WO2022211041A1 - 有機el素子 - Google Patents
有機el素子 Download PDFInfo
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- WO2022211041A1 WO2022211041A1 PCT/JP2022/016598 JP2022016598W WO2022211041A1 WO 2022211041 A1 WO2022211041 A1 WO 2022211041A1 JP 2022016598 W JP2022016598 W JP 2022016598W WO 2022211041 A1 WO2022211041 A1 WO 2022211041A1
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- 239000004065 semiconductor Substances 0.000 claims abstract description 194
- 239000000463 material Substances 0.000 claims abstract description 141
- 238000004770 highest occupied molecular orbital Methods 0.000 claims description 33
- 238000004768 lowest unoccupied molecular orbital Methods 0.000 claims description 33
- 239000002019 doping agent Substances 0.000 claims description 16
- 238000000295 emission spectrum Methods 0.000 claims description 10
- 238000000862 absorption spectrum Methods 0.000 claims description 7
- 239000010410 layer Substances 0.000 description 186
- YYMBJDOZVAITBP-UHFFFAOYSA-N rubrene Chemical compound C1=CC=CC=C1C(C1=C(C=2C=CC=CC=2)C2=CC=CC=C2C(C=2C=CC=CC=2)=C11)=C(C=CC=C2)C2=C1C1=CC=CC=C1 YYMBJDOZVAITBP-UHFFFAOYSA-N 0.000 description 50
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- JKQOBWVOAYFWKG-UHFFFAOYSA-N molybdenum trioxide Chemical compound O=[Mo](=O)=O JKQOBWVOAYFWKG-UHFFFAOYSA-N 0.000 description 18
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- H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
- H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
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- H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
- H10K50/12—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers comprising dopants
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- H10K85/6572—Polycyclic condensed heteroaromatic hydrocarbons comprising only nitrogen in the heteroaromatic polycondensed ring system, e.g. phenanthroline or carbazole
Definitions
- the present invention relates to organic EL elements.
- organic electroluminescence element is an element that has one or more organic semiconductor layers sandwiched between a pair of electrodes and emits light by applying a voltage between the electrodes.
- Non-Patent Document 1 proposes an energy up-converted organic EL device having a structure in which a rubrene layer and a C60 layer are laminated in this order.
- Non-Patent Document 1 By the way, as a result of studies by the present inventors, it has become clear that there is room for improvement in terms of luminous efficiency and luminous luminance in conventional organic EL elements such as Non-Patent Document 1.
- an object of the present invention is to provide an organic EL device that is excellent in luminous efficiency and luminance.
- the organic EL device of the present invention is An organic EL device comprising a plurality of organic semiconductor layers sandwiched between a pair of electrodes, the organic semiconductor layer has a first organic semiconductor layer comprising a first organic semiconductor material and a second organic semiconductor layer comprising a second organic semiconductor material and a third organic semiconductor material; The first organic semiconductor layer and the second organic semiconductor layer form a bonding surface, The HOMO level of the first organic semiconductor material is lower than the HOMO level of the second organic semiconductor material, and the LUMO level of the first organic semiconductor material is lower than the LUMO level of the second organic semiconductor material.
- the second organic semiconductor material is a material that undergoes triplet-triplet annihilation; the excited triplet level T1 of the second organic semiconductor material is smaller than the energy difference between the HOMO level of the second organic semiconductor material and the LUMO level of the first organic semiconductor material, The energy difference between the HOMO level of the second organic semiconductor material and the LUMO level of the first organic semiconductor material is 0.5 eV or more smaller than the energy difference between the HOMO level and the LUMO level of the second organic semiconductor material.
- the second organic semiconductor material is a host material and the third organic semiconductor material is a dopant;
- the maximum wavelength of the emission spectrum of the second organic semiconductor material is on the longer wavelength side than the maximum wavelength of the absorption spectrum of the first organic semiconductor material.
- Such an organic EL element is excellent in luminous efficiency and luminance. The reason for this is not necessarily clear, but considerations by the inventors will be explained based on FIGS. 1 to 3.
- FIG. 1 A diagrammatic representation of an organic EL element.
- FIG. 1 is a conceptual diagram showing the mechanism by which the organic EL element of the present invention emits light.
- the organic EL element 10 includes a first organic semiconductor layer 1, a second organic semiconductor layer 2 forming an interface (bonding surface) with the first organic semiconductor layer 1, and a first organic semiconductor layer It has a first electrode 3 formed on the 1 side and a second electrode 4 formed on the second organic semiconductor layer 2 side.
