JP2013021070A - Method for manufacturing organic thin film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an organic thin film solar cell, by which the domain size of a bulk hetero-junction layer can be precisely controlled.SOLUTION: In a method for manufacturing an organic thin film solar cell including a first electrode layer, a photoelectric conversion layer and a second electrode layer which are formed in the order on a substrate, a coating liquid including a p-type organic semiconductor, an n-type organic semiconductor and an organic solvent is coated on the first electrode layer, the formed coating film is dried in vacuum to remove the organic solvent, and a bulk hetero-junction layer is formed. Before, during or after the second electrode layer is formed, the bulk hetero-junction layer is heated to control the domain size of the bulk hetero-junction layer.

Description

  The present invention relates to a method for manufacturing an organic thin film solar cell in which the domain size of a bulk heterojunction layer is controlled.

  A bulk heterojunction type organic thin film solar cell in which a bulk heterojunction layer is formed between a transparent electrode layer and a counter electrode layer as one of thin film solar cells using an organic material (hereinafter referred to as an organic thin film solar cell). (See Non-Patent Document 1).

  For example, as disclosed in Patent Document 1, a bulk heterojunction type organic thin film solar cell is formed by applying a coating liquid containing a p-type organic semiconductor, an n-type organic semiconductor, and an organic solvent on one electrode layer. And a bulk heterojunction layer is formed.

  In bulk heterojunction type thin film solar cells, it is known that the domain size of the bulk heterojunction layer has a great influence on the device characteristics, and control of the domain size is extremely important. That is, when the bulk heterojunction layer absorbs light, excitons are generated in the domain, diffuse in the domain, reach the pn interface, and are separated into free charges. The exciton diffusion length in the bulk heterojunction layer is small, 10 to 20 nm. When the domain size is larger than this diffusion length, free charges are not generated because excitons are deactivated before reaching the pn interface. In a situation where domains exist separately from each other, even if free charges are generated, they cannot be conducted to the electrodes. Under these circumstances, it is ideal that the domain size of the bulk heterojunction layer is 10 nm or less and that they are in contact with each other to form a percolation structure.

  When a bulk heterojunction layer is formed by applying a coating solution in which a sample material is dissolved, a step of removing the solvent from the coating film is required after the coating solution is applied. As a method for removing the solvent, a method of heating the coating film using a heater such as a hot plate to evaporate and remove the solvent is common.

  However, when the coating film is heated in the presence of a solvent, the phase separation of the bulk heterojunction layer proceeds rapidly, and large domains inappropriate in size for the solar cell element are easily formed. This is a more significant problem in amorphous polymer materials. Amorphous materials do not proceed with crystallization even when heated, and the domains are flexible and easily deformed. Therefore, the phase separation is more rapidly advanced by heating, and the domain size is likely to increase. It was difficult to control.

  Therefore, a means of using a solvent having a low boiling point as a solvent for dissolving the sample material and heating at a low temperature (for example, 100 ° C. or less) that does not cause the progress of the phase separation to progress remarkably can be considered. However, when a solvent having a low boiling point is used, most of the solvent is removed immediately after the solution is applied, so that it is difficult to form a bulk heterojunction layer having an appropriate structure. In order to form an appropriately structured bulk heterojunction layer, the solvent must have a boiling point of at least 100 ° C. or higher, and this means that the solvent is removed by heating at a low temperature of 100 ° C. or lower. In reality, it was difficult to apply.

  Further, there is a method of removing the solvent from the coating film by blowing and drying the coating film. However, it is difficult to completely remove the solvent having a relatively high boiling point by air blowing, and the solvent tends to remain in the bulk heterojunction layer. If the solvent remains in the bulk heterojunction layer, power generation is hindered, and the solar cell characteristics (short circuit current (Jsc), open circuit voltage (Voc), FF (curve factor), energy conversion efficiency (PCE), etc.) are likely to decrease. In particular, in the case of an amorphous material, phase separation may have progressed during blow drying to increase the domain size.

JP 2009-252768 A

F. Paddinger, R.M. S. Rittberger, N.M. S. Saricifci, Adv. Funct. Mater. 2003, 13, 85

  Accordingly, an object of the present invention is to provide a method for manufacturing an organic thin film solar cell that can control the domain size of a bulk heterojunction layer with high accuracy and has excellent power generation characteristics.

