KR102251537B1 - Solar cell - Google Patents

Abstract

The present invention relates to a solar cell.
A solar cell according to an example of the present invention includes a semiconductor substrate; A first conductivity type region positioned on the front surface of the semiconductor substrate; A second conductivity type region positioned on the rear surface of the semiconductor substrate and including a polycrystalline silicon material; A first electrode positioned on the front surface of the semiconductor substrate and connected to the first conductivity type region; And a second electrode located on the rear surface of the semiconductor substrate and connected to the second conductivity type region, wherein each of the first and second electrodes includes a metal particle and a glass frit, and a glass frit per unit volume contained in the second electrode The content of is smaller than the content of the glass frit per unit volume contained in the first electrode.

Description

Solar cell {SOLAR CELL}

The present invention relates to a solar cell.

Recently, as the depletion of existing energy resources such as oil and coal is predicted, interest in alternative energy to replace them is increasing. Among them, a solar cell is a cell that produces electric energy from solar energy, and is attracting attention because it is rich in energy resources and has no problems with environmental pollution.

In general solar cells, a substrate made of semiconductors of different conductive types, such as p-type and n-type, and a first conductivity type region (emitter layer), and electrodes connected to the substrate and the first conductivity type region, respectively. Equipped. At this time, a p-n junction is formed at the interface between the substrate and the first conductivity type region.

When light is incident on such a solar cell, a plurality of electron-hole pairs are generated in the semiconductor, and the generated electron-hole pairs are separated into electrons and holes, respectively, so that the electrons and holes are directed toward the n-type semiconductor and the p-type semiconductor, for example. It moves toward the first conductivity type region and the substrate, is collected by the substrate and electrodes electrically connected to the first conductivity type region, and connects these electrodes with wires to obtain power.

Recently, among such solar cells, in order to improve the open-circuit voltage (Voc), a solar cell having a structure in which a passivation layer is formed between a semiconductor substrate and a conductive region formed by doping impurities on the rear surface of the solar cell is being developed.

However, in the solar cell of such a structure, the thickness of the conductive type region is considerably thinner than that of the prior art. When forming the rear electrode connected to the conductive type region, metal particles contained in the rear electrode are interposed between the conductive type region and the semiconductor substrate. There is a problem in that the passivation layer is penetrated and the semiconductor substrate is short-circuited, causing a defect in the solar cell.

An object of the present invention is to provide a solar cell having a structure capable of reducing defects of a solar cell while improving an open circuit voltage.

A solar cell according to an example of the present invention includes a semiconductor substrate containing impurities of a first conductivity type; A first conductivity type region located on the front surface of the semiconductor substrate and containing impurities of a second conductivity type opposite to the first conductivity type; A second conductivity type region located on a rear surface of the semiconductor substrate and including a polycrystalline silicon material doped with a higher concentration than the semiconductor substrate with impurities of the first conductivity type; A first electrode positioned on the front surface of the semiconductor substrate and connected to the first conductivity type region; And a second electrode located on the rear surface of the semiconductor substrate and connected to the second conductivity type region, wherein each of the first and second electrodes includes metal particles and glass frit, and the glass frit per unit volume contained in the second electrode The content of is smaller than the content of the glass frit per unit volume contained in the first electrode.

For example, the content of the glass frit per unit volume in the first electrode may be between 6 wt% and 8 wt%, and the content of the glass frit per unit volume in the second electrode may be between 2.50 wt% and 5 wt%.

In addition, the content of metal particles per unit volume contained in the first electrode may be greater than the content of metal particles per unit volume contained in the second electrode, for example, the content of metal particles per unit volume contained in the first electrode is 82 wt% It is between ~ 92wt%, and the content of the metal particles per unit volume contained in the second electrode may be between 68wt% ~ 73wt%.

In addition, an antireflection film is further located on the front surface of the first conductivity type region, a control passivation film including a dielectric material is further located between the rear surface of the semiconductor substrate and the second conductivity type region, and a control passivation film is located on the rear surface of the second conductivity type region. A rear passivation layer having a thicker thickness may be located, and the thickness of the rear passivation layer may be thinner than that of the antireflection layer.

For example, the thickness of the anti-reflection layer may be between 100 nm and 140 nm, and the thickness of the rear passivation layer may be between 65 nm and 105 nm in a range that is thinner than the thickness of the anti-reflection layer.

Here, the thickness of the control passivation film is thinner than that of the rear passivation film, and for example, the thickness of the control passivation film may be between 0.5 nm and 10 nm.

In addition, the thickness of the second conductivity type region may be thinner than that of the first conductivity type region. For example, the thickness of the first conductivity type region is between 300 nm and 700 nm, and the thickness of the second conductivity type region is the first conductivity type region. It may be between 290 nm and 390 nm in a range lower than the thickness of the mold region.

In addition, the glass frit included in the second electrode may be at least one of a PbO series or a BiO series.

In addition, the glass frit included in the second electrode may further include tellurium oxide (TeO).

Here, the melting point of the glass frit containing tellurium oxide (TeO) may be between 200°C and 500°C.

Such a second electrode includes a first layer in which a glass frit containing tellurium oxide (TeO) is located at an interface in contact with the second conductivity type region, and metal particles and tellurium oxide (TeO) are not contained on the first layer. A second layer on which the glass frit is located may be provided.

