JP6371894B2 - High efficiency back electrode type solar cell, solar cell module, and solar power generation system - Google Patents

Description

  The present invention relates to a high-efficiency back electrode type solar cell, a solar cell module, and a solar power generation system with good conversion efficiency.

  Generally, a solar cell is made of a plate-like polycrystalline silicon or single crystal silicon having a size of 100 to 150 mm square and a thickness of 0.1 to 0.3 mm, and is doped with a p-type impurity such as boron. The main material is a semiconductor substrate. In this solar cell, an n-type diffusion layer (emitter layer) and an antireflection film are formed on a light receiving surface that receives sunlight, and the electrode is formed so as to penetrate the antireflection film so as to be in contact with the emitter layer. .

  In solar cells, the electrode is indispensable for taking out the current obtained by photoelectric conversion, but sunlight is not incident on the part where the electrode of the light receiving surface is formed by shielding with the electrode, so the electrode area The larger the value, the lower the conversion efficiency and the current decreases. Such a loss of current due to the electrodes provided on the light receiving surface is called shadow loss.

  On the other hand, the back electrode type solar cell does not have an electrode on the light receiving surface, so there is no shadow loss, and almost 100% of incident sunlight is taken in except for the slight reflected light that cannot be suppressed by the antireflection film. Can do. Therefore, in principle, high conversion efficiency can be expected.

  Generally, the back electrode type solar cell 100 has a cross-sectional structure as shown in FIG. The back electrode type solar cell 100 includes a semiconductor substrate 101, an emitter layer 104, a BSF (Back Surface Field) layer 106, an antireflection film / passivation film 107 and 108, and electrodes 109 and 110.

  The semiconductor substrate 101 is a main material of the back electrode type solar cell 100 and is made of single crystal silicon, polycrystalline silicon, or the like. Either p-type or n-type may be used, but an n-type silicon substrate doped with an n-type impurity such as phosphorus is often used. Hereinafter, a case where an n-type silicon substrate is used will be described as an example. The semiconductor substrate 101 is preferably a plate having a size of 100 to 150 mm square and a thickness of 0.1 to 0.3 mm. One main surface is a light receiving surface and the other main surface is a non-light receiving surface ( Used as back side).

  An uneven structure for light confinement is formed on the light receiving surface. The uneven structure can be obtained by immersing the semiconductor substrate 101 in an acidic or alkaline solution for a certain period of time. Generally, this uneven structure is called a texture.

  On the back surface, an emitter layer 104 which is a p-type diffusion layer doped with a p-type impurity such as boron and a BSF layer 106 which is an n-type diffusion layer doped with an n-type impurity such as phosphorus are formed. Either the emitter layer 104 or the BSF layer 106 may be formed first. When the emitter layer 104 is formed first, for example, it is formed as follows.

First, a protective film 102 such as a silicon oxide film is formed on the entire surface of the semiconductor substrate 101. Specifically, for example, a silicon oxide film having a thickness of about 30 to 300 nm is formed by a thermal oxidation method in which the semiconductor substrate 101 is placed in a high temperature of 800 to 1100 ° C. in an oxygen atmosphere. Subsequently, a resist paste is applied by screen printing to the portion of the protective film 102 covering the region other than the region where the emitter layer 104 is formed on the back surface of the semiconductor substrate 101, and cured. Subsequently, the protective film 102 covering the region where the emitter layer 104 is formed is removed by immersion in a hydrofluoric acid aqueous solution, and further the resist paste 103 is removed by immersion in acetone or the like. Subsequently, a p-type impurity element is diffused in the region from which the protective film 102 has been removed, for example, by a thermal diffusion method, thereby forming an emitter layer 104 and a glass layer 105 which are p-type diffusion layers. Specifically, for example, by installing this semiconductor substrate 101 in a high-temperature gas at 800 to 1100 ° C. containing BBr ₃ , boron is diffused in a portion where the protective film 102 is not formed, and the sheet resistance is 20 to 300Ω. An emitter layer 104 and a glass layer 105 of about / □ are formed. Subsequently, the remaining protective film 102 and the glass layer 105 are removed by immersing them in a chemical such as a diluted hydrofluoric acid solution, and washed with pure water. Thereby, the emitter layer 104 in which the p-type impurity is diffused is formed at a desired location on the back surface of the semiconductor substrate 101.

  Subsequently, a BSF layer 106 is formed on the back surface of the semiconductor substrate 101 where the emitter layer 104 is not formed by a procedure substantially similar to that for the emitter layer 104.

  Antireflection films and passivation films 107 and 108 made of SiN (silicon nitride) are further formed on the light receiving surface on which the texture is formed and on the back surface on which the emitter layer 104 and the BSF layer 106 are formed.

  Then, the electrode 109 is formed so as to be connected to the emitter layer 104, and the electrode 110 is formed so as to be connected to the BSF layer 106. These electrodes may be formed by sputtering or the like with a contact being opened with an etching paste or the like, or may be formed using a screen printing method. When the screen printing method is used, conductive silver paste containing glass frit or the like is printed and dried at two locations of the antireflection film / passivation film 108 so as to be connected to the emitter layer 104 and the BSF layer 106 after firing. . By baking these conductive silver pastes, an electrode 109 connected to the emitter layer 104 and an electrode 110 connected to the BSF layer 106 are formed through the antireflection film and passivation films 107 and 108, respectively. Is done. The electrodes 109 and 110 are constituted by bus bar electrodes for taking out the photogenerated current generated in the back electrode type solar cell 100 to the outside, and finger electrodes for current collection connected to these bus bar electrodes (illustrated). (Omitted).

  In the general back electrode type solar cell having the structure shown in FIG. 1, the impurity diffusion profile of the emitter layer particularly affects the conversion efficiency of the solar cell. For example, by reducing the diffusion amount of impurities into the emitter layer and reducing the reverse saturation current density of the emitter layer, the open-circuit voltage of the solar cell can be increased and the conversion efficiency can be improved. However, if the surface concentration of impurities is lowered by reducing the amount of impurities diffused into the emitter layer, generally, the contact resistance with the electrode connected to the emitter layer is increased, resulting in poor conversion efficiency. Therefore, in order to improve the conversion efficiency, the contact resistance is reduced as much as possible by making the diffusion profile with a high impurity surface concentration and a shallow diffusion depth while suppressing the diffusion amount of the impurity into the emitter layer. On the other hand, it has been considered desirable to adopt a method of suppressing the reverse saturation current density from increasing as much as possible. In the emitter layer manufacturing method exemplified above, the emitter layer is often formed with a diffusion profile having a high impurity surface concentration and a shallow diffusion depth.

