TWI409961B - Solar cell - Google Patents

Abstract

The present invention relates to a solar cell. The solar cell includes a back electrode, a single crystal silicon substrate and a carbon nanotube structure. The back electrode is disposed on a lower surface of the single crystal silicon substrate, and electrically connected thereto. The carbon nanotube structure is disposed on an upper surface of the single crystal silicon substrate, and electrically connected to the upper surface of the single crystal silicon substrate. The carbon nanotube structure includes a number of carbon nanotubes oriented in a certain direction.

Description

Solar battery

The invention relates to a solar cell, in particular to a solar cell based on a carbon nanotube film.

Solar energy is one of the cleanest energy sources in today, and it is inexhaustible. Solar energy utilization includes light energy-thermal energy conversion, light energy-electric energy conversion, and light energy-chemical energy conversion. A typical example of solar cell-based light energy-electric energy conversion is made using the photovoltaic principle of semiconductor materials. At present, solar cells are mainly based on germanium-based solar cells. In a ruthenium-based solar cell, single crystal germanium is used as a material for photoelectric conversion. Therefore, in order to obtain a high conversion efficiency of a germanium solar cell, it is necessary to prepare a high purity single crystal germanium. However, the current preparation process of single crystal germanium is far from meeting the needs of the development of solar cells, and the production of single crystal germanium requires a large amount of electrical energy, which not only increases the cost of germanium solar cells, but also causes great pollution to the environment. Therefore, the development of other types of solar cells is of strategic importance.

Since the first discovery of carbon nanotubes by Japanese scientist Iijima in 1991 (see Helical microtubules of graphitic carbon, Nature, Sumio Iijima, vol 354, p56 (1991)), nanomaterials represented by carbon nanotubes are unique. The structure and nature have aroused great concern. The study found that the carbon nanotubes have high electrical conductivity, and the carbon nanotubes have a high ability to absorb sunlight, and their absorption in the visible and infrared regions is as high as 99%. Therefore, the application of carbon nanotubes in the field of solar cells will have The unparalleled advantages of the materials.

Referring to FIG. 1, the prior art carbon nanotube-based solar cell 30 includes a back electrode 32, a single crystal germanium substrate 34, and a carbon nanotube film 36. The back electrode 32 is disposed on the lower surface 342 of the single crystal germanium substrate 34. The carbon nanotube film 36 is disposed on the upper surface 341 of the single crystal germanium substrate 34. The carbon nanotube film 36 functions as a photoelectric conversion material and serves as an upper electrode. The carbon nanotube film 36 has a thickness of 50 nm to 200 nm, wherein the carbon nanotubes are disorderly distributed. The method for preparing the solar cell 30 specifically includes the steps of: providing a single crystal germanium substrate 34; depositing a metal film on the one surface of the single crystal germanium substrate 34 as the back electrode 32, and drawing it with a wire; a carbon nanotube film 36; the carbon nanotube film 36 is laid on the other side surface of the single crystal germanium substrate 34, and the carbon nanotube film 36 is brought into close contact with the single crystal germanium substrate 34, and used The wire is led out. The preparation method of the carbon nanotube film 36 specifically includes the following steps: first, oxidizing the carbon nanotubes in the air; secondly, immersing the oxidized carbon nanotubes in the hydrogen peroxide water; again, after adding the strong acid, rinsing The carbon nanotube to the rinsing liquid is neutral; again, alcohol or acetone is added dropwise to the aqueous solution of the carbon nanotubes to float the carbon nanotubes out of the water surface to form a carbon nanotube film 36. However, the solar cell in the prior art has the following disadvantages: the carbon nanotubes in the carbon nanotube film 36 are disorderly distributed and have a large resistance value, so that the conductivity of the carbon nanotube film 36 is poor, so that The solar cell produced has low photoelectric conversion efficiency. In addition, the preparation method of the carbon nanotube film 36 is complicated and is not suitable for mass production.

