JP2015076557A - Method of manufacturing organic thin-film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method enabling an organic thin-film solar cell with improved efficiency to be inexpensively and easily manufactured.SOLUTION: A method of manufacturing an organic thin-film solar cell 1 includes a film formation step (a step S104) and an electrophoresis step (a step S105). In the film formation step, a layer of a p-type organic semiconductor 12 (an electron donating layer 5) and a layer of an n-type organic semiconductor 11 (an electron accepting layer 4) are formed. In the electrophoresis step, in a state in which the electron accepting layer 4 and the electron donating layer 5 formed in the film formation step are not completely dried, an electric field is applied to the layers. In the electrophoresis step, the n-type organic semiconductor 11 in solution is electrically charged.

Description

  The present invention relates to a method for producing an organic thin film solar cell.

  Organic thin-film solar cells have many features such as being lightweight, low-cost and capable of being enlarged, and can be formed on flexible curved surfaces (or spherical surfaces). It is attracting attention as a battery. However, since the organic thin-film solar cell has a lower conversion efficiency than a conventional silicon solar cell, higher efficiency is desired.

  FIG. 10A is a schematic diagram showing a configuration of a conventionally known pn heterojunction type organic thin film solar cell 30. The organic thin film solar cell 30 is formed by laminating an electron donating layer 21 made of a p-type organic semiconductor 20 and an electron accepting layer 23 made of an n-type organic semiconductor 22 on a glass substrate 24 by an appropriate method such as coating or vapor deposition. Formed. An anode 25 made of a transparent electrode such as ITO is provided between the glass substrate 24 and the electron donating layer 21. A cathode 26 made of an electrode such as aluminum is provided on the electron accepting layer 23.

When light is incident on the organic thin film solar cell 30 thus formed from the glass substrate 24 side, the molecules of the electron donating layer 21 are mainly excited by absorbing the light, and excitons D ^* are generated. When the exciton D ^* reaches the interface (pn junction interface) between the electron donating layer 21 and the electron accepting layer 23, it passes electrons to the electron accepting layer 23 and becomes a cation D ⁺ (hole). On the other hand, the molecules of the electron-accepting layer 23 that have received electrons become anions A ⁻ . Then, holes D ⁺ generated at the pn junction interface move to the anode 25, and electrons of the anion A ⁻ move to the cathode 26, thereby generating a potential difference between the two electrodes.

In an organic thin film solar cell, it is known that the exciton D ^* after light absorption has a short lifetime and its diffusion distance is as short as several tens of nanometers. For this reason, among the excitons D ^* generated when the organic semiconductor absorbs light, those other than the excitons generated very close to the pn junction interface are deactivated before reaching the pn junction interface. Will disappear. This is cited as one of the reasons why the efficiency of the organic thin film solar cell is poor.

  Therefore, a bulk heterojunction type organic thin film solar cell 31 shown in FIG. 10B has been proposed and widely studied. In this configuration, a mixed layer 27 in which the p-type organic semiconductor 20 and the n-type organic semiconductor 22 are mixed is formed between the anode 25 and the cathode 26. As shown in FIG. 10B, in the mixed layer 27, the p-type organic semiconductor 20 and the n-type organic semiconductor 22 are filled at random. Since the bulk heterojunction type organic thin film solar cell 31 has an increased area at the pn junction interface as compared with the pn heterojunction type organic thin film solar cell 30 of FIG. It becomes easy to reach the pn junction interface, and the conversion efficiency can be improved.

  However, since the p-type organic semiconductor 20 and the n-type organic semiconductor 22 are randomly mixed, the bulk heterojunction type organic thin film solar cell 31 does not necessarily have an optimal structure from the viewpoint of charge transfer. For example, as shown in FIG. 10B, when the p-type organic semiconductor 20 is in an island shape (in a state isolated from the anode 25) in the n-type organic semiconductor 22, holes in the p-type organic semiconductor 20 are formed. The path to the anode 25 is interrupted on the way. As described above, the bulk heterojunction type organic thin film solar cell 31 has a problem in that the current does not flow smoothly because the charge transfer path may be interrupted, and there is a limit to increase the efficiency.

  Therefore, as shown in FIG. 10C, an organic thin-film solar cell 32 having an interpenetrating junction structure in which a p-type organic semiconductor 20 and an n-type organic semiconductor 22 are interleaved with each other is considered ideal. Yes. If this structure can be realized, it is possible to increase the area of the pn junction interface and secure a movement path to the electron and hole electrodes generated at the interface, so that significant improvement in the efficiency of the organic thin-film solar cell can be expected. . However, in order to actually form the organic thin film solar cell 32 having such an ideal structure, there are technical and cost problems, and an inexpensive and simple manufacturing method is required.

  Several methods for forming a comb structure (uneven structure) as shown in FIG. 10C at the interface between organic semiconductors have been proposed. For example, Patent Document 1 discloses a method of forming an uneven pattern on the surface of an organic semiconductor layer by nanoimprinting.

  Patent Document 2 relates to a dye-sensitized solar cell, and discloses a method of etching a semiconductor surface by laser light interference fringes in an electrolyte as a method of forming irregularities on the surface of a dye-carrying semiconductor layer. doing.

