KR100649743B1 - Solar cells comprising cnt and its manufacturing method - Google Patents

Abstract

A solar cell including a CNT(carbon nanotube) is provided to form a solar cell including CNT with excellent conversion efficiency by using a conductive NWNT(multi-wall carbon nanotube) as an electrode of a solar cell. A back plate(12) is formed on a substrate(11). The substrate can be a flexible substrate of one of Cu foil, Al foil, stainless steel or polymer. A conductive CNT arrangement body(13) is formed on the back plate. A p-type semiconductor layer(15) is formed between the respective CNT of the arrangement body and on the arrangement body, including Ib-IIIb-VIb group elements. An n-type semiconductor layer(16) is formed on the semiconductor layer, including IIb-Via group elements. A ZnO window layer(17) is formed on the n-type semiconductor layer.

Description

Solar cell comprising CNT and its manufacturing method {Solar cells comprising CNT and its manufacturing method}

1 is a side cross-sectional view showing a conventional solar cell structure.

2 is a side cross-sectional view of a solar cell including a CNT according to an embodiment of the present invention.

Figure 3 (a) is a schematic side view showing that light is irradiated to the solar cell according to the present invention.

FIG. 3 (b) is a FESEM photograph of MWNT at the p-n junction portion A constituting the solar cell of FIG. 3 (a).

FIG. 3 (c) is a diagram showing the principle of improvement of the collection factor in the p-n junction portion A constituting the solar cell of FIG. 3 (a).

4 is a manufacturing process chart of a CNT solar cell according to one embodiment of the present invention.

The present invention relates to a solar cell comprising a CNT and a method for manufacturing the same, and more particularly, to a solar cell having excellent conversion efficiency by using carbon nanotubes (CNT) as an electrode and a method for manufacturing the same.

Solar cells are recognized as important energy sources of the future as devices that convert the light energy of the sun into electrical energy using the characteristics of semiconductor pn junctions. Among them, ground solar cells are thin-film solar cells, which include CuInSe ₂ solar cells, amorphous Si solar cells, and CdTe solar cells. Among these, CuInSe ₂ solar cells are evaluated to be superior to amorphous Si solar cells in terms of conversion efficiency and battery stability. Group I-III-VI compound semiconductors represented by CuInSe ₂ have a direct transition energy bandgap, and have a light absorption coefficient of 1 × 10 ⁵ cm ⁻¹ , which is the highest among semiconductors, even in a thin film having a thickness of 1 to 2 μm. It is possible to manufacture high efficiency solar cell and has very good electro-optic stability in the long term. Therefore, it is emerging as a low-cost, high-efficiency solar cell material that can significantly improve the economics of photovoltaic power generation by replacing expensive crystalline silicon solar cells currently used.

The development of CIS-based solar cells is progressing toward improving the efficiency by adding Ga or S to the CIS cell.

In detail, although a borosulicate glass or a polished ceramic substrate was used as the substrate of the initial CIS solar cell, recently, a new substrate, soda-lime glass, has been used to reduce manufacturing costs. When soda-lime glass is used, the efficiency can be improved because the Na component of the substrate improves the crystallinity of the thin film and the conductivity of the thin film affects the efficiency of the device. In addition, CdS has been used as a front transparent electrode (window layer) for efficient absorption of sunlight until recently, but recently, ZnO has been used for environmental reasons. Furthermore, a process for manufacturing a flexible thin film solar cell using a substrate material such as polyimide or the like is disclosed in JP2003-179238A.

1 illustrates a conventional CuInSe ₂ using such a CIS-based material as a light absorption layer. Side cross-sectional view of a thin film solar cell. As shown in FIG. 1, a conventional solar cell 10 is largely formed on a glass substrate 1 with a back electrode 3, a light absorbing layer 5, a buffer layer 6, a front transparent electrode 7 and an antireflection layer. (9) has a structure which is formed by sequentially stacking. Compositions of the materials forming the unit membranes are varied, and the manufacturing process may use various physical chemical thin film manufacturing processes. For example, the back electrode 3 may be formed by depositing Mo using sputtering or e-beam evaporation. The light absorption layer 5 and the buffer layer 6 may be formed of Cu (In, Ga) using a CBD method. (Se, S) ₂ and CdS may be formed by vapor deposition, respectively. In addition, the front transparent electrode 7 may be formed of ZnO by sputtering or CVD.

On the other hand, the CIS-based solar cell provided as described above is a semiconductor device that converts solar energy into electrical energy has a junction type of the p-type semiconductor and the n-type semiconductor, the basic structure is the same as the diode. That is, when light is incident on the solar cell from outside, the conduction band electrons of the p-type semiconductor are excited to the valence band by the incident light energy. The excited electrons generate one electron-hole pair (EHP) inside the p-type semiconductor. The electrons of the generated low-hole pairs are transferred to the n-type semiconductor by an electric field existing between the p-n junctions to supply current to the outside.

