KR101368808B1 - Crystalline silicon solar cell comprising CNT layer and manufacturing method thereof - Google Patents

Abstract

The present invention discloses a method of manufacturing a crystalline silicon solar cell including a carbon nanotube (CNT) layer and a solar cell manufactured through the same. The manufacturing method according to the present invention includes a first step of preparing a crystalline silicon substrate of a first conductivity type; Forming a PN junction surface on the substrate; Forming a carbon nanotube (CNT) layer on the front surface of the substrate to increase light absorption; And forming a front electrode and a back electrode on the front and rear surfaces of the substrate, respectively.

According to the present invention, since the surface reflectivity can be drastically reduced in the crystalline silicon solar cell compared to the conventional texturing method, the efficiency of the solar cell can be greatly improved.

Solar cell, CNT, reflectance

Description

Crystalline silicon solar cell comprising a carbon nanotube layer and a method for manufacturing the same {Crystalline silicon solar cell comprising CNT layer and manufacturing method

The present invention relates to a crystalline silicon solar cell and a method for manufacturing the same, and more particularly, to a method for manufacturing a solar cell in which a carbon nanotube (CNT) layer is formed to greatly reduce surface reflectance.

A solar cell is a photoelectric conversion element in which a minority carrier excited by sunlight diffuses inside a PN bonded semiconductor to generate electromotive force at both ends of the cell.

In order to manufacture such solar cells, semiconductor materials such as monocrystalline silicon, polycrystalline silicon, amorphous silicon, and compound semiconductors are used. Among them, single crystal silicon has the most energy conversion efficiency, but polycrystalline silicon is used more because of its high cost.

Recently, a thin film solar cell that can be manufactured at a very low cost by depositing a thin film of amorphous silicon or a compound semiconductor on a cheap substrate such as glass or plastic has been used.

The present invention relates to a method of manufacturing a solar cell using a single crystalline or polycrystalline crystalline silicon among them.

Hereinafter, a conventional method of manufacturing a crystalline silicon solar cell will be described with reference to the process flowchart of FIG. 1 and the process cross-sectional views of FIGS. 2A to 2F.

First, as shown in FIG. 2A, the crystalline silicon substrate 10 is prepared, and the damage generated during the substrate cutting process is removed by wet etching using a base or an acid solution. For convenience, a process of manufacturing a solar cell using the p-type doped substrate 10 will be described. (ST11)

Then, a texturing process is performed on the surface of the substrate 10 to increase the light absorption rate. Texturing is a process of forming the fine concavo-convex 20 of a predetermined shape on the surface of the substrate 10 as shown in FIG. 2B. Although wet etching using a base or an acid solution is frequently used, texturing has recently been performed. The dry etching method used is also used. (ST12)

After the texturing process, ion doping is performed with an n-type dopant to form a PN junction structure in the substrate 10.

The doping method mainly used is a thermal diffusion method, in which an n-type dopant-containing gas such as POCl ₃ or PH ₃ is supplied while the substrate 10 is placed inside the high-temperature diffusion furnace.

At this time, as the n-type dopant is diffused into the substrate 10, an n + doping layer 12 having a predetermined thickness is formed on the surface layer of the substrate 10 as shown in FIG. 2C.

Hereinafter, for convenience of description, the remainder of the p-type substrate 10 that is separated from the n + doped layer 12 will be referred to as a p + layer 10 '. (ST13)

Such a high-temperature diffusion step (ST13) usually proceeds at a high temperature of 800 DEG C or higher, and by-products such as PSG (Phosphor-Silicate Glass) are formed on the surface of the substrate 10 at such a high temperature. However, since PSG plays a role of shielding the battery current, it must be removed using an etching solution in order to increase battery efficiency.

