WO2011161789A1

WO2011161789A1 - Crystalline solar cell and manufacturing method for crystalline solar cell

Info

Publication number: WO2011161789A1
Application number: PCT/JP2010/060712
Authority: WO
Inventors: 美和渡井; 一也斎藤; 小松　孝; 俊二黒岩
Original assignee: 株式会社アルバック
Priority date: 2010-06-24
Filing date: 2010-06-24
Publication date: 2011-12-29

Abstract

A crystalline solar cell (10) is provided with: a crystalline substrate (11) that achieves photovoltaic energy conversion between a light receiving surface (11i) that receives light and a back surface facing the light receiving surface; and a white coating film (14) that reflects light that has traveled through and exited the back surface (11r) of the crystalline substrate (11) back into the crystalline substrate (11).

Description

Crystal solar cell and method for manufacturing crystal solar cell

The present invention relates to a crystal solar cell and a method for manufacturing a crystal solar cell, and more particularly to a crystal solar cell that reuses transmitted light that passes through a crystalline substrate that exhibits a photoelectric conversion function, and a method for manufacturing the crystal solar cell. It is.

Solar cells that generate power using solar energy are power generation systems that are expected as alternative technologies for fossil fuels, and they tend to rapidly increase their production from the viewpoint of protecting the global environment. Such a rapid increase in production amount may cause a serious shortage of semiconductor materials as raw materials, for example, a shortage of silicon in silicon-based solar cells. Therefore, a technology capable of reducing the amount of raw material used per electric power is required for the solar cell production technology.

By the way, the types of silicon solar cells are classified into three types based on the crystallinity of the photoelectric conversion elements. First, there is an amorphous silicon solar cell using an amorphous material for a photoelectric conversion element. The junction of the photoelectric conversion element in this amorphous silicon solar cell is formed by stacking a p-type amorphous semiconductor film, an n-type amorphous semiconductor film, or the like on an insulating substrate. Second, there is a single crystal silicon solar cell using a single crystal material for a photoelectric conversion element. The junction of the photoelectric conversion element in this single crystal silicon solar cell is formed by the diffusion process of impurities with respect to the single crystal wafer cut out from the ingot. Thirdly, there is a polycrystalline silicon solar cell using a polycrystalline material for a photoelectric conversion element. The junction of the photoelectric conversion element in this polycrystalline solar cell is formed by impurity diffusion treatment on the polycrystalline wafer cut out from the ingot, as in the case of the single crystal silicon solar cell.

An amorphous film in an amorphous silicon solar cell is thinner than a wafer used for a crystalline silicon solar cell, and therefore can be composed of a small amount of raw material compared to a crystalline solar cell. . However, in the process of forming such an amorphous film, a gas phase reaction with a high-purity source gas is generally used, and in addition to the object to be formed, a large amount of amorphous film is formed on the entire inner wall of the film forming apparatus. A large amount of source gas is exhausted to the outside of the film forming apparatus. As a result, the amorphous film itself, which is a constituent element, can be composed of a small amount of raw material, but the raw material gas consumed in the production process is increased, and as a result, the raw material consumption is higher than that of the crystalline solar cell. May even be higher. In addition, the conversion efficiency of amorphous silicon solar cells is generally lower than that of crystalline silicon solar cells. Therefore, the technology for producing such an amorphous silicon solar cell requires a technology that satisfies the reduction of raw material consumption and the improvement of conversion efficiency.

On the other hand, the structure of the photoelectric conversion element in the crystalline silicon solar cell is various, such as a back contact structure having no electrode on the light receiving surface, and a pin structure using a heterojunction between single crystal silicon and amorphous silicon. The conversion efficiency is improved by the structure. In addition, wafers used for crystalline silicon solar cells have been reduced in thickness to 50 μm to 200 μm for the purpose of dealing with the above-described silicon shortage. Therefore, the production technology for crystalline silicon solar cells is expected as a technology that can reduce the amount of raw material used per electric power as compared with the above-described amorphous silicon solar cells.

