JP7633673B2 - Photovoltaic Cells and Solar Cells - Google Patents

Description

The present invention relates to solar cells and solar cells, and, for example, to technology that is effective when applied to solar cells and solar cells that use single crystal silicon.

Non-Patent Document 1 describes technology related to solar cell structures called "i-TOPCon (industrial tunnel oxide passive contact)."

Non-Patent Document 2 describes a technology that employs a so-called "back contact structure" in which both electrodes are placed on the back surface of a solar cell with a structure called "TOPCon."

Chengfa Liu etal,“Industrial TOPCon solar cells on n-type quasi-mono Si wafers with efficiencies above 23%“,Solar Energy Materials & Solar Cells 215 (2020) 110690 Paul Procel etal, “Numerical Simulations of IBC Solar Cells Based on Poly-Si Carrier-Selective Passivating Contacts”, IEEE JOURNAL OF PHOTOVOLTAICS, VOL.9 NO.2, March 2019

Renewable energy is attracting attention as a clean energy source that can be used to replace fossil fuels such as oil, coal, and natural gas, because it can be used without depletion and does not emit carbon dioxide, which causes global warming, when generating electricity.

Sunlight is one type of renewable energy, and the power generation method that uses solar cells to directly convert sunlight into electricity is called photovoltaic power generation. A solar cell is a photoelectric conversion element that absorbs light energy and converts it into electrical energy.

There are various types of solar cells, including organic solar cells and multi-junction solar cells, but crystalline silicon solar cells are the most widely used. The biggest challenge for crystalline silicon solar cells is to further improve their power generation efficiency (improve power density). In other words, there is a demand to improve the power generation efficiency of crystalline silicon solar cells, which are the most widely used.

The solar cell in one embodiment includes a single crystal silicon layer of a first conductivity type having a first surface on which a first light including visible light can be incident and a second surface on which a second light including visible light can be incident and including a first region and a second region, a first tunnel insulating layer in contact with the first region of the second surface, a first silicon layer of the first conductivity type in contact with the first tunnel insulating layer, a first electrode in contact with the first silicon layer, an emitter layer of a second conductivity type in contact with the second region of the second surface, a second tunnel insulating layer in contact with the emitter layer, a second silicon layer of the second conductivity type in contact with the second tunnel insulating layer, a second electrode in contact with the second silicon layer, and a passivation layer in contact with the second surface other than the first region and the second region.

According to one embodiment, the power density obtained from a crystalline silicon solar cell can be improved.

FIG. 1 is a diagram illustrating a schematic configuration of a typical solar power generation system. FIG. 1 is a cross-sectional view showing the configuration of an “i-TOPCon” type solar cell. FIG. 2 is a cross-sectional view showing the configuration of a solar cell. 1 is a graph showing the relationship between electrode pitch and power density. 1 is a graph showing the relationship between the impurity concentration of an emitter layer and power density. 3 is a flowchart showing the flow of a manufacturing process for a solar cell.

In all drawings used to explain the embodiments, the same components are generally given the same reference numerals, and repeated explanations will be omitted. In addition, hatching may be used even in plan views to make the drawings easier to understand.

<Solar power generation system>
For example, in a solar power generation system, a plurality of solar cell modules are connected in series to increase the system voltage.

Figure 1 is a diagram showing the configuration of a typical solar power generation system.

As shown in FIG. 1, for example, solar cell modules 10a to 10g are connected in series and connected to a power conditioner 20. The module frames of the solar cell modules 10a to 10g are electrically connected and set to ground potential (reference potential). That is, the potential (frame potential) of the module frames of the solar cell modules 10a to 10g is 0V. On the other hand, since the solar cell modules 10a to 10g are connected in series, their output voltages are added together and output to the power conditioner 20. Therefore, as shown in FIG. 1, in the solar cell module 10g, the potential (cell potential) of the solar cell is a high positive potential (several hundred V) relative to the ground potential, which is the potential of the module frame. On the other hand, in the solar cell module 10a, the potential of the solar cell is a low negative potential (-several hundred V) relative to the ground potential, which is the potential of the module frame. In this way, a solar power generation system employs a configuration in which multiple solar cell modules are connected in series. As a result, in the solar cell module closer to the output side (solar cell module 10g in FIG. 1), the cell potential of the solar cell is a positive potential that is higher than the frame potential of the module frame. On the other hand, in the solar cell module farther from the output side (solar cell module 10a in FIG. 1), the cell potential of the solar cell is a negative potential that is lower than the frame potential of the module frame. Here, each of the solar cell modules 10a to 10g includes multiple solar cell cells. In this specification, each of the solar cell modules 10a to 10g is also referred to as a solar cell. In other words, a solar cell is composed of multiple solar cell cells.