However, the p-type semiconductor used as an absorbing layer in the CIS-based solar cell has a problem of recombination of excited electrons and holes due to problems of polycrystalline material properties and bonding problems with other interfaces due to thinning. Accordingly, the CIS solar cell has been in a state of stagnation for many years, and a new solution for this situation is desired in the art.

Therefore, the present invention has been made to solve the problems of the prior art, by using a conductive MWNT (Multi-wall Carbon nanotube) as the electrode of the solar cell to provide a solar cell comprising a CNT excellent conversion efficiency compared to the prior art. For that purpose.

In addition, an object of the present invention is to provide a solar cell manufacturing method comprising a CNT having excellent change efficiency.

The present invention for achieving the above object,

A back electrode formed on the substrate;

A conductive carbon nanotube (CNT) array formed on the back electrode;

A p-type semiconductor layer comprising an Ib-IIIa-VIa element formed between and over each of the carbon nanotubes constituting the array;

An n-type semiconductor layer including an IIb-VIa group element formed on the semiconductor layer; And

ZnO window layer formed on the n-type semiconductor layer; relates to a solar cell comprising a CNT having excellent conversion efficiency.

In addition, the present invention,

Forming a back electrode on the substrate;

Forming a carbon nanotube array on the formed back electrode;

Forming a p-type semiconductor layer comprising a group Ib-IIIa-VIa element between the individual carbon nanotubes constituting the array and on top of the array;

Forming an n-type semiconductor layer comprising an IIb-VIa group element on the semiconductor layer; And

Forming a ZnO window layer on the n-type semiconductor layer; and a solar cell manufacturing method including CNTs having excellent conversion efficiency.

In addition, the present invention,

Forming a plurality of transition metal layers having a length of 3-10 nm on the back electrode of the substrate;

Forming carbon nanotubes having a predetermined length on the formed transition metal layer using a PECVD process;

Forming a p-type semiconductor layer including an Ib-IIIa-VIa group element around the formed carbon nanotubes;

Forming an n-type semiconductor layer comprising an IIb-VIa group element on the semiconductor layer; And

Forming a ZnO window layer on the n-type semiconductor layer; and a solar cell manufacturing method including CNTs having excellent conversion efficiency.

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

2 is a side cross-sectional view of a CNT solar cell according to an embodiment of the present invention.

As shown in FIG. 2, the solar cell 20 of the present invention has a back electrode 12, a conductive carbon nanotube array 13, and a group Ib-IIIb-VIb on a substrate 11. P-type semiconductor layer 15 including an element, n-type semiconductor layer 16 including an IIb-VIa group element, and ZnO window layer 17 may be sequentially stacked, and the ZnO The antireflection layer 18 and the front electrode 19 may be further included on the window layer 17.

In the present invention, it is preferable to use a flexible substrate having excellent workability as the substrate 11. Examples of such flexible substrates include polymers such as Cu foil, Al foil, stainless steel, and polyimide, and it is more desirable to use one of these as the substrate material.

The back electrode 12 is preferably formed of Mo, and more preferably is formed to a thickness of 1 ~ 2㎛ by sputtering method.

Furthermore, it is preferable to control the length of each nanotube constituting the conductive carbon nanotube array 13 to 1-3 μm.

The solar cell 20 of the present invention includes p-containing elements of Group Ib-IIIa-VIa formed between and on top of individual carbon tubes constituting the carbon nanotube array 13. -Type semiconductor layer (light absorption layer: 15). The semiconductor layer is preferably a CIS-based semiconductor layer formed of any one selected from CuInSe ₂ and Cu (In, Ga) Se ₂ . More preferably, the thickness of the p-type semiconductor layer is limited to about 3 μm.

The semiconductor layer 16 containing the IIb-VIa group element constitutes a pn junction with the p-type semiconductor layer 15 as an n-type semiconductor layer. The n-type semiconductor layer 16 is preferably a CdS semiconductor layer. More preferably, the thickness of the n-type semiconductor layer 16 is limited to 40 to 150 nm.

The solar cell 20 also includes a ZnO window layer 17 formed on the n-type semiconductor layer 16. The ZnO layer guides the light incident on the solar cell to the absorbing layer 15 and suppresses the reflection of the light.

Preferably, the thickness of the ZnO window layer 17 is limited to 50 to 100 nm.

Furthermore, in the present invention, an antireflection layer made of MgF ₂ may be selectively formed on the window layer 17. In addition, as will be apparent to those skilled in the art, the front electrode 19 made of Ni or Al may be formed on the window layer 17 or the antireflection layer 18.

