JP2008091380A - Organic photoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an organic photoelectric conversion element capable of improving open circuit voltage and photoelectric conversion efficiency. <P>SOLUTION: The organic photoelectric conversion element includes a pair of electrodes, and an electron release layer and an electron receiving layer provided between the pair of electrodes. The electron release layer has a phenanthrene skeleton of a structure indicated in the formula and is formed of at least one kind selected among a condensed polycyclic aromatic system compound A having six to ten condensed rings having a benzene ring as a basic unit and a condensed polycyclic aromatic system compound B having four to seven condensed rings linearly arranged having the benzene ring as a basic unit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an organic photoelectric conversion element using an organic material as a photoelectric conversion material.

Global warming due to the increase in CO ₂ concentration caused by the use of a large amount of fossil fuel, and the increase in energy demand accompanying population increase are recognized as problems related to the existence of humankind. For this reason, in recent years, the use of sunlight that is infinite and does not generate harmful substances has been energetically studied. What is currently put into practical use as solar energy as a clean energy source includes inorganic solar cells such as residential single crystal silicon, polycrystalline silicon, amorphous silicon, and cadmium telluride.

  These inorganic solar cells have various problems. For example, silicon-based solar cells require extremely high-purity silicon, which causes a problem that the purification process is complicated, the number of processes is large, and the manufacturing cost is high. Further, there is a demand for weight reduction and the like, and there is a disadvantage in that the payback to the user is particularly long, and there is a problem in further spread.

  On the other hand, many solar cells using organic materials have been proposed. As an organic solar cell, a Schottky photoelectric conversion element that joins an electron-donating p-type organic semiconductor and a metal having a low work function, a p-type organic semiconductor and an electron-accepting n-type inorganic semiconductor, or a p-type organic semiconductor Examples include a heterojunction photoelectric conversion element that joins an electron-accepting n-type organic semiconductor. Examples of the n-type organic semiconductor used include synthetic dyes and pigments such as chlorophyll and perylene, conductive polymer materials such as polyacetylene, and composite materials thereof. These are thinned by a vacuum deposition method, a casting method, a dipping method, or the like to form a battery material. Organic materials have advantages such as low cost and process saving, but many have low conversion efficiency of 1% or less.

  Under the circumstances as described above, the following heterojunction organic thin film solar cell (see Non-Patent Document 1) has been reported by Dr. Tan et al. Of Kodak, USA as an organic solar cell exhibiting good characteristics. Yes. That is, it has been reported that a thin film in which an electron-donating copper phthalocyanine (CuPc) and an electron-accepting perylene derivative are stacked by vacuum deposition performs photoelectric conversion with high efficiency. Although the conversion efficiency was 0.95%, it was a breakthrough of organic solar cells.

  Furthermore, it has been reported that the photoelectric conversion efficiency is improved to 3.4% by using fullerene having a long exciton diffusion length (see Non-Patent Document 2).

  A module obtained by modularizing the above-described organic solar cell has not yet been marketed, but when these elements are modularized, they are connected in series up to a desired voltage. At present, the open-circuit voltage per element is about 0.5 V, which is equivalent to or slightly inferior to other types of solar cells. As one approach, a structure in which an electron donating material-electron accepting material unit is laminated twice or more in a tandem type has been proposed (see Patent Document 1). However, there is a problem in that the current that can be taken out is smaller than in the case of one unit.

In a single device, an open circuit voltage of 0.91 V is obtained in a photoelectric conversion device using rubrene instead of electron donating copper phthalocyanine (CuPc) (see Non-Patent Document 3).
JP-T-2004-523129 Appl. Phys. Lett. , 48, 183 (1986) Appl. Phys. Lett. 79, 126 (2001) J. et al. J. et al. Appl. Phys. , 45, L995 (2006)

  The objective of this invention is providing the organic photoelectric conversion element which can raise an open circuit voltage and photoelectric conversion efficiency.