  Further, it is said that the contact resistance between the emitter layer and the electrode greatly depends on the contact area between the emitter layer and the electrode. In the case of a conventional solar cell having an electrode on the light receiving surface, in order to minimize the shadow loss due to the electrode, it is necessary to miniaturize the finger electrode connected to the emitter layer to minimize the electrode area, and the contact resistance is sufficient However, it is difficult to reduce the size of the electrode, and the electrode formation is expensive. On the other hand, in the back electrode type solar cell, since the electrode is formed on the non-light-receiving surface, it is not necessary to consider the shadow loss due to the electrode. Therefore, in the case of a back electrode type solar cell, in order to suppress the cost for electrode formation while increasing the width of the finger electrode to some extent and widening the contact area between the emitter layer and the electrode to reduce the contact resistance. In addition, it has been desirable to form a thin electrode so that the cross-sectional area (area of the surface orthogonal to the contact surface) is reduced to such an extent that the lateral flow resistance does not become too large. In the case of the electrode manufacturing method by screen printing exemplified above, an electrode having a large width and a small thickness is often formed.

  However, in order to diffuse impurities with a diffusion profile having a high surface concentration and a shallow diffusion depth, it is generally necessary to perform diffusion heat treatment at a high temperature for a short time. In this case, it is difficult to diffuse the impurities with a predetermined diffusion profile because uneven diffusion of impurities tends to occur particularly during mass production. In addition, the electrode having a large width and a small thickness often has a problem that the value of the contact resistance with the emitter layer may increase accidentally, resulting in poor yield.

  As a countermeasure against such a problem, for example, a film including a diffusion source is formed on a portion of the diffusion layer formed on the semiconductor substrate, and a heat treatment is performed in a water vapor atmosphere, so that a high temperature is provided only directly under the electrode. Patent Document 1 discloses a method for manufacturing a solar battery cell that forms a concentration diffusion layer. However, this method requires a plurality of heat treatments to form the diffusion layer, which increases the cost and causes a problem that the lifetime killer such as heavy metals diffuses into the semiconductor substrate and the yield tends to deteriorate. There is.

  Further, Patent Document 2 discloses a method for manufacturing a solar battery cell that performs uniform diffusion by applying and diffusing a dopant liquid on a substrate surface by inkjet printing. However, in the case of this method, there are problems that inkjet printing is difficult to control the nozzle and the dopant liquid, and that the formation of the diffusion source and the heat treatment are separate processes, resulting in high costs.

  Further, Patent Document 3 discloses a method for manufacturing a photovoltaic cell in which the conductive paste is screen-printed a plurality of times while changing the mask to reduce the electrode resistance. However, this method has a problem that the yield tends to be deteriorated due to the displacement of the electrodes and the cost is increased due to an increase in the amount of the conductive paste used.

  Further, Patent Document 4 discloses a method for manufacturing a solar cell in which electrodes are formed with high precision by forming electrodes by so-called gravure roll printing. However, in this method, it is difficult to control the roll and paste, and there is a problem that the roll is clogged and the yield is likely to deteriorate due to drying.

International Publication No. 2015/151288 JP 2003-168807 A International Publication No. 2011/111192 JP 2011-049514 A

  An object of the present invention is a high-efficiency back-electrode solar cell with high conversion efficiency, which has a low reverse saturation current density, a low contact resistance between an emitter layer and an electrode, and can be manufactured at a low yield with a simple method. The object is to provide a cell, a solar battery module, and a solar power generation system.

(1) In the high efficiency back electrode type solar cell of the present invention, an impurity diffusion layer in which a second conductivity type impurity is diffused is formed on the back surface which is a non-light-receiving surface of a first conductivity type semiconductor substrate, A high-efficiency back electrode type solar cell including an electrode connected to a diffusion layer, wherein the impurity surface concentration of the impurity diffusion layer is 5 × 10 ¹⁷ atms / cm ³ or more and 5 × 10 ¹⁹ atms / cm ³ or less. The impurity diffusion depth of the impurity diffusion layer is not less than 1 μm and not more than 2.9 μm from the surface of the back surface of the substrate.

  In this way, by forming an emitter layer with a lower surface concentration and a deep diffusion depth compared to conventional ones, both the reverse saturation current density and the contact resistance can be reduced, and a simple method and high efficiency at low cost. A back electrode type solar cell can be realized.

  (2) The sheet resistance of the impurity diffusion layer is preferably 60Ω / □ or more and 150Ω / □ or less.

(3) The maximum value of the impurity concentration of the impurity diffusion layer is set to 7 × 10 ¹⁷ atoms / cm ³ or more and 7 × 10 ¹⁹ atoms / cm ³ or less, and the position where the impurity concentration of the impurity diffusion layer becomes the maximum value is The depth is 0.1 μm or more and 1 μm or less from the back surface, the electrode is a sintered body containing at least glass frit, silver, and aluminum, the cross-sectional area of the electrode is 350 μm ² or more and 1000 μm ² or less, and the electrode diffuses impurities. The layer may partially penetrate, and the depth of penetration may be 0.1 μm or more and 1.9 μm or less from the front surface of the substrate.

  As a result, the contact resistance can be reduced to increase the conversion efficiency, and the manufacturing cost can also be reduced.

  (4) For example, the first conductivity type may be n-type and the second conductivity type may be p-type.

  (5) A solar cell module may be configured by electrically connecting a plurality of highly efficient back electrode type solar cells.

  (6) A photovoltaic power generation system may be configured by electrically connecting a plurality of solar cell modules.

It is a figure which shows an example of a structure of a highly efficient back electrode type photovoltaic cell. It is a flowchart which shows the manufacturing method of a highly efficient back electrode type photovoltaic cell. It is a graph which shows an example of the relationship between the depth from a substrate surface, and the impurity concentration in the depth. It is the graph which plotted the reverse direction saturation current density of each sample with respect to each of surface concentration and sheet resistance. It is the graph which plotted the contact resistance of each sample with respect to each of surface concentration and sheet resistance. It is a graph which shows the relationship between the cross-sectional area of the electrode of each sample, and contact resistance. It is the schematic which shows the structural example of the solar cell module comprised using the highly efficient back surface electrode type photovoltaic cell of this invention. It is the schematic which shows the structural example of the back surface of the solar cell module shown in FIG. It is the schematic which shows the structural example of the cross section of the solar cell module shown in FIG. It is the schematic which shows the structural example of the solar energy power generation system comprised using the solar cell module shown in FIG.

  Hereinafter, embodiments of the present invention will be described. Constituent elements in the drawings including the drawings used for the description of the background art are denoted by the same reference numerals.

