KR20180079986A - Solar cell - Google Patents

Abstract

The present invention relates to a solar cell which has an improved damp heat property while maintaining efficiency. According to an embodiment of the present invention, the solar cell comprises: a semiconductor substrate containing an impurity of a first conductivity type; an emitter unit which is positioned on a front surface of the semiconductor substrate and contains an impurity of a second conductivity type opposite to the first conductivity type; a rear electric field unit which is positioned on a rear surface of the semiconductor substrate and contains an impurity of the first conductivity type at a higher concentration than the semiconductor substrate; a rear protection film positioned on the rear electric field unit; a first electrode connected to the emitter unit; and a second electrode connected to the rear electric field unit through the rear protection film. The rear protection film includes a silicon nitride film positioned on the rear electric field unit and a silicon oxide film positioned on the silicon nitride film. The thickness of the silicon oxide film is larger than the thickness of the silicon nitride film.

Description

Solar cell {SOLAR CELL}

The present invention relates to a solar cell.

With the recent depletion of existing energy resources such as oil and coal, interest in alternative energy to replace them is increasing. Among them, solar cells produce electric energy from solar energy, and they are attracting attention because they have abundant energy resources and there is no problem about environmental pollution.

Typical solar cells have a substrate made of different conductivity type semiconductors, such as p-type and n-type, an emitter layer, 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.

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, so that electrons and holes are directed toward the n-type semiconductor and the p- And is collected by an electrode electrically connected to the substrate and the emitter portion, and these electrodes are connected to each other by electric wires to obtain electric power.

On the other hand, in order to operate the solar cell optimally, even if a solar cell is used for a long period of time, a damp heat characteristic indicating a durability of the module against moisture and heat penetration from the outside is highly required.

In addition, if the Damp Heat characteristic deteriorates, the moisture content penetrates into the solar cell, and the fill factor (FF) decreases due to the increase of the contact resistance (Rs) There is a problem that the reliability of the solar cell can be greatly lowered.

Meanwhile, the damp heat characteristics related to the reliability of the solar cell according to the long-time use are mainly performed by the protective film located on the rear surface of the semiconductor substrate provided in the solar cell. However, -2011-0139066 discloses a protective film which has a thickness irrelevant to the damp heat characteristic of the solar cell and due to the dampness of the damp heat characteristic, There is a problem.

An object of the present invention is to provide a solar cell having improved Damp Heat characteristics while maintaining efficiency properly.

A solar cell according to an example of the present invention includes: a semiconductor substrate containing an impurity of a first conductivity type; An emitter section located on the front surface of the semiconductor substrate and containing an impurity of a second conductivity type opposite to the first conductivity type; A rear electric field portion located on the rear surface of the semiconductor substrate and containing impurities of the first conductive type at a higher concentration than the semiconductor substrate; A backside shield positioned over the backside electrical portion; A first electrode connected to the emitter portion; And a second electrode connected to the rear electric part through the rear passivation film, wherein the rear passivation film comprises a silicon nitride film positioned on the rear electric field part and a silicon oxide film positioned on the silicon nitride film, Is greater than the thickness.

Specifically, the thickness of the silicon oxide film may be between two and three times the thickness of the silicon nitride film.

For example, the front surface of the semiconductor substrate has texturing irregularities, and the rear surface of the semiconductor substrate does not have texturing irregularities, and may be flatter than the front surface of the semiconductor substrate.

In such a case, the thickness of the silicon nitride film may be between 30 nm and 40 nm, and the thickness of the silicon oxide film may be between 95 nm and 105 nm.

In addition, the refractive index of the silicon oxide film may be smaller than that of the silicon nitride film.

For example, the refractive index of the silicon oxide film may be between 1.53 and 1.75.

Further, an aluminum oxide film may be further disposed on the silicon oxide film. In such a case, the thickness of the aluminum oxide film may be smaller than the thickness of the silicon oxide film and the silicon nitride film.

For example, the thickness of the aluminum oxide film may be between 1/5 and 1/3 of the thickness of the silicon nitride film.

