JP5561721B2 - Manufacturing method of organic thin film solar cell and transfer sheet used therefor - 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 bulk heterojunction structure 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, and a junction interface between a donor and an acceptor is formed. Attempts have been made to increase the photogenerated charge of organic thin-film solar cells by increasing the device.

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, in the bulk heterojunction structure by the phase separation of the mixture of donor and acceptor, the distribution of donor and acceptor is non-uniform, and the degree of non-uniformity tends to increase as the area of the solar cell increases. For this reason, there has been a problem that high conversion efficiency cannot be achieved as the variation among product lots increases and the area of the solar cell increases.

The present invention forms a donor or acceptor layer on a substrate sheet having releasability, and nanoimprints the nanoscale-width fine groove or nanoscale-sized island structure penetrating the donor or acceptor layer. Are formed, and after filling the other groove of the fine groove or island-like structure with the other donor or acceptor layer and forming an electrode thereon, the layers are transferred to the substrate of the solar cell, The other electrode is formed on the outermost surface after transfer . A method for producing an organic thin-film solar cell.

  The organic thin-film solar cell production method of the present invention is a method for forming a donor or acceptor layer on a substrate sheet having releasability and performing nanoimprint processing to penetrate the donor or acceptor layer with a fine nanoscale width. After forming grooves or nano-sized island-shaped depressions, filling the fine grooves or island-shaped depressions with the other donor or acceptor layer, forming electrodes from above, and then forming each layer It transfers to the base material of a solar cell, and the other electrode is formed in the outermost surface after transfer. Therefore, there is an effect that an organic thin-film solar cell that achieves high conversion efficiency penetrating the donor or acceptor layer can be produced.

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) is a nanoimprint process using an imprint type | mold, and a nanoscale width | variety is finely formed in the layer of a donor or an acceptor. A step of forming a groove is shown, and (b) shows a step of filling the fine groove with the other donor or acceptor layer. 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 process of forming the layer of a donor or an acceptor on the base sheet which has mold release property, (b ) Shows a step of nanoimprinting the donor or acceptor layer, (c) shows a step in which a fine groove having a nanoscale width penetrating the donor or acceptor layer is formed, and (d) Shows a step of filling the other groove of the fine groove or island-like structure with the other donor or acceptor layer, and (e), after forming an electrode from the upper layer, each layer is formed on the substrate of the solar cell. (F) shows the process of forming the other electrode on the outermost surface after the transfer. It is a schematic cross section which shows one Example of the manufacturing method of the imprint type | mold base material used for manufacture of the organic thin film solar cell of this invention, (a) is ionizing radiation solubilization on the base material of an imprint type | mold base material (B) shows a step of forming an island-shaped metal film on the ionizing radiation solubilized layer, and (c) shows irradiation with ionizing radiation using the metal film as a mask. And a step of solubilizing a part of the ionizing radiation-solubilized layer, (d) is a step of removing a part of the solubilized ionizing radiation-solubilized layer, thereby removing a recess of a nanoscale width groove. The process which formed was shown.

  The organic thin film solar cell 5 formed by the method of manufacturing an organic thin film solar cell of the present invention is subjected to nanoimprint processing using an imprint mold 30 so that a large number of island-like structures 9 are formed on the surface of the donor or acceptor layer 7. A fine groove 1 having a nanoscale width surrounding the fine groove 1 is formed (see FIG. 1A), and the fine groove 1 is filled with the other donor or acceptor layer 8 (see FIG. 1). b)). Electrodes 20 and 21 are formed on the other surfaces of the donor or acceptor layers 7 and 8 for taking out photogenerated charges and turning them into currents.

  Examples of the material of the donor layer 7 or 8 include cross-linked polythiophene, poly-3-hexylthiophene (P3HT), and a phthalocyanine derivative. Examples of the material of the acceptor layer 7 or 8 include fullerene derivatives such as PCBM and PCPDTBT, and oxidation. Although zinc etc. are mentioned, it is not limited to these.

  Examples of the method for forming the donor or acceptor layer 7 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 of the solar cell on which the electrode 20 is formed. The thickness of the donor or acceptor layer 7 is preferably about 50 to 150 nm. The thicker the thickness, the larger the interface where the photogenerated charges are generated. However, when the thickness is 100 nm or more, the rate at which the photogenerated charges disappear before reaching the electrode increases, and when the thickness is 150 nm or more, the conversion efficiency decreases.