In addition, crystallites in which metal particles and silicon of the second conductivity type region are bonded may be distributed at the interface between the first layer and the second conductivity type region.

In addition, the glass frit included in the first electrode may be at least one of PbO-based or BiO-based, and the glass frit included in the first electrode may further include tellurium oxide (TeO).

Here, the metal particles included in the first electrode include a first metal particle having a circular or elliptical shape and a second metal particle having a plate shape having a long axis and an uneven surface, and the metal particles included in the second electrode The first metal particles may be included and the second metal particles may not be included.

Here, the length of the long axis of the second metal particles included in the first electrode may be larger than the size of the first metal particles included in each of the first and second electrodes.

In addition, a solar cell according to another example of the present invention includes a semiconductor substrate containing impurities of a first conductivity type; A first conductivity type region located on the front surface of the semiconductor substrate and containing impurities of a second conductivity type opposite to the first conductivity type; A control passivation film positioned on the rear surface of the semiconductor substrate and including a dielectric material; A second conductivity type region located on a rear surface of the semiconductor substrate and including a polycrystalline silicon material doped with a higher concentration than the semiconductor substrate with impurities of the first conductivity type; A first electrode positioned on the front surface of the semiconductor substrate and connected to the first conductivity type region; And a second electrode positioned on the rear surface of the semiconductor substrate and connected to the second conductivity type region, wherein each of the first and second electrodes includes a metal particle and a glass frit, and the glass frit of the first electrode is tellurium oxide. (TeO).

In the solar cell according to the present invention, the content of the glass frit contained in the second electrode positioned on the rear surface of the semiconductor substrate is made smaller than the content of the glass frit contained in the first electrode positioned on the front surface of the semiconductor substrate, through a heat treatment process. When the second electrode is connected to the second conductivity type region, the depth at which the second electrode is fired through can be adjusted.

Accordingly, short-circuiting of the metal particles of the second electrode to the semiconductor substrate through the second conductivity type region and the control passivation layer is prevented, thereby increasing the open-circuit voltage (Voc) of the solar cell, while preventing defects that may occur during the manufacturing process. Can be prevented.

1 is a partial perspective view of a solar cell according to a first embodiment of the present invention.
2 is a cross-sectional view showing a cross-section of the solar cell shown in FIG. 1.
FIG. 3 is a table in which the level of contact resistance, passivation function (recombination degree), and open-circuit voltage (Voc) according to the content of the glass frit 150G included in the second electrode 150 is tested.
FIG. 4 shows that when the content of the glass frit 150G in FIG. 3 is excessive to an appropriate level or higher, the semiconductor substrate 110, the control passivation film 160, the second conductivity type region 170, and the second electrode ( 150) is a cross-sectional view showing an enlarged portion of the included portion.
5 illustrates a semiconductor substrate 110, a control passivation layer 160, a second conductivity type region 170, and a second electrode 150 in a solar cell when the content of the glass frit 150G in FIG. 3 is at an appropriate level. It is a cross-sectional view showing an enlarged portion of the included portion.
6 is a case in which tellurium oxide (TeO) is further included in the glass frit 150G while the content of the glass frit 150G in FIG. 4 is maintained at an appropriate level, the semiconductor substrate 110 in the solar cell, control An enlarged cross-sectional view of a portion including the passivation layer 160, the second conductivity type region 170, and the second electrode 150.
7 is a view for explaining the metal particles (M1, M2) included in the first and second electrodes (140, 150) of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and similar reference numerals are attached to similar parts throughout the specification.

In the drawings, the thicknesses are enlarged in order to clearly express various layers and regions. When a part such as a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the case where the other part is "directly above", but also the case where there is another part in between. Conversely, when one part is "directly above" another part, it means that there is no other part in the middle. In addition, when a part is "overall" formed on another part, it means that it is formed not only on the entire surface (or the entire surface) of the other part, but also not formed on a part of the edge.

In addition, hereinafter, the content of the metal particles and the glass frit means the content per unit volume unless otherwise specified.

Then, a solar cell according to an embodiment of the present invention will be described with reference to the accompanying drawings.

1 is a partial perspective view of a solar cell according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a cross-section of the solar cell shown in FIG. 1.

As shown in FIG. 1, an example of a solar cell according to the present invention includes a semiconductor substrate 110, a first conductivity type region 120, an antireflection film 130, a control passivation film 160, and a second conductivity type region. 170, a rear passivation layer 190, a first electrode 140, and a second electrode 150.

1 illustrates that the solar cell according to the present invention includes the antireflection film 130 as an example, but in the present invention, the antireflection film 130 may be omitted. However, in consideration of the efficiency of the solar cell, since the inclusion of the anti-reflection film 130 results in better efficiency, the inclusion of the anti-reflection film 130 will be described as an example.

The semiconductor substrate 110 may be formed of at least one of single crystal silicon and polycrystalline silicon doped with impurities of the first conductivity type or the second conductivity type. For example, the semiconductor substrate 110 may be formed of a single crystal silicon wafer.