<Configuration of "i-TOPCon" type solar cell>
Next, a configuration example of a solar cell will be described.

As an example of the configuration of a solar cell, there is a solar cell called an "i-TOPCon" type solar cell, so we will explain this solar cell.

Figure 2 is a cross-sectional view showing the configuration of an "i-TOPCon" type solar cell 100.

In FIG. 2, the "i-TOPCon" type solar cell 100 has a single crystal silicon layer 30 into which n-type impurities (donors) such as phosphorus (P) or arsenic (As) have been introduced. The single crystal silicon layer 30 has a surface (first surface) 30a on which sunlight is incident, and a back surface (second surface) 30b on the opposite side to the surface. A textured structure, which is called a textured structure, is formed on the surface 30a of the single crystal silicon layer 30, so that the surface 30a of the single crystal silicon layer 30 is composed of a textured surface. This makes it possible to reduce the reflectance of sunlight incident from the surface 30a side of the single crystal silicon layer 30. In other words, the textured structure formed on the surface 30a of the single crystal silicon layer 30 has the function of suppressing the reflection of sunlight incident from the surface 30a side on the surface 30a.

The "i-TOPCon" type solar cell 100 has an emitter layer 31 in contact with the surface 30a of the single crystal silicon layer 30. The emitter layer 31 is composed of a p-type silicon layer into which a p-type impurity (acceptor) such as boron (B) has been introduced. Therefore, the surface 30a is a pn junction surface where the single crystal silicon layer 30, which is an n-type semiconductor layer, and the emitter layer 31, which is a p-type semiconductor layer, are in contact. A passivation layer 32 and a metal electrode 33 are formed so as to be in contact with the emitter layer 31. The passivation layer 32 is composed of, for example, a silicon nitride film. The metal electrode 33 is composed of, for example, a laminated film of an aluminum film and a silver film.

On the other hand, a tunnel insulating layer 34 is formed on the back surface 30b of the single crystal silicon layer 30 so as to contact the back surface 30b. This tunnel insulating layer 34 is composed of, for example, a silicon oxide film, a silicon nitride film, an aluminum oxide film, or a hafnium oxide film. Next, a high-concentration polycrystalline silicon layer 35 is formed so as to contact the tunnel insulating layer 34, and a passivation layer 36 and a metal electrode 37 are formed so as to contact the high-concentration polycrystalline silicon layer 35. Here, the passivation layer 36 is composed of, for example, a silicon oxide film, while the metal electrode 37 is composed of, for example, a silver film.

In this manner, the "i-TOPCon" type solar cell 100 is constructed.

<Operation of "i-TOPCon" type solar cell>
The "i-TOPCon" type solar cell 100 is configured as described above, and the operation of the "i-TOPCon" type solar cell 100 will be described below.

2, sunlight 40 including visible light and infrared light is irradiated from above the "i-TOPCon" type solar cell 100, and reflected light 50 of sunlight 40 including visible light and infrared light is irradiated from below the "i-TOPCon" type solar cell 100. Then, sunlight 40 is irradiated into the inside of the single crystal silicon layer 30 through the passivation layer 32 and the emitter layer 31. Meanwhile, reflected light 50 is irradiated into the inside of the single crystal silicon layer 30 through the passivation layer 36, the high concentration polycrystalline silicon layer 35, and the tunnel insulating layer 34. That is, in the "i-TOPCon" type solar cell 100, sunlight 40 is irradiated into the inside of the single crystal silicon layer 30 from the front surface 30a side, and reflected light 50 is irradiated into the inside of the single crystal silicon layer 30 from the back surface 30b side. In this way, it can be seen that the "i-TOPCon" type solar cell 100 constitutes a solar cell capable of receiving light from both sides.

At this time, among the sunlight 40 and the reflected light 50, light having a light energy larger than the band gap of silicon is absorbed. Specifically, electrons in the valence band receive the light energy supplied from the sunlight and are excited to the conduction band. As a result, electrons are accumulated in the conduction band and holes are generated in the valence band. In this way, when the "i-TOPCon" type solar cell 100 is irradiated with sunlight 40 and reflected light 50, light having a light energy larger than the band gap of silicon contained in the sunlight 40 and reflected light 50 is absorbed, electrons are excited to the conduction band, and holes are generated in the valence band. The generated holes are then accumulated in the emitter layer 31, which is a p-type semiconductor layer. Meanwhile, the excited electrons tunnel from the n-type single crystal silicon layer 30 through the tunnel insulating layer 34 and are accumulated in the high-concentration polycrystalline silicon layer 35. As a result, an electromotive force is generated between the metal electrode 33 electrically connected to the emitter layer 31 and the metal electrode 37 electrically connected to the high-concentration polycrystalline silicon layer 35. For example, when a load is connected between metal electrode 33 and metal electrode 37, electrons flow from metal electrode 37 through the load to metal electrode 33. In other words, a current flows from metal electrode 33 through the load to metal electrode 37.

