JP5517640B2 - Organic thin film solar cell and manufacturing method thereof (2) - Google Patents

Description

  The present invention is an invention that can be applied to improve the conversion efficiency of organic thin-film solar cells.

  Conventionally, organic thin-film solar cells are known to have a low photoelectric conversion efficiency due to a lack of a bonding area in a two-dimensional planar bonding. Therefore, as an invention for improving the conversion efficiency of an organic thin film solar cell, a layer structure in which a bulk heterojunction is formed by phase separation of a mixture of a donor and an acceptor as in Non-Patent Document 1 and Non-Patent Document 2, Attempts have been made to increase the photogenerated charge of organic thin-film solar cells by increasing the acceptor interface.

C.J.Brabec et al., Advanced Functional Materials, Vol. 11, p. 15. J.Xue, S.Uchida, B.P.Land, S.R.Forrest, Appl.Phys.Lett., 85, p.5757 (2004)

  However, even if a layer structure in which a bulk heterojunction is formed in the film by phase separation of a mixture of a donor and an acceptor as described above and a large number of photogenerated charges are generated, the photogenerated charges are not lost. Since the distance that can be moved is at most about 100 nm, when the thickness of the film of the mixture of the donor and the acceptor exceeds 100 nm, the photogenerated charge tends to disappear before reaching the electrode. Therefore, when the thickness is increased to 100 nm or more, the conversion efficiency is lowered, and there is a problem that the conversion efficiency cannot be improved by increasing the thickness of the donor-acceptor mixture film.

The present invention forms a layer in which a bulk heterojunction by a donor and an acceptor is formed on a substrate sheet having releasability, and an island-shaped metal film on the layer in which the bulk heterojunction is formed And etching the layer in which the bulk heterojunction is formed using the metal film as a mask to form a fine groove penetrating the nanoscale width, forming an electrode in the fine groove, An organic thin film solar cell characterized in that a substrate sheet having releasability is peeled off by transferring the substrate to a substrate, and a donor layer, an acceptor layer, or a mixture layer of a donor and an acceptor is formed on the outermost surface after transfer It is a manufacturing method.

In the method for producing an organic thin-film solar cell of the present invention , an island-shaped metal film is formed on a layer in which a bulk heterojunction is formed by a donor and an acceptor, and the metal film is used as a mask to form a bulk by the donor and the acceptor. By etching the layer in which the terror junction is formed, a fine groove having a nanoscale width is formed, and an electrode is formed in the fine groove. Accordingly, the metal film having an island-like structure can be formed with a large area with high productivity, and thus there is an effect that a fine groove having a nanoscale width can be formed with high productivity .

(A) is a schematic cross-sectional view showing an embodiment of the organic thin-film solar cell of the present invention, and (b) is reflected from an electrode formed in a groove obliquely to sunlight and reflected in the film. It is a schematic cross section which shows a mode that it is confined, (c) is a schematic cross section which shows a mode that the electric charge which generate | occur | produced with sunlight moves through the electrode formed in the groove | channel. It is a schematic cross section which shows one Example of the manufacturing method of the organic thin-film solar cell of this invention, (a) is a metal film of an island-like structure on the layer in which the bulk heterojunction by a donor and an acceptor was formed. (B) shows a process in which a minute heterojunction having a nanoscale width is formed by etching a layer in which a bulk heterojunction is formed by a donor and an acceptor using the metal film as a mask. (C) shows a process in which an electrode is formed in the fine groove. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic cross section which shows one Example of the manufacturing method of the organic thin-film solar cell of this invention, (a) shows the layer by which the bulk heterojunction by the donor and the acceptor was formed on the base sheet which has mold release property. (B) shows the step of forming an island-shaped metal film on the layer in which the bulk heterojunction is formed, and (c) shows the step of forming the bulk into the bulk using the metal film as a mask. (D) shows the step of forming a fine groove penetrating the nanoscale width by etching the layer in which the terror junction is formed, (d) shows the step of forming an electrode in the fine groove, (e) And (f) shows a step of transferring each of the above layers to a base material and peeling off a substrate sheet having releasability, and (f) shows any one of a donor layer, an acceptor layer, or a mixture layer of a donor and an acceptor on the outermost surface after transfer. The process to form is shown.

  The organic thin film solar cell 5 of the present invention is formed in a number of island-like structures 9 in which the surface of the layer 7 in which the bulk heterojunction formed by the donor and the acceptor is formed is surrounded by the fine grooves 1 having a nanoscale width, It has a structure in which an electrode 21 for efficiently taking out the photogenerated charge 2 is formed in the fine groove 1. A counter electrode 20 is formed on the surface opposite to the electrode 21 (see FIG. 1A). When the electrode 20 is a transparent electrode and the electrode 21 is an electrode such as a metal that reflects light, when light 51 such as sunlight enters the organic thin film solar cell 5 from an oblique direction, the light 51 enters the groove. The light is reflected by the formed electrode 21 and confined in the film (see FIG. 1B). As a result, more photogenerated charges 2 can be generated in the vicinity of the electrode 21, so that a large amount of the photogenerated charges 2 can be moved through the electrode 21 without being lost, and a high electromotive force can be obtained. There is also an effect (see FIG. 1C).

