JP2011187906A - Solar cell element and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell element which improves reliability and makes photoelectric conversion efficiency excellent by enhancing the joining of a semiconductor substrate side and an electrode for taking out generated power and the extraction of a carrier, and a method of manufacturing the same. <P>SOLUTION: The invention relates to a solar cell element 1 which has a semiconductor substrate 2 including a semiconductor layer of one conductivity type and a semiconductor layer of a reverse conductivity type and in which at least one principal surface of the semiconductor substrate 2 is the semiconductor layer of the reverse conductivity type and electrodes 3-6 for taking out generated power are formed on the other principal surface opposed to the one principal surface of the semiconductor substrate and on the semiconductor layer of the reverse conductivity type where the electrodes 3 and 4 formed on the semiconductor layer of the reverse conductive type contain at least silver and copper. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  In a solar cell element using a semiconductor substrate, a conductive paste mainly composed of silver is applied to a light receiving surface side and a back surface side thereof in a predetermined pattern shape by using a screen printing method, so that silver is a main component. Electrode may be formed.

  For example, a conductive paste mainly composed of aluminum is applied on the back surface of a silicon substrate using a screen printing method, and this is baked to form a collecting electrode. Thereafter, a conductive paste containing silver as a main component is applied onto the current collecting electrode and then fired to form an extraction electrode (see Patent Documents 1 to 3 below).

JP 11-312813 A JP 2008-109016 A JP 2007-266649 A

  However, the ohmic contact property between the silicon substrate and the silver-based electrode is poor. For this reason, since the carrier cannot be taken out at this portion, it has been a cause of a decrease in photoelectric conversion efficiency of the solar cell element.

  The present invention has been made in view of such problems, and the object thereof is to improve the reliability and photoelectric conversion efficiency by improving the bonding between the substrate side and the electrode for taking out the generated power and the taking out of the carrier. It is providing the solar cell element excellent in, and its manufacturing method.

  A solar cell element according to an embodiment of the present invention includes a semiconductor substrate having a one-conductivity-type semiconductor layer and a reverse-conductivity-type semiconductor layer, and at least one main surface of the semiconductor substrate is a reverse-conductivity-type semiconductor layer. A solar cell element in which an electrode for taking out generated power is formed on each of the other main surface opposite to the one main surface of the semiconductor substrate and the reverse conductivity type semiconductor layer, wherein the reverse conductivity type The electrode formed on the semiconductor layer contains at least silver and copper.

  Further, in the method for manufacturing a solar cell element according to one aspect of the present invention, the electrode formed on the reverse conductivity type semiconductor layer is formed by applying a conductive paste containing a large number of copper fillers coated with silver on the surface. It is characterized by being formed by firing.

  Furthermore, in the method for manufacturing a solar cell element according to one embodiment of the present invention, the electrode formed on the reverse conductivity type semiconductor layer is applied with a conductive paste containing a large number of silver fillers and copper fillers and fired. It was formed by this.

According to the solar cell element and the manufacturing method thereof according to one embodiment of the present invention, it is possible to improve the bonding strength between the electrode and the semiconductor substrate side, and it is possible to provide a solar cell element with high reliability and excellent photoelectric conversion efficiency. .

It is a figure which shows typically an example of the double-sided electrode type solar cell element which concerns on one form of this invention, (a) is a top view which shows an example of the light-receiving surface side external appearance of a solar cell element, (b) is a solar cell element It is a top view which shows an example of the back side external appearance. (A)-(e) is sectional drawing which shows typically the manufacturing process of the double-sided electrode type solar cell element which concerns on one form of this invention. It is sectional drawing which showed typically the cross section of the copper filler which coated silver on the surface. (A), (b) is a graph which shows the relationship between the mass ratio of silver and copper of an electrically conductive paste, and the joint strength after baking of an electrically conductive paste, respectively. (A) is a top view of a test piece, (b) is a graph which shows the relationship between the mass ratio of silver and copper of an electrically conductive paste, and the resistance value after baking of an electrically conductive paste. It is a figure which shows typically an example of the back contact type solar cell element which concerns on one form of this invention, (a) is a top view which shows an example of the light-receiving surface side external appearance of a solar cell element, (b) is a solar cell element It is a top view which shows an example of the back side external appearance. It is a figure which shows typically an example of the back contact type solar cell element which concerns on one form of this invention, (a) is XX direction sectional drawing of Fig.4 (a), (b) is FIG.4 (a). It is a YY direction sectional drawing.

  Hereinafter, an example of a solar cell element according to one embodiment of the present invention will be described with reference to the drawings.

<< Basic configuration of solar cell element and manufacturing method thereof >>
The basic configuration (hereinafter referred to as type 1) of the solar cell element of this embodiment includes a semiconductor substrate having a one-conductivity-type semiconductor layer and a reverse-conductivity-type semiconductor layer, and at least one main surface of the semiconductor substrate is reverse-conductivity. A reverse-conductivity type semiconductor layer is formed on at least one main surface of the semiconductor substrate, and the other main surface (hereinafter referred to as the first surface) facing the one main surface (hereinafter referred to as the first surface) of the semiconductor substrate. It is assumed that an electrode for taking out the generated power is formed on each of the semiconductor layers of the second surface and the reverse conductivity type. For example, the electrode formed on at least one of the second surface of the semiconductor substrate and the semiconductor layer of the reverse conductivity type contains silver and copper.

  In addition, you may employ | adopt the following structures (henceforth, type 2) included in the said type 1. FIG. For example, when a semiconductor substrate of one conductivity type and a reverse conductivity type semiconductor layer formed on at least the first surface of the semiconductor substrate are provided, that is, the semiconductor substrate is regarded as a type 1 semiconductor substrate as a whole. A semiconductor substrate having a semiconductor layer and a reverse conductivity type semiconductor layer (one conductivity type semiconductor substrate + reverse conductivity type semiconductor layer or the like) may be provided. In this case, the same operation and effect as described above can be expected. .

  Here, in particular, only the electrode formed on the second surface of the semiconductor substrate may contain silver and copper. The electrode formed on the reverse conductivity type semiconductor layer may be formed only on the first surface side of the semiconductor substrate. In addition, the electrode formed on the reverse conductivity type semiconductor layer may also be formed on the second surface side of the semiconductor substrate. In this case, there are many through holes penetrating both main surfaces of the semiconductor substrate. The reverse conductivity type semiconductor layer is also formed in the through hole, a conductor is provided in the through hole, and the electrode formed on the semiconductor layer is connected to the second of the semiconductor substrate via the conductor. It may be led out and formed also on the surface side. In this case, the conductor provided in the through hole may contain at least silver and copper.

Moreover, in order to manufacture the solar cell element having the above-described configuration, the electrode formed on the reverse conductivity type semiconductor layer is applied with a conductive paste containing a large number of copper fillers coated on the surface of silver, for example, and fired. To form. Or you may form, for example by knead | mixing a silver filler, a copper filler, an organic vehicle, etc., apply | coating the electrically conductive paste adjusted to the predetermined viscosity, and baking.

  Below, a solar cell element is a double-sided electrode type solar cell element in which electrodes having different polarities are provided on a first surface which is a light-receiving surface of a semiconductor substrate and a second surface which is a back surface opposite to the first surface. A back contact solar cell element provided with a conductive electrode will be described separately.