  As a result of intensive studies, the present inventors have vacuum-dried a coating film formed by applying a coating liquid containing a p-type organic semiconductor, an n-type organic semiconductor, and an organic solvent. It was found that the coating film can be dried and solidified in a state where the n-type organic semiconductor and the n-type organic semiconductor are almost uniformly mixed. Even when an amorphous material is used, it is possible to form a dried and solidified film in which both are mixed almost uniformly. It was also found that by heating the dried and solidified film in this way, molecular diffusion is suppressed, the phase separation progressing speed is lowered, and the domain size of the bulk heterojunction layer can be accurately controlled.

  That is, the method for producing an organic thin film solar cell of the present invention is a method for producing an organic thin film solar cell in which a first electrode layer, a bulk heterojunction layer, and a second electrode layer are formed on a substrate in this order. The bulk heterojunction layer is formed by applying a coating liquid containing an organic semiconductor, an n-type organic semiconductor, and an organic solvent onto the first electrode layer, and drying the formed coating film under vacuum to remove the organic solvent. The bulk heterojunction layer is heated before, during or after the formation of the second electrode layer to control the domain size of the bulk heterojunction layer.

  In the method for producing an organic thin-film solar cell of the present invention, it is preferable that an amorphous material is used as the p-type organic semiconductor and a fullerene derivative is used as the n-type semiconductor.

  In the method for producing an organic thin-film solar cell of the present invention, the boiling point of the organic solvent is preferably 100 to 300 ° C.

As for the manufacturing method of the organic thin film solar cell of this invention, it is preferable to vacuum-dry the said coating film on the conditions whose vacuum degree is 10 ^<-2 > Pa or less and temperature is 30-70 degreeC.

  According to the present invention, a coating liquid containing a p-type organic semiconductor, an n-type organic semiconductor, and an organic solvent is applied onto the first electrode layer, and the formed coating film is vacuum dried to remove the organic solvent. By removing, the organic solvent is rapidly removed from the coating film before the phase separation between the p-type organic semiconductor and the n-type organic semiconductor proceeds, and the p-type organic semiconductor and the n-type organic semiconductor are mixed almost uniformly. A formed film is formed. Then, by performing an appropriate heat treatment in the state where the organic solvent is removed, the solvent is removed, so that the diffusion of molecules is suppressed and the progress speed of phase separation is reduced, and the domain size of the bulk heterojunction layer is reduced. It can be controlled accurately.

4 is a phase image of a bulk heterojunction layer of Test Example 1. 4 is a phase image of a bulk heterojunction layer of Test Example 2. 4 is a phase image of a bulk heterojunction layer of Test Example 3.

  The manufacturing method of the organic thin-film solar cell of this invention forms in order of a 1st electrode layer, a bulk heterojunction layer, and a 2nd electrode layer on a board | substrate.

  The substrate is not particularly limited. For example, an insulating plastic film substrate such as a polyimide film, a polyethylene terephthalate film, a polyethylene naphthalate film, a polyethersulfone film, an acrylic film, an aramid film, a glass substrate, a stainless steel substrate, or the like can be used. In addition, when this board | substrate is distribute | arranged to the light-incidence side, it cannot be overemphasized that it should comprise with a light transmissive material.

  A first electrode layer is formed on the substrate. A method for forming the first electrode layer is not particularly limited, and a conventionally known method such as a sputtering method, a CVD method, or a spray film forming method can be used.

There is no limitation in particular as an electrode material which comprises a 1st electrode layer and the 2nd electrode layer mentioned later. Examples of the electrode material of the electrode layer disposed on the light incident side include transparent conductive oxides such as ITO (indium oxide + tin oxide), ZnO, TiO ₂ , SnO ₂ , and IZO (indium oxide + zinc oxide). . Examples of the electrode material of the electrode layer disposed on the non-light-receiving side include metals such as Al, Mg, Ca, and alloys thereof.

  Next, a coating liquid containing a p-type organic semiconductor, an n-type organic semiconductor, and an organic solvent is applied to the first electrode to form a coating film, which is then vacuum dried to form a bulk heterojunction layer. To do.