  A high-efficiency back electrode type solar cell 200 according to the present invention has the same structure as the conventional back electrode type solar cell 100 shown in FIG. 1, and includes a semiconductor substrate 101, an emitter layer 104, a BSF layer 106, an antireflection coating. Film / passivation films 107 and 108 and electrodes 109 and 110 are provided. The semiconductor substrate 101 is a main material of the high-efficiency back electrode type solar cell 200, and is made of single crystal silicon, polycrystalline silicon, or the like. Either p-type or n-type may be used, but here, an example of an n-type silicon substrate containing an impurity such as phosphorus and having a specific resistance of 0.1 to 4.0 Ω · cm will be described. The semiconductor substrate 101 is preferably a plate having a size of 100 to 150 mm square and a thickness of 0.05 to 0.30 mm. One main surface is a light receiving surface and the other main surface is a non-light receiving surface ( Used as back side).

<Manufacturing procedure>
FIG. 2 shows a manufacturing procedure of the high-efficiency back electrode type solar cell 200 of the present invention. Prior to manufacturing, the semiconductor substrate 101 is immersed in an acid solution or the like to perform damage etching, and surface damage due to slicing or the like is removed, followed by washing and drying.

First, the emitter layer 104 is formed on the back surface of the semiconductor substrate 101 after the damage etching (S1). First, a protective film 102 such as a silicon oxide film is formed on the entire surface of the semiconductor substrate 101 (S1-1). For example, a silicon oxide film having a thickness of about 30 to 300 nm is formed by a thermal oxidation method in which the semiconductor substrate 101 is placed in a high temperature of 800 to 1100 ° C. in an oxygen atmosphere for a short time. Subsequently, a resist paste is applied by screen printing to a portion of the protective film 102 that covers a region other than the region where the emitter layer 104 is formed on the back surface of the semiconductor substrate 101, and is cured (S1-2). Subsequently, the protective film 102 that covers the region where the emitter layer 104 is to be formed is dipped in a hydrofluoric acid aqueous solution (S1-3), and further dipped in acetone or the like to remove the resist paste 103 (S1-4). Subsequently, a p-type impurity element is diffused in the region from which the protective film 102 has been removed, for example, by a thermal diffusion method, thereby forming an emitter layer 104 and a glass layer 105 which are p-type diffusion layers (S1-5). Specifically, for example, by placing this semiconductor substrate 101 in a high-temperature gas at 800 to 1100 ° C. containing BBr ₃ , boron is diffused in a region where the protective film 102 is not formed, and the sheet resistance is 20 to 300Ω. An emitter layer 104 and a glass layer 105 of about / □ are formed. Subsequently, the remaining protective film 102 and glass layer 105 are removed by immersing them in a chemical such as a diluted hydrofluoric acid solution, and washed with pure water (S1-6). Thereby, the emitter layer 104 in which the p-type impurity is diffused is formed at a desired location on the back surface of the semiconductor substrate 101.

  Next, a BSF layer 106 is formed in a region where the emitter layer 104 is not formed on the back surface of the semiconductor substrate 101 (S2). First, a protective film 102 such as a silicon oxide film is formed on the entire surface of the semiconductor substrate 101 (S2-1). The silicon oxide film is formed, for example, by a thermal oxidation method in which the semiconductor substrate 101 is placed at a high temperature of 800 to 1100 ° C. in an oxygen atmosphere. At this time, by increasing the installation time in high temperature, the silicon oxide film is formed, and at the same time, boron diffused near the surface of the semiconductor substrate 101 during the formation of the emitter layer 104 is diffused deeper into the semiconductor substrate 101. And can also be diffused into the formed silicon oxide film. As a result, the surface concentration of boron forming the emitter layer 104 decreases, and the sheet resistance changes accordingly. The diffusion depth, surface concentration, and sheet resistance can be appropriately adjusted by changing the thermal oxidation conditions.

Subsequently, a resist paste is applied by screen printing to the portion of the protective film 102 covering the region where the emitter layer 104 on the back surface of the semiconductor substrate 101 is formed (S2-2). Subsequently, the protective film 102 covering the region where the emitter layer 104 is not formed is removed by immersion in a hydrofluoric acid aqueous solution (S2-3), and further, the resist paste 103 is removed by immersion in acetone or the like (S2-4). ). Subsequently, the BSF layer 106 and the glass layer 105, which are n-type diffusion layers, are formed by diffusing an n-type impurity element in the region from which the protective film 102 has been removed, for example, by a thermal diffusion method (S2-5). Specifically, for example, by placing this semiconductor substrate 101 in a high temperature gas of 850 to 1100 ° C. containing POCl ₃ , phosphorus is diffused in a region where the protective film 102 is not formed, and the sheet resistance is 30 to 300Ω. A BSF layer 106 and a glass layer 105 of about / □ are formed. Subsequently, the remaining protective film 102 and glass layer 105 are removed by immersing them in a chemical such as a diluted hydrofluoric acid solution, and washed with pure water (S2-6). As a result, a BSF layer 106 in which n-type impurities are diffused is formed in a region where the emitter layer 104 is not formed on the back surface of the semiconductor substrate 101.

  Next, an uneven structure called texture is formed on the light receiving surface of the semiconductor substrate 101 (S3). The texture can be formed by immersing the semiconductor substrate 101 in an acidic or alkaline solution for a certain time. For example, the resist paste is applied and cured on the entire back surface of the semiconductor substrate 101 by screen printing, and then chemically etched with a potassium hydroxide aqueous solution or the like, washed and dried. By forming the texture, light incident from the light receiving surface is confined by multiple reflection in the semiconductor substrate 101, so that the reflectance can be effectively reduced and the conversion efficiency can be improved. Thereafter, the resist paste applied to the entire back surface of the semiconductor substrate 101 is removed by dipping in acetone or the like. Note that the texture may be applied before the emitter layer 104 and the BSF layer 106 are formed. Also, a texture may be formed on the back surface of the semiconductor substrate 101. In addition, an FSF (Front Surface Field) layer may be further formed on the light receiving surface of the semiconductor substrate 101.

Subsequently, anti-reflection films and passivation films 107 and 108 made of SiN (silicon nitride) or the like are formed on both surfaces of the semiconductor substrate 101 (S4). In the case of a silicon nitride film, for example, it is formed by a plasma CVD method or the like in which a mixed gas of SiH ₄ and NH ₃ is diluted with N ₂ and is plasmalized by glow discharge decomposition. In the formation, the refractive index is set to about 1.8 to 2.3 in consideration of the refractive index difference with the semiconductor substrate 101, and the thickness is set to about 50 to 100 nm. This film prevents the light from being reflected from the surface of the semiconductor substrate 101, and has a function of effectively taking the light into the semiconductor substrate 101, and also functions as a passivation film having a passivation effect on the n-type diffusion layer. In addition, there is an effect of improving the electrical characteristics of the solar battery cell. Note that the antireflection film / passivation films 107 and 108 may be a single-layer film such as silicon oxide, silicon carbide, amorphous silicon, aluminum oxide, or titanium oxide, or a laminated film combining these. Further, different films may be used for the light receiving surface and the back surface of the semiconductor substrate 101.