In this way, the "i-TOPCon" type solar cell 100 can be operated to drive a load.

<Advantages of "i-TOPCon" solar cells>
Next, advantages of the above-mentioned "i-TOPCon" type solar cell 100 will be described.

The first advantage is that it is possible to receive light from both sides. In other words, the "i-TOPCon" type solar cell 100 not only utilizes sunlight 40 that is directly incident on the "i-TOPCon" type solar cell 100, but also utilizes reflected light 50 that is sunlight 40 reflected by the earth's surface, which provides the advantage of improving power generation efficiency.

In particular, the reflectance of sunlight from the Earth's surface is called "albedo," and in a wide range of regions on Earth, this "albedo" is 20% or more. Because the "i-TOPCon" type solar cell 100 effectively utilizes reflected light from sunlight, it can provide solar cells with excellent power generation efficiency in a wide range of regions on Earth.

Furthermore, to make effective use of reflected light, the i-TOPCon solar cell 100 employs a PERC (Passivated Emitter and Rear Cell) structure. This PERC structure is a structure that reduces power generation losses caused by recombination of carriers (electrons and holes) by forming a passivation layer (inactivation layer) on the back side of the solar cell.

The second advantage is that a tunnel insulating layer 34 is provided. In particular, by appropriately adjusting the material and thickness of this tunnel insulating layer 34, it functions as a layer with carrier selectivity that allows majority carriers to pass while blocking minority carriers. Specifically, in the "i-TOPCon" type solar cell 100 shown in FIG. 2, the tunnel insulating layer 34 has carrier selectivity that allows electrons, which are majority carriers, to pass while blocking holes, which are minority carriers.

For example, by irradiating the solar light 40 and the reflected light 50, electrons are excited in the single crystal silicon layer 30 and holes are generated, but the electrons, which are majority carriers, can tunnel through the tunnel insulating layer 34 and move to the high-concentration polycrystalline silicon layer 35. On the other hand, the holes, which are minority carriers, cannot tunnel through the tunnel insulating layer 34 and cannot move to the high-concentration polycrystalline silicon layer 35. As a result, in the "i-TOPCon" type solar cell 100, the diffusion of the holes, which are minority carriers, to the high-concentration polycrystalline silicon layer 35 can be suppressed. This means that the recombination of electrons and holes in the high-concentration polycrystalline silicon layer 35 is suppressed, and thus, according to the "i-TOPCon" type solar cell 100, the power generation loss caused by the recombination of electrons and holes can be reduced. In this way, the "i-TOPCon" type solar cell 100 has the advantage of being able to reduce the power generation loss caused by the recombination of electrons and holes by providing the tunnel insulating layer 34.

<Consideration of improvements>
From the viewpoint of improving power generation efficiency, the present inventor is considering adopting a so-called "back contact structure" in which both electrodes are disposed on the back surface of the "i-TOPCon" type solar cell 100 having the above-mentioned advantages. This is because, with the "back contact structure", there is no structure (electrodes) that blocks the sunlight entering from the front surface side, and it is believed that this will enable further improvement in power generation efficiency.

However, since the "i-TOPCon" type solar cell 100 is a bifacial solar cell, it is important from the viewpoint of further improving power generation efficiency to maintain a configuration that allows bifacial light reception even when the "back contact structure" is adopted. This is because if the adoption of the "back contact structure" results in the inability to allow bifacial light reception, it is considered difficult to achieve the desired improvement in power generation efficiency, since while the "back contact structure" can improve the efficiency of using sunlight incident from the front side, it will not be possible to use sunlight incident from the back side. Therefore, from the viewpoint of further improving power generation efficiency, it is desirable to devise a way to maintain a configuration that allows bifacial light reception while adopting the "back contact structure" in the "i-TOPCon" type solar cell 100.

In this embodiment, therefore, in order to further improve power generation efficiency, the "i-TOPCon" type solar cell 100 is designed to maintain a configuration that allows bilateral light reception while adopting a "back contact structure." The technical concept of this embodiment that incorporates this design is explained below.

First, according to the inventor's investigation, in order to maintain a configuration that allows bilateral light reception while adopting a "back contact structure" in the "i-TOPCon" type solar cell 100, it is essential to devise a tunnel insulating layer. For this reason, we will first explain the necessity of devising a tunnel insulating layer.

