JP2023033939A - Solar battery cell and solar battery - Google Patents

Abstract

[Problem] To improve the power density obtained by a crystalline silicon solar cell. [Solution] A solar cell 100A includes a first conductivity type monocrystalline silicon layer 30 having a front surface 30a on which a first light including visible light can be incident, and a back surface 30b on which a second light including visible light can be incident and which includes a first region and a second region, an emitter layer 31 of a second conductivity type in contact with the front surface 30a, a metal electrode 33 in contact with the emitter layer 31, a tunnel insulating layer 34a in contact with a first region R1 of the back surface 30b, a high concentration polycrystalline silicon layer 35a of the first conductivity type in contact with the tunnel insulating layer 34a, a metal electrode 37 in contact with the high concentration polycrystalline silicon layer 35a, and a passivation layer 36 in contact with a second region R2 of the back surface 30b. [Selected Figure] FIG.

Description

TECHNICAL FIELD The present invention relates to a solar cell and a solar cell, and for example, to a technique effectively applied to a solar cell and a solar cell using monocrystalline silicon.

Non-Patent Document 1 describes a technology related to a solar cell having a structure called “i-TOPCon (industrial Tunnel Oxide Passivated Contact)”.

Chengfa Liu et al,“Industrial TOPCon solar cells on n-type quasi-mono Si wafers with efficiencies above 23%“, Solar Energy Materials & Solar Cells 215 (2020) 110690

Renewable energy can be used without depletion of energy resources and does not emit carbon dioxide, which causes global warming, during power generation, so it can be used as a clean energy alternative to fossil fuels such as oil, coal, and natural gas. Attention has been paid.

One type of renewable energy is sunlight, and a power generation method in which solar cells are used to directly convert sunlight into electric power 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 such as organic solar cells and multi-junction solar cells, but crystalline silicon solar cells are the most popular. The biggest challenge for crystalline silicon solar cells is to further improve power generation efficiency (improve power density). That is, it is desired to improve the power generation efficiency of crystalline silicon solar cells, which are the most widely used.

A solar cell in one embodiment has a first surface capable of receiving first light containing visible light, and a second surface capable of receiving second light containing visible light and including a first region and a second region. a second conductivity type emitter layer in contact with the first surface; a first electrode in contact with the emitter layer; a tunnel insulating layer in contact with the first region of the second surface; A first conductivity type silicon layer in contact with the tunnel insulating layer, a second electrode in contact with the silicon layer, and a passivation layer in contact with the second region of the second surface.

According to one embodiment, the power density obtained with crystalline silicon solar cells can be increased.

It is a figure which shows typically the structure of a typical photovoltaic power generation system. 1 is a cross-sectional view showing the configuration of an “i-TOPCon” type solar cell; FIG. 1 is a cross-sectional view showing the configuration of a solar cell in an embodiment; FIG. 4 is a graph showing the relationship between back electrode pitch and short-circuit current density. 5 is a graph showing the relationship between back electrode pitch and open-circuit voltage; 5 is a graph showing the relationship between back electrode pitch and fill factor; 4 is a graph showing the relationship between back electrode pitch and conversion efficiency. 4 is a graph showing the relationship between electrode pitch and power density. It is the table|surface which put together the verification result. 4 is a flow chart showing the flow of a manufacturing process for a photovoltaic cell.

In principle, the same members are denoted by the same reference numerals throughout the drawings for describing the embodiments, and repeated description thereof will be omitted. In order to make the drawing easier to understand, even a plan view may be hatched.

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

FIG. 1 is a diagram schematically showing the configuration of a typical photovoltaic power generation system.

As shown in FIG. 1, for example, solar cell modules 10 a to 10 g are connected in series and connected to a power conditioner 20 . Each module frame of the solar cell modules 10a to 10g is electrically connected and set to a ground potential (reference potential). That is, the potential (frame potential) of each module frame 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 respective output voltages are added and output to the power conditioner 20. FIG. Therefore, as shown in FIG. 1, in the solar cell module 10g, the potential of the solar cell (cell potential) is a positive potential (several hundred volts) higher than 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 becomes a negative potential (-several hundred volts) lower than the ground potential, which is the potential of the module frame. As described above, in the photovoltaic power generation system, a configuration in which a plurality of photovoltaic modules are connected in series is adopted. On the other hand, in the solar cell module far from the output side (solar cell module 10a in FIG. 1), the cell potential of the solar cell is higher than the frame potential of the module frame. The cell potential becomes a low negative potential.Here, each of the solar cell modules 10a to 10g includes a plurality of solar cells.In this specification, each of the solar cell modules 10a to 10g is referred to as a solar cell. In other words, a solar battery is composed of a plurality of solar cells.

