JP2008117798A - Organic thin-film element and tandem type photoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve current/voltage characteristics in an organic thin-film element. <P>SOLUTION: In the organic thin-film element, a plurality of functional elements having at least one organic thin film layer are laminated. The organic thin-film element uses a conductive organic compound, wherein at least one cyano group is coordinated to an electron transporting organic material as a connection layer for mutually connecting the functional elements. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thin film element, and more particularly to an organic thin film element and a tandem photoelectric conversion element in which a plurality of functional element portions each having an organic thin film layer are stacked.

  Organic thin film devices have been developed in many fields such as solar cells, LEDs, TFTs, and semiconductor sensors.

  Taking organic solar cells as an example, organic solar cells have characteristics not found in silicon devices, such as low energy costs in the manufacturing process and application of printing technology as a manufacturing process suitable for large area. Has been studied since.

  As one means for improving the efficiency performance, a tandem structure in which elements are stacked has been reported. A tandem element is a structure in which a plurality of heterojunction semiconductors are stacked with a connection layer therebetween to form one element. The tandem type device has a double open-circuit voltage (in the case of two layers) when there is no loss of the connection layer compared to a single layer type device (single device; an element having only one heterojunction semiconductor). Become.

  S. R. Forrest et al., In “Appl. Phys. Lett. 80, 1667 (2002)”, a metal cluster is used as an internal electrode to reduce the film thickness of the front cell and the back cell to balance light absorption. We have reported an example of successful conversion efficiency improvement compared to a single-layer device by making the photocurrent generated in the cell and the back cell substantially the same.

In addition, tandem-type high brightness and long-life devices have been reported for organic LEDs that are light-emitting elements. In Japanese Patent Application Laid-Open No. 2003-272860, a layer connecting light emitting elements is called a CGL layer, and a conductor ITO (indium tin oxide) or an insulator V ₂ O ₅ (vanadium pentoxide): αNPD, 4F- A device using a layer in which a charge transfer complex is formed by a combination of TCNQ (tetracyanoquinodimethane): αNPD or the like has been proposed. With the tandem structure, the luminance equivalent to the stacked elements can be obtained with the same current as that of the single element, so that the luminance efficiency (cd / A) per current increases. Further, in the case of emitting light with the same brightness as that of a single element, less current is required than that of a single element, so there is an advantage that the life is extended.

JP 2003-272860 A A. Yakimov and S.M. R. Forrest, Appl. Phys. Lett. 80, 1667 (2002)

  Organic solar cells have been improved as a result of the above research, but there is a problem that the energy conversion efficiency is lower than that of currently used silicon (single crystal silicon, polycrystalline silicon, amorphous silicon) devices. It has not been put into practical use. Even in a tandem organic solar cell for improving efficiency, when a conductive metal is used for the connection layer, the transmittance is low, so that light absorption is reduced as the element is farther from the incident light side, and the power generation amount is reduced. The method using metal clusters in the connection layer reported by Forrest et al. Improves the transmittance problem, but it is difficult to control the film thickness as compared to other structures.

When ITO or a charge transfer complex such as V ₂ O ₅ : αNPD or 4F-TCNQ: αNPD is used as a tandem organic LED, sputter damage, low transmittance, V ₂ O ₅ or 4F-TCNQ are specified as deleterious substances Development of a new element is required because it is a substance.

  An object of the present invention is to provide an organic thin film element with improved performance and an organic semiconductor element using the same.

  According to one aspect of the present invention, between a pair of electrodes, a plurality of functional element units formed between the pair of electrodes and having at least one organic thin film layer, and the plurality of functional element units. And an organic thin film element having a connection layer using an electron transporting organic compound coordinated with at least one cyano group.

  According to another aspect of the present invention, a plurality of unit cells formed between a transparent electrode, a counter electrode, the transparent electrode and the counter electrode, and having at least one organic thin film layer; There is provided a tandem photoelectric conversion element having a connection layer using an electron transporting organic compound formed between them and coordinated with at least one cyano group.

-The transmittance of the connection layer is improved.
・ It becomes easier to control the film thickness.
・ Spatter damage can be avoided.
・ Use of deleterious substances can be avoided.
-The affinity with the electron transport layer in contact with the connection layer is improved, and the electron barrier of the junction is lowered.
-As a result, the performance as an organic thin film element improves.

