JP2010287849A - Organic thin film solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic thin film solar cell improved in photoelectric conversion efficiency by preventing a carrier generated in a photoelectric conversion layer from being recombined in the photoelectric conversion layer, dispenses with a transparent electrode using price-increased In as a raw material thereby preventing the attenuation of incident light caused by the transparent electrode. <P>SOLUTION: A photoelectric conversion layer 12 configured by alternately laminating electron donor layers 12A and electronic accepter layers 12B is directly formed on a transparent substrate 11 and light is directly made incident on the photoelectric conversion layer through the transparent substrate. One or more first through electrodes 13 and one or more second through electrodes 14 are buried in the photoelectric conversion layer and these through electrodes are arranged so as to divide the photoelectric conversion layer. When built-in potential between the electron donor layer and the electronic acceptor layer is small, it is desirable that a work function of a conductive material making the first through electrode is different from that of a conductive material making the second through electrode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an organic thin film solar cell, which increases photoelectric conversion efficiency and eliminates the need for a transparent electrode.

An organic thin film solar cell is known as one type of solar cell.
FIG. 3 shows a typical example of a conventional organic thin film solar cell. Reference numeral 1 in the figure denotes a transparent substrate. The transparent substrate 1 is made of a transparent material such as a glass plate, and a transparent electrode 2 made of ITO (indium tin oxide) or the like is formed on one surface thereof.
A photoelectric conversion layer 3 is formed on the transparent electrode 2. In the photoelectric conversion layer 3, a plurality of electron donor layers 31 and electron acceptor layers 32 are alternately stacked.

The electron donor layer 31 is made of a thin film made of, for example, a porphyrin metal complex, and the electron acceptor layer 32 is made of a thin film made of, for example, fullerene.
A back electrode 4 made of a conductive material such as aluminum is provided on the photoelectric conversion layer 3.

In the organic thin film solar cell having such a configuration, excitons (electrons) generated in the electron donor layer 31 when the photoelectric conversion layer 3 is irradiated with light such as sunlight through the transparent substrate 1 and the transparent electrode 2. As a result of the separation of electrons and holes at the interface between the electron donor layer 31 and the electron acceptor layer 32, holes (holes, h ⁺ ) are generated in the electron donor layer 31, and the electron acceptor layer In 32, electrons (e ⁻ ) are generated, and holes move to the transparent electrode 2, and electrons move to the back electrode 4, so that photovoltaic power generation is performed.

  However, in the organic thin film solar cell having such a structure, there are cases where holes generated in the electron donor layer 31 and electrons generated in the electron acceptor layer 32 (hereinafter, holes or electrons or both are collectively referred to as carriers). ) Move to the electrode 2 (4), the carriers cross the electron donor layer 31 and the electron acceptor layer 32, and recombination of the carriers occurs when passing through the interface between the two electrodes 2 (4). ) Has decreased, and as a result, the photoelectric conversion efficiency cannot be increased.

In addition, ITO that constitutes the transparent electrode 2 is mainly made of indium, which is a rare metal, but recently, the consumption of indium has increased worldwide, making it difficult to procure, and its price has soared. Therefore, the manufacturing cost of ITO is increasing.
Furthermore, since incident light passes through the transparent electrode 2 and enters the photoelectric conversion layer 3, there is attenuation of light at the transparent electrode 2, which also reduces the photoelectric conversion efficiency.

JP 2004-103939 A JP 2005-236278 A JP 2006-351721 A JP 2007-288161 A JP 2007-59457 A

  Therefore, the problem in the present invention is that it is possible to prevent the carriers generated in the photoelectric conversion layer of the organic thin film solar cell from recombining and decreasing in the photoelectric conversion layer, and to increase the photoelectric conversion efficiency, and the price is high. The purpose is to eliminate the need for a transparent electrode made of soaring indium as a raw material, thereby reducing manufacturing costs and preventing attenuation of incident light by the transparent electrode.