  Examples of the donor material include cross-linked polythiophene, poly-3-hexylthiophene (P3HT), and phthalocyanine derivatives. Examples of the acceptor material include fullerene derivatives such as PCBM and PCPDTBT, and zinc oxide. Not. However, it is necessary that the donor and the acceptor be phase-separated to form a bulk heterojunction structure.

  Examples of the method for forming the layer 7 in which the bulk heterojunction is formed include various coating methods such as spin coating, various printing methods such as gravure printing, and the like, which are formed on the substrate 14 on which the electrode 20 is formed. . The thickness can be in the range of about 100 to 700 nm, and is preferably about 300 to 500 nm. In a conventional organic thin-film solar cell with a flat electrode, when the thickness is 100 nm or more, the photogenerated charge 2 disappears before reaching the electrode 21 and the conversion efficiency is greatly reduced. The photogenerated charges 2 can easily reach the electrode 21 even if the thickness is somewhat increased. Therefore, the thicker the thickness, the larger the interface where the photogenerated charges 2 are generated, and the conversion efficiency is improved. However, when the thickness exceeds 500 nm, the disappearance of the photogenerated charges 2 that move to the electrode 20 side increases.

The fine groove 1 has a width of about 1 to 500 nm, and the average area per layer 7 in which bulk heterojunctions of a number of island-like structures 9 surrounded by the fine groove 1 are formed is It is preferable that the average area per one of the many island-like structures surrounded by the fine grooves is about 10 to 10,000 nm ² , and among them, the total area of the island-like structures 9 and the total cross-sectional area of the fine grooves 1 However, it is most preferable that the width of the fine groove 1 is 100 to 300 nm and the average area of the island-like structure 9 is 100 to 6500 nm ² .

It is difficult to form an island-like structure 9 in which the width of the fine groove 1 is less than 1 nm or greater than 500 nm, and if it is less than 1 nm, the electric resistance of the electrode 21 is high, and if it is greater than 500 nm, a bulk heterojunction is formed. Further, the ratio of the layer 7 is reduced, the interface where the photogenerated charges 2 are generated is reduced, and the conversion efficiency is lowered. Further, it is technically difficult to make the average area per one of the island structure 9 below 10 nm ^2, the proportion of photo-generated charges 2 disappears before reaching the electrode 21 exceeds 10000 nm ² Get higher.

  As a method of forming such a fine groove 1 having a nanoscale width and a large number of island-like structures 9 surrounded by the fine groove 1, first, on the surface of the layer 7 where the bulk heterojunction is formed, After the island-shaped metal film 3 is formed (see FIG. 2A), the layer 7 in which the bulk heterojunction is formed is etched using the metal film 3 with the island-shaped structure as a mask to make a fine nanoscale width. There is a method of forming a simple groove (see FIG. 2B).

  The island-shaped metal film 3 includes a layer made of tin, indium, bismuth, lead, and alloys thereof, and may be formed by a vacuum deposition method, a sputtering method, an ion plating method, or the like. The thickness is preferably about 10 to 80 nm, and if the light transmittance is measured, the thickness is preferably about 4% to 15%. With the above metal material and appropriate forming means, the island-shaped metal film 3 was formed with the value indicating the light transmittance, and a bulk heterojunction was formed using the island-shaped metal film 3 as a mask. When the layer 7 is etched, the above-described nanoscale-width fine grooves 1 and a large number of island-like structures 9 surrounded by the fine grooves 1 are formed.

  Etching may be performed by any method as long as the layer 7 in which the bulk heterojunction is formed is more easily etched than the metal film 3 having an island-like structure, and an anisotropic etching method is particularly preferable. Anisotropic etching is etching having a property that etching is suppressed with respect to the orientation in the film surface direction, and this makes it possible to dig a fine groove 1 that is thin and deep (high aspect ratio). is there. Specifically, a dry etching method using plasma of oxygen, argon, fluorine gas or the like can be used.

  Note that the island-shaped metal film 3 having the function of a mask may be left as it is, or by selecting a material that can be slightly etched by etching or setting the thickness to be thin, the island-shaped metal film 3 Alternatively, the etching may be performed little by little so that the island-shaped metal film 3 disappears simultaneously with the formation of the fine groove 1.