In view of this, it is necessary to provide a solar cell having high photoelectric conversion efficiency, uniform resistance distribution, good light transmittance, and simple preparation method. .

A solar cell includes a back electrode, a single crystal germanium substrate, and a carbon nanotube structure. The back electrode is disposed on a lower surface of the single crystal germanium substrate and is in ohmic contact with a lower surface of the single crystal germanium substrate. The carbon nanotube structure is disposed on an upper surface of the single crystal germanium substrate and is in contact with an upper surface of the single crystal germanium substrate. The carbon nanotube structure includes a plurality of ordered carbon nanotubes.

Compared with the prior art, the carbon nanotubes in the solar cell structure of the solar cell are arranged in an orderly manner, have a relatively uniform structure, and have good electrical conductivity. Therefore, using a carbon nanotube structure as an upper electrode can make solar energy. The battery has a uniform electrical resistance, so that the solar cell has a high photoelectric conversion efficiency.

The solar cell of the present technical solution will be described in detail below with reference to the accompanying drawings.

Referring to FIG. 2 and FIG. 4 , the embodiment of the present invention provides a solar cell 10 including a back electrode 12 , a single crystal germanium substrate 14 , and a carbon nanotube structure 16 . The back electrode 12 is disposed on the lower surface 141 of the single crystal germanium substrate 14 and is in ohmic contact with the lower surface 141 of the single crystal germanium substrate 14. The carbon nanotube structure 16 is disposed on the upper surface 142 of the single crystal germanium substrate 14 and is in contact with the upper surface 142 of the single crystal germanium substrate 14.

The solar cell 10 further includes at least one electrode 18, the material of which is a conductive material such as silver, gold or carbon nanotubes. The shape and thickness of the electrode 18 are not limited and may be disposed on the carbon nanotube structure 16 Surface 161 or lower surface 162 is in electrical contact with upper surface 161 or lower surface 162 of carbon nanotube structure 16. The arrangement of the electrodes 18 can be used to collect current flowing through the carbon nanotube structure 16 and to connect to an external circuit.

The solar cell 10 further includes at least one passivation layer 20, and the material of the passivation layer 20 is ruthenium dioxide or ruthenium tetranitride or the like. The shape and thickness of the passivation layer 20 are not limited, and may be disposed between the upper surface 142 of the single crystal germanium substrate 14 and the lower surface 162 of the carbon nanotube structure 16 to reduce electrons and holes. The recombination speed of the contact surface of the single crystal germanium substrate 14 and the carbon nanotube structure 16 is further increased, thereby further improving the photoelectric conversion efficiency of the solar cell 10.

The material of the back electrode 12 may be a metal such as aluminum, magnesium or silver. The back electrode 12 has a thickness of 10 micrometers to 300 micrometers. The shape and thickness of the back electrode 12 are not limited.

The single crystal germanium substrate 14 is a p-type single crystal germanium sheet or an n-type single crystal germanium sheet. The single crystal germanium substrate 14 has a thickness of 200 μm to 300 μm. The single crystal germanium substrate 14 forms a heterojunction structure with the carbon nanotube structure 16, thereby effecting conversion of light energy to electrical energy in the solar cell 10.

The carbon nanotube structure 16 is a layered structure comprising a plurality of ordered carbon nanotubes. The carbon nanotubes in the carbon nanotube structure 16 are evenly distributed and parallel to the surface of the carbon nanotube structure 16 so that the solar cell 10 has a uniform electrical resistance. The plurality of carbon nanotubes are arranged in a preferred orientation along a fixed direction to provide the solar cell 10 with good electrical conductivity and high photoelectric conversion efficiency.