To solve this problem,
According to the first aspect of the present invention, a photoelectric conversion layer in which an electron donor layer and an electron acceptor layer are alternately laminated is directly provided on a transparent substrate, and light passes through the transparent substrate and directly enters the photoelectric conversion layer. An organic thin film solar cell,
One or more first through electrodes and two or more through electrodes are embedded in the photoelectric conversion layer, and the through electrodes are arranged so as to divide the photoelectric conversion layer. .

  The invention according to claim 2 is characterized in that the conductive material forming the first through electrode and the conductive material forming the second through electrode have different work functions. It is a battery.

  According to a third aspect of the present invention, in the first and second through electrodes, the conductive portion and the insulating portion are alternately connected in series, and the interface between the conductive portion and the insulating portion is a photoelectric conversion layer. The conductive part of the first through electrode and the conductive part of the second through electrode are made of the same material, and are configured to coincide with the interface between the electron donor layer and the electron acceptor layer. It is an organic thin-film solar cell of description.

According to the first aspect of the present invention, when the carrier generated in the photoelectric conversion layer moves toward the electrode, the carrier does not cross the photoelectric conversion layer. For this reason, the frequency of the recombination in the photoelectric conversion layer of a carrier reduces significantly, and the carrier which reaches | attains an electrode does not reduce.
In addition, since the transparent electrode is not necessary, an increase in manufacturing cost can be suppressed, and the attenuation of incident light by the transparent electrode is eliminated. Furthermore, the moving distance of carriers moving in the photoelectric conversion layer is shortened, and this also suppresses the decrease in carriers.

According to the invention of claim 2, even when the driving force to the electrode of the carrier generated in the photoelectric conversion layer is small, by changing the work function of the material constituting each through electrode, The driving force is improved.
According to the invention of claim 3, when the driving force to the electrode of the carrier generated in the photoelectric conversion layer is large, the conductive portion of the first through electrode and the conductive portion of the second through electrode can be formed of the same material. This makes it possible to simplify the production of each through electrode having a relatively complicated structure.

It is a schematic block diagram which shows the 1st example of the organic thin film solar cell of this invention. It is a schematic block diagram which shows the 2nd example of the organic thin film solar cell of this invention. It is a schematic block diagram which shows the conventional organic thin film solar cell.

FIG. 1 shows a first example of the organic thin-film solar cell of the present invention. In FIG. 1, the code | symbol 11 shows the transparent substrate which consists of transparent materials, such as a glass plate and a transparent polymer film.
The photoelectric conversion layer 12 is directly provided on one surface of the transparent substrate 11. That is, the photoelectric conversion layer 12 is formed in a state of being in direct contact with the surface of the transparent substrate 11, and there is no transparent electrode. The photoelectric conversion layer 12 is configured by alternately laminating about 1 to 10 electron donor layers 12A and electron acceptor layers 12B.
In this example, the layer that is in direct contact with the surface of the transparent substrate 11 is the electron donor layer 12A, but may be the electron acceptor layer 12B.

The electron donor layer 12A is a layer that generates holes (h ⁺ ) upon incidence of light, and is a thin film having a thickness of 0.5 to 100 nm made of a porphyrin metal complex such as a syn-type octaethylporphyrin metal complex. is there.
The electron acceptor layer 12B is a layer that generates electrons (e ⁻ ) upon incidence of light, and is formed of a thin film having a thickness of 1 to 100 nm made of a fullerene derivative such as a fullerene polymer.

  As a method for forming the electron donor layer 12A and the electron acceptor layer 12B forming the photoelectric conversion layer 12, an appropriate method is used depending on the material constituting the layers 12A and 12B. A jet deposition method (LB method), a spin coating method, an ink jet method, a printing method, or the like is used, and a vacuum deposition method that can obtain a thin film with high purity is preferable.

  In addition, as a method of forming the electron acceptor layer 12B, when the electron acceptor layer 12B is made of a fullerene polymer, a fullerene polymer is formed by forming a thin film made of fullerene and then irradiating light, electron beam, or the like. A method using a fullerene polymer is preferred.

