JP2018125434A - Organic el device and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic EL element that emits light in the near infrared range and a method of manufacturing the same.SOLUTION: In an organic EL device using an organic material as a light emitting layer, the light emitting layer is formed of a narrow band gap polymer and emits light in the near infrared range.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an organic EL (Electro Luminescence) element. In particular, the present invention relates to an organic EL element that emits light in the near-infrared region and a manufacturing method thereof.

  Applicants are paying attention to near-infrared rays that are absorbed by a living tissue as a probe for obtaining biological information. An organic EL element that is easily flexible is advantageous as a light source for a wearable device that constantly measures human life information. However, at present, organic EL elements are mainly used for displays such as displays and for lighting (see, for example, cited document 1), and there are only a few research examples of light emitting materials and elements other than visible light including the near infrared region. However, the present situation is that it has not yet been commercialized (see, for example, Patent Document 2).

JP 2014-72120 A Japanese Patent Laid-Open No. 10-36829

  An object of this invention is to provide the organic EL element which light-emits in a near infrared region, and its manufacturing method.

  An organic EL element of the present invention includes a light emitting layer that generates light by injecting current carriers, and a carrier injection unit that injects current carriers into the light emitting layer, and uses an organic material as the light emitting layer. The light emitting layer is formed of a narrow band gap polymer and emits light in the near infrared region.

  It is desirable that the narrow band gap polymer is formed so as to be oriented in one direction within the light emitting layer. Due to the orientation of the molecules, the organic EL device of the present invention emits polarized light along the orientation direction. As a narrow band gap polymer forming the light emitting layer, PTB7 (poly {4,8-bis [(2-ethylhexyl) oxy] benzo [1,2-b: 4,5-b ′] dithiophene-2,6 -Diyl-alt-3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno [3,4-b] thiophene-4,6-diyl} can be used.

  A layer that emits visible light is preferably stacked in contact with the light emitting layer. As a material for the layer that emits visible light, F8BT (poly (9,9-dioctylfluorene-alt-benzodiazole)) can be used. When the narrow band gap polymer forming the light emitting layer is oriented, it is desirable that the molecules of the visible light emitting layer are also oriented along the orientation of the narrow band gap polymer.

  The organic EL device manufacturing method of the present invention is characterized in that in the organic EL device manufacturing method using an organic material as the light emitting layer, the light emitting layer is formed of a narrow band gap polymer. It is desirable to form the narrow band gap polymer by aligning it in one direction along the light emitting layer by a friction transfer method.

  A layer that emits visible light can be stacked in contact with the light-emitting layer. In the case where the narrow band gap polymer is oriented, the visible light emitting layer is heat-treated so that the molecules of the layer can be oriented along the orientation of the narrow band gap polymer.

  According to the present invention, an organic EL device that emits light in the near infrared region can be obtained. Furthermore, polarized light emission is possible by orienting the molecules of the material of the light emitting layer. In addition, by stacking a layer that emits visible light on the light emitting layer, light emission efficiency can be increased by energy transfer.

FIG. 1 is a diagram for explaining a first embodiment of the present invention, and schematically shows a laminated structure of organic EL elements. FIG. 2 shows the chemical structure of PTB7. FIG. 3 shows a polarized UV-visible spectrum of the PTB7 alignment film. FIG. 4 shows a polarized fluorescence spectrum of the PTB7 alignment film. FIG. 5 is a diagram for explaining a second embodiment of the present invention, and schematically shows a laminated structure of organic EL elements. FIG. 6 shows the chemical structure of F8BT. FIG. 7 shows the voltage versus current density / output power characteristics of the organic EL device of Example 1. FIG. 8 shows the voltage versus current density / output power characteristics of the organic EL device of Example 2. FIG. 9 shows the measurement results of the emission spectrum of the organic EL device of Example 2. FIG. 10 shows the measurement result of the polarized emission spectrum of the organic EL device of Example 2. FIG. 11 shows the measurement results of the emission spectrum of the organic EL device of Example 3. FIG. 12 shows the voltage versus current density / output power characteristics of the organic EL device of Example 4. FIG. 13 shows the measurement results of the emission spectrum of the organic EL device of Example 4. FIG. 14 shows the measurement results of the polarized emission spectrum of the organic EL device of Example 4.

  FIG. 1 is a diagram for explaining a first embodiment of the present invention, and schematically shows a laminated structure of organic EL elements. This organic EL element has a structure in which a transparent electrode 2, a hole injection layer 3, a light emitting layer 4, a hole blocking layer 5 and an electrode 6 are laminated on a glass substrate 1. The light emitting layer 4 is a layer that generates light by injection of current carriers, and the transparent electrode 2 and the hole injection layer 3, and the hole blocking layer 5 and the electrode 6 inject current carriers into the light emitting layer 4. Configure the means.

