KR102411967B1 - Solar cell - Google Patents

Abstract

The present invention relates to a method for manufacturing a solar cell.
A method of manufacturing a solar cell according to an example of the present invention includes: forming a tunnel layer on a rear surface of a single crystal silicon substrate; depositing a polysilicon rear surface field part on the rear surface of the tunnel layer; depositing a back protection layer on the polycrystalline back field part; printing an electrode paste on the back protective layer; and heat-treating the upper electrode paste to form a rear electrode connected to the polycrystalline rear electric field part through the rear protective layer.

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 has abundant energy resources and has no problems with respect to environmental pollution.

A typical solar cell includes a substrate and an emitter layer made of semiconductors of different conductive types, such as p-type and n-type, and electrodes connected to the substrate and the emitter, respectively. At this time, a p-n junction is formed at the interface between the substrate and the emitter part.

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 emitter portion and the substrate, and is collected by electrodes electrically connected to the substrate and the emitter portion, and electric power is obtained by connecting these electrodes with an electric wire.

An object of the present invention is to provide a solar cell.

A method of manufacturing a solar cell according to an example of the present invention includes: forming a tunnel layer on a rear surface of a single crystal silicon substrate; depositing a polysilicon back surface field part on the back surface of the tunnel layer; depositing a back protection layer on the polycrystalline back field part; printing an electrode paste on the back protective layer; and heat-treating the upper electrode paste to form a rear electrode connected to the polycrystalline rear electric field part through the rear protective layer.

In the forming of the back electrode, at least a portion of the back electrode is impregnated into the polysilicon back field part, and at least a part of the back electrode is recessed into the polysilicon back field part. A plurality of metal crystals including the same metal material as the metal material included in the rear electrode may be formed inside the rear electric field part.

In addition, the plurality of metal crystals may not be formed inside the tunnel layer and inside the polysilicon back field part in a region where the back electrode is not formed.

And a portion of the plurality of metal crystals may be directly contacted with at least a portion of the rear electrode impregnated into the polycrystalline silicon rear surface field part, and some of the plurality of metal crystals may be impregnated into the polycrystalline silicon rear surface electric field part. It may be spaced apart from at least a part of the rear electrode.

In addition, the plurality of metal crystals may be formed such that a length from at least a portion of the back electrode impregnated into the polysilicon back surface field portion toward the tunnel layer is 2/3 of a thickness of the polysilicon back surface field portion.

In the step of forming the rear electrode, a plurality of finger electrodes elongated in a first direction and a plurality of bus bars elongated in a second direction intersecting the first direction and to which the plurality of finger electrodes are commonly connected are formed. The content of the glass frit per unit volume included in each of the bus bars may be different from the content of the glass frit per unit volume included in each of the finger electrodes.

For example, the content of the glass frit per unit volume included in each of the finger electrodes may be greater than the content of the glass frit per unit volume included in each of the bus bars.

As another example, each of the bus bars may be formed so as not to directly contact the polysilicon rear surface electric field.

The content of the metal material per unit volume included in each of the finger electrodes may be greater than the content of the metal material per unit volume included in each of the bus bars.

The content of the metal material per unit volume included in each of the finger electrodes may be 80 wt% or more and 95 wt% or less, and the content of the metal material per unit volume included in each of the bus bars is 60 wt% or more, 80 wt% or less can be formed with

The method for manufacturing a solar cell may further include forming an emitter portion on the entire surface of the single crystal silicon substrate, wherein in the forming of the emitter portion, after doping an impurity on the entire surface of the single crystal silicon substrate, the The emitter portion may be formed by thermally diffusing impurities into the entire surface of the single crystal silicon substrate.

The method of manufacturing a solar cell may further include forming a front electrode connected to the emitter part, and the content of the glass frit per unit volume included in each of the finger electrodes is determined by determining the content of the glass frit per unit volume included in the front electrode. The content of the metal material per unit volume included in each of the finger electrodes may be the same as the content of the metal material per unit volume included in the front electrode.

The solar cell according to the present invention allows at least a portion of the second electrode to be formed by being recessed into the rear electric field, thereby further increasing the efficiency of the solar cell.

1 to 4 are diagrams for explaining a solar cell according to a first embodiment of the present invention.
5 is a view for explaining a comparative example different from the first embodiment of the present invention.
6 is a view for explaining a solar cell according to a second embodiment of the present invention.
7 is a comparison of photo luminescence (PL) photographs showing the degree of deterioration of the semiconductor substrate 110 according to the firing temperature during the heat treatment process when the material of the second busbar paste 153P is the same as that of the second finger paste. yes it's a picture
8 is a diagram showing the deterioration of the semiconductor substrate 110 according to the firing temperature during the heat treatment process when the material of the second bus bar paste 153P and the material of the second finger paste are different from each other according to the second embodiment of the present invention. This is a photo taken with PL (photo luminescence).

Hereinafter, with reference to the accompanying drawings, the embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

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

In addition, the front surface may be one surface of the semiconductor substrate on which direct light is incident, and the rear surface may be the opposite surface of the semiconductor substrate through which direct light is not incident or reflected light other than direct light is incident.

In addition, the fact that any two values are the same means that they are the same within an error range of 10% or less.