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

As a configuration example of a solar cell, there is a solar cell called an “i-TOPCon” type solar cell, and this solar cell will be described.

FIG. 2 is a cross-sectional view showing the configuration of the “i-TOPCon” type solar cell 100. As shown in FIG.

In FIG. 2, the “i-TOPCon” type solar cell 100 has a single crystal silicon layer 30 into which an n-type impurity (donor) such as phosphorus (P) or arsenic (As) is introduced. The monocrystalline silicon layer 30 has a front surface (first surface) 30a on which sunlight is incident and a rear surface (second surface) 30b opposite to the front surface. The surface 30a of the single-crystal silicon layer 30 is formed with an uneven structure called a texture structure, and as a result, the surface 30a of the single-crystal silicon layer 30 is composed of an uneven surface. Thereby, the reflectance of sunlight incident from the surface 30a side of the single crystal silicon layer 30 can be reduced. That is, the textured structure formed on the surface 30a of the single-crystal silicon layer 30 has a function of suppressing reflection on the surface 30a of sunlight incident from the surface 30a side.

The “i-TOPCon” type solar cell 100 has an emitter layer 31 in contact with the surface 30a of the monocrystalline silicon layer 30. As shown in FIG. The emitter layer 31 is composed of a p-type silicon layer into which a p-type impurity (acceptor) such as boron (B) is introduced. Therefore, the surface 30a serves as a pn junction surface where the monocrystalline 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 with each other. A passivation layer 32 and a metal electrode 33 are formed in contact with the emitter layer 31 . This passivation layer 32 is composed of, for example, a silicon nitride film. Also, 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 be in contact with 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. Subsequently, a high-concentration polycrystalline silicon layer 35 is formed in contact with the tunnel insulating layer 34 , and a passivation layer 36 and a metal electrode 37 are formed in contact with the high-concentration polycrystalline silicon layer 35 . Here, the passivation layer 36 is made of, for example, a silicon oxide film, while the metal electrode 37 is made of, for example, a silver film.

The “i-TOPCon” type solar cell 100 is configured as described above.

<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.

First, in FIG. 2, sunlight 40 including visible light and infrared light is irradiated from above the “i-TOPCon” type solar cell 100, and visible from below the “i-TOPCon” type solar cell 100. Reflected light 50 of sunlight 40 including light and infrared light is irradiated. Then, sunlight 40 is irradiated into the single crystal silicon layer 30 through the passivation layer 32 and the emitter layer 31 . On the other hand, the inside of single crystal silicon layer 30 is irradiated with reflected light 50 through passivation layer 36 , high-concentration polycrystalline silicon layer 35 and tunnel insulating layer 34 . That is, in the “i-TOPCon” type solar cell 100, the inside of the single crystal silicon layer 30 is irradiated with sunlight 40 from the front surface 30a side, and the reflected light 50 is reflected inside the single crystal silicon layer 30 from the back surface 30b side. is irradiated to Thus, 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, of the sunlight 40 and the reflected light 50, light having optical energy greater than the bandgap of silicon is absorbed. Specifically, electrons present in the valence band receive light energy supplied from sunlight and are excited to the conduction band. This accumulates electrons in the conduction band and creates holes in the valence band. In this way, the “i-TOPCon” type solar cell 100 is irradiated with the sunlight 40 and the reflected light 50, so that light energy larger than the bandgap of silicon contained in the sunlight 40 and the reflected light 50 is generated. The light is absorbed, electrons are excited in the conduction band, and holes are generated in the valence band. The generated holes are accumulated in the emitter layer 31, which is a p-type semiconductor layer. On the other hand, the excited electrons tunnel from the n-type monocrystalline 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 metal electrode 33 electrically connected to emitter layer 31 and metal electrode 37 electrically connected to high-concentration polycrystalline silicon layer 35 . Then, for example, when a load is connected between the metal electrode 33 and the metal electrode 37, electrons flow from the metal electrode 37 to the metal electrode 33 through the load. In other words, current flows from metal electrode 33 through the load to metal electrode 37 .

By operating the “i-TOPCon” type solar cell 100 in this manner, the load can be driven.

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

First, 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 the sunlight 40 directly incident on the “i-TOPCon” type solar cell 100, but also uses the reflected light 50 of the sunlight 40 reflected on the ground surface. Since it is used, there is an advantage that power generation efficiency can be improved.

