Method for manufacturing organic thin film solar cell and organic thin film solar cell

The present invention relates to a method for manufacturing a bulk hetero type organic thin film solar cell and an organic thin film solar cell.

In recent years, as a new energy alternative to fossil fuels, solar cells, which can convert almost inexhaustible and clean sunlight into electricity, have been attracting attention. Silicon-based solar cells are the mainstream, but they are expensive in terms of materials and manufacturing processes. In order to popularize solar cells, it is indispensable to reduce the price.

Therefore, in order to manufacture solar cells inexpensively and easily, solar cells other than silicon-based batteries are being actively developed. For example, Patent Document 1 below discloses an organic thin-film solar cell. In this organic thin film solar cell, the inorganic nanoparticles in the organic thin film have a concentration gradient. In order to contain the inorganic nanoparticles, a method of dispersing the inorganic nanoparticles in a solvent and forming a film by spin coating is adopted. Examples of the inorganic nanoparticles include metal oxides and copper-indium-selenium compounds (CuInSe, commonly known as CIS), which improve the light absorption rate at short wavelengths.

However, since the inorganic nanoparticles have a size of about several nm, it is difficult to completely disperse the inorganic nanoparticles in a solvent. Therefore, it becomes difficult to distribute the inorganic nanoparticles with a concentration gradient in the organic thin film, which may hinder charge transport.

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2009-158730 (paragraph numbers 0021, 0024)</text></patcit></p>

<p> An object of the present invention is to provide a method for producing a bulk hetero type organic thin film solar cell in which nanoparticles can be easily distributed in an organic thin film, and to provide an organic thin film solar cell.</p>

<p> The method for manufacturing an organic thin-film solar cell of the present invention includes a step of preparing a substrate, a step of forming a first electrode on one surface of the substrate, a step of forming a bulk hetero-type organic thin film on the first electrode, and an organic thin film. It has a step of forming a second electrode on the surface. The step of forming the organic thin film is a step of dissolving a p-type semiconductor material, an n-type semiconductor material and a liquid nanoparticle material in a solvent, and each material containing the nanoparticle material is melted on the first electrode. It has a step of forming a film of the solvent and a step of heating the film.</p><p> The step of forming the second electrode includes a step of forming a metal layer and a step of heating the metal layer. Nanoparticles are formed in the organic thin film by the step of heating the film and the step of heating the metal layer. Nanoparticles are Ge nanoparticles.</p><p> An electron block layer may be formed on the first electrode between the step of forming the first electrode and the step of forming the organic thin film.</p><p> The melting step, the film forming step, and the film heating step are repeated a plurality of times, and when the number of times is repeated, the concentration of the nanoparticle material is increased later. A concentration gradient is provided so that the concentration of nanoparticles in the organic thin film gradually increases as it approaches the second electrode.</p>

<p> According to the present invention, since the material of nanoparticles is in a liquid state, it can be easily dissolved in a solvent, and nanoparticles can be easily formed in an organic thin film. Unlike Si-based solar cells, it can be manufactured at low cost by spin coating or the like. Nanoparticles improve light absorption and power generation efficiency.</p>

<figref num="1">It is a figure which shows the structure of the organic thin film solar cell.</figref><figref num="2">It is a figure which shows the difference in the light absorption rate of the solar cell containing Ge nanoparticles and the solar cell which does not contain Ge nanoparticles.</figref><figref num="3">It is a figure of the energy band of the solar cell containing the nanoparticles of Ge.</figref>

The method for manufacturing the organic thin-film solar cell of the present invention will be described with reference to the drawings.

The organic thin-film solar cell 10 shown in FIG. 1 has a structure in which a first electrode 14, an electron block layer 16, an organic thin film 18 containing nanoparticles, and a second electrode 20 are sequentially laminated on a substrate 12.

The substrate 12 is a transparent substrate made of glass or resin. The first electrode 14 is formed on one surface of the substrate 12, and the other surface serves as a light incident surface. An antireflection film may be provided on the other surface to increase the efficiency of light incident on the organic thin film 18. The substrate 12 may be flexible. If the substrate 12 is flexible, the solar cell 10 itself becomes flexible and can be attached to clothing or the like. It can be used as a power source for mobile devices. It is also possible to attach the solar cell 10 to a curved surface such as a car body to use it as a power source.

The first electrode 14 is a transparent electrode such as ITO (Indium Tin Oxide) or ZnO (Zinc Oxide). The first electrode 14 serves as an anode. The first electrode 14 may be one for one substrate 12, or may be divided into a plurality of the first electrodes 14.

The electron block layer 16 is a layer having an electron blocking effect. The electron block layer 16 prevents some electrons from flowing from the organic thin film 18 to the first electrode 14, and prevents a decrease in power generation efficiency. Examples of the material include poly (3,4-ethylenedioxythiophene) -poly (styrene sulfonate) (commonly known as PEDOT: PSS). The electron block layer 16 may be omitted if it is not considered that some electrons flow to the first electrode 14.