  The material used for the power generation part of the solar cell element is not limited as long as it can be produced even at a temperature (500 ° C. or higher) at which the electrode material for extracting power from the power generation part is sintered, For the sake of simplicity, this embodiment will describe type 1 of a silicon-based solar cell element.

<< Double-sided electrode type solar cell element >>
As shown in FIGS. 1A and 1B, a double-sided electrode type solar cell element 1 includes a first surface 2a that is a light receiving surface on which light is incident and a second surface 2b that is a back surface opposite to the first surface 2a. A semiconductor substrate 2, a bus bar electrode 3 and a finger electrode 4 provided on the first surface 2a of the semiconductor substrate 2, a current collecting electrode 5 provided on the second surface 2b, an output extraction electrode 6, Have

  The semiconductor substrate 2 is made of, for example, a silicon wafer made of, for example, single crystal silicon or polycrystalline silicon, and has a rectangular flat plate shape with a side of about 150 to 160 mm, for example. The semiconductor substrate 2 has a one-conductivity-type semiconductor layer and a reverse-conductivity-type semiconductor layer. That is, inside the silicon wafer, there are a p-type silicon layer and an n-type silicon layer, and a junction (pn junction) portion is formed. In this silicon wafer, as will be described later, for example, a pn junction is formed by a bulk layer of one conductivity type and a surface layer of reverse conductivity type. As described above, the solar cell element 1 mainly includes the one-conductivity-type semiconductor substrate 2, and the reverse-conductivity-type semiconductor layer is formed on at least one main surface of the semiconductor substrate 2.

  The electrodes formed on the first surface 2a are provided so as to intersect the bus bar electrode 3 having a width of about 1 mm to 3 mm and the bus bar electrode 3 so as to be substantially perpendicular to the bus bar electrode 3, and have a width of about 50 to 200 μm. It consists of finger electrodes 4. The thickness of the bus bar electrode 3 and the finger electrode 4 is about 10 to 20 μm. Further, it is desirable to form an antireflection film 8 in advance on the entire surface of the first surface 2a.

  The electrodes formed on the second surface 2 b are the collector electrode 5 and the output extraction electrode 6. The thickness of the output extraction electrode 6 is about 10 μm to 20 μm, and the width is about 3.5 mm to 7 mm. Moreover, the thickness of the current collection electrode 5 is about 15 micrometers-50 micrometers.

  The finger electrode 4 and the current collecting electrode 5 have a role of collecting generated carriers, and the bus bar electrode 3 and the output extraction electrode 6 are carriers (electric power) collected by the finger electrode 4 and the current collecting electrode 5. Has a role to collect and output to the outside.

  Next, the operation of the solar cell element 1 will be described. When light enters from the first surface 2 a side of the solar cell element 1, this light is absorbed and photoelectrically converted (electron-hole pairs (electron carriers and hole carriers) are generated) in the semiconductor substrate 2. The electron carriers and hole carriers (photogenerated carriers) originating from the photoexcitation are collected on the electrodes provided on the first surface 2a and the second surface 2b of the solar cell element 1 by the above-described action of the pn junction, A potential difference occurs between the electrodes.

<< Method for Manufacturing Solar Cell Element >>
Next, an example of a method for manufacturing this type of solar cell element 1 will be described.

  First, as shown in FIG. 2A, a semiconductor substrate 2 made of single conductivity type single crystal or polycrystalline silicon is prepared. The semiconductor substrate 2 is preferably a p-type substrate having a p-type conductivity such as boron (B) and having a specific resistance of about 0.2 to 2.0 Ω · cm. In some cases, an n-type substrate may be used as one conductivity type. Hereinafter, a p-type substrate will be described as an example.

  When the semiconductor substrate 2 is a single crystal silicon wafer, it is manufactured by a pulling method such as the Czochralski method. When the semiconductor substrate 2 is a polycrystalline silicon wafer, it is manufactured by a casting method or the like.

  Since a polycrystalline silicon wafer can be mass-produced and is more advantageous than a single crystal silicon wafer in terms of manufacturing cost, an example in which polycrystalline silicon is used as the semiconductor substrate 2 will be described below.

  The polycrystalline silicon ingot is sliced to a thickness of 350 μm or less, more preferably 200 μm or less, using a wire saw, for example, to form the semiconductor substrate 2. In order to clean the contaminated layer at the time of slicing attached to the surface of the semiconductor substrate 2, it is desirable that the surface be etched by a very small amount using NaOH, KOH, a mixed solution of hydrofluoric acid and hydrofluoric acid, or the like.

  Next, on the first surface 2a side of the semiconductor substrate 2, using a dry etching method or a wet etching method, an unevenness (roughened surface) having a light reflectance reduction function using an RIE (reactive ion etching) apparatus or the like. It is preferable to form a structure.

  Thereafter, as shown in FIG. 2B, an n-type layer 9 is formed on the entire surface of the semiconductor substrate 2. P (phosphorus) is preferably used as the n-type doping element, and the n-type having a sheet resistance of about 30 to 300 Ω / □ is used. As a result, a pn junction is formed between the n-type layer 9 and the p-type bulk region 10.

The n-type layer 9 is formed, for example, in a POCl ₃ (phosphorus oxychloride) atmosphere in which the semiconductor substrate 2 is heated to about 700 to 900 ° C. and kept in this temperature and in a gas state used as the diffusion source 22. Then, it is performed by treating for about 20 to 40 minutes by vapor phase thermal diffusion method or the like. Thereby, the n-type layer 9 is formed to a thickness of about 0.2 to 0.7 μm. At this time, phosphorous glass is formed on the entire surface of the semiconductor substrate 2. Therefore, in order to remove the phosphorous glass, it is necessary to immerse the semiconductor substrate 2 in hydrofluoric acid and to wash and dry it.

  After that, as shown in FIG. 2C, the portion of the n-type layer 9 formed on the outer peripheral portion of the end surface of the second surface 2b of the semiconductor substrate 2 is removed, and pn separation is performed by the removing portion 7. The removal of the n-type layer 9 is performed by a sandblasting method in which alumina or silicon oxide particles are sprayed onto the outer peripheral portion of the second surface 2b of the silicon wafer at a high pressure, or a YAG (yttrium, aluminum, garnet) laser, etc. This is done by forming a separation groove reaching the pn junction. Thereby, pn separation can be performed.

Further, after this pn separation, an antireflection film 8 is formed on the first surface 2a as shown in FIG. Examples of the material of the antireflection film 8 include a SiNx film (wherein the composition ratio “x” has a width centered on Si ₃ N ₄ stoichiometry), a TiO ₂ film, a SiO ₂ film, a MgO film, and an ITO film. A SnO ₂ film, a ZnO film, or the like can be used. The thickness of the antireflection film 8 is appropriately selected depending on the material so that an antireflection condition can be realized with respect to appropriate incident light. For example, in the case of the semiconductor substrate 2, the refractive index may be about 1.8 to 2.3 and the thickness may be about 500 to 1200 mm. As a manufacturing method of the antireflection film 8, a PECVD method, a vapor deposition method, a sputtering method, or the like can be used.

