JP2006351721A - Stacked organic solar cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stacked organic solar cell having a high conversion efficiency. <P>SOLUTION: In the stacked organic solar cell, a plurality of organic solar cells are stacked having a photoelectric transfer layer 20 formed by blending a donor material with an acceptor material. A recoupling layer 23 which recouples electrons generated from first and second organic solar cells 21, 22 to holes is inserted into between the first organic solar cell 21 disposed on a side on which light is incident and the second organic solar cell 22 which is disposed and stacked on a side opposing to the incident side of the light of the first organic solar cell 21. The recoupling layer 23 is formed with conductive layers 24, 25 of two layers of a different work function, and also, of the conductive layers 24, 25 of two layers of the recoupling layer 23, the work function of the conductive layer 25 on a side of the second organic solar cell 22 is greater than the work function of the conductive layer 24 on a side of the firs organic solar cell 21. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a stacked organic solar cell formed by laminating a plurality of layers of organic solar cells that generate light by receiving light.

  Conventionally, inorganic solar cells made of thin films such as Si, GaAs, and CuInGaSe have been developed. However, it is necessary to use an expensive semiconductor manufacturing apparatus, and the energy required for manufacturing is large. It is difficult to realize a power generation cost equivalent to or less than the electricity bill of the future, and the future prospects are severe. Therefore, in recent years, development of organic solar cells that do not require expensive semiconductor manufacturing facilities has become active.

Organic solar cells can be broadly classified as follows: Dye-sensitized solar cells in which a dye is supported on porous TiO ₂ and filled with an electrolyte; Schottky barrier type using p-type barrier formed by solid organic thin film and metal thin film; p-type Bilayer pn-junction type laminated organic semiconductor thin film and n-type organic semiconductor thin film, p-type organic semiconductor material (acceptor) and n-type organic semiconductor material (donor) are dissolved in solvent, blended in solution, applied and thin film applied There is a bulk heterojunction junction type to be formed.

  Of these, the dye-sensitized type already has a conversion efficiency of over 10%, but this one uses a liquid electrolyte and thus has low reliability. In order to obtain high efficiency, Ru, a platinum electrode, etc. are expensive. There is a problem that a new material is necessary and the cost is not reduced, and that conversion efficiency is greatly reduced when the material is changed to an inexpensive material. On the other hand, the type using an all-solid polymer organic semiconductor may be manufactured at low cost by a coating method. In particular, a bulk heterojunction type organic solar cell made by blending a conductive polymer and a fullerene derivative has a conversion efficiency of 3%. As a solar cell having a possibility of high efficiency at a low cost, the development is actively carried out.

  FIG. 3 shows a low-molecular organic solar cell in which a p-type semiconductor layer 1 is formed by Cu phthalocyanine (CuPc) and an n-type semiconductor layer 2 is formed by PTCBI by vapor deposition. 3 is a transparent substrate such as glass, 4 Is a transparent electrode, and 5 is an electrode such as Ag. In this structure, a built-in electric field is generated in the vicinity of the pn junction between the p-type semiconductor layer 1 and the n-type semiconductor layer 2, and when excitons generated in the p-type semiconductor layer 1 of CuPc are moved to the vicinity of the pn junction by photoexcitation, charges are generated by the built-in electric field. Separation occurs, and electricity is generated by being divided into electrons and holes and transported to the opposite electrodes 4 and 5. The problem here is that the distance that excitons in the p-type semiconductor layer 1 can move is short, and the thickness of the built-in electric field layer is also thin, so that the film thickness must be reduced. Insufficient conversion efficiency cannot be obtained.

  FIG. 4 shows an example of a bulk heterojunction type organic solar cell. In this example, a fullerene derivative 6 as an acceptor and a conductive polymer 7 as a donor are blended to form a thin film of the photoelectric conversion layer 8. It is like that. 3 is a transparent substrate such as glass, 4 is a transparent electrode, 5 is an electrode such as Al, and 9 is a hole transport layer. In this structure, in the film of the photoelectric conversion layer 8, the nano-sized fullerene 6 that is a p-type organic semiconductor material is uniformly dispersed in the conductive polymer 7 that is an n-type organic semiconductor material. In other words, the pn junctions are dispersed in the entire portion 8. For this reason, even if the exciton movement distance is short, the pn junction always exists within the exciton movement distance, so that the extinction of exciton can be reduced. After charge separation at the pn junction, electrons fall to the fullerene 6 according to the energy level, hop between the fullerenes 6 and reach the Al electrode 5, and the holes become conductive polymer 7. The inside is transported to reach the transparent electrode 4 and the output current can be taken out. As a result, a conversion efficiency exceeding 3% has been reported recently.