JP 2009-88045 A JP-A-7-176773

  In the case of forming irregularities on the surface of the organic semiconductor by the nanoimprint method as in Patent Document 1, a nanoimprint mold is necessary. For this reason, when manufacturing a large-sized organic thin-film solar cell, since a big nanoimprint metal mold | die is needed, it becomes a factor of manufacturing cost increase. Moreover, in the manufacturing method of patent document 1, since an unevenness | corrugation must be formed by nanoimprint and a photoelectric converting layer must be formed along an unevenness | corrugation after that, simple film-forming methods, such as a spray method and a spin coat method, cannot be utilized. . Patent Document 1 discloses a method of forming a photoelectric conversion layer by an alternate adsorption method, but the alternate adsorption method takes time and causes an increase in manufacturing cost. Note that Patent Document 1 discloses that a vacuum vapor deposition method may be used for film formation of the photoelectric conversion layer, but the vacuum vapor deposition method is expensive and has a large apparatus.

  The etching process by laser melting of laser interference fringes disclosed in Patent Document 2 cannot be used for organic semiconductors. In addition to this, Patent Document 2 describes that irregularities can be formed in the semiconductor layer by mechanical processing, chemical processing, electrochemical processing, electron beam processing, ion beam processing, plasma processing, and the like. There is no specific description of this processing method, and it is unclear whether it can be applied to uneven processing on the surface of an organic semiconductor.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a manufacturing method that can easily and inexpensively manufacture an organic thin film solar cell with improved efficiency.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

  According to the viewpoint of this invention, the manufacturing method of an organic thin film solar cell is provided as follows. That is, this manufacturing method includes a film forming process and an electrophoresis process. In the film forming step, a p-type organic semiconductor layer and an n-type organic semiconductor layer, or a layer in which both are mixed is formed. In the migration step, an electric field is applied to the layer in a state where the layer formed in the film formation step is not completely dried. In the migration step, at least one of the p-type organic semiconductor and the n-type organic semiconductor is charged.

  In the present specification, “the organic semiconductor layer is not completely dried” refers to a state in which at least a part of the organic semiconductor constituting the layer is dissolved in some solvent.

  In this manner, by charging the organic semiconductor and applying an electric field after the film formation, the organic semiconductor can be migrated to form an organic semiconductor layer having a desired structure.

  In the method for manufacturing the organic thin film solar cell, a non-uniform electric field may be applied in the migration step.

  In this way, by applying a non-uniform electric field, the distance at which the organic semiconductor migrates can be varied depending on the strength of the electric field. Therefore, an organic semiconductor layer having a desired structure can be formed by applying an electric field with strength and weakness.

  According to another viewpoint of this invention, another manufacturing method of an organic thin-film solar cell is provided as follows. That is, this manufacturing method includes a film forming process and an electrophoresis process. In the film forming step, a p-type organic semiconductor layer and an n-type organic semiconductor layer, or a layer in which both are mixed is formed. In the migration step, a magnetic field is applied to the layer in a state where the layer formed in the film formation step is not completely dried. In the migration step, a magnetic material is added to either the p-type organic semiconductor or the n-type organic semiconductor.

  Thus, if a magnetic substance is added to an organic semiconductor, the organic semiconductor can be migrated by applying a magnetic field to form an organic semiconductor layer having a desired structure.

  In the method of manufacturing the organic thin film solar cell, in the film forming step, the p-type organic semiconductor solution and the n-type organic semiconductor solution are stacked and applied to form the p-type organic semiconductor layer and the n-type organic semiconductor layer. It is preferable to form an organic semiconductor layer.

  As described above, the p-type organic semiconductor layer and the n-type organic semiconductor solution are layered and applied, and an electric field (or magnetic field) is applied to migrate the organic semiconductor, whereby the p-type organic semiconductor layer and the n-type organic semiconductor are moved. The interface of the semiconductor layer can be raised. Thereby, since unevenness | corrugation is formed in the said interface, the organic thin-film solar cell of an ideal structure can be manufactured.

  In the method of manufacturing the organic thin film solar cell, in the film formation step, a mixed solution of the p-type organic semiconductor and the n-type organic semiconductor is applied to mix the p-type organic semiconductor and the n-type organic semiconductor. A layer may be formed.

  As described above, by applying an electric field (or magnetic field) to the liquid mixture of the p-type organic semiconductor and the n-type organic semiconductor to cause migration, the interface shape of the p-type organic semiconductor and the n-type organic semiconductor in the liquid mixture is changed. Can be made. Further, in the bulk heteroconnection structure that has been randomly dispersed in the past, the p-type organic semiconductor and the n-type organic semiconductor can be brought to one side, so that a charge transfer path is easily formed. Thereby, the organic thin-film solar cell of an ideal structure can be manufactured.

The typical sectional view showing the composition of the organic thin film solar cell manufactured by the manufacturing method of the present invention. The flowchart figure of the manufacturing method of 1st Embodiment. The figure explaining the manufacturing method of 1st Embodiment. The figure which shows the modification of 1st Embodiment. The figure which shows another modification of 1st Embodiment. The figure which shows another modification of 1st Embodiment. The figure explaining the manufacturing method of 2nd Embodiment. The figure explaining the modification of 2nd Embodiment. The figure explaining the manufacturing method of 3rd Embodiment. The figure explaining the structure of an organic thin-film solar cell.