  Subsequently, electrodes 109 and 110 are formed (S5). The electrode may be formed by sputtering with an opening provided in the antireflection film / passivation film 108 with an etching paste or the like, or may be formed by screen printing. In the case of the screen printing method, first, for example, silver on each part of the antireflection film / passivation film 108 where the electrode 109 connected to the emitter layer 104 and the electrode 110 connected to the BSF layer 106 are formed. A conductive paste containing powder, glass frit, aluminum powder, varnish, and the like is screen-printed and dried. At this time, the width and cross-sectional area of the electrode can be adjusted as appropriate by changing the mesh roughness, emulsion thickness, opening size, etc. of the screen mask used for screen printing.

  The conductive paste printed in this manner is baked at a temperature of about 500 ° C. to 950 ° C. for about 1 to 60 seconds to penetrate the antireflection film / passivation film 108 (fire through). As a result, the sintered body containing silver, glass frit, and aluminum is electrically connected to the emitter layer 104 or the BSF layer 106 and becomes the electrodes 109 and 110. Note that the firing at the time of electrode formation may be performed at once or may be divided into a plurality of times. The conductive paste applied on the emitter layer 104 and the conductive paste applied on the BSF layer 106 may be different.

<Examination of problem solving means>
By the manufacturing method described above, a plurality of samples for measuring the reverse saturation current density of the emitter layer were produced while changing the thermal oxidation conditions. In addition, since an electrode is unnecessary for the measurement of reverse direction saturation current density, the electrode is not formed. The specific resistance of the n-type semiconductor substrate used for fabrication is 1 Ω · cm, the doping concentration of phosphorus is about 5 × 10 ¹⁵ atoms / cm ³ , and the anti-reflection film and passivation film are made of SiH ₄ , NH ₃ , and N ₂ . It is a silicon nitride film with a thickness of 100 nm formed by the plasma CVD method used.

For each sample, the diffusion profile of boron into the emitter layer was measured by SIMS (ims-4f, primary ion O ₂ ⁺ , primary ion energy 10.5 keV manufactured by CAMECA, used area, scanning area 200 × 200 μm, detection area) 104 μmφ, secondary ion polarity (Positive). FIG. 3 is a graph showing the relationship between the depth from the substrate surface and the concentration of boron, which is an impurity at that depth, obtained as a measurement result of a certain sample. As can be seen from FIG. 3, extreme density fluctuations are suddenly observed at a depth of 0 to 0.02 μm near the outermost surface. This density variation is considered to be a variation in the measured value due to the influence of foreign matter or unevenness on the substrate surface, and contains many errors. Therefore, in the following, the surface concentration is defined as a concentration around 0.03 μm. When defined in this way, the surface concentration of each sample produced was 1 × 10 ¹⁷ to 1 × 10 ²⁰ atoms / cm ³ . The diffusion depth is defined as a depth at which the diffused boron concentration obtained by SIMS measurement is equal to the phosphorus doping concentration to the n-type semiconductor substrate. When defined in this way, the diffusion depth of each produced sample was 0.7 to 3.5 μm.

  After measurement of the diffusion profile, the reverse saturation current density of each sample for measuring the reverse saturation current density was measured by the QSSPC method (WCT-100 manufactured by Sinton Consulting Co., Ltd.). FIG. 4 shows a graph in which the reverse saturation current density of each sample obtained by the QSSPC measurement is plotted with respect to the surface concentration and the sheet resistance. 4A is a graph plotted against the surface concentration, and FIG. 4B is a graph plotted against the sheet resistance. FIG. 4 shows that the reverse saturation current density tends to decrease as the surface concentration decreases, but has no correlation with the sheet resistance. That is, it can be said that the open circuit voltage can be increased by lowering the surface concentration, thereby improving the conversion efficiency.

  Next, a conductive paste was applied to each sample for measuring the reverse saturation current density in a pattern based on the TLM method, and baked at 800 ° C. for 10 seconds to prepare a plurality of samples for contact resistance measurement. The TLM method is widely used as a method for accurately measuring the contact resistance of a contact in such a manner that a current that enters the contact surface perpendicularly breaks at the device surface and flows in the horizontal direction. FIG. 5 shows a graph in which the contact resistance of each sample measured by the TLM method is plotted with respect to the sheet resistance and the surface concentration. FIG. 5 shows that the contact resistance has a positive correlation with the sheet resistance, but has no correlation with the surface concentration.

  From the above, in order to realize an emitter layer having a low reverse saturation current density and a low contact resistance, an emitter layer having a low surface concentration and a low sheet resistance may be formed. This condition can be easily satisfied by forming an emitter layer having a low surface concentration and a large diffusion depth. This is because the sheet resistance generally increases when the surface concentration is lowered, but the increase can be suppressed by increasing the diffusion depth.

  Next, among the contact resistance measurement samples, for the sheet resistance of 70 Ω / □, the finger electrode in contact with the emitter layer is formed with a constant width (60 μm) and the cross-sectional area changed, Contact resistance was measured. At this time, the cross-sectional area of the electrode was measured using a laser microscope VK-8500 manufactured by Keyence Corporation, and the contact resistance was measured using the TLM method. The cross-sectional area was changed by changing the thickness of the screen printing plate and the emulsion thickness. The contact resistance of the electrode thus measured was plotted against the cross-sectional area (FIG. 6). FIG. 6 shows that even if the electrode contact area is constant, the contact resistance increases and the conversion efficiency deteriorates when the cross-sectional area decreases. Therefore, it can be said that it is desirable to increase the cross-sectional area of the electrode as long as the cost permits.

  One of the reasons why the contact resistance is smaller when the electrode cross-sectional area is larger is as follows.

  When the electrode was formed by firing the conductive paste, a portion where the electrode penetrated into the substrate to a depth of about 2 μm at maximum was observed. Here, the penetration depth was measured by removing the electrode from the substrate by immersion in hydrofluoric acid and nitric acid, and observing the removal trace on the substrate with an SEM. The relationship between electrode penetration depth and contact resistance was confirmed for multiple samples. As a result, electrodes with high contact resistance with the emitter layer had almost no penetration and connection, and in rare cases, penetration occurred. Although it was shallow, the electrode with low contact resistance with the emitter layer was found to be deeply penetrated by many penetrations and connections. In other words, it is considered that the deeper the electrode penetrates, the lower the contact resistance. From this, it is considered that the contact resistance depends not only on the surface dopant concentration but also on the change in the dopant concentration in the depth direction. Specifically, it is considered that the contact resistance can be further reduced by the electrode penetrating to a depth that almost covers the range in which the impurity is diffused at a high concentration.