However, even in crystalline silicon solar cells that employ the element structure described above, as the photoelectric conversion element becomes thinner, more light cannot be absorbed by the photoelectric conversion element, and the utilization efficiency of sunlight itself improves. Technology is required. As an example of a structure that improves the utilization efficiency of sunlight, a solar cell described in Patent Document 1 is filled with a light-reflective filler in the gap between adjacent photoelectric conversion elements. According to the solar cell using such a filler, since light incident between adjacent photoelectric conversion elements is reflected into the photoelectric conversion element by the filler, even light incident between the photoelectric conversion elements is generated. Will contribute. Therefore, it is possible to compensate for a part of the decrease in the use efficiency of sunlight.
JP 2006-073707 A

Incidentally, the solar cell described in Patent Document 1 uses sunlight from the light receiving surface and the back surface for power generation, respectively, by a structure in which the light receiving surface and the back surface of the photoelectric conversion element are covered with a light transmitting plate. Such a structure is useful in an environment where sufficient sunlight can be supplied to the back surface of the photoelectric conversion element. However, in an environment where sunlight cannot be supplied to the back side of the photoelectric conversion element, a structure or process for guiding the transmitted light that passes through the photoelectric conversion element itself to the photoelectric conversion element in order to improve the utilization efficiency of sunlight. Technology is needed.

In order to meet such a demand, for example, a configuration that imparts high light reflectivity to the back electrode of the photoelectric conversion element is conceivable. However, the constituent materials and design rules for the back electrode of solar cells are severely constrained to reduce power loss in the first place. Therefore, in order to impart light reflectivity to such a back electrode, it is necessary to select expensive silver or the like as the electrode material among the metal materials. Moreover, even if the back electrode can be provided with light reflectivity, there is a possibility that an electrode film thickness for exhibiting sufficient light reflectivity cannot be adopted under the above-described restrictions.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a crystal solar cell and a method for manufacturing the crystal solar cell that can easily reuse light emitted through the back surface of the crystalline substrate. Is to provide.

One embodiment of the present invention is a crystalline solar cell. The crystalline solar cell includes a crystalline substrate that exhibits a photoelectric conversion function between a light-receiving surface that receives light and a back surface that faces the light-receiving surface, and light that is transmitted through the back surface of the crystalline substrate. A white coating film reflecting into the crystalline substrate.

Another aspect of the present invention is a method for manufacturing a crystalline solar cell. The method includes forming a crystalline substrate having a light-receiving surface that receives light and a back surface opposite to the light-receiving surface and expressing a photoelectric conversion function therebetween, and transmitting the back surface of the crystalline substrate. Forming a white coating film that reflects the emitted light into the crystalline substrate.

The perspective view which shows the cross-sectional perspective structure of the crystal solar cell concerning 1st Embodiment. The perspective view which shows the cross-sectional perspective structure of the crystal solar cell concerning 2nd Embodiment. The perspective view which shows the cross-sectional perspective structure of the crystal solar cell concerning 3rd Embodiment. The perspective view which shows the cross-sectional perspective structure of the crystal solar cell concerning the example of a change. The perspective view which shows the cross-sectional perspective structure of the crystal solar cell concerning the example of a change. The perspective view which shows the cross-sectional perspective structure of the crystal solar cell concerning the example of a change.

(First embodiment)
Hereinafter, a first embodiment of a crystalline solar cell embodying the present invention will be described with reference to FIG. FIG. 1 shows a cross-sectional perspective structure of a crystalline solar cell 10 according to the first embodiment.