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

1 to 4 are diagrams for explaining a solar cell according to a first embodiment of the present invention, and FIG. 5 is a diagram for explaining a comparative example different from the first embodiment of the present invention.

More specifically, FIG. 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 illustrating the solar cell shown in FIG. 1 taken along line II-II. In addition, FIG. 3 is an enlarged view of part K in FIG. 2 , and FIG. 4 shows a real photograph of a contact portion between the second electrode 150 and the rear electric field unit 170 .

As shown in FIG. 1 , an example of a solar cell according to the present invention is a semiconductor substrate 110 , an emitter unit 120 , an anti-reflection film 130 , a tunnel layer 160 , a rear electric field unit 170 , and a rear protective film. 190 , a first electrode 140 and a second electrode 150 are included.

Although FIG. 1 illustrates that the solar cell according to the present invention includes the anti-reflection film 130 as an example, in the present invention, the anti-reflection film 130 may be omitted. However, when the efficiency of the solar cell is considered, the inclusion of the anti-reflection film 130 results in better efficiency, and thus the inclusion of the anti-reflection film 130 will be described as an example.

The semiconductor substrate 110 is a semiconductor semiconductor substrate 110 made of silicon containing impurities of a first conductivity type, for example, a p-type conductivity type. For example, the semiconductor substrate 110 may be a semiconductor wafer made of single crystal silicon or polycrystalline silicon.

When the semiconductor substrate 110 has a p-type conductivity, it contains impurities of a trivalent element such as boron (B), gallium, indium, or the like. However, alternatively, the semiconductor substrate 110 may be of an n-type conductivity type, and may be made of a semiconductor material other than silicon. When the semiconductor substrate 110 has an n-type conductivity, the semiconductor substrate 110 may contain impurities of a pentavalent element, such as phosphorus (P), arsenic (As), or antimony (Sb). Hereinafter, a case in which the semiconductor substrate 110 has an n-type conductivity type will be described as an example.

As shown in FIGS. 1 and 2 , the surface of the semiconductor substrate 110 may have a texturing surface that is an uneven surface subjected to texturing.

The emitter unit 120 is located on the front surface of the semiconductor substrate 110 on which light is incident, and contains impurities of a second conductivity type opposite to the conductivity type of the semiconductor substrate 110 , for example, an n-type conductivity type. to form a p-n junction with the semiconductor semiconductor substrate 110 .

By such a p-n junction, an electron-hole pair, which is a carrier generated when light is incident on the semiconductor substrate 110 from the outside, is separated into an electron and a hole, so that the electron moves toward the n-type and the hole moves toward the p-type. Accordingly, when the semiconductor substrate 110 is p-type and the emitter unit 120 is n-type, the separated holes may move toward the semiconductor substrate 110 and the separated electrons may move toward the emitter unit 120 .

However, in contrast to this, when the semiconductor substrate 110 has an n-type conductivity, the emitter unit 120 has a p-type conductivity. In this case, the separated electrons may move toward the semiconductor substrate 110 and the separated holes may move toward the emitter unit 120 .

When the emitter part 120 has an n-type conductivity type, the emitter part 120 is doped with an impurity of a pentavalent element, such as phosphorus (P), arsenic (As), or antimony (Sb), into the semiconductor substrate 110 . In the case of having a p-type conductivity, it may be formed by doping the semiconductor substrate 110 with impurities of a trivalent element such as boron (B), gallium, indium, or the like.

The emitter part 120 may be formed by diffusion of impurities of the second conductivity type on the front surface of the semiconductor substrate 110 . In this case, the emitter part 120 may be made of the same silicon material as that of the semiconductor substrate 110 . can be formed with

For example, when the semiconductor substrate 110 is formed of a polycrystalline silicon wafer, the emitter unit 120 may also be formed of a polycrystalline silicon material, and the semiconductor substrate 110 is formed of a single crystal silicon wafer. 120) may also be formed of a single-knotted silicon material.

The anti-reflection film 130 is positioned on the emitter part 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), a single film or It may be formed as a multilayer film.

In FIGS. 1 and 2 , the case in which the anti-reflection film 130 is formed as a single film is illustrated as an example, but it is not necessarily limited to a single film.

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

The first electrode 140 is disposed in direct contact with the emitter part 120 and is electrically connected to the emitter part 120 . As shown in FIG. 1 , the first electrode 140 may include a plurality of first finger electrodes 141 and a plurality of first bus bars 143 .

Here, the plurality of first finger electrodes 141 may be positioned on the emitter part 120 to be electrically connected to the emitter part 120 , and may be spaced apart from each other and extend in the first direction (x).

As shown in FIGS. 1 and 2 , the plurality of first finger electrodes 141 are carriers that move toward the p-type emitter unit 120 when the semiconductor substrate 110 is an n-type carrier, for example. , can collect holes.

In addition, the plurality of first bus bars 143 are positioned on the same layer as the plurality of first finger electrodes 141 on the emitter unit 120 , and electrically connect the plurality of first finger electrodes 141 to each other, may extend in a second direction y crossing the first finger electrode 141 of the .