  Here, the conversion efficiency is limited by the distance that the carrier can be transported, which is currently about 100 nm. Therefore, if the film thickness of the photoelectric conversion layer 8 is greater than this, the probability that electrons and holes cannot be re-combined and disappeared without reaching the electrodes 4 and 5 is increased. Will be reduced. However, if the film thickness of the photoelectric conversion layer 8 is 100 nm or less, light absorption is insufficient, so that a higher conversion efficiency cannot be desired.

  As described above, the common problem of organic solar cells is that the carrier transport capability is low, so that the film thickness cannot be increased and light absorption is insufficient. There is a means. One is to increase the mobility and carrier life of the organic semiconductor material, and this is expected to require a long development period. The other is a method of increasing light absorption while using the current organic semiconductor material, and is a stacked organic solar cell formed by stacking a plurality of photoelectric conversion layers of an organic solar cell (for example, Patent Document 1). And non-patent document 1).

  FIG. 5 shows a low molecular weight stacked organic solar cell developed so far (see Non-Patent Document 1), in which a p-type semiconductor layer 10 made of CuPc and an n-type semiconductor layer 11 made of PTCBI are deposited. The first organic solar cell 12 stacked by the method, and the second organic solar cell 15 stacked by the vapor deposition method of the p-type semiconductor layer 13 made of CuPc and the n-type semiconductor layer 14 made of PTCBI are made of an Ag electrode. These are stacked via the recombination layer 16. 3 is a transparent substrate such as glass, 4 is a transparent electrode, and 5 is an electrode such as Ag.

  By laminating the organic solar cells 12 and 15 in this way, the light that has passed through the first organic solar cell 12 is absorbed by the second organic solar cell 15 and can increase light absorption as a whole. Efficiency can be increased. In such a stacked organic solar cell, in order to obtain an output of power generation, a recombination layer 16 that recombines electrons and holes between the first organic solar cell 12 and the second organic solar cell 15 is provided. I need it. That is, the electrons generated in the first organic solar cell 12 and the holes generated in the second organic solar cell 15 disappear through the recombination layer 16, and the holes in the first organic solar cell 12 and the second The electrons of the organic solar cell 15 reach the electrodes 3 and 4 and can be taken out as an output current.

Here, the recombination layer 16 is required to have conductivity for recombining holes and electrons, and the n-type semiconductor layer 11 of the first organic solar cell 12 and the second organic solar cell 15. To have an ohmic junction with the p-type semiconductor layer 13 and to pass unabsorbed light of the first organic solar cell 12 through the second organic solar cell 15 as much as possible. Is to make it thinner. For this reason, in the above-mentioned Non-Patent Document 1, the recombination layer 16 is formed of an ultra-thin Ag film having a thickness of 5 mm.
Japanese Patent Publication No. 8-31616 Apply Physics Letter Vol80 No9 March 2002 page1667

  Here, in the bulk heterojunction type stacked organic solar cell in which a plurality of organic solar cells are stacked, by optimizing the work function difference between the electrodes on both sides sandwiching each organic solar cell, an electric field is generated in the film thickness direction, This contributes to the improvement of the generated current and the generated voltage, and the conversion efficiency can be increased. However, when the recombination layer is formed of a single ultrathin film as described above, it is difficult to apply an electric field due to a work function difference, and the appropriate work function differs between the anode and cathode electrodes in each organic solar cell. When the recombination layer is one layer, it is difficult to select a material having an appropriate work function, and it is difficult to increase the conversion efficiency.

  The present invention has been made in view of the above points, and aims to provide a stacked organic solar cell with high conversion efficiency, and can be manufactured at low cost. An object of the present invention is to provide a manufacturing method.

  The stacked organic solar cell according to claim 1 of the present invention is a stacked organic solar cell in which a plurality of organic solar cells having a photoelectric conversion layer formed by blending a donor material and an acceptor material are stacked. Between the first organic solar cell arranged on the side and the second organic solar cell laminated on the side opposite to the light incident side of the first organic solar cell. A recombination layer for recombination of electrons and holes generated from the organic solar cell is formed, and the recombination layer is formed with two conductive layers having different work functions. Among the layers, the work function of the conductive layer on the second organic solar cell side is larger than the work function of the conductive layer on the first organic solar cell side.