When the front and rear surfaces of the semiconductor substrate are provided with texturing irregularities, the thickness of the silicon oxide film may be between 125 nm and 145 nm.

The solar cell according to the present invention can improve the reliability of the solar cell by further improving the damp heat characteristics of the rear passivation layer while minimizing the deterioration of the efficiency of the solar cell by forming the silicon oxide film thicker than the silicon nitride film .

1 and 2 are views for explaining a solar cell according to an example of the present invention.
FIG. 3 is a graph illustrating the Damp Heat characteristic according to the thickness of the silicon oxide film shown in FIG. 2. FIG.
4 is a graph illustrating a contact resistance between the second electrode and the rear electric field depending on the thickness of the silicon oxide film shown in FIG.
FIG. 5 is a graph illustrating the rate of efficiency change of the solar cell according to the thickness of the silicon oxide film shown in FIG. 2. FIG.
6 is a view for explaining a solar cell according to another example of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

In the drawings, the thicknesses are enlarged to clearly indicate layers and regions. When a layer, film, region, plate, or the like is referred to as being "on" another portion, it includes not only the case directly above another portion but also the case where there is another portion in between. Conversely, when a part is "directly over" another part, it means that there is no other part in the middle. Also, when a part is formed as "whole" on the other part, it means not only that it is formed on the entire surface (or the front surface) of the other part but also not on the edge part.

The front surface may be a surface of the semiconductor substrate to which the direct light is incident, and the rear surface may be the opposite surface of the semiconductor substrate on which no direct light is incident or on which reflected light other than direct light may be incident.

In addition, the fact that any two values are equal means that the error range is equal to or less than 10%.

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

1 and 2 are views for explaining a solar cell according to an example of the present invention. Specifically, FIG. 1 is a perspective view of a solar cell according to an example of the present invention, and FIG. 2 is a cross- Fig.

1, an example of a solar cell according to the present invention includes a semiconductor substrate 110, an emitter section 120, an antireflection film 130, a rear electric section 170, a rear protective film 190, An electrode 140 and a second electrode 150. [

Although the solar cell according to the present invention includes the antireflection film 130 in FIG. 1, the antireflection film 130 may be omitted in the present invention. However, in consideration of the efficiency of the solar cell, since it is more efficient to include the antireflection film 130, it will be explained that the antireflection film 130 is included as an example.

The semiconductor substrate 110 may be a silicon semiconductor substrate 110 containing an impurity of the first conductivity type.

Here, the impurity of the first conductivity type may be any one of impurities of the p-type conductivity type or the n-type impurity type.

In addition, the silicon semiconductor substrate 110 may be a single crystal silicon wafer substrate or a polycrystalline silicon wafer substrate.

Here, for example, when the semiconductor substrate 110 is a p-type conductive type, it may contain an impurity of a trivalent element such as boron (B), gallium, indium, or the like.

However, when the semiconductor substrate 110 is an n-type conductive type, impurities such as phosphorus (P), arsenic (As), antimony (Sb), and the like may be contained. Hereinafter, a case where the impurity of the first conductivity type of the semiconductor substrate 110 is an n-type conductivity type will be described as an example.

In addition, as shown in FIGS. 1 and 2, the front surface of the semiconductor substrate 110 may have a texturing surface that is an uneven surface that is entirely textured.

In addition, the rear surface of the semiconductor substrate 110 is not textured and may have a relatively flat surface than the front surface of the semiconductor substrate 110.

The emitter section 120 is disposed on the front surface of the semiconductor substrate 110 on which light is incident and includes a second conductive type opposite to the conductive type of the semiconductor substrate 110, for example, a p-type conductive type impurity So that a pn junction with the semiconductor substrate 110 can be formed.

The pair of electrons and holes, which are carriers generated by light incident on the semiconductor substrate 110 from the outside by the p-n junction, are separated into electrons and holes, electrons move toward the n-type, and holes move toward the p-type. Therefore, when the semiconductor substrate 110 is n-type and the emitter section 120 is p-type, the separated electrons can move toward the rear surface of the semiconductor substrate 110 and the separated holes can move toward the emitter section 120.