The plurality of first bus bars 143 are connected to an interconnector (not shown) that connects the solar cells to each other, and the carriers collected and moved by the plurality of first finger electrodes 141 are collected and used as an external device. print out

The plurality of first finger electrodes 141 and the first bus bar 143 are made of at least one conductive metal material, and examples of these conductive metal materials include nickel (Ni), copper (Cu), silver (Ag), It may be at least one selected from the group consisting of aluminum (Al), tin (Sn), zinc (Zn), indium (In), titanium (Ti), gold (Au), and combinations thereof, but other conductive metal materials can be made with

After the anti-reflection film 130 is formed on the entire surface of the semiconductor substrate 110 , the first electrode paste for forming the first electrode 140 is applied on the entire surface of the anti-reflection film 130 . After patterning and application, the first electrode paste may be formed while being fired by passing through the anti-reflection film 130 and connected to the emitter unit 120 through a heat treatment process.

To this end, the first electrode 140 may contain glass frit in addition to the above-described metal material.

The tunnel layer 160 is disposed on the rear surface of the semiconductor substrate 110 and may include a dielectric material.

For example, as shown in FIGS. 1 and 2 , the tunnel layer 160 may be formed on the rear surface of the semiconductor substrate 110 , and may be formed in direct contact with the rear surface of the semiconductor substrate 110 .

In addition, the tunnel layer 160 may be formed on the entire rear surface of the semiconductor substrate 110 .

The tunnel layer 160 may pass carriers generated in the semiconductor substrate 110 in the direction of the rear electric field unit 170 , and may perform a passivation function for the rear surface of the semiconductor substrate 110 . In addition, the tunnel layer 160 may serve to increase the open circuit voltage (Voc) of the solar cell.

As such, the tunnel layer 160 may be formed of a dielectric material formed of SiCx or SiOx, which is durable even in a high-temperature process of 600° C. or higher. However, it is also possible to form silicon nitride (SiNx), hydrogenated SiNx, aluminum oxide (AlOx), silicon oxynitride (SiON) or hydrogenated SiON.

Also, the thickness T160 of the tunnel layer 160 may be formed to be between 0.5 nm and 2.5 nm. The tunnel layer 160 may be formed by an oxidation process, an LPCVD process, or a PECVD deposition process.

Here, limiting the thickness T160 of the tunnel layer 160 to 0.5 nm to 2.5 nm is to implement the tunneling effect, and it is possible to slightly exceed the limited range of 0.5 nm to 2.5 nm. may decrease the effectiveness of

More specifically, it is practically very difficult to form the tunnel layer 160 with a thickness T160 of 0.5 nm or more of the tunnel layer 160 being less than 0.5 nm, and the thickness T160 of the tunnel layer 160 The reason why is less than 2.5 nm is because the tunneling effect may hardly occur when it exceeds 2.5 nm.

In addition, the tunnel layer 160 may also partially perform a passivation function for the rear surface of the semiconductor substrate 110 .

Next, the rear electric field unit 170 is positioned on the rear surface of the semiconductor substrate 110 , contains impurities of the first conductivity type at a higher concentration than the semiconductor substrate 110 , and may include a polycrystalline silicon material.

That is, as shown in FIGS. 1 and 2 , the rear electric field unit 170 is formed on the rear surface of the tunnel layer 160 formed on the rear surface of the semiconductor substrate 110 and is spaced apart from the semiconductor substrate 110 . can be formed.

The rear electric field unit 170 is not formed in the semiconductor substrate 110 , and as shown in FIGS. 1 and 2 , the rear electric field unit 170 is formed on the rear surface of the semiconductor substrate 110 , the semiconductor substrate 110 . ) and spaced apart from each other and formed of a polysilicon material on the rear surface of the tunnel layer 160, the open circuit voltage (Voc) of the solar cell can be further improved.

In addition, since the rear electric field unit 170 is formed on the outside of the semiconductor substrate 110 without forming the rear electric field unit 170 in the semiconductor substrate 110 , in the process of forming the rear electric field unit 170 in the manufacturing process , it is possible to minimize thermal damage to the semiconductor substrate 110 , thereby preventing deterioration of the characteristics of the semiconductor substrate 110 . Accordingly, the solar cell as shown in FIGS. 1 and 2 can further improve efficiency.

As such, the thickness T170 of the rear electric field unit 170 may be formed between 50 nm and 500 nm.

The second electrode 150 is disposed on the rear surface of the rear electric field unit 170 and is electrically connected to the rear electric field unit 170 . As shown in FIGS. 1 and 2 , the second electrode 150 may include a plurality of second finger electrodes 151 and a plurality of second bus bars 153 .

Here, the plurality of second finger electrodes 151 may be spaced apart from each other on the rear surface of the rear electric field unit 170 and extend in the first direction (x), a carrier moving toward the rear electric field unit 170, for example, , can collect holes.

In addition, the plurality of second bus bars 153 are located on the same layer as the plurality of second finger electrodes 151 on the rear electric field unit 170 and electrically connect the plurality of second finger electrodes 151 to each other, The plurality of second finger electrodes 151 may extend in a second direction (y) intersecting each other.

The plurality of second bus bars 153 are connected to an interconnector (not shown) for connecting solar cells to each other, collect carriers that are collected by the second finger electrode 151 and move, and output them to an external device. .

Here, the longitudinal direction of the second bus bar 153 is the same as the longitudinal direction of the first bus bar 143 , and the longitudinal direction of the second finger electrode 151 is also the same as the longitudinal direction of the first finger electrode 141 . The material of the second electrode 150 may be the same as that of the first electrode 140 .