  According to a second aspect of the present invention, in the first aspect, the total thickness of the two conductive layers is 2 to 40 nm.

  The invention of claim 3 is characterized in that, in claim 1 or 2, a light-transmitting electrical insulating layer is inserted between the two conductive layers.

  According to a fourth aspect of the present invention, there is provided a method for manufacturing a stacked organic solar cell according to any one of the first to third aspects, wherein Al, Ca, Mg, Ti, Ag, A conductive layer on the first organic solar cell side is formed by applying a paste in which a particulate material having a particle size of 100 nm or less selected from Mo and In is dispersed in a solvent, and is selected from Pd, Au, ITO, and PEDOT A conductive layer on the second organic solar cell side is formed by applying a paste in which a particulate material having a particle size of 100 nm or less is dispersed in a solvent.

  According to the present invention, the recombination layer inserted between the first and second organic solar cells is formed of two conductive layers having different work functions, and the work of the conductive layer on the second organic solar cell side is performed. Since the function is set to be larger than the work function of the conductive layer on the first organic solar cell side, a work function difference can be provided between the electrode and the conductive layer in each organic solar cell, Using the electric field due to the work function difference as a driving force, the current generated by each organic solar cell can be efficiently taken out from the electrode, thereby improving the conversion efficiency.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 1 shows an example of an embodiment of the present invention. In this embodiment, a bulk heterojunction type is adopted, and the photoelectric conversion layer 20 constituting the first organic solar cell 21 and the second organic solar cell 22 is composed of a fullerene derivative 6 as an acceptor material (electron-accepting material). The conductive polymer 7 is used as a donor material (electron-donating material), and these are blended and applied. And after forming the transparent electrode 29 and the positive hole transport layer 30 on the surface of the transparent substrates 28, such as glass, the photoelectric converting layer 20 which comprises the 1st organic solar cell 21 is laminated | stacked on this, and 1st organic After forming the recombination layer 23 on the solar cell 21, the photoelectric conversion layer 20 which comprises the 2nd organic solar cell 22 is laminated | stacked on this, and also electrode 31, such as Al, is formed on this. A laminated organic solar cell can be produced.

  In this stacked organic solar cell, the exciton generated by photoexcitation in each photoelectric conversion layer 20 of the first and second organic solar cells 21 and 22 is a fullerene derivative that is an acceptor material (p-type organic semiconductor material). 6 and the pn junction at the interface between the conductive polymer 7 which is a donor material (n-type organic semiconductor material), and the electrons are transferred to the acceptor and the holes are transferred to the donor. Thereafter, holes move in the network of the donor conductive polymer 7 and electrons move in the network of the acceptor fullerene derivative 6, and at this time, the holes are generated by the difference in work functions of the electrodes 29 and 31 on both sides. Since the electric field is applied to the entire photoelectric conversion layers 20 of the first and second organic solar cells 21 and 22, electrons and holes reach the electrodes 29 and 31 with a high probability using the electric field as a driving force. The transparent electrode 29 can be used as a positive electrode and the electrode 31 can be used as a negative electrode to extract current.

  Also in this bulk heterojunction type stacked organic solar cell, a recombination layer 23 is provided between the first organic solar cell 21 and the second organic solar cell 22, and electrons generated from the first organic solar cell 21 Although it is necessary to recombine the holes generated from the second organic solar cell 22, when it is formed as an ultrathin layer of about 5 mm like the low molecular type recombination layer 16 of FIG. 5 described above, Although it functions to recombine electrons and holes, an electric field due to the work function difference necessary for the bulk heterojunction type can be applied between the recombination layer 16 and the electrodes 4 and 5 in FIG. Can not.