  The present invention is an organic photoelectric conversion device comprising a pair of electrodes, an electron donating layer and an electron accepting layer disposed between the pair of electrodes, wherein the electron donating layer has a phenanthrene skeleton having the structure shown below. A condensed polycyclic aromatic compound A having a benzene ring as a basic unit and a number of condensed rings in the range of 6 to 10 and a condensed ring having a benzene ring as the basic unit in the range of 4 to 7 It is characterized by being formed of at least one selected from condensed polycyclic aromatic compounds B having a structure arranged in a shape.

  Examples of the condensed polycyclic aromatic compound A include those represented by the following general formula (1).

(Wherein, R ₁ to R ₄ is an alkyl group, an alkenyl group, an aryl group, an aralkyl group, a heterocyclic group, may be different from each other.)
Examples of the alkyl group include a methyl group, an ethyl group, and an isopropyl group. Examples of the alkenyl group include a vinyl group and a cyclohexenyl group. Examples of the aryl group include a phenyl group and a naphthyl group. Examples of the aralkyl group include a benzyl group and a 1-naphthylmethyl group. Examples of the heterocyclic group include a furyl group, a thienyl group, and an indolyl group.

  Moreover, said alkyl group, alkenyl group, aryl group, aralkyl group, and heterocyclic group may have a substituent. Specific examples of the substituent include the above-mentioned alkyl groups; alkoxy groups such as methoxy group, ethoxy group and n-hexyloxy group; alkylthio groups such as methylthio group and n-hexylthio group; phenoxy group, 1-naphthyloxy group and the like An arylthio group such as a phenylthio group; a halogen atom such as chlorine or bromine; a disubstituted amino group such as a dimethylamino group or a diphenylamino group; an aryl group as described above; a heterocyclic group as described above; a carboxyl group; Carboxyalkyl groups such as sulfonyl groups; sulfonylalkyl groups such as sulfonylpropyl groups; acidic groups such as phosphoric acid groups and hydroxamic acid groups; electron withdrawing groups such as cyano groups, nitro groups, and trifluoromethyl groups. Can do.

  Examples of the condensed polycyclic aromatic compound B include those represented by the following general formula (2).

(In the formula, Ar _{1 to} Ar ₄ represent an aryl group, and at least one of them is a naphthyl group, and may be different from each other.)
Ar _{1 to} Ar ₄ may have a substituent similarly to R _{1 to} R ₄ described above.

  Specific examples of the condensed polycyclic aromatic compound A include those having the structure of the following formula (3).

  Specific examples of the condensed polycyclic aromatic compound B include those having the structure of the following formula (4).

  The electron-accepting layer in the present invention is not particularly limited as long as it can be used as an electron-accepting layer in an organic photoelectric conversion element. For example, a material such as naphthalene, carbon nanotube, or perylene can be used.

  In the present invention, an exciton blocking layer is preferably provided between the electron accepting layer and the electrode. The exciton blocking layer functions to confine excitons generated by light in a region near the charge separation interface and prevent deactivation of the excitons at the electron accepting layer / electrode interface (see Patent Document 1). . The exciton blocking layer in the present invention is not particularly limited as long as it can be used as an exciton blocking layer. For example, BCP (2,9-dimethyl-4,7-diphenyl-1,10- Phenanthroline), PTCBI (3,4,9,10-perylenetetracarboxylic bis-benzimidazole), PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride), PTCDI (3,4,9, Materials such as 10-perylenetetracarboxylic diimide), NTCDA (1,4,5,8-naphthalenetetracarboxylic dianhydride), and derivatives thereof can be used.

  The electrode in the present invention is not particularly limited as long as it can be used as an electrode of an organic photoelectric conversion element. For example, Al, Au, Ag, Sb, Sn, In, or Mg and Ag as metal materials. Or a metal oxide can be used.

  ADVANTAGE OF THE INVENTION According to this invention, an open circuit voltage can be raised and it can be set as the organic photoelectric conversion element excellent in photoelectric conversion efficiency.

  Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to the following examples.

(Example 1)
An organic photoelectric conversion device having the structure shown in FIG. 1 was produced. As shown in FIG. 1, an electron donating layer 2 and an electron accepting layer 3 are formed on the first electrode 1, and an exciton blocking layer 4 is formed on the electron accepting layer 3. . A second electrode 5 is formed on the exciton block layer 4.

Using a glass substrate on which an ITO (indium tin oxide film) film was formed, an organic material film was formed by heating and vapor deposition on the ITO film to be the first electrode 1 as follows. The vapor deposition conditions were room temperature, a pressure of 10 ⁻⁵ Pa, and a deposition rate of 0.05 to 0.2 nm / second.

  The electron donating layer 2 was formed with a thickness of 20 nm using 9,10,15,16-tetraphenyldibenzo [a, c] tetracene having the structure of the above formula (3). The electron-accepting layer 3 was formed using fullerene (C60) so as to have a film thickness of 40 nm. The exciton blocking layer 4 was formed using BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) so as to have a film thickness of 10 nm.

The second electrode 5 was formed by depositing Al (aluminum) using a shadow mask of 0.03 cm ² . The thickness of each layer can be controlled by using, for example, a crystal oscillator film thickness monitor.

  BCP has the following structure.

The organic photoelectric conversion element produced as described above was irradiated with pseudo-sunlight generated from a solar simulator (air mass 1.5G spectrum, irradiation intensity 100 mW / cm ² ) as a light source, and its characteristics were evaluated. As a result, an open circuit voltage of 1.02 V, a short-circuit current density of 2.47 mA / cm ² , a shape factor of 0.53, and a conversion efficiency of 1.77% were obtained.

(Example 2)
The electron donating layer 2 is formed in the same manner as in Example 1 except that 5,6,11,12-tetranaphthyltetracene having the structure of the above formula (4) is used and the film thickness is 30 nm. A photoelectric conversion element was produced.

As a result of evaluating the characteristics of the produced organic photoelectric conversion element in the same manner as in Example 1, the open circuit voltage was 0.93 V, the short-circuit current density was 2.56 mA / cm ² , the form factor was 0.50, and the conversion efficiency was 1.57. % And a good value were obtained.

(Comparative Example 1)
An organic photoelectric conversion element was produced in the same manner as in Example 1 except that the electron donor layer 2 was formed using rubrene having the following structure so as to have a film thickness of 40 nm.

As a result of evaluating the characteristics in the same manner as in Example 1, a result with an open circuit voltage of 0.91 V, a short circuit current density of 2.63 mA / cm ² , a form factor of 0.53, and a conversion efficiency of 1.48% was obtained.

  From the above, the organic photoelectric conversion element using the condensed polycyclic aromatic compound of the present invention for the electron donating layer has higher open-circuit voltage and conversion efficiency than the conventional organic photoelectric conversion element using rubrene for the electron donating layer. It can be seen that

<Method for synthesizing electron donating layer material>
(Method for synthesizing 9,10,15,16-tetraphenylcybenzo [a, c] tetracene)

  Fencyclone 4.0 g (10.4 mmol, compound 1), 1,4-naphthoquinone 1.7 g (10.5 mmol, compound 2) and triglyme 50 ml were mixed and stirred at 200 ° C. overnight.

  The reaction solution was diluted to 1 L with MeOH, and the precipitated crystals were separated by filtration. The crude product was reprecipitated with toluene and hexane to obtain 4.0 g of yellow crystals (compound 3, yield 75%).

  Under a stream of argon, 16 ml (16 mmol) of phenylmagnesium bromide (1M THF solution) was added to 2.0 g (3.9 mmol) of Compound 3 in 20 ml of diethyl ether at less than 5 ° C. Stir at room temperature for 2 hours.

  Water was added to the reaction solution and stirred for a while, and then the solvent was concentrated under reduced pressure. The precipitated crystals were separated by filtration and purified by silica gel column chromatography to obtain 1.2 g (compound 4, yield 46%) of white crystals.