<Necessity for ingenuity in tunnel insulating layer>
For example, a configuration that allows for double-sided light reception while adopting a "back contact structure" can be realized by limiting the areas of the first electrode and the second electrode formed on the back surface and making the other areas of the back surface, excluding the first electrode formation area and the second electrode formation area, a light transmitting area. Therefore, by adopting this configuration in an "i-TOPCon" type solar cell, it is believed that a configuration that allows for double-sided light reception while adopting a "back contact structure" can be realized.

Here, in "TOPCon" type solar cells that use a tunnel insulating layer, it is implicitly recognized as common knowledge that the tunnel insulating layer is formed on the entire back surface of the monocrystalline silicon layer. This is clear, for example, from Non-Patent Document 2 described in the "Background Art". That is, Non-Patent Document 2 describes a technology that employs a "back contact structure" in "TOPCon" type solar cells that use a tunnel insulating layer formed on the entire back surface of the monocrystalline silicon layer, and as shown in Figure 2 of Non-Patent Document 2, Non-Patent Document 2 assumes a configuration in which a tunnel insulating layer is formed on the entire back surface of the monocrystalline silicon layer, even while employing a "back contact structure".

In this regard, as can be seen from Non-Patent Document 2, in order to realize a "back contact structure" in a configuration in which a tunnel insulating layer is formed on the entire back surface of a single crystal silicon layer, the tunnel insulating layer is required to have a first region in contact with an n-type silicon layer and a second region in contact with a p-type silicon layer. The first region of the tunnel insulating layer in contact with the n-type silicon layer is required to have carrier selectivity that allows electrons to pass while blocking holes, and the second region of the tunnel insulating layer in contact with the p-type silicon layer is required to have carrier selectivity that allows holes to pass while blocking electrons. In order to realize such carrier selectivity, the technology described in Non-Patent Document 2 adopts an "n-type sandwich structure" in which the first region of the tunnel insulating layer is sandwiched between n-type silicon layers, as shown in Figure 2 of Non-Patent Document 2, and adopts a "p-type sandwich structure" in which the second region of the tunnel insulating layer is sandwiched between p-type silicon layers.

As described above, in order to adopt a "back contact structure" in a "TOPCon" type solar cell that uses a tunnel insulating layer formed on the entire back surface of a single crystal silicon layer, a complex configuration that is difficult to manufacture is required. Therefore, in order to realize a "back contact structure" in a simple configuration in a "TOPCon" type solar cell that uses a tunnel insulating layer, some ingenuity is required regarding the tunnel insulating layer. In other words, in order to realize a "back contact structure" in a simple configuration in a "TOPCon" type solar cell that uses a tunnel insulating layer, it is necessary to make a change that overturns the implicit common sense of forming a tunnel insulating layer on the entire back surface of a single crystal silicon layer.

In this regard, the inventors have conducted extensive research into whether it is possible to realize a "back contact structure" in a "TOPCon" type solar cell with a simpler configuration, and have come up with the technical idea described below, which will now be explained.

<Technical Concept of the Embodiment>
The technical idea of the present embodiment is a combination of the idea of limiting the areas of the first electrode and the second electrode formed on the back surface and making the other area of the back surface, excluding the first electrode formation area and the second electrode formation area, a light transmitting area, as a configuration that enables bilateral light reception while adopting a "back contact structure" in a "TOPCon" type solar cell, and the idea of forming a tunnel insulating layer for the first electrode and a tunnel insulating layer for the second electrode as separate, separated layers, rather than forming a tunnel insulating layer on the entire back surface of the single crystal silicon layer. According to this technical idea, in a "TOPCon" type solar cell using a tunnel insulating layer, a configuration that enables bilateral light reception while adopting a "back contact structure" can be realized with a simple configuration, and the power density of the solar cell can be improved.

The reason is that the technical concept of this embodiment is believed to be able to improve the power density of the solar cell by achieving a synergistic effect of increasing the amount of incident light from the front side due to the "back contact structure", increasing the amount of incident light due to double-sided light reception, and suppressing the recombination of electrons and holes due to the carrier selectivity of the tunnel insulating layer.

In particular, in this embodiment, instead of forming a tunnel insulating layer on the entire back surface of the single crystal silicon layer, the idea exists of forming a tunnel insulating layer for the first electrode and a tunnel insulating layer for the second electrode as separate, separated layers, which is advantageous in that a configuration that enables double-sided light reception can be realized with a simple configuration while adopting a "back contact structure."