  The inventors have invented the use of an organic compound in which at least one cyano group (CN) is coordinated in a connection layer connecting the stacked elements in a tandem organic thin film element. This is because the use of an organic material improves the problem of metal transmittance, the problem of thin film thickness control, the problem of sputter damage, the use of a deleterious substance designated substance, and the like.

  The inventors prepared a sample SA of a tandem photoelectric conversion element that can be used as a solar cell, using an organic compound A (described later) for the connection layer, and investigated its characteristics.

  FIG. 1 is a schematic sectional view showing the structure of the sample SA. The transparent electrode 2 and the counter electrode 6 made of ITO are composed of two unit cells (functional element portions) 3 and 5 formed between the two electrodes, and a connection layer 4 formed between the unit cells. Hereinafter, the unit cell formed on the transparent electrode 2 side is referred to as a front cell 3, and the unit cell formed on the counter electrode 6 side is referred to as a back cell 5. The illustrated sample SA was produced as follows.

  A glass plate with an ITO electrode 2 was used as the substrate 1. The ITO electrode 2 was formed by sputtering on a glass plate and then patterned by photolithography.

  The patterned substrate 1 was subjected to ultrasonic cleaning in a neutral detergent for 10 minutes. Then, ultrasonic rinse was performed 3 times for 10 minutes in pure water to give a pure rinse. Subsequently, ultrasonic cleaning using acetone and ultrasonic cleaning of isopropyl alcohol (IPA) were performed for 10 minutes for dehydration and degreasing.

After placing the substrate in the IPA vapor tank for 20 minutes, the substrate 1 was introduced into a vacuum chamber in which the organic tank and the electrode tank were connected, and the pressure in the container was evacuated to about 1 × 10 ⁻⁵ Pa. Then, in order to form an organic layer pattern, the organic substance was vapor-deposited through the vapor deposition mask made from stainless steel (SUS430). The vapor deposition rate of each material was monitored with a quartz resonator and ULVAC CRTM-9000, and maintained at 1-2 Å / s.

  An organic layer was formed as follows. First, the front cell 3 was produced. First, a copper phthalocyanine (CuPc) layer was deposited to a thickness of 20 nm to form a hole transport layer 3a. Next, CuPc: fullerene (C60) was co-deposited at a deposition rate of 1 Å / s to obtain an active layer 3b having a thickness of 10 nm. Third, C60 was deposited by 30 nm to form the electron transport layer 3c. Furthermore, bathocuproine was vapor-deposited by 10 nm thereon to form a hole blocking layer 3d, and a front cell 3 was produced.

  Subsequently, the connection layer 4 using the compound A was deposited on the front cell 3 by 10 nm.

  FIG. 2 shows the chemical structural formula of Compound A. As shown in FIG. 2, Compound A has “aluminum tris (3, 6 dicyano-8-quinolinolate)” = “Tris (3,6-dicyano-8-quinolinolato) in which CN is coordinated to an aluminum quinolinol complex. Aluminum ".

  On the connection layer, layers 5a, 5b, 5c, and 5d having the same material and film thickness as the three layers 3a, 3b, 3c, and 3d of the front cell were laminated in this order to produce the back cell 5.

  Then, it moved to the electrode tank, maintaining the vacuum, and using the vapor deposition mask of the electrode pattern, 100 nm of aluminum was vapor-deposited by resistance heating on the back cell, and the electrode 6 as a cathode was formed.

  The substrate 1 that had been formed up to the formation of the electrode 6 was introduced into a glove box in a nitrogen gas atmosphere without being exposed to the atmosphere, and sealed with a stainless steel plate having a recess. The stainless steel plate was subjected to ultrasonic cleaning with IPA and acetone for 10 minutes for degreasing, respectively, and then UV ozone cleaning was performed for 30 minutes before introduction into the glove box.

  As a getter agent, a Desicant manufactured by Gore-Tex was attached to the concave portion of the stainless steel plate, and a seal was drawn with an epoxy resin manufactured by Nagase Chemtex.

  The substrate 1 having the above laminated structure (electrode 2, front cell 3, connection layer 4, back cell 5, electrode 6) and a stainless steel plate with a sealing material are brought into close contact (with the laminated structure inside and accommodated in a stainless steel plate recess). Only the seal portion was irradiated with UV for 180 seconds with a UV lamp to cure the seal resin.

  Thus, a sample SA of a tandem photoelectric conversion element using the compound A for the connection layer 4 was produced.