  The method of forming the fine grooves 1 having a nanoscale width and a large number of island structures 9 surrounded by the fine grooves 1 is obtained by reversing the shapes of the desired fine grooves 1 and the large number of island structures 9. The imprint mold 30 is prepared, set on the donor or acceptor layer 7, and formed by a so-called room-temperature nanoimprint method or thermal nanoimprint method that is pressed at a constant pressure while applying room temperature or heat. Alternatively, if the donor or acceptor layer 7 can be made into an ultraviolet curable type, it may be formed by a so-called UV nanoimprint method in which the donor or acceptor layer 7 is hardened by being pressed with a slightly weak pressure and irradiated with ultraviolet rays to have a predetermined shape.

The fine grooves 1 have a width of about 1 to 50 nm, and the average area of each of the donor or acceptor layers 7 of a large number of island-like structures 9 surrounded by the fine grooves 1 is about 10 to 500 nm ^2. Among them, the total area of the island-like structure 9 and the total cross-sectional area of the fine groove 1 are approximately the same, that is, the width of the fine groove 1 is 5 to 30 nm, and the average area of the island-like structure 9 is 100 to 300 nm. ² is most preferable.

In order to make the width of the fine groove 1 less than 1 nm, it is necessary to make the width of the convex portion 38 of the imprint mold 30 less than 1 nm, which causes a problem that the strength and durability of the imprint mold 30 are insufficient. If the width of 1 is made larger than 50 nm, the number of interfaces where photogenerated charges are generated decreases, and the rate at which photogenerated charges disappear is increased. Further, it is necessary to the size of the convex portion of the island-like structure of the imprint mold base material 31 to be described below to the average area per one of the island structure 9 below 10 nm ² to less than 10 nm ² imprint type There arises a problem that the strength and resistance of the base material 31 are insufficient, and when the thickness exceeds 500 nm ² , the interface where the photogenerated charges are generated decreases, and the rate at which the photogenerated charges disappear is increased.

  As a method for producing an imprint base material 31 having a shape obtained by inverting the shapes of desired fine grooves 1 and a large number of island-like structures 9, first, an imprint base material 32 is prepared. An ionizing radiation solubilized layer 35 is formed on the substrate 32 of the printed mold base (see FIG. 3A), and a number of island-shaped metal films 3 are formed on the ionizing radiation solubilized layer 35. (See FIG. 3 (b)), the ionizing radiation 33 is irradiated with the metal film 3 as a mask to solubilize a part of the ionizing radiation solubilized layer 35 (see FIG. 3 (c)) and solubilized. A method of forming a concave portion 37 of a groove having a nanoscale width by peeling and removing a part of the ionizing radiation solubilized layer 35 (see FIG. 3D) can be mentioned. The imprint mold 30 having the convex portions 38 obtained by inverting the shape of the imprint mold base material 31 is obtained by a method such as nickel electroforming with respect to the obtained imprint mold base material 31.

  Alternatively, an ionizing radiation cured layer is formed instead of the ionizing radiation solubilized layer 35, and the ionizing radiation cured layer is cured by irradiating the ionizing radiation 33, and the uncured ionizing radiation cured layer other than the cured portion is cured. The method of forming the recessed part of an island-like structure of nanoscale size by peeling and removing is mentioned. In this case, a method such as nickel electroforming may be repeated twice, or the imprint mold base material 31 itself may be used as it is as the imprint mold 30.

  Alternatively, a method of forming a recess of a nanoscale width groove by forming a layer to be etched instead of the ionizing radiation solubilizing layer 35 and performing anisotropic etching described later using a metal film having an island-like structure as a mask Etc. If the base material 32 of the imprint base material itself has ionizing radiation solubilization, ionizing radiation curing or etching characteristics, the ionizing radiation solubilization layer 35 and the like are omitted, and The metal film 3 having an island-like structure may be directly formed on the base material 32 and processed.

  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 5 to 60 nm, and if the light transmittance is measured, the thickness is preferably about 7% to 20%. The island-shaped metal film 3 is formed with the above metal material and an appropriate forming means with the value indicating the light transmittance, and the island-shaped metal film 3 is used as a mask to ionize radiation-solubilizing layer and ionizing radiation. If the hardened layer, the layer to be etched, etc. are patterned, the above-described fine groove recesses having a nanoscale width or nanoscale island-shaped recesses are formed. The island-shaped metal film 3 having the function of a mask may be left as it is after peeling or etching, or may be set to disappear by peeling or etching.