In other words, the technical idea of this embodiment is an extremely excellent and innovative technical idea in that it realizes a simple configuration that allows for bilateral light reception while adopting a "back contact structure" in a "TOPCon" type solar cell by making a change that overturns the implicit common sense that exists in "TOPCon" type solar cells, which is to form a tunnel insulating layer on the entire back surface of the single crystal silicon layer.

For example, in a "TOPCon" type solar cell that does not employ a "back contact structure," there is no need to pattern the tunnel insulating layer, so it is natural to adopt a configuration in which the tunnel insulating layer is left formed on the entire back surface of the single crystal silicon layer, without taking the trouble of patterning the tunnel insulating layer. Therefore, in a "TOPCon" type solar cell that did not anticipate a "back contact structure," it is thought that forming a tunnel insulating layer on the entire back surface of the single crystal silicon layer is recognized as tacit common sense.

In contrast, if a "back contact structure" is adopted in a "TOPCon" type solar cell, following this common sense would require a complex and difficult to manufacture structure, such as the technology described in Non-Patent Document 2 (see Figure 2 in Non-Patent Document 2). In this regard, Non-Patent Document 2 is a document related to simulations, and since it does not take into account actual manufacturing at all, it is believed to be premised on the tacit common sense that a tunnel insulating layer is formed on the entire back surface of the single crystal silicon layer.

In this regard, the inventor, taking into consideration the actual manufacture of solar cells, discovered that when a "back contact structure" is adopted in a "TOPCon" type solar cell, a simpler configuration can be achieved by deliberately adopting a technique for patterning the tunnel insulating layer, and came up with the idea of forming the tunnel insulating layer for the first electrode and the tunnel insulating layer for the second electrode as separate, separated layers, as described above. The inventor's discovery is novel in that it goes beyond tacit common sense and deliberately adopts a configuration for patterning the tunnel insulating layer, and is a discovery that even a person skilled in the art would not easily have come up with.

The following describes the configuration of a solar cell that embodies the technical idea of this embodiment, which was conceived based on this knowledge.

Note that "power density" as used in this specification is used synonymously with "power generation efficiency (conversion efficiency)." However, "power generation efficiency (conversion efficiency)" is usually used under the assumption that standard sunlight is irradiated onto the solar cell from one side, so for bifacial solar cells that receive sunlight from one side as well as reflected light from the opposite side, power generation efficiency is evaluated using a physical quantity called "power density." Therefore, a high "power density" means high power generation efficiency.

<Solar cell configuration>
FIG. 3 is a cross-sectional view showing the configuration of the solar cell 100A.

In FIG. 3, the solar cell 100A has a single crystal silicon layer 30 into which an n-type impurity (donor) has been introduced. This single crystal silicon layer 30 has a front surface 30a (first surface) on which sunlight is incident, and a back surface 30b (second surface) opposite the front surface 30a.

In this embodiment, the premise is basically an arrangement (first arrangement) of the solar cell 100A in which sunlight 40 is incident on the "front surface 30a (first surface)" of the single crystal silicon layer 30, while reflected light 50 of the sunlight 40 is incident on the "back surface 30b (second surface)" of the single crystal silicon layer 30.

However, this is not limited to this, and does not exclude an arrangement (second arrangement) of the solar cell 100A in which reflected light 50 of sunlight 40 is incident on the "front surface 30a (first surface)" of the single crystal silicon layer 30, while sunlight 40 is incident on the "back surface 30b (second surface)" of the single crystal silicon layer 30. For example, the solar cell 100A can be installed not only at an incline with respect to the ground, but also vertically. In this case, for example, if the first arrangement is realized in the morning, the direction of the sun will inevitably change in the evening, resulting in the second arrangement being realized.

Taking this into consideration, the claims specify "a single crystal silicon layer of a first conductivity type having a first surface onto which the first light can be incident and a second surface onto which the second light can be incident." This is intended to describe a broad concept that includes cases where the "first light" is sunlight 40 and the "second light" is reflected light 50, and cases where the "first light" is reflected light 50 and the "second light" is sunlight 40.

The surface 30a of the single crystal silicon layer 30 has an uneven structure called a texture structure, so that the surface 30a of the single crystal silicon layer 30 is composed of an uneven surface. This makes it possible to reduce the reflectance of sunlight 40 incident on the surface 30a side of the single crystal silicon layer 30. In other words, the texture structure formed on the surface 30a of the single crystal silicon layer 30 has the function of suppressing the reflection of sunlight 40 incident on the surface 30a side at the surface 30a.

The solar cell 100A has a passivation layer 32 that contacts the surface 30a of the single crystal silicon layer 30. This passivation layer 32 is made of, for example, a silicon nitride film.