  Next, a first embodiment of the present invention will be described. FIG. 1 is a schematic cross-sectional view showing a configuration of an organic thin-film solar cell 1 manufactured by the manufacturing method according to the first embodiment of the present invention. In the following description, expressions such as “upper” and “lower” may be used, which means the vertical direction in the drawings for convenience of description, such as the arrangement direction of the organic thin-film solar cell 1 and the like. It is not intended to limit.

  As shown in FIG. 1, the organic thin film solar cell 1 has a configuration in which a substrate 2, a cathode 3, an electron accepting layer 4, an electron donating layer 5, and an anode 6 are laminated in this order.

  The substrate 2 is configured as a plate-like or thin-film member made of a transparent material that transmits light. The substrate 2 of the present embodiment is a glass substrate, but the material of the substrate 2 is not limited to glass. Moreover, although the board | substrate 2 shown in FIG. 1 is comprised by flat form, it may be comprised not only in this but in the shape of a curved surface (or spherical shape). By making the substrate 2 curved (or spherical), the entire organic thin-film solar cell 1 can be formed into a curved surface (or spherical). Further, for example, by using the substrate 2 as a flexible material, the entire organic thin-film solar cell 1 can be configured flexibly.

  The cathode 3 of the organic thin film solar cell 1 is composed of a conductive transparent electrode having a high light transmittance. In the field of organic thin-film solar cells, ITO (Indium Tin Oxide) is generally used as a transparent electrode, so the cathode 3 of this embodiment is also made of ITO. However, the material of the cathode 3 is not particularly limited to this. The cathode 3 is formed as a thin film layer parallel to the upper surface of the substrate 2. Although not shown, the cathode 3 is patterned so as to form an appropriate pattern on the substrate 2.

  In addition, from the viewpoint of preventing a short circuit between the electron-accepting layer 4 and the electron-donating layer 5 formed on the cathode 3, the upper surface of the cathode 3 of this embodiment is formed smoothly. However, the present invention is not limited to this, and some unevenness may be formed on the surface of the cathode 3.

  An electron accepting layer 4 made of an n-type organic semiconductor (electron acceptor) 11 is formed in a thin film on the upper surface of the cathode 3 (the surface opposite to the substrate 2). As the n-type organic semiconductor 11, perylene diimide derivatives, perfluoroacenes, fullerenes, fullerene derivatives, and the like can be used.

  An electron donating layer 5 made of a p-type organic semiconductor (electron donor) 12 is formed in a thin film on the upper surface of the electron accepting layer 4 (the surface opposite to the cathode 3). As the p-type organic semiconductor 12, π electron donating polymers such as acenes, phthalocyanines, polythiophenes, rubrene, triarylamines and the like can be used.

  In addition, as an organic semiconductor, it is not limited to what was illustrated, Organic-semiconductor materials other than this can also be used. However, in this embodiment, since the electron-accepting layer 4 and the electron-donating layer 5 are formed by coating, the n-type organic semiconductor 11 and the p-type organic semiconductor 12 may be a high-molecular organic semiconductor material that can be used in a solvent. preferable.

  On the upper surface of the electron donating layer 5 (surface opposite to the electron accepting layer 4), the anode 6 of the organic thin film solar cell 1 is formed in a thin film shape. The material of the anode 6 is not particularly limited, but the anode 6 of this embodiment is an aluminum electrode.

  As shown in FIG. 1, the organic thin-film solar cell 1 of the present embodiment has an uneven portion 17 in which the interface between the electron accepting layer 4 and the electron donating layer 5 is uneven and interleaved in a comb shape. Is formed. Thus, the organic thin-film solar cell 1 of this embodiment has a structure close to the interpenetrating junction (FIG. 10C), which is an ideal structure. Thereby, the organic thin film solar cell 1 of this embodiment can implement | achieve high conversion efficiency.

  Then, the manufacturing method of said organic thin film solar cell 1 is demonstrated, referring FIG.2 and FIG.3.

  First, ITO is vapor-deposited on the surface of the glass substrate 2 to form the cathode 3 (step S101, substrate preparation step). The cathode 3 is patterned so as to have a predetermined wiring pattern.

  Subsequently, the substrate 2 on which the cathode 3 is formed is cleaned (step S102, substrate cleaning process). In the cleaning method, for example, the substrate 2 on which the cathode 3 is formed is immersed in a detergent diluent and subjected to ultrasonic treatment, and then rinsed with ultrapure water and dried. This may be followed by UV / ozone treatment.

  Further, before and after the preparation of the substrate 2 (steps S101 to S102), the solution of the n-type organic semiconductor 11 and the solution of the p-type organic semiconductor 12 are respectively adjusted (step S103, organic semiconductor solution adjustment step). That is, an n-type organic semiconductor solution having an appropriate concentration is prepared by appropriately measuring a material used as the n-type organic semiconductor 11 and dissolving the material in an appropriate solvent. Similarly, a p-type organic semiconductor solution having an appropriate concentration is prepared by appropriately measuring a material used as the p-type organic semiconductor 12 and dissolving the material in an appropriate solvent. In this organic semiconductor solution adjustment step, the viscosity of the solution of the n-type organic semiconductor 11 and the p-type organic semiconductor 12 may be adjusted.

