JP5908763B2 - Photoelectric conversion element and method for producing photoelectric conversion element - Google Patents

Description

  The present invention relates to a photoelectric conversion element and a method for manufacturing the photoelectric conversion element.

  At present, in the research and development of a semiconductor substrate having a photoelectric conversion layer for photoelectrically converting light and an electrode (finger electrode and bus bar electrode) provided on the semiconductor substrate, a semiconductor substrate between the semiconductor substrate and the electrode For the purpose of suppressing the surface recombination of carriers generated inside, it is required to reduce the contact area between the electrode and the semiconductor substrate (see, for example, Patent Document 1).

JP 2010-34499 A

  However, in the photoelectric conversion element described in Patent Document 1, particularly when the contact area between the bus bar electrode and the semiconductor substrate is reduced, the electrical resistance of the bus bar electrode itself is increased. As a result, power generated in the semiconductor substrate is consumed by the bus bar electrode, and there is a problem that power taken out from the photoelectric conversion element is reduced.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a photoelectric conversion element and a photoelectric conversion element capable of maintaining the electrical resistance of the bus bar electrode while reducing the contact area between the electrode and the semiconductor substrate. It is to provide a manufacturing method.

  The photoelectric conversion element of the present invention includes a semiconductor substrate having a photoelectric conversion layer for photoelectrically converting incident light, a finger electrode provided on a main surface of the semiconductor substrate, and a plurality of electrode fingers, and the semiconductor substrate. A protective film made of an insulating material provided so as to be positioned between each of the plurality of electrode fingers on the main surface, and a plurality of the electrode fingers provided on the protective film and the finger electrodes. A bus bar electrode to be connected.

  The method for producing a photoelectric conversion element of the present invention includes a preparation step of preparing a semiconductor substrate having a photoelectric conversion layer that photoelectrically converts incident light, and a coating that covers the main surface of the semiconductor substrate with a protective film made of an insulating material A coating step of applying a conductive paste on a pattern of a finger electrode having a plurality of electrode fingers on the protective film, and heating the protective film and the conductive paste after the coating step, First electrode for forming a finger electrode having a plurality of electrode fingers each having the protective film disposed therebetween, by intruding into the protective film in the pattern and curing on the main surface of the semiconductor substrate. A forming step and a second electrode forming step of forming a bus bar electrode connecting the plurality of electrode fingers on the protective film and the finger electrode.

  According to the photoelectric conversion element of the present invention, since the bus bar electrode is provided on the finger electrode and the protective film provided on the main surface of the semiconductor substrate, the area of the bus bar electrode can be reduced while reducing the area in contact with the semiconductor substrate. Electric resistance can be maintained. As a result, the amount of power extracted from the photoelectric conversion element can be improved.

It is a perspective view of the photoelectric conversion element which concerns on one Embodiment of this invention. It is a figure which shows the cross section of the photoelectric conversion element shown in FIG. 1, and is equivalent to a cross section when cut | disconnected by the A-A 'line | wire of FIG. It is a top view when the photoelectric conversion element shown in FIG. 1 is seen from the top. It is sectional drawing which shows the modification of the photoelectric conversion element of this invention, and is equivalent to the figure which expanded a part of cross section when it cut | disconnects by the D-D 'line | wire of FIG. It is sectional drawing which shows the modification of the photoelectric conversion element of this invention, and is equivalent to the figure which expanded a part of cross section when it cut | disconnects by the A-A 'line | wire of FIG. It is the expanded sectional view which expanded a part of photoelectric conversion element shown in FIG. It is a top view which shows the modification of the photoelectric conversion element of this invention. It is a figure which shows the cross section of the photoelectric conversion element shown in FIG. 7, and is equivalent to the figure which expanded a part of cross section when it cut | disconnects by the E-E 'line | wire of FIG. It is sectional drawing which shows 1 process of the manufacturing method of the photoelectric conversion element of this invention, (a) is cut | disconnected by the BB 'line of FIG. 1, (b) is cut | disconnected by the CC' line of FIG. Correspond to each. It is sectional drawing which shows the next process of the manufacturing method of the photoelectric conversion element shown in FIG. 5, (a) and (b) respond | correspond to FIG. 9 (a) and FIG.9 (b), respectively. It is sectional drawing which shows the next process of the manufacturing method of the photoelectric conversion element shown in FIG. 5, (a) and (b) respond | correspond to FIG. 9 (a) and FIG.9 (b), respectively. It is sectional drawing which shows the next process of the manufacturing method of the photoelectric conversion element shown in FIG. 5, (a) and (b) respond | correspond to FIG. 9 (a) and FIG.9 (b), respectively. It is sectional drawing which shows the next process of the manufacturing method of the photoelectric conversion element shown in FIG. 5, (a) and (b) respond | correspond to FIG. 9 (a) and FIG.9 (b), respectively.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings.