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

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

A second advantage is that the tunnel insulating layer 34 is provided. In particular, the tunnel insulating layer 34 functions as a layer having carrier selectivity that allows passage of majority carriers while blocking passage of minority carriers by appropriately adjusting the material and thickness of the tunnel insulation layer 34 . 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 through while blocking holes, which are minority carriers, from passing through. have.

For example, when irradiated with sunlight 40 and reflected light 50, electrons are excited and holes are generated in the single crystal silicon layer 30. Electrons, which are majority carriers, tunnel through the tunnel insulating layer 34. It can move to the high-concentration polysilicon layer 35 . On the other hand, holes, which are minority carriers, cannot tunnel through tunnel insulating layer 34 and therefore cannot move to high-concentration polycrystalline silicon layer 35 . As a result, in the “i-TOPCon” type solar cell 100, diffusion of holes, which are minority carriers, into 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. It is possible to reduce the power generation loss caused by the recombination of the Thus, in the “i-TOPCon” type solar cell 100, by providing the tunnel insulating layer 34, it is possible to obtain the advantage of being able to reduce power generation loss caused by recombination of electrons and holes.

<Consideration of improvement>
From the viewpoint of improving power generation efficiency, the present inventors have studied the "i-TOPCon" type solar cell 100 having the above-described advantages, and found that the "i-TOPCon" type solar cell 100 has room for improvement. Since it was newly found to exist, this point will be explained.

For example, as shown in FIG. 2, in the “i-TOPCon” type solar cell 100, a tunnel insulating layer 34 is formed on the entire back surface 30b of the monocrystalline silicon layer 30, and the back surface of the tunnel insulating layer 34 is formed. A high concentration polycrystalline silicon layer 35 is formed on the entire surface.

Hereinafter, this structure will be referred to as a "back surface entire surface formation structure". Since the high-concentration polycrystalline silicon layer 35 is formed on the entire back surface of the tunnel insulating layer 34 in the "back surface forming structure", the resistance of the path reaching the metal electrode 37 through the high-concentration polycrystalline silicon layer 35 is reduced. can be reduced. Since this means that the open-circuit voltage and fill factor of the solar cell can be improved, the “i-TOPCon” type solar cell 100 improves the performance of the solar cell by improving the open-circuit voltage and fill factor. It can be said that it is excellent from the point of view.

However, the present inventors have recognized that the short-circuit current density is the most effective factor in improving the performance of a solar cell, and as a result of focusing on the improvement of the short-circuit current density, the "i-TOPCon" type The inventors have newly found that the solar cell 100 has room for improvement from the viewpoint of improving the short-circuit current density. This point will be described below.

Since the “i-TOPCon” type solar cell 100 shown in FIG. and the tunnel insulating layer 34 to reach the interior of the single-crystal silicon layer 30 . At this time, in the high-concentration polycrystalline silicon layer 35 , light absorption loss increases due to free carrier absorption (FCA) of the reflected light 50 .

Free carrier absorption refers to the transition to a higher energy level within the conduction band as a result of electrons existing in the energy level near the lower end of the conduction band gaining energy by absorbing light. Light is absorbed in this process. Therefore, when free carrier absorption occurs in the reflected light 50, the amount of the reflected light 50 reaching the inside of the single crystal silicon layer 30 is reduced. The light energy contributing to the excitation of will be reduced. This means that power generation efficiency is lowered. That is, more free carrier absorption leads to increased optical absorption loss.

In this regard, the high-concentration polycrystalline silicon layer 35 has a high concentration of conductive impurities. This means that there are many electrons in the conduction band. Therefore, in the high-concentration polycrystalline silicon layer 35, free carrier absorption in the conduction band increases. Therefore, in the “i-TOPCon” type solar cell 100 adopting the “structure with the entire back surface formed”, free carrier absorption increases, and as a result, the amount of reflected light 50 reaching the inside of the single crystal silicon layer 30 is reduced. In other words, in the “i-TOPCon” type solar cell 100 adopting the “structure formed on the entire back surface”, the short-circuit current density due to the reflected light 50 decreases.

From the above, it can be seen that the “i-TOPCon” type solar cell 100 has room for improvement from the viewpoint of improving the short-circuit current density. Therefore, in the present embodiment, measures are taken to overcome the room for improvement that exists in the “i-TOPCon” type solar cell 100. FIG. In the following, the technical idea of this embodiment with this ingenuity will be described.