  In the organic semiconductor solution adjustment step of the present embodiment, when adjusting the organic semiconductor solution, an operation of charging the organic semiconductor in the solution is performed. Specifically, the organic semiconductor is chemically modified as necessary to give the organic semiconductor in the solution a desired charge. You may adjust pH of a solution as needed.

  The n-type organic semiconductor 11 and the p-type organic semiconductor 12 may be used as the organic semiconductor to be charged. When only one of the n-type organic semiconductor 11 and the p-type organic semiconductor 12 is charged (when the other organic semiconductor is electrically neutral), it may be charged with a positive charge, It may be negatively charged. In the present embodiment, it is assumed that the n-type organic semiconductor 11 is negatively charged and the p-type organic semiconductor 12 is electrically neutral.

  Subsequently, the organic semiconductor solution prepared in step S103 is applied on the cathode 3 cleaned in step S102 to form an organic semiconductor layer (step S104, film formation process). In the film forming process of this embodiment, a solution of the n-type organic semiconductor 11 and a solution of the p-type organic semiconductor 12 are laminated and applied.

  First, the n-type organic semiconductor 11 solution is applied in a thin film on the upper surface of the cathode 3 to form the electron-accepting layer 4. As a method for applying the solution of the n-type organic semiconductor 11, a general application method such as a spin coating method or a spray method can be used. As described above, since the upper surface of the cathode 3 of the present embodiment is smooth, the electron accepting layer 4 having good adhesion to the upper surface of the cathode 3 by a simple coating method such as spin coating or spraying. Can be formed.

  Subsequently, a solution of the p-type organic semiconductor 12 is applied in a thin film on the electron-accepting layer 4 formed as described above to form the electron-donating layer 5. As a method for applying the solution of the p-type organic semiconductor 12, as with the n-type organic semiconductor 11, a general application method such as a spin coating method or a spray method can be used. But the application method of the solution of the n-type organic semiconductor 11 and the application method of the solution of the p-type organic semiconductor 12 do not need to be the same, and they may be applied by different application methods. Through the film forming process described above, the electron accepting layer 4 and the electron donating layer 5 are laminated on the cathode 3 as shown in FIG.

  In the conventional method for manufacturing an organic thin film solar cell, when an n-type organic semiconductor and a p-type organic semiconductor are stacked and applied, the lower organic semiconductor is completely dried, and then the upper organic semiconductor is formed thereon. Was applied.

  In this regard, in the film forming process of the present embodiment, the electron donating layer 5 is formed without performing the process of drying the electron accepting layer 4. That is, in the film forming process of this embodiment, before the solution of the n-type organic semiconductor 11 applied on the upper surface of the cathode 3 is dried, the solution of the p-type organic semiconductor 12 is applied thereon.

  Therefore, when the electron donating layer 5 is formed, the electron accepting layer 4 and the electron donating layer 5 are not dried (in a solution state). In this state, the n-type organic semiconductor 11 in the electron accepting layer 4 is negatively charged. FIG. 3 schematically shows a state in which the molecules of the n-type organic semiconductor 11 in the electron-accepting layer 4 are negatively charged with a minus sign.

  Subsequently, before the electron-accepting layer 4 and the electron-donating layer 5 are completely dried, an electric field is applied to the electron-accepting layer 4 and the electron-donating layer 5 (Step S105, migration step). Specifically, it is as follows.

  As shown in FIG. 3B, a pair of external electrodes 7 and 8 are arranged so as to sandwich the electron accepting layer 4 and the electron donating layer 5 in the thickness direction. Each of the external electrodes 7 and 8 is a plate-like metal member, and is disposed substantially parallel to the electron accepting layer 4 and the electron donating layer 5. Of the pair of external electrodes 7 and 8, the one disposed on the electron accepting layer 4 side is referred to as the first external electrode 7, and the one disposed on the electron donating layer 5 side is referred to as the second external electrode 8.

  Then, a DC power supply 9 is connected to the external electrodes 7 and 8 to generate a potential difference between the external electrodes 7 and 8. Thereby, an electric field is formed so that electric lines of force pass through the electron accepting layer 4 and the electron donating layer 5 in the thickness direction. As described above, since the external electrodes 7 and 8 are formed in a flat plate shape and arranged in parallel, a uniform electric field is applied to the electron accepting layer 4 and the electron donating layer 5. Since the electron-accepting layer 4 and the electron-donating layer 5 are in a solution state and the n-type organic semiconductor 11 in the electron-accepting layer 4 is charged, the n-type organic semiconductor is applied by applying an electric field as described above. 11 is electrophoresed along the lines of electric force. The power source connected to the external electrodes 7 and 8 is not limited to the DC power source 9, and an appropriate power source can be used.