  Therefore, in the present invention, as shown in FIG. 1, the recombination layer 23 is formed in a two-layer structure of a conductive layer 24 on the first organic solar cell 21 side and a conductive layer 25 on the second organic solar cell side. In the first organic solar cell 21, a work function difference is provided between the transparent electrode 29 or the hole transport layer 30 and the conductive layer 24, and the second organic solar cell 22 has a difference between the electrode 31 and the conductive layer 25. A work function difference is provided between them. The two conductive layers 24 are formed so that the work function of the conductive layer 25 on the second organic solar cell 22 side is larger than the work function of the conductive layer 24 on the first organic solar cell 21 side. It is. As a result, the work function of the conductive layer 24 is smaller than the work functions of the transparent electrode 29 and the hole transport layer 30 in the first organic solar cell 21, and the work of the electrode 31 in the second organic solar cell 22. The work function of the conductive layer 25 can be designed to be larger than the function.

  Here, the work function of the transparent electrode 29 generally formed of ITO (indium tin oxide) is 4.5 to 5.1 eV, PEDOT: PSS (poly (3,4-ethylenedioxythiophene): poly (4 -The work function of the hole transport layer 30 formed of styrene sulfonate)) or the like is 5.1 to 5.3 eV, so that the work function of the conductive layer 24 on the first organic solar cell 21 side is 4. 5 eV or less is preferable, and 4.2 eV or less is preferable in order to obtain a stronger electric field. Further, the work function of the electrode 31 formed of Al on the back side of the second organic solar cell 22 is 3.5 to 4.2 eV although it varies depending on the film forming method. The work function of the conductive layer 25 is preferably 4.2 eV or more, and is preferably 4.5 eV or more in order to obtain a stronger electric field. By setting the work function of the conductive layer 25 on the second organic solar cell 22 side to be larger than the work function of the conductive layer 24 on the first organic solar cell 21 side, the first and second A high electric field is applied to both of the organic solar cells 21 and 22, and a highly efficient stacked organic solar cell can be obtained. The work function values of the two conductive layers 24 and 25 are set according to the work functions of the transparent electrode 29, the hole transport layer 30 and the electrode 31 used.

  As a material satisfying such specifications, there are Al, Ca, Mg, Ti, Ag, Mo, In and the like as the conductive layer 24 on the first organic solar cell 21 side, and on the second organic solar cell 22 side. Examples of the conductive layer 25 include Pd, Au, ITO, PEDOT, and the like. It is preferable to form the conductive layers 24 and 25 using a material selected from these. The work functions of these materials are as follows. Al: 3.5-4.2 eV, Ca: 2.9 eV, Mg: 3.7 eV, Ti: 4.3 eV, Ag: 4.5 eV, Mo: 4.2 eV, In: 4.2 eV, Pd: 4. 8 eV, Au: 4.6 eV, ITO: 4.5 to 5.1 eV, PEDOT: 5.1 to 5.3 eV.

  In addition, in order for an electric field due to a predetermined work function difference to act on the first and second organic solar cells 21 and 22, the thickness of the two conductive layers 24 and 25 must be a certain thickness or more. However, if the film thickness is too thick, the amount of light transmitted through the conductive layers 24 and 25 decreases, so the film thickness must be kept below a certain level. Therefore, in the present invention, it is preferable that the total thickness of the two conductive layers 24 and 25 is set to 2 to 400 nm. Type organic solar cell can be obtained. Here, since it is necessary for the conductive layers 24 and 25 to transmit light, it is preferable that the conductive layers 24 and 25 are formed to have a thickness of 10 nm or less when formed of metal, and the conductive layers 24 and 25 are formed to a thickness of 400 nm when formed of transparent oxide such as ITO. can do. If it is thicker than this, the series resistance is increased, and there is a risk of degrading the characteristics.

  FIG. 2 shows another embodiment of the present invention, in which an electrical insulating layer 26 is inserted between the two conductive layers 24 and 25 described above. The electrical insulating layer 26 can be formed of an inorganic thin film such as a silicon oxide film or an organic film, and is not particularly limited. Other configurations are the same as those in FIG.

  In this structure, the first and second organic solar cells 21 and 22 are not stacked in series, but are separated by an electrical insulating layer 26. Therefore, the current generated by the first organic solar cell 21 can be taken out using the transparent electrode 29 as a positive electrode and the conductive layer 24 as a negative electrode, and the current generated by the second organic solar cell 22 is extracted from the conductive layer 24. Can be taken out as a positive electrode and the electrode 31 as a negative electrode, and the first and second organic solar cells 21 and 22 can be connected in series or in parallel with an external wiring. Even in this case, the specifications of the work functions of the two conductive layers 24 and 25 are the same as those in FIG.

