JP2015135988A - Solar cell and manufacturing method of solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maximally suppress a decrease in generation efficiency caused when incident light intensity is biased by solving a problem that a power generation amount decreases due to a bias in the incident light intensity in a solar cell module more cheaply and easily.SOLUTION: A solar cell comprises at least: a semiconductor substrate of a first conductivity type; an emitter layer of a second conductivity type; a conductive layer of the first conductivity type located between the semiconductor substrate and the emitter layer; a light-receiving surface finger electrode electrically connected to the emitter layer; and a rear-surface finger electrode electrically connected to the semiconductor substrate. The conductive layer has a lower resistivity than the semiconductor substrate and coats 80% or more of the light-receiving surface of the semiconductor substrate. The conductive layer is a thin film which transmits incident light.

Description

  The present invention relates to a solar cell that provides an inexpensive and stable power supply, and a method for manufacturing the solar cell.

FIG. 6 is a schematic view of a cross-sectional structure of a solar battery cell 600 (hereinafter sometimes abbreviated as a cell) that has been put into practical use. An emitter layer 602 having a conductivity type opposite to that of the substrate is provided on the light receiving surface side of the substrate 601, and a light receiving surface finger electrode 603 is provided thereon. As a method for forming the emitter layer, a thermal diffusion method is widely used. The substrate is put into a heat treatment furnace. When the substrate conductivity type is n-type, B, Al, Ga, In, etc., and when the substrate conductivity type is p-type, P, As, Sb, etc. are used as diffusion sources. The emitter layer is formed by allowing the substrate to stay at a predetermined temperature for a predetermined time and thermally diffusing from the surface of the substrate.
In order to reduce reflection loss, an antireflection film 604 is often provided in the light receiving region. Further, the back finger electrode 605 is also formed on the side opposite to the light receiving surface (back surface).

  Since solar cells can usually generate only a voltage of about 0.5V, in order to use them in general, in order to obtain sufficient power generation, dozens of cells are connected in series and processed into a solar cell module. The Since the solar cells generate power only when the substrate surface is irradiated with light, the solar cells have a tiled structure in the module.

  If light of uniform intensity is incident on the entire surface of the solar cell module, the amount of current generated in each cell is the same, and this current becomes the output current. However, since the module is often used outdoors, the intensity of incident light on a part of the module may be reduced, or light may not enter at all (behind the shadows). In these cases, the generated current as a module is limited to the lowest generated current value of each cell, and furthermore, the low output cell becomes a load and consumes the electric power generated by the surrounding cells. As a result, there arises a problem that the output as the solar cell module is significantly reduced.

  In order to avoid this problem, a bypass diode for current bypass is often provided. FIG. 7 shows a schematic diagram of a solar cell module 700 provided with an external diode. A bypass diode 704 is provided in parallel for every several to several tens of sheets (string). As the incident light intensity on a portion of the string decreases, the operating voltage of the string decreases. In this case, since the current flows through the bypass diode, this string does not become a load with respect to the other strings, and consumption of the power generated by the other strings can be avoided.

  When the bypass diode having the above structure operates, all the cells in one string are bypassed. Therefore, even if only one cell in one string stops operating (becomes shaded), the power generation amount for several to tens of cells that would have been obtained can be obtained by bypass. It will disappear. In order to improve this, it is possible to reduce the number of constituent cells in one string and install a large number of bypass diodes. However, not only the cost is increased, but also the module structure becomes complicated. It happens and is not realistic.

With respect to the problem that the module structure becomes complicated, Patent Documents 1 and 2 disclose a structure in which a bypass diode is built in the cell itself. In this method, a high concentration p ⁺ n junction region is scattered under the emitter layer by an ion implantation method, and this junction region is used as a Zener diode. This method is a method of incorporating a so-called bypass diode because the Zener diode has a function of bypassing the current. According to this method, since it is not necessary to attach a bypass diode externally, it is an excellent method that facilitates the production of a solar cell module.