  In the migration step, an electric field is applied so that the n-type organic semiconductor 11 migrates toward the anode 6 (not shown in FIG. 3) and the p-type organic semiconductor 12 migrates toward the cathode 3 side. It is suitable if applied. In the present embodiment, since the n-type organic semiconductor 11 is negatively charged, the first external electrode 7 is placed on the negative side of the DC power source 9 and the second external electrode 8 as shown in FIG. Are connected to the positive side of the DC power source 9 to apply an electric field from top to bottom. Thus, the negatively charged n-type organic semiconductor 11 is electrophoresed upward (toward the anode 6 side).

  Electrophoresis of the organic semiconductor as described above causes the interface (pn junction interface) between the electron-accepting layer 4 and the electron-donating layer 5 to be raised, and unevenness is generated at the interface (the state shown in FIG. 3B). . By appropriately controlling the strength of the electric field applied by the external electrodes 7 and 8 and the application time of the electric field, irregularities having a desired structure can be formed.

  Subsequently, while applying the electric field as described above or after completing the application of the electric field, the electron-accepting layer 4 and the electron-donating layer 5 are heated to dry the electron-accepting layer 4 and the electron-donating layer 5. (Step S106, drying process). Thereby, the uneven structure at the interface between the electron accepting layer 4 and the electron donating layer 5 is fixed, and the uneven portion 17 is formed.

  Then, annealing is performed as necessary (step S107, annealing process), and finally, the anode 6 is formed by vacuum-depositing aluminum on the electron donating layer 5 (step s108, electrode deposition process). The organic thin film solar cell 1 shown in FIG. 1 can be manufactured by the above manufacturing method.

  As described above, the method for manufacturing the organic thin-film solar cell 1 according to the present embodiment includes the film forming process (step S104) and the migration process (step S105). In the film forming step, a layer of p-type organic semiconductor 12 (electron donating layer 5) and a layer of n-type organic semiconductor 11 (electron accepting layer 4) are formed. In the migration step, an electric field is applied to the layer in a state where the electron accepting layer 4 and the electron donating layer 5 formed in the film forming step are not completely dried. In the migration step, the n-type organic semiconductor 11 in the electron accepting layer 4 is charged.

  As described above, the organic semiconductor is charged with a charge and an electric field is applied after the film formation, whereby the organic semiconductor is electrophoresed to form an uneven structure at the interface between the electron accepting layer 4 and the electron donating layer 5. According to this, for example, the uneven structure can be formed with a simple apparatus without using a nanoimprint mold as in Patent Document 1. Moreover, it can respond easily also to manufacture of a large sized organic thin-film solar cell. Further, the electron accepting layer 4 and the electron donating layer 5 can be formed by a simple film forming method such as a spray method or a spin coating method. Therefore, the uneven structure at the interface between the electron-accepting layer 4 and the electron-donating layer 5 can be formed inexpensively and easily.

  Subsequently, a modified example of the first embodiment will be described.

  In the above embodiment, only the n-type organic semiconductor 11 is charged, but both the n-type organic semiconductor 11 and the p-type organic semiconductor 12 may be charged. However, in this case, it is preferable that both have opposite charges. For example, when the n-type organic semiconductor 11 is negatively charged, the p-type organic semiconductor 12 is positively charged. According to this, as shown in FIG. 4, since the n-type organic semiconductor 11 and the p-type organic semiconductor 12 can be electrophoresed in opposite directions in the migration step, the effect of the electrophoresis can be increased. .

  Next, another modification of the first embodiment will be described.

  In the first embodiment, the flat external electrodes 7 and 8 are arranged in parallel with the electron accepting layer 4 and the electron donating layer 5, so that a uniform electric field is generated with respect to the electron accepting layer 4 and the electron donating layer 5. Applied. However, the present invention is not limited to this, and a non-uniform electric field may be applied to the electron-accepting layer 4 and the electron-donating layer 5. As one method for applying a non-uniform electric field, the external electrodes 7 and 8 may be arranged so as not to be parallel to the electron accepting layer 4 and the electron donating layer 5. For example, in FIG. 5, a part of the lower surface of the external electrode 8 is formed in a needle shape so as to protrude toward the electron donating layer 5. According to this, since the strength of the electric field applied to the electron accepting layer 4 and the electron donating layer 5 varies depending on the location, the distance at which the organic semiconductor moves in the migration process varies depending on the location. Thus, by devising the shape of the external electrode, the electric field applied to the electron-accepting layer 4 and the electron-donating layer 5 can be increased or decreased, so that the uneven portion 17 having an arbitrary structure can be formed.

  Next, still another modification of the first embodiment will be described.

  In the first embodiment, the external electrodes 7 and 8 are provided as electrodes for applying an electric field in the migration process. Instead, one or both of the external electrodes 7 and 8 can be substituted with the cathode 3 or the anode 6 provided in the organic thin film solar cell 1. For example, FIG. 6 shows an example in which the cathode 3 of the organic thin film solar cell 1 is used in place of the first external electrode 7 in the migration step. That is, in the migration step, the cathode 3 of the organic thin film solar cell 1 is connected to the negative side of the DC power source 9, and the second external electrode 8 is connected to the positive side of the DC power source 9. An electric field is formed between them. According to this, since the 1st external electrode 7 required by the migration process of the said 1st Embodiment can be abbreviate | omitted, the apparatus used in order to apply an electric field can be simplified, and the manufacturing cost of the organic thin film solar cell 1 is reduced. it can. In addition, when the anode 6 can be formed in advance before the migration step, the anode 6 can be used in place of the second external electrode 8. In this case, the second external electrode 8 can be omitted.