Here, an impurity of a first conductivity type or an impurity of a second conductivity type contained in the semiconductor substrate 110 may be included. Here, the impurity of the first conductivity type may be one of an n-type or p-type conductivity type, and the impurity of the second conductivity type may be an impurity opposite to a conductivity type of an impurity selected as an impurity of the first conductivity type.

As an example, when the first conductivity type is p-type, the second conductivity type may be n-type. Alternatively, when the first conductivity type is n-type, the second conductivity type may be p-type.

Hereinafter, a case where the first conductivity type is p-type and the second conductivity type is n-type will be described as an example, and a case in which the semiconductor substrate 110 contains an n-type impurity, which is an impurity of the second conductivity type, will be described as an example. .

When the semiconductor substrate 110 has a p-type conductivity type, an impurity of a trivalent element such as boron (B), gallium, or indium is doped into the semiconductor substrate 110. However, when the semiconductor substrate 110 has an n-type conductivity type, impurities of pentavalent elements such as phosphorus (P), arsenic (As), and antimony (Sb) may be doped into the semiconductor substrate 110.

Hereinafter, a case where the impurities contained in the semiconductor substrate 110 are of the second conductivity type and is of the n-type will be described as an example. However, it is not necessarily limited thereto.

The semiconductor substrate 110 may have a plurality of tecturing uneven surfaces on the front and rear surfaces of the semiconductor substrate 110. Accordingly, the first conductivity type region 120 located on the front surface of the semiconductor substrate 110 may also have an uneven surface, and the second conductivity type region 170 located on the rear surface of the semiconductor substrate 110 may also have an uneven surface. have.

Here, the texturing irregularities means irregularities formed on the surface of the solar cell to reduce reflected light, and for example, the texturing irregularities may have a pyramid shape.

As a result, the amount of light reflected from the front surface of the semiconductor substrate 110 may decrease, so that the amount of light incident into the semiconductor substrate 110 may increase.

The first conductivity type region 120 is located on the entire surface of the semiconductor substrate 110 to which light is incident, and may contain any one of impurities of a first conductivity type or impurities of a second conductivity type.

Accordingly, the first conductivity type region 120 may contain either an n-type conductivity type impurity or a p-type conductivity type impurity.

For example, when the semiconductor substrate 110 contains an n-type conductivity type impurity, the first conductivity type region 120 contains a p-type conductivity type impurity, thereby forming a pn junction with the semiconductor substrate 110. In this case, the first conductivity type region 120 may serve as an emitter part.

Alternatively, on the contrary, when the semiconductor substrate 110 contains an n-type conductivity type impurity, the first conductivity type region 120 contains an n-type conductivity type impurity at a higher concentration than the semiconductor substrate 110, The 1-conductivity type region 120 may serve as a front electric field.

Conversely, even when the semiconductor substrate 110 contains an impurity of a p-type conductivity type, the first conductivity-type region 120 may contain an impurity of an n-type or p-type conductivity. When 120 is formed as an n-type conductivity type, impurities of pentavalent elements such as phosphorus (P), arsenic (As), and antimony (Sb) are diffused through a heat treatment process on the entire surface of the semiconductor substrate 110. , A first conductivity type region 120 may be formed.

However, on the contrary, when the first conductivity-type region 120 is formed in a p-type conductivity type, impurities of trivalent elements such as boron (B), gallium, indium, etc. are diffused to the entire surface of the semiconductor substrate 110 through a heat treatment process. As a result, the first conductivity type region 120 may be formed.

Hereinafter, a case where the first conductivity type region 120 contains an impurity of a conductivity type opposite to that of the semiconductor substrate and serves as an emitter unit will be described as an example.

As described above, since the first conductivity type region 120 is formed by diffusion of p-type or n-type conductivity type impurities on the entire surface of the semiconductor substrate 110, the first conductivity type region 120 It may be formed of the same single crystal silicon or polycrystalline silicon material.

Accordingly, when the semiconductor substrate 110 is formed of a single crystal silicon wafer, the first conductivity type region 120 is also formed of a single crystal silicon wafer, and when the semiconductor substrate 110 is formed of a polycrystalline silicon wafer, the first conductivity type region ( 120) It may also be formed of a polycrystalline silicon wafer.

The thickness of the first conductivity type region 120 may be formed between 300 nm and 700 nm.

The antireflection film 130 is positioned on the first conductivity type region 120 and may be formed of at least one of an aluminum oxide film (AlOx), a silicon nitride film (SiNx), a silicon oxide film (SiOx), and a silicon oxynitride film (SiOxNy), Although it can be formed as a single film, it can also be formed as a plurality of films.

The antireflection film 130 reduces the reflectivity of light incident on the solar cell and increases selectivity in a specific wavelength region, thereby increasing the efficiency of the solar cell.

The thickness of the anti-reflection layer 130 may be formed between 100 nm and 140 nm.

The first electrode 140 is disposed in direct contact with the first conductivity type region 120 and may be electrically connected to the first conductivity type region 120.

As shown in FIG. 1, the first electrode 140 includes a plurality of first finger electrodes 141 extending in a first direction x and a second crossing the plurality of first finger electrodes 141. It may be formed to include a plurality of first busbar electrodes 142 extending in the direction y and connecting the plurality of first finger electrodes 141 to each other.