<Photoelectric conversion element>
FIG. 1 is a diagram illustrating a photoelectric conversion element 1 according to an embodiment of the present invention. As shown in FIG. 1, the photoelectric conversion element 1 specifically includes a semiconductor substrate (hereinafter simply referred to as a substrate) 2, finger electrodes 3, a protective film 4, and a bus bar electrode 5.

  For example, a semiconductor substrate or the like can be used as the substrate 2. The board | substrate 2 can use a plate-shaped thing. The substrate 2 has a light receiving surface (the lower surface direction in FIG. 1 and hereinafter referred to as a first surface) 2A on which light is incident, and a back surface (the upper surface direction in FIG. 1) located on the back side with respect to the first surface 2A. , Hereinafter referred to as the second surface) 2B.

  The substrate 2 has a photoelectric conversion layer 2a that converts light into electricity between the first surface 2A and the second surface 2B. The photoelectric conversion layer 2a can be formed, for example, in the vicinity of the interface between the one conductivity type semiconductor and the reverse conductivity type semiconductor. Therefore, for example, a semiconductor substrate having one conductivity type can be used as the substrate 2. By forming the opposite conductivity type layer 2 ′ on the second surface 2 B side of the substrate 2, the one conductivity type and the opposite conductivity type are formed. The photoelectric conversion layer 2a can be formed between the two.

As the substrate 2, a plate-like semiconductor having one conductivity type (for example, p-type) can be used. As a semiconductor constituting the substrate 2, a silicon crystal such as single crystal silicon or polycrystalline silicon can be used. The thickness of the substrate 2 can be set to, for example, 250 μm or less. Although the shape of the board | substrate 2 is not specifically limited, From a viewpoint on a manufacturing method, it is good also as a square shape by planar view.

  In the present embodiment, an example in which a silicon substrate having p-type conductivity is used as the substrate 2 will be described. When the substrate 2 made of a silicon substrate has a p-type, for example, boron or gallium can be used as the dopant element.

  The reverse conductivity type layer 2 ′ is a semiconductor layer that forms a pn junction with the substrate 2. The reverse conductivity type layer 2 ′ is a layer having a conductivity type opposite to that of the substrate 2, and is provided on the first surface 2 </ b> A side of the substrate 2. The reverse conductivity type layer 2 ′ can be set to be, for example, 30 nm or more and 2 μm or less. If the substrate 2 has a p-type conductivity type, the reverse conductivity type layer 2 'is formed to have an n-type conductivity type. On the other hand, if the substrate 2 has an n-type conductivity type, the reverse conductivity type layer 2 'is formed to have a p-type conductivity type.

  The reverse conductivity type layer 2 ′ may be formed or bonded on the first surface 2 </ b> A of the substrate 2, or may be formed in the substrate 2 by implanting and diffusing ions into the substrate 2. Specifically, in the case where the substrate 2 is a silicon substrate having a p-type conductivity type and the reverse conductivity type layer 2 ′ is formed in the silicon substrate, for example, the reverse conductivity type layer 2 ′ is the second conductivity type in the silicon substrate. It can be formed by diffusing impurities such as phosphorus on the surface 2B side.

  In the present embodiment, the reverse conductivity type layer 2 ′ is patterned along the finger electrode 3 described later. Specifically, the reverse conductivity type layer 2 ′ is patterned along one of the finger electrodes 3 (finger electrode 3 a or finger electrode 3 b) connected to one conductivity type.