- the first organic semiconductor layer 1 serves as an electron transport layer
- the second organic semiconductor layer 2 serves as a light emitting layer
- the first electrode 3 serves as a cathode
- the second organic semiconductor layer 2 serves as a cathode. corresponds to the anode.
- FIG. 2 is a diagram showing the energy levels of rubrene, PTCDI-C8 and C60 used in Examples.
- PTCDI-C8 and C60 correspond to the first organic semiconductor material, and rubrene to the second organic semiconductor material.
- the HOMO level of the first organic semiconductor material is lower than the HOMO level of the second organic semiconductor material
- the LUMO level of the first organic semiconductor material is lower than the LUMO level of the second organic semiconductor material
- the energy difference between the HOMO level of the second organic semiconductor material and the LUMO level of the first organic semiconductor material is 0.5 eV or more than the energy difference between the HOMO level and the LUMO level of the second organic semiconductor material. Since it is small, it is thought that electron ( ⁇ )/hole (+) pairs injected from the electrode can form a CT state at the junction surface between the first organic semiconductor layer 1 and the second organic semiconductor layer 2 . be done.
- FIG. 3 shows the energy transfer up to light emission by the organic EL device of the example using PTCDI-C8 as the first organic semiconductor material, rubrene as the second organic semiconductor material, and DBP as the third organic semiconductor material. It is a schematic diagram which shows a mechanism.
- the excited triplet level T1 of the organic semiconductor material is 1.1 eV.
- the excited triplet level T 1 of the second organic semiconductor material is smaller than the energy difference between the HOMO level of the second organic semiconductor material and the LUMO level of the first organic semiconductor material, electrons (-) and holes It is believed that the (+) pair can generate triplet states of the second organic semiconductor material in the second organic semiconductor layer 2 via CT states.
- the first organic semiconductor material emits light from the organic EL element. It is possible to suppress a decrease in emission intensity due to absorption.
- the first organic semiconductor layer 1 may be an electron injection layer or a hole blocking layer.
- the organic EL device of the present invention is excellent in luminous efficiency and luminance.
- FIG. 2 is a conceptual diagram showing the mechanism by which the organic EL device of the present invention emits light.
- FIG. 3 is a diagram showing energy levels of rubrene, PTCDI-C8 and C60 used in Examples. It is a schematic diagram which shows the energy transfer mechanism until light emission by the organic EL element of an Example. It is a figure which shows the absorption spectrum or emission spectrum of the compound used in the Example.
- FIG. 11 shows the PL intensity for a single rubrene layer.
- FIG. 2(A) shows the V-luminance characteristics of the organic EL devices of Example 1 and the like, and (B) shows the external quantum yield (EQE) of the organic EL devices of Example 1 and the like.
- FIG. 1 shows the V-luminance characteristics of the organic EL devices of Example 1 and the like
- EQE external quantum yield
- FIG. 10 is a diagram showing V-luminance characteristics of the organic EL element of Example 2;
- FIG. 10 is a diagram showing V-luminance characteristics of the organic EL elements of Example 3 and the like;
- FIG. 10 is a diagram showing external quantum yields (EQE) of organic EL devices such as Example 4;
- A) is a diagram showing EL emission spectra of organic EL elements such as Example 5, and
- B) is a diagram showing V-luminance characteristics of the organic EL elements such as Example 5.
- FIG. FIG. 10 is a diagram showing V-luminance characteristics of organic EL elements such as Example 6;
- FIG. 10 (A) is a diagram showing the V-luminance characteristics of the organic EL device of Example 7 and the like, and (B) is a diagram showing the external quantum yield (EQE) of the organic EL device of Example 7 and the like.
- FIG. 4 shows an absorption spectrum of NDI-bis-HFI;
- FIG. 10 is a diagram showing V-luminance characteristics of organic EL elements such as Example 8;
- the organic EL device of this embodiment includes a plurality of organic semiconductor layers sandwiched between a pair of electrodes. Further, the organic EL device of the present embodiment may further include an inorganic compound layer such as a molybdenum trioxide (MoO 3 ) layer (hole injection layer) or a lithium fluoride layer (electron injection layer) between the electrodes. good.
- MoO 3 molybdenum trioxide
- the organic semiconductor layer has a first organic semiconductor layer containing a first organic semiconductor material and a second organic semiconductor layer containing a second organic semiconductor material and a third organic semiconductor material, The organic semiconductor layer and the second organic semiconductor layer form a bonding surface.