Next, as shown in FIG. 2D, the collector electrode 5 is formed on the second surface 2 b side of the semiconductor substrate 2. The current collecting electrode 5 is formed by applying a paste mainly composed of aluminum to substantially the entire second surface 2b except for the outer peripheral portion of about 1 to 5 mm on the second surface 2b. As the coating method, a screen printing method or the like can be used. The paste used to form the current collecting electrode 5 is made of aluminum powder and an organic vehicle. After applying this paste, heat treatment (firing) is performed at a temperature of about 700 to 850 ° C. to bake aluminum onto the semiconductor substrate 2. . This aluminum paste is printed and fired. As a result, aluminum, which is a p-type impurity, can be diffused at a high concentration in the coated portion of the semiconductor substrate 2, and the n-type layer formed also on the back surface side can be made p ⁺ -type.

  Next, as shown in FIG. 2E, electrodes (bus bar electrodes 3 and finger electrodes 4) on the first surface 2a and output extraction electrodes 6 on the second surface 2b are formed.

  Thus, the output extraction electrode 6 on the second surface 2b can be formed by applying the conductive paste.

  Hereinafter, the case where a coating filler is used and the case where a mixed filler is used as the conductive paste will be described.

<Example using coating filler>
The example using the copper filler which coated silver on the surface is demonstrated. As shown in FIG. 3, the copper filler 13 coats the surface of the copper body 14 with the silver layer 15. Here, the copper filler 13 is, for example, a spherical shape having a diameter of about 0.1 to 10 μm, but is not limited to this shape. For example, the copper filler 13 may have a rugby ball shape having an elliptical cross section or a polyhedral shape having corners. Good. Note that fine irregularities may be formed on the surface of the copper body 14. The material of the copper filler 14 is preferably copper having a purity of 99.9% by mass or more. In particular, in order to reduce the series resistance component of the solar cell element 1, oxygen-free copper having a low resistance can be more suitably used.

  The surface of the copper body 14 is coated with a silver layer 15 with a thickness of about 0.005 μm to 0.1 μm. Since this coating can be performed with a uniform thickness, it is desirable to carry out the replacement method. The silver layer 15 to be coated preferably has a purity of 99.9% by mass or more.

  The conductive paste forming the output extraction electrode 6 on the second surface 2b is composed of a large number of copper fillers 13 coated with a silver layer 15 on the surface, an organic vehicle and glass frit, and a copper filler 13 coated with a silver layer 15 on the surface. What added 10-20 mass parts of organic vehicles and 5-15 mass parts of glass frit with respect to 100 mass parts which consist of many is added. Furthermore, what adjusted the viscosity of the grade of 50-200 Pa * s using solvents, such as a terpineol, can be used.

  As the coating method, a screen printing method or the like can be used, and it is preferable that the solvent is evaporated and dried at a predetermined temperature after coating.

After applying a conductive paste containing a copper filler 13 coated with a silver layer 15 on the surface of the collecting electrode 5, firing is performed at a maximum temperature of 500 to 650 ° C. for several tens of seconds to several tens of minutes in a firing furnace. Thus, back electrodes (collecting electrode 5, output extraction electrode 6) are formed. In firing the conductive paste containing the copper filler 13 having the silver layer 15 coated on the surface, the copper filler 13
In order to suppress the oxidation, it is desirable to introduce an inert gas such as nitrogen gas into the furnace so that the oxygen concentration near the peak temperature in the furnace becomes 100 ppm to 500 ppm.

  Usually, in the formation of the output extraction electrode 6 of the solar cell element 1, when a conductive paste mainly composed of silver is used, the bonding strength between the current collection electrode 5 mainly composed of aluminum and the output extraction electrode 6 is weak. This is because sufficient adhesive force cannot be obtained due to the surface oxidation of aluminum in the collecting electrode 5 mainly composed of aluminum.

  For this reason, in the solar cell module manufacturing process after the completion of the solar cell element 1, the output extraction electrode 6 may be peeled off due to soldering of the connection tab for connecting the solar cell elements to the output extraction electrode 6 or the like. was there. Therefore, as a countermeasure against this, when a paste mainly composed of aluminum for forming the collecting electrode 5 is applied to the second surface 2b, a part of the aluminum is mainly disposed at a position where the output extraction electrode 6 is disposed. The part to which the paste to be applied is not intentionally produced. As a result, a portion where the semiconductor substrate 2 and the output extraction electrode 6 are in direct contact with each other was produced, and the peeling of the output extraction electrode 6 in the subsequent process was suppressed by utilizing the strong bonding strength of this portion.

  However, with such a structure, the p-type silicon and the silver electrode have poor ohmic contact properties, so that the photogenerated carriers cannot be taken out at this portion, so that loss occurs and the photoelectric conversion efficiency of the solar cell element decreases. It was a cause.

  On the other hand, in the solar cell element of the present embodiment, the output extraction electrode 6 on the second surface 2b is formed by applying a conductive paste containing a copper filler 13 having a silver layer 15 coated on the surface. For this reason, it is possible to sufficiently strengthen the bonding strength between aluminum and copper, which are the main components of the current collecting electrode 5, so that there is no fear of peeling of the output extraction electrode 6 even in the above-described solar cell module process. Thereby, reliability can be improved. Moreover, when forming the current collection electrode 5, it is not necessary to provide the part in which the paste which mainly has aluminum as a main component is not apply | coated. Thereby, the part which the semiconductor substrate 2 and the output extraction electrode 6 contact | connect directly can be eliminated, and it becomes possible to improve the photoelectric conversion efficiency of a solar cell element. Furthermore, the amount of expensive silver used in the conductive paste can be reduced.

  In addition, the electrode forming step on the second surface 2b side is a conductive paste containing a large number of copper fillers coated with silver on the surface after applying and baking aluminum paste as described above to form the current collecting electrode 5 May be applied and baked to form the output extraction electrode 6, and the baking process may be made separate. Or after apply | coating and drying an aluminum paste, the electrically conductive paste containing many copper fillers which coated silver on the surface may be apply | coated, and both may be baked simultaneously.

  Next, the electrodes (bus bar electrode 3 and finger electrode 4) on the first surface 2a of the semiconductor substrate 2 can be formed by using a conductive paste containing a copper filler 13 coated with a silver layer 15 in the same manner. It is. That is, the bus bar electrode 3 and the finger electrode 4 are formed on the antireflection film 8 by directly applying and baking the conductive paste containing the copper filler 13 having the silver layer 15 coated on the surface. As a result, the glass component in the electrode breaks through the antireflection film 8 when the electrode on the first surface 2a is baked, and the n-type layer 9 is directly below the electrode. Thereby, the bus-bar electrode 3 and the finger electrode 4 of the 1st surface 2a, and the n-type layer 9 can be made to contact electrically. If the conductive paste containing the copper filler 13 having the surface coated with the silver layer 15 is used for the electrode of the first surface 2a, the manufacturing cost may be improved.

Moreover, it is also possible to form the electrode of the 1st surface 2a with the electrically conductive paste which has normal silver as a main component. The conductive paste containing silver as a main component is obtained by adding 5 to 30 parts by mass of an organic vehicle and 0.1 to 10 parts by mass of glass frit with respect to 100 parts by mass of metal powder silver composed of silver, It can be formed by applying a paste-like silver paste in a predetermined electrode shape and firing it at a maximum temperature of 600 to 850 ° C. for several tens of seconds to several tens of minutes. As the coating method, a known method such as a screen printing method can be used.

<Electrode formation using mixed filler>
The conductive paste for forming the output extraction electrode 6 includes, for example, a large number of silver fillers, a large number of copper fillers, an organic vehicle, and a glass frit with respect to a total of 100 parts by mass of silver and copper, respectively. .1-15 parts by mass, kneaded, and adjusted to a viscosity of about 50-200 Pa · s using a solvent may be used.