The second electrode 150 is a second electrode paste for forming the second electrode 150 on the rear protective film 190 in a state in which a rear protective film 190 to be described later is formed on the rear electric field unit 170 . It may be formed through a heat treatment process in a state formed by patterning.

Here, the width of the second finger electrode 151 may be, for example, 150 μm to 400 μm, and the width of the second bus bar 153 is formed to be larger than the width of the second finger electrode 151, 1 mm to 3 mm. It can be determined in the range between. However, the present invention is not necessarily limited thereto, and may have other widths.

Next, as shown in FIGS. 1 and 2 , the rear protective layer 190 may be positioned on the entire rear surface of the rear electric field unit 170 except for the region in which the second electrode 150 is formed.

Such a back protective 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 back surface electric field unit 170 .

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

Such a rear protective layer 190 may perform a function of passivating the rear surface of the rear electric field unit 170 .

1 and 2, the operation of the solar cell according to the present embodiment having such a structure is as follows.

When light is irradiated to the solar cell and is incident on the semiconductor substrate 110 of the semiconductor through the anti-reflection film 130 and the emitter unit 120 , electron-hole pairs are generated in the semiconductor substrate 110 of the semiconductor by the light energy. In this case, the reflection loss of light incident to the semiconductor substrate 110 is reduced by the anti-reflection layer 130 , and thus the amount of light incident to the semiconductor substrate 110 is increased.

These electron-hole pairs are separated from each other by the p-n junction of the semiconductor substrate 110 and the emitter part 120 so that holes and electrons are, for example, the emitter part 120 having a p-type conductivity type and the n-type junction. Each moves toward the semiconductor substrate 110 having the conductivity type. As such, the holes moving toward the emitter unit 120 are collected by the first finger electrode 141 and transferred to the first bus bar 143 , and then to the rear electric field unit 170 located at the rear side of the semiconductor substrate 110 . The moved electrons may be collected by the second finger electrode 151 and transferred to the second bus bar 153 .

In addition, when the first and second bus bars 143 and 153 of solar cells adjacent to each other are connected to each other through an interconnector (not shown), current flows, and this can be used as electric power from the outside.

Meanwhile, in the solar cell according to the present invention, as shown in FIGS. 1 to 3 , at least a portion of the second electrode 150 may be formed by being recessed into the rear electric field unit 170 . As a specific example, both the second finger electrode 151 and the second bus bar 153 forming the second electrode 150 may be formed by being recessed into the rear electric field unit 170 .

In other words, the first interface BS1 in which the rear electric field unit 170 and the second electrode 150 contact each other is greater than the second interface BS2 in which the rear electric field unit 170 and the rear protective layer 190 contact each other. It may be formed and located more adjacent to the semiconductor substrate 110 direction.

Although the second finger electrode 151 is illustrated as an example in FIG. 3 , the second bus bar 153 may have the same structure recessed into the rear electric field unit 170 like the second finger electrode 151 .

As described above, the shape in which the second electrode 150 is recessed into the rear electric field unit 170 is formed by patterning the second electrode paste for forming the second electrode 150 on the rear surface of the rear protective film 190 . It is a shape that may appear when the second electrode paste is connected while penetrating into the rear electric field unit 170 through the rear protective film 190 through the heat treatment process in the state.

As described above, when the second electrode 150 is formed using the second electrode paste, the cost is relatively low compared to the plating method, and the process time can be shortened.

Here, the height difference between the first interface BS1 and the second interface BS2 may be between 1 nm and 20 nm, and the height difference TBS between the first and second interfaces BS1 and BS2 is the second electrode. It may vary depending on the time of the heat treatment process for forming 150 and the content of glass frit included in the second electrode paste.

1 to 3 , a case in which both the plurality of second bus bars 153 and the plurality of second finger electrodes 151 forming the second electrode 150 are recessed into the rear electric field unit 170 is an example. Although illustrated, the present invention is not limited thereto, and only the plurality of second finger electrodes 151 among the second electrodes 150 may be formed by being recessed into the rear electric field unit 170 . As such, the configuration in which only the plurality of second finger electrodes 151 are recessed into the rear electric field unit 170 will be described in more detail below with reference to FIG. 6 .

Therefore, in the solar cell according to the present invention, as shown in FIG. 3 , the second electrode 150 is recessed into the rear electric field unit 170 , and the rear surface at the first interface BS1 of the rear electric field unit 170 is The electric field unit 170 and the second electrode 150 may contact each other.

In this case, as shown in FIG. 2 , a plurality of metal crystals MC may be further included in the electrode formation region 170OA in which the second electrode 150 is formed in the rear electric field unit 170 .

For example, as shown in FIG. 3 , a plurality of metal crystals MC may be further included in the finger forming region 170OF in which the second finger electrode 151 is formed in the rear electric field unit 170 . In FIG. 3 , only the electrode finger forming region 170OF is shown among the electrode forming regions 170OA of the rear electric field unit 170 , but the bus bar forming region 170OB may also include a plurality of metal crystals MC in the same manner. have.