  Usually, the photoelectric conversion layer 20 constituting the first organic solar cell 21 and the second organic solar cell 22 is produced by a wet process in which a polymer or the like is dissolved in a solvent and applied. The first organic solar cell After the photoelectric conversion layer 20 of 21 is produced and the conductive layers 24 and 25 of the recombination layer 23 are formed on the photoelectric conversion layer 20 by vapor deposition or the like, the second organic solar cell 22 of the second organic solar cell 22 is formed thereon by a wet process. When the photoelectric conversion layer 20 is produced, if there are pinholes in the conductive layers 24 and 25, the solvent reaches the photoelectric conversion layer 20 of the first organic solar cell 21 through the pinholes, and the photoelectric conversion layer 20. There is a risk of melting a part of. In particular, if the conductive layers 24 and 25 are thinned in order to increase the amount of light transmission, pinholes are likely to occur, and such problems are likely to occur. At this time, if the electric insulating layer 26 is interposed between the two conductive layers 24 and 25 as described above, even if pinholes exist in the conductive layers 24 and 25, the electric insulating layer 26 infiltrates the solvent. Therefore, the influence on the photoelectric conversion layer 20 of the first organic solar cell 21 can be eliminated.

  Next, the manufacturing method of the laminated organic solar cell of this invention is demonstrated. Taking the stacked organic solar cell of FIG. 1 as an example, each layer is formed by forming the transparent electrode 29 and the hole transport layer 30 formed on the transparent substrate 28 by a vacuum process such as sputtering or vacuum deposition. The photoelectric conversion layer 20 constituting the first organic solar cell 21 and the photoelectric conversion layer 20 constituting the second organic solar cell 22 are coated with a coating solution prepared by blending a donor material and an acceptor material and dissolving in a solvent. Further, the electrode 31 is manufactured by a vacuum process such as sputtering or vacuum deposition. The conductive layers 24 and 25 of the recombination layer 16 formed between the first organic solar cell 21 and the second organic solar cell 22 may be produced by a vacuum process such as sputtering or vacuum deposition. In this case, the entire process is alternately replaced by a process different from vacuum-printing-vacuum-printing-vacuum, resulting in a discontinuous process, which leads to a decrease in productivity.

  Therefore, the conductive layers 24 and 25 of the recombination layer 16 are produced by a printing process using a coating-type conductive material, and the entire process is vacuum-printing-printing-printing-vacuum, and the vacuum process is first and last. In the meantime, it is preferable that the printing process is entered so that the continuity of the process is maintained. Conventionally, there is a conductive film material for printing such as an Ag paste as a coating type conductive material, but since this has a baking temperature of 120 to 150 ° C., it can be used on the first organic solar cell 21. Moreover, it is difficult to form the conductive layers 24 and 25 whose film thickness needs to be adjusted on the order of 10 nm.

  For this reason, by applying and drying a paste in which a particulate material having a particle size of 100 nm or less selected from Al, Ca, Mg, Ti, Ag, Mo, and In is dispersed in a solvent, the first organic solar cell 21 The conductive layer 24 on the side is prepared by a printing process, and a second organic solar cell is applied by applying a paste in which a particulate material having a particle size of 100 nm or less selected from Pd, Au, ITO, and PEDOT is dispersed in a solvent. The conductive layer 25 on the battery 22 side is produced by a printing process. As described above, a particulate material having a particle size of 100 nm or less is used as a material for forming the conductive layer 24 or a material for forming the conductive layer 25, and a conductive material layer 24 is applied and dried by applying a paste dispersed in a solvent. , 25 can be formed to a thickness adjusted to the order of 10 nm. The particle size of these particulate materials is preferably as small as possible within the available range, and therefore the lower limit of the particle size is not particularly set.

  Next, the present invention will be specifically described with reference to examples.

Example 1
As a transparent electrode, a glass substrate with ITO provided with ITO having a film thickness of 150 nm on one side was used, and a PEDOT solution (“AI4083” manufactured by Bayer) was applied to the surface of the ITO of the glass substrate with ITO at 3000 rpm, 1 The hole transport layer which consists of PEDOT with a film thickness of 30 nm was formed by apply | coating on the conditions of minutes.