<Basic idea in the embodiment>
Based on the inventor's insight that the most important factor for improving the power generation efficiency of a solar cell is the short-circuit current density, the basic idea of the present embodiment is to improve the open-circuit voltage, which is another factor. And the idea is to adopt a structure that gives priority to improving the short-circuit current density, even if the improvement of the fill factor is somewhat sacrificed. The basic idea is that the contributions from multiple factors (short-circuit current density, open-circuit voltage and fill factor) to improve the power generation efficiency of a solar cell are not even, and that the factor with the largest contribution is found and the other factors It is a novel idea that the power generation efficiency of a photovoltaic cell is finally improved by improving this factor, even if it sacrifices a little, and it has great technical significance as an approach for improving the power generation efficiency. Specifically, compared to a structure that aims to improve the power generation efficiency of a solar cell, priority is given to improving the short-circuit current density while sacrificing somewhat the improvements in open-circuit voltage and fill factor. It is of great technical significance to find out that the power generation efficiency of the solar cell can be improved overall by adopting such a structure.

In particular, from the viewpoint of improving the power generation efficiency of the photovoltaic cell, by improving the above-mentioned "structure with a full back surface" to improve the short-circuit current density, the "improvement in power generation efficiency" due to this improvement will increase the open-circuit voltage. The present inventor's insight that the power generation efficiency can be finally improved as a result of significantly exceeding the "decrease in power generation efficiency" due to the sacrifice of the fill factor and the fill factor is excellent.

The configuration of a solar cell embodying this basic concept will be described below.

The term "power density" used in this specification has the same meaning as the term "power generation efficiency (conversion efficiency)". However, "power generation efficiency (conversion efficiency)" is usually used as a precondition for irradiating a solar cell with standard sunlight from one side. In a double-sided photovoltaic cell that also receives light, power generation efficiency is evaluated using a physical quantity called "power density." Therefore, a high "power density" means high power generation efficiency.

<Structure of Solar Battery Cell in Embodiment>
Below, the configuration of a solar battery cell embodying the basic concept of the present embodiment will be described.

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

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

In the present embodiment, basically, the sunlight 40 is incident on the “front surface 30 a (first surface)” of the single crystal silicon layer 30 , while the “back surface 30 b (second surface)” of the single crystal silicon layer 30 The arrangement (first arrangement) of the solar cells 100A on which the reflected light 50 of the sunlight 40 is incident is assumed.

However, the present invention is not limited to this, and while the reflected light 50 of the sunlight 40 is incident on the “front surface 30 a (first surface)” of the single crystal silicon layer 30 , the “back surface 30 b (second surface)” of the single crystal silicon layer 30 However, the arrangement (second arrangement) of the solar cells 100A in which the sunlight 40 is incident on is not excluded. For example, as an installation method of the solar battery cell 100A, not only an installation method in which the solar cell 100A is arranged with an inclination with respect to the ground, but also an installation method in which the solar cell 100A is installed vertically is possible. In this case, for example, if the first arrangement is realized in the morning, the second arrangement will inevitably be realized in the evening as a result of a change in the direction of the sun.

In consideration of this, the claims define "a first conductivity type single crystal silicon layer having a first surface capable of receiving the first light and a second surface capable of receiving the second light". . This is the case where the “first light” is the sunlight 40 and the “second light” is the reflected light 50, or the “first light” is the reflected light 50 and the “second light” is the sunlight. It is intended to describe the broad concept encompassing the case of light 40 .

The surface 30a of the single-crystal silicon layer 30 is formed with an uneven structure called a texture structure, and as a result, the surface 30a of the single-crystal silicon layer 30 is composed of an uneven surface. Thereby, the reflectance of the sunlight 40 incident from the surface 30a side of the single crystal silicon layer 30 can be reduced. That is, the textured structure formed on the surface 30a of the single crystal silicon layer 30 has a function of suppressing the reflection of the sunlight 40 incident from the surface 30a side on the surface 30a.

Solar cell 100 A has emitter layer 31 in contact with surface 30 a of 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) is introduced. Therefore, the surface 30a serves as a pn junction surface where the monocrystalline 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 with each other. A passivation layer 32 and a metal electrode 33 are formed in contact with the emitter layer 31 . This passivation layer 32 is composed of, for example, a silicon nitride film. Also, the metal electrode 33 is composed of, for example, a laminated film of an aluminum film and a silver film.