The carbon nanotubes in the carbon nanotube structure 16 are single-walled carbon nanotubes, double-walled carbon nanotubes or multi-walled carbon nanotubes. Among them, multi-walled carbon nanotubes are metal-based, single-walled carbon nanotubes are classified into semiconductors and metals according to their chirality and diameter, and the properties of double-walled carbon nanotubes are metallic. When the carbon nanotubes in the carbon nanotube structure 16 are single-walled carbon nanotubes, the single-walled carbon nanotubes have a diameter of 0.5 nm to 50 nm. When the carbon nanotubes in the carbon nanotube structure 16 are double-walled carbon nanotubes, the double-walled carbon nanotubes have a diameter of 1.0 nm to 50 nm. When the carbon nanotubes in the carbon nanotube structure 16 are multi-walled carbon nanotubes, the diameter of the multi-walled carbon nanotubes is from 1.5 nm to 50 nm. Since the carbon nanotubes in the carbon nanotube structure 16 are very pure, and because the specific surface area of the carbon nanotubes themselves is very large, the carbon nanotube structure 16 itself has a strong viscosity. The carbon nanotube structure 16 can be directly fixed to the surface of the single crystal germanium substrate 14 by its own viscosity.

Specifically, the carbon nanotube structure 16 includes an ordered carbon nanotube film 163. Referring to FIG. 3, the ordered carbon nanotube film 163 can be obtained by directly stretching a carbon nanotube array. The ordered carbon nanotube film 163 includes carbon nanotubes oriented in the direction of stretching. Specifically, the ordered carbon nanotube film 163 includes a plurality of carbon nanotube bundles 164 that are connected end to end and of equal length. Both ends of the carbon nanotube bundle 164 are connected to each other by a van der Waals force. Each of the carbon nanotube bundles 164 includes a plurality of carbon nanotubes 165 of equal length and arranged in parallel. The adjacent carbon nanotubes 165 are tightly bonded by van der Waals force. The ordered carbon nanotube film 163 is further processed by a carbon nanotube array, so its length is related to the width and the size of the substrate on which the carbon nanotube array is grown. Can be based on actual demand Got it. In this example, a super-sequential carbon nanotube array was grown on a 4 inch substrate using vapor deposition. The ordered carbon nanotube film 163 may have a width of 0.01 cm to 10 cm and a thickness of 10 nm to 100 μm. In the ordered carbon nanotube film 163, a plurality of carbon nanotubes are uniformly distributed and parallel to the surface of the carbon nanotube structure 16. The plurality of carbon nanotubes are arranged in a preferred orientation along the stretching direction.

It will be understood that the carbon nanotube structure 16 may further comprise at least two of the above-described ordered carbon nanotube films 163 arranged in an overlapping manner. Specifically, the carbon nanotubes in the adjacent two ordered carbon nanotube films 163 have a cross angle α and 0 degrees ≦α ≦ 90 degrees, which can be prepared according to actual needs. It can be understood that, since the plurality of ordered carbon nanotube films 163 in the carbon nanotube structure 16 can be overlapped, the thickness of the above-mentioned carbon nanotube structure 16 is not limited, and can be made to have any thickness according to actual needs. Nano carbon tube structure 16. In the carbon nanotube structure 16, a plurality of carbon nanotubes are evenly distributed and parallel to the surface of the carbon nanotube structure 16. The plurality of carbon nanotubes are arranged in a preferred orientation along the stretching direction.

When the solar cell 10 is applied, sunlight is irradiated to the carbon nanotube structure 16, and incident photons are absorbed by the carbon nanotube structure 16, after the single crystal germanium substrate 14 and the carbon nanotube A large number of excitons, i.e., pairs of electrons and holes, are generated on the contact surface of structure 16. These excitons will be separated into two free carriers, wherein free hole carriers are transported through the single crystal germanium substrate 14 to the back electrode 12 and collected by the back electrode 12. The transport of free electron carriers through the carbon nanotube structure is transmitted and collected by the carbon nanotube structure 16 which is also used as the upper electrode. Further, the current collected by the carbon nanotube structure 16 is collected again by the at least one electrode 18. . The arrangement of the at least one passivation layer 20 can reduce the recombination speed of electrons and holes in the contact faces of the single crystal germanium substrate 14 and the carbon nanotube structure 16, thereby further improving the photoelectric conversion of the solar cell 10. effectiveness. If a load is applied to both ends of the back electrode 12 and the at least one electrode 18 in the solar cell 10, current flows through the load in the external circuit.