If the p-type dopant containing boron (B) is diffused to the n-type substrate, BSG (Boro-Silicate Glass) is produced, and this BSG also serves to reduce the efficiency of the battery and should be removed in the same manner. (ST14)

Meanwhile, in the diffusion process ST13, the n + doped layer 12 is formed at the edge portion of the substrate 10 as shown in FIG. 2C. However, since the leakage current between the front electrode and the rear electrode may be generated through the doped layer 12 at the edge portion, the n + doped layer formed at the edge of the substrate 10 as shown in FIG. 2D to increase the efficiency of the battery. 12) must be removed.

This process is called edge isolation. Specifically, the edge portion is etched using a laser, or the edge portion is etched by wet etching or dry etching. However, the edge isolation process may proceed just before completing the solar cell and performing the test. (ST15)

Next, as shown in FIG. 2E, an antireflection film 14 is formed on the n + doped layer 12. In particular, when the SiN thin film is formed of the antireflection film 14, it plays a role of surface passivation and hydrogen passivation of the substrate as well as enhancing the solar absorption rate. The SiN thin film is mainly formed by plasma enhanced chemical vapor deposition (PECVD), and may also be deposited by sputtering. (ST16)

After the antireflection film 14 is formed using SiN, the electrodes are formed on the front and rear surfaces of the substrate 10 using a conductive material.

To this end, conductive paste containing Al or Ag is applied to the front and rear surfaces of the substrate 10 in a predetermined pattern by using a screen printing technique, and the substrate 10 is sintered in a high temperature furnace. .

As the conductive paste is sintered, front electrodes 18 and back electrodes 16 are formed on the front and rear surfaces of the substrate 10 as shown in FIG. 2F.

Specifically, the conductive paste coated on top of the SiN antireflection film 14 penetrates the antireflection film 14 by a redox reaction during the sintering process and contacts the n + doped layer 12 during the sintering process. Is formed.

In addition, when the Al paste is applied to the rear surface of the substrate 10 and then sintered, the p ++ doped layer 13 is formed while Al diffuses into the n + doped layer 12 during the sintering process. As such, when the p ++ doped layer 13 is formed on the rear surface of the p-type substrate 10, a back surface field is formed on the rear surface of the substrate 10.

The rear electric field increases the efficiency of the solar cell by allowing electrons excited by sunlight in the substrate 10 to move to the rear electrode 16 and not to disappear, but to the front electrode 18 to contribute to the photocurrent. Play a role. (ST17)

After the electrode forming process is completed, the efficiency of the battery is tested, and classification is performed according to the result. Before the test, edge isolation may be performed to cut or etch the edge portion of the substrate 10 to remove leakage current generated at the edge portion of the solar cell.

Then, a solar cell module is manufactured through a modular process of connecting a plurality of completed solar cells. (ST18)

In the manufacturing process of the crystalline solar cell, the texturing process plays a very important role in improving the efficiency of the solar cell as a process for reducing the reflectance of sunlight.

However, in the conventional wet etching method using acid or base solution, since the etching rate is different from several tens to several hundred times depending on the crystal plane, it is difficult to obtain uniform surface roughness in polycrystalline silicon and the effect of reducing the reflectance is not so great.

In addition, the dry etching method using the plasma can obtain a lower surface reflectivity than the wet etching method, but there is still a considerable difficulty in achieving a surface reflectivity of less than 10%.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a crystalline silicon solar cell and a method of manufacturing the same, which dramatically reduce the surface reflectivity of a substrate in order to improve energy efficiency.

According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: preparing a crystalline silicon substrate of a first conductivity type; Forming a PN junction surface on the substrate; Forming a carbon nanotube (CNT) layer on the front surface of the substrate to increase light absorption; It provides a method of manufacturing a crystalline silicon solar cell comprising a fourth step of forming a front electrode and a back electrode on the front and back of the substrate, respectively.

In the method of manufacturing the crystalline silicon solar cell, the third step may include forming a catalyst metal layer on the substrate; Converting the catalytic metal layer into metal particles; It may be characterized in that it comprises the step of growing the CNT on the particles of the catalyst metal produced in the conversion step.