  Next, a manufacturing method according to the second embodiment of the present invention will be described with reference to FIG. The following second embodiment is different from the first embodiment only in the organic semiconductor solution adjustment process, the film forming process, and the migration process. Therefore, the description of the processes common to the first embodiment is omitted. There is.

  In the organic semiconductor solution adjustment step of the second embodiment, a mixed solution of the n-type organic semiconductor 11 and the p-type organic semiconductor 12 is adjusted. That is, an appropriate amount of each of the n-type organic semiconductor 11 and the p-type organic semiconductor 12 is weighed and dissolved in an appropriate solvent. Thereby, the mixed solution in which the n-type organic semiconductor 11 and the p-type organic semiconductor 12 are mixed at a predetermined concentration is adjusted. In the organic semiconductor solution adjustment process of the second embodiment, at least one of the n-type organic semiconductor 11 and the p-type organic semiconductor 12 is charged. In the present embodiment, description will be made assuming that the n-type organic semiconductor 11 is negatively charged.

  In the film forming process of the second embodiment, the mixed solution prepared as described above is applied to the upper surface of the cathode 3. Thereby, as shown in FIG. 7A, a mixed layer 14 in which the n-type organic semiconductor 11 and the p-type organic semiconductor 12 are mixed at random is formed.

  In the migration step of the second embodiment, an electric field is applied to the mixed layer 14 before the mixed layer 14 applied as described above is completely dried. As a result, an organic semiconductor having an electric charge in the mixed layer 14 (in this embodiment, the n-type organic semiconductor 11) is electrophoresed.

  In the migration step of the second embodiment, the p-type organic semiconductor is migrated toward the anode 6 (not shown in FIG. 7) so that the n-type organic semiconductor 11 is migrated toward the cathode 3. Apply an electric field. In this embodiment, since the n-type organic semiconductor 11 is negatively charged, the first external electrode 7 is placed on the positive side of the DC power source 9 and the second external electrode 8 is placed as shown in FIG. The electric field is connected to the negative side of the DC power supply 9 and applied from the bottom to the top. That is, in the migration process of the second embodiment, an electric field in the opposite direction to the migration process of the first embodiment is applied. Thereby, the negatively charged n-type organic semiconductor 11 is electrophoresed toward the cathode 3 side (downward in FIG. 7).

  As a result, the n-type organic semiconductor 11 that is randomly dispersed in the mixed layer 14 can be brought closer to the cathode 3 side. As a result, the p-type organic semiconductor 12 that is randomly dispersed in the mixed layer 14 approaches the anode 6 side (the state shown in FIG. 7B). In other words, the distribution of the organic semiconductor in the mixed layer 14 is in the thickness direction (vertical direction in FIG. 7) so that there are many n-type organic semiconductors 11 on the cathode 3 side and many p-type organic semiconductors 12 on the anode side. Can be biased. By heating and drying the mixed layer 14 in this state (drying process), a structure in which the distribution of the organic semiconductor in the mixed layer 14 is biased can be fixed. By forming the anode 6 on the mixed layer 14 formed as described above, for example, an organic thin film solar cell 29 as shown in FIG. 7C can be obtained.

  In the conventional manufacturing method, the bulk heterostructure (FIG. 10B) formed by applying a mixed solution of an n-type organic semiconductor and a p-type organic semiconductor is a random structure, and is optimal from the viewpoint of a charge transfer path. It wasn't. In this regard, as in the above-described embodiment, an electric field is applied to the mixed solution of the n-type organic semiconductor and the p-type organic semiconductor, and the randomly dispersed organic semiconductor is electrophoresed to thereby form the n-type organic semiconductor 11. The p-type organic semiconductor 12 can be brought closer to the anode 6 side on the cathode 3 side. Thereby, for example, as shown in FIG. 7C, an electron moving path to the cathode 3 and a hole moving path to the anode 6 are easily formed. Note that even if the distribution of the n-type organic semiconductor 11 and the p-type organic semiconductor 12 in the mixed layer 14 is biased by electrophoresis, the two are not completely separated. ), A complicated and complicated structure is obtained, and as a result, a large area of the pn junction interface can be secured. Thus, according to the manufacturing method of 2nd Embodiment, the ideal structure close | similar to the interpenetrating connection structure of FIG.10 (c) can be formed.

  Subsequently, a modification of the second embodiment will be described.

  The manufacturing method of the present invention can also be applied to an organic thin film solar cell having a tandem structure (including a pin junction structure) in which three or more organic semiconductor layers are stacked. For example, the manufacturing method of the second embodiment can be applied to a manufacturing method of a so-called pin junction type organic thin-film solar cell 41 as shown in FIG.