As shown in FIGS. 1 and 2, when the semiconductor substrate 110 is an n-type, the first electrode 140 is charged toward the p-type first conductivity-type region 120, for example, , You can collect holes.

The first electrode 140 is connected to an interconnector (not shown) that connects solar cells to each other, and collects and moves electric charges collected by the first electrode 140 and outputs it to an external device.

The first electrode 140 may include metal particles and glass frit, and specifically, the metal particles include nickel (Ni), copper (Cu), silver (Ag), aluminum (Al), tin (Sn), and zinc. It may be at least one selected from the group consisting of (Zn), indium (In), titanium (Ti), gold (Au), and combinations thereof.

Here, the melting point of the metal particles may be higher than the melting point of the glass frit. Therefore, after the first electrode 140 is completed, the metal particles can maintain their original shape in the pasted state, and since the glass frit is fired after being completely melted, it is completely different from the shape in the pasted state. It can have a different shape.

The first electrode 140 is formed by patterning a first electrode paste on the antireflection film 130 while the antireflection film 130 is formed on the entire surface of the first conductivity type region 120, and then heat treatment. Through the process, the first electrode paste fire-throug the anti-reflective film 130, pierce the anti-reflection film 130, and is fired in a state electrically connected to the first conductivity type region 120. , Can be formed.

The control passivation layer 160 is entirely positioned on the rear surface of the semiconductor substrate 110 and may include a dielectric material.

As an example, the control passivation layer 160 may be formed on the rear surface of the semiconductor substrate 110, as shown in FIGS. 1 and 2, but may be formed in direct contact with the rear surface of the semiconductor substrate 110.

In addition, the control passivation layer 160 may be formed over the entire area except for the rear edge of the semiconductor substrate 110.

Such a control passivation layer 160 may play a role of controlling a dopant or a diffusion barrier to prevent excessive diffusion of the dopant of the second conductivity type region 170 to the semiconductor substrate 110. In addition, the semiconductor substrate It is possible to perform a passivation function for the rear surface of (110).

In addition, the control passivation layer 160 may control diffusion of a dopant and may include various materials capable of transmitting multiple carriers. For example, the control passivation layer 160 may include oxides, nitrides, semiconductors, conductive polymers, and the like.

For example, the control passivation layer 160 may be a silicon oxide layer including silicon oxide. This is because a silicon oxide film has excellent passivation properties and a smooth carrier transfer film.

In addition, the silicon oxide film can be easily formed on the surface of the semiconductor substrate 110 by various processes.

Here, the control passivation layer 160 may be formed by various methods such as vapor deposition, thermal oxidation, and chemical oxidation. However, the control passivation layer 160 is not an essential component.

In addition, the thickness of the control passivation layer 160 is thinner than that of the rear passivation layer 190, and may be formed between 0.5 nm and 10 nm, for example. The control passivation layer 160 may be formed by an oxidation process, an LPCVP process, or a PECVD deposition process.

Here, limiting the thickness T160 of the control passivation layer 160 to 0.5 nm to 10 nm is to implement the tunneling effect. In addition, the control passivation layer 160 may perform a part of the passivation function for the rear surface of the semiconductor substrate 110.

Next, the second conductivity type region 170 is located on the rear surface of the semiconductor substrate 110 and may contain an impurity of a conductivity type opposite to the impurity contained in the first conductivity type region 120, and is made of polycrystalline silicon. It can be formed as

Accordingly, when the first conductivity type region 120 serves as an emitter portion, the second conductivity type region 170 may serve as a rear electric field portion.

That is, the second conductivity type region 170 may be formed on the rear surface of the control passivation layer 160 as shown in FIGS. 1 and 2, and may be spaced apart from the semiconductor substrate 110.

The second conductivity type region 170 may be formed by depositing on the control passivation layer 160 by a chemical vapor deposition (CVD) method, and (1) impurities of the first conductivity type on the control passivation layer 160 After the polycrystalline silicon material is deposited and formed, or (2) an amorphous silicon material containing impurities of the first conductivity type is deposited on the control passivation film 160, amorphous silicon is crystallized into polycrystalline silicon through a heat treatment process. Can be formed.

Accordingly, the second conductivity type region 170 is not formed in the semiconductor substrate 110, and as shown in FIGS. 1 and 2, the second conductivity type region 170 is on the rear surface of the semiconductor substrate 110. It is formed, but is spaced apart without direct contact with the semiconductor substrate 110, when formed on the rear surface of the control passivation layer 160, it is possible to further improve the open-circuit voltage (Voc) of the solar cell.

In addition, since the second conductivity type region 170 is formed outside the semiconductor substrate 110 without forming the second conductivity type region 170 in the semiconductor substrate 110, the second conductivity type region 170 is formed in the manufacturing process. In the process of forming ), the heat treatment for the semiconductor substrate 110 can be minimized, so that the characteristics of the semiconductor substrate 110 can be prevented from deteriorating. Accordingly, the solar cell as shown in FIGS. 1 and 2 can further improve efficiency.

As such, the thickness of the second conductivity type region 170 is determined in consideration of the deposition time of the second conductivity type region 170 and an appropriate thickness at which the function of the second conductivity type region 170 can be sufficiently exhibited, For example, it may be formed between 290 nm and 390 nm within a range that is thinner than the thickness of the first conductivity type region 120.