Japanese Patent Laid-Open No. 5-110121 Japanese Patent Laid-Open No. 2001-189483

However, since the cell implantation process uses an ion implantation method with extremely poor productivity and requires a process of masking a region not having a p ⁺ n junction, the cell conversion process becomes expensive and in reality. Not right. Furthermore, since p ⁺ n junction regions for current bypass are scattered, the saturation resistance when a cell is regarded as a bypass diode is inevitably higher than that of a cell without a bypass diode. Therefore, even if the bypass diode is operated once, power consumption by the bypass diode occurs, and in some cases, the power consumption may cause heat generation or ignition.
Further, in order to p ⁺ n junction area is stably secured to bypass current as a Zener diode, a certain degree of cross-sectional area in the p ⁺ region of the p ⁺ n junction region is required. Therefore, p ⁺ n
In the case where the junction regions are scattered, a certain amount of film thickness is required for the p ⁺ region in order to ensure this stability, and the present inventor absorbs incident light by the film thickness of the p ⁺ region. It has been found that the intensity of incident light reaching the substrate is weakened. That is, incident light irradiated to the p ⁺ region is converted only to light that reaches the substrate, and as a result, if a bypass diode is built in, the power generation efficiency of the cell itself is reduced.
The present invention is intended to solve the problem of a decrease in the amount of power generation due to a bias in incident light intensity in a solar cell module at a lower cost and in a simple manner, and a decrease in power generation efficiency that occurs when the incident light intensity is biased. The aim is to suppress as much as possible.

In order to solve the above-mentioned problems, the present inventor can efficiently convert power into power without reducing incident light intensity even if a current bypass function is built in the cell, and the cell itself. The solar cell in which the power generation efficiency does not decrease was studied earnestly. A Zener diode was adopted as a means for bypassing the current, and attention was paid to the effect of the cross-sectional area on the current bypass stability and the influence of the film thickness on the incident light intensity.
As a result, a configuration in which a thin-film conductive layer having the same conductivity type as the substrate and having a lower resistivity than the substrate is positioned between the substrate and the emitter layer so as to cover most of the light receiving surface of the substrate. If the conductive layer is thin, the incident light intensity is not reduced, and the conductive layer covers most of the light-receiving surface of the substrate. The inventors have found that a cross-sectional area that can bypass the above can be secured, and have arrived at the present invention.

That is, the present invention relates to a first conductivity type semiconductor substrate, a second conductivity type emitter layer, a first conductivity type conductive layer located between the semiconductor substrate and the emitter layer, the emitter layer, A solar cell having at least a light receiving surface finger electrode to be electrically connected and a back finger electrode to be electrically connected to the semiconductor substrate, wherein the conductive layer has a lower resistivity than the semiconductor substrate, A solar cell that is a thin film that covers 80% or more of a light receiving surface of a semiconductor substrate and transmits incident light.
Further, the present invention is a thin film that has a resistivity lower than that of the semiconductor substrate on the light receiving surface of the first conductivity type semiconductor substrate, covers 80% or more of the light receiving surface of the semiconductor substrate, and transmits incident light. First
A step of forming a conductive layer of a conductive type; a step of forming an emitter layer on the light receiving surface of the semiconductor substrate not covered by the conductive layer; and a light receiving surface finger electrode electrically connected to the emitter layer And a step of forming a back finger electrode electrically connected to the semiconductor substrate, wherein the emitter layer is formed by epitaxial growth. It is a manufacturing method of a solar cell.
The present invention is a first thin film that has a resistivity lower than that of the semiconductor substrate on the light receiving surface of the first conductivity type semiconductor substrate, covers 80% or more of the light receiving surface of the semiconductor substrate, and transmits incident light. A step of forming a conductive layer of a conductive type; a step of forming an emitter layer on the light receiving surface of the semiconductor substrate not covered by the conductive layer; and a light receiving surface finger electrode electrically connected to the emitter layer And a step of forming a back surface finger electrode that is electrically connected to the semiconductor substrate, wherein a boron compound and a phosphorus compound are formed on the light receiving surface of the semiconductor substrate. A method for manufacturing a solar cell, wherein the conductive layer and the emitter layer are formed simultaneously by gas-surface diffusion.
The present invention is a first thin film that has a resistivity lower than that of the semiconductor substrate on the light receiving surface of the first conductivity type semiconductor substrate, covers 80% or more of the light receiving surface of the semiconductor substrate, and transmits incident light. A step of forming a conductive layer of a conductive type; a step of forming an emitter layer on the light receiving surface of the semiconductor substrate not covered by the conductive layer; and a light receiving surface finger electrode electrically connected to the emitter layer And a step of forming a back surface finger electrode that is electrically connected to the semiconductor substrate, wherein the light receiving surface of the semiconductor substrate includes a material containing a boron compound and A material containing a phosphorus compound is applied, and the boron compound and the phosphorus compound are simultaneously thermally diffused to form the conductive layer and the emitter layer simultaneously. The method of manufacture is,.

