CN100530744C - Structure of organic solar cell and organic solar cell produced with the same structure - Google Patents

Abstract

The invention discloses a structure of an organic solar cell and an organic solar cell prepared by using the structure. The structure of the organic solar cell at least includes a positive electrode, a negative electrode and an organic layer with photovoltaic properties prepared on a substrate. There is a hole transport layer composed of aligned carbon nanotube arrays between the organic layers. In the invention, the oriented carbon nanotube is deposited on the positive electrode of the solar battery, and good ohmic contact is formed with the positive electrode. The array of aligned carbon nanotubes is parallel to the substrate, and the carbon nanotubes are parallel to each other and less entangled. The photovoltaic characteristic organic material layer in the organic solar cell fills in the gaps of the carbon nanotube array, and forms a good coating on the carbon nanotubes. Since the carbon nanotube array provides the maximum exciton separation interface, and the aligned carbon nanotube array significantly reduces the electron transport path, thereby reducing the recombination probability of photogenerated carriers and improving the light energy conversion efficiency of solar cells.

Description

A structure of an organic solar cell and an organic solar cell prepared by the structure

technical field

The invention relates to a solar cell, in particular to a structure of an organic solar cell and an organic solar cell prepared by using the structure. The structure of the organic solar cell uses an array of aligned carbon nanotubes as a hole transport layer to improve hole transport. The probability of being transported to the positive electrode shortens the transmission path for the holes to be transported to the positive electrode, thereby improving the efficiency of the solar cell.

Background technique

In the 21st century, the world's energy will undergo tremendous changes. The energy structure dominated by fossil energy with limited resources and serious pollution will gradually transform into a diversified and composite energy structure dominated by clean and renewable energy with unlimited resources. As an inexhaustible and inexhaustible clean energy, solar energy has always been one of the ideal energy alternatives in people's minds. Photovoltaic power generation, which directly converts solar energy into electrical energy, is the most flexible and most universal of all solar energy utilization methods. Solar cells are the core components of photovoltaic power generation systems. The advancement of solar cell technology is of great significance to the promotion of solar energy utilization. Improving efficiency and reducing costs are the current guidelines for the development of solar cell technology.

Silicon material solar cells have been developed for many years, but the price of solar-grade silicon materials used to make batteries is very expensive, coupled with factors such as complex battery manufacturing processes, large equipment investment, material consumption and large electricity consumption, the price of Gui solar cells Higher, thus limiting its larger-scale promotion and application. Organic solar cells based on dye molecules or polymers are gaining increasing attention. Its biggest advantage lies in the simple manufacturing process and low cost. At present, the main problem of organic solar cells is their low photoelectric conversion efficiency, and improving the efficiency of organic solar cells has become the key to their popularization and application.

The reason for the low efficiency of organic solar cells is the carrier transport in organic materials. The HOMO and LUMO energy levels in organic semiconductor materials do not form conduction bands and valence bands, and the transport of carriers is completed by jumping between local energy states, and their mobility is significantly smaller than that of inorganic semiconductor materials. It is difficult for the carriers in the material to reach the electrodes, which limits the photoelectric conversion efficiency. In addition, the electron-hole pairs generated by organic matter under photoexcitation are relatively strongly bound to each other and often form excitons. However, excitons usually need to be dissociated under the action of an interfacial electric field, which is usually located at the interface between organic matter and metal electrodes. However, the contact surface between organic matter and metal electrodes is very limited, and only the excitons in the region not exceeding the exciton diffusion length from the interface can effectively reach the exciton separation interface. Therefore, increasing the effective exciton dissociation site and providing effective transport channels for electrons and holes become the key to improving the photoelectric conversion efficiency of organic solar cells.