  Finger electrodes 3 are provided on the second surface 2B of the substrate 2. The finger electrode 3 has a one-conductivity-type finger electrode 3a connected to the p-type conductivity-type substrate 2 and a reverse-conductivity-type finger electrode 3b connected to the reverse-conductivity-type layer 2 ′. . In the following description, the finger electrode 3 refers to either the finger electrode 3a or the finger electrode 3b unless otherwise specified.

  The finger electrode 3 is composed of a plurality of electrode fingers 3 '. The electrode finger 3 ′ is provided in a polygonal shape such as a rectangular parallelepiped extending in one direction, for example. The cross section perpendicular to the longitudinal direction of the electrode finger 3 ′ can be set to a plan view shape such as a square shape or a trapezoidal shape. The electrode finger 3 'may be formed of one metal layer or a plurality of metal layers. The thickness of the electrode finger 3 ′ can be set to be, for example, 100 nm or more and 200 μm or less.

The contact area between the lower surface of the electrode finger 3 ′ and the substrate 2 may be set as appropriate depending on the area of the substrate 2. Specifically, the contact area is such that the area where all the electrode fingers 3 ′ (finger electrodes 8) are in contact with the substrate 2 is, for example, 1% or more and 90% or less with respect to the area of the second surface 2 </ b> B of the substrate 2. It should be set as follows. Specifically, when the second surface 2B of the substrate 2 is 156 mm □, the lower surface of one electrode finger 3 ′ can be set to be, for example, 0.3 mm ² or more and 30 mm ² or less.

  The finger electrode 3 has a plurality of electrode fingers 3 ′ arranged in one direction. Specifically, the plurality of electrode fingers 3 ′ are arranged in a direction intersecting with the longitudinal direction. The plurality of electrode fingers 3 ′ are arranged such that the electrode fingers 3 ′ are spaced apart from each other by a predetermined distance. The interval between the electrode fingers 3 ′ is set to be 10 μm or more and 5 mm or less, for example. In the present embodiment, a case where the plurality of electrode fingers 3 ′ are all separated from each other will be described, but a part of them may be electrically connected.

The finger electrode 3 is made of a conductive material that can be electrically connected to the substrate 2. Specifically, as a material of the finger electrode 3, for example, a metal material such as gold, copper, silver, aluminum, zinc, nickel, chromium, platinum, lead, molybdenum, vanadium, indium or magnesium, a semiconductor material such as silicon, Alternatively, a conductive film containing indium oxide and tin oxide can be used. As the finger electrode 3, for example, by setting the film thickness so that the transmittance is 50% or more, or using a transparent conductive film, the finger electrode 3 has a main surface (first surface) on the side on which light is incident. It may be provided on one surface 2A).

  The finger electrode 3a and the finger electrode 3b may be formed of the same material or different materials. In the case of forming with different materials, the material of the finger electrode 3a and the finger electrode 3b can be changed depending on the conductivity of the substrate 2 to be connected. Specifically, as the material of the finger electrode 3a and the finger electrode 3b, the one connected to the p-type conductivity type is configured to include aluminum, and the one connected to the n-type conductivity type includes silver. Can be configured. Thus, by changing the material of the finger electrode 3 in accordance with the conductivity type, the finger electrode 3 can easily make ohmic contact with the conductivity type.

  A protective film 4 is provided on the second surface 2B of the substrate 2. As shown in FIG. 2, the protective film 4 is located between the plurality of electrode fingers 3 '. More specifically, the protective film 4 is disposed so as to contact a side surface of each electrode finger 3 ′ and a part of the second surface 2 </ b> B of the substrate 2 so as to fill a space between the plurality of electrode fingers 3 ′. . In the present embodiment, the protective film 4 is provided so as to cover not only between the electrode fingers 3 ′ but also the entire second surface 2 </ b> B of the substrate 2. Thereby, the insulation of the 2nd surface 2B of the board | substrate 2 can be improved.