The emitter layer 120 may be formed by diffusing a second conductive type impurity into the front surface of the semiconductor substrate 110. In this case, the emitter layer 120 may be formed of the same silicon material as the semiconductor substrate 110 As shown in FIG.

For example, when the semiconductor substrate 110 is formed of a polycrystalline silicon wafer, the emitter section 120 may be formed of a polycrystalline silicon material. When the semiconductor substrate 110 is formed of a wafer of monocrystalline silicon, The tip portion 120 may also be formed of a single-sided silicon material.

The antireflection film 130 is disposed on the emitter layer 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) Layer film.

Although FIGS. 1 and 2 illustrate the case where the anti-reflection film 130 is formed as a single film, it is not limited to a single film.

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

The first electrode 140 may be disposed directly on the emitter section 120 and may be electrically connected to the emitter section 120.

The first electrode 140 may include a plurality of first finger electrodes 141 and a plurality of first connection electrodes 143, as shown in FIG.

The plurality of first finger electrodes 141 are located on the emitter section 120 and are electrically connected to the emitter section 120 and extended in one direction. Can be spaced apart.

The plurality of first finger electrodes 141 may collect the carriers that have migrated toward the emitter unit 120.

The plurality of first connection electrodes 143 are located on the same layer as the plurality of first finger electrodes 141 on the emitter section 120 and electrically connect the plurality of first finger electrodes 141 to each other, The first finger electrode 141 of FIG.

The plurality of first connection electrodes 143 are connected to an interconnector (not shown) for connecting the solar cells to each other. The plurality of first connection electrodes 143 collect the carriers collected by the plurality of first finger electrodes 141, Output.

The plurality of first finger electrodes 141 and the first connection electrodes 143 are formed of at least one conductive metal material. Examples of the conductive metal materials include nickel (Ni), copper (Cu), silver (Ag) May be at least one selected from the group consisting of aluminum (Al), tin (Sn), zinc (Zn), indium (In), titanium (Ti), gold (Au) ≪ / RTI >

The first electrode 140 is formed on the entire surface of the semiconductor substrate 110 and then the electrode forming paste for forming the first electrode 140 is formed on the front surface of the anti- After the patterning is applied, an electrode forming paste may be formed through the heat treatment process and connected to the emitter section 120 through the anti-reflection film 130.

Although the first electrode 140 includes the first finger electrode 141 and the first connection electrode 143 in FIG. 1, the first connection electrode 143 may be omitted in some cases. And may be selectively provided so that only a part of the first finger electrodes 141 of the plurality of first finger electrodes 141 are connected to each other.

The rear electric field portion 170 is located on the rear surface of the semiconductor substrate 110 and impurities of the first conductive type may be contained at a higher concentration than the semiconductor substrate 110.

The rear electric field portion 170 is located entirely on the rear surface of the semiconductor substrate 110 to prevent the holes from moving toward the rear surface of the semiconductor substrate 110 and electrons to move toward the rear surface of the semiconductor substrate 110 It can be done more smoothly.

The rear electric field portion 170 may be formed by diffusing impurities of the first conductive type on the rear surface of the semiconductor substrate 110. As a result, And may be formed of a material.

For example, when the semiconductor substrate 110 is formed of a wafer of monocrystalline silicon, the rear electric section 170 may be formed of a single crystal silicon material. When the semiconductor substrate 110 is formed of a polycrystalline silicon wafer, The rear electric section 170 may also be formed of a polycrystalline silicon material.

The thickness of the rear electric section 170 may be in the range of 1 [mu] m to 1.4 [mu] m.

1 and 2, the rear protective layer 190 may be located on the entire surface of the back surface of the rear electric part 170 except the area where the second electrode 150 is formed.

The rear protective layer 190 may be formed of a dielectric material or may be formed of a plurality of layers.

The rear protective layer 190 may function to passivate the rear surface of the rear electric part 170 and may block the heat and moisture flowing into the rear surface of the semiconductor substrate 110 from the outside, Can be performed together.