A typical organic solar cell is a sandwich structure composed of three parts: positive electrode (anode), photovoltaic organic layer and negative electrode (cathode). The positive electrode material is a high work-function material similar to a p-type-metal contact, such as ITO transparent conductive oxide. The material of the negative electrode is similar to n-type-metal contact low work function (low work-function) material, such as metal aluminum and the like. On the basis of this typical structure, in order to improve the energy conversion efficiency, it is further proposed to add an electron transport layer and a hole transport layer between the organic layer and the electrode (as shown in Figure 1). The transport layer should have such characteristics: an effective exciton dissociation site can be provided at the interface between them and the photovoltaic organic layer, and the electron transport layer is easy to obtain excited state electrons and has good electron transport ability, and the hole transport layer It is easy to obtain holes and has good hole transport ability. Studies have shown that the introduction of the transport layer can often increase the conversion efficiency of organic solar cells by an order of magnitude. Fullerene is one of the transmission layer materials widely used at present. As a kind of fullerene, carbon nanotubes are a very potential transport layer material. At the same time, as a one-dimensional wire, it can quickly transport carriers to the electrode, thereby effectively separating excitons and improving the photoelectric conversion efficiency of the battery.

The separation efficiency of excitons is related to the separation interface of excitons and the transport paths of electrons and holes. In order to increase the separation interface of excitons, the concept of bulk heterojunction (bulk heterojunction) was proposed, that is, the electron transport layer and the hole transport layer interpenetrate to increase the contact interface. However, with the increase of penetration, the transport paths of electrons and holes gradually become longer, thereby increasing the recombination probability, resulting in a decrease in the exciton separation efficiency. If carbon nanotubes are used as the transport layer, the existing approach is to mix carbon nanotubes with photovoltaic organics. Although this method can provide a sufficient interface for exciton separation, the function of carbon nanotubes as a good carrier transport channel is far from being fully utilized. Because many carbon nanotubes dispersed in organic matter are not in contact with the electrode, the carriers obtained by these carbon nanotubes must pass through the tunnel effect between carbon nanotubes to reach the electrode. At the same time, because the carbon nanotubes dispersed in the organic matter have no definite orientation, the transport path of the charge carriers becomes tortuous.

Contents of the invention

The object of the present invention is to provide a structure of an organic solar cell and an organic solar cell prepared by using the structure. In the structure of the organic solar cell, an array of aligned carbon nanotubes is used as a hole transport layer, which can increase the hole density. The probability of being transported to the positive electrode shortens the transmission path of holes to the positive electrode, thereby improving the efficiency of the solar cell.

In order to realize above-mentioned task, the present invention adopts following technical solution:

A structure of an organic solar cell, comprising at least a positive electrode, a negative electrode, and a photovoltaic-characteristic organic layer prepared on a substrate, characterized in that, between the positive electrode and the photovoltaic-characteristic organic layer, there is a hole transport system composed of an array of oriented carbon nanotubes layer.

The organic solar cell prepared by adopting the structure of the above organic solar cell includes a substrate, which is characterized in that, there is a battery negative electrode made of continuous low work function material on the substrate, and a comb finger-shaped strip-shaped insulating layer is made on the negative electrode, and the insulating layer The carbon nanotubes parallel to the substrate are arranged on the upper surface, the carbon nanotubes are suspended between the comb finger insulating strips, and the insulating strips have conductive strips made of high work function materials, and the conductive strips are well formed with the carbon nanotubes on the insulating layer. The ohmic contact, the conductive strip is led out through the bus electrode at one end of the substrate to form the positive electrode of the battery, and the photovoltaic characteristic organic layer is filled between the carbon nanotubes on the surface of the negative electrode, completely wrapping the suspended carbon nanotubes, and forming with the negative electrode on the substrate good touch.

The hole transport layer used in the present invention is parallel carbon nanotubes arranged between comb-finger electrodes, and the excitons can be effectively ionized near the interface between the carbon nanotubes and photovoltaic organic matter. At the same time, the carbon nanotubes are directly connected to the strip electrodes, and the holes generated after the excitons are separated can reach the electrodes smoothly, thereby improving the photoelectric conversion efficiency of the solar cell.

Description of drawings

Figure 1 is a typical structure of an organic solar cell with an electron transport layer and a hole transport layer.

FIG. 2 is a schematic diagram of a three-dimensional structure of a solar cell using carbon nanotube arrays arranged in parallel substrates.

Fig. 3 is a schematic cross-sectional structure diagram of a solar cell using carbon nanotube arrays arranged in parallel substrates.