As shown in FIG. 1, the crystalline solar cell 10 includes a crystalline substrate 11, a first electrode 12, a second electrode 13, and a white coating film 14. The crystalline substrate 11 is a crystalline semiconductor substrate. For example, a p-type silicon substrate having a thickness of 50 μm to 200 μm and containing p-type impurities can be used. As such a silicon substrate, a wafer cut from a single crystal silicon ingot formed by a pulling method, a wafer cut from a polycrystalline silicon ingot formed by a casting technique, or the like can be used.

A first electrode 12 electrically connected to the surface 11i is formed on the surface 11i, which is one main surface of the crystalline substrate 11, over substantially the entire surface 11i. The first electrode 12 is formed of a conductive material having a light transmission property that transmits sunlight. When sunlight (arrow in FIG. 1) is irradiated toward the first electrode 12, the sunlight transmitted through the first electrode 12 reaches the surface 11i, and the surface 11i of the crystalline substrate 11 receives sunlight. It functions as a light receiving surface. As a constituent material of the first electrode 12, for example, a transparent conductive material such as zinc oxide, tin oxide, or indium tin oxide can be used.

On the other hand, the second electrode 13 electrically connected to the back surface 11r is formed on substantially the entire back surface 11r on the back surface 11r which is another main surface facing the front surface 11i. The second electrode 13 is formed of a conductive material selected according to the structure and process design of the crystalline solar cell 10. As the constituent material of the second electrode 13, for example, a low resistance material such as aluminum selected so as to suppress power loss, and further, like the first electrode 12, a transparent conductive material having a light transmission property that transmits light. Materials and the like can be used.

The crystalline substrate 11 is formed with a semiconductor layer formed by diffusing impurities on the front surface 11i side. The entire crystalline substrate 11 includes a first semiconductor layer 11a constituting the back surface 11r in the thickness direction. And the second semiconductor layer 11b constituting the surface 11i. The first semiconductor layer 11a and the second semiconductor layer 11b are in a reverse conductive relationship. For example, when a p-type silicon substrate is used as the crystalline substrate 11, the first semiconductor layer 11a is a p-type Si film. The second semiconductor layer 11b is an n-type semiconductor layer.

When the surface 11i of the crystalline substrate 11 receives sunlight, the sunlight incident from the surface 11i passes through the second semiconductor layer 11b and further enters the pn junction and the first semiconductor layer 11a. Next, the light absorbed in each part of the crystalline substrate 11 generates electrons and holes that are carriers. The generated carriers are separated into the first semiconductor layer 11a and the second semiconductor layer 11b according to the potential gradient of the pn junction that is the junction between the first semiconductor layer 11a and the second semiconductor layer 11b. The carriers separated in this way are collected by the first electrode 12 and the second electrode 13 to be converted into electric energy. That is, the light absorbed by the crystalline substrate 11 is converted into electric energy by the photoelectric conversion function of the crystalline substrate 11.

Note that the thickness of the first semiconductor layer 11a and the thickness of the second semiconductor layer 11b described above are such that the p-type Si film is relatively thick and the n-type semiconductor layer is relatively thin. Is preferred. With such a thickness, recombination of carriers generated in the crystalline substrate 11 is reduced, and conversion efficiency is improved.

Furthermore, it is preferable that the impurity concentration in the depth direction of the first semiconductor layer 11 a described above is relatively high in the vicinity of the interface with the second electrode 13. With such a concentration distribution configuration, since an internal electric field based on the concentration difference is formed in the first semiconductor layer 11a, carriers generated in the first semiconductor layer 11a resist the potential gradient of the pn junction. The direction, that is, the flow to the bonding surface between the crystalline substrate 11 and the second electrode 13 stops, and recombination is further reduced.

On the second electrode 13 described above, a white coating film 14 that reflects light is formed so as to face the back surface 11r across the second electrode 13. The white coating film 14 is a white coating film having a high reflectance in the region of the absorption wavelength of the crystalline substrate 11, and the white component is at least selected from the group consisting of barium sulfate, magnesium oxide and titanium oxide. A kind of compound can be used. The white coating film 14 is formed by applying a white paint composed of the white component fine particles, a binder, and a solvent to the back surface 11r. The white coating film 14 having such a configuration functions as a reflecting surface that diffusely reflects a part of sunlight, which is light transmitted through the back surface 11r of the crystalline substrate 11 and emitted to the back surface 11r.