The catalyst metal may be any one of Fe, Ni, and Co, or an alloy made of two or more of the Fe, Ni, and Co.

The step of converting the catalyst metal layer into a metal particle may be characterized in that it comprises a process of etching the catalyst metal layer using a high temperature heat treatment or an etching gas, wherein the etching gas is NH ₃ or H ₂ days Can be.

In addition, the CNT may be characterized by growing by plasma chemical vapor deposition (PECVD) using at least one of the raw materials of C ₂ H ₂ , CH ₄ , C ₂ H ₄ , C ₂ H ₆ , CO.

In addition, the CNT layer may be characterized in that formed at a height of 10 ~ 500nm.

In the second step, a first conductive doping layer having a greater doping concentration than the substrate may be formed on the rear surface of the substrate, and a second conductive doping layer may be formed on the front surface of the substrate. have.

The present invention also includes a crystalline silicon substrate having a carbon nanotube (CNT) layer on the surface to increase light absorption and having a PN junction surface therein; A first electrode formed on one surface of the substrate; It provides a crystalline silicon solar cell comprising a second electrode formed on the other surface of the substrate.

According to the present invention, the surface reflectivity of the crystalline silicon solar cell can be drastically reduced as compared to the conventional texturing method, thereby greatly improving the efficiency of the solar cell.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

The present invention provides a carbon nanotube (CNT) layer on the surface of a crystalline silicon substrate by removing the surface of the crystalline silicon substrate from a conventional texturing method in which the surface of the crystalline silicon substrate is wet or dry to form an uneven pattern. It is characterized by the fact that it is possible to significantly reduce the surface reflectivity of the substrate by forming a thickness.

That is, when the CNT layer is grown to a level of about 500 nm on the crystalline silicon substrate as shown in FIG. 3A, the surface reflectivity can be greatly reduced because incident light is incident on the surface of the substrate while being diffusely reflected between the bundles of CNTs.

Figure 3b is a graph showing the reflectance of the Si surface on which the CNT layer is formed and the etched Si surface, it can be seen that the reflectivity near 0% when the CNT layer is formed, the present invention is such a This is to improve the light absorption rate of solar cells by using the characteristics.

In general, CNT growth on the surface of a substrate includes vapor phase growth, arc discharge, laser vaporization, plasma chemical vapor deposition (PECVD), and thermal chemical vapor deposition. (thermal CVD) method.

However, the gas phase synthesis method has a difficulty in forming a single walled nanotube, the electric discharge method has a high impurity content, and the laser deposition method has a problem in that mass synthesis is difficult. In addition, thermal chemical vapor deposition has a problem that the process proceeds at a high temperature of about 650 degrees or more.

In contrast, the PECVD method can grow CNTs on the surface of a solar cell substrate as in the present invention because it can grow CNTs in a direction perpendicular to the surface of the substrate in a relatively low temperature environment, and in particular, can grow CNTs in a large area. In order to make it, it is preferable to apply PECVD method.

Hereinafter, a process of growing CNTs on the substrate 10 will be described with reference to the process flowchart of FIG. 4 and the process cross-sectional views of FIGS. 5A to 5H.

For convenience, as shown in FIG. 5A, a crystalline silicon substrate 100 doped with a p-type is prepared. (ST21)

Subsequently, a PN junction surface should be formed inside the substrate 100. In this embodiment, ion doping is performed using plasma.

Plasma ion doping is very advantageous in terms of productivity because the doping concentration or PN junction depth can be controlled relatively accurately, and PSG or BSG is not generated and there is no need to proceed with the removal process and there is no need to proceed with the isolation process. However, the present invention does not exclude the method of forming the PN junction surface by applying the high temperature diffusion method as in the prior art.