  As the p-type organic semiconductor, any organic material having an electron donating property can be used. For example, compounds such as thiophene, phenylene vinylene, thienylene vinylene, carbazole, vinyl carbazole, pyrrole, isothiaphene, isothiaphene and heptadiene, and hydroxyl groups, alkyl groups, amino groups, methyl groups, nitro groups and halogen groups, etc. Examples thereof include polymers of derivatives of the above compounds, but are not limited thereto. In addition, these may be used independently and may be used in combination of 2 or more types. For example, the compounds of the following formulas (1) to (14) are exemplified.

  5-150 is preferable and, as for n in said formula (1)-(14), 10-100 are more preferable.

  Among the above compounds, the compounds represented by the formulas (1) and (6) are crystalline compounds. Moreover, the compounds represented by the formulas (7) to (14) are amorphous (non-crystalline). The p-type organic semiconductor may be crystalline or amorphous (amorphous), and the degree of stereoregularity is not questioned. According to the method of the present invention, even if an amorphous material is used, an increase in domain size can be suppressed, and the domain size can be controlled with high accuracy, and therefore an amorphous material is particularly preferably used.

  The weight average molecular weight of the p-type organic semiconductor depends on the material to be used and cannot be generally mentioned, but is preferably 2,000 to 150,000.

As the n-type organic semiconductor constituting the bulk heterojunction layer, any organic material having an electron accepting property can be used. Examples thereof include fullerene derivatives and perylene derivatives. Among these, fullerene derivatives are particularly preferable because electron transfer from the p-type organic semiconductor is particularly fast. Preferred examples of the fullerene derivative include a fullerene C ₆₀ derivative, a fullerene C ₇₀ derivative, and a fullerene C ₈₀ derivative. As a specific _{example, Phenyl-C 61 -Butyric-Acid} -Methyl Ester ( hereinafter, also referred to as _"PCBM"), etc. Bisadduct-Phenyl-C 61 -Butyric- Acid-Methyl Ester and the like.

  The mixing ratio of the p-type organic semiconductor and the n-type organic semiconductor in the coating solution is a molar ratio, preferably p-type organic semiconductor: n-type organic semiconductor = 1: 0.5-7, 1: 0.7- 3 is more preferable.

  The organic solvent is desirably one having sufficient solubility for the p-type organic semiconductor and the n-type organic semiconductor. Moreover, if the boiling point of the organic solvent is too low, the solvent volatilizes immediately after application of the coating liquid, and the original purpose of rapidly removing the solvent by a vacuum process may not be achieved. Therefore, it is desirable that the organic solvent has a boiling point higher than a certain level, specifically 100 to 300 ° C is preferable, and 120 to 250 ° C is more preferable. Preferable specific examples of the organic solvent include chlorobenzene (boiling point: 131 ° C.), anisole (boiling point: 154 ° C.), 1,2-dichlorobenzene (boiling point: 181 ° C.), 1,2,3-trichlorobenzene (boiling point: 221). ° C) and the like.

  70-99.9 mass% is preferable and, as for content of the organic solvent in a coating liquid, 80-99 mass% is more preferable. When the content of the organic solvent is less than 70% by mass, polymer compounds that are solutes are aggregated and phase separation tends to hardly occur. If it exceeds 99.9% by mass, the viscosity of the solution decreases, and it becomes difficult to form a thin film having an appropriate film thickness by the coating process.

  The coating liquid can contain additives such as an antioxidant, a compatibilizing agent, and a crystallization accelerator within a range that does not impair the physical properties.

  The coating method of the coating liquid is not particularly limited, and conventionally known methods such as spin coating, dip coating, spray coating, ink jet printing, and screen printing can be used.

  In the present invention, the bulk heterojunction layer is formed by vacuum drying the coating film formed by applying the coating liquid. By vacuum-drying the coating film made of the coating solution, the organic layer is removed from the coating film before the phase separation between the p-type organic semiconductor and the n-type organic semiconductor proceeds, as shown in Test Example 1 of Examples described later. The solvent is removed rapidly. By removing the solvent from the coating film, the speed of phase separation is reduced, so that subsequent phase separation does not proceed rapidly during the heat treatment, and the increase in domain size can be suppressed. It can be controlled well.