  The p-i-n junction type organic thin film solar cell 41 includes an n-type organic semiconductor and a p-type layer between an electron-accepting layer 4 made of an n-type organic semiconductor 11 and an electron-donating layer 5 made of a p-type organic semiconductor 12. The organic semiconductor mixed layer (i layer) 14 is provided. Electrophoresis of the organic semiconductor in the mixed layer (i layer) 14 by the manufacturing method of the second embodiment facilitates the formation of a charge transfer path in the mixed layer (i layer) 14, and pn Since a large area of the joint interface can be secured, the conversion efficiency can be improved.

  From the viewpoint of electrophoresis of the organic semiconductor in the mixed layer (i layer) 14, it is not necessary to perform the electrophoresis of the organic semiconductor in the electron accepting layer 4 and the electron donating layer 5. The layers that do not need to be electrophoresed (in the above case, the electron-accepting layer 4 and the electron-donating layer 5) can be formed by a film-forming method other than coating (for example, a vapor deposition method). Of course, the layer that does not need to be electrophoresed may be completely dried at the stage of the electrophoresis process. According to this, since the electron accepting layer 4 and the electron donating layer 5 can be formed using an organic semiconductor that is hardly soluble in an organic solvent, the degree of freedom in material selection is improved.

  However, when manufacturing an organic thin film solar cell having a pin junction structure, the organic semiconductor in the electron accepting layer 4 and the electron donating layer 5 should not be electrophoresed. For example, before the organic semiconductors in the electron accepting layer 4, the mixed layer 14, and the electron donating layer 5 are each charged with an appropriate charge, each layer is formed by coating, and each layer applied by stacking is completely dried. When an electric field is applied to the organic semiconductor, the organic semiconductors in each layer can be electrophoresed together. Thus, even when three or more layers of organic semiconductors are stacked, if an electric field is applied before each layer is completely dried, the organic semiconductors of three or more layers are electrophoresed together. Can be made.

  According to this, as shown in FIG. 8B, irregularities are formed at the interface between the electron accepting layer 4 and the mixed layer (i layer) 14 and at the interface between the mixed layer (i layer) 14 and the electron donating layer 5, respectively. The p-i-n junction type organic thin film solar cell 42 can be obtained. Even in this case, the organic semiconductor in the mixed layer (i-layer) 14 is unevenly distributed in the thickness direction, and a charge transfer path is easily formed. Therefore, the organic thin-film solar cell 42 (FIG. 8B) manufactured in this way has the effect of the first embodiment that the unevenness is formed at the interface of the organic semiconductor layer, and the organic semiconductor in the mixed layer 14. Since the effect which combined the effect of 2nd Embodiment of giving the bias | inclination of the distribution in a thickness direction is acquired, conversion efficiency can be improved further.

  Subsequently, a third embodiment of the present invention will be described. In the following third embodiment, only the organic semiconductor solution adjustment step and the migration step are different from the first embodiment, and therefore, the description of the steps common to the first embodiment may be omitted.

  In the first embodiment and the second embodiment, the example in which the organic semiconductor is electrophoresed has been described. On the other hand, this 3rd Embodiment makes an organic semiconductor magnetophoresis. This will be specifically described below.

  In the organic semiconductor solution adjustment step of the third embodiment, a magnetic material is added to either the n-type organic semiconductor 11 solution or the p-type organic semiconductor 12 solution. The magnetic substance added to the solution is preferably particles such as magnetic beads. This magnetic bead is suitable if it has selectivity for the organic semiconductor in the added solution.

  In the case of magnetophoresis, unlike electrophoresis, the n-type organic semiconductor 11 and the p-type organic semiconductor 12 cannot be migrated in opposite directions. Therefore, in the organic semiconductor solution adjustment step of the third embodiment, the magnetic material is added only to one of the n-type organic semiconductor 11 and the p-type organic semiconductor 12, and the magnetic material is not added to the other. In the present embodiment, description will be made assuming that magnetic beads are added to the solution of the n-type organic semiconductor 11.

  In the film forming process of the third embodiment, the solution of the n-type organic semiconductor 11 adjusted as described above is applied to the upper surface of the cathode 3 to form the electron accepting layer 4. Then, before the electron accepting layer 4 is dried, a solution of the p-type organic semiconductor 12 is laminated and applied on the upper surface of the electron accepting layer 4 to form the electron donating layer 5. The situation at this time is shown in FIG. In FIG. 9, the magnetic beads 16 added to the electron-accepting layer 4 are schematically shown by black circles.

  In the migration step of the third embodiment, before the electron accepting layer 4 and the electron donating layer 5 formed as described above are completely dried, a magnetic field is applied to the electron accepting layer 4 and the electron donating layer 5. Apply.

  The method for applying the magnetic field is not particularly limited. For example, as shown in FIG. 9B, the configuration in which the magnetic field is applied by the electromagnet 15 is preferable because the strength of the magnetic field, the application time of the magnetic field, and the like can be easily controlled. It is. At this time, it is preferable that a magnetic field is formed so that the magnetic lines of force pass through the electron accepting layer 4 and the electron donating layer 5 in the thickness direction.