For reference, referring to FIG. 2 , among the rear electric field units 170 , the region of the rear electric field unit 170 positioned in the space between the second finger electrode 151 and the tunnel layer 160 is a finger forming region 170OF. ), and the region of the rear electric field unit 170 located in the space between the second bus bar 153 and the tunnel layer 160 is referred to as a bus bar formation region 170OB, and among the rear electric field units 170 , the finger An area other than the formation area 170OF and the bus bar formation area 170OB is referred to as a non-formation area 170NO. In addition, the finger forming region 170OF and the bus bar forming region 170OB are collectively referred to as an electrode forming region 170OA.

The plurality of metal crystals MC has relatively low resistance compared to the rear electric field unit 170 formed of polycrystalline silicon, and as shown in FIG. 3 , the tunnel layer 160 is removed from the semiconductor substrate 110 . Carriers passing through and moving to the rear electric field unit 170, for example, electrons move directly to the second electrode 150 through the metal crystal MC, or jump between the metal crystal MC and the metal crystal MC. to move to the second electrode 150 . Accordingly, the plurality of metal crystals MC may serve to help carriers more easily move to the second electrode 150 .

Accordingly, the metal crystal MC may further reduce a substantial distance between the semiconductor substrate 110 and the second electrode 150 due to low resistance.

In addition, when the second electrode 150 is connected to the rear electric field unit 170 , the metal crystal MC is formed around the first interface BS1 that is the boundary between the second electrode 150 and the rear electric field unit 170 . Since it is formed in the direction of the semiconductor substrate 110 , the contact resistance between the second electrode 150 and the rear electric field unit 170 may be lowered.

Accordingly, as in the present invention shown in FIG. 3 , when a plurality of metal crystals MC are further included in the rear electric field unit 170 between the second electrode 150 and the tunnel layer 160 , the solar cell Efficiency can be further improved.

The metal crystal MC is located in the electrode formation region 170OA in which the second electrode 150 is formed in the rear electric field unit 170 , and the second electrode 150 is not formed in the rear electric field unit 170 . The metal crystal MC may not be located in the non-formation region 170NO.

As such, the metal crystals MC are located only in the electrode formation region 170OA of the rear electric field unit 170 and are not located in the non-formation region 170NO, such that the plurality of metal crystals MC are formed in the second electrode ( This is because the metal escaping from the second electrode 150 is recrystallized during the heat treatment process for forming the 150 ).

For example, the plurality of second electrodes 150 may include at least one conductive metal material. Here, the conductive metal material included in the plurality of second electrodes 150 is, for example, nickel (Ni), copper (Cu), silver (Ag), aluminum (Al), tin (Sn), zinc (Zn), It may be at least one selected from the group consisting of indium (In), titanium (Ti), gold (Au), and combinations thereof, but may be made of other conductive metal materials.

Here, the plurality of metal crystals MC may be formed while the metal material included in the second electrode 150 escapes and recrystallizes during the heat treatment process for forming the second electrode 150 , and thus the second electrode The same metal material as the metal material included in 150 may be included. Accordingly, for example, when the second electrode 150 includes silver (Ag), the metal crystal MC may also include silver (Ag).

Also, as shown in FIGS. 3 and 4 , the metal crystal MC is located in the rear electric field unit 170 but may not be located in the tunnel layer 160 .

That is, as in the comparative example shown in FIG. 5 , when such a metal crystal MC is located in the tunnel layer 160 , the function of the tunnel layer 160 may be deteriorated, and the metal crystal MC is formed in the tunnel layer 160 . When penetrating through 160 and penetrating into the back surface of the semiconductor substrate 110 , the semiconductor substrate 110 ? The open-circuit voltage (Voc) characteristic exhibited by the structure formed of the tunnel layer 160 - rear electric field unit 170 may be deteriorated, and thus the semiconductor substrate 110 may be deteriorated.

As such, when the semiconductor substrate 110 is deteriorated, characteristics of the semiconductor substrate 110 , for example, characteristics such as carrier life time may be deteriorated.

However, as in the present invention, when the metal crystal MC is located in the rear electric field part 170 but not in the tunnel layer 160 , such deterioration of properties can be prevented.

As shown in FIG. 3 , a part MC1 of the plurality of metal crystals MC may be in direct contact with the second electrode 150 , and, in addition, at least one of the plurality of metal crystals MC. Above (MC2) may be spaced apart from the second electrode 150 and located in the rear electric field unit 170 .

Here, the length LMC of the plurality of metal crystals MC in the direction from the second electrode 150 to the tunnel layer 160 may be less than or equal to 2/3 of the thickness of the rear electric field unit 170 . As described above, limiting the length LMC of the metal crystal MC to 2/3 or less of the thickness of the rear electric field unit 170 makes the length LMC of the metal crystal MC excessively long, as described above. , in order not to damage the tunnel layer 160 or the semiconductor substrate 110 .

A width WMC of some of the plurality of metal crystals MC may decrease from the second electrode 150 toward the tunnel layer 160 . That is, as shown in FIG. 3 or FIG. 4 , the surface direction (x, y) width WMC of the portion adjacent to the second electrode 150 in the metal crystal MC is the width WMC of the portion adjacent to the semiconductor substrate 110 side. It may be smaller than the width.

The size of the metal crystal MC may be determined in proportion to the sintering temperature of the heat treatment process for forming the second electrode 150 .