Such a rear protective film 190 will be described in more detail after describing the remaining components of the solar cell.

The second electrode 150 is disposed on the rear surface of the rear electric part 170 and is electrically connected to the rear electric part 170.

The second electrode 150 may include a plurality of second finger electrodes 151 and a plurality of second connection electrodes 153, as shown in FIG.

Here, the plurality of second finger electrodes 151 may extend in a direction away from each other on the rear surface of the rear electric unit 170, and may include a carrier moved toward the rear electric unit 170, for example, Can be collected.

The plurality of second connection electrodes 153 are located on the same layer as the plurality of second finger electrodes 151 on the rear electric unit 170 and electrically connect the plurality of second finger electrodes 151 to each other, And may extend in a direction intersecting the plurality of second finger electrodes 151.

The plurality of second connection electrodes 153 are connected to an interconnector (not shown) for connecting the solar cells to each other. The second connection electrodes 153 collect the carriers collected by the second finger electrodes 151 and output the collected carriers to an external device .

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

In addition, the line widths of the first and second finger electrodes 141 and 151 and the line widths of the first and second connection electrodes 143 and 153 may be the same.

In the second electrode 150, the electrode forming paste is patterned on the rear protective layer 190, and then the electrode forming paste penetrates the rear protective layer 190 through the heat treatment process, As shown in FIG.

Although the second electrode 150 includes the second finger electrode 151 and the second connection electrode 153 in FIG. 1 as an example, the second connection electrode 153 may be omitted in some cases. And it is also possible to selectively connect only the second finger electrodes 151 of a plurality of the second finger electrodes 151 to each other.

Meanwhile, the solar cell according to an exemplary embodiment of the present invention may have a structure in which the rear protective layer 190 has a plurality of functional layers in order to improve the passivation function of the rear protective layer 190 and further improve the damp heat characteristic .

For example, the rear protective layer 190 may include a silicon nitride (SiNx) layer 190a and a silicon oxide (SiOx) layer 190b, as shown in FIG.

Here, the silicon nitride film 190a is located in contact with the surface of the rear electric section 170 and contains a large amount of hydrogen, thereby performing the passivation function on the rear surface of the semiconductor substrate 110. [

Here, a PECVD (Plasma Enhanced Chemical Vapor Deposition) method can be used for the process of containing hydrogen in the silicon nitride film.

For example, in order to connect the hydrogen to the dangling bond ring existing in the SiNx layer because of the amorphous state, the amorphous SiNx layer is formed by applying plasma in the state of injecting SiH4, NH3, N2 gas, (H). ≪ / RTI >

The silicon oxide film 190b is located on the silicon nitride film 190a and performs a capping function to prevent the hydrogen contained in the silicon nitride film 190a from being discharged to the outside. Thus, the Damp Heat characteristic of the rear passivation film 190 can be further improved.

Here, since the silicon oxide film 190b has a considerable thickness and needs to be formed in a short time, it can be manufactured by the PECVD method like the silicon nitride film 190a.

The thickness T2 of the silicon oxide film 190b may be greater than the thickness T1 of the silicon nitride film 190a to further improve the Damp heat characteristics of the rear surface protection film 190. [

For example, the thickness T2 of the silicon oxide film 190b may be between two and three times the thickness of the silicon nitride film 190a.

The reason why the thickness T2 of the silicon oxide film 190b is made to be twice or more the thickness of the silicon nitride film 190a is to further improve the Damp Heat characteristic of the silicon oxide film 190b and to make the thickness thereof 3 times or less When the thickness T2 of the silicon oxide film 190b is excessively increased, the second electrode 150 penetrates the rear protective film 190 and is electrically connected to the rear electric part 170 during the cell manufacturing process, The contact resistance between the second electrode 150 and the rear electric section 170 increases, and the reduction rate of the cell efficiency can be relatively increased.

For example, the thickness T1 of the silicon nitride film 190a in the solar cell according to the present invention may be between 30 nm and 40 nm.