When the surface 11i of the crystalline substrate 11 receives sunlight, the sunlight incident from the surface 11i is absorbed by the first semiconductor layer 11a and the second semiconductor layer 11b. However, when the thickness of the crystalline substrate 11 is reduced in order to reduce the amount of raw material used on the crystalline solar cell 10, the amount of light that cannot be absorbed by the crystalline substrate 11 increases, and a part of the sunlight incident from the surface 11i is increased. It passes through the crystalline substrate 11. In this way, a part of the light transmitted through the crystalline substrate 11 and emitted from the back surface 11 r is transmitted through the second electrode 13 and reaches the white coating film 14. At this time, the light reaching the white coating film 14 is reflected by the light reflectivity of the white coating film 14. Then, the light reflected by the white coating film 14 passes through the second electrode 13 again and is absorbed by the crystalline substrate 11. That is, part of the light transmitted through the crystalline substrate 11 is also converted into electric energy by the light reflecting function of the white coating film 14.

Therefore, the light reflection function of the white coating film 14 can improve the light use efficiency in the crystalline solar cell 10. In addition, the constituent material, film thickness, position, and the like of the white coating film 14 can be changed according to the optical characteristics of the crystalline substrate 11, the first electrode 12, and the second electrode 13, which are other constituent requirements. Therefore, by appropriately selecting such a configuration of the white coating film 14, reuse of transmitted light can be realized more appropriately and easily. Therefore, the crystalline substrate 11, the first electrode 12, and the second electrode 13 are not forced to change their constituent materials and design rules, and the light utilization efficiency can be improved.

When a silicon substrate is used as the crystalline substrate 11, the white coating film 14 described above preferably has a reflectance of 90% or more particularly in a wavelength region of 500 nm to 1200 nm. With the configuration having such a reflectance, light that can be absorbed by the crystalline substrate 11 out of the light transmitted through the crystalline substrate 11 can be efficiently reflected.

Furthermore, as the constituent material of the second electrode 13 described above, it is preferable to use a transparent conductive material having a light-transmitting property that transmits light, as in the case of the first electrode. With such a material, the light transmitted through the crystalline substrate 11 is hardly absorbed by the second electrode 13 and reenters the crystalline substrate 11, thereby further improving the light utilization efficiency. it can.

The crystal solar cell 10 described above is formed by the following manufacturing process. First, a diffusion process using an ion implantation method or a thermal diffusion method is performed on the surface 11i of the crystalline substrate 11, thereby forming a second semiconductor layer 11b which is an impurity diffusion layer. Next, a film forming process using a sputtering method, a printing method, or a coating method is performed on the surface 11 i of the crystalline substrate 11, thereby forming the first electrode 12. Further, a film forming process using a sputtering method, a printing method, or a coating method is performed on the back surface 11r of the crystalline substrate 11, whereby the second electrode 13 is formed.

Then, a film forming process using a coating method using a white paint is performed on the second electrode 13, thereby forming a white coating film 14. The coating method, which is a method for forming the white coating film 14, is a method in which mechanical and thermal distortion is less likely to be applied to the substrate that is the target of film formation, as compared with the other film formation methods described above. Therefore, according to such a manufacturing method, the thinning of the crystalline substrate 11 itself is not hindered regardless of the additional manufacturing process of the white coating film 14. Therefore, it is possible to sufficiently cope with a reduction in the amount of raw material used in the crystalline solar cell 10.