That is, the length or width of the metal crystal MC has a characteristic that increases as the sintering temperature of the heat treatment process for forming the second electrode 150 increases and decreases as the sintering temperature of the second electrode 150 increases, and the second electrode 150 is the source of the metal crystal MC. As the width of the electrode 150 increases, the length or width of the metal crystal MC may increase.

However, when the sintering temperature of the heat treatment process for forming the second electrode 150 is excessively low, the contact resistance between the second electrode 150 and the rear electric field unit 170 may increase.

Accordingly, in the first embodiment of the present invention, both the second finger electrode 151 and the second bus bar 153 forming the second electrode 150 are recessed into the rear electric field unit 170, so that the rear electric field unit The case in which the metal crystal MC is formed in both the finger forming region 170OF and the bus bar forming region 170OB in 170 has been described as an example, but in order to further improve efficiency, only the second finger electrode 151 is used. The metal crystal MC may be formed only in the back electric field part 170 , and only in the finger formation region 170OF. This will be described in more detail with reference to FIGS. 6 to 8 below.

6 is a view for explaining a solar cell according to a second embodiment of the present invention.

In the description of FIG. 6 , descriptions of parts overlapping with those described in the first embodiment will be omitted, and parts different from those of the first embodiment will be mainly described.

As shown in FIG. 6 , in the solar cell according to the second embodiment of the present invention, at least a portion of the second electrode 150 is recessed into the rear electric field unit 170 , but a plurality of the second electrodes 150 are Only the second finger electrode 151 may be formed such that it penetrates the rear protective layer 190 and is recessed into the rear electric field unit 170 .

In this case, the metal crystal MC is formed only in the finger forming region 170OF of the rear electric field unit 170 , the plurality of second bus bars 153 are not recessed into the rear electric field unit 170 , and the rear protective layer It may be formed on the back side of 190 .

Accordingly, the metal crystal MC may not be formed in the bus bar formation region 170OB of the rear electric field unit 170 .

In this way, only the plurality of second finger electrodes 151 among the second electrodes 150 penetrate the rear protective layer 190 and are recessed into the rear electric field unit 170 to form a finger forming region 170OF among the rear electric field units 170 . The metal crystal MC is formed in the bus bar formation region 170OB of the rear electric field unit 170 by forming the metal crystal MC only on This is to prevent the metal crystal MC from being located in the tunnel layer 160 or from being connected to the semiconductor substrate 110 through the tunnel layer 160, as described in FIGS. 3 to 5 above. .

More specifically, in the case of the second bus bar 153, as described above with reference to FIGS. 1 and 2 , since the width is relatively larger than that of the second finger electrode 151 , a relatively large road during the heat treatment process is performed. A metal crystal MC having a width or width is formed in the rear electric field unit 170 , so that the metal crystal MC is located in the tunnel layer 160 or connected to the semiconductor substrate 110 as shown in FIG. 5 . It is possible to block this in advance.

Accordingly, in the solar cell according to the second embodiment of the present invention, only the second finger electrode 151 of the second finger electrode 151 and the second bus bar 153 penetrates the rear protective film 190 and the rear electric field unit 170 ), since it has a structure formed by being recessed inside, only the rear electric field unit 170 and the second finger electrode 151 are in contact with each other at the first interface BS1 of the rear electric field unit 170, and the rear electric field unit 170 A plurality of metal crystals MC may be included only in the finger forming region 170OF in which the second finger electrode 151 is formed among the electrode forming regions 170OA of A plurality of metal crystals MC may not be located in the bus bar formation region 170OB of the step unit 170 .

To this end, in the present invention, the material included in the plurality of second finger electrodes 151 and the material included in the plurality of second bus bars 153 may be different from each other.

More specifically, the second finger electrode 151 penetrates the rear protective film 190 and is recessed into the rear electric field unit 170, and the second bus bar 153 penetrates the rear protective film 190 and the rear electric field unit ( 170) In order to prevent or minimize penetration into the interior, the content of the glass frit per unit volume included in the plurality of second bus bars 153 is determined by the content of the glass frit per unit volume included in the plurality of second finger electrodes 151 . may be smaller or absent.

That is, the content of the glass frit per unit volume of the second bus bar paste for forming the second bus bar 153 is determined as the glass frit per unit volume included in the second finger paste for forming the second finger electrode 151 . It can be made smaller than the content of , or glass frit is not included.

The reason for doing this is that, in the heat treatment process for forming the second electrode 150 , the second bus bar paste is formed while the second finger paste penetrates the rear protective layer 190 and is penetrated into the rear electric field unit 170 . This is to prevent the rear protective film 190 from being penetrated into the rear electric field unit 170 even if it is connected to the rear electric field unit 170 through the rear surface protective film 190 or to prevent the rear electric field unit 170 from being penetrated at all.

In this way, it is possible to prevent the metal crystal MC from being formed in the bus bar formation region 170OB of the rear electric field unit 170 and to prevent the semiconductor substrate 110 from being deteriorated.

In addition, the content of the glass frit per unit volume included in the plurality of second finger electrodes 151 may be the same as the content of the glass frit per unit volume included in the first electrode 140 .