The sample SA was irradiated with light from a high-pressure discharge lamp in the visible light region having an energy of 26.6 mW / cm ² from the glass substrate side, and current-voltage characteristics were measured.

As a comparative example, an element sample SB in which the connection layer of the tandem photoelectric conversion element having the above structure was changed to a silver thin film (0.5 nm) was produced. In addition, a single element sample SC in which the cell was only a front cell and an aluminum Al cathode of 100 nm was deposited on the front cell was also produced. These samples were irradiated with light from a high-pressure discharge lamp in the visible light region having an energy of 26.6 mW / cm ² from the glass substrate side, and current-voltage characteristics were measured. The energy conversion efficiency was calculated from the obtained current-voltage characteristics.

  FIG. 3A shows current-voltage characteristics obtained from samples SA, SB, and SC, and FIG. 3B shows various characteristics. As shown in FIG. 3B, the tandem element sample SA using the compound A is equivalent to the short-circuit current of the single element sample SC and the open circuit voltage is about 1.7 times, so that the front cell and the back cell are connected layers. It can be seen that there are few barriers through the connection. When an Ag thin film is used for the connection layer, the characteristics are inferior to those of others. Although the thickness of the silver thin film was changed to 1 nm and 10 nm, the characteristics were not improved.

  It can be seen that the silver thin film does not function in the configuration using bathocuproine and copper phthalocyanine as in this comparative sample SB, and it is understood that the use of silver for the connection layer 4 is not necessarily appropriate for all materials.

  Subsequently, the inventors created a sample SD using the compound B described later in the connection layer in the same process as the above sample. As the front cell 3, CuPc was deposited at 10 nm, and then a 1: 1 mixed layer of CuPc and C60 was deposited at 10 nm, C60 at 10 nm, and bathocuproine at 10 nm. Compound B, which is a hexaazotriphenylene derivative provided with a cyano group, was deposited as a connection layer by 10 nm.

  FIG. 4 shows the chemical structural formula of Compound B. As shown, compound B is hexanitrile hexaazotriphenylene in which CN is coordinated to hexaazotriphenylene.

  Subsequently, the back cell 5 was formed. The back cell was deposited with 10 nm of CuPc, 10 nm of a 1: 1 mixed layer of CuPc and C60, 30 nm of C60, and 10 nm of bathocuproine. Al was deposited on the cathode 6 by resistance heating. The sealing step was performed in the same manner as the sample SA, and a tandem photoelectric conversion element sample SD was produced.

  As a comparative example, a single element sample SE in which the cell was only a front cell similar to the sample SD and an aluminum Al cathode of 100 nm was deposited on the front cell was prepared.

  FIG. 5A shows current-voltage characteristics obtained from samples SD and SE, and FIG. 5B shows various characteristics. As shown in FIG. 5B, the tandem element sample SD using the compound A is equivalent to the short-circuit current of the single element sample SE and has an open circuit voltage of about 2 as in the sample SA using the compound A for the connection layer. Because it is 3 times (there is a large variation in each element, there are cases where it is more than twice the theoretical value in measurement, but the effect that the connection barrier is smaller compared to the prior art can be asserted) It can be seen that the back cell can be connected through the connection layer with few barriers.

  The reason why various characteristics are improved by using Compound A or Compound B in the connection layer is considered as follows. The organic substance that can be used for the connection layer has a structure having a cyano group (CN) that is an electron-withdrawing group in an organic substance having high electron conductivity. Organic substances having high electron conductivity have electron accepting properties and are known as electron transporting materials. By substituting this material with a cyano group having an electron withdrawing function, it is possible to have a function of generating holes. For this reason, electrons and holes, which are the role of the connection layer, are generated and can themselves have the same function as the wiring. Furthermore, since the connection layer has an electron transport material as a basic skeleton, it is considered that the connection layer has a high affinity with the n-type organic semiconductor or the electron transport layer in contact with the connection layer, and can be bonded with few barriers.

  Based on the above consideration, as another organic compound whose characteristics are improved by using it for the connection layer, a derivative of a compound (mainly an aromatic compound) recognized by those skilled in the art as an electron transporting material, It is considered that a compound in which at least one of these is coordinated can be applied.

  6A and 6B show chemical structural formulas of compounds A2 and A3 in which the coordination between compounds A and CN is changed with an aluminum quinolinol complex. From the above consideration, in the aluminum quinolinol complex, the properties of the tandem element will be improved even with the compounds A2 and A3 in which the coordination between the compounds A and CN is changed.