On the other hand, the back surface 30b of the single crystal silicon layer 30 has a first region R1 and a second region R2. Here, a tunnel insulating layer 34a is formed so as to be in contact with the first region R1 of the back surface 30b. In other words, the tunnel insulating layer 34a is formed so as to be in contact with the first region R1 of the back surface 30b but not in contact with the second region R2 of the back surface 30b. The 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 having carrier selectivity that allows majority carriers to pass through but prevents minority carriers from passing through. In this case, the majority carriers are electrons and the minority carriers are holes. Therefore, the tunnel insulating layer 34a can be said to be a film having carrier selectivity that allows electrons to pass through but holes to pass through.

Carrier selectivity of the tunnel insulating layer 34a can be realized by adjusting the thickness of the tunnel insulating layer 34a. For example, if the thickness of the tunnel insulating layer 34a is too thick, not only minority carriers but also majority carriers will not pass. On the other hand, if the thickness of the tunnel insulating layer 34a is too thin, not only majority carriers but also minority carriers will pass through. That is, if the thickness of the tunnel insulating layer 34a is too thick or too thin, the tunnel insulating layer 34a cannot exhibit carrier selectivity. Therefore, it is necessary to develop 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 and the minority carriers do not pass through. be.

Subsequently, a high-concentration polycrystalline silicon layer 35a is formed in contact with tunnel insulating layer 34a. The impurity concentration of the conductive type impurity (donor) introduced into the high-concentration polycrystalline silicon layer 35 a is higher than the impurity concentration of the conductive type impurity (donor) introduced into the single crystal silicon layer 30 . A metal electrode 37 made of, for example, a silver film is formed in contact with the high-concentration polycrystalline silicon layer 35a.

On the other hand, a passivation layer 36 is formed so as to be in contact with the second region R2 on the rear surface 30b of the single crystal silicon layer 30. As shown in FIG. This passivation layer 36 is composed of, for example, a silicon nitride film.

The metal electrode 37 (back electrode) can be formed with a unit width of 100 μm, for example. In this case, the ratio "R1:R2" between the first region R1 and the second region R2 is "100 μm: electrode pitch (μm)−100 μm".

The solar battery cell 100A is configured as described above.

<Features of the embodiment>
A characteristic point of the present embodiment is, for example, the concept of forming the tunnel insulating layer 34a and the high-concentration polycrystalline silicon layer 35a only in a region planarly overlapping with the metal electrode 37, as shown in FIG. In other words, the feature of this embodiment is that the tunnel insulating layer 34a is formed so as to contact only the first region R1, not the second region R2, of the back surface 30b of the single crystal silicon layer 30, and the tunnel insulating layer 34a is in contact with the first region R1. , the high-concentration polycrystalline silicon layer 35a is formed so as to be in contact with the . As described above, the characteristic point of the present embodiment is that the regions for forming the tunnel insulating layer 34a and the high-concentration polycrystalline silicon layer 35a are limited.

For example, if a structure in which the tunnel insulating layer 34a and the high-concentration polycrystalline silicon layer 35a are formed only in a region planarly overlapping with the metal electrode 37 is called a "back surface partial formation structure", the features of this embodiment are , it can be said that the reason for this is the adoption of a "partial back surface formation structure" instead of a "back surface entire structure". According to this characteristic point, the reflected light 50 transmitted through the passivation layer 36 can reach the inside of the single crystal silicon layer 30 without passing through the tunnel insulating layer 34a and the high-concentration polycrystalline silicon layer 35a.

As a result, according to the present embodiment, free carrier absorption of reflected light 50 caused by high-concentration polycrystalline silicon layer 35a can be suppressed. In other words, according to the feature point, since the high-concentration polycrystalline silicon layer 35a having large free carrier absorption does not exist in the passage path of the reflected light 50, the light absorption loss of the reflected light 50 caused by the free carrier absorption can be reduced. be. This means that the proportion of the reflected light 50 that contributes to the excitation of electrons from the valence band to the conduction band inside the single crystal silicon layer 30 can be increased. In other words, adopting the feature point means that the short-circuit current density of the solar cell 100A can be improved, thereby improving the power density of the solar cell 100A.

According to the mechanism described above, it is considered that the "back surface partial formation structure" can improve the short-circuit current density of the solar cell 100A. However, in the "rear surface partial formation structure", the tunnel insulating layer 34a and the high-concentration polycrystalline silicon layer 35a are not formed over the entire rear surface. From this, it can be considered that the resistance of the path reaching the metal electrode 37 through the high-concentration polycrystalline silicon layer 35 is higher in the "rear surface partial formation structure" than in the "rear surface full formation structure". This means that it is presumed that the open-circuit voltage and fill factor of the solar cell are lower in the "partially formed back surface" structure than in the "entirely formed back surface" structure.