  Examples of the ionizing radiation solubilizing layer 35 include acrylic, pyrimidine, and novolak resists. Examples of the method for forming the ionizing radiation solubilizing layer 35 include general-purpose printing methods such as gravure printing, dipping, coater, and coating. The thickness is preferably about 0.02 to 2 μm. For the peeling of the ionizing radiation solubilized layer 35, an organic solvent such as toluene is used.

  Examples of the ionizing radiation-cured layer include resists such as calixarene. The formation method and thickness of the ionizing radiation cured layer may be the same method as the ionizing radiation solubilized layer 35. For removing the uncured ionizing radiation-cured layer, an organic solvent such as toluene can be used. Examples of ionizing radiation include visible light, ultraviolet light, infrared light, electron beam, X-ray, and gamma ray.

  Examples of the layer to be etched include acrylic, vinyl, polyester, polyamide, and urethane polymers. The formation method and thickness of the layer to be etched may be the same as that of the ionizing radiation solubilized layer 35. Etching may be a method in which the etched layer is more easily etched than the metal film 3 having an island-like structure, and an anisotropic etching method is particularly preferable. Anisotropic etching refers to the orientation in the film surface direction. This is because the etching has such a property that the etching is suppressed, and this makes it possible to dig a thin and deep (high aspect ratio) fine groove 1. Specifically, a dry etching method using plasma of oxygen, argon, fluorine gas or the like can be used.

  By nanoimprinting using the imprint mold 30 created as described above, a large number of island-like structures 9 and nanoscale-width fine grooves 1 surrounding the island-like structure 9 are formed on the surface of the donor or acceptor layer 7, and The fine groove 1 is filled with the other donor or acceptor layer 8. The material of the other donor or acceptor layer 8 may be the same as the material of the donor or acceptor layer 7 mentioned above. However, of course, if the aforementioned layer 7 is a donor, it is the acceptor layer 8 that fills the fine groove 1, and if the aforementioned layer 7 is an acceptor, the fine groove 1 is filled by the donor layer. 8

  As a method for filling the fine groove 1 with the other donor or acceptor layer 8, various coating methods such as spin coating, various printing methods such as gravure printing, and other methods such as vapor deposition and sputtering are listed. It is done. The filling of the other donor or acceptor layer 8 is most preferably just to fill the fine groove 1, and a part may be covered up to a number of island-like structures 9. However, when the thickness of the island-like structure 9 covered exceeds several tens of nm, the conversion efficiency may be lowered.

  An electrode 20 is formed below the donor or acceptor layer 7 and an electrode 21 is formed on the other donor or acceptor layer 8. 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 material such as aluminum, gold, silver, or copper. Further, between the electrode 20 and the donor, poly 3,4-ethylenedioxythiophene (PEDOT / PSS) using polystyrene sulfonic acid as a dopant, and between the electrode 21 and the acceptor layer 8 such as titanium oxide A buffer layer may be provided, and the conversion efficiency is further improved by adding these layers.

  The fine groove 1 may completely penetrate the donor or acceptor layer 7 or may be up to the middle of the layer. However, if it is attempted to penetrate completely with the above-described configuration, the convex portion 38 of the imprint mold 30 must be inserted not only into the donor or acceptor layer 7 but also into a part of the electrode 20 during the nanoimprint processing. Therefore, there is a problem that the electrode 20 is damaged. Accordingly, when forming the fine groove 1 completely penetrating the donor or acceptor layer 7, the donor or acceptor layer 7 is formed on the substrate sheet 12 having releasability (see FIG. 2A). Nanoimprinting the donor or acceptor layer 7 (see FIG. 2 (b)), forming nanoscale-width fine grooves that penetrate the donor or acceptor layer 7 (see FIG. 2 (c)), After filling the other groove or island-shaped concave portion with the other donor or acceptor layer 8 (see FIG. 2 (d)) and forming the electrode 21 thereon, each of the layers is formed into a solar cell substrate. 14 is peeled off (see FIG. 2 (e)), and the other electrode 20 is formed on the outermost surface after the transfer (see FIG. 2 (f)). Prefer to do .

  In this method, even if the convex portion 38 of the imprint mold 30 is inserted not only into the donor or acceptor layer 7 but also to a part of the substrate sheet 12 having releasability, the electrode 20 is not formed at that time, Then, since the electrode 20 is formed, the problem that the electrode 20 is damaged does not occur. The structure thus obtained is close to an ideal upright superlattice structure and can exhibit high conversion efficiency. Examples of the base sheet 12 having releasability include a polyester film coated with a fluoroacrylic resin having releasability and thermoformability, and a fluoroacrylic coextruded film.