  As a result, the n-type organic semiconductor 11 in the electron accepting layer 4 to which the magnetic beads 16 have been added migrates toward the electromagnet 15, so that the interface between the electron accepting layer 4 and the electron donating layer 5 (pn junction interface). Bulges and irregularities occur at the interface. By appropriately controlling the strength of the magnetic field applied by the electromagnet 15 and the application time of the magnetic field, irregularities having a desired structure can be formed. Then, in the state where the magnetic field is applied as described above or after the application of the magnetic field is completed, the electron accepting layer 4 and the electron donating layer 5 are heated to dry the electron accepting layer 4 and the electron donating layer 5. (Drying process). Thereby, the uneven structure at the interface between the electron accepting layer 4 and the electron donating layer 5 is fixed, and the uneven portion 17 is formed.

  As described above, in the organic semiconductor solution adjustment process of the third embodiment, the magnetic beads 16 are added to the n-type organic semiconductor 11. In the migration process of the third embodiment, a magnetic field is applied to the layer in a state where the electron accepting layer 4 and the electron donating layer 5 formed in the film forming process are not completely dried. Thereby, an organic semiconductor layer having a desired structure can be formed by magnetophoresis of the organic semiconductor.

  Electrophoresis as in the first and second embodiments cannot be used for organic semiconductor materials that are difficult to charge. However, even such semiconductor materials are magnetic as in the third embodiment. Magnetophoresis can be performed by adding beads and applying a magnetic field. Thereby, the freedom degree of material selection improves.

  The preferred embodiments and modifications of the present invention have been described above, but the above configuration can be modified as follows, for example.

  The anode 6 is formed by vacuum vapor deposition, but the present invention is not limited to this. For example, the anode 6 may be formed by applying a conductive paste on the upper surface of the electron donating layer 5.

  In the first and third embodiments, the n-type organic semiconductor 11 solution is first applied to form the electron-accepting layer 4, and then the p-type organic semiconductor 12 solution is applied thereon to provide electrons. Although the layer 5 is formed, the order of forming the electron accepting layer 4 and the electron donating layer 5 is not limited to this, and the order may be reversed.

  In the first embodiment described above, the electric field is applied so that the n-type organic semiconductor 11 migrates toward the anode 6 and the p-type organic semiconductor migrates toward the cathode 3. In this respect, it is preferable to apply the electric field in terms of forming a comb-shaped concavo-convex structure as seen in the interpenetrating junction structure. However, even when the electric field is applied to the electron accepting layer 4 and the electron donating layer 5 in other directions, the structure of the interface between the electron accepting layer 4 and the electron donating layer 5 is caused by electrophoresis of the organic semiconductor. Can give some change. Thus, the direction in which the electric field is applied is not limited to that in the above embodiment. Similarly, even when the magnetic field is generated by applying a magnetic field as in the third embodiment, the direction in which the magnetic field is applied is not limited.

  A buffer layer may be provided between the cathode 3 or the anode 6 and the organic semiconductor.

  In the first embodiment and the third embodiment, the electron accepting layer 4 and the electron donating layer 5 may be in a state where they are not completely dried at the stage of the migration process. Even if the electron-accepting layer 4 or the electron-donating layer 5 may be completely dried before the migration step, it is sufficient that the electron-accepting layer 4 or the electron-donating layer 5 is again dissolved in the solvent at the stage of the migration step. Further, it is not necessary that the entire electron-accepting layer 4 and the electron-donating layer 5 are dissolved in the solvent at the stage of the migration process, and at least the interface portion of the electron-accepting layer 4 and the electron-donating layer 5 is dissolved in the solvent. It is sufficient if it is in a state. Similarly, in the second embodiment, the mixed layer 14 may be in a state where it is not completely dried at the stage of the migration process.

DESCRIPTION OF SYMBOLS 1 Organic thin film solar cell 3 Cathode 4 Electron acceptance layer 5 Electron donation layer 6 Anode 7 1st external electrode 8 2nd external electrode

Claims (5)

a film forming step of forming a layer of a p-type organic semiconductor and an n-type organic semiconductor, or a mixture of both;
A migration step of applying an electric field to the layer in a state where the layer formed in the film formation step is not completely dry;
Including
In the migration step, at least one of the p-type organic semiconductor and the n-type organic semiconductor is charged. It is a manufacturing method of the organic thin film solar cell of Claim 1,
In the said film-forming process, a nonuniform electric field is applied, The manufacturing method of an organic thin-film solar cell characterized by the above-mentioned. a film forming step of forming a layer of a p-type organic semiconductor and an n-type organic semiconductor, or a mixture of both;
A migration step of applying a magnetic field to the layer in a state where the layer formed in the film-forming step is not completely dry;
Including
In the migration step, a magnetic material is added to any one of the p-type organic semiconductor and the n-type organic semiconductor. It is a manufacturing method of the organic thin film solar cell according to any one of claims 1 to 3,
In the film forming step, the p-type organic semiconductor layer and the n-type organic semiconductor solution are stacked and applied to form a p-type organic semiconductor layer and an n-type organic semiconductor layer. The manufacturing method of an organic thin-film solar cell. It is a manufacturing method of the organic thin film solar cell according to any one of claims 1 to 3,
In the film forming step, the mixed layer of the p-type organic semiconductor and the n-type organic semiconductor is applied to form a mixed layer of the p-type organic semiconductor and the n-type organic semiconductor. Manufacturing method of thin film solar cell.

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