Therefore, it is self-evident whether the "partially formed back surface" structure, which can improve the short-circuit current density, can improve the power density compared to the "entirely formed back surface" structure, which has advantages in open-circuit voltage and fill factor. isn't it. In other words, it is not obvious whether the solar cell 100A (see FIG. 3) of the present embodiment can improve the power density as compared with the “i-TOPCon” type solar cell 100 (see FIG. 2).

In this regard, the inventor's insight is that from the viewpoint of improving the power generation efficiency of a solar cell, "improved power generation efficiency" by improving the short-circuit current density is "power generation efficiency" by sacrificing the open-circuit voltage and fill factor. As a result, according to the solar cell 100A of the present embodiment, compared to the “i-TOPCon” type solar cell 100, the power generation efficiency can be finally improved.

Below, we describe the results of the tests that support this insight.

<Verification result>
FIG. 4 is a graph showing the relationship between the electrode pitch (back surface) and the short circuit current density (Jsc).

In FIG. 4, graphs (1) and (2) are graphs showing short-circuit current densities based on sunlight incident from the surface side, and graph (1) shows solar cell 100A in the present embodiment. On the other hand, graph (2) shows the “i-TOPCon” type solar cell 100. FIG. From graphs (1) and (2) shown in FIG. 4, it can be seen that the short-circuit current density based on sunlight incident from the surface side is substantially the same for the solar cell 100A and the “i-TOPCon” type solar cell 100. I understand.

On the other hand, graphs (3) and (4) are graphs showing short-circuit current densities based on reflected light incident from the back side, and graph (3) shows solar cell 100A in the present embodiment. On the other hand, graph (4) shows the “i-TOPCon” type solar cell 100. FIG. From the graphs (3) and (4) shown in FIG. 4, the short-circuit current density based on the reflected light incident from the back side is higher for the solar cell 100A than for the “i-TOPCon” type solar cell 100. I understand. In particular, it can be seen that the solar cell 100A in the present embodiment can obtain a short-circuit current density of 3 mA/cm ² or more at the maximum as compared with the “i-TOPCon” type solar cell 100. FIG. Thus, according to the features of the present embodiment described above, it can be seen that the short-circuit current density based on the reflected light incident from the back side can be improved. That is, from the viewpoint of improving the short-circuit current density, it can be said that the "rear surface partial formation structure" is superior to the "rear surface entire formation structure".

FIG. 5 is a graph showing the relationship between the electrode pitch (back surface) and the open-circuit voltage (Voc).

In FIG. 5, graphs (1) and (2) are graphs showing open-circuit voltages based on sunlight incident from the surface side, and graph (1) shows solar cell 100A in the present embodiment. On the other hand, graph (2) shows the “i-TOPCon” type solar cell 100 . From graphs (1) and (2) shown in FIG. 5, it can be seen that the open-circuit voltage of the solar cell 100A based on sunlight incident from the surface side is higher than that of the “i-TOPCon” type solar cell 100. I understand.

On the other hand, graphs (3) and (4) are graphs showing open-circuit voltages based on reflected light incident from the rear surface side, and graph (3) shows solar cell 100A in the present embodiment. On the other hand, graph (4) shows the “i-TOPCon” type solar cell 100 . From the graphs (3) and (4) shown in FIG. 5, it can be seen that the open-circuit voltage based on the reflected light incident from the back side is higher in the “i-TOPCon” type solar cell 100 than in the solar cell 100A. Recognize. In other words, from the viewpoint of improving the open-circuit voltage, it can be said that the "structure with full back surface" is superior to the "structure with partial back surface".

FIG. 6 is a graph showing the relationship between the electrode pitch (back surface) and the fill factor (FF).

In FIG. 6, graphs (1) and (2) are graphs showing fill factors based on sunlight incident from the surface side, and graph (1) shows solar cell 100A in the present embodiment. On the other hand, graph (2) shows the “i-TOPCon” type solar cell 100 . From graphs (1) and (2) shown in FIG. 6, it can be seen that the fill factor based on the sunlight incident from the surface side is larger for the “i-TOPCon” type solar cell 100 than for the solar cell 100A. I understand.

On the other hand, graphs (3) and (4) are graphs showing fill factors based on reflected light incident from the rear surface side, and graph (3) shows solar cell 100A in the present embodiment. On the other hand, graph (4) shows the “i-TOPCon” type solar cell 100 . From graphs (3) and (4) shown in FIG. 6, it can be seen that the “i-TOPCon” type solar cell 100 also has a larger fill factor based on the reflected light incident from the back side than the solar cell 100A. Recognize. That is, from the viewpoint of improving the fill factor, it can be said that the "structure with full back surface" is superior to the "structure with partial back surface".