Fig. 4 is a schematic diagram of a three-dimensional structure of a solar cell with a carbon nanotube array arranged in parallel substrates and a hole transport layer.

Fig. 5 is a schematic cross-sectional structure diagram of a solar cell with a carbon nanotube array arranged in parallel substrates and a hole transport layer.

The numbers in the above figure represent respectively: 1. Substrate, 2. Negative electrode, 3. Insulating layer, 4. Catalyst layer, 5. Comb-fingered positive electrode, 6. Positive electrode bus electrode, 7. Horizontally oriented carbon nanotubes, 8. Organic Photovoltaic layer, 9. Electron transport layer.

In order to further illustrate the content of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments given by the inventor.

Detailed ways

The structure of an organic solar cell provided by the present invention at least includes a positive electrode, a negative electrode and a photovoltaic characteristic organic layer prepared on a substrate, and there is a hole formed by an aligned carbon nanotube array between the positive electrode and the photovoltaic characteristic organic layer transport layer.

The above-mentioned oriented carbon nanotube array is a large number of aligned carbon nanotubes deposited on the positive electrode, and forms an ohmic contact with the positive electrode. The carbon nanotube carbon nanotube is a single-walled carbon nanotube parallel to the substrate, or a multi-walled carbon nanotube tubes, or a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes.

On the basis of the above structure, an electron transport layer can be added between the negative electrode and the photovoltaic organic material.

The high work function material of the positive electrode can be ITO, platinum;

The low work function material of the negative electrode can be aluminum, calcium, magnesium, magnesium/indium;

The photovoltaic organic materials include: polymers: P3OT, P3HT, polyvinylcarbozole (PVK, polyvinylcarbazolamine), polysulfurnitride (polysulfur nitrogen), polyacetylene (polyacetylene), polythiophene (polythiophene) , PPV, MEH-PPV, cyano-PPV; dye molecules include: anthrancene (anthracene), porphyrin (porphyrin), phthalocyanine (phthalocyanine).

The photovoltaic organic material is not limited to one of the above materials, but also includes combinations thereof.

The substrate material includes: a ceramic substrate, a silicon substrate, a quartz substrate or a glass substrate;

The realization method of the solar cell provided by the present invention is as follows:

1) Deposit a layer of continuous low work function conductive material on the substrate as the negative electrode of the solar cell;

2) Depositing an insulating layer on the negative electrode by a conventional thin film process;

3) Depositing a layer of carbon nanotube growth catalyst on the insulating layer by a conventional thin film process;

4) Deposit a layer of conductive material with high work function on the catalyst layer by conventional thin film technology;

5) Through the conventional photolithography process, the high work function conductive layer, catalyst layer and insulating layer are etched layer by layer to produce a three-layer stack of slender comb finger-shaped insulating layer, catalyst layer and high work function conductive layer structure;

6) By chemical vapor deposition (CVD), carbon nanotubes parallel to the substrate are grown between adjacent fingers;

7) Fill the organic photovoltaic material on the surface of the negative electrode by dipping, spin coating or vacuum sputtering, and fully wrap the carbon nanotubes between the fingers;

or:

1) Depositing a continuous layer of low work function conductive material on the substrate as the negative electrode of the solar cell;

2) Depositing an insulating layer on the positive electrode by a conventional thin film process;

3) Deposit a layer of carbon nanotubes aligned parallel to the substrate on the insulating layer through a self-assembly process;

4) Depositing a layer of conductive material with high work function on the carbon nanotube layer;

5) Comb finger-shaped metal strips are etched by photolithography, and the metal strips are perpendicular to the arrangement direction of the carbon nanotubes;

6) further etching comb-finger-shaped insulating layer strips under the comb-finger-shaped metal strips by photolithography, exposing the suspended carbon nanotubes between the comb fingers and the negative electrode on the substrate;

7) Fill the photovoltaic organic material on the surface of the negative electrode by dipping, spin coating or vacuum sputtering, and fully wrap the carbon nanotubes suspended between the fingers;

If the solar cell provided by the present invention includes an electron transport layer, an electron transport layer fabrication step should be added to the above implementation method.

The following are examples given by the inventors.