  The thickness of the protective film 4 can be set to be smaller than the thickness of the electrode finger 3 ′, for example. In the present embodiment, a case where the thickness of the protective film 4 and the thickness of the electrode finger 3 ′ are set to be the same will be described. Since the protective film 4 is configured with the same thickness as the electrode finger 3 ′, the upper surface of the electrode finger 3 ′ is exposed, and is easily electrically connected to a bus bar electrode 5 described later. . In this way, by setting the thickness of the protective film 4 to be the same as the thickness of the electrode finger 3 ′, pyroelectricity generated between the electrode fingers 3 ′ can be suppressed. In addition, by making the thickness of the protective film 4 smaller than the thickness of the electrode finger 3 ′, it can be more easily electrically connected to the bus bar electrode 5.

  The protective film 4 is made of an insulating material. Specifically, as the material of the protective film 4, an oxide such as magnesium oxide, aluminum oxide, silicon oxide, or titanium oxide, a fluoride such as magnesium fluoride, and a nitride such as silicon nitride can be used. . The protective film 4 may be formed as a single layer made of one material, or may be formed by laminating a plurality of layers made of different materials. In the present embodiment, a case where the protective film 4 is a single layer made of aluminum oxide will be described as an example.

  As shown in FIG. 3, the bus bar electrode 5 is provided on the protective film 4 and the finger electrodes 3. The bus bar electrode 5 is provided across the plurality of electrode fingers 3 ′ via the protective film 4, and is connected to the plurality of electrode fingers 3 ′. The bus bar electrode 5 is provided so as to extend in the arrangement direction of the finger electrodes 3. More specifically, the bus bar electrode 5a is connected to the finger electrode 3a, and the bus bar electrode 5b is connected to the finger electrode 3b.

  The bus bar electrode 5 can be selected from the conductive materials mentioned for the finger electrode 3. For example, the bus bar electrode 5 may be formed of the same material as that of the finger electrode 3 or may be formed of a material different from that of the finger electrode 3. In this embodiment, the case where the bus bar electrode 5 is formed of a material having an electric resistance smaller than that of the finger electrode 3 (electrode finger 3 ′) will be described as an example.

  The volume of the bus bar electrode 5 can be set as appropriate. By adjusting the material and volume of the bus bar electrode 5, the electric resistance flowing through the bus bar electrode 5 can be adjusted. In the present embodiment, the bus bar electrode 5 is formed to have a larger volume than the electrode finger 3 ′ of the finger electrode 3. Thus, when formed so that it may become a volume larger than electrode finger 3 ', since it is comprised with the material whose electric resistance is smaller than electrode finger 3', when flowing to electrode finger 3 ', it is more than electric resistance. The electrical resistance when flowing to the bus bar electrode 5 can be made smaller.

  The bus bar electrode 5 may be set so that the electric resistance is smaller than that of the electrode finger 3 '. Here, as a method of comparing the electric resistances of the two, for example, a method of calculating and comparing the electric resistance value per volume in consideration of the electric resistivity of the constituent material can be used.

  Since the bus bar electrode 5 is provided on the finger electrode 3 and the protective film 4 as described above, the photoelectric conversion element of the present embodiment is not in contact with the substrate 2. The area where the finger electrode 3 and the bus bar electrode 5) come into contact can be reduced. For this reason, since the surface recombination of carriers generated between the substrate 2 and the electrode can be suppressed, the lifetime of carriers generated in the substrate 2 can be extended.

  In addition, since the bus bar electrode 5 is disposed on the finger electrode 3 and the protective film 4, the bus bar electrode 5 can be made larger than the conventional one, so that the electrical resistance of the bus bar electrode 5 can be reduced. Therefore, the power consumed by the electrical resistance at the bus bar electrode 5 can be reduced.

  As described above, the photoelectric conversion element 1 can increase the amount of electric power extracted from the photoelectric conversion element 1 because the lifetime of carriers generated in the substrate 2 can be increased and the electrical resistance of the bus bar electrode 5 can be decreased. Can do.

  In the conventional photoelectric conversion element, the bus bar electrode and the finger electrode are provided on the main surface of the substrate. Therefore, when the bus bar electrode is reduced and the contact area with the substrate is reduced, the electric resistance of the bus bar electrode is increased. Increasing the bus bar electrode to reduce the electrical resistance increases the contact area with the substrate. Therefore, in the photoelectric conversion element, it is difficult to reduce surface recombination and reduce electrical resistance.