The reason why the thickness T1 of the silicon nitride film 190a is set to 30 nm or more is that the passivation function of the silicon nitride film 190a is sufficiently exhibited, .

In addition, the thickness (T2) of the silicon oxide film 190b may be between 95 nm and 105 nm. Here, the thickness T2 of the silicon oxide film 190b will be described with reference to FIGS. 3 to 5. FIG.

FIG. 3 is a graph showing the Damp Heat characteristics according to the thickness T2 of the silicon oxide film 190b shown in FIG. 2. FIG. 4 is a graph showing the thickness T2 of the silicon oxide film 190b shown in FIG. FIG. 5 is a graph showing the contact resistance between the second electrode 150 and the rear electric field portion 170 according to the thickness T2 of the silicon oxide layer 190b shown in FIG. FIG.

3 is a result of the Damp Heat characteristic test. Normally, the Damp Heat characteristic can be satisfied only when it is performed at a temperature of 85 ° C and a humidity of 85% for 1000 hours, and does not show a visual abnormality or an output drop of 5% or more.

In the present invention, however, the damp heat characteristics are satisfied even though the experiment was performed for 2000 hours or more, which is 1000 hours or more.

3, when the thickness T2 of the silicon oxide film 190b is 90 nm or less, the Damp heat is low to -4% or less and the slope indicating the degree of improvement of the Damp Heat is somewhat moderate. However, 190b is 95 nm, the Damp heat is greatly improved to -3.2%. On the other hand, the improvement rate of the damp heat is gradually decreased from -395% to -2.5% from 95 nm or more.

Therefore, in the solar cell according to an exemplary embodiment of the present invention, the thickness T2 of the silicon oxide film 190b may be 95 nm or more in consideration of the damp heat characteristics.

However, when the thickness T2 of the silicon oxide film 190b becomes excessively larger than 110 nm, the contact resistance between the second electrode 150 and the rear electric section 170 becomes excessively large as shown in FIG. .

That is, when the thickness T2 of the silicon oxide film 190b is between 105 nm and 110 nm, the increase rate of the contact resistance is greatly increased as compared with the case where the thickness T2 of the silicon oxide film 190b is 105 nm or less.

5, when the thickness T2 of the silicon oxide film 190b is between 105 nm and 110 nm, the change rate of the cell efficiency is relatively largely decreased as shown in FIG. 5 have.

Therefore, in consideration of such contact resistance and cell efficiency, the solar cell according to an exemplary embodiment of the present invention can make the thickness T2 of the silicon oxide film 190b 105 nm or less.

The refractive index of the silicon oxide film 190b may be less than the refractive index of the silicon nitride film 190a while the refractive index of the silicon oxide film 190b may be between 1.53 and 1.75.

Here, the refractive index of the silicon oxide film 190b is set to 1.75 or less because this value is the maximum value of the refractive index that can be realized by the silicon oxide film 190b.

In addition, the refractive index of the silicon oxide film 190b is set to be larger than 1.53 in order to prevent the density of the silicon oxide film 190b from decreasing. That is, the density of the silicon oxide film 190b is related to the refractive index. The lower the refractive index, the lower the density. The higher the refractive index, the higher the density.

Therefore, the refractive index is adjusted so that the density of the silicon oxide film 190b is set to an appropriate level or higher, so that external moisture can be prevented from penetrating into the silicon oxide film 190b. As a result, Damp heat can be further improved.

2, in addition to the silicon nitride film 190a and the silicon oxide film 190b, an aluminum oxide film (AlOx, 190c) is further formed on the rear surface of the silicon oxide film 190b, . The aluminum oxide film 190c may be omitted depending on the case.

However, when the aluminum oxide film 190c is provided, the capping function and the damp heat characteristic of the silicon oxide film 190b can be assisted.

The thickness T3 of the aluminum oxide film 190c is set to a thickness of the silicon oxide film 190b and the thickness of the silicon nitride film 190a in order to prevent the contact resistance between the second electrode 150 and the rear electric part 170 from being damaged. (T1, T2).

Therefore, the thickness T3 of the aluminum oxide film 190c may be between 1/5 and 1/3 of the thickness T1 of the silicon nitride film 190a.

In this case, the aluminum oxide film 190c may be formed by PECVD or the like, and ALD may be used so that stack coverage can be secured easily.

In the solar cell according to an example of the present invention, texturing irregularities are provided on the front surface of the semiconductor substrate 110, texturing irregularities are not formed on the rear surface of the semiconductor substrate 110, ) Than that of the front surface. However, the solar cell according to the present invention is not limited thereto.

6 is a view for explaining a solar cell according to another example of the present invention.

6, texturing irregularities may be provided on the front and rear surfaces of the semiconductor substrate 110, respectively.

When the texturing irregularities are provided on the rear surface of the semiconductor substrate 110, the capping function and the damp heat characteristic of the silicon oxide film 190b are substantially the same as those of the semiconductor substrate 110 in FIGS. 1 and 2 , It can be relatively lowered.

Therefore, in order to complement the capping function and the damp heat characteristic of the silicon oxide film 190b when the texturing irregularities are provided on the rear surface of the semiconductor substrate 110, the silicon oxide film 190b described in FIGS. Can be relatively thicker than the thickness T2.

For this, the thickness T2 of the silicon oxide film 190b in the solar cell according to another embodiment of the present invention is 25% ~ 35% larger than the thickness T2 of the silicon oxide film 190b described in Figures 1 to 5 .

For example, the thickness T2 of the silicon oxide film 190b may be between 125 nm and 145 nm. In this case, the Damp heat characteristic and the contact resistance characteristic as described with reference to FIGS. 3 to 5 can be maintained.

As described above, in the solar cell according to the present invention, the thickness T2 of the silicon oxide film 190b is made larger than the thickness T1 of the silicon nitride film 190a, It is possible to further improve the reliability of the solar cell by further improving the damp heat characteristic.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

Claims (12)

A semiconductor substrate containing an impurity of a first conductivity type;
An emitter section located on the front surface of the semiconductor substrate and containing an impurity of a second conductivity type opposite to the first conductivity type;
A rear electric field located on the rear surface of the semiconductor substrate and containing impurities of the first conductive type at a higher concentration than the semiconductor substrate;
A rear protective film located on the rear electric field portion;
A first electrode connected to the emitter; And
And a second electrode connected to the rear electric part through the rear protective film,
Wherein the rear protective film comprises a silicon nitride film located on the rear electric field portion and a silicon oxide film located on the silicon nitride film,
Wherein the thickness of the silicon oxide film is larger than the thickness of the silicon nitride film. The method according to claim 1,
Wherein a thickness of the silicon oxide film is between two times and three times the thickness of the silicon nitride film. The method according to claim 1,
Wherein a front surface of the semiconductor substrate has texturing irregularities,
Wherein a back surface of the semiconductor substrate has no texturing irregularities and is flatter than a front surface of the semiconductor substrate. The method of claim 3,
Wherein the silicon nitride film has a thickness of 30 nm to 40 nm. The method of claim 3,
Wherein the thickness of the silicon oxide film is between 95 nm and 105 nm. The method according to claim 1,
Wherein the refractive index of the silicon oxide film is smaller than the refractive index of the silicon nitride film. The method according to claim 6,
And the refractive index of the silicon oxide film is between 1.53 and 1.75. The method according to claim 1,
And an aluminum oxide film is further disposed on the silicon oxide film. 8. The method of claim 7,
Wherein the thickness of the aluminum oxide film is smaller than the thickness of the silicon oxide film and the silicon nitride film. 10. The method of claim 9,
Wherein the thickness of the aluminum oxide film is between 1/5 and 1/3 of the thickness of the silicon nitride film. The method according to claim 1,
Wherein a front surface and a rear surface of the semiconductor substrate have texturing irregularities. The method according to claim 1,
Wherein the thickness of the silicon oxide film is between 125 nm and 145 nm.

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