In the carbon nanotube structure of the solar cell, the carbon nanotubes are arranged in an orderly manner, have a relatively uniform structure, and have good electrical conductivity. Therefore, using a carbon nanotube structure as an upper electrode can make the solar cell have a uniform electrical resistance. Thereby the solar cell has a high photoelectric conversion efficiency.

The method for preparing the ordered carbon nanotube film 163 comprises the following steps: First, an array of carbon nanotubes is provided on a substrate, and preferably the array is a super-sequential carbon nanotube array.

In this embodiment, the method for preparing the super-sequential carbon nanotube array adopts a chemical vapor deposition method, and the specific steps include: (a) providing a flat substrate, the substrate may be selected from a P-type or N-type germanium substrate, or selected The tantalum substrate is formed with an oxide layer. In this embodiment, a 4-inch tantalum substrate is preferably used; (b) a catalyst layer is uniformly formed on the surface of the substrate, and the catalyst layer material may be iron (Fe), cobalt (Co) or nickel ( One of the alloys of Ni) or any combination thereof; (c) annealing the substrate on which the catalyst layer is formed in air at 700 ° C to 900 ° C for about 30 minutes to 90 minutes; (d) placing the treated substrate in the reaction In the furnace, it is heated to 500 ° C ~ 740 ° C in a protective gas atmosphere, and then reacted with a carbon source gas for about 5 minutes to 30 minutes to grow a super-aligned carbon nanotube array having a height of 200 μm to 400 μm. The super-sequential carbon nanotube array is at least two parallel to each other and perpendicular to the substrate A pure carbon nanotube array formed by a carbon nanotube. The super-sequential carbon nanotube array contains substantially no impurities such as amorphous carbon or residual catalyst metal particles, etc., by controlling the growth conditions described above. The carbon nanotubes in the array of carbon nanotubes are in close contact with each other to form an array by van der Waals force. The area of the carbon nanotube array is substantially the same as the area of the substrate described above.

The above carbon source gas may be selected from acetylene, ethylene, methane and other chemically active hydrocarbons. The preferred carbon source gas in this embodiment is acetylene; the shielding gas is nitrogen or an inert gas, and the preferred shielding gas in this embodiment is argon. .

It can be understood that the carbon nanotube array provided in this embodiment is not limited to the above preparation method, and may be a graphite electrode constant current arc discharge deposition method, a laser evaporation deposition method or the like.

Next, the above carbon nanotube array is pulled by a stretching tool to obtain a carbon nanotube film 163.

In this embodiment, the method for drawing the carbon nanotube array by using a stretching tool to obtain a carbon nanotube film 163 comprises the following steps: (a) selecting a plurality of widths from the array of carbon nanotubes. a carbon nanotube bundle segment; (b) stretching the plurality of carbon nanotube bundle segments substantially perpendicular to the growth direction of the carbon nanotube array to obtain a continuous carbon nanotube film 163, the carbon nanotube film 163 The extending direction of the carbon nanotubes is parallel to the stretching direction of the carbon nanotube film 163.

In the above stretching process, the plurality of carbon nanotube bundle segments are gradually separated from the substrate in the stretching direction by the tensile force, and the selected plurality of carbon nanotube bundle segments are respectively associated with the other naphthalenes due to the van der Waals force. Meter The carbon tube bundle segments are continuously pulled out end to end to form a carbon nanotube film 163.