FIG. 7 is a graph showing the relationship between electrode pitch (rear surface) and conversion efficiency (Eff).

In FIG. 7, graphs (1) and (2) are graphs showing conversion efficiency based on sunlight incident from the surface side, and graph (1) shows solar cell 100A in the present embodiment. On the other hand, graph (2) shows the “i-TOPCon” type solar cell 100 . From graphs (1) and (2) shown in FIG. 7, it can be seen that the solar cell 100A and the “i-TOPCon” type solar cell 100 have substantially the same conversion efficiency based on sunlight incident from the surface side. Recognize.

On the other hand, graphs (3) and (4) are graphs showing conversion efficiency based on reflected light incident from the rear surface side, and graph (3) shows solar cell 100A in the present embodiment. On the other hand, graph (4) shows the “i-TOPCon” type solar cell 100 . From graphs (3) and (4) shown in FIG. 7, it can be seen that the solar cell 100A has a higher conversion efficiency based on the reflected light incident from the back side than the “i-TOPCon” type solar cell 100. Recognize. In particular, it can be seen that the solar cell 100A in the present embodiment can improve the conversion efficiency by 1% or more compared to the “i-TOPCon” type solar cell 100. FIG. As described above, according to the features of the present embodiment described above, it can be seen that the conversion efficiency based on the reflected light incident from the back side can be improved. In other words, it can be said that the "back partial formation structure" is superior to the "back surface entire formation structure" from the viewpoint of improving the conversion efficiency.

FIG. 8 is a graph showing the relationship between electrode pitch (rear surface) and power density.

In FIG. 8, graph (1) shows the solar cell 100A in this embodiment, while graph (2) shows the “i-TOPCon” type solar cell 100. In FIG. From graphs (1) and (2) shown in FIG. 8, it can be seen that the power density of the solar cell 100A is higher than that of the “i-TOPCon” type solar cell 100. FIG. In particular, it can be seen that the solar cell 100A in the present embodiment can achieve a maximum performance improvement of 0.8 mW/cm ² compared to the “i-TOPCon” type solar cell 100. FIG.

As described above, according to the features of the present embodiment described above, it can be seen that the power density, which is the ultimate goal, can be improved. In other words, it can be said that the "rear surface partial formation structure" is superior to the "rear surface full formation structure" from the viewpoint of improving the final power density.

Based on the above verification results, from the viewpoint of improving the power density of solar cells, "improving power density" by improving short-circuit current density is "decreasing power density" by sacrificing open-circuit voltage and fill factor. As a result, the inventor's insight that the solar cell 100A according to the present embodiment can ultimately improve the power density compared to the "i-TOPCon" type solar cell 100 is correct. is backed up.

FIG. 9 is a table summarizing the verification results described above. As shown in FIG. 9, each of the solar cell 100A and the “i-TOPCon” type solar cell 100 in this embodiment has merits and demerits. In this regard, the improvement in short-circuit current density in the solar cell 100A is by far the best, and the solar cell 100A improves the final power density by 0.8 mW/cm ² . The technical significance of being able to In particular, this verification result is a result that exceeds the future prediction of the "TOPCon" type solar cell system roadmap. Therefore, it can be said that the technical idea of the present embodiment is a very excellent technical idea in that it is possible to obtain remarkable effects that are difficult to predict even for those skilled in the art.

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

FIG. 10 is a flow chart showing the flow of manufacturing steps for the solar cell 100A.

First, in FIG. 10, 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 damage layer removal process, a surface flattening process, and the like are performed. Next, a textured structure having an uneven shape is formed on the surface 30a of the single crystal silicon layer 30 (S102). This textured structure is implemented, for example, in a wet etching process. After that, the emitter layer 31 is formed by introducing boron (B) into the surface 30a of the single crystal silicon layer 30 (S103).

Next, for example, by using a thermal oxidation method, a tunnel insulating layer 34a made of silicon oxide is formed on the back surface 30b of the single crystal silicon layer 30 (S104). Then, for example, by using the CVD method (Chemical Vapor Deposition), after forming an intrinsic polycrystalline silicon layer in contact with the tunnel insulating layer 34a (S105), phosphorus (which is an n-type impurity) is added to the intrinsic polycrystalline silicon layer. P) is diffused (S106). Thereby, a high-concentration polycrystalline silicon layer 35a made of an n-type semiconductor layer in contact with the tunnel insulating layer 34a can be formed.