This may be formed by applying the first electrode paste to the first electrode 140 and then passing through the anti-reflection film 130 and connecting to the emitter part 120. Glass per unit volume included in the second finger paste By making the content of the frit the same as that of the first electrode 140 , in the same heat treatment process, the speed at which the first electrode paste penetrates the anti-reflection film 130 and enters the emitter part 120 and the second finger paste is applied to the rear protective film The speed of penetration into the rear electric field unit 170 through the hole 190 may be approximately equal to each other.

Accordingly, the speed of the second finger electrode 151 may be limited while the temperature of the heat treatment process for forming the first electrode 140 and the second electrode 150 may be the same.

Also, the content of the metal material per unit volume included in the plurality of second finger electrodes 151 may be greater than the content of the metal material per unit volume included in the plurality of second bus bars 153 .

As a more specific example, the content of the metal material per unit volume included in the plurality of second finger electrodes 151 is 80 wt% or more and 95 wt% or less, and the content of the metal material per unit volume included in the plurality of second bus bars 153 is may be 60 wt% or more and 80 wt% or less.

In this way, when the content of the metal material per unit volume included in the second finger electrode 151 is 80 wt% or more and 95 wt% or less, the second finger paste penetrates the rear protective film 190 and enters the rear electric field unit 170. In this state, the metal crystal MC is sufficiently formed as described with reference to FIG. 3 , and the resistance of the relatively narrow second finger electrode 151 is sufficiently lowered.

In addition, the content of the metal material per unit volume included in the second bus bar 153 is set to be 60 wt % or more and 80 wt % or less, so that a part of the second bus bar paste penetrates the rear protective film 190 and the rear electric field unit 170 ), the metal crystal MC is not formed in the bus bar formation region 170OB of the rear electric field unit 170 by the metal material included in the second bus bar paste, or the metal crystal MC is Even if it is formed, as described above with reference to FIG. 4 , even if the metal crystal MC is formed in the tunnel layer 160 , it can be prevented from being formed while being connected to the semiconductor substrate 110 .

In addition, the content of the metal material per unit volume included in the plurality of second finger electrodes 151 may be the same as the content of the metal material per unit volume included in the first electrode 140 .

By forming the second finger electrode 151 and the second bus bar 153 having different materials as described above, the deterioration of the semiconductor substrate 110 can be prevented, and the efficiency of the solar cell can be further prevented from being lowered. can

As described above, deterioration of the semiconductor substrate 110 may occur during a heat treatment process for forming the second electrode 150 , and if the temperature of the heat treatment process is too low, the contact resistance of the second electrode 150 becomes excessive. This can increase the efficiency of the solar cell.

Here, the deterioration of the semiconductor substrate 110 can be confirmed in the following FIGS. 7 and 8 .

7 is a comparison of the degree of deterioration of the semiconductor substrate 110 according to the firing temperature during the heat treatment process when the material of the second busbar paste 153P is the same as that of the second finger paste by photo luminescence (PL) photography. It is an example photograph, and FIG. 8 shows the semiconductor substrate according to the firing temperature during the heat treatment process when the material of the second bus bar paste 153P and the material of the second finger paste are different from each other according to the second embodiment of the present invention. 110) is a photograph taken by PL (photo luminescence).

In the PL image showing the open circuit voltage (Voc) of the semiconductor substrate 110 , deterioration as the metal crystal MC penetrates the semiconductor substrate 110 according to the heat treatment process temperature can be seen.

In the PL image, the darker the partial region of the semiconductor substrate 110 is, the lower the open circuit voltage is, which means that the deterioration of the semiconductor substrate 110 is deepened. It means that there is little or no deterioration.

More specifically, in the PL image, when the shaded area increases as the heat treatment process temperature increases, the metal crystal MC penetrates into the tunnel layer 160 or the semiconductor substrate 110 and the open circuit voltage decreases to reduce the open circuit voltage of the semiconductor substrate 110 . ), and when the shaded area does not increase as the heat treatment process temperature increases, the metal crystals MC do not penetrate into the tunnel layer 160 or the semiconductor substrate 110, so that the open circuit voltage is lowered. It is maintained in a sufficiently high state, which means that there is little or little deterioration of the semiconductor substrate 110 .

In FIGS. 7 and 8 , only the image of the second bus bar 153 having a relatively large width is shown, and the image of the second finger electrode 151 does not look too small in width, but substantially each of the second bus bars 153 . ), a plurality of second finger electrodes 151 are formed to cross each other.

In FIG. 7 , the second bus bar paste 153P made of the same material as the second finger paste is used, and in FIG. 8 , as described in FIG. 6 above, the second bus bar paste made of a material different from the second finger paste. This is the case in which yeast 153P is used.

In FIG. 7 , since the same material of the second bus bar 153 and the second finger electrode 151 is the same, the second bus bar paste 153P also penetrates the rear protective film 190 and is applied to the rear electric field unit 170 . The metal crystal MC may be formed by being recessed into the bus bar forming region 170OB of the rear electric field unit 170 .