  A polyethylene terephthalate film having a thickness of 25 μm is prepared as a base material for an imprint base material, and an ionizing radiation solubilized layer mainly composed of a 2,4-dichloropyrimidine derivative is gravured on the base material for the imprint base material. A thickness of 0.2 μm was formed by a printing method, and a large number of island-like metal films made of tin and having a thickness of 10 nm were formed on the ionizing radiation solubilized layer by a vacuum deposition method. Next, an electron beam was irradiated using the metal film as a mask to solubilize a part of the ionizing radiation solubilized layer, and the solubilized portion was peeled and removed with an organic solvent containing toluene as a main component.

The imprint base material thus obtained was formed with concave portions of fine grooves with a width of about 20 nm, and the convex portions had a large number of island structures with an average area of about 300 nm ^2. Copper is vacuum-deposited on the entire surface of the material, and then by nickel electroforming, a large number of island-shaped concave portions having an average area of about 300 nm ² and a width of about 20 nm surrounding it are obtained by reversing the shape of the imprint base material. Thus, a sheet-like imprint mold having a convex portion with a height of about 150 nm was obtained.

  On the other hand, a polyethylene terephthalate film having a thickness of about 100 μm obtained by gravure printing on the surface with a fluoroacrylic resin having a thickness of about 1 μm is used as a substrate sheet having releasability. ) With a coater to a thickness of 100 nm. Next, the sheet-like imprint mold was placed on the donor layer and pressed at a pressure of 2 atm while being heated to 80 ° C. to laminate the sheet-like imprint mold. When the sheet-like imprint mold was peeled off after being allowed to cool, a large number of fine grooves having a width of about 20 nm reaching the fluoroacrylic resin layer through the donor layer were formed.

  Next, fullerene 60 was filled as an acceptor layer into the formed many fine grooves by a vacuum deposition method. Next, a film made of titanium oxide as a buffer layer is formed on the acceptor layer with a thickness of 200 nm by sputtering, and an aluminum film is formed as an electrode with a thickness of 800 nm on the acceptor layer by vacuum evaporation, on which a vinyl chloride system is formed. The adhesive layer was formed on the entire surface by gravure printing, 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, an aqueous dispersion of PEDOT / PSS is formed on the exposed outermost surface with a coater, and after drying, an indium tin oxide film is sputtered thereon as a transparent electrode With a thickness of 200 nm, an organic thin film solar cell was obtained. The cross section of this organic thin-film solar cell is an almost super-ideal nanostructure with an upright superlattice structure in which the donor layer and the acceptor layer completely penetrate both electrodes, and the conventional non-uniform bulk heterojunction junction structure Unlikely, the conversion efficiency was also greatly improved. In addition, this structure was almost maintained even in a large area.

  A polyethylene terephthalate film having a thickness of 25 μm is prepared as a base material for an imprint base material, and an ionizing radiation cured layer mainly composed of chloromethylated calixarene is formed on the base material of the imprint base material by a gravure printing method. A plurality of island-shaped metal films made of indium and having a thickness of 5 nm were formed on the ionizing radiation-cured layer using a vacuum deposition method. Next, an electron beam was irradiated using the metal film as a mask to cure a part of the ionizing radiation-cured layer, and an ineffective portion was peeled and removed with an organic solvent containing toluene as a main component.

The imprint base material obtained above was formed with concave portions of fine grooves with a width of about 30 nm, and the convex portions had a large number of island structures with an average area of about 200 nm ^2. the copper was vacuum-deposited on the entire surface against the timber, followed by nickel electroforming, the recess and the width 30nm approximately surrounding the said imprint basic material a number of islands average area of about 200 nm ² of the shape obtained by inverting the Thus, a sheet-like imprint mold having a convex portion with a height of about 170 nm was obtained.

  On the other hand, a fluoroacrylic film having a thickness of 100 μm was used as a substrate sheet having releasability, and a coating film containing C70 phenylbutyric acid methyl ester (PC70BM) as an acceptor layer was formed on the surface thereof with a coater to a thickness of 100 nm. Next, the sheet-like imprint mold was placed on the acceptor layer and pressed at a pressure of 5 atm while being heated to 50 ° C. to laminate the sheet-like imprint mold. When the sheet-like imprint mold was peeled off after standing cooling, a large number of fine grooves having a width of about 40 nm that penetrated through the acceptor layer and reached the fluoroacrylic film were formed.