  In this kneading, a large number of silver fillers, an organic vehicle, and glass frit are kneaded in the above ratio to form a paste. In parallel with this operation, a large number of copper fillers, organic vehicle, and glass frit are kneaded at the above ratios to form a paste. Then, these two pastes are prepared in advance, these pastes are kneaded at a predetermined ratio, and then a predetermined viscosity is adjusted using a solvent. Thereby, since the filler of silver and copper mixes more uniformly, it is preferable.

  As the coating method, a screen printing method or the like can be used, and it is preferable that the solvent is evaporated and dried at a predetermined temperature after coating.

  After applying and drying a conductive paste containing silver and copper on the collecting electrode 5, the output extraction electrode 6 is baked for several tens of seconds to several tens of minutes at a maximum temperature of 500 to 650 ° C. in a baking furnace. Form. In firing the conductive paste containing silver and copper, in order to prevent oxidation of the contained copper filler, nitrogen gas or the like is not used so that the oxygen concentration near the peak temperature in the furnace is less than 500 ppm. It is desirable to introduce the active gas into the furnace.

  Usually, in the formation of the output extraction electrode 6 of the solar cell element, when a conductive paste mainly composed of silver is used, the bonding strength between the current collection electrode 5 mainly composed of aluminum and the output extraction electrode 6 is weakened. For this reason, in the solar cell module manufacturing process after the completion of the solar cell element, there is a concern that peeling of the output extraction electrode 6 may occur due to soldering of the connection tab for connecting the solar cell elements to the output extraction electrode 6. there were. As a countermeasure for this, when a paste mainly composed of aluminum for forming the collecting electrode 5 is applied to the second surface 2b, aluminum is partially used where the output extraction electrode 6 is disposed. The part where the paste as a component was not applied was intentionally made. As a result, a portion where the semiconductor substrate 2 and the output extraction electrode 6 are in direct contact with each other is manufactured, and peeling of the output extraction electrode 6 in a later process is prevented by utilizing the strong bonding strength of this portion.

  However, with such a structure, the p-type silicon and the silver electrode have poor ohmic contact properties, so that the photogenerated carriers cannot be taken out at this portion, causing a loss and a factor in reducing the photoelectric conversion efficiency of the solar cell element. It was.

  On the other hand, in the solar cell element according to the present invention, the output extraction electrode 6 on the second surface 2b is formed by applying a conductive paste containing silver and copper, and thus is the main component of the current collecting electrode 5. The bonding strength between aluminum and copper can be sufficiently strengthened so that the output extraction electrode 6 does not have to be peeled off even in the above-described solar cell module process, and the reliability can be improved.

  Further, when forming the current collecting electrode 5, it is not necessary to intentionally make a part where a paste mainly composed of aluminum is not applied, and a part where the semiconductor substrate 2 and the output extraction electrode 6 are in direct contact may be eliminated. It is possible to improve the photoelectric conversion efficiency of the solar cell element. Furthermore, since the amount of silver used in the conductive paste can be reduced, the manufacturing cost is sufficient.

  Furthermore, as a result of tests repeatedly conducted by the inventors, it is desirable that the mass ratio of silver and copper contained in the conductive paste is in the range of silver: copper = 2: 8 to 7: 3.

  FIG. 4A shows a collector electrode formed by applying and baking a paste mainly composed of aluminum as described above on the semiconductor substrate 2 over substantially the entire second surface 2b using a screen printing method. The current collector of the output extraction electrode 6 formed by applying a conductive paste in which the mass ratio of silver and copper is changed onto a predetermined electrode pattern using a screen printing method and baking at a maximum temperature of about 600 ° C. It is the result of measuring the bonding strength with the electrode 5.

  As shown in FIG. 4A, in the output extraction electrode 6 on the collector electrode 5 on the second surface 2b, the silver: copper mass ratio of silver and copper is in the range of 10: 0 to 8: 2. Bonding strength is weak due to insufficient copper / aluminum alloy formation, and silver: copper increases from 10: 0 to 7: 3 due to an increase in copper / aluminum alloy formation, which shows a sharp rise. it is conceivable that. Furthermore, in the range of silver: copper = 2: 8 to 0:10, the ratio of oxidized copper increases, so it seems that the ratio rapidly decreases from silver: copper = 2: 8 to 0:10.

  Further, in the electrode forming step on the second surface 2b side, as described above, the aluminum paste is applied and baked to form the collecting electrode 5, and then the conductive paste containing silver and copper is applied and baked for output. The extraction electrode 6 may be formed to separate the firing process, or after applying and drying an aluminum paste, applying a conductive paste containing a copper filler coated with silver on the surface, and firing both at the same time Good.

  Next, electrodes (bus bar electrodes 3 and finger electrodes 4) on the first surface 2a of the semiconductor substrate 2 are formed. The bus bar electrode 3 and the finger electrode 4 are also preferably formed by applying a conductive paste containing silver and copper according to the present invention.

  The conductive paste for forming the bus bar electrode 3 and the finger electrode 4 is, for example, 5 to 30 parts by mass of silver filler, copper filler, organic vehicle and glass frit with respect to 100 parts by mass of silver and copper, respectively. 0.1 to 15 parts by mass, kneaded and adjusted to a viscosity of about 50 to 200 Pa · s using a solvent.

  As the coating method, a screen printing method or the like can be used, and it is preferable that the solvent is evaporated and dried at a predetermined temperature after coating.

  After applying and drying a conductive paste for forming the bus bar electrode 3 and the finger electrode 4, the bus bar electrode 3 and the finger are fired at a maximum temperature of 500 to 650 ° C. for several tens of seconds to several tens of minutes after drying. The electrode 4 is formed. In firing the conductive paste containing silver and copper, in order to prevent oxidation of the contained copper filler, nitrogen gas or the like is not used so that the oxygen concentration near the peak temperature in the furnace is less than 500 ppm. It is desirable to introduce the active gas into the furnace.

  In addition, the baking of the conductive paste for forming the bus bar electrode 3 and the finger electrode 4 is performed simultaneously with the baking of the conductive paste for forming the output extraction electrode 6, rather than the baking of the bus bar electrode 3 separately. Both the finger electrode 4 and the output extraction electrode 6 are desirable because firing is performed once and copper oxidation can be suppressed.

  In this way, the conductive paste containing silver and copper is directly applied to the predetermined shape of the bus bar electrode 3 and the finger electrode 4 on the antireflection film 8 and fired to thereby form the bus bar electrode 3 and the finger electrode 4 on the first surface. The n-type layer 9 is brought into electrical contact.

  As a result, both silver and copper particles come into contact with the n-type layer 9, so that the ohmic contact property is improved and the photoelectric conversion efficiency of the completed solar cell element can be improved. Furthermore, it is desirable in terms of manufacturing cost to use a conductive paste containing silver and copper.

  In addition, when a conductive paste containing silver and copper is used for forming the bus bar electrode 3 and the finger electrode 4, as shown in FIG. The mass ratio of silver and copper contained is preferably in the range of silver: copper = 9: 1 to 3: 7.

  In FIG. 4B, a silicon nitride film having a thickness of about 700 to 900 mm is formed as an antireflection film on the semiconductor substrate 2 using a plasma CVD apparatus, and the mass ratio of silver and copper is set on the antireflection film. As a result of measuring the bonding strength of the output extraction electrode 6 formed by applying the changed conductive paste to a predetermined electrode pattern using a screen printing method and baking it at a maximum temperature of about 600 ° C. is there.