On the other hand, Figure 3 (a) is a schematic side view showing that the light is irradiated to the solar cell according to the present invention. 3 (b) is a FESEM photograph of a multi-wall carbon nanotube (MWNT) at the pn junction portion (A) constituting the solar cell of FIG. 3 (a), and FIG. The figure shows the principle of improvement of the collection factor at the pn junction (A) constituting the solar cell.

As shown in FIG. 3A, when light is irradiated to the cell, photon energy passes through the ZnO window layer 17, and then passes through the CdS n-type semiconductor layer 16 to surface the p-type semiconductor layer 15. Is absorbed in. As such, when light energy is absorbed, electrons are excited by the pn junction principle, which affects the electromotive force. However, in the present invention, as shown in Figure 3 (a), (b), a vertically grown carbon nanotube array 13 is used as an electrode, the nanotube electrode is the absorption region as shown in Figure 3 (c) Will be nearby. Therefore, since the excited electrons can flow directly through the carbon nanotube electrode without recombination of the electron holes generated in the conventional CIS solar cell, the conversion efficiency can be maximized. In addition, as shown in FIG. 3 (c), since the surface area of the junction in the semiconductor can be maximized, the number of minority carriers directly affecting the conversion efficiency can be increased to further improve the collection factor.

Next, the CNT solar cell manufacturing process of this invention is demonstrated.

4 is a manufacturing process chart of a CNT solar cell according to one embodiment of the present invention.

As shown in FIG. 4A, first, the back electrode 42 is formed on the substrate 41. It is desirable that the substrate be a flexible substrate in consideration of the workability of the manufactured solar cell. Preferably, the substrate 41 is formed of one selected from Cu foil, Al foil, stainless steel, and a polymer material.

The back electrode 42 may be formed by sputtering Mo on the substrate 41. More preferably, the thickness of the back electrode 42 is limited to 1 to 2 μm.

Subsequently, in the present invention, the carbon nanotube array 43 is formed on the formed rear electrode 42.

Specifically, in the present invention, as shown in Figure 4 (b), the transition metal is formed on the back electrode 42 by deposition. Deposition of such transition metal may be performed using a conventional E-beam evaporator.

In the present invention, it is preferable to use one selected from Fe or Ni as the transition metal. More preferably, the length of the formed transition metal layer 43a is limited to 3 to 10 nm.

In the present invention, as shown in Figure 4 (c), by using a normal PECVD process to impose a field on the formed transition metal layer (43a) using the reaction gases ammonia (NH ₃ ) and acetylene (C ₂ H ₂ ) By decomposition, the carbon nanotube array 43 is formed. At this time, in the present invention, it is preferable to limit the length of the nanotubes constituting the array 43 to 1 ~ 2㎛.

In the present invention, as shown in Fig. 4 (d), the light absorbing layer of the solar cell using a material containing a group Ib-IIIa-VIa element between the individual carbon tubes constituting the array and on the upper portion The p-type semiconductor layer 45 is formed. That is, the semiconductor layer 45 may be formed by depositing the material around the formed carbon nanotubes using the Co-evaporator method. In the present invention, the semiconductor layer 45 is preferably a CIS-based semiconductor layer formed of any one selected from CuInSe ₂ and Cu (In, Ga) Se ₂ .

More preferably, the thickness of the p-type semiconductor layer 45 is limited to about 3 μm.

Next, as shown in FIG. 4E, the n-type semiconductor layer 46 is formed on the formed p-type semiconductor layer 45 by using a material containing a IIb-VIa group element. The type semiconductor layer 46 may preferably be provided using a chemical bath deposition (CBD) method.

It is also preferable that the n-type semiconductor layer 46 is a CdS semiconductor layer. More preferably, the thickness of the n-type semiconductor layer is limited to 40 to 150 nm.

Subsequently, in the present invention, as shown in FIG. 4 (f), the ZnO window layer 47 is formed on the n-type semiconductor layer 46 by using a conventional sputtering method or the like. Preferably, the thickness of the ZnO window layer 47 is limited to 50 to 100 nm.

Subsequently, in the present invention, as shown in FIG. 4 (g), an anti-reflection layer 48 made of MgF ₂ may be formed on the window layer 47 by using an E-beam evapotator method.

The solar cell including the carbon nanotube array 43 may be formed by depositing and forming a front electrode 49 made of Ni or Al on the anti-reflection layer 48 using a conventional E-beam evaporator method. It is.

As described above, the present invention can realize a solar cell having excellent conversion efficiency by using a vertically grown conductive carbon nanotube array as an electrode of a CIS solar cell.