  Next, an electrode 21 is formed in the formed fine groove 1 (see FIG. 2C). The electrode 20 and the electrode 21 are made of indium tin oxide, zinc oxide, or a transparent conductive film containing silver nanowires or carbon nanotubes on the side on which sunlight is incident. These electrodes may be formed of a metal material such as aluminum, gold, silver, or copper, or an ink containing the metal material.

  The method of forming the electrode 21 in the fine groove 1 and the method of forming the electrode 20 include not only forming the metal material by a method such as vapor deposition, sputtering, and plating, but also ink containing the metal material and their nanowires. And the like by various coating methods such as spin coating and various printing methods such as gravure printing. It is best to form the electrode 21 so as to completely fill the fine groove 1, and a part of the electrode 21 may be covered up to many island-like structures 9.

  Between the electrode 20 and the layer 7 where the bulk heterojunction is formed, a buffer layer such as poly 3,4-ethylenedioxythiophene (PEDOT / PSS) using titanium sulfonic acid as a dopant or titanium oxide. The conversion efficiency can be further improved by adding these layers. Before forming the electrode 21 in the fine groove 1, a buffer layer such as poly 3,4-ethylenedioxythiophene (PEDOT / PSS) using polystyrene sulfonic acid as a dopant in the fine groove 1 or titanium oxide. May be formed very thin.

  The fine groove 1 must be formed within a range of 1 to 100 nm before completely penetrating the layer 7 in which the bulk heterojunction is formed. If the fine groove 1 is completely penetrated, the electrode 20 and the electrode 21 are short-circuited, and if not reaching 100 nm before penetration, the photogenerated charge 2 is lost before reaching the electrode 21 Becomes higher and the conversion efficiency decreases.

  When it is difficult to control the etching of such fine grooves 1, a layer 7 in which bulk heterojunction is formed is formed on a substrate sheet 12 having releasability (see FIG. 3A). A metal film 3 having an island-like structure is formed on the layer 7 where the bulk heterojunction is formed (see FIG. 3B), and a fine groove 1 having a nanoscale width is formed by etching (FIG. 3). (See (c)), electrodes 21 are formed in the fine grooves 1 (see FIG. 3 (d)), and after the respective layers are transferred to the substrate 15 and the base sheet 12 having releasability is peeled off (see FIG. 3) (See (e)), a donor layer, an acceptor layer or a mixture layer of donor and acceptor (whether or not a bulk heterojunction may be formed) 50 is formed on the outermost surface after transfer, and from above You may form by the process (refer FIG.3 (f)) which forms the electrode 20. FIG. .

  A polyethylene terephthalate film with a thickness of 100 μm is used as a base material, an indium tin oxide film is formed as a transparent electrode with a thickness of 200 nm on the surface by sputtering, and an aqueous dispersion of PEDOT / PSS is formed thereon with a coater. After drying, a mixture containing poly-3hexylthiophene (P3HT) as a donor layer and fullerene 60 as an acceptor layer was formed thereon with a coater to a thickness of 200 nm. The formed layer had a bulk heterostructure.

Next, a large number of island-like metal films made of tin and having a thickness of 30 nm were formed by vacuum deposition. The island-shaped metal film had a light transmittance of 10%, the average area of each island was about 1200 nm ² , and a gap of about 10 to 40 nm was formed between the islands. Next, a fine groove is formed by plasma etching using carbon tetrafluoride gas using the above-mentioned many island-like metal films as a mask, and the fine groove completely penetrates the layer in which the bulk heterojunction is formed. Etching was performed up to a range of 50 nm in front. As a result, it was possible to form a large number of fine grooves having a side wall angle of almost vertical, thin, and having a deep aspect ratio of 10 in the layer where the bulk heterojunction was formed.

  Next, a gold film was formed as an electrode in the formed many fine grooves by a vacuum vapor deposition method to obtain an organic thin film solar cell. Unlike the conventional flat electrode structure, the cross section of the organic thin film solar cell has a structure in which the gold electrode is inserted deep into the layer in which the bulk heterojunction is formed, and the conversion efficiency has been remarkably improved. In addition, this structure was almost maintained even in a large area.

  A polyethylene terephthalate film having a thickness of 100 μm was used as a substrate, an aluminum film was formed as an electrode on the surface with a thickness of 800 nm by vacuum vapor deposition, and then a film made of titanium oxide was formed thereon as a buffer layer with a thickness of 500 nm by sputtering. A coating film of a mixture containing zinc-doped phthalocyanine as a donor layer and C70 phenylbutyric acid methyl ester (PC70BM) as an acceptor layer was formed thereon with a coater at a thickness of 150 nm. The formed layer had a bulk heterostructure.

Next, a large number of island-shaped metal films made of indium and having a thickness of 20 nm were formed by vacuum deposition. The island-shaped metal film had a light transmittance of 13%, the average area of each island was about 500 nm ² , and a gap of about 5 to 25 nm was formed between the islands.