The second electrode 150 is disposed in direct contact with the second conductivity type region 170 and may be electrically connected to the second conductivity type region 170.

As shown in FIGS. 1 and 2, the second electrode 150 crosses a plurality of second finger electrodes 151 and a plurality of second finger electrodes 151 elongated in the first direction (x). It may be provided to include a plurality of second bus bar electrodes 152 that extend elongated in the second direction y and connect the plurality of second finger electrodes 151 to each other.

The second electrode 150 is connected to an interconnector (not shown) that connects the solar cells to each other, and collects and moves electric charges collected by the second electrode 150 and outputs them to an external device.

The second electrode 150 may include metal particles and glass frit, and specifically, metal particles having a melting point higher than that of the glass frit are nickel (Ni), copper (Cu), silver (Ag), and aluminum (Al). , Tin (Sn), zinc (Zn), indium (In), titanium (Ti), gold (Au), and may be at least one selected from the group consisting of a combination thereof.

The second electrode 150 is formed by patterning a second electrode paste on the rear surface of the rear passivation layer 190 while the rear passivation layer 190 is formed on the rear surface of the second conductivity type region 170 Then, through a heat treatment process, the second electrode paste fire-througs the rear passivation layer 190 while passing through the rear passivation layer 190 to electrically By firing in a connected state, it can be formed.

Next, as shown in FIGS. 1 and 2, the rear passivation layer 190 may be positioned on the entire area of the rear surface of the second conductivity type area 170 except for the area in which the second electrode 150 is formed.

The rear passivation layer 190 may be formed of a dielectric material, may be formed of a single layer or a plurality of layers, and may have a specific fixed charge in consideration of the polarity of the second conductivity type region 170.

The material of the rear passivation layer 190 may be formed of at least one of SiCx, SiOx, silicon nitride (SiNx), hydrogenerated SiNx, aluminum oxide (AlOx), silicon oxynitride (SiON), or hydrogenerated SiON.

The rear passivation layer 190 may perform a function of passivating the rear surface of the second conductivity type region 170.

Such a rear passivation layer 190 may have a thickness greater than that of the control passivation layer 160 in order to perform a sufficient passivation function for the rear surface of the second conductivity type region 170, but the antireflection layer 130 May be thinner than the thickness of

Accordingly, the thickness of the rear passivation layer 190 is thicker than the control passivation layer 160 and thinner than the anti-reflection layer 130, and may be formed between 65 nm and 105 nm, for example.

Until now, the case where the first conductivity type region 120 serves as an emitter unit and the second conductivity type region 170 serves as a rear electric field unit has been described as an example.

However, the present invention is not necessarily limited to such a structure, and unlike the foregoing, the semiconductor substrate 110 contains p-type impurities, and the first conductivity-type region 120 contains p-type impurities. In addition, it is possible to perform a role as a front electric field part, and to contain an n-type impurity in the second conductivity type region 170 to play a role as a rear emitter part.

Meanwhile, in such a solar cell, each of the first and second electrodes 140 and 150 may include the aforementioned metal particles and glass frit.

Here, the metal particle may be silver (Ag), for example, and is related to the conductivity of each of the first and second electrodes 140 and 150, and the glass frit is a fire-through of each of the first and second electrodes 140 and 150. It can be related to the depth of being fired through.

In addition, the glass frit used for the first and second electrodes 140 and 150 of the present invention may be at least one of a PbO series or a BiO series.

Here, the content of the metal particles and the content of the glass frit included in each of the first and second electrodes 140 and 150 of the present invention are the material and thickness of the first and second conductive regions 120 and 170. In consideration of, each can be done differently.

For example, the content of the metal particles per unit volume contained in the first electrode 140 may be greater than the content of the metal particles per unit volume contained in the second electrode 150.

In this way, to relatively increase the content of metal particles per unit volume contained in the first electrode 140, the first electrode 140 collects holes having a relatively slow moving speed, and receives a greater amount of sunlight. In order to do this, since it is necessary to make the line width of the first electrode 140 smaller than the line width of the second electrode 150, a relatively higher conductivity than the second electrode 150 may be required.

To this end, the content of the metal particles per unit volume contained in the first electrode 140 may be greater than the content of the metal particles per unit volume contained in the second electrode 150.

As an example, the content of metal particles per unit volume contained in the first electrode 140 may be formed between 82 wt% to 92 wt%, and the content of metal particles per unit volume contained in the second electrode 150 is 68 wt% to 73 wt% It can be formed between %.

In addition, as described above in FIGS. 1 and 2, in the solar cell structure of the present invention, the first conductivity type region 120 is formed of the same single crystal silicon substrate as the semiconductor substrate 110, for example, and the second conductivity type region 170 may be formed of a polycrystalline silicon material, the thickness of the second conductivity type region 170 may be formed to be relatively thinner than the thickness of the first conductivity type region 120, the rear passivation layer 190 The thickness may be thinner than the thickness of the antireflection layer 130.