As described above, according to the first embodiment, the following effects can be obtained.
(1) The white coating film 14 provided on the second electrode 13 guides the light transmitted through the crystalline substrate 11 to the crystalline substrate 11 again. Therefore, the reuse of transmitted light can be realized appropriately and easily only by appropriately changing the constituent material, film thickness, position, etc. of the white coating film 14 according to other constituent requirements. Therefore, the crystalline substrate 11, the first electrode 12, and the second electrode 13 are not forced to change their constituent materials or design rules. As a result, the crystalline solar cell 10 secures the degree of freedom of design for the crystalline substrate 11, the first electrode 12, and the second electrode 13 that is the back electrode, and further recycles the light transmitted through the crystalline substrate 11. Can be used.

(2) Since the white component of the white coating film 14 is at least one of barium sulfate, magnesium oxide, and titanium oxide, a high solar reflectance can be achieved in the white coating film 14, and as a result, It becomes possible to improve utilization efficiency more.

(3) Light corresponding to the absorption wavelength of the crystalline substrate 11 is reflected by the white coating film 14 with a high probability of 90% or more. As a result, the light use efficiency can be improved more effectively.
(4) The white coating film 14 is formed by a coating method, which is a method that hardly gives mechanical and thermal strain to the crystalline substrate 11. Therefore, the thinning of the crystalline substrate 11 itself is not hindered regardless of the additional manufacturing process of the white coating film 14. Therefore, it is possible to sufficiently cope with a reduction in the amount of raw material used in the crystalline solar cell 10.

(Second Embodiment)
Hereinafter, a second embodiment of a crystalline solar cell embodying the present invention will be described with reference to FIG. In the second embodiment, the back surface passivation film 15 is added to the crystalline solar cell 10 of the first embodiment, and the structure of the second electrode 13 is changed accordingly. Therefore, in the following, these changes will be described in detail. FIG. 2 shows a cross-sectional perspective structure of the crystalline solar cell 10 according to the second embodiment.

As shown in FIG. 2, between the back surface 11r of the crystalline substrate 11 and the second electrode 13, a back surface passivation film 15 having optical transparency is formed over substantially the entire back surface 11r. The second electrode 13 is partially connected to the back surface 11r through a contact 13a that penetrates the back surface passivation film 15 in the film thickness direction. The back surface passivation film 15 limits the contact area between the back surface 11r and the second electrode 13 from its structure, and reduces crystal defects contained in the crystalline substrate 11 based on the constituent elements of the back surface passivation film 15. The back surface passivation film 15 having such a configuration improves conversion efficiency by reducing carrier recombination at the interface between the back surface 11r and the second electrode 13, recombination of carriers due to crystal defects, and the like. As such a back surface passivation film 15, for example, a silicon oxide film, a silicon nitride film, an aluminum oxide film, or the like can be used.

Note that the back surface passivation film 15 described above is preferably an oxide or nitride formed by oxidizing or nitriding a constituent element common to the crystalline substrate 11. With such a constituent element, the back surface passivation film 15 can be formed by oxidizing or nitriding the back surface 11r of the crystalline substrate 11. In addition, since the refractive index of the back surface passivation film 15 is lower than that of the crystalline substrate 11, light that is transmitted through the crystalline substrate 11 and emitted from the back surface 11 r has a critical angle or more. Is reflected. Only light smaller than the critical angle passes through the back surface passivation film 15 and reaches the white coating film 14.

That is, according to the crystalline solar cell 10 having such a configuration, the direction of light reaching the white coating film 14 is generally defined by the refractive indexes of the crystalline substrate 11 and the back surface passivation film 15. Therefore, it is possible to appropriately grasp the optical characteristics required for the white coating film 14 itself based on the optical characteristics of the crystalline substrate 11 and the back surface passivation film 15. By designing the constituent material and film thickness of the white coating film 14, the light utilization efficiency itself can be greatly improved.