  As shown in the figure, a plurality of first through electrodes 13 and a plurality of second through electrodes 14 are embedded in the photoelectric conversion layer 12 in a state of being embedded in the photoelectric conversion layer 12. Yes. The individual first and second through electrodes 13 and 14 are in a state of being set up perpendicular to the substrate 11 directly on the transparent substrate 11, and the individual through electrodes 13. The photoelectric conversion layer 12 is in a divided state.

Further, when the photoelectric conversion layer 12 is viewed from above, the planar arrangement of the first through electrodes 13... And the second through electrodes 14. ing. The interval between the adjacent through electrodes 13 and 14 is about 1 to 4 mm, and the smaller the interval, the lower the recombination frequency during the movement of the carrier, which is preferable, but the production becomes troublesome. .
The first and second through electrodes 13 and 14 are film-like in which the width (thickness) is 10 nm to 75 μm, and the width (thickness) direction is orthogonal to the thickness direction of the photoelectric conversion layer 12. In other words, in other words, it is provided on the transparent substrate 11 so as to stand directly upright with respect to the substrate 11.

  Further, the upper end portions of the first through electrodes 13... And the second through electrodes 14... Are exposed from the photoelectric conversion layer 12, and a first current collector such as copper (not shown) is exposed in this exposed portion. All the first electrodes 13 are connected to the electrodes, and all the second electrodes 14 are connected to a second collector electrode such as copper (not shown).

  Further, a protective layer (not shown) is provided on the photoelectric conversion layer 12 and the first through electrode 13 ... and the second through electrode 14 ... so as to block these components from the outside air. .

In this example, when the built-in potential of the photoelectric conversion layer 12 is small, the first through electrode 13 and the second through electrode 14 are made of materials having different work functions.
The built-in potential of the photoelectric conversion layer 12 refers to a potential difference corresponding to a work function difference between materials constituting the electron donor layer 31 and the electron acceptor layer 32, and is also referred to as a diffusion potential.

For example, the work function of fullerene C60 is 6.6 eV, and the work function of the octaethylporphyrin zinc complex is 5.03 eV. Therefore, the built-in potential of the photoelectric conversion layer 12 composed of this combination is equivalent to 1.57 eV.
Since the work function of the octaethylporphyrin copper complex is 6.6 eV, the built-in potential of the photoelectric conversion layer 12 obtained by combining this with fullerene C60 is equivalent to 0 eV.

When the built-in potential is small, the driving force for moving the generated carriers to the through electrode is relatively low, and the work functions of the first through electrode 13 and the second through electrode 14 are different from each other. Carrier movement is enhanced by using the material.
Conversely, when the photoelectric conversion layer 12 has a high built-in potential, even if the first through electrode 13 and the second through electrode 14 are made of the same material, the degree to which carrier movement is suppressed is small.

  In this example, when the built-in potential is small, the first through electrodes 13... Are made of a conductive material having a work function higher than that of the second through electrodes 14. For example, the first electrode 13 is made of gold (work function 4.6 eV), platinum (work function 5.3 eV), and the second electrode 14 is made of aluminum (work function 3.5 eV), copper (work function 4). .4 eV) or the like is used.

For this reason, holes generated in the electron donor layer 12A move toward the second through electrodes 14 made of a conductive material having a low work function, and electrons generated in the electron acceptor layer 12B It moves toward the first through electrode 13 ... made of a conductive material having a high function, and the through electrode can be made to have selectivity between holes and electrons, and this also causes the carrier to move. Recombination can be suppressed.

Next, an example of the manufacturing method of the organic thin film solar cell of this example is demonstrated.
Here, the case where the electron donor layer 12A is made of a porphyrin metal complex and the electron acceptor layer 12B is made of a fullerene polymer will be described.

  First, a transparent substrate 11 having a thickness of 2 to 3 mm made of quartz glass or hard glass is prepared. After the surface of the transparent substrate 11 is cleaned, a porphyrin metal complex is formed to a thickness of 0.5 to 100 nm by a vacuum deposition method or the like, and a fullerene derivative is formed thereon to a thickness of 1 to 100 nm by a vacuum deposition method or the like. Vapor deposition. This deposition is repeated a required number of times to create a laminated film, which is used as the photoelectric conversion layer 12.