The ordered carbon nanotube film 163 is further processed by a carbon nanotube array, and its length and width can be controlled more accurately. The carbon nanotubes in the ordered carbon nanotube film 163 are connected end to end, and have the same length and uniform distribution, and there are gaps between the adjacent carbon nanotubes, so that the carbon nanotube structure is uniform. Resistance distribution and light transmission characteristics. Therefore, by using the carbon nanotube structure as the upper electrode, the photoelectric conversion efficiency of the solar cell can be correspondingly improved. Further, the preparation method of the carbon nanotube structure is simple and easy to implement, and is suitable for mass production.

It can be understood that the carbon nanotube structure 16 can also be other carbon nanotube structures. For example, a plurality of carbon nanotube long lines are laid parallel to each other on the surface of the single crystal germanium substrate 14 to form a carbon nanotube. Structure 16; or the carbon nanotube structure is a layered structure, each layer includes a plurality of long carbon nanotubes laid parallel to each other on the surface of the single crystal germanium substrate 14, and nanoparticles in two adjacent layers The long length of the carbon tube has a crossing angle β, and 0 degrees ≦β≦90 degrees; or a plurality of long carbon nanotubes are laid parallel to each other on the surface of a carbon nanotube film to form a layered structure, at least one layer structure Forming a carbon nanotube structure 16; or a composite material formed by mixing a carbon nanotube powder and a metal is applied to the surface of the single crystal germanium substrate 14, forming a carbon nanotube structure 16 or the like, and only needs to have a good Characteristics such as absorbance, conductivity, and durability are sufficient.

Please refer to Table 1, which is a list of various parameter indexes of the solar cell 10 made of the ordered carbon nanotube film 163. Wherein n-Si indicates that the single crystal germanium substrate 14 is an n-type single crystal germanium sheet, and p-Si indicates the single crystal germanium substrate 14 It is a p-type single crystal wafer. The cross-laying means that at least two layers of ordered carbon nanotube film 163 are cross-laid to form a carbon nanotube structure 16, and the angle of intersection between the carbon nanotubes in the ordered carbon nanotube film 163 is 90 degrees. . As can be seen from FIG. 5, in the present embodiment, the solar cell 10 made of the n-type single crystal crucible and the p-type single crystal crucible has a photovoltaic phenomenon, in which four ordered carbon nanotube films 163 are used. The solar cell 10 produced by cross-laying has the highest photoelectric conversion efficiency of 0.84%. The photoelectric conversion efficiency of the solar cell 10 made of an n-type single crystal crucible is higher than that of the solar cell 10 made of a p-type single crystal crucible.

In summary, the present invention has indeed met the requirements of the invention patent, and has filed a patent application according to law. However, the above description is only a preferred embodiment of the present invention, and it is not possible to limit the scope of the patent application of the present invention. Equivalent modifications or variations made by persons skilled in the art in light of the spirit of the invention are intended to be included within the scope of the following claims.

10,30‧‧‧ solar cells

12,32‧‧‧Back electrode

14,34‧‧‧ Single crystal germanium substrate

141,342‧‧‧ The lower surface of the single crystal substrate

142,341‧‧‧ The upper surface of the single crystal germanium substrate

16‧‧‧Nano Carbon Tube Structure

161‧‧‧ upper surface of the carbon nanotube structure

162‧‧‧The lower surface of the carbon nanotube structure

163, 36‧‧‧Nano Carbon Tube Film

164‧‧・Nano carbon tube bundle

165‧‧・nano carbon tube

18‧‧‧ electrodes

20‧‧‧ Passivation layer

1 is a schematic structural view of a solar cell in the prior art.

2 is a schematic side view showing the structure of a solar cell according to an embodiment of the present technical solution.

FIG. 3 is a partially enlarged schematic view showing the structure of a carbon nanotube in a solar cell according to an embodiment of the present technical solution.

4 is a schematic top plan view of a solar cell according to an embodiment of the present technical solution.