Therefore, on the control passivation film 160, the second conductivity type region 170, and the rear passivation film 190 having a very thin or relatively thin thickness, a glass frit equal to the content of the glass frit of the first electrode paste When the second electrode paste having content is patterned and heat treated, the second electrode paste penetrates not only the rear passivation film 190 and the second conductivity type region 170 but also the control passivation film 160 during the heat treatment process. It may be directly connected to the semiconductor substrate 110 and short-circuited.

Accordingly, according to the present invention, the content of the glass frit included in the second electrode 150 may be different from the content of the glass frit included in the first electrode 140.

More specifically, in order to adjust the depth at which the second electrode paste penetrates the rear passivation layer 190 and is fired through in the direction of the second conductivity type region 170, the second electrode 150 The content of the glass frit per unit volume contained in) may be smaller than the content of the glass frit per unit volume contained in the first electrode 140.

Here, the content of the glass frit per unit volume is adjusted because the depth at which the second electrode paste is fired through can be adjusted using the glass frit.

As a more specific example, when the content of the glass frit per unit volume in the first electrode 140 is between 6wt% and 8wt%, the content of the glass frit per unit volume in the second electrode 150 is 2.5wt% to 5.owt% It can be between.

In this way, by forming the content of the glass frit per unit volume in the second electrode 150 between 2.5wt% and 5.owt%, the contact resistance between the second electrode 150 and the second conductivity type region 170 is sufficiently increased. It can be maintained at a low level, and the second electrode 150 penetrates not only the rear passivation film 190 and the second conductivity type region 170 but also the control passivation film 160 and prevents short circuit with the semiconductor substrate 110. , By preventing recombination that may occur on the rear surface of the semiconductor substrate 110 by the metal particles contained in the second electrode 150, the passivation function by the control passivation film 160 can be sufficiently performed. In addition, by preventing damage to the control passivation film 160, the open circuit voltage Voc of the solar cell can be improved to a good level.

Hereinafter, the effect of the content of the glass frit 150G of the second electrode 150 will be described in more detail with reference to FIGS. 3, 4, and 5 below.

FIG. 3 is a table in which the levels of contact resistance, passivation function (recombination degree), and open-circuit voltage (Voc) according to the content of the glass frit 150G included in the second electrode 150 are tested.

In addition, FIG. 4 shows that when the content of the glass frit 150G in FIG. 3 is excessive to an appropriate level or higher, the semiconductor substrate 110, the control passivation layer 160, the second conductivity type region 170, and the second It is a cross-sectional view showing an enlarged portion of the electrode 150 included.

In addition, FIG. 5 shows that when the content of the glass frit 150G in FIG. 3 is at an appropriate level, the semiconductor substrate 110, the control passivation film 160, the second conductivity type region 170, and the second electrode ( 150) is a cross-sectional view showing an enlarged portion of the included portion.

The content of the glass frit of the second electrode 150 described in the table in FIG. 3 is a content per unit volume, and may be slightly different from the content per unit volume of the glass frit 150G included in the paste for the second electrode.

This, in addition to the metal particles 150M and the glass frit 150G, the paste for the second electrode before the heat treatment process may further include a binder and a solvent made of a resin material, and such a binder and This is because most of the solvent can be oxidized or evaporated during the heat treatment process.

Accordingly, metal particles 150M and glass frit 150G may be present in the second electrode 150 after the heat treatment process, as shown in FIGS. 4 and 5.

Accordingly, the content of the glass frit 150G of the paste for the second electrode and the content of the glass frit 150G of the second electrode 150 fired after the heat treatment process may be different. For example, the glass frit 150G The content of) may increase by about 0.5 wt% to 1.0 wt% compared to before firing the second electrode 150.

In addition, the content of the glass frit 150G of the second electrode 150 described in the table of FIG. 3 is the content in the state in which the second electrode 150 is fired after the heat treatment process, and is used for the second electrode before the heat treatment process. The appropriate level content of the glass frit (150G) included in the paste is between 2.0 wt% and 4.owt%, and such a numerical range is 2.5 wt% to 5.owt%, which is the appropriate level content shown in the table of FIG. 3 May correspond to the numerical range of.

Since the present invention relates to a solar cell structure, the following description will be made based on the content of the glass frit 150G of the second electrode 150 fired after the heat treatment process.

In addition, in the table of FIG. 3, the contact resistance refers to the resistance between the second electrode 150 and the second conductivity type region 170. Therefore, the meaning of poor contact resistance means that the depth at which the second electrode paste is fired through is too thin, so that the second electrode 150 cannot penetrate the rear passivation layer 190, and thus the second electrode 150 ) And the second conductivity type region 170 are not properly electrically connected, and good means a case where the electrical connection is properly made.

In addition, the passivation function (recombination degree) refers to the passivation function of the control passivation layer 160. Therefore, good passivation function means that the control passivation film 160 is not damaged, and that the passivation function is bad means that the control passivation film 160 is damaged by the second electrode 150 and thus the second electrode This refers to a case in which recombination occurs at the rear surface of the semiconductor substrate 110 by the metal particles 150M of 150.

In addition, the good open-circuit voltage (Voc) means a case where the second conductivity type region 170 is separated from the semiconductor substrate 110 by the control passivation film 160 so that the solar cell generates a good level of open-circuit voltage. And, the open voltage is bad means that the control passivation film 160 is damaged while the second electrode 150 penetrates deeply into the second conductivity type region 170, and thus the second electrode 150 and the semiconductor substrate 110 are damaged. ) Means a short circuit.