Example 1:

In this embodiment, a carbon nanotube array parallel to the substrate is used as the hole transport layer. Make it according to the structure shown in Figure 2. An Al ₂ O ₃ ceramic sheet is used as the substrate 1 . An aluminum (Al) conductive negative electrode 2 with a thickness of 0.3 micron to 1 micron is deposited on the substrate 1 by magnetron sputtering. Then magnetron sputtering is used to deposit a SiO ₂ insulating layer 3 with a thickness of 10 nanometers to 10 micrometers on the conductive negative electrode 2 . Then a layer of carbon nanotube growth catalyst 4 is coated on the insulating layer 3 . Then another layer of ITO (indium tin oxide) is deposited, and the metal ITO (indium tin oxide) layer is photoetched into a comb-fingered positive electrode 5 and a positive electrode bus electrode 6 by using a conventional photolithography process. The finger width of the comb finger positive electrode 5 is 100 nm to 10 microns, the finger spacing is 100 nm to 1 mm, the finger length is 1 micron to 1 cm, and the electrode width of the positive bus electrode 6 is 1 micron to 1 mm. Further, the catalyst layer 4 and the insulating layer 3 are respectively etched by using the comb-finger electrode 5 and the positive electrode bus electrode 6 as masks. The suspended carbon nanotubes 7 are grown on the side of the catalyst layer by chemical vapor deposition. During the growth of carbon nanotubes, a certain voltage is applied between adjacent comb finger electrodes 5 to maintain an electric field of 0.1v/μm to 1v/μm between the fingers to guide the directional growth of carbon nanotubes. Then, the chloroform solution of P3OT was spin-coated on the surface of the sample, and after the chloroform solution was evaporated, an organic layer 9 with photovoltaic characteristics of P3OT was obtained. In order to make P3OT fully fill between the suspended carbon nanotubes 7 and the negative electrode 2 and coat the suspended carbon nanotubes 7 well, the sample can be immersed in the chloroform solution of P3OT for a period of time, and then obtained by spin coating Uniform P3OT filling layer. The negative electrode 2 and the positive electrode bus electrode 6 are finally led out from both sides of the substrate to form the positive electrode and the negative electrode of the solar cell. The cover glass on the P3OT photovoltaic organic matter 9 is used as a cover plate to package a complete solar cell.

Example 2:

In this embodiment, a carbon nanotube array parallel to the substrate is used as the hole transport layer. Make it according to the structure shown in Figure 4. Glass was used as the substrate 1 . An aluminum (Al) conductive negative electrode 2 with a thickness of 0.3 micron to 1 micron is deposited on the substrate 1 by magnetron sputtering. Then magnetron sputtering or chemical vapor deposition (CVD) is used to deposit a SiO ₂ insulating layer 4 with a thickness of 10 nanometers to 10 micrometers on the conductive negative electrode 2 . The insulating layer is etched into a pattern corresponding to the comb-finger electrode and the bus electrode by using a conventional photolithography process. Then a layer of PPV is deposited on the aluminum electrode by vacuum coating process. Mask photolithography is used to remove the PPV covered on the comb-finger insulating strip to expose the comb-finger insulating layer 3 and ensure that the height of the insulating strip is not lower than the surface of the PPV. Then, the solution dispersed with carbon nanotubes was applied to the surface of the sample PPV with the finger-shaped insulating layer exposed by using the air-flow blowing method, and the direction of air flow was perpendicular to the finger-shaped insulating layer 3 . After the solution is evaporated to dryness, horizontally aligned carbon nanotubes 7 arranged in vertical comb-like insulating strips are obtained. Then deposit one layer of ITO (Indium Tin Oxide) as the negative electrode of the solar cell, and adopt the conventional photolithography process to photoetch the ITO (Indium Tin Oxide) layer into a comb finger-shaped positive electrode 5 and a positive electrode bus electrode 6; the comb finger-shaped positive electrode 5 A good ohmic contact is formed with the carbon nanotubes on the surface of the insulating layer 3 , and the positive bus electrode 6 is covered on the insulating layer 3 . The planar pattern parameters of the finger-shaped positive electrode 6 and the finger-shaped insulating layer 3 are similar, and in typical cases, the pattern parameters of the two are the same. The finger width of the comb-fingered positive electrode 5 is 100 nanometers to 10 micrometers, the finger spacing is 100 nanometers to 1 millimeter, and the finger length is 1 micrometer to 1 centimeter; the electrode width of the positive bus electrode 6 is 1 micrometer to 1 millimeter. After photoetching out the conductive positive electrode, that is, the finger-shaped positive electrode 5 and the positive electrode bus electrode 6, a layer of PPV is deposited in the area where the finger-shaped positive electrode 5 is distributed, that is, the light-absorbing area of the solar cell, using a vacuum coating process, which is the same as the previous step. The deposited PPV fully wraps the carbon nanotubes 7 together to form the organic photovoltaic layer 8 of the light-absorbing exciton generation layer. The negative electrode 2 and the positive electrode bus electrode 6 are finally led out from both sides of the substrate to form the positive electrode and the negative electrode of the solar cell. The cover glass on the organic photovoltaic layer 8 is used as a cover plate to package a complete solar cell.