The crystal solar cell 10 described above is formed by the following manufacturing process. First, as in the first embodiment, a diffusion process using an ion implantation method or a thermal diffusion method is performed on the surface 11i of the crystalline substrate 11, thereby forming a second semiconductor layer 11b which is an impurity diffusion layer. The Next, a film forming process using a thermal oxidation method, a thermal nitridation method, a CVD method, or the like is performed on the back surface 11r of the crystalline substrate 11, whereby the back surface passivation film 15 is formed. Further, a patterning process using a photolithography method, a laser processing method, or the like is performed on the back surface passivation film 15, thereby forming a through hole (contact hole) corresponding to the contact 13a. Then, a film forming process using a sputtering method, a printing method, or a coating method is performed on the back surface passivation film 15, thereby forming the second electrode 13.

Thereafter, as in the first embodiment, a film forming process using a sputtering method, a printing method, or a coating method is performed on the surface 11 i of the crystalline substrate 11, thereby forming the first electrode 12. And the film-forming process using the apply | coating method using a white paint is given to the 2nd electrode 13, and, thereby, the white coating film 14 is formed.

As described above, according to the second embodiment, in addition to the effects of the first embodiment, the following effects can be obtained.
(5) Since the back surface passivation film 15 is interposed between the back surface 11r and the white coating film 14, the conversion efficiency can be improved. In addition, the optical characteristics required for the white coating film 14 itself can be properly grasped based on the optical characteristics of the crystalline substrate 11 and the back surface passivation film 15. Then, by designing the material and film thickness of the white coating film 14 under such grasped characteristics, it becomes possible to greatly improve the light utilization efficiency itself.

(6) The white coating film 14 and the crystalline substrate 11 hardly contact each other because the back surface passivation film 15 is interposed between the back surface 11r and the white coating film 14. Therefore, the constituent material of the white coating film 14 and the substrate contamination that may occur in the formation process thereof can be greatly suppressed, so that the selection range of materials applicable to the white coating film 14 can be expanded.

(Third embodiment)
Hereinafter, a third embodiment of a crystalline solar cell embodying the present invention will be described with reference to FIG. In the third embodiment, the semiconductor layer 11b of the crystalline substrate 11 of the first embodiment is changed. Therefore, in the following, these changes will be described in detail. FIG. 3 shows a cross-sectional perspective structure of the crystalline solar cell 10 according to the third embodiment.

The crystal solar cell 10 has a basic structure of a pin structure in which an i-type semiconductor film is interposed between a crystalline substrate having an inverse conductivity type relationship and an amorphous semiconductor film. Specifically, as shown in FIG. 3, the crystalline substrate 11a is an n-type silicon (Si) substrate, and an i-type amorphous Si (a-Si) film is formed on the surface of the crystalline substrate 11a. A certain i-type surface Si film 11bi is laminated. An i-type back Si film 11ci, which is also an i-type a-Si film, is laminated on the back surface of the crystalline substrate 11a. Further, a p-type Si film 11bp which is a p-type a-Si film is laminated on the i-type front surface Si film 11bi, and an n-type a-Si film is formed on the i-type back surface Si film 11ci. A type Si film 11cn is laminated.

In such a configuration, the i-type front surface Si film 11bi and the i-type back surface Si film 11ci are depleted. Most of the carriers excited by sunlight are generated by the i-type surface Si film 11bi and the i-type back surface Si film 11ci, and are generated by an internal electric field applied to the i-type surface Si film 11bi and the i-type back surface Si film 11ci. , It is transported to the corresponding first electrode 12 or second electrode 13. As a result, the conversion efficiency is increased.

The crystal solar cell 10 described above is formed by the following manufacturing process. First, a film forming process using the CVD method is performed on the surface of the crystalline substrate 11a, whereby the i-type surface Si film 11bi and the p-type Si film 11bp are sequentially stacked. Next, a film forming process using a CVD method is performed on the back surface of the crystalline substrate 11a, whereby the i-type back surface Si film 11ci and the n-type Si film 11cn are sequentially stacked. Then, as in the first embodiment, a film forming process using a sputtering method, a printing method, or a coating method is performed on the front surface 11i of the p-type Si film bp and the back surface 11r of the n-type Si film cn. A first electrode 12 and a second electrode 13 are formed. And the film-forming process using the apply | coating method using a white paint is given to the 2nd electrode 13, and, thereby, the white coating film 14 is formed.