  As shown in FIG. 4B, in the bus bar electrode 3 and the finger electrode 4 on the first surface 2a, silver: copper, which is the mass ratio of silver to copper, is 10: 0, the bonding strength is to glass frit silicon. It is considered that a sharp rise is observed because the penetration of glass frit into silicon is promoted by copper in the range of silver: copper from 10: 0 to 9: 1. Furthermore, in the range of silver: copper = 3: 7 to 0:10, the ratio of oxidized copper increases, so it seems that the ratio rapidly decreases from silver: copper = 3: 7 to 0:10.

  FIG. 5A is a plan view of a test piece prepared for measuring the resistance of the junction between this electrode and the n-type layer 9. This is because an n-type layer 9 is formed by diffusing phosphorus on the surface of a p-type polycrystalline silicon substrate 2 of about 150 mm square so that the sheet resistance is about 50 to 100 Ω / □, and about 50 mm in the central part thereof. Electrodes 12a and 12b are formed by screen-printing a conductive paste with a gap D, a length of about 130 mm and a width of about 2 mm, and changing the mass ratio of silver and copper, followed by firing. After firing, the thickness of each of the electrodes 12a and 12b was about 13 μm. Thereafter, the resistance between the electrodes 12a and 12b was measured.

  FIG.5 (b) is a graph which shows the relationship between the mass ratio of silver and copper contained in the used electrically conductive paste, and the resistance value after baking of an electrically conductive paste.

  As is clear from this, when the mass ratio of silver and copper is in the range of 9: 1 to 3: 7, the resistance value is a small value of less than 100 mΩ and the ohmic contact property is good, but outside this range, It turns out that it is rising rapidly.

  The reason for this is thought to be the effect of increasing the proportion of oxidized copper when the mass ratio of silver to copper is in the range of 0:10 to 2: 8, and also due to copper at the mass ratio of silver to copper of 10: 0. This is probably because the effect of improving the ohmic contact property is not seen.

<< Back contact solar cell element >>
Next, a back contact type solar cell element will be described.

  As shown in FIGS. 6 and 7, the solar cell element 21 of the present embodiment includes a first surface 21 a serving as a sunlight receiving surface and a second surface 21 b serving as the back surface thereof. It consists of a semiconductor substrate 25 having a plurality of through holes 28 penetrating the two surfaces 21b.

Further, the inside of the through hole 28 is filled with a conductive filler G which is a conductor, and the through hole electrode 2
2b is formed.

  As shown in FIG. 6 (a), the light receiving surface electrode 22a formed on the first surface 21a of the solar cell element 21 is provided with a plurality of linear thin line-like electrodes provided at substantially equal intervals, and further each one. About 1 to 5 through-hole electrodes 22b are connected to the light receiving surface electrode 22a at substantially the same position. Thus, one light-receiving surface electrode 22a is provided with one or more through-hole electrodes 22b, the density of photocurrent in one through-hole electrode 22b can be reduced, and the resistance component of the solar cell element Can be lowered.

  The shape of the electrode formed on the second surface 21b corresponding to the electrode of the first surface 21a was first electrically connected to this directly below the through-hole electrode 22b, as shown in FIG. 6B. A plurality of rectangular first electrodes 22c are arranged on a straight line at substantially constant intervals. One or a plurality of through-hole electrodes 22b are connected to one of the first electrodes 22c.

  Further, the second surface 21b is provided with a second electrode 23 having a polarity different from that of the first electrode 22c. The second electrode 23 includes a collecting electrode 23a and an output extraction electrode 23b.

  That is, the current collecting electrode 23a is disposed in a portion other than the linearly arranged first electrode 22c and its peripheral portion, and the output extraction electrode 23b is formed on the current collecting electrode 23a.

  The output extraction electrodes 23b are provided at opposing positions on the current collecting electrodes 23a. The two regions of the output output electrode 23 b facing each other are electrically connected by the third electrode 24.

  The semiconductor substrate 25 has one conductivity type, and a reverse conductivity different from the conductivity type of the semiconductor substrate 25 is formed on the first surface 21a and the back surface 1b of the semiconductor substrate 25 as shown in FIGS. Type semiconductor layer 26 (first reverse conductivity type layer 26a, third reverse conductivity type layer 26c). A second reverse conductivity type layer 26 b is provided on the inner surface of the electrode through hole 28 of the semiconductor substrate 25.

  When a p-type silicon substrate is used as the semiconductor substrate 25 exhibiting one conductivity type, such a reverse conductivity type layer 26 becomes n-type. For example, an n-type impurity such as phosphorus is introduced on the surface of the semiconductor substrate 25 and the electrode through hole 28. It is formed by diffusing on the inner surface.

  7A and 7B, when aluminum is mainly used as the electrode material of the current collecting electrode 23a, the heavily doped layer 30 is formed when the current collecting electrode 23a is formed by applying and baking it. Can be formed simultaneously. That is, the current collecting electrode 23 a is formed on the high concentration doped layer 30. Thereby, carriers generated in the semiconductor substrate 25 are efficiently collected. Here, the high concentration means that the impurity concentration is higher than the concentration of one conductivity type impurity in the semiconductor substrate 25.

  As described above, in the solar cell element 21 of the present embodiment, the light receiving surface electrode 22a and the through hole electrode 22b are provided in the first surface 21a and the through hole 28, and on the second surface 21b, the reverse is provided. A first electrode 22 c is provided on the conductive semiconductor layer 26, and a current collecting electrode 23 a and an output extraction electrode 23 b are provided as the second electrode 23 in a portion where the reverse conductive semiconductor layer 26 is not formed.

  Further, in order to electrically isolate (pn-separate) one conductivity type (for example, p-type) and reverse conductivity type layer (for example, n-type) of the semiconductor substrate 25, as shown in FIG. In the periphery of the semiconductor substrate 25, a separation groove 29 a is provided, and a separation groove 29 b is provided at the outer peripheral end of the back surface 21 b of the semiconductor substrate 25.

  The output extraction electrode 23b on the current collecting electrode 23a of this embodiment is formed by applying and baking a conductive paste containing a large number of copper fillers coated with silver on the surface by a printing method or the like. Thereby, the joining strength of the current collection electrode 2 and the output extraction electrode 23b can be improved, and it becomes possible to provide the solar cell element 21 with higher reliability.

<< Method for Manufacturing Back-Contact Solar Cell Element >>
Next, the manufacturing method of the solar cell element 21 of this embodiment is demonstrated.

<Preparation process of semiconductor substrate>
First, as a semiconductor substrate 25 having one conductivity type, for example, a p-type silicon substrate doped with boron or the like is prepared. As the silicon substrate, a silicon substrate made of a single crystal silicon substrate or a polycrystalline silicon substrate cut out from a silicon ingot may be used, and the size of the silicon substrate is, for example, a square or a rectangle having a side of about 140 to 180 mm, and its thickness is What is necessary is just to be about 150 micrometers-300 micrometers.

<Through-hole formation process>
Next, a through hole 28 is formed between the first surface 21 a and the back surface 21 b of the semiconductor substrate 25. The through hole 28 is formed from the second surface 21b side of the semiconductor substrate 25 toward the first surface 21a side, for example, using a mechanical drill, a water jet, a laser device, or the like. In particular, a laser or the like is preferably used in order to suppress the occurrence of microcracks during or after the formation of the through hole 28. As such a laser, for example, an excimer laser, a YAG (yttrium, aluminum, garnet) laser, a YVO ₄ (yttrium vanadate) laser, or the like can be used. The diameter of the through hole 28 to be formed is preferably about 20 to 50 μm.