  To a solution of 0.50 g (0.75 mmol) of Compound 4 in 10 ml of THF, 5 g of 47% hydroiodic acid was added and stirred at room temperature for 1 hour.

  300 ml of water was added to the reaction solution, and the precipitated crystals were washed with MeOH. Purification by silica gel column chromatography gave 0.19 g of 9,10,15,16-tetraphenyldibenzo [a, c] tetracene yellow crystals (compound 5, yield 40%).

  (Method for synthesizing 5,6,11,12-tetranaphthyltetracene)

  Compound 1: 4 g (11.1 mmol), 1,2-dibromoethylene 4.1 g (22.1 mmol), p-toluenesulfonic acid 50 mg and toluene 15 ml were mixed and refluxed overnight.

  Methanol was added to the reaction solution, and the precipitated crystals were filtered. This was recrystallized from ethanol-toluene to obtain compound 2: 0.5 g (yield 8.4%).

  Compound 2: 0.62 g (1.15 mmol), Compound 1: 0.41 g (1.11 mmol) in anhydrous THF 10 ml solution, 1.6 MBuLi (n hexane solution) 0.71 ml (1.14 mmol) − Added at 78 ° C. and stirred overnight.

  10 ml of water was added to the reaction solution, and the precipitated crystals were separated by filtration. This was recrystallized from ethanol-toluene to obtain 0.50 g (yield 60.1%) of Compound 3:

Compound 3: 0.75 ml (0.75 mmol) of AlBr ₃ (1.0 M dibromomethane solution) was added to a solution of 0.51 g (0.68 mmol) and 0.53 g (2.04 mmol) of cesium iodide in 10 ml of chloroform. Added at -75 ° C.

  The reaction was warmed to room temperature and 10 ml of water was added. The organic layer was separated and washed twice with 10 ml of water. The extract was dried over magnesium sulfate and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (silica gel 100 g, eluent toluene / hexane = 5/1) and then recrystallized from ethanol-toluene to give 5,6,11,12-tetranaphthyltetracene (compound 4: 0.22 g (44% yield)) was obtained.

The typical sectional view showing the organic photoelectric conversion element of one example according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st electrode 2 ... Electron donation layer 3 ... Electron acceptance layer 4 ... Exciton block layer 5 ... 2nd electrode

Claims (6)

An organic photoelectric conversion device comprising a pair of electrodes, and an electron donating layer and an electron accepting layer disposed between the pair of electrodes,
The electron donating layer has a phenanthrene skeleton having the structure shown below, and the condensed polycyclic aromatic compound A having a benzene ring as a basic unit and having a number of condensed rings in the range of 6 to 10, and a benzene ring. An organic photoelectric conversion element comprising at least one selected from condensed polycyclic aromatic compounds B having a structure in which a condensed ring as a basic unit is linearly arranged in a range of 4 to 7.

2. The organic photoelectric conversion device according to claim 1, wherein the condensed polycyclic aromatic compound A is represented by the following general formula (1).

(Wherein, R ₁ to R ₄ is an alkyl group, an alkenyl group, an aryl group, an aralkyl group, a heterocyclic group, may be different from each other.) 2. The organic photoelectric conversion device according to claim 1, wherein the condensed polycyclic aromatic compound B is represented by the following general formula (2).

(In the formula, Ar _{1 to} Ar ₄ represent an aryl group, and at least one of them is a naphthyl group, and may be different from each other.) 2. The organic photoelectric conversion device according to claim 1, wherein the condensed polycyclic aromatic compound A has a structure represented by the following formula (3).

2. The organic photoelectric conversion device according to claim 1, wherein the condensed polycyclic aromatic compound B has a structure represented by the following formula (4).

  The organic photoelectric conversion element according to claim 1, wherein an exciton blocking layer is provided between the electron accepting layer and the electrode.

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