  Next, the formed fine grooves were filled with a coating solution in which zinc-doped phthalocyanine was dissolved in dibutyl ether as a donor layer and dried. A transparent conductive ink containing silver nanowires as a transparent electrode is formed thereon with a thickness of 500 nm by gravure printing, and a vinyl chloride adhesive layer is formed on the entire surface by gravure printing thereon and placed on an acrylic plate, The layers were transferred to an acrylic plate by applying heat and pressure.

  Next, the substrate sheet having releasability is peeled and removed, a film made of titanium oxide is formed as a buffer layer on the exposed outermost surface with a thickness of 500 nm by a sputtering method, and an aluminum film as an electrode is vacuum-deposited thereon. The organic thin film solar cell was obtained with a thickness of 800 nm. The cross section of this organic thin-film solar cell is an almost super-ideal nanostructure with an upright superlattice structure in which the donor layer and the acceptor layer completely penetrate both electrodes, and the conventional non-uniform bulk heterojunction junction structure Unlikely, the conversion efficiency was also greatly improved. In addition, this structure was almost maintained even in a large area.

  A 25 μm-thick polyethylene terephthalate film is prepared as a base material for an imprint base material, and an etching target layer mainly composed of a vinyl chloride vinyl acetate copolymer resin is formed on the base material for the imprint base material. Then, a large number of island-like metal films made of tin and having a thickness of 60 nm were formed on the layer to be etched using a vacuum deposition method. Next, reactive etching using argon plasma was performed using the metal film as a mask.

The imprint base material thus obtained was formed with concave portions of fine grooves having a width of about 7 nm, and the convex portions had a large number of island structures with an average area of about 500 nm ^2. Copper is vacuum-deposited on the entire surface of the material, then nickel electroforming is used to invert the shape of the imprint base material, and an average area of about 500 nm ^{2 and} a plurality of island-shaped recesses and a width of about 7 nm surrounding it. Thus, a sheet-like imprint mold having a convex portion having a height of about 80 nm was obtained.

  On the other hand, an indium tin oxide film having a thickness of 200 nm is formed as a transparent electrode on an acrylic plate by sputtering, and an aqueous dispersion of PEDOT / PSS is formed thereon with a coater. After drying, a donor layer is formed thereon. Zinc-doped phthalocyanine was filled with a coating solution dissolved in dibutyl ether and dried. Next, the sheet-like imprint mold was placed on the donor layer and pressed at a pressure of 3 atm while being heated to 60 ° C. to laminate the sheet-like imprint mold. When the sheet-shaped imprint mold was peeled off after standing cooling, a large number of fine grooves having a depth of about 60 nm and a width of about 8 nm were formed in the donor layer.

  Next, fullerene 60 was filled as an acceptor layer into the formed many fine grooves by a vacuum deposition method. Next, a film made of titanium oxide as a buffer layer is formed on the acceptor layer with a thickness of 200 nm by a sputtering method, and an aluminum film is formed thereon as an electrode with a thickness of 800 nm by a vacuum evaporation method to obtain an organic thin film solar cell. It was. In the cross section of this organic thin film solar cell, the portion where the donor layer and the acceptor layer are mixed has a PIN structure of 60 nm, and the conversion efficiency is significantly improved compared to the conventional one. In addition, this structure was almost maintained even in a large area.

DESCRIPTION OF SYMBOLS 1 Fine groove | channel 3 Metal film 5 Organic thin film solar cell 7 Donor or acceptor layer 8 The other donor or acceptor layer 9 Numerous island structure 12 Base sheet having releasability 14 Solar cell base material 20, 21 Electrode 30 Imprint type 31 Imprint type base material 32 Base material of imprint type base material 33 Ionizing radiation 35 Ionizing radiation solubilized layer 37 Concave portion of nanoscale width groove 38 Imprint type convex portion

Claims (2)

  A donor or acceptor layer is formed on a releasable substrate sheet, and nanoimprint processing is performed to form a nanoscale-width fine groove or a nanoscale-sized island-shaped recess that penetrates the donor or acceptor layer. Then, after filling the other groove of the fine groove or the island structure with the other donor or acceptor layer and forming an electrode from the upper layer, the layer is transferred to the substrate of the solar cell, and after the transfer, A method for producing an organic thin-film solar cell, wherein the other electrode is formed on the surface. A layer of the donor or acceptor is formed on a substrate sheet having releasing property, recess nanoimprint processed into an island-like structure of the donor or nanoscale fine grooves or nanoscale size width through the layer of acceptor form A transfer sheet in which the minute groove or the recess of the island structure is filled with the other donor or acceptor layer, and an electrode is formed thereon .

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