  However, if the cross-sectional area of the electrode is small at this time, the absolute amount of a substance that contributes to conduction with the emitter layer such as glass frit and aluminum constituting the electrode is insufficient, and the contact resistance increases. Therefore, in order to avoid an increase in contact resistance and to obtain a stable yield, it can be said that it is desirable to penetrate the electrode into the emitter layer to some extent, and to increase the cross-sectional area within the cost.

  The validity of the problem solving means identified by the above examination was verified using a plurality of products manufactured with different impurity diffusion profiles and electrode shapes. The manufacturing method and verification results of each product are shown below.

<First common process>
N-type silicon made of n-type single crystal silicon doped with phosphorus and sliced to a thickness of 0.2 mm and having a specific resistance of about 1 Ω · cm and a doping concentration of about 5 × 10 ¹⁵ atms / cm ³ A substrate was prepared, and outer diameter processing was performed to form a square plate with a side of 15 cm. The substrate was immersed in a fluorinated nitric acid solution for 15 seconds for damage etching, and then washed with pure water and dried.

A silicon oxide film having a thickness of 50 nm was formed on both surfaces of the substrate by thermally oxidizing the damaged n-type silicon substrate in an oxygen atmosphere at a temperature of 1000 ° C. for 45 minutes. Then, a resist paste was screen-printed on the BSF layer formation planned portion of the silicon oxide film formed on the back surface of the substrate, and dried by heating at a temperature of 100 ° C. Here, the screen printing plate was formed in such a pattern as to form an interdigitated back contact cell in which the emitter layer was 800 μm wide, the BSF layer was 200 μm wide, and the emitter layer and the BSF layer were alternately formed. As the resist paste, 185 paste manufactured by LEKTRACHEM was used. By immersing the substrate in a 2% hydrofluoric acid aqueous solution, the silicon oxide film is partially removed, leaving the portion where the BSF layer is to be formed, and then immersed in acetone to remove the resist paste. Washed with pure water and dried. Next, a thermal diffusion treatment is performed on the back surface of the substrate in a BBr ₃ gas atmosphere at a temperature of 900 ° C. for 20 minutes, whereby a p-type diffusion layer and a glass layer, which are emitter layers, are formed on the back surface of the substrate. Formed. The formed p-type diffusion layer had a sheet resistance of about 70Ω / □ and a diffusion depth of 0.5 μm. Thereafter, the substrate was immersed in a 25% hydrofluoric acid aqueous solution, washed with pure water, and dried to remove the silicon oxide film and the glass layer.

<Comparative Example 1>
Comparative Example 1 is a case in which the manufacturing method of the conventional product is employed because the thermal oxidation time performed in the protective film (silicon oxide film) forming process performed after forming the emitter layer as described above is short (45 minutes). . Specifically, after performing the following steps, the second and third common steps described later are performed to manufacture a back electrode type solar cell.

A silicon oxide film having a thickness of 50 nm was formed on both surfaces of the substrate by thermally oxidizing the substrate on which the emitter layer was formed as described above in an oxygen atmosphere at a temperature of 1000 ° C. for 45 minutes. By the heat treatment at this time, boron diffused in the emitter layer was re-diffused. The boron diffusion profile of the emitter layer after re-diffusion was measured by SIMS (ims-4f manufactured by CAMCA, primary ion O ₂ ⁺ , primary ion energy 10.5 keV, scanning area 200 × 200 μm, detection area 104 μmφ) Secondary ion polarity (Positive). As a result, the surface concentration is 1.0 × 10 ²⁰ atms / cm ³ , the maximum concentration is 1.4 × 10 ²⁰ atms / cm ³ , the maximum concentration depth is 0.07 μm, and the diffusion depth is 0.5 μm. became. The sheet resistance of the emitter layer was about 50Ω / □.

<Example 1>
In Example 1, the thermal oxidation time was extended to 90 minutes in Comparative Example 1.

The substrate on which the emitter layer was formed as described above was thermally oxidized in an oxygen atmosphere at a temperature of 1000 ° C. for 90 minutes, thereby forming a silicon oxide film with a thickness of 80 nm on both surfaces of the substrate. By the heat treatment at this time, boron diffused in the emitter layer was re-diffused. When the boron diffusion profile of the emitter layer after re-diffusion is measured by SIMS, the surface concentration is 5.0 × 10 ¹⁹ atms / cm ³ , the maximum concentration is 7 × 10 ¹⁹ atms / cm ³ , and the depth is the maximum concentration. Was 0.1 μm and the diffusion depth was 1.0 μm. The sheet resistance of the emitter layer was about 60Ω / □.

<Example 2>
In Example 2, the thermal oxidation time was extended to 120 minutes in Comparative Example 1.

A silicon oxide film having a thickness of 100 nm was formed on both surfaces of the substrate by thermally oxidizing the substrate on which the emitter layer was formed as described above in an oxygen atmosphere at a temperature of 1000 ° C. for 120 minutes. By the heat treatment at this time, boron diffused in the emitter layer was re-diffused. When the diffusion profile of boron in the emitter layer after re-diffusion is measured by SIMS, the surface concentration is 1.0 × 10 ¹⁹ atms / cm ³ , the maximum concentration is 1.2 × 10 ¹⁹ atms / cm ³ , and the maximum concentration is obtained. The depth was 0.4 μm and the diffusion depth was 2.0 μm. Further, the sheet resistance of the emitter layer was about 70Ω / □.

<Example 3>
In Example 3, the thermal oxidation time was extended to 180 minutes in Comparative Example 1.

The substrate on which the emitter layer was formed as described above was thermally oxidized in an oxygen atmosphere at a temperature of 1000 ° C. for 180 minutes, thereby forming a silicon oxide film with a thickness of 130 nm on both surfaces of the substrate. By the heat treatment at this time, boron diffused in the emitter layer was re-diffused. When the diffusion profile of boron in the emitter layer after re-diffusion is measured by SIMS, the surface concentration is 5.0 × 10 ¹⁸ atoms / cm ³ , the maximum concentration is 8.0 × 10 ¹⁸ atoms / cm ³ , and the maximum concentration is obtained. The depth was 0.7 μm and the diffusion depth was 2.3 μm. Further, the sheet resistance of the emitter layer was about 90Ω / □.