The layer thickness of the electron block layer 16 is about 5 to 50 nm. This is because the conductivity is insufficient below 5 nm, and the electrical resistance may increase above 50 nm.

The organic thin film 18 has a bulk heterojunction. Bulk heterojunction is a mixture of p-type semiconductors and n-type semiconductors in an irregular manner, and the boundary area between them, which is a pn junction, is widened. As the p-type semiconductor material, a material having solubility in an organic solvent is used. For example, metallic phthalocyanine (MPc) or metallic tetraphenylporphyrin (MTPP). Examples of the metal (M) among these include Cu, Zn, Fe, Co, Ni, Pb and Sn. By selecting the metal (M), the wavelength of light that can be absorbed can be selected. In addition, poly 3hexylthiophene (P3HT), polyparaphenylene vinylene (PPV), pentacene, tetracyanoquinodimethane (TCNQ) and the like can also be used.

The n-type semiconductor material also uses a material that is soluble in an organic solvent. n-type semiconductor material has excellent electron acceptability C₆₀And perylene.

Further, the organic thin film 18 is configured to contain nanoparticles. The nanoparticles use Ge nanoparticles that improve long wavelength light absorption. A liquid containing the nanoparticle material is used during production to form Ge nanoparticles. For example, GeBr₄Use the solution of. GeBr₄Since the melting point of is 26.1 ° C, it should be used in a solution state at a temperature higher than that, for example, 30 ° C or higher. GeBr like this₄If so, it can be easily dissolved in a solvent, and Ge nanoparticles can be easily dispersed in the organic thin film 18. In addition to Ge, an organic solution containing Si or a solution of polysilane may be used.

Solvents that dissolve p-type semiconductor materials, n-type semiconductor materials, and nanoparticles solutions are aromatic solvents such as orthodichlorobenzene, benzene, toluene, and xylene, and halogens such as chlorobenzene, bromobenzene, dichlorobenzene, dichloroethane, and trichloroethane. Examples thereof include a chemical aromatic solvent and a halogenated aliphatic solvent. Two or more of these may be used in combination.

The film thickness of the organic thin film 18 is about 50 to 300 nm. If it is less than 50 nm, problems such as non-uniformity of film thickness and transmission of sunlight without absorbing it occur. In addition, if it exceeds 300 nm, there is a problem that the electric resistance becomes high. The size of the nanoparticles is in the range of 2 nm to 200 nm, for example 100 nm.

The second electrode 20 is a metal electrode such as Al. The second electrode 20 serves as a cathode. The material is selected in consideration of the lowest unoccupied molecular orbital (LUMO) of the n-type semiconductor and the work function of the second electrode so that the organic thin film 18 and the second electrode 20 form an ohmic contact. Ag (-4.3eV), Au (-5.2eV), Cu (-4.7eV) can be used in addition to Al (-4.3eV). The thickness of the second electrode 20 is 50 to 500 nm. Since the current flows in the lateral direction in the second electrode 20, the electric resistance increases when it becomes thin, and when it becomes thick, it peels off due to the distortion of the metal film, resulting in an increase in cost.

A buffer layer of lithium fluoride (LiF) may be provided between the organic thin film 18 and the second electrode 20 to increase the power generation efficiency.

A method for manufacturing the organic thin-film solar cell 10 will be described. (1) Prepare a substrate 12 such as glass. This preparation involves cutting and cleaning the substrate 12 into a desired shape.

(2) The first electrode 14 is formed on one surface of the substrate 12. Vacuum film formation of ITO with a sputtering device or a thin film deposition device. If necessary, the ITO is patterned (etched) into a desired shape.

(3) An electron block layer 16 of PEDOT: PSS is formed on the first electrode 14. To form the electron block layer 16, a solution of PEDOT: PSS material is applied in a nitrogen atmosphere and dried. From the viewpoint of carrier transport efficiency and ease of handling the solution, an aqueous solution containing 0.5 to 5 wt% of poly (3,4-ethylenedioxythiophene) -poly (styrene sulfonate) is applied and dried. If it is less than 0.5 wt%, the conductivity will be insufficient, and if it exceeds 5 wt%, the thickness may become uneven. Examples of the forming method include spin coating, an inkjet method, and thin film forming using a doctor blade. If the electronic block layer 16 is omitted, this step is omitted.

(4) An organic thin film 18 is formed on the electron block layer 16. A solution containing a powdered p-type semiconductor material, a powdered n-type semiconductor material, and a liquid nanoparticle material is dissolved in a solvent and spin-coated in an atmosphere of an inert gas. CuPc is used for the p-type semiconductor material, and C is used for the n-type semiconductor material.₆₀To use. The liquid of the nanoparticle material is the liquid GeBr.₄Is. The solvent is an orthodichlorobenzene solution. Examples of the inert gas include nitrogen, helium, and carbonic acid gas.

CuPc is 0.5mg ~ 10mg, C for 1ml of ortodichlorobenzene₆₀Is 1mg-40mg, GeBr₄Is 0.1 ml to 1.0 ml. If it is within this range, it can be changed as appropriate.