<Surface etching>
The semiconductor substrate 25 provided with the through-holes 28 is etched by about 5 to 20 μm with an aqueous sodium hydroxide solution of 60 to 90 ° C. with sodium hydroxide of about 10 to 30% by mass. Thereby, the side surface inside the through hole 28 is also etched, and the surface thereof is roughened. By this roughening, the contact area with the conductive filler G can be increased, and the adhesive strength between them can be improved. In addition, this etching can also remove the damage layer generated when the silicon ingot is cut out. Furthermore, the 1st surface 21a can also be roughened, the reflection of the light which injected into the solar cell element 21 can be suppressed, and the photoelectric conversion efficiency can be improved more.

<Reverse conductivity type layer formation process>
Next, the reverse conductivity type layer 26 is formed on the surface of the semiconductor substrate 25. As an n-type doping element for forming the reverse conductivity type layer 26, phosphorus (P) is used, and an n ⁺ type having a sheet resistance of about 60 to 300Ω / □ is used. As a result, a pn junction is formed between the reverse conductivity type layer 26 and the p-type bulk region.

  Furthermore, for example, when the vapor phase diffusion method is used for the reverse conductivity type layer 26, the reverse conductivity type layer 26 can be simultaneously formed on both surfaces of the semiconductor substrate 25 and the inner wall of the through hole 28. By forming the reverse conductivity type layer 26b on the inner wall of the through hole 28, it becomes possible to suppress the leakage current of this portion.

<Antireflection film formation process>
Next, it is preferable to form the antireflection film 27 on the first reverse conductivity type layer 26a. As the material of the antireflection film 27, a silicon nitride film or a titanium oxide film can be used. As a method of forming the antireflection film 27, PECVD, vapor deposition, sputtering, or the like can be used.

<Step of forming light-receiving surface electrode and through-hole electrode>
Next, the light receiving surface electrode 22 a and the through hole electrode 22 b are formed on the semiconductor substrate 25. These electrodes are formed by applying a conductive paste containing a large number of copper fillers coated on the surface of the first surface 1c of the semiconductor substrate 5 using a coating method such as a screen printing method, and baking it.

  Moreover, you may form the light-receiving surface electrode 22a and the through-hole electrode 22b by apply | coating and baking this using the electrically conductive paste which has normal silver as a main component.

<Formation process of current collecting electrode>
Next, the collector electrode 23 a is formed on the back surface 21 b of the semiconductor substrate 25. This is done by applying a conductive paste mainly composed of aluminum to a predetermined electrode shape on the back surface 21b of the semiconductor substrate 25 using a screen printing method, and then baking it as described above to collect the collecting electrode 23a. Form. This also makes it possible to form a heavily doped layer 30 in which one conductivity type semiconductor impurity is diffused at a high concentration.

<Formation process of 1st electrode, output extraction electrode, and 3rd electrode>
Next, the first electrode 22 c, the output extraction electrode 23 b, and the third electrode 24 are formed on the second surface 21 b of the semiconductor substrate 25. In the solar cell element 21 of this embodiment, the first electrode 22c, the output extraction electrode 23b, and the third electrode 24 are made of a large number of copper fillers coated with a silver layer on the surface as described in the double-sided electrode type solar cell element. The conductive paste contained is used.

  That is, by using the screen printing method, the shape of the first electrode 22c, the output extraction electrode 23b, and the third electrode 24 as shown in FIG. As shown, a conductive paste containing a large number of copper fillers 13 coated with a silver layer 15 is applied, and then fired as described above, whereby the first electrode 2c, the output extraction electrode 3b, and the third electrode 4 are formed. Form.

<Pn separation step>
For example, when the reverse conductivity type layer is formed using the above-mentioned vapor phase diffusion method, the reverse conductivity type layer 26 is simultaneously formed on both surfaces of the semiconductor substrate 25 and the inner wall of the through hole 28. For this reason, the reverse conductivity type layers of the first surface 21a and the back surface 21b of the semiconductor substrate 25 are separated (pn-separated). This pn separation may be performed by blasting a powder such as silicon oxide or alumina at a high pressure only on the periphery of the back surface 21b to scrape away the reverse conductivity type layer on the periphery of the back surface 21b, or on the peripheral edge of the back surface 21b. It is possible by a laser processing method to form

  Next, pn separation is performed around the first electrode 22c. The periphery of the first electrode 22c, that is, the portion of the semiconductor substrate 25 formed between the first electrode 22c and the current collecting electrode 23a and the third electrode 24 is irradiated with laser light using a YAG laser (wavelength 1064 nm) or the like, The separation groove 29a is formed in a rectangular shape.

  As described above, a back contact type solar cell element capable of producing the same effect as the double-sided electrode type solar cell element is completed. The back contact solar cell element is not limited to the solar cell element described above, and can be applied to a back contact solar cell element having an IBC (Interdigitated Back Contact) structure in which no through hole is formed.

<< About Type 2 >>
Although the case of type 2 was not described in detail, for example, i-type and p-type amorphous silicon layers are formed in this order on one main surface of an n-type silicon substrate, and i-type and p-type amorphous silicon layers are formed on the other main surface. When forming a single semiconductor substrate as a whole by depositing n-type and n-type amorphous silicon layers in this order, this embodiment is also applied to a solar cell element having a so-called heterostructure. It is possible to expect the same actions and effects as Type 1.

  Below, the Example of a double-sided electrode type solar cell element is described.

<Preparation of Example 1>
First, a semiconductor substrate 2 made of polycrystalline silicon prepared by a casting method was prepared. This semiconductor substrate 2 contains boron (B), which is a p-type impurity, at about 1 × 10 ¹⁶ to 10 ¹⁸ atoms / cm ³ , and has a size of about 150 mm square and a thickness of about 0.2 mm. belongs to.

  In order to clean the surface of the semiconductor substrate 2, the surface was etched by a very small amount with an aqueous sodium hydroxide solution having a concentration of about 20% and washed.

  Next, a fine unevenness (roughening) structure having a light reflectance reduction function was formed on the first surface 2a side of the semiconductor substrate 2 serving as a light incident surface by using an RIE (reactive ion etching) apparatus. .

  Thereafter, the n-type layer 9 was formed on the entire surface of the semiconductor substrate 2. As the n-type doping element, phosphorus (P) was used, and the n-type having a sheet resistance of about 50 to 100Ω / □ was used. As a result, a pn junction was formed between the n-type layer 9 and the p-type bulk region.

The n-type layer 9 was formed as follows. While the semiconductor substrate 2 is heated to about 700 to 900 ° C. and maintained, the gas phase thermal diffusion method is performed for about 20 to 40 minutes in a phosphorus oxychloride (POCl ₃ ) atmosphere in a gas state as a diffusion source. The mold layer 9 was formed to a depth of about 0.3 to 0.6 μm. In this case, since phosphorous glass is formed on the entire surface of the semiconductor substrate 2, in order to remove the phosphorous glass, the semiconductor substrate 2 was immersed in hydrofluoric acid for about 10 seconds, washed and dried.