(Modification 1 of photoelectric conversion element)
The bus bar electrode 5 may be made of a conductive material different from that of the finger electrode 3. Specifically, the bus bar electrode 5 is made of a conductive material having an electric resistance smaller than that of the finger electrode 3. In this way, by configuring the bus bar electrode 5 with a conductive material having an electric resistance smaller than that of the finger electrode 3, the electric resistance of the bus bar electrode can be reduced. That is, since the choice of the material of the bus-bar electrode 5 can be expanded, the freedom degree of design of a photoelectric conversion element can be raised.

  In the conventional photoelectric conversion element, the finger electrode 3 and the bus bar electrode 5 are formed in the same process because they are formed on the same main surface of the substrate. Therefore, the finger electrode 3 and the bus bar electrode 5 are made of the same material, and it is difficult to make the finger electrode 3 and the bus bar electrode 5 of different materials.

(Modification 2 of the photoelectric conversion element)
The bus bar electrode 5 may be set so that the thickness is larger than the thickness of the finger electrode 3. By increasing the thickness of the bus bar electrode 5, the electrical resistance can be made smaller than that of the finger electrode 3 (electrode finger 3 ′).

  In the conventional photoelectric conversion element, as described above, since the finger electrode 3 and the bus bar electrode 5 are formed on the same main surface in the same process, the finger electrode 3 and the bus bar electrode 5 can be formed with different thicknesses. It was difficult.

(Modification 3 of photoelectric conversion element)
On the protective film 4 and the finger electrode 3, you may have the 2nd protective film 6 provided so that it might not overlap with the bus-bar electrode 5, as shown in FIG. The second protective film 6 can be made of the same material as the protective film 4.

  Thus, by having the 2nd protective film 6 on the finger electrode 3, the area | region exposed from the protective film 6 of the finger electrode 3 can be coat | covered, and it suppresses that the finger electrode 3 is oxidized. can do.

  Further, the second protective film 6 may have a refractive index larger than that of the protective film 4. In the present embodiment, since aluminum oxide is used as the protective film 4, a material having a refractive index larger than 1.6 that is the refractive index of aluminum oxide can be used.

  As described above, when the refractive index of the second protective film 6 is larger than the refractive index of the protective film 4, when incident light passes through the substrate 2, the interface between the protective film 4 and the second protective film is used. It can be easily reflected to the protective film 4 side. As a result, light that has once passed through the substrate 2 can easily enter the substrate 2 again, so that the photoelectric conversion efficiency in the substrate 2 can be improved.

(Modification 4 of photoelectric conversion element)
As shown in FIG. 5, the thickness of the electrode finger 3 ′ is set to be thicker than the thickness of the protective film 4, and the bus bar electrode 5 may be provided on the electrode finger 3 ′. As shown in FIG. 6, the bus bar electrode 5 is provided so as to cover the surface of the protruding region 3′a protruding from the protective film 4 in the electrode finger 3 ′. In addition, the bus-bar electrode 5 should just contact from the whole upper surface of electrode finger 3 'to the side surface.

  Thus, since the bus bar electrode 5 is provided so as to cover the protruding region 3 ′ a of the electrode finger 3 ′, the contact resistance between the electrode finger 3 ′ and the bus bar electrode 5 can be reduced. Thereby, the electric power taken out from the photoelectric conversion element can be improved.

  In addition, since the bus bar electrode 5 is provided so as to cover the protruding region 3 ′ a of the electrode finger 3 ′, the area of the electrode finger 3 ′ with which the bus bar electrode 5 contacts can be increased. Can be prevented from peeling off from the electrode finger 3 ′ and the protective film 4.

  Furthermore, since the electrode finger 3 ′ has the protruding region 3 ′, the bus bar electrode 5 formed on the electrode finger 3 ′ and the protective film 4 can be raised. Thus, when the photoelectric conversion element 1 is mounted on another circuit board, the electrical wiring formed on the circuit board and the bus bar electrode 5 can be reliably electrically connected.