  According to the solar cell of the present invention, it is possible to greatly suppress the decrease in power generation efficiency that occurs when the incident light intensity is biased. Moreover, according to the method for manufacturing a solar cell of the present invention, a current bypass function that does not impair the power generation performance of the solar cell can be easily incorporated in each cell.

It is an arrangement view of an example of a solar cell according to the present invention. It is a figure which shows the cross-section of an example of the solar cell concerning this invention. It is a figure which shows the structure of a solar cell module. It is a figure which shows the cross-section of a solar cell module. It is a flowchart which illustrates roughly an example of the manufacturing process of the solar cell which concerns on this invention. It is a figure which shows the structure of the cross section of a common solar cell. It is a figure which shows arrangement | positioning of the bypass diode in a solar cell module.

The present invention will be described below.
The solar cell according to the present invention has a first conductive type conductive layer between a first conductive type semiconductor substrate and a second conductive type emitter layer provided on the light receiving surface side of the semiconductor substrate. The first conductivity type means P type or N type, and the second conductivity type means N type or P type opposite to the first conductivity type. For example, when the first conductivity type is n-type, the second conductivity type is P-type.
In the present invention, the resistivity of the conductive layer is lower than the resistivity of the semiconductor substrate, and the conductive layer is a thin film that transmits incident light covering 80% or more of the light receiving surface of the semiconductor substrate. Features. Due to the low resistivity, when the incident light intensity is reduced, the junction between the emitter layer and the conductive layer can function as a Zener diode that bypasses the current. Further, by covering 80% or more of the light receiving surface of the semiconductor substrate, a cross-sectional area capable of stably bypassing current can be secured even for a thin film. Furthermore, if it is a thin film which permeate | transmits incident light, incident light intensity will not fall and the power generation performance of a solar cell will not be impaired.

It is preferable that the dopant concentration of the conductive layer is 1 × 10 ¹⁷ / cm ³ to 1 × 10 ²⁰ / cm ³ . This is because if the concentration is lower than 1 × 10 ¹⁷ / cm ³ , the operating voltage when the Zener diode is formed becomes too high, and if it is higher than 1 × 10 ²⁰ / cm ³ , the distortion of the crystal lattice of the substrate becomes large. This is because the photoelectric conversion efficiency is lowered. If the dopant concentration is within the above range, problems of operating voltage and photoelectric conversion efficiency do not occur.

  The conductive layer preferably has a thickness of 0.01 μm to 2 μm. If the thickness is less than 0.01 μm, a sufficient cross-sectional area cannot be secured, and stability as a Zener diode that bypasses the current is impaired. On the other hand, if the thickness is larger than 2 μm, the amount of incident light absorbed by the conductive layer becomes too large, which may impair the power generation performance. In consideration of the function of bypassing current and the power generation performance, the thickness of the conductive layer is more preferably 0.1 μm to 1 μm.

  Preferably, the first conductivity type and the second conductivity type are n-type and p-type, respectively, the dopant of the emitter layer is boron (B), and the dopant of the conductive layer is phosphorus (P). . This is because it is cheaper than other dopants and has a small influence on environmental pollution.