  After applying the coating liquid to form a coating film, it is preferable that the time from the start of vacuum drying is as short as possible so that the organic solvent does not volatilize naturally from the coating film. Although the specific time depends on the vapor pressure of the solvent and the production environment, it cannot be generally specified, but is preferably within 15 minutes, more preferably within 5 minutes. Even if an organic solvent with a low vapor pressure is used, if the evaporation of the organic solvent proceeds while left in the atmosphere, phase separation between the p-type organic semiconductor and the n-type organic semiconductor proceeds, The effect expected in the present invention is reduced.

The coating film is preferably vacuum-dried for 30 minutes or more under the conditions of a degree of vacuum of 10 ⁻² Pa or less and a temperature of 30 to 150 ° C. The degree of vacuum is more preferably 10 ⁻³ Pa or less, and particularly preferably 10 ⁻⁴ Pa or less. The drying temperature is more preferably 50 to 120 ° C, particularly preferably 70 to 100 ° C. By vacuum drying under the above conditions, the organic solvent can be easily removed from the coating film before the phase separation between the p-type organic semiconductor and the n-type organic semiconductor proceeds.

Incidentally, the bulk binding layer, deposited metal film, TiO _x film was produced by a sol-gel method, by inserting the elution preventive film, such as such as ZnO nanoparticles, similarly, applying the coating solution onto the elution preventing film Alternatively, a bulk hetero-bonding layer may be formed by vacuum drying to form a tandem structure.

  The bulk heterojunction layer thus formed is heat-treated to adjust the domain size. The domain size of the bulk heterojunction layer is preferably 1 to 30 nm, and more preferably 1 to 10 nm. When the thickness is less than 1 nm, it is difficult to form a percolation structure in which adjacent domains are in contact with each other. If it exceeds 30 nm, the exciton is deactivated before reaching the pn interface, and it becomes difficult to generate free charges.

  In the phase separation of polymers, there are many cases where there is an upper limit and a lower limit in the critical temperature at which phase separation occurs, and the heat treatment conditions for adjusting the domain size must be values between these. As a result of the investigation, it was revealed that the upper limit is about 200 ° C. and the lower limit is about 50 ° C. for many p-type polymer semiconductors and n-type organic semiconductors. Furthermore, in order to form the optimal domain size as described above, 100 to 150 ° C. is more preferable. Regarding the heating time, if it is 10 minutes or less, the phase separation does not reach an equilibrium structure, and the phase separation structure no longer changes even if it continues for 30 minutes or more. From these circumstances, the heat treatment conditions for adjusting the domain size are 50 to 200 ° C., preferably 10 to 30 minutes, more preferably 100 to 150 ° C. and more preferably 10 to 30 minutes.

  The domain size of the bulk heterojunction layer can be measured by observing a phase image using an atomic force microscope (AFM).

  The heat treatment of the bulk heterojunction layer may be performed at any stage before, during, or after the formation of the second electrode layer. However, if the heat treatment is performed with the surface of the bulk heterojunction layer open, It is preferable to carry out after forming the second electrode layer because the molecular components are easily segregated on the surface.

  After forming the bulk heterojunction layer, a second electrode layer is formed on the bulk heterojunction layer using a conventionally known method such as sputtering, CVD, or vacuum deposition, and the bulk heterojunction layer is heat-treated as necessary. Thus, an organic thin film solar cell in which the domain size of the bulk heterojunction layer is controlled is obtained.

(Test Example 1)
20 mg of poly-3-hexylthiophene (P3HT) as p-type organic semiconductor and 14 mg of Phenyl-C ₆₁ -Butyric-Acyl-Methyl Ester (PCBM) as n-type organic semiconductor were collected and solvent chlorobenzene (boiling point 131 ° C.) It was dissolved in 1 mL and stirred for 20 hours to prepare a coating solution.
A glass substrate on which a first electrode (ITO) was formed was prepared, and the surface was dry-cleaned with oxygen plasma. Then, the said coating liquid was apply | coated on the board | substrate using the spin coater. The rotation condition was 2000 rpm × 120 s. Application was performed in a glove box filled with dry nitrogen.
Immediately after applying the coating solution, the substrate was taken out of the glove box and set in a bell jar type vacuum deposition apparatus. The degree of vacuum reached 10 ⁻³ Pa in about 30 minutes. Thereafter, vacuuming was performed for 30 minutes, and vacuum drying was performed for 30 minutes under a heating condition of 50 ° C. at a vacuum degree of 10 ⁻³ Pa to form a bulk heterojunction layer.
The bulk heterojunction layer after vacuum drying was observed using an atomic force microscope (AFM) to examine the phase separation structure. The observation using the phase image was performed so that the difference of the domain component could be detected sharply. The results are shown in FIG.
Next, after depositing and forming the second electrode (Al) on the bulk heterojunction layer, the substrate is returned to the glove box and subjected to heat treatment (130 ° C. × 15 minutes) using a hot plate to form an organic thin film. A solar cell was manufactured.