10‧‧‧ solar cells

12‧‧‧ Back electrode

14‧‧‧ Single crystal germanium substrate

141‧‧‧ The lower surface of the single crystal germanium substrate

142‧‧‧ Upper surface of single crystal germanium substrate

16‧‧‧Nano Carbon Tube Structure

161‧‧‧ upper surface of the carbon nanotube structure

162‧‧‧The lower surface of the carbon nanotube structure

18‧‧‧ electrodes

20‧‧‧ Passivation layer

Claims (17)

A solar cell comprising: a single crystal germanium substrate; a back electrode disposed on a lower surface of the single crystal germanium substrate and in ohmic contact with a lower surface of the single crystal germanium substrate; a carbon nanotube structure, wherein the carbon nanotube structure is disposed on an upper surface of the single crystal germanium substrate and is in contact with an upper surface of the single crystal germanium substrate; and the improvement is that the carbon nanotube structure includes plural An ordered array of carbon nanotubes, the plurality of carbon nanotubes being aligned parallel to the surface of the carbon nanotube structure. The solar cell according to claim 1, wherein the carbon nanotubes in the carbon nanotube structure are single-walled carbon nanotubes, double-walled carbon nanotubes or multi-walled carbon nanotubes. The solar cell according to claim 2, wherein the single-walled carbon nanotube has a diameter of 0.5 nm to 50 nm, and the double-walled carbon nanotube has a diameter of 1.0 nm to 50 nm. The diameter of the multi-walled carbon nanotubes is from 1.5 nm to 50 nm. The solar cell according to claim 1, wherein the carbon nanotubes in the carbon nanotube structure are uniformly distributed and arranged in a preferred orientation along a fixed direction. The solar cell of claim 4, wherein the carbon nanotube structure comprises at least one ordered carbon nanotube film. The solar cell of claim 5, wherein the ordered carbon nanotube film comprises a plurality of carbon nanotube bundles connected end to end and of equal length, the ends of the carbon nanotube bundle passing through the van der Waals Force connected to each other The carbon nanotube bundles comprise a plurality of carbon nanotubes of equal length and arranged in parallel. The solar cell of claim 5, wherein the carbon nanotube structure comprises at least two ordered carbon nanotube films arranged in an overlapping manner. The solar cell of claim 7, wherein the carbon nanotubes in the adjacent two ordered carbon nanotube films have an intersection angle α between 0 degrees and ≦α≦90 degrees. . The solar cell of claim 1, wherein the carbon nanotube structure comprises a plurality of long carbon nanotubes laid parallel to each other. The solar cell according to claim 1, wherein the carbon nanotube structure is a layered structure, and each layer comprises a plurality of long carbon nanotubes laid parallel to each other, and the adjacent two layers are The carbon nanotubes have a cross angle β between the long lines and 0 degrees ≦β≦90 degrees. The solar cell of claim 1, wherein the carbon nanotube structure comprises at least one carbon nanotube film and a plurality of nano carbon tube long wires, and the plurality of carbon nanotube long lines are laid in parallel with each other. On the surface of the carbon nanotube film. The solar cell according to claim 1, wherein the carbon nanotube structure is a structure in which a plurality of layers of carbon nanotube film and a plurality of carbon nanotube long lines overlap each other. The solar cell according to claim 1, wherein the single crystal germanium substrate is an n-type single crystal germanium or a p-type single crystal germanium, and the single crystal germanium substrate has a thickness of 200 μm to 300 Micron. The solar cell of claim 1, wherein the back electrode is made of aluminum, magnesium or silver, and the back electrode has a thickness of 10 micrometers to 300 micrometers. The solar cell of claim 1, wherein the solar cell further comprises at least one electrode in electrical contact with an upper surface of the carbon nanotube structure. The solar cell of claim 1, wherein the solar cell further comprises at least one passivation layer disposed between the single crystal germanium substrate and the carbon nanotube structure. The solar cell of claim 16, wherein the passivation layer is made of hafnium oxide or hafnium nitride.