FIG. 1 shows an overview of the solar battery cell 100 of the present invention described above. As the current collecting electrode on the light receiving surface, there are many electrodes having a width of several hundred μm to several tens μm called light receiving surface finger electrodes 101, and the light receiving surface bus bar electrode 102 is used as a current collecting electrode for connecting solar cells. Have a few.
FIG. 2 shows a cross-sectional structure of a solar battery cell 100 according to an example of the present invention, and is a cross-sectional structure of a portion indicated by AA in FIG. Between the emitter layer (p ⁺ layer) 103 on the light receiving surface and the n-type substrate 104, a thin conductive layer (n ⁺ layer) 105 is provided over substantially the entire surface of the substrate. The back surface electric field layer (n ⁺ layer) 106 and the back surface passivation film 107 are not necessarily required, but are preferably provided in order to obtain high photoelectric conversion efficiency.

  FIG. 3 shows an overview of a solar cell module 300 processed by connecting the solar cells of the present invention in series. The solar battery cell 100 has a tiled structure in the solar battery module, and generates power only when light is applied to the light receiving surface of the substrate. Unlike the conventional solar cell module (FIG. 7), it is not necessary to provide an external bypass diode because the current bypass function is built in the solar cell.

FIG. 4 is a schematic cross-sectional view of a solar cell module 300 in which solar cells are connected in series. It is not necessary to provide an external bypass diode, and the light receiving surface bus bar electrode 102 and the back surface bus bar electrode 304 of each solar battery cell may be connected by a ribbon wire 301 to form a series circuit.
When the conductivity type of the substrate is n-type, the light-receiving surface bus bar electrode is a positive electrode and the back surface bus bar electrode is a negative electrode, and vice versa when the conductivity type of the substrate is p-type.

Next, the manufacturing method of the solar cell concerning this invention is demonstrated.
As the semiconductor substrate, for example, a single crystal silicon substrate or a polycrystalline silicon substrate manufactured by a method such as CZ method or FZ method can be used. For example, the conductive layer is formed by a vapor phase diffusion method using phosphorus oxychloride, or a phosphorus compound such as phosphorus pentachloride, phosphorus oxychloride (POCl ₃ ), or phosphine (PH ₃ ) as a diffusion source. It is possible to use a method in which the coating agent is applied to the surface of the semiconductor substrate with a brush, ink-jet, screen-printed or spin-coated and then heat-treated. The conductive layer may be provided not only on the light receiving surface side but also on the back surface side of the semiconductor substrate. The conductive layer on the back side can serve as a back surface field layer (BSF) and can increase the photoelectric conversion efficiency.

The manufacturing method of the present invention is characterized in that after forming a conductive layer, an emitter layer is formed by epitaxial growth on the surface of the conductive layer from which glass formed on the surface is removed with hydrofluoric acid or the like. As a specific epitaxial growth method, the semiconductor substrate after the formation of the conductive layer is placed in a vacuum chamber and heated to 900 ° C. to 1200 ° C., and any of SiH ₄ , SiH ₃ Cl, SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , There is a method in which H ₂ is used as a reaction gas and B ₂ H ₆ , BCl ₃ , BBr ₃ or the like is used as a dopant gas to form an emitter layer having a thickness of about 0.1 μm to 1 μm. The sheet resistance is preferably about 25Ω to 300Ω.