In detail, first, as shown in FIG. 5B, the p ++ doped layer 110 is formed on the rear surface of the substrate 100 to form a backside electric field. To this end, a p-type dopant containing a boron (B) component, such as B ₂ H ₆ , is supplied in a state where the p-type substrate 100 is placed inside the plasma generator.

Hereinafter, for convenience of description, the remaining part in which the p ++ doped layer 110 is formed in the p-type substrate 100 will be referred to as a p + layer 100 '.

The back electric field formed between the p + layer 100 ′ and the p ++ doped layer 110 of the substrate 100 does not dissipate electrons excited by sunlight in the substrate 100 by moving to the back electrode, By moving toward the front electrode to contribute to the photocurrent plays a role of increasing the efficiency of the solar cell.

As such, when the backside electric field is formed using the p ++ doped layer 110, the thickness of the solar cell can be reduced as compared with the case of forming the backside electric field by applying Al paste as in the prior art. It can prevent.

Subsequently, the substrate 100 is inverted to form an n + layer 120 on the front surface of the substrate 100 as shown in FIG. 5C. Also in this case, the n + layer 120 is formed by using the plasma ion doping method, and for example, a material containing phosphorus (P) is used as the N-type dopant.

As described above, after plasma ion doping is performed on the back and front surfaces of the substrate 100, it is preferable to go through an activation process of heating the substrate 100 to an appropriate temperature as shown in FIG. 5D.

The activation process is a process of activating the doped ions by supplying additional energy to the substrate 100 so that the doped ions can be combined with Si. Without this activation process, doped ions will act as simple impurities.

On the other hand, in order to form a PN junction surface inside the substrate 100, it is also possible to apply a high temperature diffusion method as in the prior art. In this case, the n + doped layer 120 should be formed on both sides of the p-type substrate 100, and then an Al paste or the like should be applied to the backside of the substrate in the electrode formation step to form a backside electric field. (ST22)

After the p ++ doping layer 110 and the n + layer 120 are formed on the back and front surfaces of the substrate 100, respectively, Fe, Ni, Co, or the like may be formed on top of the n + layer 120 as shown in FIG. 5E. A catalyst metal layer 130 made of an alloy is deposited by sputtering. (ST23)

The catalyst metal layer 130 serves as a seed of CNT formation, and must be converted into a metal particle through a predetermined treatment procedure. To this end, the catalyst metal layer 130 may be heat treated at a high temperature, or may be etched using an etching gas of NH ₃ or H ₂ , as shown in FIG. 5F, or both methods may be used.

When the catalyst metal layer 130 is etched by using an etching gas, nano-sized fine catalyst metal particles may be formed, and thus, CNTs may be grown to a uniform density. (ST24)

After the particles of the catalyst metal are formed as described above, CNTs are grown using particles of the catalyst metal as seeds using the PECVD apparatus 30 as shown in FIG. 6.

The PECVD apparatus 30 includes a chamber 31 forming a reaction space, a substrate support 32 positioned inside the chamber 31, and a plasma electrode coupled to seal the upper portion of the substrate support 32. (33), through the gas distribution plate 34 which is fixed to the lower portion of the plasma electrode 33 spaced apart by a predetermined interval, the high frequency power source 36 for applying high frequency power to the plasma electrode 33, the plasma electrode 33 It includes a gas supply pipe 35 for supplying the raw material to the upper portion of the gas distribution plate 34, the exhaust port 37 formed in the lower portion of the chamber 31.

In the PECVD apparatus 30, the carbon-containing gas is supplied through the gas distribution plate 34 and the plasma electrode is placed on the substrate support 32 after the etching of the catalyst metal layer 130 is placed. When high frequency power is applied to (33), plasma is generated while electrons accelerated by a high frequency electric field formed between the grounded substrate stabilizer 32 and the plasma electrode 33 collide with the neutral gas to cause glow discharge. do.