(Modification 5 of the photoelectric conversion element)
As described above, the electrode finger 3 ′ does not need to have a polygonal shape such as a rectangular parallelepiped extending in one direction. For example, as shown in FIGS. 7 may be used. FIG. 7 is a diagram illustrating a positional relationship between the electrode portion 3 ″, the second finger electrode 8, and the bus bar electrode 5. FIG. Here, in FIG. 7, the electrode portion 3 ″ is connected to one conductivity type as the electrode portion 3 ′.
"A" and the electrode connected to the opposite conductivity type are indicated as electrode part 3 "b.

  The electrode part 3 ″ a and the electrode part 3 ″ b are each formed with a second finger electrode 8 that connects the electrode parts 3 ″ of the same conductivity type. Specifically, the second finger electrode 8 is in one direction. The second finger electrode 8 is connected to the plurality of electrode portions 3 "a, and is connected to the second finger electrode 8a and the plurality of electrode portions 3" b. This is shown as the second finger electrode 8b.

  The electrode portion 3 ″, the second finger electrode 8 and the bus bar electrode 5 may be made of different materials or the same material. When different materials are used, suitable materials for the respective electrodes. Therefore, the electrical resistance can be easily reduced. Also, since the area of the electrode (electrode part 3 ″) in contact with the substrate 2 can be reduced, surface recombination that occurs at the interface between the two can be achieved. Can be reduced. As a result, since carriers generated in the photoelectric conversion layer are converted into electric power, the amount of electric power extracted from the photoelectric conversion element can be improved.

  Further, as described in the above-described modification example 4, the electrode portion 3 ″ may be provided with a protruding region. Thus, the electrode portion 3 ″ is provided with a protruding region, and the surface of the protruding portion of the electrode portion 3 ″ is provided. The surface of the second finger electrode 8 can be raised by covering the surface with the second finger electrode 8. In this case, when the photoelectric conversion element 1 is mounted on the circuit board without providing the bus bar electrode 5, a circuit is formed. The electrical wiring formed on the substrate and the second finger electrode 8 can be reliably electrically connected.

<Method for producing photoelectric conversion element>
The manufacturing method of the photoelectric conversion element 1 of the present invention includes a preparation step for preparing the substrate 2, a coating step for covering with the protective film 4, a coating step for applying the conductive paste 6, a first electrode forming step for forming the finger electrodes 3, And a second electrode forming step for forming the bus bar electrode 5.

  Each process of the manufacturing method of the photoelectric conversion element 1 will be described below in detail with reference to FIGS. 9 to 13 correspond to the cross-section when (a) is cut along the line BB 'in FIG. 1, and (b) is the cross-section when cut along the line CC' in FIG. Equivalent to. Figures (a) and (b) with the same figure number are diagrams of the same process.

(Preparation process)
A process of preparing the substrate 2 having the photoelectric conversion layer 2a will be described. In this embodiment, the substrate 2 uses a p-type semiconductor substrate to form an n-type reverse conductivity type layer 2 ′, thereby forming a pn junction that is the photoelectric conversion layer 2a. When the substrate 2 is a single crystal silicon substrate, it is formed by, for example, a pulling method. When the substrate 2 is a polycrystalline silicon substrate, it is formed by, for example, a casting method. In the following description, an example in which the substrate 2 is a p-type polycrystalline silicon substrate will be described.

First, a polycrystalline silicon ingot is produced by, for example, a casting method. Next, the ingot is sliced to a thickness of 250 μm or less, for example. At this time, the ingot is sliced using a fixed abrasive type wire saw device that slices with an abrasive fixed wire in which abrasive particles are fixed to the wire from the beginning. Thereafter, the substrate 2 contaminated in the slicing process is cleaned using a cleaning liquid. At this time, a mechanical damage layer exists on the cut surface of the substrate 2. When the cut surface of the substrate 2 is observed with a scanning electron microscope, the number of microcracks is small and the depth thereof can be reduced to about 1 μm or less as compared with the case of using the free abrasive grain type.

Further, when the residual stress on the surface of the substrate 2 is evaluated using micro Raman spectroscopy, in the case of the fixed abrasive type, there is a compressive stress of 200 MPa or more and 500 MPa or less, whereas in the case of the free abrasive type. The compression stress is 200 MPa or less. That is, it can be inferred that by using the fixed abrasive type, the substrate 2 having a small mechanical damage layer and a small release of residual stress due to the occurrence of microcracks or the like can be obtained.