Subsequently, the high-concentration polycrystalline silicon layer 35a and the tunnel insulating layer 34a are patterned by using photolithography technology and etching technology (S107). Thus, the tunnel insulating layer 34a and the high-concentration polycrystalline silicon layer 35a can be formed only in the first region R1 of the rear surface 30b of the monocrystalline silicon layer 30. As shown in FIG.

After that, a passivation layer 32 is formed in contact with the emitter layer 31 by using the CVD method, for example. Similarly, for example, by using the CVD method, a passivation layer 36 is formed in contact with the second region R2 of the back surface 30b of the single crystal silicon layer 30 (S108). Next, a metal electrode 33 connecting with the emitter layer 31 is formed. Similarly, a metal electrode 37 is formed to connect with the high-concentration polycrystalline silicon layer 35a (S109). As described above, the solar cell 100A (see FIG. 3) can be manufactured.

The method for manufacturing the solar cell 100A in the present embodiment is basically different from the method for manufacturing the “i-TOPCon” type solar cell 100 by using the “tunnel insulating layer 34a” and the “high-concentration polycrystalline silicon layer 35a.” can be realized by adding a patterning step for patterning. That is, the method for manufacturing the solar cell 100A has few steps added to the method for manufacturing the “i-TOPCon” type solar cell 100, and utilizes the know-how of the method for manufacturing the “i-TOPCon” type solar cell 100. It is useful in that it can

Although the invention made by the present inventor has been specifically described based on the embodiment, the invention is not limited to the above embodiment, and can be variously modified without departing from the gist of the invention. Needless to say.

In the above embodiment, the solar cell 100A in which the “first conductivity type” is the “n type” and the “second conductivity type” is the “p type” has been described as an example. The technical idea in the form is not limited to this, and can be applied to a solar cell in which, for example, the "first conductivity type" is set to "p-type" and the "second conductivity type" is set to "n-type". .

That is, in the above embodiment, the single crystal silicon layer 30 shown in FIG. 3 is composed of an n-type single crystal silicon layer, but this single crystal silicon layer 30 may be composed of a p-type single crystal silicon layer. . In this case, the high-concentration polycrystalline silicon layer 35a is also composed of the p-type high-concentration polycrystalline silicon layer. In this case as well, if the "structure formed on the entire back surface" is adopted, the light absorption loss increases due to free carrier absorption of the reflected light 50 in the high-concentration polycrystalline silicon layer 35a. However, in the free carrier absorption in this case, electrons located deep in the valence band (low energy from an electronic point of view) absorb light energy from holes located at the top of the valence band, It arises by moving to holes (vacancies) located at the top of the valence band.

In this respect, by adopting the "partial back surface formation structure" instead of the "back surface entire structure", free carrier absorption of the reflected light 50 caused by the high-concentration polycrystalline silicon layer 35a can be suppressed. That is, in this case as well, since the high-concentration polycrystalline silicon layer 35a having large free carrier absorption does not exist in the passage path of the reflected light 50, the light absorption loss of the reflected light 50 due to free carrier absorption can be reduced.

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 monocrystalline silicon layer 30a front surface 30b rear surface 31 emitter layer 32 passivation layer 33 metal electrode 34 Tunnel insulating layer 34a Tunnel insulating layer 35 High-concentration polycrystalline silicon layer 35a High-concentration polycrystalline silicon layer 36 Passivation layer 37 Metal electrode 40 Sunlight 50 Reflected light 100 "i-TOPCon" solar cell 100A Solar cell

Claims (5)

First conductivity type single crystal silicon having a first surface into which first light containing visible light can be incident and a second surface into which second light containing visible light can be incident and which includes a first region and a second region layer and
a second conductivity type emitter layer in contact with the first surface;
a first electrode in contact with the emitter layer;
a tunnel insulating layer in contact with the first region of the second surface;
the first conductivity type silicon layer in contact with the tunnel insulating layer;
a second electrode in contact with the silicon layer;
a passivation layer in contact with the second region of the second surface;
A solar cell. In the solar cell according to claim 1,
The solar battery cell, wherein the impurity concentration of the conductive impurity introduced into the silicon layer is higher than the impurity concentration of the conductive impurity introduced into the single crystal silicon layer. In the solar cell according to claim 1,
The solar battery cell, wherein the tunnel insulating layer is a film having carrier selectivity that allows majority carriers to pass through and minority carriers to pass through. In the solar cell according to claim 1,
The solar cell, wherein the silicon layer is a polycrystalline silicon layer. A solar battery comprising a plurality of solar battery cells according to any one of claims 1 to 4.

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