As shown in the table shown in FIG. 3, when the content per unit volume contained in the second electrode 150 is less than 2.5 wt%, the depth at which the second electrode paste is fired through is too thin, and the second electrode ( It can be seen that 150) is not properly connected to the second conductivity type region 170.

In addition, when the content per unit volume contained in the second electrode 150 exceeds 5.0 wt%, as shown in FIG. 4, the second electrode 150 is not only the second conductivity type region 170, but also the control passivation film 160 ) And short-circuited with the semiconductor substrate 110, the function of the control passivation layer 160 is impaired, and the open-circuit voltage Voc is also deteriorated.

For reference, 150M in FIG. 4 refers to the metal particles 150M contained in the second electrode 150, and 150G refers to the glass frit 150G contained in the second electrode 150.

In addition, when the content per unit volume contained in the second electrode 150 is maintained at an appropriate level between 2.5 wt% and 5.0 wt%, the depth at which the second electrode paste is fired through is appropriate, Accordingly, it can be seen that the contact resistance, the passivation function, and the open-circuit voltage are all maintained at very good levels.

In addition, when the content per unit volume contained in the second electrode 150 is maintained at an appropriate level between 2.5 wt% and 5.0 wt%, the second electrode 150 forms the rear passivation layer 190 as shown in FIG. 5. It penetrates into the second conductivity type region 170 to an appropriate depth, and at this time, the metal particles of the second electrode 150 are at the interface between the second electrode 150 and the second conductivity type region 170. 150M) and silicon of the second conductivity type region 170 may be combined to form an alloy or crystallite (hereinafter referred to as a “crystal”).

The metal particle 150M-silicon crystal 153 may further lower the contact resistance between the second electrode 150 and the second conductivity type region 170.

Until now, in order to control the depth at which the second electrode 150 is fired through the rear passivation layer 190 and is fired through the inside of the second conductivity type region 170, The numerical value of the content per unit volume of the glass frit (150G) was described.

Hereinafter, the second electrode 150 penetrates the rear passivation layer 190 and fires appropriately in the direction of the second conductivity type region 170, but the second electrode 150 is formed in the second conductivity type region ( In order to connect to the surface of 170) at an optimum level, a case where tellurium oxide (TeO) is further included in the glass frit 150G will be described.

6 is a case in which tellurium oxide (TeO) is further included in the glass frit 150G while the content of the glass frit 150G in FIGS. 3 and 4 is maintained at an appropriate level, the semiconductor substrate 110 in the solar cell ), the control passivation layer 160, the second conductivity type region 170, and a cross-sectional view showing an enlarged portion of the second electrode 150.

As described above, the second electrode 150 according to the present invention has a content per unit volume of the glass frit 150G between 2.5 wt% and 5.0 wt%, and the glass frit 150G is among the PbO series or the BiO series. It may further include at least one of and tellurium oxide (TeO).

In this way, the glass frit 150G containing tellurium oxide (TeO) may have a relatively lower melting point, and as an example, the melting point of the glass frit 150G containing tellurium oxide (TeO) is 200°C. It can be formed between ~500 ℃.

Accordingly, when the glass frit 150G containing tellurium oxide (TeO) is fired through the second electrode paste in the heat treatment process and the rear passivation layer 190 is etched, tellurium oxide (TeO) The glass frit 150G containing) may be melted first.

At this time, the glass frit 150G containing tellurium oxide (TeO) may be first widely positioned on the surface of the second conductivity type region 170 to form a layer, and thereafter, the tellurium oxide (TeO) is contained. A glass frit 150G that does not contain metal particles 150M and tellurium oxide (TeO) may be positioned on the layer where the glass frit 150G is located.

Accordingly, the second electrode 150 is a first layer in which a glass frit 150G containing tellurium oxide (TeO) is located at an interface in contact with the second conductivity type region 170 as shown in FIG. 6. It may be formed including a second layer L2 in which a glass frit 150G not containing metal particles 150M and tellurium oxide (TeO) is positioned on the (L1) and the first layer (L1).

In addition, a crystal 153 in which the metal particles 150M and silicon of the second conductivity type region 170 are bonded may be distributed at the interface between the first layer L1 and the second conductivity type region 170.

Accordingly, while further improving the contact resistance between the second electrode 150 and the second conductivity type region 170, the open-circuit voltage Voc can be further improved, and in addition, the paste for the second electrode is fired. The depth of fire through can be more easily adjusted, which can further improve the process margin.

Until now, the material and content values of the second electrode 150 that can be adjusted to a good level at which the depth at which the second electrode paste is fired through has been described.

However, the glass frit 150G including tellurium oxide (TeO) is not limited to the second electrode 150 and may also be applied to the first electrode 140.

As an example, the glass frit 150G included in the first electrode 140 may be formed to include at least one of a PbO series or a BiO series, and the glass frit 150G of the first electrode 140 is It may be formed by further including tellurium oxide (TeO).

Until now, in the present invention, only the glass frit included in the first and second electrodes 140 and 150 has been mainly described, but hereinafter, the metal particles included in the first and second electrodes 140 and 150 will be described in more detail. .