Example 3:

The difference between this embodiment and embodiment 2 is that, after the insulating layer pattern is photoetched, a layer of PCBM is deposited on the conductive negative electrode 2 as the electron transport layer 9 by vacuum coating process, and then the PPV layer is deposited. In addition, before depositing carbon nanotubes, it is also necessary to remove the PCBM covered on the comb finger insulating strips.

As mentioned above, the hole transport layer used in the present invention is parallel carbon nanotubes arranged between comb finger electrodes. Excitons can ionize efficiently near the interface between carbon nanotubes and photovoltaic organics. At the same time, the carbon nanotubes are directly connected to the strip electrodes, and the holes generated after the excitons are separated can reach the electrodes smoothly, thereby improving the photoelectric conversion efficiency of the solar cell.

Claims (8)

1. An organic solar cell, comprising a positive electrode, a negative electrode, and an organic layer of photovoltaic properties prepared on a substrate, between the positive electrode and the organic layer of photovoltaic properties, there is a hole transport layer composed of an array of oriented carbon nanotubes, characterized in That is, there is a battery negative electrode composed of a continuous low work function material on the substrate, and a comb finger-shaped strip-shaped insulating layer is made on the negative electrode. Between the strips, there is a conductive strip made of high work function material on the insulating strip. The conductive strip forms a good ohmic contact with the carbon nanotubes on the insulating layer. The conductive strip is led out through the bus electrode at one end of the substrate to form the positive electrode of the battery. The photovoltaic characteristic organic layer is filled between the carbon nanotubes on the surface of the negative electrode, completely wraps the suspended carbon nanotubes, and forms a good contact with the negative electrode on the substrate. 2. organic solar cell as claimed in claim 1, is characterized in that, described directional carbon nanotube array is the carbon nanotube of the directional alignment that is deposited on a large number of positive poles, and forms ohmic contact with positive pole, and carbon nanotube is Single-wall carbon nanotubes parallel to the substrate, or multi-wall carbon nanotubes, or a mixture of single-wall carbon nanotubes and multi-wall carbon nanotubes. 3. The organic solar cell according to claim 1, wherein the negative electrode material comprises at least one or a mixture of aluminum, calcium, magnesium or magnesium/indium. 4. The organic solar cell according to claim 1, wherein the material of the positive electrode is selected from indium tin oxide. 5 . The organic solar cell according to claim 1 , wherein the photovoltaic characteristic organic layer is in contact with the positive electrode. 6 . The organic solar cell according to claim 1 , wherein an electron transport layer is sandwiched between the photovoltaic characteristic organic layer and the negative electrode. 7 . 7 . The organic solar cell according to claim 1 , wherein the organic layer with photovoltaic properties is a dye molecule or a polymer with photovoltaic properties. 8. The organic solar cell according to claim 7, wherein the dye molecule is anthracene, porphyrin or phthalocyanine, or a combination of two or more of them; The polymer is one or a combination of two or more of pvk, polynitrogen sulfide, polyacetylene, polythiophene, PPV, MEH-PPV, and cyano-PPV.

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