<Example 4>
In Example 4, the thermal oxidation time was extended to 240 minutes in Comparative Example 1.

The substrate on which the emitter layer was formed as described above was thermally oxidized in an oxygen atmosphere at a temperature of 1000 ° C. for 240 minutes, thereby forming a silicon oxide film with a thickness of 150 nm on both surfaces of the substrate. By the heat treatment at this time, boron diffused in the emitter layer was re-diffused. When the diffusion profile of boron in the emitter layer after re-diffusion is measured by SIMS, the surface concentration is 5.0 × 10 ¹⁷ atms / cm ³ , the maximum concentration is 7.0 × 10 ¹⁷ atms / cm ³ , and the maximum concentration is obtained. The depth was 1.0 μm and the diffusion depth was 2.9 μm. The sheet resistance of the emitter layer was about 280Ω / □.

<Comparative example 2>
Comparative Example 2 is a case where the thermal oxidation time is extended to 300 minutes in Comparative Example 1.

The substrate on which the emitter layer was formed as described above was thermally oxidized in an oxygen atmosphere at a temperature of 1000 ° C. for 300 minutes, thereby forming a silicon oxide film with a thickness of 160 nm on both surfaces of the substrate. By the heat treatment at this time, boron diffused in the emitter layer was re-diffused. When the diffusion profile of boron in the emitter layer after re-diffusion is measured by SIMS, the surface concentration is 3.0 × 10 ¹⁷ atms / cm ³ , the maximum concentration is 5.0 × 10 ¹⁷ atms / cm ³ , and the maximum concentration is obtained. The depth was 1.1 μm and the diffusion depth was 3.3 μm. Further, the sheet resistance of the emitter layer was about 320Ω / □.

<Second common process>
A resist paste is screen-printed on the portion where the emitter layer is formed in the silicon oxide film formed in the process shown in the first comparative example or the second comparative example, or the first, second, third, or fourth example. And dried by heating. Here, as the resist paste, 185 paste manufactured by LEKTRACHEM was used. The substrate on which the resist paste is printed is immersed in a 2% aqueous hydrofluoric acid solution to remove the silicon oxide film at the portion other than the portion where the emitter layer is formed (the portion where the BSF layer is formed). It was removed by immersion.

Subsequently, a thermal diffusion treatment was performed on the back surface of the substrate from which the silicon oxide film was partially removed in a POCl ₃ gas atmosphere at a temperature of 930 ° C. for 20 minutes, and the silicon oxide film was removed. Phosphorus was diffused to form an n-type diffusion layer as a BSF layer and a glass layer. The formed n-type diffusion layer had a sheet resistance of about 30Ω / □ and a diffusion depth of 0.5 μm. After that, these substrates were immersed in a 25% hydrofluoric acid aqueous solution, washed with pure water, and dried to remove the silicon oxide film and the glass layer.

  Subsequently, a resist paste was screen-printed on the entire back surface of the substrate and dried by heating at a temperature of 100 ° C. Here, as the resist paste, 185 paste manufactured by LEKTRACHEM was used. The substrate was chemically etched with a 70 ° C. solution containing 2% potassium hydroxide and 2% IPA for 5 minutes, washed with pure water, and dried to form a textured structure on the light receiving surface of the substrate. Thereafter, the substrate was immersed in acetone to remove the resist paste.

Subsequently, a silicon nitride film, which is an antireflection film and a passivation film, was formed with a thickness of 100 nm on both surfaces of the substrate by plasma CVD using SiH ₄ , NH ₃ , and N ₂ .

<Third common process>
A conductive silver paste was printed by a screen printing method on the emitter layer of the substrate that had been treated so far, and dried at 150 ° C. As the conductive silver paste, SOL9383M manufactured by Heraeus was used. On the BSF layer of the substrate, a conductive silver paste was printed by a screen printing method using a plate having a mesh 325, an emulsion thickness of 20 μm, and a linear opening having a width of 50 μm and dried at 150 ° C. Then, the printed conductive silver paste was baked at a maximum temperature of 800 ° C. for 5 seconds to form electrodes, and back electrode type solar cells according to respective comparative examples and examples were produced.

<Result 1>
The average conversion efficiency, average short-circuit current density, average open-circuit voltage, and average of back-electrode-type solar cells produced by 100 pieces each through the steps of Comparative Example 1 or 2, or Examples 1, 2, 3, or 4 The fill factor is shown in Table 1.

By making the surface concentration of the impurity of the emitter layer 5 × 10 ¹⁹ atms / cm ³ or less (Examples 1 to 4), the conversion efficiency is improved compared to the case of the conventional product having a high surface concentration (Comparative Example 1). I was able to increase it. This is presumably because the reverse saturation current density decreases and the open circuit voltage increases due to the decrease in the impurity surface concentration. At this time, the short-circuit current also rises. This is considered to be due to the fact that the gettering of the metal impurity to the diffusion layer has progressed due to the extension of the oxidation time, and the lifetime of the substrate has risen. However, if the surface concentration is too low as in Comparative Example 2, the lateral flow resistance of the emitter layer is increased, and the conversion efficiency cannot be sufficiently increased. Therefore, the upper limit of the surface concentration is desirably 5 × 10 ¹⁹ atms / cm ^3, which is thinner than the surface concentration of the conventional product shown in Comparative Example 1, and the lower limit is desirably 5 × 10 ¹⁷ atms / cm ³ . From the results of Examples 1 to 4, the lower limit of the diffusion depth is desirably 1 μm or more, which is deeper than the diffusion depth of the conventional product shown in Comparative Example 1, and the upper limit is desirably 2.9 μm or less. From the results of Examples 1 to 4, it is desirable that the lower limit of the sheet resistance is 60Ω / □, and the upper limit is 280Ω / □. However, if the upper limit is higher than 150Ω / □, the sheet resistance varies when produced in large quantities. Is so large that it becomes difficult to control, so the upper limit is more preferably set to 150Ω / □.

  Next, the effect of changing the shape of the electrode for reducing the contact resistance on the conversion efficiency will be verified.

<Comparative Example 3>
A conductive silver paste was printed on the BSF layer of the substrate subjected to the processing in Example 2 and the second common process by using a screen printing method, and dried at 150 ° C. As the conductive silver paste, SOL9412 manufactured by Heraeus was used. The main solid components of SOL9412 are silver and glass frit, and no aluminum powder is added.