  Next, a fine groove is formed by plasma etching using oxygen gas using the above-described many island-like metal films as a mask, and the fine groove completely reaches the layer in which the bulk heterojunction is formed 30 nm before Etching was performed inward. As a result, it was possible to form a large number of fine grooves with a side wall angle of approximately vertical and thin and having a deep aspect ratio of 8 in the layer where the bulk heterojunction was formed.

  Next, a transparent conductive ink containing silver nanowires as electrodes was formed in the formed many fine grooves by a gravure printing method to obtain an organic thin film solar cell. Unlike the conventional flat electrode structure, this organic thin-film solar cell has a structure in which a transparent conductive ink electrode containing silver nanowires is embedded deep into the layer where the bulk heterojunction is formed, and the conversion efficiency is also high. It was much improved. In addition, this structure was almost maintained even in a large area.

  A 25 μm-thick polyethylene terephthalate film coated with a melamine resin is prepared as a substrate sheet having releasability, and poly 3-hexylthiophene (P3HT) is used as a donor on the surface, and C60 phenylbutyric acid methyl ester (PC60BM) is used as an acceptor. A coating solution contained at a weight ratio of 1: 1 was formed with a coater to a thickness of 500 nm. The formed layer had a bulk heterostructure.

Next, a large number of island-shaped metal films made of tin and having a thickness of 50 nm were formed by vacuum evaporation. The island-shaped metal film had a light transmittance of 6%, the average area of each island was about 8000 nm ² , and a gap of about 15 to 60 nm was formed between the islands.

  Next, plasma etching was performed using argon gas using the above-described many island-shaped metal films as a mask, and this treatment was performed until the fine groove penetrated the donor layer and reached the melamine resin layer. As a result, it was possible to form a large number of fine grooves having a side wall angle of almost vertical, thin, and having a deep aspect ratio of 10 in the layer where the bulk heterojunction was formed.

  Next, an indium tin oxide film is formed as a transparent electrode in a fine groove of this bulk heterojunction layer with a thickness of 200 nm by a sputtering method, and a vinyl chloride adhesive layer is formed on the entire surface by gravure printing thereon, The layers were placed on an acrylic plate and heat and pressure were applied to transfer each layer into an acrylic plate shape.

  Next, the substrate sheet having releasability is peeled and removed, and a mixture of poly (3 hexylthiophene) (P3HT) and C70 phenylbutyric acid methyl ester (PC70BM) in a weight ratio of 1: 1 is formed on the exposed outermost surface to a thickness of 30 nm. A film made of titanium oxide as a buffer layer is formed thereon with a thickness of 200 nm by sputtering, and an aluminum film is formed thereon as an electrode with a thickness of 800 nm by vacuum evaporation. A solar cell was obtained.

  Unlike the conventional heterogeneous bulk heterojunction junction structure, the organic thin film solar cell has a structure in which the electrode of the indium tin oxide film is deeply embedded in the layer where the bulk heterojunction is formed, The conversion efficiency was also greatly improved. In addition, this structure was almost maintained even in a large area.

DESCRIPTION OF SYMBOLS 1 Fine groove | channel 2 Photogenerated electric charge 3 Metal film 5 Organic thin-film solar cell 7 Layer in which the bulk heterojunction was formed 9 Numerous island-like structure 12 Base sheet 14 with a releasability 14, 15 Base material 20, 21 Electrode 50 Donor layer, acceptor layer or donor-acceptor mixture layer (with or without a bulk heterojunction formed)
51 light

Claims (4)

  Forming a layer having a bulk heterojunction formed by a donor and an acceptor on a substrate sheet having releasability, and forming an island-shaped metal film on the layer having the bulk heterojunction formed; Etching the layer where the bulk heterojunction is formed using the metal film as a mask to form a fine groove penetrating the nanoscale width, forming an electrode in the fine groove, and then transferring each layer to the substrate A method for producing an organic thin-film solar cell, comprising peeling off a substrate sheet having releasability and forming any of a donor layer, an acceptor layer, or a mixture layer of a donor and an acceptor on the outermost surface after transfer.   The method for producing an organic thin-film solar cell according to claim 1, wherein the island-shaped metal film is made of any one of tin, indium, bismuth, lead, and alloys thereof. The width of the fine grooves is 1 to 500 nm, an organic according to claim 1 or claim 2 average area per one of the plurality of islands surrounded by the fine grooves is 10 to 10,000 nm ² Manufacturing method of thin film solar cell. A layer in which a bulk heterojunction by a donor and an acceptor is formed is formed on a substrate sheet having releasability, and an island-shaped metal film is formed on the layer in which the bulk heterojunction by a donor and an acceptor is formed. A transfer sheet formed by etching the layer on which the bulk heterojunction is formed using the metal film as a mask to form fine grooves penetrating the nanoscale width, and forming electrodes in the fine grooves .

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