On the other hand, the rear surface 30b of the single crystal silicon layer 30 has a first region R1 and a second region R2. Here, the tunnel insulating layer 34a is formed so as to contact the first region R1 of the rear surface 30b. In other words, the tunnel insulating layer 34a is formed so as to contact the first region R1 of the rear surface 30b but not to contact the second region R2 of the rear surface 30b. This tunnel insulating layer 34a is composed of, for example, a silicon oxide film, a silicon nitride film, an aluminum oxide film, or a hafnium oxide film.

The tunnel insulating layer 34a is a film that has carrier selectivity that allows majority carriers to pass while blocking minority carriers. In this case, the single crystal silicon layer 30 and the high concentration polycrystalline silicon layer 35a that sandwich the tunnel insulating layer 34a are n-type semiconductor layers, so the majority carriers are electrons and the minority carriers are holes. For this reason, the tunnel insulating layer 34a can be said to be a film that has carrier selectivity that allows electrons to pass while blocking holes.

The carrier selectivity of the tunnel insulating layer 34a can be achieved by adjusting the thickness of the tunnel insulating layer 34a. For example, if the tunnel insulating layer 34a is too thick, not only the minority carriers but also the majority carriers will not pass through. On the other hand, if the tunnel insulating layer 34a is too thin, not only the majority carriers but also the minority carriers will pass through. In other words, if the tunnel insulating layer 34a is too thick or too thin, carrier selectivity cannot be expressed in the tunnel insulating layer 34a. For this reason, it is necessary to express carrier selectivity in the tunnel insulating layer 34a by appropriately adjusting the thickness of the tunnel insulating layer 34a so that the majority carriers pass through while the minority carriers are not passed through.

Next, a high-concentration polycrystalline silicon layer 35a is formed so as to contact the tunnel insulating layer 34a. The impurity concentration of the conductive impurity (donor) introduced into this high-concentration polycrystalline silicon layer 35a is higher than the impurity concentration of the conductive impurity (donor) introduced into the single crystal silicon layer 30. Then, a metal electrode 37a made of, for example, a silver film is formed so as to contact this high-concentration polycrystalline silicon layer 35a.

On the other hand, an emitter layer 31 is formed so as to contact the second region R2 of the back surface 30b. This emitter layer 31 is composed of, for example, a p-type silicon layer. Then, a tunnel insulating layer 34b is formed so as to contact the emitter layer 31. This tunnel insulating layer 34b is composed of, for example, a silicon oxide film, a silicon nitride film, an aluminum oxide film, or a hafnium oxide film.

The tunnel insulating layer 34b is a film having carrier selectivity that allows majority carriers to pass while blocking minority carriers. In this case, the emitter layer 31 and the high-concentration polycrystalline silicon layer 35b that sandwich the tunnel insulating layer 34b are p-type semiconductor layers, so the majority carriers are holes and the minority carriers are electrons. For this reason, the tunnel insulating layer 34b can be said to be a film having carrier selectivity that allows holes to pass while blocking electrons. This tunnel insulating layer 34b is also configured to exhibit carrier selectivity by appropriately adjusting the thickness, similar to the tunnel insulating layer 34a.

Next, a high-concentration polycrystalline silicon layer 35b is formed so as to contact the tunnel insulating layer 34b. This high-concentration polycrystalline silicon layer 35b is a p-type semiconductor layer. Then, a metal electrode 37b made of, for example, a silver film is formed so as to contact this high-concentration polycrystalline silicon layer 35b.

Furthermore, as shown in FIG. 3, in the solar cell 100A, a passivation layer 36 is formed on the rear surface 30b of the single crystal silicon layer 30 so as to contact the area other than the first region R1 and the second region R2.

This is how the solar cell 100A is constructed.

<Features of the embodiment>
A feature of this embodiment is that, for example, as shown in Fig. 3, in a "TOPCon" type solar cell, while adopting a "back contact structure", the areas of the metal electrodes 37a and 37b formed on the back surface are limited to enable bilateral light reception, and the other areas of the back surface, excluding the first region R1 and the second region R2, are made light transmitting regions. As a result, according to this embodiment, a synergistic effect is obtained that combines the increase in the amount of incident light from the front surface side due to the "back contact structure", the increase in the amount of incident light due to bilateral light reception, and the suppression of recombination of electrons and holes due to the carrier selectivity of the tunnel insulating layer, and thus the power density of the solar cell can be improved.