As described above, according to the third embodiment, in addition to the effects of the first embodiment, the following effects can be obtained.
(7) Since the pin structure using the crystalline substrate and the amorphous semiconductor film is a basic structure, the conversion efficiency can be improved in addition to the improvement of the utilization efficiency by the white coating film 14.

In addition, the said embodiment can also be changed and implemented as follows.
In the second embodiment, the configuration in which the second electrode 13 is interposed between the crystalline substrate 11 and the white coating film 14 has been described. By changing this, the second electrode 13 may not be interposed between the crystalline substrate 11 and the white coating film 14. Specifically, as shown in FIG. 4, the back surface passivation film 15, the white coating film 14, and the second electrode 13 may be stacked in order from the back surface 11 r of the crystalline substrate 11. According to such a configuration, the light transmitted through the crystalline substrate 11 is not absorbed by the second electrode 13. Therefore, the use efficiency can be improved more effectively by the amount that the second electrode 13 is not interposed between the crystalline substrate 11 and the white coating film 14.

In the second embodiment, the first electrode 12 is formed on the front surface 11 i of the crystalline substrate 11, and the second electrode 13 is formed on the rear surface 11 r of the crystalline substrate 11 via the back surface passivation film 15. Explained. By changing this, the first electrode 12 and the second electrode 13 may be formed on the common back surface 11r. Specifically, as shown in FIG. 5, the second semiconductor layer 11b and the third semiconductor layer 11c, which are in a reverse conductive relationship with each other, are formed so as to be exposed from the back surface 11r. Note that the third semiconductor layer 11c may be the first semiconductor layer 11a. The first electrode 12 and the second electrode 13 are electrically connected to the third semiconductor layer 11b and the second semiconductor layer 11c, respectively, through the back surface passivation film 15 in the film direction. That is, the first and

second electrodes

12 and 13 are disposed on the back surface 11r as two back surface electrodes. And it can also be actualized to the structure by which the white coating film 14 is laminated | stacked so that these 1st electrode 12, 2nd electrode 13, and back surface passivation film 15 may be covered. According to such a configuration, sunlight can be received more effectively by the amount that the first electrode 12 can be omitted from the surface 11i that is the light receiving surface. In this case, a configuration in which the light-transmitting surface passivation film 16 is formed over substantially the entire surface 11i, that is, a configuration in which the passivation film is provided on both the front surface 11i and the back surface 11r is preferable. According to such a configuration, the effect of improving the conversion efficiency obtained by the back surface passivation film 15 can be further obtained by the surface passivation film 16.

In the above-described two embodiments, the configuration in which the passivation film 15 is formed on the back surface 11r of the crystalline substrate 11 has been described. By changing this, the passivation film may be formed on the front surface 11 i and the back surface 11 r of the crystalline substrate 11. Specifically, as shown in FIG. 6, a surface passivation film 16 having optical transparency is formed over substantially the entire surface 11 i, and the first electrode 12 penetrates the surface passivation film 16 in the film thickness direction. Is partially connected to the surface 11i. According to such a configuration, the effect of improving the conversion efficiency obtained by the back surface passivation film 15 can be further obtained by the surface passivation film 16.

As shown in FIG. 6, an antireflection film 17 may be laminated on the surface passivation film 16 so as to suppress the reflection loss of sunlight on the surface. Alternatively, when there is no surface passivation film 16, an antireflection film 17 may be laminated on the surface 11i. As a constituent material of the antireflection film 17, for example, silicon oxide, silicon nitride, cerium oxide, aluminum oxide, tin dioxide, titanium dioxide, magnesium fluoride, and tantalum oxide can be used.