The reverse conductivity type layer 2 ′ is formed from the first surface 2 A side of the substrate 2. The reverse conductivity type layer 2 ′ has a coating thermal diffusion method in which P ₂ O ₅ in a paste state is applied to the surface of the semiconductor substrate 1 for thermal diffusion, and POCl ₃ (phosphorus oxychloride) in a gas state is used as a diffusion source. It is formed by a vapor phase thermal diffusion method or the like. The reverse conductivity type layer 2 ′ is formed so as to have a sheet resistance of, for example, a depth of 0.2 μm or more and 2 μm or less, for example, 40Ω / □ or more and 200 or less Ω / □ or less.

In the vapor phase thermal diffusion method, for example, 600 ° C. in an atmosphere having a diffusion gas composed of POCl ₃ or the like.
At a temperature of 800 ° C. or lower, the substrate 2 is heat-treated for 5 minutes or longer and 30 minutes or shorter to convert the phosphor glass into the substrate 2
Form on the surface. Thereafter, the substrate 2 is subjected to heat treatment in an inert gas atmosphere such as argon or nitrogen at a high temperature of, for example, 800 ° C. or more and 900 ° C. or less, for example, for 10 minutes or more and 40 minutes or less. The reverse conductivity type layer 2 ′ is formed by diffusion.

  In the present embodiment, the substrate is then etched into a predetermined pattern as shown in FIG. 9 so that the conductive surface of the substrate is exposed on the second surface 2B side. Specifically, the etching pattern is etched so that the exposed surface of the substrate 2 has a pattern along either the finger electrode 3a or the finger electrode 3b. For the etching, a known method such as a method using a photomask can be used. In the following description, the surface on the second surface 2B side where the pattern is formed (the substrate surface exposed by etching and the second surface 2B remaining after etching) is referred to as a second surface 2B ′.

  By forming the reverse conductivity type layer 2 ′ on the substrate 2 in this manner, the vicinity of the interface between the substrate 2 and the reverse conductivity type layer 2 ′ becomes a pn junction, and the vicinity of the interface becomes the photoelectric conversion layer 2 a. Thus, the board | substrate 2 which has the photoelectric converting layer 2a as shown in FIG. 2 can be prepared.

(Film formation process)
Next, as shown in FIG. 10, the second surface 2B ′ of the substrate 2 is covered with a protective film 4 made of an insulating material. Specifically, the protective layer 4 is formed by forming an aluminum oxide film on the second surface 2B ′ by laminating aluminum by an atomic deposition method in an atmosphere containing oxygen. The protective film 4 may be formed on the first surface 2A of the substrate 2 or may be formed on the side surface. In the present embodiment, a case where the protective film 4 is formed only on the second surface 2B ′ will be described.

  The protective film 4 can be formed using, for example, an atomic deposition method, a sputtering method, a CVD method, an evaporation method, or the like. In this embodiment, a case where film formation is performed using an atomic deposition method will be described.

  When film formation is performed using a sputtering method, the film formation rate can be set at, for example, 5 nm / min or more. Since the sputtering method is used, even if the film formation rate is increased, the film quality of the aluminum film 4 is hardly deteriorated, so that it may be set to 10 nm / min or more. Since the film formation rate can be increased in this way, the productivity of this step can be improved.

(Coating process)
Thereafter, the conductive paste 6 is applied onto the protective film 4 in a finger electrode pattern having a plurality of electrode fingers as shown in FIG. As the conductive paste 6, for example, aluminum, tin, magnesium, silver, or the like can be used. The material of the conductive paste 6 can be determined by the conductivity type of the semiconductor to be connected. The thickness of the conductive paste 6 may be set as appropriate depending on the thickness of the protective film 4, but can be set to be, for example, 500 nm or more and 30 μm or less. As a method of applying the conductive paste 6, for example, a screen printing method or the like can be used.