Next, the laminated film is irradiated with light or an electron beam to polymerize the fullerene derivative, thereby changing to a fullerene polymer. When light irradiation is performed, it is necessary to prevent photodegradation of the porphyrin metal complex of the adjacent electron donor layer 12A, and it is preferable to use ultraviolet rays having a wavelength of 300 to 400 nm. The electron acceptor layer 12B made of a fullerene polymer is preferable because the carrier moving speed is higher than that of a fullerene.
From the beginning, a fullerene polymer can be laminated as the electron acceptor layer 12B.

  Next, using a focused ion beam device, a portion of the photoelectric conversion layer 12 where the first through electrodes 13... And the second through electrodes 14. Etching is removed to form a plurality of trenches having a width of about 10 μm.

Further, using a focused ion beam device in the plurality of grooves, for example, aluminum and gold, for example, are vapor-deposited, and the grooves are filled to form the first through electrode 13..., The second through electrode 14. . At this time, it goes without saying that every other groove is filled with the same metal.
Next, a first collector electrode made of copper tape or the like is attached to the end of the first electrode 13... And a second collector electrode made of copper tape or the like is attached to the end of the second electrode 14. .

  As a manufacturing method other than this, a polymer transparent film such as a polyethylene terephthalate (PET) film is used as the transparent substrate 11, and the photoelectric conversion layer 12 is formed thereon by a vacuum deposition method or the like. Next, for example, two types of bonding wires made of gold, platinum, aluminum, and copper having an outer diameter of 20 to 50 μm are prepared, and these bonding wires are alternately arranged in parallel on the photoelectric conversion layer 12 and then mechanically bonded to the bonding wires. There is also a method in which the first through electrode 13... And the second through electrode 14. In this manufacturing method, the manufacturing is simplified and the manufacturing efficiency is high. Further, the photoelectric conversion layer 12 can be formed by a printing method.

In the organic thin film solar cell of this example, the distance between the first electrode 13... And the second electrode 14. The recombination of carriers at is suppressed. Further, all the generated holes move to the second through electrodes 14 made of a material having a small work function, and all the generated electrons move to the first through electrodes 13. This also suppresses carrier recombination.
Furthermore, a transparent electrode made of ITO is unnecessary, it is not necessary to use indium that is difficult to procure, and there is no attenuation of incident light by the transparent electrode.

FIG. 2 shows a second example of the organic thin film solar cell of the present invention.
Also in this example, similarly to the first example, a plurality of first through electrodes 13... And a plurality of second through electrodes 14... Are alternately embedded in the photoelectric conversion layer 12. It has been. Similar to the first example, the individual first and second electrodes 13 and 14 are in a state of being set up perpendicular to the substrate 11 directly on the transparent substrate 11. Thus, the photoelectric conversion layer 12 is in a divided state.

  Further, when the photoelectric conversion layer 12 is viewed from above, the planar arrangement of the first through electrodes 13... And the second through electrodes 14. ing. And the space | interval between the adjacent penetration electrodes 13 and 14 is about 1-4 mm.

  In addition, in this example, the first through electrode 13... And the second through electrode 14. It has become a form. Each interface between the conductive part A and the insulating part B is configured to substantially coincide with the interface between the electron donor layer 12A and the electron acceptor layer 12B of the photoelectric conversion layer 12.

  Further, in the adjacent first through electrode 13 and the second through electrode 14, the stacking order of the conductive portion A and the insulating portion B is different, and the conductive portion A where the first through electrode 13 is located has a second adjacent second portion. It arrange | positions so that the insulation parts B and B of the penetration electrode 14 may oppose. In other words, as shown in FIG. 2, when the solar cell is viewed from the side, the conductive portions A and the insulating portions B of the through electrodes 13..., 14. It has become.