  For example, ITO (indium tin oxide) is used as the material of the transparent electrode 2. As a material for the hole injection layer 3, for example, PEDOT: PSS (poly (3,4-ethylenedioxythiophene): polystyrene sulfate) is used. As a material of the hole block layer 5, for example, BCP (Bathocupline) is used. As the electrode 6, Al (aluminum) or Ag (silver) is used. Further, as part of the electrode 6, a LiF (lithium fluoride) layer can be provided on the hole block layer 5 side. When the LiF layer is provided on a part of the electrode 6, the hole block layer 5 can be omitted. The above materials are general materials for forming an organic EL element.

As the material of the light emitting layer 4, a narrow band gap polymer is used in which the energy difference (band gap) between the highest occupied orbit (HOMO) and the lowest unoccupied orbit (LUMO) is in the infrared region. The narrow band gap polymer is a material that has a small band gap and absorbs light in the visible light range, and is used as a material for organic solar cells. The approximate range of the band gap is 0.01 to 1.7 eV, and for this purpose, a range of about 1.3 to 1.7 eV is desirable. As such a narrow band gap polymer,
PTB7 (poly {4,8-bis [(2-ethylhexyl) oxy] benzo [1,2-b: 4,5-b ′] dithiophene-2,6-diyl-alt-3-fluor-2-[( 2-ethylhexyl) carbonyl] thieno [3,4-b] thiophene-4,6-diyl}),
PCPDTBT (Poly [2,1,3-benzothiadiazole-4,7-diyl [4,4-bis (2-ethylhexyl) -4H-cyclopenta [2,1-b: 3,4-b ′] dithiophene-2, 6-diyl]]),
PSiF-DBT poly [2,7- (9,9-bis (2-ethylhexyl) -dibenzosilol) -alt-4,7-bis (thiophen-2-yl) benzo-2,1,3-thiadiazole,
PSBTBT-8 (poly (4,4-dioctyldithione (3,2-b: 2 ′, 3′-d) silole) -2,6-diyl-alt- (2,1,3-benzothiadiazole) -4,7 -Diyl),
Si-PCDTBT (Poly [N-9′-heptadecanyl-2,7-carbazole-alt-5,5- (4 ′, 7′-di-2-thienyl-2 ′, 1 ′, 3′-benzothiadiazole) ], Poly [[9- (1-octylnonyl) -9H-carbazole-2,7-diyl] -2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5 -Thiophenediyl]),
PCDT () BT) (poly [N-9′-heptadecanyl-2,7-carbazole-alt-5,5- (4 ′, 7′-di-2-thienyl-2 ′, 1 ′, 3′-benzo Thiadiazole)], poly [[9- (1-octylnonyl) -9H-carbazole-2,7-diyl] -2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2 , 5-thiophenediyl]),
APF03 (Poly [2,7- (9,9-dioctylfluorene) -alt-5,5- (4 ′, 7′-di-2-thienyl-2 ′, 1 ′, 3-benzothiazole))
Can be given. On the other hand, such a material may emit light in the near infrared region because the band gap reaches the infrared region. By using such a narrow band gap polymer in the light emitting layer 4 of the organic EL element, a near infrared light source can be obtained. Furthermore, a near-infrared light source that emits polarized light can be obtained by orienting molecules of the material of the light-emitting layer 4 in one direction within the layer. Polarized near-infrared light is particularly promising as a probe for obtaining biological information. Near-infrared light is generally in the wavelength range of 0.7 to 1.4 μm, but for this purpose, about 700 nm to 900 nm is desirable.

  As a narrow band gap polymer, PTB7 will be described as an example. The chemical structure of PTB7 is shown in FIG. PTB7 is a narrow bandgap polymer developed for organic thin-film solar cells, has light absorption in almost the entire visible light region, and emits light in the near infrared region of around 770 nm.

  In order to investigate the characteristics of PTB7, an oriented thin film was prepared by a friction transfer method. Specifically, PTB7 was pressure-formed under vacuum to form pellets, which were pressed against a cleaned glass substrate heated to a constant temperature at a constant pressure and rubbed at a constant speed to perform friction transfer. Various film forming conditions were examined, and it was found that a good alignment thin film was obtained under appropriate conditions. The substrate temperature can be 70 to 100 ° C., the sweep rate can be 10 to 100 cm / min, and the pressure can be 1 to 5 MPa. As optimum conditions, the substrate temperature was 90 ° C., the sweep rate was 20 cm / min, and the pressure was 2 MPa. The thin film was evaluated by polarizing microscope, polarized ultraviolet-visible (UV-vis) spectrum, thin film X-ray diffraction using synchrotron radiation, and the like. FIG. 3 shows a polarized UV-vis spectrum of the PTB7 oriented thin film. A Gran Taylor prism was used for the spectrum measurement. FIG. 3 shows that linearly polarized light parallel to the friction direction is absorbed more strongly than the vertical direction over almost the entire visible light region. This indicates that the PTB7 main chain is arranged parallel to the friction direction in the film.