  Furthermore, in the quinolinol metal complex, substantially the same properties are obtained even with other derivatives other than compounds A, A2, and A3 in which at least one CN is coordinated to the 2-7 position of the quinoline ring, and the connection layer has It can be used.

  FIG. 7 shows a chemical structural formula of a quinolinol metal complex derivative (referred to as compound A0. Compound A0 includes compounds A, A2, and A3) that can be used for the connection layer. In the figure, M is a metal, and Zn, Ga, and Li may be coordinated in addition to Al. In the figure, hydrogen H or CN is coordinated to R1 to R6, and at least one is CN. n varies depending on the coordinated metal and is 3 in the case of Al.

  Similar to the quinolinol metal complex derivative, the hexaazotriphenylene derivative to which the compound B belongs can be used in the connection layer as long as it is a hexaazotriphenylene derivative coordinated with at least one CN.

  FIG. 8 shows a chemical structural formula of a hexaazotriphenylene derivative (referred to as compound B0. Compound B0 includes compound B) that can be used for the connection layer. In the figure, any one of H, an alkyl group, a phenyl group, a naphthyl group, and CN is coordinated with R1 to R6, and at least one is coordinated with CN.

  In addition, it is considered that a derivative in which at least one CN is coordinated to phenanthroline, triazine, or oxadiazole recognized as a material having an electron transport property by those skilled in the art can be used for the connection layer.

  FIG. 9 shows a chemical structural formula of a phenanthroline derivative (compound C0) that can be used for the connection layer. In the drawing, any one of H, an alkyl group, a phenyl group, a naphthyl group, and a cyano group (CN) is coordinated with R1 to R8, and at least one is coordinated with CN.

  For example, CN is coordinated to R1 and R8, “1,10-Phenanthroline-2, 9-dinitride”, CN is coordinated to R1, R3, R6, and R8, “1,10-Phenanthhroline-2, 4 , 7, 9-tetranitride ", CN is coordinated to R1, R2, R7 and R8, CN is coordinated to" 1, 10-Phenanthroline-2, 3, 8, 9-tetranitride ", R1 and R8, Examples include compounds such as "1, 10-phenanthroleline-2, 9-dinitride-4, 7-diphenyl" in which a phenyl group is coordinated to R3 and R6 (all compounds have other coordination positions, H is substituted).

  FIG. 10 shows a chemical structural formula of a triazine derivative (compound D0) that can be used for the connection layer. Any structure in which at least one CN is coordinated to positions 4, 5, and 6 of the three pyrimidine rings in the figure can be used for the connection layer. In the drawing, any one of H, an alkyl group, a phenyl group, a naphthyl group, and CN is coordinated with R1 to R9, and at least one is coordinated with CN. For example, a compound in which CN is coordinated to R2, R5 and R8 (H is coordinated to R1, R3, R4, R6, R7 and R9), or CN is coordinated to R1, R3, R4, R6, R7 and R9. Compounds that are coordinated (H is coordinated to R2, R5, and R8).

  FIG. 11 shows a chemical structural formula of an oxadiazole derivative (compound E0) that can be used for the connection layer. In the figure, any one of H, an alkyl group, a phenyl group, a naphthyl group, and CN is coordinated to R1 to R8, and at least one is coordinated with CN. Examples thereof include compounds in which CN is coordinated to R2 and R4, and H is coordinated to R1, R3, and R5 to R8.

  In the above, the configuration of the tandem organic solar cell has been shown, but the embodiment of the present invention is not limited to the above. The unit cell (functional element part) may be three or more, and the configuration of the unit cell is appropriately designed according to desired characteristics. Further, the configuration of each unit cell may be different. For example, in the tandem organic solar cell, unit cells having different absorption wavelength ranges such as a combination of a front cell that absorbs visible light and a back cell that absorbs infrared light can be stacked.