(Test Example 2)
Under the same conditions as in Test Example 1, a coating liquid was applied onto a glass substrate, and the substrate coated with the coating liquid was naturally dried in a glove box for 60 minutes to form a bulk heterojunction layer.
The bulk heterojunction layer after natural drying was observed using an atomic force microscope (AFM) to examine the phase separation structure. The observation using the phase image was performed so that the difference of the domain component could be detected sharply. The results are shown in FIG.
Then, on the bulk heterojunction layer, after forming the second electrode in the same manner as in Test Example 1, the substrate is returned to the glove box and subjected to heat treatment (130 ° C. × 15 minutes) using a hot plate, An organic thin film solar cell was manufactured.

(Test Example 3)
Under the same conditions as in Test Example 1, a coating solution was applied onto a glass substrate, and the substrate coated with the coating solution was subjected to heat treatment (130 ° C. × 15 minutes) using a hot plate in a glove box, and bulk hetero A bonding layer was formed. The bulk heterojunction layer after the heat treatment was observed using an atomic force microscope (AFM) to examine the phase separation structure. The observation using the phase image was performed so that the difference of the domain component could be detected sharply. The results are shown in FIG.
Then, the second electrode was formed on the bulk heterojunction layer in the same manner as in Test Example 1 to manufacture an organic thin film solar cell.

  Referring to FIG. 1, it can be seen that the boundary between the domains of the phase separation cannot be clearly confirmed, and the film is formed in a state where the two components are uniformly mixed. Thus, the phase separation could be suppressed by vacuum drying the coating film. On the other hand, as shown in FIGS. 2 and 3, phase separation occurred in Test Example 2 in which the coating film was naturally dried at room temperature and then heat-treated, and in Test Example 3 in which the coating film was heat-treated as it was.

  In addition, the light receiving cell (2 mm × 2 mm) of the organic thin film solar battery of Test Examples 1 to 3 is irradiated with simulated sunlight (AM1.5), and the solar battery characteristics (short circuit current (Jsc), open circuit voltage (Voc) ), FF (fill factor), energy conversion efficiency (PCE)). OTE-XL manufactured by Spectrometer Co., Ltd. was used for irradiation with simulated sunlight. For measurement of current density and voltage, 2400 made by KEITHLEY was used. Table 1 summarizes the results.

  As shown in Table 1, Test Example 1 showed the highest efficiency. On the other hand, in the devices of Test Examples 2 and 3, Jsc and FF were particularly lowered as compared with Test Example 1. These are considered to be influenced by the trapping of the carrier by the residual solvent. In particular, in the element of Test Example 3, the decrease in FF was significant. The decrease in FF is considered to be due to the segregation of the polymer due to heating with the film surface exposed.

Claims (4)

A method for producing an organic thin-film solar cell, which is formed on a substrate in the order of a first electrode layer, a bulk heterojunction layer, and a second electrode layer,
A coating liquid containing a p-type organic semiconductor, an n-type organic semiconductor, and an organic solvent is applied onto the first electrode layer, the formed coating film is vacuum dried to remove the organic solvent, and the bulk hetero An organic layer comprising: forming a bonding layer, and heating the bulk heterojunction layer before, during or after forming the second electrode layer to control a domain size of the bulk heterojunction layer Manufacturing method of thin film solar cell.   The method for producing an organic thin-film solar cell according to claim 1, wherein an amorphous material is used as the p-type organic semiconductor, and a fullerene derivative is used as the n-type semiconductor.   The manufacturing method of the organic thin-film solar cell of Claim 1 or 2 whose boiling point of the said organic solvent is 100-300 degreeC. The manufacturing method of the organic thin-film solar cell of any one of Claims 1-3 which vacuum-dry the said coating film on conditions with a vacuum degree of 10 ^<-2 > Pa or less and the temperature of 30-70 degreeC.