Further, in one electrode 13 (14), a plurality of conductive portions A are electrically connected to each other, and are further connected to each other between the same type of electrodes, and are connected to a collecting electrode (not shown). .
The conductive part A is made of a conductive material such as gold or platinum, and the insulating part B is made of an electrical insulating material such as aluminum oxide or nickel oxide.

In this example, when the built-in potential of the photoelectric conversion layer 12 is large, the first through electrode 13 and the second through electrode 14 are made of materials having the same work function.
When this built-in potential is large, the driving force for movement of the generated carriers to the through electrode is relatively high, and as a material forming the conductive portion A of the first through electrode 13 and the second through electrode 14 Even if materials having the same work function are used, carrier movement does not decrease.

  In the manufacture of the organic thin film solar cell of this example, a plurality of grooves are formed in the photoelectric conversion layer 12 using a focused ion beam device as in the previous example, and the conductive portion A is also formed in this groove using the focused ion beam device. It is possible to make the metal and the insulator to be the insulating part B by alternately controlling the thickness and filling them.

  In the organic thin-film solar cell having such a configuration, for example, only holes generated in the electron donor layer 12A move to the conductive portions A of the first electrodes 13. Only the electrons generated in the electron acceptor layer 12B move to the conductive parts A of. That is, holes and electrons selectively move to different electrodes, and recombination of carriers during the movement can be suppressed.

Further, the distance between the first electrode 13... And the second electrode 14... And the carrier generation position is shortened, the carrier moving distance is shortened, and recombination of carriers during the movement is suppressed.
In addition, the conductive portion A of the first through electrode 13 and the conductive portion A of the second through electrode 14 can be made of the same material, and the manufacture of each through electrode having a relatively complicated structure can be simplified.
Further, like the organic thin film solar cell of the first example, a transparent electrode made of ITO is unnecessary, it is not necessary to use indium that is difficult to procure, and there is no attenuation of incident light by the transparent electrode.

Specific examples are shown below.
Example 1
A cell having the structure of the present invention shown in FIG. 1 was produced.
A borosilicate glass plate having a thickness of 1.1 mm was used as the transparent substrate, and the surface thereof was cleaned. A photoelectric conversion layer was formed by masking the portion other than the central portion of the glass plate. A glass plate is placed in a chamber of a vacuum deposition apparatus, and 2,3,7,8,12,13,17,18-octaethyl-21H, 23H porphin zinc (II) (Zn (OEP) is used as a deposition source to be an electron donor layer. )) Were alternately vacuum deposited using fullerene C60 as the deposition source to be the electron acceptor layer. The degree of vacuum was about 5 × 10 ⁻³ Pa, the time was about 1 minute, and the lamination was repeated in the order of Zn (OEP) and fullerene C60 to form a photoelectric conversion layer.

The thickness of the Zn (OEP) layer was about 100 nm, and the thickness of the fullerene C60 layer was about 100 nm. After the predetermined number of depositions, the mask was removed.
Thereafter, using a focused ion beam device (Quanta 200 3D manufactured by FEI Company), a metal ion such as gallium is provided in the portion where the first through electrode 13... And the second through electrode 14. Was irradiated with a beam diameter of 10 μm, and the photoelectric conversion layer 12 was removed by etching to form a plurality of trenches having a width of about 10 μm.

Further, using the same focused ion beam apparatus in the plurality of grooves, aluminum and gold are alternately deposited and filled in the grooves to form first through electrodes 13..., Second through electrodes 14. did. The beam diameter was 10 μm, and the film formation rate was about 20 nm / second.
Next, a first collector electrode made of copper tape or the like is attached to the end of the first electrode 13... And a second collector electrode made of copper tape or the like is attached to the end of the second electrode 14. It was.

  About the obtained cell, the lamination | stacking frequency | count of Zn (OEP) layer and fullerene C60 layer was changed, the short circuit current density and the open circuit voltage at that time were measured, and the result is shown in Table 1.