  Specifically, for example, aluminum can be suitably selected for the conductive paste 6 when connected to a p-type conductive semiconductor, and silver is preferably selected when connected to an n-type semiconductor. be able to. In this embodiment, a case will be described in which a material containing aluminum as a main component is used as the finger electrode 3a connected to the p-type, and silver is used as the main component as the finger electrode 3b connected to the n-type. In the following description, the finger electrode 3a will be described.

(First electrode forming step)
After the coating process, the protective film 4 and the conductive paste 5 are heated. The heating temperature and the heating time can be appropriately set depending on the material and thickness of the protective film 4 and the conductive paste 5. The heating temperature can be set to be, for example, 500 ° C. or more and 900 ° C. or less, and the heating time can be set to be, for example, 1 minute or more and 30 minutes or less.

  By this heating, a part of the aluminum contained in the conductive paste 5 can penetrate into the protective film 4 to form the conductive path 7 as shown in FIG. The end of the conductive path 7 comes into contact with a part of the second surface 2B ′ of the substrate 2. Furthermore, a part of the conductive path 7 in contact with the substrate 2 is diffused into the substrate 2 and is in ohmic contact with the substrate 2. Then, by curing the conductive path 7 and the protective film 4, the finger electrode 3 including the electrode finger 3 'can be obtained.

  As described above, when the finger electrode 3 is formed by diffusing a part of the conductive paste 5 in the protective film 4, a part of the applied conductive paste 5 remains. Therefore, when it becomes the electrode finger 3 ′, it is possible to have a protruding region 3 ′ a protruding from the protective film 4 as shown in the above-described third modification.

(Second electrode forming step)
Next, as shown in FIG. 13, bus bar electrodes 5 connected to the plurality of electrode fingers 3 ′ are formed on the protective film 4 and the finger electrodes 3. The bus bar electrode 5 is provided so as to be connected to the plurality of electrode fingers 3 ′ and straddle the protective film 4. Since the bus bar electrode 5 can be formed in a process different from the finger electrode 3 as described above, the material and thickness can be freely changed.

  When the bus bar electrode 5 is cut in a direction perpendicular to the BB ′ line or the CC ′ line (a direction parallel to the AA ′ line), the photoelectric conversion element 1 formed in this way is described above. As shown in the modified example 3 of the photoelectric conversion element, since the electrode finger 3 ′ protrudes from the protective film 4, the bus bar electrode 5 has a raised shape.

DESCRIPTION OF SYMBOLS 1 Photoelectric conversion element 2 Board | substrate 3 Finger electrode 3 'Electrode finger 3'a Protrusion area | region 4 Protective film 5 Bus bar electrode 6 2nd protective film 7 Conductive path 8 2nd finger electrode

Claims (6)

A one-conductivity-type semiconductor substrate having a photoelectric conversion layer for photoelectrically converting incident light provided with a reverse conductivity-type layer on the main surface ;
The semiconductor substrate and the opposite conductivity type layer formed on the main surface et al are of, and having a plurality of electrode fingers, reverse connected to the finger electrode and the opposite conductivity type layer of one conductivity type side connected to the semiconductor substrate A finger electrode on the conductive side ;
A protective film made of an insulating material provided on the main surface of the semiconductor substrate and the reverse conductivity type layer so as to be located between each of the plurality of electrode fingers;
Have a bus bar electrode connected provided on the protective film and the one conductivity-type-side finger electrodes and the opposite conductivity type side of the finger electrodes on the plurality of the electrode fingers,
A part of the reverse conductivity type layer is a photoelectric conversion element located below a bus bar electrode connected to the finger electrode on the one conductivity type side .   The photoelectric conversion element according to claim 1, wherein the bus bar electrode is made of a conductive material different from the finger electrode.   The photoelectric conversion element according to claim 1, wherein the bus bar electrode has a thickness greater than a thickness of the finger electrode.   The photoelectric conversion element according to claim 1, further comprising a second protective film provided on the protective film and the finger electrode so as not to overlap the bus bar electrode.   The photoelectric conversion element according to claim 4, wherein the second protective film has a refractive index larger than that of the protective film. The photoelectric conversion element according to claim 1, wherein the reverse conductivity type layer is located in the semiconductor substrate.

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