  The polarized fluorescence spectrum of this oriented thin film was measured. Excitation light was non-polarized light (600 nm), and fluorescence was measured through a polarizing plate. FIG. 4 shows a polarized fluorescence spectrum of the PTB7 alignment film. Near infrared emission having a peak at 770 nm was exhibited. It was found that the PTB7 alignment film exhibits polarized fluorescence. In the embodiment shown in FIG. 1, this PTB7 alignment film is used as the light emitting layer 4.

  FIG. 5 is a diagram for explaining a second embodiment of the present invention, and schematically shows a laminated structure of organic EL elements. This organic EL element is different from the first embodiment shown in FIG. 1 in that a visible light emitting layer 7 is laminated between the light emitting layer 4 and the hole blocking layer 5 in contact with the light emitting layer 4. It is.

  The visible light emitting layer 7 is a layer that can emit visible light by itself, but the light emission characteristics of the light emitting layer 4 can be enhanced by energy transfer. In particular, when the narrow bandgap polymer forming the light emitting layer 4 is oriented, the visible light emitting layer 7 molecules can be aligned along the orientation of the narrow bandgap polymer, so that a great effect can be obtained. found.

  As a material of the visible light emitting layer 7, F8BT (poly (9,9-dioctylfluorene-alt-benzothiadiazole)) or MEH-PPV (poly [2-methoxy-5- (2-ethylhexyloxy) -1,4-phenylene) is used. ) Can be used. F8BT has a liquid crystal transition temperature of about 150 ° C., and when the narrow band gap polymer forming the light emitting layer 4 is oriented, it tends to be oriented by heat treatment at that temperature. At this time, the heat treatment may be performed only on the visible light emitting layer 7 or on the entire laminated layer.

  Examples of organic EL elements using the friction transfer PTB 7 as the light emitting layer 4 will be described below.

[Element using friction transfer PTB7 as light emitting layer]
As an element substrate, an ITO substrate in which a striped ITO having a width of 2 mm was attached as a transparent electrode 2 to a glass substrate 1 was used. A hole injection layer 3 was formed by spin coating PEDOT: PSS on the ITO substrate. The PTB7 powder was pressed under vacuum and molded into a plate shape having a thickness of about 1 mm. This is cut linearly, and the cut surface is pressed against an ITO substrate coated with PEDOT: PSS heated to 70 ° C. at a pressure of 2 MPa and rubbed at a speed of 20 cm / min. The light emitting layer 4 was formed. On this light emitting layer 4, BCP was vacuum-deposited to 30 nm to form a hole blocking layer 5, and Al was vacuum-deposited to 50 nm to laminate an electrode 6 to produce an organic EL device having a light emitting area of 2 mm × 2 mm.

  FIG. 7 shows the voltage versus current density / output power characteristics of the produced organic EL element. The voltage-to-current characteristics were measured using a source meter, Keithley 2400. Infrared output was measured by a power meter Nova manufactured by Offiel with a thermopile detector. When a direct current voltage was applied using ITO as an anode and Al as a cathode, infrared light emission began to be observed from 9V, and light emission of 1.2 mW was observed at 18V (conversion efficiency 0.7%). An infrared light emitting EL element having the friction transfer PTB7 as a light emitting layer was produced.

[Laminated element of F8BT and PTB7 (polarized light)]
A PTB7 friction transfer film was formed on an ITO substrate coated with PEDOT: PSS under the same conditions as in Example 1, and then F8BT was spin-coated from a chloroform solution (30 g / l) at 2000 rpm to form a visible light emitting layer 7. Furthermore, LiF0.5nm and Al50nm were vacuum-deposited as the electrode 6, and the organic EL element was produced. The hole block layer 5 is not provided.

  FIG. 8 shows the voltage versus current density / output power characteristics of the produced organic EL element. When the same measurement as in Example 1 was performed and a direct current voltage was applied using ITO as an anode and Al as a cathode, infrared light emission started to be observed from 8V, and light emission of 8.8 mW was observed at 20V (conversion efficiency 1%) ). The difference from Example 1 is that the laminated F8BT emits visible light, and the emission energy is transferred to PTB7 to emit infrared light. In this element, the energy transfer does not occur completely, and the visible light emission from the F8BT of the visible light emitting layer 7 remained, and the light emission could be confirmed visually.