(Conventional example)
A cell having the conventional structure shown in FIG. 3 was produced.
As a substrate, a soda glass with an ITO film having a thickness of 1.1 mm was used, and the ITO film in an excessive range was removed and the surface was cleaned. A glass plate is placed in a chamber of a vacuum deposition apparatus, and 2,3,7,8,12,13,17,18-octaethyl-21H, 23H porphin zinc (II) (Zn (OEP) is used as a deposition source to be an electron donor layer. )) Were alternately vacuum deposited using fullerene C60 as the deposition source to be the electron acceptor layer. The degree of vacuum was about 5 × 10 ⁻³ Pa, the time was about 1 minute, and the lamination was repeated on the ITO film in the order of Zn (OEP) and fullerene C60 to form a photoelectric conversion layer.

The thickness of the Zn (OEP) layer was about 100 nm, and the thickness of the fullerene C60 layer was about 100 nm.
After vapor deposition a predetermined number of times, aluminum was vapor-deposited on the surface of the photoelectric conversion layer to form an electrode. The degree of vacuum was about 5 × 10 ⁻³ Pa and the time was about 1 minute.

  For the obtained cell, similarly, the number of lamination of the Zn (OEP) layer and the fullerene C60 layer was changed, the short-circuit current density and the open-circuit voltage at that time were measured, and the results are shown in Table 2.

  From the results of Tables 1 and 2, the organic thin-film solar cell having the structure of the present invention shows excellent values of short-circuit current density and open-circuit voltage as compared with the conventional one, and has high photoelectric conversion efficiency. It became clear that there was.

(Example 2)
The organic thin film solar cell having the structure shown in FIG. 1 was manufactured by another method. A transparent polyethylene terephthalate (PET) film having a thickness of 0.5 mm was used as a transparent substrate, and this surface was wiped with an organic solvent. In the same manner as in Example 1, on the surface of this film, Zn (OEP) and fullerene C60 were alternately deposited by vacuum deposition 5 times in order, thereby forming a photoelectric conversion layer 12 having a thickness of about 1 μm.
Next, two types of bonding wires made of gold and aluminum having an outer diameter of 50 μm are prepared, and the bonding wires are alternately arranged in parallel at intervals of 1 mm on the photoelectric conversion layer 12, and then the bonding wires are mechanically connected to the photoelectric conversion layer. The first through electrodes 13... And the second through electrodes 14... Made of bonding wires were formed.

A plurality of gold bonding wires to be the first through electrodes 13 were collectively connected to the copper tape, and a plurality of aluminum bonding wires to be the second through electrodes 14 were collectively connected to the copper tape.
When the characteristics of the cell were measured, the open circuit voltage was 0.35 V, and the short-circuit current density was 7.2 × 10 ⁻⁴ mA / cm ² .

DESCRIPTION OF SYMBOLS 11 ... Transparent substrate, 12 ... Photoelectric conversion layer, 12A ... Electron donor layer, 12B ... Electron acceptor layer, 13 ... 1st penetration electrode, 14 ... 2nd penetration electrode, A ... Conducting part, B ... Insulating part

Claims (3)

An organic thin film solar cell in which a photoelectric conversion layer in which an electron donor layer and an electron acceptor layer are alternately laminated is directly provided on a transparent substrate, and light is transmitted through the transparent substrate and directly incident on the photoelectric conversion layer. And
One or more 1st penetration electrodes and 2nd penetration electrodes are embed | buried in the said photoelectric converting layer, respectively, These organic electrodes are distribute | arranged so that these penetration electrodes may divide a photoelectric converting layer,   2. The organic thin-film solar cell according to claim 1, wherein the conductive material forming the first through electrode and the conductive material forming the second through electrode have different work functions.   The first and second through electrodes have conductive portions and insulating portions alternately connected in series, and an interface between the conductive portions and the insulating portions is an electron donor layer and an electron acceptor layer of a photoelectric conversion layer. The organic thin-film solar cell according to claim 1, wherein the organic thin-film solar cell is configured so as to coincide with the interface of the first through-electrode and the conductive portion of the second through-electrode is made of the same material.

Images