In the manufacturing method of the present invention, the conductive layer and the emitter layer can be formed simultaneously by simultaneously vapor-diffusing a boron compound and a phosphorus compound on the light receiving surface of the semiconductor substrate. As the boron compound, boron trichloride, boranes (BH ₃ , B ₂ H ₆ ), BHCl ₂ , B (OEt) ₃ and B (OMe) ₃ can be used.
Specifically, the textured and cleaned semiconductor substrate is placed in a heat treatment furnace at about 900 ° C. to 1100 ° C., and boron trichloride, boranes (BH ₃ , B, etc.) are used using N ₂ , Ar or the like as a carrier gas. ₂ H ₆ ), BHCl ₂ , B (OEt) ₃ , B (OMe) _{3 and the} like boron compound and phosphorus pentachloride, phosphorus oxychloride (POCl ₃ ), phosphine (PH ₃ ) and other phosphorus compounds are mixed. Then, it is introduced into the furnace and diffused in the gas phase under heating conditions for about 5 to 60 minutes. Since the phosphorus compound has a larger diffusion coefficient than the boron compound, it penetrates deeper into the semiconductor substrate, so that the conductive layer is formed between the semiconductor substrate and the emitter layer. Focusing on the difference in diffusion coefficient between phosphorus compounds and boron compounds, controlling the amount of carrier gas, the temperature of the diffusion source, etc., and increasing the amount of boron compound introduced relative to the phosphorus compound, the emitter near the surface A conductive layer can be formed immediately below the layer. In addition, in order to form the emitter layer only on one side, diffusion is performed with the back surfaces of the semiconductor substrates being overlapped with each other, or a SiO ₂ film or SiN _x film is used as a diffusion mask on the back surface of the semiconductor substrate before diffusion. It may be formed and devised so that a PN junction cannot be formed on the back surface.

  Further, as a manufacturing method of the present invention, a conductive layer and an emitter layer are formed by applying a material containing a boron compound and a material containing a phosphorus compound to the light receiving surface of a semiconductor substrate, and simultaneously thermally diffusing the boron compound and the phosphorus compound. They can be formed simultaneously. Specifically, after applying a coating agent containing a boron compound and a phosphorus compound to a textured and cleaned semiconductor substrate with a brush, inkjet, screen printing, spin coating, or the like, In this method, the coated substrate is heat-treated at 900 ° C. to 1100 ° C. for 5 to 60 minutes to form a conductive layer and an emitter layer. As in the case of the air-layer diffusion method, the conductive layer is formed between the semiconductor substrate and the emitter layer due to the difference in the diffusion coefficient between the phosphorus compound and the boron compound. Either the boron compound coating agent or the phosphorus compound coating agent may be applied first, or may be a multi-layer coating, or these coating agents may be mixed before application. Unlike the vapor phase diffusion method, this method can selectively form a diffusion layer only on one side of a semiconductor substrate.

An example of the manufacturing method of the solar cell concerning this invention is described below using the flowchart shown in FIG. However, the present invention is not limited to the solar cell manufactured by this method.
A high-purity silicon substrate is doped with a group V element such as P, As, or Sb, and the slice damage on the surface of an as-cut single crystal {100} n-type silicon substrate having a specific resistance of 0.1 Ω · cm to 5 Ω · cm Etching is performed using a high concentration alkali such as 5% to 60% sodium hydroxide or potassium hydroxide, or a mixed acid of hydrofluoric acid and nitric acid.

  Subsequently, minute unevenness called texture is formed on the substrate surface. Texture is an effective way to reduce solar cell reflectivity. The texture is immersed for about 10 to 30 minutes in an alkali solution (concentration 1% to 10%, temperature 60 ° C. to 100 ° C.) such as heated sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate. It is produced by. In many cases, a predetermined amount of 2-propanol is dissolved in the solution to promote the reaction.

  After texture formation, washing is performed in an acidic aqueous solution of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, or the like, or a mixture thereof. From an economic and efficient standpoint, washing in hydrochloric acid is preferred. In order to improve the cleanliness, 0.5% to 5% hydrogen peroxide may be mixed in a hydrochloric acid solution and heated to 60 ° C. to 90 ° C. for washing. A conductive layer 105 and an emitter layer 103 are formed on the substrate 104 thus prepared (FIG. 5A) (FIGS. 5B and 5C). The method for forming the conductive layer and the emitter layer is as described above.

  The conductive layer also functions as a gettering layer and contributes to improvement in photoelectric conversion efficiency. That is, it also serves to alleviate the lifetime reduction that occurs in the heat treatment process such as the diffusion process. The conductive layer can be formed as the back electrolysis layer 106 not only on the light receiving surface side but also on the back surface side of the semiconductor substrate (FIG. 5B). The conductive layer on the back side can serve as a back surface field layer (BSF) and can increase the photoelectric conversion efficiency.