In particular, in this embodiment, a tunnel insulating layer is not formed on the entire back surface 30b of the single crystal silicon layer 30, but the tunnel insulating layer 34a in contact with the first region R1 of the back surface 30b and the tunnel insulating layer 34b in contact with the second region R2 of the back surface 30b are formed as separate, separate layers. This provides the advantage of being able to realize a "back contact structure" and a double-sided light receiving structure with a simpler configuration than a configuration that enables double-sided light receiving while adopting a "back contact structure" on the premise that a tunnel insulating layer is formed on the entire back surface 30b. This feature is innovative, having been conceived from an idea that is not bound by the tacit common sense of forming a tunnel insulating layer on the entire back surface of the single crystal silicon layer.

Specifically, in this embodiment, as shown in FIG. 3, the back surface 30b of the single crystal silicon layer 30 has a first region R1, a second region R2, and a third region R3. The first region R1 and the second region R2 are physically separated from each other and do not contact each other. The third region is a region of the back surface 30b other than the first region R1 and the second region R2, and in this third region R3, the passivation film 36 is in direct contact with the single crystal silicon layer 30.

In this embodiment, therefore, the tunnel insulating layer 34a in contact with the first region R1 of the back surface 30b and the tunnel insulating layer 34b in contact with the second region R2 of the back surface 30b can be formed as separate, separated layers, and the passivation film 36 can be brought into direct contact with the single crystal silicon layer 30 in the third region R3. As a result, according to this embodiment, a "back contact structure" and a double-sided light receiving structure can be realized with a simple configuration.

Furthermore, in this embodiment, as shown in FIG. 3, a feature is that the area of the tunnel insulating layer 34b in contact with the emitter layer 31 is smaller than the area of the emitter layer 31. That is, as shown in FIG. 3, the back surface of the emitter layer 31 has a fourth region R4 and a fifth region R5, and the tunnel insulating layer 34b is formed so as to be in contact with the fourth region R4. In this case, the area of the metal electrode 37b can also be reduced, thereby improving the back surface light receiving area.

<Verification of effectiveness>
Below, a description will be given of verification results that quantitatively show that the power density can be improved according to the solar cell 100A of the present embodiment.

Figure 4 is a graph showing the relationship between electrode pitch (rear surface) and power density for solar cell 100A. Figure 4 shows the results when the substrate resistivity is 70 Ω cm.

As shown in Fig. 4, at room temperature (25°C), the power density reaches 29.9 mW/ ^cm2 when the electrode pitch is 1.1 mm (1100 µm). This is the highest performance of a single-junction crystalline silicon solar cell at present.

In particular, the results of this verification exceed the future predictions of the "TOPCon" solar cell roadmap. Therefore, it can be said that the solar cell 100A of this embodiment is extremely superior in that it can achieve remarkable effects that are difficult even for those skilled in the art to predict.

<Further improvement in power density>
As described above, the solar cell 100A in this embodiment can achieve a maximum power density of 29.9 mW/cm ^2. Furthermore, the present inventor has found that the power density can be further improved by providing a BSF layer (back surface field layer) not shown in Fig. 3 for the solar cell 100A and increasing the impurity concentration of the conductive impurity introduced into this BSF layer and the emitter layer 31, and this point will be described below.

The BSF layer is a layer that has the function of separating electrons and holes near the back surface to reduce recombination, and is effective in improving power density.

Figure 5 is a graph showing the relationship between the impurity concentration of the emitter layer 31 and the power density.

Graph (1) is a graph in which the impurity concentration of the BSF layer is 1×10 ¹⁷ /cm ³ , graph (2) is a graph in which the impurity concentration of the BSF layer is 1×10 ¹⁸ /cm ³ , graph (3) is a graph in which the impurity concentration of the BSF layer is 1×10 ¹⁹ /cm ³ , and graph (4) is a graph in which the impurity concentration of the BSF layer is 1×10 ²⁰ /cm ³ .

5, it can be seen that the power density improves as the impurity concentration of the conductive impurity introduced into the emitter layer 31 and the BSF layer is increased. In particular, it can be seen that a power density of up to 30.03 mW/ ^cm2 can be realized by setting the impurity concentration of the conductive impurity introduced into the emitter layer ³¹ and the BSF layer to 1× ¹⁰ /cm.

<Method of manufacturing solar cell>
The solar cell 100A in the present embodiment is configured as described above, and a manufacturing method thereof will be described below. The manufacturing method of the solar cell 100A described here is one example, and the present invention is not limited to this.

Figure 6 is a flowchart showing the manufacturing process for solar cell 100A.