  9 and 10 show the measurement results of the emission spectrum. FIG. 9 shows the entire emission spectrum, and FIG. 10 shows the polarization spectra in the direction parallel to and perpendicular to the orientation direction of PTB7. The emission spectrum was measured using an Optoirius USB2000 fiber spectrometer. The polarization spectrum was measured using a polarizer. The 530 nm emission is derived from F8BT, and the 770 nm emission is derived from PTB7. From this measurement, it was confirmed that infrared light was efficiently emitted by energy transfer from the visible light-emitting polymer to PTB7, and that polarized light was emitted in a direction parallel to the alignment direction of PTB7.

[Improvement of energy transfer by heat treatment]
In the element having the same configuration as that of Example 2, an element that was heat-treated at 160 ° C. under vacuum was prepared before the electrodes were stacked. F8BT is a liquid crystal polymer, and when it is in a liquid crystal state at 160 ° C., the F8BT main chain direction is rearranged parallel to the main chain direction of PTB7 (confirmed by polarized UV-vis spectrum).

  FIG. 11 shows the measurement result of the emission spectrum. In the device of Example 3, the energy transfer efficiency increased compared to the device of Example 2, and the emission in the near-infrared region at 770 nm was relatively stronger than the emission of visible light at 530 nm. This is presumably because the heat transfer facilitates the energy transfer because the emission transition vectors of F8BT and PTB7 become parallel. As in Example 2, a polarized EL spectrum was also confirmed.

[Select electrode]
An element equivalent to Example 3 was fabricated using Ag as the electrode 6 instead of Al. FIG. 10 shows voltage versus current density / output power characteristics of the produced organic EL device, FIG. 11 shows the measurement result of the emission spectrum, and FIG. 12 shows the polarized emission spectrum. The threshold voltage at which light emission started decreased to 6 V, and the device emitted light stably even at a low voltage.

[Material selection of visible light emitting layer]
As a material for the visible light emitting layer 7 in Example 2, an organic EL element in which MEH-PPV was spin-coated under the same conditions instead of F8BT was produced. It started to shine when a voltage of 9 V was applied, and infrared emission of 11.5 mW (conversion efficiency 0.8%) was confirmed at 16 V. However, since MEH-PPV did not undergo liquid crystal transition, the heat treatment effect could not be confirmed.

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Hole injection layer 3 Light emitting layer 5 Hole block layer 6 Electrode 7 Visible light emitting layer

Claims (12)

A light emitting layer that generates light by injection of current carriers;
Carrier injection means for injecting current carriers into the light emitting layer;
With
In the organic EL element using an organic material as the light emitting layer,
An organic EL element, wherein the light emitting layer is formed of a narrow band gap polymer and emits light in the near infrared region.   2. The organic EL element according to claim 1, wherein the narrow band gap polymer is formed to be oriented in one direction in the light emitting layer.   3. The organic EL element according to claim 2, wherein the light emitting layer emits polarized light along the orientation direction.   4. The organic EL element according to claim 1, wherein the narrow band gap polymer is PTB7. 5.   5. The organic EL device according to claim 1, wherein a layer that emits visible light is stacked in contact with the light emitting layer. 6.   6. The organic EL element according to claim 5, wherein the visible light emitting layer is formed of F8BT.   4. The organic EL device according to claim 2, wherein a layer that emits visible light is stacked in contact with the light emitting layer, and molecules of the layer that emits visible light follow the orientation of the narrow band gap polymer. An organic EL element characterized by being oriented.   8. The organic EL element according to claim 7, wherein the narrow band gap polymer is PTB7 and the visible light emitting layer is formed of F8BT. In the method for producing an organic EL element using an organic material as the light emitting layer,
The method for producing an organic EL element, wherein the light emitting layer is formed of a narrow band gap polymer.   10. The method of manufacturing an organic EL element according to claim 9, wherein the narrow band gap polymer is formed by being oriented in one direction within the light emitting layer by a friction transfer method. Manufacturing method.   11. The method of manufacturing an organic EL element according to claim 9, wherein a layer that emits visible light is laminated in contact with the light emitting layer. In the manufacturing method of the organic EL element of Claim 9,
The narrow band gap polymer is oriented in one direction along the light emitting layer by a friction transfer method to form the light emitting layer,
A layer that emits visible light is laminated in contact with the light emitting layer,
A method for producing an organic EL device, wherein the visible light emitting layer is heat-treated to align the molecules of the visible light emitting layer along the orientation of the narrow band gap polymer.

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