After forming the conductive layer and the emitter layer, the antireflection film 108 on the light receiving surface is formed (FIG. 5D). For film formation, a SiN _x film is formed to a thickness of about 100 nm using a plasma CVD apparatus or the like. As the reaction gas, monosilane (SiH ₄ ) and ammonia (NH ₃ ) are often mixed and used. However, nitrogen can be used instead of NH ₃ , and the process pressure can be adjusted and the reaction gas diluted. Furthermore, when polycrystalline silicon is used for the substrate, hydrogen may be mixed into the reaction gas in order to promote the bulk passivation effect of the substrate. As a method for exciting the reactive gas in CVD, thermal CVD, photo-CVD, or the like may be used in addition to the above-described plasma.
Further, under the same conditions as the formation of the antireflection film, a SiNx film may be formed on the back surface to form the back surface passivation film 107 (FIG. 5D).

Next, the back surface finger electrode 109 and the light receiving surface finger electrode 101 are formed (FIG. 5E). Examples of the forming method include a vapor deposition method, a sputtering method, and a printing method. From an economical point of view, it is preferable to use a printing method such as inkjet or screen printing. A conductive paste in which metal fine particles such as Ag are dispersed in an organic solvent is printed in an electrode pattern on the back surface and the light receiving surface of the substrate and dried. The light-receiving surface electrode often takes a comb-teeth shape as shown in FIG. The back electrode may cover the entire surface of the substrate, may have the same comb-teeth shape as the light receiving surface, or may take various forms such as a lattice shape. After these printings, heat treatment at about 600 ° C. to 900 ° C. causes Ag to be sintered and silver powder to penetrate through the SiN _x film (fire-through) to make the electrode and silicon conductive. The back electrode and the light receiving surface electrode may be fired separately or at a time.

EXAMPLES Hereinafter, although this invention is demonstrated based on an Example and a comparative example, this invention is not limited to an Example and a comparative example.
In order to confirm the effectiveness of the present invention, a method of forming an emitter layer by epitaxial growth after forming a conductive layer (Example 1), a mixed gas of phosphorus oxychloride (POCl ₃ ) and boron tribromide (BBr ₃ ) A solar cell was manufactured by a method (Example 2) in which a conductive layer and an emitter layer were formed simultaneously by gas-phase diffusion, and the cells were connected in series to evaluate performance as a solar cell module. As a comparative example, a solar cell (Comparative Example 1) manufactured by a method in which gas diffusion is performed only with boron tribromide (BBr ₃ ) gas and only an emitter layer is formed without forming a conductive layer is also connected in series. The performance of the solar cell module was evaluated.

A 60 × 100 mm ² , 250 μm thick, specific resistance 1 Ω · cm, phosphorus-doped {100} n-type as-cut silicon substrate with 60 layers removed with a hot concentrated aqueous solution of potassium hydroxide, potassium hydroxide / 2- It was immersed in a propanol aqueous solution to form a texture, and subsequently washed in a hydrochloric acid / hydrogen peroxide mixed solution.

Subsequently, a conductive layer and an emitter layer were formed by the following method.
<Example 1>
The 20 substrates were heat-treated at 870 ° C. for 40 minutes in a phosphorus oxychloride gas atmosphere, and only the conductive layer was formed by gas layer diffusion. The dopant concentration of the conductive layer was 1 × 10 ¹⁸ / cm ³ , the thickness of the conductive layer was 1 μm, and the sheet resistance was about 31Ω. Since no measures were taken to prevent wrapping around the back surface, a conductive layer having a thickness of 1 μm was also formed on the back surface. After air layer diffusion, the glass was removed with hydrofluoric acid, washed and dried.

Next, these substrates are put into a vacuum chamber, the substrate temperature is heated to 1000 ° C., processed in a mixed gas atmosphere of SiH ₂ Cl ₂ , H ₂ and B ₂ H ₆ for 20 minutes, and only on the light receiving surface by epitaxial growth. An emitter layer was formed. The sheet resistance was about 34Ω.