In the above embodiments, the configuration in which the front surface 11i and the back surface 11r are flat surfaces has been described. Not limited to such a configuration, at least one of the front surface 11i and the back surface 11r can also have a texture for confining sunlight in the crystalline substrate. Such a texture can be embodied by, for example, a large number of protrusions having a quadrangular pyramid shape. Moreover, such a texture can be embodied by, for example, a method in which the front surface 11i or the back surface 11r that is the target surface is immersed in an aqueous potassium hydroxide solution. According to such a configuration, the white coating film 14 and the texture cooperate to confine sunlight in the crystalline substrate 11, and as a result, the utilization efficiency of sunlight is further improved.

Claims

A crystalline solar cell,
A crystalline substrate that expresses a photoelectric conversion function between a light-receiving surface that receives light and a back surface that faces the light-receiving surface;
A crystalline solar cell comprising: a white coating film that reflects light emitted through the back surface of the crystalline substrate into the crystalline substrate.
The crystalline solar cell according to claim 1 further comprises:
Comprising a back electrode electrically connected to the back surface of the crystalline substrate;
The crystalline solar cell, wherein the white coating film is adjacent to the back electrode.
The crystalline solar cell according to claim 2,
The crystal solar cell, wherein the back electrode is located between the back surface of the crystalline substrate and the white coating film.
The crystalline solar cell according to claim 2,
The crystalline solar cell, wherein the white coating film is located between the back surface and the back electrode of the crystalline substrate.
The crystalline solar cell according to claim 1,
The crystalline substrate is a silicon substrate;
The crystal solar cell further includes
A passivation film covering the back surface of the silicon substrate;
The crystalline solar cell, wherein the passivation film is located between the back surface of the silicon substrate and the white coating film.
The crystalline solar cell according to claim 5 further comprises:
A crystal solar cell comprising a back electrode provided between the white coating film and the passivation film and partially penetrating the passivation film and electrically connected to the back surface of the silicon substrate.
In the crystalline solar cell according to claim 6,
The silicon substrate includes first and second semiconductor layers having opposite conductivity, and the back electrode is disposed on the back surface of the silicon substrate and electrically connected to the first semiconductor layer,
The crystal solar cell further includes
A crystalline solar cell comprising a second back electrode disposed on the back surface of the silicon substrate and electrically connected to the second semiconductor layer.
The crystalline solar cell according to claim 5 further comprises:
A crystal solar cell comprising a back electrode penetrating the white coating film and the passivation film and electrically connected to the back surface of the silicon substrate.
The crystalline solar cell according to claim 5 further comprises:
A crystalline solar cell comprising another passivation film disposed on a surface of the silicon substrate functioning as the light receiving surface.
The crystalline solar cell according to any one of claims 1 to 9, wherein the white coating film contains at least one white component selected from the group consisting of barium sulfate, magnesium oxide and titanium oxide. .
The crystalline substrate is a silicon substrate;
The crystalline solar cell according to any one of claims 1 to 10, wherein the white coating film has a reflectance of 90% or more at a wavelength of 500 nm to 1200 nm.
The crystalline solar cell according to any one of claims 1 to 11, wherein the crystalline substrate is a silicon substrate having a thickness of 50 袖 m to 200 袖 m.
A method for producing a crystalline solar cell, comprising:
Forming a crystalline substrate that has a light-receiving surface that receives light and a back surface that faces the light-receiving surface and expresses a photoelectric conversion function between them;
Forming a white coating film that reflects light emitted through the back surface of the crystalline substrate into the crystalline substrate;
A method comprising the steps of:
The method of claim 13, wherein
The crystalline substrate is a silicon substrate, and the method further includes:
Depositing a passivation film on the back surface of the silicon substrate;
Laminating the white coating film on the passivation film;
A method comprising the steps of: