KR20120085074A - Solar cell and fabrication method thereof - Google Patents

Abstract

PURPOSE: A solar cell and a manufacturing method thereof are provided to easily form an uneven portion having a fine and uniform shape since a silicon semiconductor substrate is textured by easily using an alkali aqueous solution including an organic solvent. CONSTITUTION: An uneven portion(115) is formed on one side of a substrate(110). The uneven portion is formed by dipping the substrate in an etchant mixing an organic solvent with an alkali aqueous solution. An emitter layer(120) is formed on one side of the substrate on which the uneven portion is formed. A reflection preventing layer(130) is formed on the emitter layer. A front electrode(140) is connected with the emitter layer through the reflection preventing layer.

Description

Solar cell and its manufacturing method {Solar cell and fabrication method

The present invention relates to a solar cell and a method for manufacturing the same, and more particularly, to a solar cell and a method for manufacturing the same, including a silicon semiconductor substrate formed with fine irregularities.

Recently, with the anticipation of depletion of existing energy sources such as oil and coal, there is increasing interest in alternative energy to replace them. Among them, solar cells are in the spotlight as next generation cells that directly convert solar energy into electrical energy using semiconductor devices.

A solar cell is a device that converts light energy into electrical energy using a photovoltaic effect, and it is very important to increase conversion efficiency related to the rate of converting incident solar light into electrical energy. Such solar cells may be classified into silicon solar cells, thin film solar cells, dye-sensitized solar cells, organic polymer solar cells, and the like according to their constituent materials, and silicon solar cells are the mainstream.

On the other hand, in order to improve conversion efficiency in silicon solar cells, the incident surface of the silicon semiconductor substrate to which sunlight is incident is formed to form an uneven structure, which increases the optical path into the solar cell, and thus It is an effective way to increase the absorption rate.

The uneven structure may be formed by performing a texturing process of etching a silicon semiconductor substrate with an aqueous solution of KOH or the like mixed with isopropyl alcohol (IPA). However, the texturing process is carried out at a temperature of about 80 ° C., and the IPA has a high volatility, especially a boiling point of 82.3 ° C., which has a value similar to that of the texturing process. Therefore, it is difficult to maintain the KOH / IPA concentration ratio because the amount of IPA is evaporated and consumed during the texturing process, it is difficult to perform uniform texturing.

In addition, when the silicon semiconductor substrate is etched with an etching solution having a KOH / IPA composition, it is difficult to control the size of the unevenness to be formed, and the unevenness having a large shape of about 10 μm and a depth of about 20 μm is formed. Is formed. Therefore, the emitter doping profile may be non-uniform in the hills and valleys of the unevenness, and in particular, since the depth of the unevenness is formed to be around 20 μm, the thickness of the silicon semiconductor substrate becomes thin after texturing to a silicon semiconductor substrate having a thickness of 180 μm or less. Can be difficult to apply.

SUMMARY OF THE INVENTION An object of the present invention is to provide a solar cell and a method for manufacturing the same, including a silicon semiconductor substrate having irregularities having a uniform and fine shape.

In the solar cell manufacturing method according to the present invention for achieving the above object, the step of forming irregularities on one surface of the substrate, the step of forming an emitter layer on one surface of the substrate on which the irregularities are formed, the anti-reflection film on the emitter layer And forming a front electrode connected to the emitter layer through the anti-reflection film, wherein the unevenness may be formed by immersing the substrate in an etching solution in which an organic solvent is mixed with an alkaline aqueous solution.

In addition, the alkaline aqueous solution may be a mixture of water and KOH.

In addition, the organic solvent may be NMP (N-Methyl-2-Pyrrolidone).

In addition, the volume ratio of KOH and the organic solvent may be 1: 0.5 to 1: 2.

In addition, the height of the unevenness may be formed to 10 to 15㎛.

In addition, the size of the unevenness may be formed to 1 to 5㎛.

In addition, the solar cell according to the present invention for achieving the above object is connected to the emitter layer through the silicon semiconductor substrate with the irregularities, the emitter layer on one surface of the substrate with the irregularities, the antireflection film on the emitter layer and the antireflection film It includes a front electrode, the size of the unevenness is 1 to 5㎛, the height of the unevenness may be 10 to 15㎛.

According to the present invention, by forming uniform and fine irregularities in the silicon semiconductor substrate, the emitter layer can have a uniform doping concentration, thereby improving the uniformity of the P-N junction can increase the efficiency of the solar cell.

1 is a cross-sectional view showing a cross section of a solar cell according to an embodiment of the present invention;
2 is a view illustrating a method of manufacturing the solar cell of FIG. 1, and
3 is a diagram illustrating a silicon semiconductor substrate having irregularities included in the solar cell of FIG. 1.

In the drawings, each component is exaggerated, omitted, or schematically illustrated for convenience and clarity of description. In addition, the size of each component does not necessarily reflect the actual size.

Hereinafter, with reference to the drawings will be described the present invention in more detail.

1 is a cross-sectional view illustrating a structure of a solar cell according to an embodiment of the present invention.

Referring to FIG. 1, the solar cell 100 according to the present invention includes a silicon semiconductor substrate 110, an emitter layer 120 on the substrate 110, an antireflection film 130 and an antireflection film (on the emitter layer 120). It may include a front electrode 140 penetrating 130 and connected to the emitter layer 120.

The substrate 110 may be formed of single crystal or polycrystalline silicon, and may be implemented in P type by doping with group III elements B, Ga, In, etc. as P type impurities.

In addition, one surface of the substrate 110 may be textured to include irregularities 115 of various shapes such as pyramids, squares, triangles, and the like. Texturing refers to forming a concave-convex 115-shaped pattern on the surface of the substrate 110. When the surface of the substrate 110 is roughened by texturing, the reflectance of incident light decreases. Light capture may increase. Thus optical losses can be reduced.

Uneven | corrugated 115 can be formed by immersing the board | substrate 110 in the etching solution which mixed alkali aqueous solution and the organic solvent, as mentioned later in FIG. The organic solvent may be a substance having a higher boiling point than IPA (Isopropyl Alcohol) and having a chemical stability when mixed with an alkaline aqueous solution such as KOH aqueous solution. For example, the organic solvent may be NMP (N-Methyl-2-Pyrrolidone), NMP has a boiling point of about 200 ℃ much higher than the texturing process conditions, weak volatile, can solve the problem of natural disappearance during the process .

The irregularities 115 formed as described above may have a size of 1 to 5 μm and may be uniformly formed on the entire substrate 110. Herein, the size of the unevenness 115 means the width. In addition, the concave-convex 115 may have a depth (or height) of 10 to 15㎛, it can be applied to the substrate 110 having a thickness of less than 180㎛, in particular having a height of about 20㎛ conventional In contrast, as the height difference between the peaks and valleys of the unevenness 115 decreases, the emitter layer 120 may have a uniform doping profile.

The emitter layer 120 may be formed on the substrate 110 with a conductivity type opposite to that of the substrate 110. For example, the emitter layer 120 may be doped with impurities such as P, As, and Sb, which are Group 5 elements, as N-type impurities. As described above, when impurities of the opposite conductivity type are doped to the substrate 110 and the emitter layer 120, a PN junction is formed at the interface between the substrate 110 and the emitter layer 120, and light is applied to the PN junction. When irradiated, photovoltaic power may be generated by the photoelectric effect.

On the other hand, as described above, the emitter layer 120 on the substrate 110 including the unevenness 115 has a smaller height difference between the peaks and valleys of the unevenness 115 than in the related art, and thus is uniform in the peaks and valleys of the unevenness 115. It can have one doping concentration, whereby the uniformity of the PN junction can also be improved.

The anti-reflection film 130 is positioned on the emitter layer 120, and immobilizes defects existing in the surface or the bulk of the emitter layer 120 and reduces the reflectance of sunlight incident on the entire surface of the substrate 110.

When the defect present in the emitter layer 120 is immobilized, the recombination site of the minority carriers is removed to increase the open voltage Voc of the solar cell 100. When the reflectance of the solar light is reduced, the amount of light reaching the P-N junction is increased to increase the short-circuit current Isc of the solar cell 100.

As such, when the open voltage and the short-circuit current of the solar cell 100 are increased by the anti-reflection film 130, the conversion efficiency of the solar cell 100 may be improved.

The anti-radiation film 130 is, for example, a silicon nitride film, a silicon nitride film including hydrogen, a silicon oxide film, a silicon oxide nitride film, any one single film selected from the group consisting of MgF ₂ , ZnS, TiO ₂ and CeO ₂ or two or more. The membrane may have a combined multilayer structure.

For example, the front electrode 140 may be formed by screen printing the front electrode paste on the front electrode 140 and then performing heat treatment. The front electrode 140 penetrates the anti-reflection film 130 and comes into contact with the emitter layer 120 and is used as a movement path of a carrier generated by the photoelectric effect.

Meanwhile, the emitter layer 120 and the anti-reflection film 130 sequentially formed on the substrate 110 on which the unevenness 115 is formed are formed along the shape of the unevenness 115. As the concave-convex 115 has a fine shape having a size of 1 to 5 μm and a depth of 10 to 15 μm, as described above, the front electrode 140 paste printed on the antireflection film 130 is particularly preferably The concave portion formed according to the shape can be filled and printed. Therefore, it is possible to prevent the generation of voids between the anti-reflection film 130, thereby reducing the resistance of the front electrode 140.

The rear electrode 150 acts as a movement path for another carrier generated by the photoelectric effect. Meanwhile, a back surfacefield layer 160 may be formed on the interface between the back electrode 150 and the substrate 110. The rear electric field layer 160 may prevent the carrier from moving back to the rear surface of the substrate 110 and may be prevented from being recombined. When the carrier is prevented from recombining, the open voltage may be increased to improve the efficiency of the solar cell 100.

FIG. 2 is a diagram illustrating a method of manufacturing the solar cell of FIG. 1.

Referring to FIG. 2, a method of manufacturing the solar cell 100 will be described. First, as shown in (a), the unevenness 115 is formed on one surface of the silicon semiconductor substrate 110.

The unevenness 115 may be formed by immersing the substrate 110 in an etching solution.

The etching solution may be a solution obtained by mixing an alkaline aqueous solution and an organic solvent. For example, the alkaline aqueous solution may be a KOH aqueous solution, and the organic solvent may be chemically stable when mixed with the alkaline aqueous solution, and may have a higher boiling point than IPA (Isopropyl Alcohol). For example, the organic solvent may be NMP (N-Methyl-2-Pyrrolidone), NMP has a boiling point of about 200 ℃ much higher than the texturing process conditions, weak volatile, can solve the problem of natural disappearance during the process .

When the substrate 110 is immersed in such an etching solution, the organic solvent is adhered to the surface of the substrate 110 to uniform the surface potential of the substrate 110, thereby achieving an equilibrium state of the etching reaction. When etching is performed in this state, a uniform etching may be performed on the surface of the substrate 110.

On the other hand, the ratio of KOH and the organic solvent contained in the etching solution may be included with a volume ratio of 1: 0.5 to 1: 2. When the volume ratio of the organic solvent is less than 0.5 compared to KOH, excessive etching may occur. On the other hand, when the volume ratio of the organic solvent is larger than 2 compared to KOH, not only etching is performed but texture is not uniformly formed. Unevenness to be 115 may be nonuniform. Therefore, the ratio of KOH and the organic solvent included in the etching solution is preferably included in a volume ratio of 1: 0.5 to 1: 2 so that uniform unevenness 115 is formed on the substrate 110.

The irregularities 115 formed as described above may have a size of 1 to 5 μm and a depth of 10 to 15 μm. Therefore, it can be applied to the substrate 110 having a thickness of 180 μm or less.

Next, as shown in (b), the emitter layer 120 and the antireflection film 130 are sequentially formed on the substrate 110 on which the unevenness 115 is formed. The emitter layer 120 and the anti-reflection film 130 may be formed along the shape of the concave-convex 115 formed on the substrate 110.

The emitter layer 120 may be formed by a method such as a diffusion method, a spray method, or a printing process method. For example, the emitter layer 120 may be formed by injecting N-type impurities into the P-type semiconductor substrate 110.

On the other hand, since the unevenness 115 formed on the substrate 110 has a height difference between the peaks and valleys as compared with the conventional height of about 20 μm, the doping concentration of the emitter layer 120 is increased by the peaks and valleys of the unevenness 115. Since it can be formed uniformly, the uniformity of the PN junction can be improved.

The anti-reflection film 130 may be formed by vacuum deposition, chemical vapor deposition, spin coating, screen printing, or spray coating, but is not limited thereto.

Subsequently, as shown in (c), the front electrode paste 145 is printed on the antireflection film 130, and the back electrode paste 155 is printed on the rear surface of the substrate 110.

The front electrode paste 145 may include silver (Ag), glass frit, a binder, a solvent, or the like. For example, the front electrode paste 145 may be screen printed using a screen mask (not shown) having an opening selectively formed to correspond to a position where the front electrode 140 is to be formed.

Meanwhile, the anti-reflection film 130 is formed along the shape of the unevenness 115 formed on the substrate 110, and the front electrode paste 145 is printed on the anti-reflection film 130. In addition, as described above, since the concave-convex 115 has a fine shape having a depth of 10 to 15 μm, the front electrode paste 145 printed on the anti-reflection film 130 may have reflections formed according to the shape of the concave-convex 115. The concave portion of the protection layer 130 may be completely filled and printed. Therefore, it is possible to prevent the generation of voids between the anti-reflection film 130 and the front electrode paste 145, thereby reducing the resistance of the front electrode 140 formed.

As an example, a back electrode paste 155 to which aluminum, quartz silica, a binder, or the like is added is printed on the back surface of the substrate 110.

Next, as shown in (d), the front electrode paste 145 and the back electrode paste 155 are heat treated to form the front electrode 140 and the rear electrode 150.

During the heat treatment of the front electrode paste 145, the silver contained therein becomes a liquid at high temperature and recrystallized into a solid phase, and thus the front electrode is formed by a fire through phenomenon which penetrates the anti-reflection film 130 through the glass frit. 140 is connected to the emitter layer 120.

In addition, the rear electrode paste 155 is heat-treated, such that aluminum included in the rear electrode paste 155 diffuses through the rear surface of the substrate 110, and thus the rear electrode paste 155 is formed at the interface between the rear electrode 150 and the substrate 110. Form layer 160. The back field layer 160 minimizes back recombination of electrons generated by sunlight, contributing to the improvement of solar cell efficiency.

3 is a diagram illustrating a silicon semiconductor substrate having irregularities included in the solar cell of FIG. 1.

Figure 3 (a) is a case where the irregularities are formed on the silicon semiconductor substrate using a KOH aqueous solution containing IPA as in the conventional method, (b) is a KOH aqueous solution containing NMP in accordance with an embodiment of the present invention It is a case where the unevenness | corrugation was formed in the silicon semiconductor substrate using this. Here, in (a) and (b), the substrate used a 156mm mono wafer, and texturing was performed at 80 ° C. for 23 minutes. In addition, texturing was performed by immersing two LSCs containing 100 wafers simultaneously.

As can be seen from (a), when the unevenness is formed on the silicon semiconductor substrate using the KOH aqueous solution containing IPA, it is understood that the unevenness is formed and the uniformity of the texturing is reduced. On the other hand, in the case of (b) it can be seen that irregularities are formed uniformly on the substrate as a whole.

On the other hand, (c) is the road measured by SEM in the case of (b), it can be seen that in the case of (b) the size of the unevenness formed is within 5㎛. As described above, according to the present invention, the silicon semiconductor substrate is textured using an alkaline aqueous solution containing an organic solvent, thereby making it possible to form irregularities having a fine and uniform shape.

Table 1 below is a result of measuring the efficiency of the solar cell including the substrate of Figure 3 (a) and (b).

Number of solar cells Voc (mV) Jsc (mA / cm ² ) FF (%) EF (%) (a) 1146 623 35.75 78.50 17.49 (b) 773 624 36.08 78.45 17.59

As shown in Table 1, the case of Figure 3 (b), it can be seen that the current increased by the uniform texturing compared to (a), it can be seen that the efficiency of the solar cell is increased by 0.1% accordingly .

As described above, the emitter layer is formed on the substrate with a uniform doping concentration, thereby improving the uniformity of the P-N junction.

In addition, according to the present invention, since the alkaline aqueous solution containing the organic solvent does not have a problem of natural annihilation during the process, not only can uniformly texture all 200 substrates, but also can be processed up to 10 times in succession of solar cells. Mass productivity can be improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limiting the scope of the invention as defined by the appended claims. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

100: solar cell 110: substrate
115: unevenness 120: emitter layer
130: antireflection film 140: front electrode
150: rear electrode 160: rear field layer

Claims (12)

Forming irregularities on one surface of the substrate;
Forming an emitter layer on one surface of the substrate on which the unevenness is formed;
Forming an antireflection film on the emitter layer; And
Forming a front electrode penetrating the anti-reflection film to connect with the emitter layer;
The unevenness is a solar cell manufacturing method formed by immersing the substrate in an etching solution mixed with an organic solvent in an aqueous alkaline solution. The method of claim 1,
The alkaline aqueous solution is a solar cell manufacturing method of mixing water and KOH. The method of claim 1,
The organic solvent is NMP (N-Methyl-2-Pyrrolidone) solar cell manufacturing method. The method of claim 2,
The volume ratio of the KOH and the organic solvent is 1: 0.5 to 1: 2 solar cell manufacturing method. The method of claim 1,
The height of the unevenness is a solar cell manufacturing method is formed in 10 to 15㎛. The method of claim 1,
The uneven size of the solar cell manufacturing method is formed to 1 to 5㎛. The method of claim 1,
The front electrode is formed by applying a front electrode paste on the anti-reflection film and heat treatment. The method of claim 7, wherein
The front electrode passes through the anti-reflection film during the heat treatment. The method of claim 1,
A solar cell manufacturing method comprising the step of forming a back electrode on the back of the substrate. 10. The method of claim 9,
A solar cell manufacturing method comprising a back field layer is formed between the substrate and the back electrode. A silicon semiconductor substrate having irregularities formed thereon;
An emitter layer on one surface of the substrate on which the unevenness is formed;
An anti-reflection film on the emitter layer; And
A front electrode penetrating the anti-reflection film and connected to the emitter layer;
The size of the unevenness is 1 to 5㎛, the height of the unevenness is a solar cell of 10 to 15㎛. The method of claim 11,
A rear electrode on the back of the substrate,
A solar cell comprising a back field layer between the substrate and the back electrode.

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