In this process, the dissociated carbon atoms are bonded to the catalyst metal particles to grow into CNTs, thereby forming the CNT layer 140 as shown in FIG. 5G on the substrate 100.

At this time, the carbon-containing gas may be at least one gas of C ₂ H ₂ , CH ₄ , C ₂ H ₄ , C ₂ H ₆ , CO.

The height of the CNT layer 140 may vary depending on the application, and in the case of reducing the surface reflectivity as in the present invention, the height of the CNT layer 140 may be about 500 nm or less.

On the other hand, since the single-wall CNT has a diameter of about 1 nm and an aspect ratio of 10 or more, the height of the grown CNT is at least 10 nm. (ST25, ST26)

After the CNT layer 140 is formed on the surface of the crystalline silicon substrate 10, the front electrode 160 and the rear electrode 150 are formed as shown in FIG. 5H.

The front electrode 160 is formed by applying an electrode paste containing Al or Ag on the CNT layer 140 in a lattice form or a predetermined pattern and then sintering it.

An anti-reflection film may be formed on the CNT layer 140, but the anti-reflection film may be omitted in view of the fact that the surface reflectivity of the CNT layer 140 is significantly low.

Since the rear field is already formed by the p ++ layer 110 on the rear surface of the substrate 100, there is no need to separately perform the rear field formation process, and after applying the electrode paste on the rear surface of the substrate in a predetermined pattern, the back surface is sintered. The electrode 150 may be formed. (ST27)

Subsequently, one solar cell module is completed by performing modularization through efficiency testing and classification.

FIG. 1 is a flow chart showing a manufacturing process of a conventional crystalline silicon solar cell.

FIGS. 2A to 2F are cross-sectional views showing a manufacturing process of a conventional crystalline silicon solar cell

3A and 3B are SEM photographs and reflectance graphs of CNT layers formed on silicon substrates, respectively.

4 is a flowchart illustrating a process of forming a CNT on a substrate according to an embodiment of the present invention.

5A to 5H are cross-sectional views of forming a CNT on a substrate.

6 is a schematic configuration diagram of a PECVD apparatus for forming a CNT

Description of the Related Art [0002]

100: substrate 110: p + + layer

120: n + layer 130: catalyst metal layer

140: CNT layer

Claims (9)

A first step of preparing a crystalline silicon substrate of a first conductivity type; Forming a PN junction surface on the substrate; Forming a carbon nanotube (CNT) layer on the front surface of the substrate to increase light absorption; And a fourth step of forming a front electrode and a back electrode on the front and rear surfaces of the substrate, respectively. The third step includes forming a catalyst metal layer on the substrate, converting the catalyst metal layer into metal particles, and growing CNTs on particles of the catalyst metal produced in the conversion step, The step of converting the catalyst metal layer into a metal particle, the method of manufacturing a crystalline silicon solar cell, characterized in that including the process of etching the catalyst metal layer using a high temperature heat treatment or an etching gas. delete The method of claim 1, The catalyst metal is any one of Fe, Ni, Co, or a method of producing a crystalline silicon solar cell, characterized in that the alloy consisting of two or more of the metals of Fe, Ni, Co. delete The method of claim 1, The etching gas is a method of manufacturing a crystalline silicon solar cell, characterized in that NH ₃ or H ₂ . The method of claim 1, The CNT is a crystalline silicon solar cell, characterized in that grown by plasma chemical vapor deposition (PECVD) method using at least one of the raw material of C ₂ H ₂ , CH ₄ , C ₂ H ₄ , C ₂ H ₆ , CO Manufacturing Method The method of claim 1, The CNT layer is a manufacturing method of the crystalline silicon solar cell, characterized in that formed in a height of 10 ~ 500nm. The method of claim 1, In the second step, the first conductive doping layer having a greater doping concentration than the substrate is formed on the rear surface of the substrate, the crystalline silicon, characterized in that to form a second conductive doping layer on the front surface of the substrate Manufacturing method of solar cell delete

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