Therefore, when the heat treatment process temperature for forming the second electrode 150 is relatively low, about 820 ° C or 795 ° C, as shown in FIGS. 7 (c) and (d), the metal crystal ( MC) is hardly formed, and deterioration of the semiconductor substrate 110 hardly occurs. can

However, when the heat treatment process temperature for forming the second electrode 150 is relatively high, about 870°C or 845°C, as shown in FIGS. 7A and 7B , the shaded area on the semiconductor substrate 110 increases. and relatively deepened, the metal crystal MC of the rear electric field unit 170 formed by the second busbar paste 153P penetrates into the tunnel layer 160 or the semiconductor substrate 110 to the semiconductor substrate 110 . It can be seen that the deterioration of

However, as described above with reference to FIG. 6 , when the materials of the second finger electrode 151 and the second bus bar 153 are different from each other according to the second embodiment of the present invention, the heat treatment process temperature is relatively low. It can be seen that the shaded area of the semiconductor substrate 110 is hardly increased even in the cases of (c) and (d) of FIG. 8 as well as in the relatively high levels of FIGS.

This is because the materials of the second finger electrode 151 and the second bus bar 153 are different from each other, so that the second bus bar 153 penetrates the rear protective film 190 and is not connected to the rear electric field unit 170, This is because, even when connected, the metal crystal MC of the rear electric field unit 170 formed by the second bus bar 153 does not penetrate into the tunnel layer 160 or the semiconductor substrate 110 .

As described above, in the solar cell according to the second embodiment of the present invention, the open circuit voltage (Voc) of the solar cell is set to a sufficiently high state by making the materials of the second finger electrode 151 and the second bus bar 153 different from each other. By maintaining the semiconductor substrate 110, it is possible to prevent deterioration and further improve the efficiency of the solar cell.

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 as defined in the following claims are also provided. is within the scope of the right.

Claims (16)

forming a tunnel layer on a rear surface of the single crystal silicon substrate;
depositing a polysilicon rear surface field part on the rear surface of the tunnel layer;
depositing a back protection layer on the polysilicon back surface field part;
printing an electrode paste on the back protective layer; and
heat-treating the upper electrode paste to form a rear electrode connected to the polysilicon rear surface field part through the rear protective film
including,
In the step of forming the rear electrode,
at least a portion of the back electrode is impregnated into the polysilicon back field part;
A plurality of metal crystals including the same metal material as the metal material included in the back electrode are formed inside the polysilicon back field part at a portion where at least a part of the back electrode is recessed into the inside of the polysilicon back field part and
The method of manufacturing a solar cell, characterized in that the plurality of metal crystals are not formed in the tunnel layer. delete In claim 1,
In the step of forming the rear electrode,
A method of manufacturing a solar cell in which the plurality of metal crystals are not formed inside the polysilicon back field part in a region where the back electrode is not formed. In claim 1,
In the step of forming the rear electrode,
A method of manufacturing a solar cell in which a portion of the plurality of metal crystals is in direct contact with at least a portion of the rear electrode impregnated into the polycrystalline silicon rear surface field part. In claim 1,
In the step of forming the rear electrode,
A method of manufacturing a solar cell in which a portion of the plurality of metal crystals is spaced apart from at least a portion of the rear electrode impregnated into the polycrystalline silicon rear surface field part. In claim 1,
In the step of forming the rear electrode,
Manufacturing of a solar cell in which the plurality of metal crystals are formed such that a length from at least a portion of the back electrode impregnated into the polysilicon back surface field part to the tunnel layer is 2/3 of the thickness of the polysilicon back surface field part Way. In claim 1,
In the step of forming the rear electrode,
a plurality of finger electrodes elongated in a first direction and a plurality of bus bars elongated in a second direction intersecting the first direction and to which the plurality of finger electrodes are commonly connected;
A method of manufacturing a solar cell in which a content of glass frit per unit volume included in each of the bus bars is different from a content of glass frit per unit volume included in each of the finger electrodes. In claim 7,
In the step of forming the rear electrode,
A method of manufacturing a solar cell in which a content of glass frit per unit volume included in each of the finger electrodes is greater than a content of glass frit per unit volume included in each of the bus bars. In claim 7,
In the step of forming the rear electrode,
A method of manufacturing a solar cell in which each of the bus bars is formed so as not to come into direct contact with the polycrystalline silicon rear surface electric field. In claim 7,
A method of manufacturing a solar cell, wherein the content of the metal material per unit volume included in each of the finger electrodes is greater than the content of the metal material per unit volume included in each of the bus bars. In claim 10,
The content of the metal material per unit volume included in each of the finger electrodes is formed to be 80 wt% or more and 95 wt% or less,
A method of manufacturing a solar cell, wherein the content of the metal material per unit volume included in each of the bus bars is 60 wt% or more and 80 wt% or less. 12. In any one of claims 7 to 11,
The method of manufacturing a solar cell further comprising the step of forming an emitter portion on the entire surface of the single crystal silicon substrate. In claim 12,
In the step of forming the emitter part,
A method of manufacturing a solar cell, comprising: doping the entire surface of the single crystal silicon substrate with impurities, and then thermally diffusing the impurities into the entire surface of the single crystal silicon substrate to form the emitter part. In claim 13,
The method of manufacturing a solar cell further comprising the step of forming a front electrode connected to the emitter part. 15. In claim 14,
A method of manufacturing a solar cell, wherein the content of the glass frit per unit volume included in each of the finger electrodes is the same as the content of the glass frit per unit volume included in the front electrode. 15. In claim 14,
A method of manufacturing a solar cell, wherein the content of the metal material per unit volume included in each of the finger electrodes is the same as the content of the metal material per unit volume included in the front electrode.

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