  Next, an antireflection film 5 was formed. That is, a silicon nitride (SiNx) film was formed as a reflection preventing film 8 on the first surface 2a side with a PECVD apparatus using monosilane gas or ammonia gas at a temperature of about 450 ° C. This silicon nitride (SiNx) film has a refractive index of about 2.0 and a film thickness of about 80 nm in order to exhibit an antireflection effect.

  Thereafter, in order to perform pn separation, the outer peripheral end of the semiconductor substrate 2 on the second surface 2b side was irradiated with a laser beam, and a separation groove was formed beyond the depth reaching the pn junction. This laser apparatus was a YAG laser apparatus. Thereafter, the collector electrode 5 was formed on the second surface 2 b side of the semiconductor substrate 2. The current collecting electrode 5 was formed by applying a paste containing aluminum as a main component to a substantially entire surface of the second surface 2b using a screen printing method except for an outer peripheral portion of about 1 to 3 mm on the second surface 2b. .

  The paste used for forming the current collecting electrode 5 is made of an aluminum powder and an organic vehicle. After applying the paste, the aluminum is baked at a temperature of about 800 to 850 ° C. and the aluminum is baked on the semiconductor substrate (silicon wafer) 2. It was. The thickness of the collector electrode 5 after firing was about 30-50 μm.

  Next, the light receiving surface side bus bar electrode 3 and the light receiving surface side finger electrode 4 were formed on the antireflection film 8 by directly applying a conductive paste in a predetermined pattern using a screen printing method and baking it.

  The conductive paste used for this is obtained by adding 5 to 30 parts by mass and 0.1 to 10 parts by mass of silver powder, organic vehicle and glass frit, respectively, with respect to 100 parts by mass of silver. Firing was carried out by applying and drying the conductive paste, followed by firing for several seconds at a maximum temperature of 700 to 850 ° C. in a firing furnace. The thickness of the light-receiving surface side bus bar electrode 3 and the light-receiving surface side finger electrode 4 after baking was about 10 to 20 μm.

  Next, an output extraction electrode 6 is formed by applying a conductive pattern containing a large number of copper fillers coated with a silver layer on the surface of the current collecting electrode 5 on the second surface 2b side and baking it. did.

  As described above, this conductive paste has a copper filler coated with a silver layer, an organic vehicle, and a glass frit, and 100 parts by mass of copper filler 13 coated with silver on the surface, 15 parts by mass of an organic vehicle, glass frit, 12 parts by mass is added. Furthermore, what adjusted the viscosity to about 150 Pa.s using terpineol was used.

  As a coating method, a screen printing method was used. After coating, the solvent was evaporated and dried in a drying furnace at about 80 to 120 ° C. for about 10 to 20 minutes.

  After applying a conductive paste containing a large number of copper fillers coated on the surface with a silver layer on the current collecting electrode 5, it was fired in a baking furnace at a maximum temperature of 500 to 600 ° C. for several tens of seconds to several tens of minutes. In firing the conductive paste containing a large number of copper fillers coated on the surface of silver, in order to suppress oxidation of the copper filler, nitrogen concentration is set so that the oxygen concentration near the peak temperature in the furnace becomes 180 ppm to 370 ppm. Gas was introduced into the furnace. The thickness of the output extraction electrode 6 after firing was about 10 to 20 μm.

<Preparation of product 2>
The process from the preparation of the semiconductor substrate 2 to the formation of the collecting electrode 5 was performed in the same process as that of the product 1. After forming the current collecting electrode 5, an antireflection film 5 was formed. That is, a silicon nitride (SiNx) film was formed as a reflection preventing film 8 on the first surface 2a side surface with a PECVD apparatus at a temperature of about 450 ° C. using monosilane gas or ammonia gas. This silicon nitride (SiNx) film has a refractive index of about 2.0 and a film thickness of about 80 nm in order to exhibit an antireflection effect.

  Thereafter, in order to perform pn separation, a laser beam is irradiated to the outer peripheral end of the semiconductor substrate 2 on the second surface 2b side, and a separation groove is formed beyond the depth reaching the PN junction. This laser apparatus was a YAG laser apparatus.

  Thereafter, the collector electrode 5 was formed on the second surface 2 b side of the semiconductor substrate 2. The current collecting electrode 5 was formed by applying a paste containing aluminum as a main component to the substantially entire surface of the second surface 2b using a screen printing method except for about 1 mm of the outer peripheral portion of the second surface 2b.

  The paste used for forming the current collecting electrode 5 is made of an aluminum powder and an organic vehicle. After applying the paste, the paste is baked at a maximum temperature of about 800 to 850 ° C. to bake aluminum onto the semiconductor substrate (silicon wafer) 2. It was. The thickness of the collector electrode 5 after firing was about 30-50 μm.

  Next, the light receiving surface side bus bar electrode 3 and the light receiving surface side finger electrode 4 were formed on the antireflection film 8 by directly applying a conductive paste in a predetermined pattern and baking it.

  The conductive paste used for this has a mass ratio of silver and copper of 6: 4, with 15 parts by mass of organic vehicle and 12 parts by mass of glass frit added to 100 parts by mass of the total amount of silver and copper. is there. Furthermore, what adjusted the viscosity of about 150 Pa.s using terpineol was used. As a coating method, a screen printing method was used. After coating, the solvent was evaporated and dried in a drying furnace at about 80 to 90 ° C. for about 20 minutes.

  Next, an output extraction electrode 6 was formed by applying a conductive paste in a predetermined pattern on the current collecting electrode 5 on the second surface 2b side and baking it.

  The conductive paste used for this has a mass ratio of silver and copper of 5: 5, with 15 parts by mass of organic vehicle and 12 parts by mass of glass frit added to 100 parts by mass of the total amount of silver and copper. is there. Furthermore, what adjusted the viscosity of about 150 Pa.s using terpineol was used. As a coating method, a screen printing method was used. After coating, the solvent was evaporated and dried in a drying furnace at about 80 to 90 ° C. for about 20 minutes.

  Thereafter, the conductive paste applied on the antireflection film 8 and the conductive paste applied on the collector electrode 5 were baked. In this baking, after applying and drying the conductive paste, baking is performed in an atmosphere where the maximum temperature is 500 to 600 ° C. for several minutes in the baking furnace, and the oxygen concentration near the peak temperature in the furnace is 180 ppm to 370 ppm. It was done by doing. The thickness of the light-receiving surface side bus bar electrode 3, the light-receiving surface side finger electrode 4, and the output extraction electrode 6 after firing was about 10 to 20 μm.

<Preparation of Implementation Product 3>
The process from the preparation of the semiconductor substrate 2 to the formation of the collecting electrode 5 was performed in the same process as that of the product 1. After the current collecting electrode 5 is formed, the light receiving surface side bus bar electrode 3 and the light receiving surface side finger electrode are formed by directly applying a conductive paste on the antireflection film 8 in a predetermined pattern using a screen printing method and baking it. 4 was formed.

  The conductive paste used for this is obtained by adding 15 parts by mass and 12 parts by mass of silver powder, an organic vehicle and glass frit to 100 parts by mass of silver, respectively, and further using terpineol to a degree of 150 Pa · s. What was adjusted to the viscosity of was used. After coating, the solvent was evaporated and dried in a drying oven at about 80 to 90 ° C. for about 20 minutes.

  Next, an output extraction electrode 6 was formed by applying a conductive paste in a predetermined pattern on the current collecting electrode 5 on the second surface 2b side and baking it.