Also, conductive silver paste is printed on the emitter layer of the substrate using a screen printing method using a mesh 360, an emulsion thickness of 10 μm, and a plate that is linearly opened with a width of 60 μm, and is dried at 150 ° C. I let you. Then, the board | substrate which printed the electroconductive silver paste was baked for 5 second at the maximum temperature of 800 degreeC, and the electrode was formed. The formed electrode had a width of about 70 μm, a thickness of about 8 μm, and a cross-sectional area of about 250 μm ² . Moreover, when the electrode on the semiconductor substrate formed in this way was removed with hydrofluoric acid and nitric acid and the penetration depth into the diffusion layer was measured by SEM, no penetration was found.

<Comparative example 4>
The comparative example 4 is a case where what added the aluminum powder as a conductive silver paste in the comparative example 3 is applied.

  A conductive silver paste was printed on the BSF layer of the substrate subjected to the processing in Example 2 and the second common process by using a screen printing method, and dried at 150 ° C. As the conductive silver paste, SOL9383M manufactured by Heraeus was used. The main solid components of SOL9343M are silver, glass frit and aluminum powder.

Also, conductive silver paste is printed on the emitter layer of the substrate using a screen printing method using a mesh 360, an emulsion thickness of 10 μm, and a plate that is linearly opened with a width of 60 μm, and is dried at 150 ° C. I let you. Then, the board | substrate which printed the electroconductive silver paste was baked for 5 second at the maximum temperature of 800 degreeC, and the electrode was formed. The formed electrode had a width of about 70 μm, a thickness of about 8 μm, and a cross-sectional area of about 250 μm ² . Moreover, when the electrode on the semiconductor substrate thus formed was removed with hydrofluoric acid and nitric acid, and the penetration depth into the emitter layer was measured by SEM, the maximum value of the penetration depth was 0.05 μm.

<Example 5>
In Example 5, the mesh applied to screen printing in Comparative Example 4 is 325, and the emulsion thickness is 20 μm.

  A conductive silver paste was printed on the BSF layer of the substrate subjected to the processing in Example 2 and the second common process by using a screen printing method, and dried at 150 ° C. As the conductive silver paste, SOL9383M manufactured by Heraeus was used.

Also, a conductive silver paste is printed on the emitter layer of the substrate using a screen printing method using a mesh 325, an emulsion thickness of 20 μm, and a plate that is linearly opened with a width of 60 μm and dried at 150 ° C. I let you. Then, the board | substrate which printed the electroconductive silver paste was baked for 5 second at the maximum temperature of 800 degreeC, and the electrode was formed. The formed electrode had a width of about 70 μm, a thickness of about 12 μm, and a cross-sectional area of about 350 μm ² . Moreover, when the electrode on the semiconductor substrate formed in this way was removed with hydrofluoric acid and nitric acid and the penetration depth into the diffusion layer was measured by SEM, the maximum value of the penetration depth was 0.1 μm.

<Example 6>
In Example 6, the mesh applied to screen printing in Comparative Example 4 is 290, and the emulsion thickness is 30 μm.

  A conductive silver paste was printed on the BSF layer of the substrate subjected to the processing in Example 2 and the second common process by using a screen printing method, and dried at 150 ° C. As the conductive silver paste, SOL9383M manufactured by Heraeus was used.

Also, conductive silver paste is printed on the emitter layer of the substrate using a screen printing method using a mesh 290, an emulsion thickness of 30 μm, and a straight plate with a width of 60 μm and dried at 150 ° C. I let you. Then, the board | substrate which printed the electroconductive silver paste was baked for 5 second at the maximum temperature of 800 degreeC, and the electrode was formed. The formed electrode had a width of about 70 μm, a thickness of about 15 μm, and a cross-sectional area of about 600 μm ² . Moreover, when the electrode on the semiconductor substrate thus formed was removed with hydrofluoric acid and nitric acid, and the penetration depth into the diffusion layer was measured by SEM, the maximum value of the penetration depth was 0.9 μm.

<Example 7>
In Example 7, the mesh applied to screen printing in Comparative Example 4 is 250, and the emulsion thickness is 30 μm.

  A conductive silver paste was printed on the BSF layer of the substrate subjected to the processing in Example 2 and the second common process by using a screen printing method, and dried at 150 ° C. As the conductive silver paste, SOL9383M manufactured by Heraeus was used.

On the emitter layer of the substrate, a conductive silver paste is printed using a plate having a mesh 250, an emulsion thickness of 30 μm, and a straight line having a width of 60 μm using a screen printing method, and dried at 150 ° C. I let you. Then, the board | substrate which printed the electroconductive silver paste was baked for 5 second at the maximum temperature of 800 degreeC, and the electrode was formed. The formed electrode had a width of about 70 μm, a thickness of about 15 μm, and a cross-sectional area of about 950 μm ² . Moreover, when the electrode on the semiconductor substrate thus formed was removed with hydrofluoric acid and nitric acid, and the penetration depth into the diffusion layer was measured by SEM, the maximum value of the penetration depth was 1.5 μm.

<Example 8>
In Example 8, the mesh applied to screen printing in Comparative Example 4 is 250, and the emulsion thickness is 40 μm.

  A conductive silver paste was printed on the BSF layer of the substrate subjected to the processing in Example 2 and the second common process by using a screen printing method, and dried at 150 ° C. As the conductive silver paste, SOL9383M manufactured by Heraeus was used.

Also, a conductive silver paste is printed on the emitter layer of the substrate using a screen printing method using a mesh 250, an emulsion thickness of 40 μm, and a plate that is linearly opened with a width of 60 μm and dried at 150 ° C. I let you. Then, the board | substrate which printed the electroconductive silver paste was baked for 5 second at the maximum temperature of 800 degreeC, and the electrode was formed. The formed electrode had a width of about 70 μm, a thickness of about 15 μm, and a cross-sectional area of about 1050 μm ² . Moreover, when the electrode on the semiconductor substrate formed in this way was removed with hydrofluoric acid and nitric acid and the penetration depth into the diffusion layer was measured by SEM, the maximum value of the penetration depth was 1.9 μm.

<Result 2>
Using the substrate subjected to the treatment shown in the above Comparative Example 3 or 4, or Example 5, 6, 7 or 8, 100 back electrode type solar cells according to each Comparative Example and Example were produced. , Average conversion efficiency, average short circuit current density, average open circuit voltage, and average fill factor were measured. The measurement results are shown in Table 2.

  From the comparison between Comparative Example 3 and Comparative Example 4, in order to penetrate the electrode into the emitter layer, it is desirable to form these sintered bodies by adding aluminum powder in addition to silver and glass frit to the conductive paste. I understand that. It can also be seen that the conversion efficiency is greatly improved by penetrating the emitter layer even a little.