In addition to spin coating, the organic thin film 18 may be formed by an inkjet method or thin film formation using a doctor blade.

(5) After forming the organic thin film 18 by spin coating, it is heated in a constant temperature bath. Since a plurality of materials are dissolved in a solvent and spin-coated, the formed organic thin film 18 has a bulk heterojunction. The heating conditions are 80 to 160 ° C and 10 to 60 minutes.

(6) The second electrode 20 is formed on the organic thin film 18. A metal such as Al is vacuum-deposited and heated in a constant temperature bath. If necessary, the second electrode 20 may be patterned during or after the vapor deposition.

GeBr by the heat treatment of (5) and (6) above₄Is thermally decomposed and Ge nanoparticles are formed in the organic thin film 18, Br.₂Gas is generated.

FIG. 2 shows the difference in light absorption rate between the solar cell 10 containing Ge nanoparticles of the present invention and the conventional solar cell not containing Ge nanoparticles. Ge nanoparticles improve the light absorption rate in the long wavelength band, and can generate electricity in a wide wavelength band.

As shown in Fig. 3, normally, power is generated when light energy (hν) of 1.7 eV or more is incident, but since the energy gap of Ge is 0.7 eV, power generation is generated if the light energy is 0.7 eV or more. It is possible. If the light has a short wavelength, the amount of power generation is large, and if the wavelength is long, the amount of power generation is small.

Next, the experiments actually performed with respect to the above (1) to (6) will be described. For (1) and (2) above, a 20 mm × 20 mm glass substrate 12 coated with ITO (film thickness 200 nm, sheet resistance 10 Ω / ) was used. Polish the surface of ITO with fine gloves until the surface becomes smooth, wash the substrate 12 with ultrapure water, take out the substrate 12 from the ultrapure water, blow off the water on the substrate 12 with nitrogen gas injection, and acetone. And ultrasonically washed with methanol. Further, after ultrasonic cleaning, the substrate 12 was washed with ultrapure water and water was removed by nitrogen gas injection.

Regarding (3) above, in order to form the electron block layer 16, an aqueous solution of poly (3,4-ethylenedioxythiophene) -poly (styrene sulfonate) was spin-coated under a nitrogen atmosphere. The rotation speed of the spin coat was rotated to 2000 rpm over 35 seconds, maintained for 10 seconds, and then decelerated. After spin coating, heat treatment was performed at 100 ° C. for 10 minutes to form the electron block layer 16.

Regarding (4) above, 1 ml of ortodichlorobenzene, 2 mg of CuPc, and C₆₀16 mg, GeBr₄Was dissolved in 0.3 ml. Spin coating was performed in an atmosphere of nitrogen gas. The conditions for spin coating are 800 rpm and 80 seconds. The spin coating time can be changed from 30 to 200 seconds.

Regarding (5) above, after forming the organic thin film 18 by spin coating, heat treatment was performed at 100 ° C. for 30 minutes. The thickness of the organic thin film 18 was about 100 nm.

Regarding (6) above, Al having a thickness of about 150 nm was vacuum-deposited and heat-treated at 140 ° C. for 20 minutes to form the second electrode 20.

Table 1 shows a comparison between the solar cell 10 containing Ge nanoparticles and the solar cell not containing Ge nanoparticles, including the solar cell 10 produced by the above experiment. This comparison uses a solar simulator manufactured by Sanaga Denki Seisakusho Co., Ltd. The thickness of each layer of the solar cell 10 is set under the same conditions. The solar cell 10 is of two types using CuPc or ZnTPP as a p-type semiconductor. Each solar cell 10 includes an electronic block layer 16. It can be seen that the power generation efficiency is improved by an order of magnitude by dispersing the Ge nanoparticles in the organic thin film 18.

<tables num="1"><img file="JP2012142467A_D0001.tif" /></tables>

As described above, since the present invention uses a solution of the nanoparticle material, it is easy to dissolve in a solvent. It is easy to uniformly disperse nanoparticles in the organic thin film 18. Since the nanoparticles used are Ge, it is possible to enhance the absorption of long-wavelength light and widen the wavelength at which light can be absorbed. See-through solar cells can also be manufactured by selecting the material of the organic thin film 18.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, the above (4) and (5) are divided into a plurality of times. GeBr in solvent gradually over time₄Gradually increase the concentration of. In the organic thin film 18 of the manufactured solar cell 10, the concentration of Ge nanoparticles gradually increases as it approaches the second electrode 20. Nanoparticles are distributed near the electrode interface so that they do not become a barrier to charge transport. Unlike Reference 1, since the nanoparticle material is in the form of a solution by the method of the present application, it is easy to create a desired concentration gradient.

In addition, the present invention can be carried out in a mode in which various improvements, modifications and changes are made based on the knowledge of those skilled in the art without departing from the gist thereof.

10: Organic thin-film solar cells 12: Board 14: 1st electrode 16: Electronic block layer 18: Organic thin film containing nanoparticles 20: 2nd electrode