of the solar cell element measured in the same manner as in Example 1 was 18.9%.

[Comparative Example 2]
Without dividing the p-type diffusion layer into a high-concentration region and a low-concentration region, a p-type diffusion layer composition is applied to the entire surface of one surface of an n-type silicon substrate to obtain a sheet resistance of 70 Ω / sq. A solar cell element was produced in the same manner as in Example 1 except that the solar cell element was formed as follows. The power generation efficiency of the solar cell element measured in the same manner as in Example 1 was 19.2%.

10 n-type silicon substrate 20 p-type diffusion layer 1 (first p-type diffusion layer)
21 p-type diffusion layer 2 (second p-type diffusion layer)
30 electrodes 1
40 n-type diffusion layer 1
41 n-type diffusion layer 2
50 electrodes 2

Claims (6)

A step of applying a p-type diffusion layer forming composition containing a glass compound containing an acceptor element to at least a partial region of at least one surface of the semiconductor substrate,
The semiconductor substrate is subjected to a thermal diffusion process in an atmosphere having an oxygen concentration of 5% by volume or less, and a first p-type diffusion layer is formed in a region of the semiconductor substrate provided with the p-type diffusion layer forming composition. Forming a second p-type diffusion layer having a lower acceptor element concentration than the first p-type diffusion layer in at least a part of a region to which the p-type diffusion layer forming composition has not been applied; When,
A method for manufacturing a solar cell element having: The concentration of the acceptor element in the first p-type diffusion layer is 1 × 10 ²⁰ atom / cm ³ or more at a point at a distance of 0.05 μm from the surface of the semiconductor substrate, and the acceptor in the second p-type diffusion layer The method for manufacturing a solar cell element according to claim 1, wherein the concentration of the element is 5 × 10 ¹⁹ atoms / cm ³ or less at a point at a distance of 0.05 μm from the surface of the semiconductor substrate. When the glass compound containing the acceptor element is SiO ₂ , Al ₂ O _3, K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , The method for manufacturing a solar cell element according to claim 1, wherein the method includes at least one glass component selected from SnO, MoO ₃ , GeO ₂ , Y ₂ O ₃ , CsO ₂ , TiO _2, and ZrO ₂ .   4. The method according to claim 1, wherein the acceptor element includes at least one selected from the group consisting of B (boron) and Al (aluminum). 5.   The method for manufacturing a solar cell element according to claim 1, wherein the solar cell element is a double-sided light receiving type.   A solar cell element manufactured by the method for manufacturing a solar cell element according to claim 1.