  Comparing Comparative Example 4 with Examples 5 to 8, it can be seen that the conversion efficiency is better in the example. Especially the conversion efficiency in Examples 6-8 is excellent. This is because the electrode having a large cross-sectional area penetrates deeply beyond the maximum impurity concentration depth, so that the contact resistance is stably lowered and it is difficult to cause a significant decrease in the fill factor.

In addition, even if the cross-sectional area of the electrode is set to 1000 μm ² or more as in Example 8, it does not lead to a significant increase in conversion efficiency compared to the case of less than that. Rather, the cost increases due to an increase in the amount of electrode used, the risk that the electrode penetrates the emitter layer and the parallel resistance decreases due to the penetration depth becoming too deep, and the silver powder is sintered by increasing the cross-sectional area of the electrode. Considering that the formed silver electrode is likely to be peeled off from the substrate because of excessive sintering, it can be said that the upper limit of the electrode cross-sectional area is preferably about 1000 μm ² .

Therefore, from the results of Examples 5 to 8, the penetration depth is desirably 0.1 μm or more and 1.9 μm or less, and the cross-sectional area is desirably 350 μm ² or more and 1000 μm ² or less. The cross-sectional area and penetration depth of the electrode can be adjusted as appropriate by changing the roughness of the mesh and the emulsion thickness.

The above-described results of the method of Comparative Example 3 or 4, or Example 5, 6, 7 or 8 relate to the case where the electrode is formed on the substrate on which the emitter layer is formed by the method of Example 2. However, even when the electrode is formed on the substrate on which the emitter layer is formed by the method of Example 1, 3 or 4, the desired penetration depth and cross-sectional area of the electrode are the same. Therefore, based on the results of Examples 1 to 4, it is desirable that the maximum value of the impurity concentration in the emitter layer be 7 × 10 ¹⁷ atoms / cm ³ or more and 7 × 10 ¹⁹ atoms / cm ³ or less. The depth to be formed is desirably 0.1 μm or more and 1 μm or less from the front surface of the substrate.

  With the above configuration, it is possible to provide a high-efficiency back electrode type solar cell with good conversion efficiency that can be manufactured at a low yield and high cost by a simple method.

  The high-efficiency back electrode solar cell 200 manufactured according to the above embodiment can be used for a solar cell module. FIG. 7 is a schematic diagram illustrating a configuration example of the solar cell module 300. The solar cell module 300 has a structure in which a plurality of high-efficiency back electrode type solar cells 200 are tiled. The plurality of high efficiency back electrode type solar cells 200 are electrically connected in series with several to several tens adjacent to each other to form a series circuit called a string. An overview of the string is shown in FIG. FIG. 8 corresponds to a schematic diagram of the inner back surface side of the solar cell module 300 that is not normally touched by human eyes. In addition, in FIG. 8, illustration of a finger and a bus bar is abbreviate | omitted for clarity of description. In order to configure a series circuit, the P bus bar and the N bus bar of the high efficiency back electrode type solar cells 200 adjacent to each other are connected by the lead wire 320. FIG. 9 shows a schematic cross-sectional view of the solar cell module 300. As described above, the string is formed by connecting a plurality of high-efficiency back electrode type solar cells 200 to the bus bar 310 and the lead wires 320. The string is usually sealed with a light-transmitting filler 330 such as EVA (ethylene vinyl acetate), the non-light-receiving surface (back surface) side is a weather-resistant resin film 340 such as PET (polyethylene terephthalate), and the light-receiving surface is soda. It is covered with a light-receiving surface protective material 350 having high translucency and high mechanical strength such as lime glass. As the filler 330, polyolefin, silicone, or the like can be used in addition to EVA.

  Furthermore, a solar power generation system can be configured by connecting a plurality of solar cell modules. FIG. 10 is a schematic diagram showing a configuration example of a solar power generation system 400 in which a plurality of solar battery modules 300 each including a plurality of high-efficiency back electrode type solar cells 200 of the present invention are connected. In the solar power generation system 400, a plurality of solar cell modules 300 are connected in series by a wiring 410 and supplies generated power to the external load circuit 430 via the inverter 420. Although not shown in FIG. 10, the solar power generation system 400 may further include a secondary battery that stores the generated power.

  The present invention is not limited to the above-described embodiments and examples, and has substantially the same configuration as the technical idea described in the claims of the present invention, and has the same functions and effects. Any changes made are included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 100 Back electrode type solar cell 101 Semiconductor substrate 102 Protective film 103 Resist paste 104 Emitter layer 105 Glass layer 106 BSF layer 107,108 Antireflection film and passivation film 109,110 Electrode 200 High-efficiency back electrode type solar cell 300 Solar cell Module 310 Bus bar 320 Lead wire 330 Filler 340 Weather resistant resin film 350 Light-receiving surface protective material 400 Photovoltaic power generation system 410 Wiring 420 Inverter 430 External load circuit

Claims (6)

A high-efficiency back-electrode solar comprising an impurity diffusion layer formed by diffusing impurities of the second conductivity type on the back surface, which is a non-light-receiving surface of the first conductivity type semiconductor substrate, and an electrode connected to the impurity diffusion layer In battery cells,
The impurity surface concentration of the impurity diffusion layer is 5 × 10 ¹⁷ atoms / cm ³ or more and 5 × 10 ¹⁹ atoms / cm ³ or less,
Diffusion depth of the impurity of the impurity diffusion layer, Ri Oh on 1μm or more from the back surface,
The maximum value of the impurity concentration of the impurity diffusion layer is 7 × 10 ¹⁷ atoms / cm ³ or more and 7 × 10 ¹⁹ atoms / cm ³ or less,
The position where the impurity concentration of the impurity diffusion layer becomes the maximum value is at a depth of 0.1 μm or more and 1 μm or less from the surface of the back surface,
The electrode is
The impurity diffusion layer are partially penetrate the high efficiency back contact solar cell the depth of penetration is characterized 1.9μm or less der Rukoto least 0.1μm from the surface of the back side.   2. The high-efficiency back electrode solar cell according to claim 1, wherein the impurity diffusion layer has a sheet resistance of 60Ω / □ or more and 150Ω / □ or less. The electrode is
A sintered body containing at least glass frit, silver and aluminum,
High efficiency back contact solar cell according to claim 1 or 2 cross-sectional area is equal to or is 350 .mu.m ² or more 1000 .mu.m ² or less.   The high efficiency back electrode type solar cell according to any one of claims 1 to 3, wherein the first conductivity type is n-type and the second conductivity type is p-type.   The solar cell module formed by electrically connecting a plurality of high-efficiency back electrode type solar cells according to any one of claims 1 to 4.   A photovoltaic power generation system formed by electrically connecting a plurality of the solar cell modules according to claim 5.

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