7 is a view for explaining the metal particles (M1, M2) included in the first and second electrodes (140, 150) of the present invention.

In FIG. 7 below, only the metal particles M1 and M2 included in the first and second electrodes 140 and 150 are shown, and the glass frit previously described in FIGS. 5 to 7 is omitted for convenience of description. .

As shown in FIG. 7, metal particles M1 and M2 may be included in the first and second electrodes 140 and 150.

More specifically, the metal particles included in the first electrode 140 have a spherical first metal particle M1 having a circular or elliptical shape and a flake having a long axis and an uneven plate shape. ) Shape of the second metal particle M2, and the second electrode 150 may include the first metal particle M1 and may not include the second metal particle M2.

For example, as shown in FIG. 7, the first finger electrode 141 of the first electrode 140 includes a first metal particle M1, and the first bus bar electrode 142 is a first metal particle It may be formed including (M1) and the second metal particle (M2).

In addition, the second finger electrode 151 and the second busbar electrode 152 of the second electrode 150 may include the first metal particle M1 and may not include the second metal particle M2. .

Here, the length of the long axis of the second metal particles M2 included in the first electrode 140 may be larger than the size of the first metal particles M1 included in each of the first and second electrodes 140 and 150. .

For example, the diameter of the first metal particle M1 may be between 200 nm and 2.5 μm, more preferably between 300 nm and 2.0 μm. In addition, the second metal particle M2 may be between 3 um and 6 um.

Accordingly, the first electrode 140 may include metal particles M2 having a larger volume than the second electrode 150.

In this way, by including the second metal particles M2 having a relatively large size in the first electrode 140, the reactivity of the metal particles may be more improved during the heat treatment process for firing, and a relatively lower The electrode can be more easily fired at a temperature, and in addition, the electrical characteristics (eg, resistance) of the first electrode 140 can be further improved.

The first electrode 140 may be formed through two printing processes of the first electrode 140 paste, and the second electrode 150 may be formed through a single printing process.

More specifically, the first electrode 140 extends the first busbar paste including the first and second metal particles M1 and M2 on the front surface of the semiconductor substrate 110 in the second direction in the first printing process. After printing, drying, and printing the first finger paste including the first metal particles M1 in a first direction in a second printing process, drying, and then forming through a heat treatment process.

The second electrode 150 includes a second finger electrode 151 pattern and a second bus bar electrode 152 pattern on the rear surface of the semiconductor substrate with a paste for the second electrode 150 including the first metal particles M1. It can be formed by printing once and heat treatment according to.

However, the metal particles M1 and M2 included in the first and second electrodes 140 and 150 are not necessarily limited to FIG. 7 and may be formed differently from FIG. 7.

As an example, in order to form the first electrode 140, a first electrode paste including first and second metal particles M1 and M2 is used as a first finger electrode 141 and a first bus bar electrode 142. ) After first printing and drying according to the pattern, a separate first electrode paste containing only the first metal particles (M1) is secondarily applied to the first finger electrode 141 and the first bus bar electrode 142 It is also possible to form the first electrode 140 by printing according to a pattern.

In this case, not only the first busbar electrode 142 but also the first finger electrode 141 may include the second metal particles M2 having a relatively larger volume.

Accordingly, the first electrode 140 may include metal particles having a relatively larger volume than the second electrode 150.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

Claims (8)

A crystalline silicon substrate;
A tunneling film positioned on the rear surface of the crystalline silicon substrate;
A polycrystalline silicon layer positioned on the tunneling layer and doped with an impurity of a first conductivity type to a higher concentration than the crystalline silicon substrate;
A rear passivation layer on the polysilicon layer; And
A rear electrode passing through the rear passivation layer and in contact with the polycrystalline silicon layer
Including,
The rear electrode includes a glass frit containing silver (Ag) particles and tellurium oxide (TeO),
The content of the glass frit per unit volume in the rear electrode is 2.5 wt% to 5.0 wt%,
The rear electrode is
A first layer located at an interface in contact with the polycrystalline silicon layer and on which a glass frit containing the tellurium oxide is located,
It is located on the first layer and includes a second layer on which a glass frit containing the silver particles and not containing the tellurium oxide is located,
A solar cell in which a metal-silicon crystal in which the silver particles and silicon of the polycrystalline silicon layer are bonded is distributed at an interface between the first layer and the polycrystalline silicon layer. In claim 1,
The metal-silicon crystal is not formed on the tunneling layer and the substrate. In claim 1,
Solar cell further comprising a front electrode positioned on the front surface of the crystalline silicon substrate. In paragraph 3,
The front electrode contains silver (Ag), and the silver content of the front electrode is greater than the silver content of the rear electrode. In claim 1,
The solar cell further comprising an emitter layer disposed on a rear surface of the crystalline silicon substrate and in which an impurity of a second conductivity type opposite to the first conductivity type is diffused. In claim 1,
The tunneling layer is a solar cell formed of silicon oxide (SiO). In claim 1,
The rear passivation layer is a solar cell comprising aluminum oxide and silicon nitride. In claim 1,
The melting point of the glass frit containing the tellurium oxide is 200 ℃ ~ 500 ℃ solar cell.

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