<Example 2>
Twenty textured substrates were heat-treated at 980 ° C. for 40 minutes in a mixed gas atmosphere of boron tribromide and phosphorus oxychloride for gas layer diffusion to form a conductive layer and an emitter layer at the same time. In order to prevent boron tribromide and phosphorus oxychloride from entering the back surface, heat treatment was performed in a state where the back surfaces of the substrate were overlapped back to back. The carrier gas flow rate of boron tribromide was 200 ml / min, and the carrier gas flow rate of phosphorus oxychloride was 25 ml / min. The dopant concentration of the conductive layer was 1 × 10 ¹⁸ / cm ³ , the thickness of the conductive layer was 1 μm, and the sheet resistance of the light receiving surface was about 38Ω. After diffusion, the glass was removed with hydrofluoric acid, washed and dried.

<Comparative example 1>
Twenty textured substrates were heat-treated at 980 ° C. for 40 minutes in a boron tribromide gas atmosphere to perform gas-phase diffusion to form an emitter layer. In order to prevent boron tribromide from encroaching on the back surface, heat treatment was performed in a state where the back surfaces of the substrate were overlapped back to back in the same manner as in Example 2. The carrier gas flow rate of boron tribromide was 200 ml per minute. The sheet resistance of the light receiving surface was about 32Ω. After diffusion, the glass was removed with hydrofluoric acid, washed and dried.

  After the above treatment, a SiNx film was formed as a light-receiving surface antireflection film on all samples using a plasma CVD apparatus. The refractive index of the SiNx film was about 2.1 and the film thickness was 95 nm. A SiNx film was also formed on the back surface under the same conditions as the back surface passivation film.

  Next, Ag paste was screen-printed with a comb-like pattern on the back surface and the light-receiving surface of all samples, and dried. The Ag paste is obtained by dispersing Ag fine particles of several nm to several tens of nm in an organic solvent. Then, it heat-processed for about 10 second in 750 degreeC air atmosphere, Ag was sintered, the back surface finger electrode and the light-receiving surface finger electrode were formed, and the solar cell was completed.

Using a solar simulator manufactured by Yamashita Denso Co., Ltd., the solar cell characteristics of 20 produced cells were measured under the conditions of AM 1.5 spectrum, irradiation intensity 100 mW / cm ² and 25 ° C. The average value of the obtained results is shown in Table 1.

  Examples 1 and 2 both showed the same maximum output as Comparative Example 1, and the power generation characteristics were sufficient. From this result, it was confirmed that the conductive layer provided between the emitter layer and the semiconductor substrate in Examples 1 and 2 did not inhibit the incident light and did not affect the power generation characteristics.

Next, in order to confirm the effect of bypassing the current, 10 cells were connected in series for each cell of Examples 1 and 2 and Comparative Example 1. Specifically, the light receiving surface bus bar electrode and the back surface bus bar electrode of the adjacent cell were soldered with a ribbon wire to form a string of 10 sheets in series. Three strings were arranged on the same stage under outdoor sunlight, and the characteristics of each solar cell were measured. When the incident light intensity was simultaneously measured using a standard cell, it was about 120 mW / cm ² . At this time, the maximum output for 10 cells showed almost the same output of 22 to 23 W for each of the strings of Examples 1 and 2 and Comparative Example 1, and an appropriate result was obtained.

  Next, each cell of each string was covered with a dark curtain so as to completely cover the light receiving surface, and a pseudo shade was made so that sunlight did not enter only one cell, and the solar cell characteristics were measured. . The results are shown in Table 2.

  Example 1 and Example 2 showed a maximum output of about 20 W corresponding to an output amount of about 90% of the maximum output of 22 to 23 W for 10 cells. From this result, it is clear that the cells in which sunlight was not incident in the shade completely bypassed the current without becoming a load on other cells, and the nine cells in which sunlight was incident It has become possible to make the maximum output the output of the string itself. On the other hand, in Comparative Example 1, the shaded cell became a load on other cells, and the entire string did not generate power at all and could not be measured.