  Further, when the functional element portion includes at least a light emitting layer and appropriately includes an electron transport layer, an electron injection layer, a hole transport layer, a hole injection layer, a hole blocking layer, and the like, Type organic LED is constructed. For example, a tandem white organic LED can be formed by forming a blue light emitting element part, a connection layer, a yellow light emitting element part, and a counter electrode on a transparent substrate on which a transparent electrode is formed. The blue light-emitting element part is a hole transport layer made of α-NPD, a blue light-emitting layer made of 4, 4′-Bis (2, 2-diphenyl-ethen-1-yl) diphenyl, Tris (8-hydroxyquinolineate). It can be composed of an electron transport layer made of aluminum (hereinafter referred to as Alq8), and the yellow light emitting element part is a yellow transport layer made of α-NPD, a yellow light made of Alq8 doped with 5, 6, 11, 12-tetraphenylnaphthacene. The light-emitting layer can be composed of an electron transport layer made of Alq8.

  Therefore, the organic thin film element of the present invention can be configured by laminating a plurality of functional element portions each composed of a thin film layer mainly composed of an organic compound via the same connection layer.

  FIG. 12 shows a schematic cross-sectional view of a basic organic thin film element Y using these compounds X (compounds A0, B0, C0, D0, E0, which are collectively referred to as compound X here) as a connection layer. . As shown in the figure, a functional element portion (corresponding to a unit cell of a sample element in the above embodiment) OC1 to OCn mainly composed of an organic compound is laminated on a substrate 7 having an electrode 8 on the upper part, and further on it. An electrode 9 is formed. The structure of each functional element portion is configured according to the desired function and characteristics of the organic thin film element Y. The connection layer J is formed between the functional element portions, and at least one of the compounds X is used.

  FIG. 13 shows an application example of the organic thin film element Y. As shown in FIG. 13, the organic thin film element Y shown in FIG. 12 can be applied to various products as an organic semiconductor element by being connected to a black box BB which is an external circuit. For example, if the black box BB is a load circuit, it can be used as a solar cell if light is supplied to the organic thin film element Y, and can be used as an organic LED if the black box BB is a power supply circuit. Besides these, it could be used for organic TFTs, organic thin film sensors and their application products.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

FIG. 1 is a schematic cross-sectional view showing the structure of a sample SA. FIG. 2 is a chemical structural formula of Compound A. FIG. 3A shows current-voltage characteristics obtained from samples SA, SB, and SC, and FIG. 3B is a table of these characteristics. FIG. 4 is a chemical structural formula of Compound B. FIG. 5A shows current-voltage characteristics obtained from the samples SD and SE, and FIG. 5B shows these characteristics. 6A and 6B are chemical structural formulas of the compounds A2 and A3, which are derivatives of an aluminum quinolinol complex and in which the coordination between the compounds A and CN is changed. FIG. 7 is a chemical structural formula of a derivative of a quinolinol metal complex that can be used for a connection layer. FIG. 8 is a chemical structural formula of a hexaazotriphenylene derivative that can be used for the connection layer. FIG. 9 is a chemical structural formula of a phenanthroline derivative that can be used for the connection layer. FIG. 10 is a chemical structural formula of a triazine derivative that can be used for the connection layer. FIG. 11 is a chemical structural formula of an oxadiazole derivative that can be used for the connection layer. FIG. 12 is a schematic cross-sectional view of an organic thin film element using at least one of compounds X as a connection layer. FIG. 13 is a schematic view showing an application example of the organic semiconductor device using the organic thin film element shown in FIG.

Explanation of symbols

1, 7 Substrate 2, 6 Electrode 3 Front cell 3a, 5a Hole transport layer 3b, 5b Active layer 3c, 5c Electron transport layer 3d, 5d Hole block layer 4 Connection layer 5 Back cell 8, 9 Electrode BB Black box OC1, OC2 , OCn Functional element Y Organic thin film element

Claims (5)

A pair of electrodes;
A plurality of functional element portions formed between the pair of electrodes and having at least one organic thin film layer;
An organic thin film element having a connection layer using an electron transporting organic compound formed between the plurality of functional element parts and coordinated with at least one cyano group.   2. The organic thin film element according to claim 1, wherein the electron transporting organic compound is an aromatic compound or an organometallic compound.   The organic thin film element according to claim 2, wherein at least one of hexaazatriphenylene, phenanthroline, triazine, and oxadiazole is used as the aromatic compound.   The organic thin film element according to claim 2, wherein an aluminum quinolinol complex is used as the organometallic compound. A transparent electrode;
A counter electrode;
A plurality of unit cells formed between the transparent electrode and the counter electrode and having at least one organic thin film layer;
A tandem photoelectric conversion element having a connection layer using an electron-transporting organic compound formed between the unit cells and coordinated with at least one cyano group.

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