First, in FIG. 6, a semiconductor substrate (semiconductor wafer) having an n-type single crystal silicon layer 30 is prepared (S101). At this stage, for example, a cleaning process, a process for removing a damaged layer, a process for flattening the surface, etc. are performed. Next, a textured structure consisting of an uneven shape is formed on the surface 30a of the single crystal silicon layer 30 (S102). This textured structure is formed, for example, by a wet etching process. Then, a silicon layer is formed on the back surface 30b of the single crystal silicon layer 30, boron (B) is introduced into this silicon layer, and the silicon layer into which boron has been introduced is patterned to form an emitter layer 31 consisting of a p-type semiconductor layer that contacts the second region R2 of the back surface 30b (S103).

Next, an insulating layer made of, for example, a silicon oxide film is formed on the entire back surface 30b covering the emitter layer 31 (S104), and then the insulating layer is patterned using photolithography and etching techniques (S105). This forms a tunnel insulating layer 34a that contacts the first region R1 of the back surface 30b, and a tunnel insulating layer 34b that contacts the emitter layer 31.

Next, by using film formation and patterning techniques, a high-concentration polycrystalline silicon layer 35a (n-type) is formed in contact with the tunnel insulating layer 34a, and a high-concentration polycrystalline silicon layer 35b (p-type) is formed in contact with the tunnel insulating layer 34b (S106).

Then, for example, a passivation layer 32 is formed in contact with the surface 30a of the single crystal silicon layer 30. Similarly, for example, a passivation layer 36 is formed in contact with the rear surface 30b of the single crystal silicon layer 30 other than the first region R1 and the second region R2 (S107).

Next, a metal electrode 37a is formed to connect to the high-concentration polycrystalline silicon layer 35a. Similarly, a metal electrode 37b is formed to connect to the high-concentration polycrystalline silicon layer 35b (S108).

In this manner, solar cell 100A (see Figure 3) can be manufactured.

The invention made by the inventor has been specifically described above based on the embodiment thereof, but it goes without saying that the invention is not limited to the above embodiment and can be modified in various ways without departing from the gist of the invention.

In the above embodiment, the solar cell 100A is described as an example in which the "first conductivity type" is "n-type" and the "second conductivity type" is "p-type." However, the technical idea of the above embodiment is not limited to this, and can also be applied to, for example, a solar cell in which the "first conductivity type" is "p-type" and the "second conductivity type" is "n-type."

10a Solar cell module 10b Solar cell module 10c Solar cell module 10d Solar cell module 10e Solar cell module 10f Solar cell module 10g Solar cell module 20 Power conditioner 30 Single crystal silicon layer 30a Front surface 30b Back surface 31 Emitter layer 32 Passivation layer 33 Metal electrode 34 Tunnel insulating layer 34a Tunnel insulating layer 34b Tunnel insulating layer 35 Highly concentrated polycrystalline silicon layer 35a Highly concentrated polycrystalline silicon layer 35b Highly concentrated polycrystalline silicon layer 36 Passivation layer 37 Metal electrode 37a Metal electrode 37b Metal electrode 40 Sunlight 50 Reflected light 100 "i-TOPCon" type solar cell 100A Solar cell R1 First region R2 Second region

Claims (5)

a single crystal silicon layer of a first conductivity type having a first surface onto which a first light including visible light can be incident and a second surface onto which a second light including visible light can be incident, the second surface including a first region and a second region;
a first tunnel insulating layer in contact with the first region of the second surface;
a first silicon layer of the first conductivity type in contact with the first tunnel insulating layer;
a first electrode in contact with the first silicon layer;
an emitter layer of a second conductivity type in contact with the second region of the second surface;
a second tunnel insulating layer in contact with the emitter layer;
a second silicon layer of the second conductivity type in contact with the second tunnel insulating layer;
a second electrode in contact with the second silicon layer;
a passivation layer in contact with the second surface other than the first region and the second region;
Equipped with
The emitter layer is
a third surface in contact with the second surface;
a fourth surface opposite to the third surface; and
having
The fourth surface is
a first contact region where the emitter layer and the second tunnel insulating layer contact each other;
a second contact region where the emitter layer and the passivation layer meet;
A solar cell having the above structure. The solar cell according to claim 1 ,
A solar cell, wherein a concentration of a conductive impurity introduced into the first silicon layer is higher than a concentration of a conductive impurity introduced into the single crystal silicon layer. The solar cell according to claim 1 ,
the first tunnel insulating layer has a carrier selectivity that allows majority carriers of the first conductivity type to pass while blocking minority carriers;
The second tunnel insulating layer has a carrier selectivity that allows majority carriers of the second conductivity type to pass therethrough while blocking minority carriers. The solar cell according to claim 1 ,
the first silicon layer is a polycrystalline silicon layer;
The solar cell, wherein the second silicon layer is a polycrystalline silicon layer. A solar cell comprising a plurality of solar cells according to any one of claims 1 to 4.

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