  The conductive paste used for this has a mass ratio of silver and copper of 5: 5, with 15 parts by mass of organic vehicle and 12 parts by mass of glass frit added to 100 parts by mass of the total amount of silver and copper. is there. Furthermore, what adjusted the viscosity of about 150 Pa.s using terpineol was used. As a coating method, a screen printing method was used. After coating, the solvent was evaporated and dried in a drying furnace at about 80 to 90 ° C. for about 20 minutes.

  Thereafter, the conductive paste applied on the antireflection film 8 and the conductive paste applied on the collector electrode 5 were baked. In this baking, after applying and drying the conductive paste, baking is performed in an atmosphere where the maximum temperature is 500 to 600 ° C. for several minutes in the baking furnace, and the oxygen concentration near the peak temperature in the furnace is 180 ppm to 370 ppm. It was done by doing. The thickness of the light-receiving surface side bus bar electrode 3, the light-receiving surface side finger electrode 4, and the output extraction electrode 6 after firing was about 10 to 20 μm.

  That is, the difference between the implementation product 2 and the implementation product 3 is that the light-receiving surface-side bus bar electrode 3 and the light-receiving surface-side finger electrode 4 arranged on the first surface 2a side are formed of the conductive paste containing silver and copper in the implementation product 2. In contrast, the product 3 is formed of a conductive paste containing only silver.

<Production of comparison product>
The steps from the preparation of the semiconductor substrate 2 to the pn separation were performed in the same process as that in the case of the implementation product 1 described above.

  The current collecting electrode 5 is made of the same paste as that of the test products 2 and 3, which is made of aluminum. The outer peripheral portion of the second surface 2 b is about 1 to 3 mm, and the silicon electrode is used to prevent the output extraction electrode 6 from peeling. Except for the part for making the part which 2 and the output extraction electrode 6 contact | connect directly, it formed by apply | coating and baking to the substantially whole surface of the 2nd surface 2b using the screen printing method. The area of the portion where the semiconductor substrate 2 and the output extraction electrode 6 are in direct contact is about 7 to 8% of the total area of the semiconductor substrate 2 on the second surface 2b side.

  Next, a conductive paste containing silver as a main component is directly applied to a predetermined pattern on the antireflection film 8 by using a screen printing method and baked to thereby receive the light receiving surface side bus bar electrode 3 and the light receiving surface side finger electrode. 4 was formed.

  Next, an output extraction electrode 6 was formed on the current collecting electrode 5 by applying a conductive paste mainly composed of silver in a predetermined pattern and baking it.

  These conductive pastes are obtained by adding 15 parts by mass and 8 parts by mass of silver powder, an organic vehicle, and glass frit to 100 parts by mass of silver, respectively. Firing was performed by baking the conductive paste at a maximum temperature of 500 to 600 ° C. for several minutes after applying and drying the conductive paste. The thickness of the light-receiving surface side bus bar electrode 3 and the light-receiving surface side finger electrode 4 after baking was about 10 to 20 μm.

<Evaluation of implemented products and comparative products>
The output characteristics of the four types of solar cell elements of Example Product 1, Example Product 2, Example Product 3 and Comparative Product produced in this way are expressed as pseudo-sunlight with an element temperature of 25 ° C., AM 1.5, and 100 mW / cm ² . It was as shown in Table 1 when measured by. In Table 1, the short circuit current (Isc), the open circuit voltage (Voc), the fill factor (FF), and the photoelectric conversion efficiency (η) are expressed as indices when the test product is 100.

  As shown in Table 1, in the solar cell elements of Examples 1 to 3, improvements were observed in the short-circuit current, the open-circuit voltage, and the fill factor compared to the comparative products, thereby improving the photoelectric conversion effect and confirming the effect. It was.

In addition, the output extraction electrode 6 formed of a conductive paste containing a large number of copper fillers coated with silver on the surface of the collecting electrode 5 as in the case of the product 1 does not peel at all and has sufficient bonding strength. Confirmed that.

  Moreover, in the comparison of the implementation product 2 and the implementation product 3, the improvement of the implementation product 2 is seen especially by a fill factor, and the bus bar electrode 3 and the finger electrode 4 arranged on the first surface 2a side contain silver and copper. The effect of improving the ohmic contact property by forming with the conductive paste was confirmed.

  In the solar cell element of Example 3, the improvement of the fill factor was particularly observed as compared with the comparative product, thereby improving the photoelectric conversion efficiency and confirming the effect.

  In addition, the output extraction electrode 6 formed of a conductive paste containing a large number of silver fillers and copper fillers on the current collecting electrode 5 as in the case of the product 2 and the product 3 does not peel at all and has sufficient bonding strength. I confirmed that I had it.

DESCRIPTION OF SYMBOLS 1, 2: 1: Solar cell element 2, 25: Semiconductor substrate 2a, 21a: 1st surface 2b, 21b: 2nd surface 3: Bus-bar electrode 4, 22a: Finger electrode 5, 23a: Current collection electrode 6, 23b: Output extraction Electrode 7: removal part 8, 27: antireflection film 9, 26: reverse conductivity type layer (semiconductor layer)
10: p-type bulk region 13: copper filler 14: copper body 15: silver layer 22b: through-hole electrode 22c: first electrode 23: second electrode 24: third electrode 26a: first reverse conductivity type layer 26b: second Reverse conductivity type layer 26c: third reverse conductivity type layer 28: electrode through holes 29a, 29b: separation groove 30: highly doped layer

Claims (8)

  A semiconductor substrate having a semiconductor layer of one conductivity type and a semiconductor layer of reverse conductivity type, wherein at least one main surface of the semiconductor substrate is a semiconductor layer of reverse conductivity type, and the other facing the one main surface of the semiconductor substrate A solar cell element in which an electrode for taking out generated power is formed on each of a main surface and the reverse conductivity type semiconductor layer, wherein the other main surface of the semiconductor substrate and the reverse conductivity type semiconductor layer The electrode formed on at least one contains silver and copper, The solar cell element characterized by the above-mentioned.   2. The solar cell element according to claim 1, wherein only an electrode formed on the other main surface of the semiconductor substrate contains silver and copper.   2. The solar cell element according to claim 1, wherein the electrode formed on the reverse conductivity type semiconductor layer is formed only on one main surface side of the semiconductor substrate.   The solar cell element according to claim 1, wherein the electrode formed on the reverse conductivity type semiconductor layer is also formed on the other main surface side of the semiconductor substrate.   A plurality of through holes penetrating both main surfaces of the semiconductor substrate, the reverse conductivity type semiconductor layer is also formed in the through hole, a conductor is provided in the through hole, and the reverse conductivity 5. The solar cell element according to claim 4, wherein the electrode formed on the semiconductor layer of the mold is led out to the other main surface side of the semiconductor substrate via the conductor. .   The solar cell element according to claim 5, wherein the conductor provided in the through hole contains at least silver and copper.   The method for manufacturing a solar cell element according to claim 1, wherein the electrode formed on the reverse conductivity type semiconductor layer is applied with a conductive paste containing a large number of copper fillers coated with silver on the surface, A method for producing a solar cell element, characterized by being formed by firing.   2. The method for manufacturing a solar cell element according to claim 1, wherein the electrode formed on the reverse conductivity type semiconductor layer is applied with a conductive paste containing a large number of silver fillers and copper fillers and fired. The manufacturing method of the solar cell element characterized by the above-mentioned.

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