  According to the solar cell of the present invention, it is possible to greatly suppress the decrease in power generation efficiency that occurs when the incident light intensity is biased. Moreover, according to the method for manufacturing a solar cell of the present invention, a current bypass function that does not impair the power generation performance of the solar cell can be easily incorporated in each cell.

DESCRIPTION OF SYMBOLS 100 Solar cell 300 Solar cell module 600 Solar cell 700 Solar cell module 104,601 Substrate 102 Light-receiving surface bus-bar electrode 101,603 Light-receiving surface finger electrode 108,604 Antireflection film 103,602 Emitter layer 109,605 Back surface finger electrode 304 Back surface bus bar electrode 107 Back surface passivation film 106 Back surface electric field (BSF) layer 105 Conductive layer 301, 701 Ribbon wire 302, 702 Module negative electrode 303, 703 Module positive electrode 704 Bypass diode

Claims (7)

A first conductivity type semiconductor substrate;
An emitter layer of a second conductivity type;
A conductive layer of a first conductivity type located between the semiconductor substrate and the emitter layer;
A light-receiving surface finger electrode electrically connected to the emitter layer;
A back finger electrode electrically connected to the semiconductor substrate;
A solar cell having at least
The solar cell according to claim 1, wherein the conductive layer is a thin film that has a resistivity lower than that of the semiconductor substrate, covers 80% or more of the light receiving surface of the semiconductor substrate, and transmits incident light. The solar cell according to claim 1, wherein the conductive layer has a dopant concentration of 1 × 10 ¹⁷ to 1 × 10 ²⁰ / cm ³ .   The solar cell according to claim 1, wherein the conductive layer has a thickness of 0.01 to 2 μm.   2. The first conductivity type and the second conductivity type are n-type and p-type, respectively, the dopant of the emitter layer is boron (B), and the dopant of the conductive layer is phosphorus (P). The solar cell in any one of -3. The first conductive type conductive substrate is a thin film that has a resistivity lower than that of the semiconductor substrate, covers 80% or more of the light receiving surface of the semiconductor substrate, and transmits incident light. Forming a layer;
Forming an emitter layer on the light receiving surface of the semiconductor substrate that is not covered with the conductive layer and the conductive layer;
Forming a light-receiving surface finger electrode electrically connected to the emitter layer;
Forming a back finger electrode electrically connected to the semiconductor substrate;
A method for producing a solar cell comprising at least
The method of manufacturing a solar cell, wherein the emitter layer is formed by epitaxial growth. The first conductive type conductive substrate is a thin film that has a resistivity lower than that of the semiconductor substrate, covers 80% or more of the light receiving surface of the semiconductor substrate, and transmits incident light. Forming a layer;
Forming an emitter layer on the light receiving surface of the semiconductor substrate that is not covered with the conductive layer and the conductive layer;
Forming a light-receiving surface finger electrode electrically connected to the emitter layer;
Forming a back finger electrode electrically connected to the semiconductor substrate;
A method for producing a solar cell comprising at least
A method for manufacturing a solar cell, wherein a boron compound and a phosphorus compound are simultaneously diffused into the light receiving surface of the semiconductor substrate to form the conductive layer and the emitter layer simultaneously. The first conductive type conductive substrate is a thin film that has a resistivity lower than that of the semiconductor substrate, covers 80% or more of the light receiving surface of the semiconductor substrate, and transmits incident light. Forming a layer;
Forming an emitter layer on the light receiving surface of the semiconductor substrate that is not covered with the conductive layer and the conductive layer;
Forming a light-receiving surface finger electrode electrically connected to the emitter layer;
Forming a back finger electrode electrically connected to the semiconductor substrate;
A method for producing a solar cell comprising at least
Applying a material containing a boron compound and a material containing a phosphorus compound to the light receiving surface of the semiconductor substrate, and simultaneously thermally diffusing the boron compound and the phosphorus compound to form the conductive layer and the emitter layer simultaneously. A method for manufacturing a solar cell.

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