As described above, the present invention has been described with reference to a preferred embodiment, but the present invention is not limited to the above description. That is, various imitations or improvements are possible within the scope of the appended claims, and all of them belong to the technical scope of the present application.

As described above, the present invention has a useful effect of effectively converting light energy absorbed in the absorber layer into electrical energy by maximizing the p-n juncton surface area by using conductive carbon nanotubes as electrodes of CIS solar cells.

Claims (25)

A back electrode formed on the substrate; A conductive carbon nanotube (CNT) array formed on the back electrode; A p-type semiconductor layer comprising an Ib-IIIb-VIb group element formed between and on the individual carbon nanotubes constituting the array; An n-type semiconductor layer including an IIb-VIa group element formed on the semiconductor layer; And ZnO window layer formed on the n- type semiconductor layer; including a CNT having excellent conversion efficiency. The solar cell of claim 1, wherein the substrate is a flexible substrate selected from Cu foil, Al foil, stainless steel, and a polymer. The solar cell of claim 1, wherein the back electrode is made of Mo and has a thickness of 1 to 2 µm. The solar cell of claim 1, wherein the carbon nanotubes constituting the conductive carbon nanotube array have a length of 1-3 μm. The p-type semiconductor layer of claim 1, wherein the p-type semiconductor layer including the Group Ib-IIIa-VIa element is a CIS-based semiconductor layer formed of any one selected from CuInSe ₂ and Cu (In, Ga) Se ₂ . Solar cell comprising a CNT. The solar cell of claim 1, wherein the n-type semiconductor layer including the IIb-VIa element is a CdS semiconductor layer. The solar cell of claim 1, wherein the n-type semiconductor layer has a thickness of 40 to 150 nm. The solar cell of claim 1, wherein the ZnO window layer has a thickness of 50 nm to 100 nm. The solar cell of claim 1, wherein an antireflection layer made of MgF ₂ is formed on the window layer. Forming a back electrode on the substrate; Forming a carbon nanotube array on the formed back electrode; Forming a p-type semiconductor layer comprising an Ib-IIIb-VIb group element between individual carbon nanotubes constituting the array and on top of the array; Forming an n-type semiconductor layer comprising an IIb-VIa group element on the semiconductor layer; And Forming a ZnO window layer on the n-type semiconductor layer; solar cell manufacturing method comprising a CNT having excellent conversion efficiency. The method of claim 10, wherein the substrate is a CNT, Al foil, stainless steel, or a solar cell manufacturing method including a CNT, wherein the flexible substrate is one selected from a polymer. The method of claim 10, wherein the back electrode is formed by sputtering Mo. The method of claim 10, wherein the length of the carbon nanotubes constituting the conductive carbon nanotube array is 1-3 μm. The CNT-based semiconductor layer according to claim 10, wherein the semiconductor layer including the Ib-IIIa-VIa element is a CIS-based semiconductor layer formed of any one selected from CuInSe ₂ and Cu (In, Ga) Se ₂ . Solar cell manufacturing method comprising. The method of claim 10, wherein the semiconductor layer including the IIb-VIa element is a CdS semiconductor layer. The method of claim 10, wherein the n-type semiconductor layer has a thickness of 40 to 150 nm and is formed by a CBD method. The solar cell of claim 10, wherein the ZnO window layer has a thickness of 50 nm to 100 nm. The method of claim 10, wherein the antireflection layer of MgF ₂ is further formed on the window layer. Forming a plurality of transition metal layers having a length of 3-10 nm on the back electrode of the substrate; Forming carbon nanotubes having a predetermined length on the formed transition metal layer using a PECVD process; Forming a p-type semiconductor layer including an Ib-IIIa-VIa group element around the formed carbon nanotubes; Forming an n-type semiconductor layer comprising an IIb-VIa group element on the semiconductor layer; And Forming a ZnO window layer on the n-type semiconductor layer; solar cell manufacturing method comprising a CNT having excellent conversion efficiency. 20. The method of claim 19, wherein the substrate is a flexible substrate selected from Cu foil, Al foil, stainless steel, and a polymer. The method of claim 19, wherein the transition metal layer is formed by sputtering at least one transition metal selected from Fe and Ni. The method of claim 19, wherein the length of the carbon nanotubes constituting the conductive carbon nanotube array is 1-3 μm. 20. The CNT according to claim 19, wherein the semiconductor layer including the Ib-IIIa-VIa element is a CIS-based semiconductor layer formed of any one selected from CuInSe ₂ and Cu (In, Ga) Se ₂ . Solar cell manufacturing method comprising. 20. The method of claim 19, wherein the semiconductor layer including the IIb-VIa group element is a CdS semiconductor layer. 20. The method of claim 19, wherein the antireflection layer of MgF ₂ is further formed on the window layer.

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