  Next, a fullerene derivative ([6,6] -phenyl C61-butylic acid methyl ester) is used as an acceptor material, and a conductive polymer MDMO-PPV (poly (2-methoxy-5- (3,7-) is used as a donor material. Using dimethyloctyloxy) -1,4-phenylenevinylene)), a fullerene derivative and MDMO-PPV were mixed at a mass ratio of 1: 4 and dissolved in chlorobenzene to prepare a blend solution. The photoelectric conversion layer which forms a 80-nm-thick 1st organic solar cell was formed by apply | coating on the surface of a hole transport layer on condition of 4000 rpm and 40 second with a spin coat method.

  Next, a first conductive layer made of an Al film with a thickness of 10 nm was formed by vacuum-depositing Al on the surface of the photoelectric conversion layer constituting the first organic solar cell. Furthermore, the 2nd conductive layer which consists of a PEDOT film | membrane with a film thickness of 30 nm was formed in the surface of a 1st conductive layer by apply | coating similarly using said PEDOT solution. Note that the work function of the first conductive layer formed of Al is 4.2 eV, and the work function of the second conductive layer formed of PEDOT is 5.1 eV.

  Next, by applying the same fullerene derivative and MDMO-PPV blend liquid as described above to the surface of the second conductive film by spin coating method at 2500 rpm for 40 seconds, the second organic sun having a thickness of 100 nm is applied. A photoelectric conversion layer constituting the battery was formed.

Finally, Al was vacuum-deposited on the surface of the photoelectric conversion layer constituting the second organic solar cell to form an Al electrode having a film thickness of 150 nm, thereby obtaining the stacked organic solar cell having the layer configuration of FIG. . In this stacked organic solar cell, the effective power generation area was 6 mm ² .

(Example 2)
Using the same glass substrate with ITO as in Example 1, a hole transport layer was formed in the same manner as in Example 1. Next, the same fullerene derivative as in Example 1 is used as an acceptor material, and conductive polymer P3HT (poly-3hexylthiophene) is used as a donor material. The fullerene derivative and P3HT are mixed at a mass ratio of 1: 4 and dissolved in chlorobenzene. By preparing a blend solution and applying this blend solution to the surface of the hole transport layer by spin coating at 4000 rpm for 40 seconds, a first organic solar cell having a thickness of 80 nm is formed. A photoelectric conversion layer was formed.

  Next, a photoelectric conversion layer constituting the first organic solar cell is formed using a paste in which Ag particles having a particle diameter of 10 to 100 nm synthesized by a liquid phase reduction method are dispersed in alcohol at a content of 96% by mass. The first conductive layer was formed by applying this paste to the surface of the substrate and baking it at 120 ° C. Furthermore, the 2nd conductive layer was formed in the surface of the 1st conductive layer by apply | coating the paste of PEDOT-PSS and baking at 120 degreeC.

  Next, a second organic solar cell having a film thickness of 100 nm is formed by applying the same fullerene derivative and P3HT blend liquid as described above to the surface of the second conductive film by spin coating at 2500 rpm for 40 seconds. A constituent photoelectric conversion layer was formed.

  Finally, Al was vacuum-deposited on the surface of the photoelectric conversion layer constituting the second organic solar cell to form an Al electrode having a film thickness of 150 nm, thereby obtaining the stacked organic solar cell having the layer configuration of FIG. .

(Comparative Example 1)
In Example 1, the recombination layer was formed only with a conductive layer made of an Al film instead of being formed with a conductive layer made of an Al film and a conductive layer made of a PEDOT film. Others were carried out similarly to Example 1, and obtained the laminated organic solar cell.

(Comparative Example 2)
In Example 1, the recombination layer was formed only with the conductive layer made of the PEDOT film, instead of the two layers of the conductive layer made of the Al film and the conductive layer made of the PEDOT film. Others were carried out similarly to Example 1, and obtained the laminated organic solar cell.

(Comparative Example 3)
In Example 1, instead of forming the recombination layer with the first conductive layer made of the Al film and the second conductive layer made of the PEDOT film, the first is made of the Au film having a thickness of 5 nm by vacuum evaporation of Au. And a second conductive layer made of an Ag film having a thickness of 5 nm formed by vacuum deposition of Ag. Others were carried out similarly to Example 1, and obtained the laminated organic solar cell. Note that the work function of the first conductive layer formed of Au is 4.6 eV, and the work function of the second conductive layer formed of Ag is 4.5 eV.

  The stacked organic solar cells of Examples 1 and 2 and Comparative Examples 1 to 3 manufactured as described above were irradiated with simulated sunlight (AM1.5) by a solar simulator (manufactured by Yamashita Denso Co., Ltd.), and output characteristics were obtained. Evaluated. As a result, the results shown in Table 1 were obtained.

  As can be seen in Table 1, when the two-layer organic solar cell is stacked via the conductive layer, a conductive layer having a two-layer structure in which the work function of the second conductive layer is larger than that of the first conductive layer is formed. In Examples 1 and 2, the work functions of the second conductive layer are smaller than those of Comparative Example 1 and Comparative Example 2 in which the conductive layer is formed as a single layer. Compared to Comparative Example 3 in which a conductive layer having a layer structure was formed, the open circuit voltage was almost doubled, and high conversion efficiency could be obtained. And the light absorption characteristic of the photoelectric converting layer which comprises a 1st organic solar cell or a 2nd organic solar cell is adjusted, a 1st organic solar cell is made into a high band gap, and a 2nd organic solar cell is made low. When the band gap is adopted, the light absorption is further increased and the open circuit voltage is increased, so that higher conversion efficiency can be obtained.

  In Example 1, Al is vacuum-deposited on the surface of the first organic solar cell to form a first conductive layer, and then a PEDOT solution is applied to the surface of the Al conductive layer to form a second conductive layer. An Al conductive layer can prevent the PEDOT solution from acting on the first organic solar cell. On the other hand, in Comparative Example 2, the PEDOT solution is directly applied to the surface of the first organic solar cell to form a conductive layer, and the PEDOT solution acts on the first organic solar cell and deteriorates. It is conceivable that the characteristics are particularly low.

  In addition, since the solar cell characteristics in the single layer type when P3HT is used are characterized in that the generated current is higher and the generated voltage is lower than that of MDMO-PPV, the first embodiment and the first embodiment are also used in the stacked type. As shown in FIG. In Comparative Example 3, since the work function of the second conductive layer is smaller than that of the first conductive layer, the work functions of the electrodes on both sides of the first and second organic solar cells are reduced, and the generated current and generated voltage are reduced. However, since both the first conductive layer and the second conductive layer are metal layers, light transmission is reduced and current generated in the second organic solar cell is reduced. The efficiency was further reduced.

It is a figure which shows the layer structure of an example of embodiment of this invention. It is a figure which shows the layer structure of the other example of embodiment of this invention. It is a figure which shows the layer structure of the conventional low molecular weight type | system | group organic solar cell. It is a figure which shows the layer structure of the conventional bulk heterojunction type organic solar cell. It is a figure which shows the layer structure of the conventional low molecular type laminated | stacked organic solar cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Photoelectric conversion layer 21 1st organic solar cell 22 2nd organic solar cell 23 Recombination layer 24 Conductive layer 25 Conductive layer 26 Electrical insulation layer

Claims (4)

  In a stacked organic solar cell in which a plurality of organic solar cells each having a photoelectric conversion layer formed by blending a donor material and an acceptor material are stacked, the first organic solar cell disposed on the light incident side and the first organic solar cell Electrons and holes generated from the first and second organic solar cells are recombined between the second organic solar cell and the second organic solar cell which is stacked on the opposite side of the light incident side of the organic solar cell. A recombination layer is inserted, the recombination layer is formed with two conductive layers having different work functions, and among the two conductive layers of the recombination layer, the conductive layer on the second organic solar cell side The stacked organic solar cell is characterized in that the work function of is higher than the work function of the conductive layer on the first organic solar cell side.   2. The stacked organic solar cell according to claim 1, wherein the total thickness of the two conductive layers is 2 to 400 nm.   The stacked organic solar cell according to claim 1, wherein a light-transmitting electrical insulating layer is inserted between the two conductive layers. In manufacturing the stacked organic solar cell according to any one of claims 1 to 3, a particulate material having a particle size of 100 nm or less selected from Al, Ca, Mg, Ti, Ag, Mo, and In is dispersed in a solvent. By forming a conductive layer on the first organic solar cell side by applying a paste, and applying a paste in which a particulate material having a particle size of 100 nm or less selected from Pd, Au, ITO, and PEDOT is dispersed in a solvent A method for producing a stacked organic solar cell, comprising forming a conductive layer on the second organic solar cell side.

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