- the first organic semiconductor layer may be formed only from the first organic semiconductor material, or may contain materials other than the first organic semiconductor material within a range that does not significantly impair the effects of the present invention.
- the second organic semiconductor layer may be formed only from the second organic semiconductor material and the third organic semiconductor material, and a material other than the second organic semiconductor material within a range that does not significantly impair the effects of the present invention. may contain
- the HOMO level of the first organic semiconductor material is lower than the HOMO level of the second organic semiconductor material.
- the difference between the HOMO level of the first organic semiconductor material and the HOMO level of the second organic semiconductor material is 0.5 eV or more from the viewpoint of highly preventing hole leakage and further improving light emission efficiency. and preferred.
- the upper limit of the difference between the HOMO level of the first organic semiconductor material and the HOMO level of the second organic semiconductor material is not particularly limited, it can be, for example, 2 eV or less.
- the LUMO level of the first organic semiconductor material is lower than the LUMO level of the second organic semiconductor material.
- the difference between the LUMO level of the first organic semiconductor material and the LUMO level of the second organic semiconductor material is 0.5 eV or more from the viewpoint of highly preventing electron leakage and further improving luminous efficiency. and preferred.
- the upper limit of the difference between the LUMO level of the first organic semiconductor material and the LUMO level of the second organic semiconductor material is not particularly limited, it can be, for example, 2 eV or less.
- the second organic semiconductor material is a material that undergoes triplet-triplet annihilation
- the excited triplet level T1 of the second organic semiconductor material is the HOMO level of the second organic semiconductor material and the first It is smaller than the energy difference of the LUMO levels of the organic semiconductor material.
- the difference between the excited triplet level T1 of the second organic semiconductor material and the energy difference between the HOMO level of the second organic semiconductor material and the LUMO level of the first organic semiconductor material is less than 0.8 eV. It is preferably less than 0.65 eV, and even more preferably less than 0.5 eV. If these differences are small, the light emission start voltage can be lowered.
- the energy difference between the HOMO level of the second organic semiconductor material and the LUMO level of the first organic semiconductor material is 0.5 eV or more smaller than the energy difference between the HOMO level and the LUMO level of the second organic semiconductor material. , is preferably smaller than 0.7 eV.
- the upper limit of the energy difference between the HOMO level of the second organic semiconductor material and the LUMO level of the first organic semiconductor material is not particularly limited, it can be, for example, 2 eV or less.
- the second organic semiconductor material is the host material and the third organic semiconductor material is the dopant.
- the energy difference between the HOMO and LUMO levels of the third organic semiconductor material is preferably smaller than the energy difference between the HOMO and LUMO levels of the second organic semiconductor material.
- the maximum wavelength of the emission spectrum of the third organic semiconductor material, which is the dopant is on the longer wavelength side than the maximum wavelength of the emission spectrum of the second organic semiconductor material, which is the host material.
- the content of the third organic semiconductor material in the second organic semiconductor layer is, for example, 0.01 to 50% by volume, preferably 0.1 to 10% with respect to 100% by volume of the total amount of the second organic semiconductor layer. It can be volume %.
- the maximum wavelength of the emission spectrum of the second organic semiconductor material is on the longer wavelength side than the maximum wavelength of the absorption spectrum of the first organic semiconductor material. As a result, it is possible to suppress excess absorption loss of light emitted by a layer other than the second organic semiconductor layer, for example, the first organic semiconductor layer.
- the first organic semiconductor material for example, a conventionally known electron-transporting material can be adopted. Specific examples thereof include the compounds shown below.
- the following compounds that are reported to generate TTA can be employed.
- Energy levels such as the HOMO level, the LUMO level, and the excited triplet level T1 of these compounds are inherent to the material, and literature values and the like can be referred to.
- a conventionally known luminescent material can be used as the third organic semiconductor material.
- Specific examples of the third organic semiconductor material include the following compounds.
- the organic EL element of the present embodiment may be formed of a pair of electrodes, a first organic semiconductor layer, and a second organic semiconductor layer. It may be provided with an organic semiconductor layer, an inorganic compound layer, or the like.
- the layers that the organic EL element of the present embodiment may have between a pair of electrodes include, for example, a hole injection layer, an electron blocking layer, a hole transport layer, a light emitting layer, an electron transport layer, in this order from the anode. layers, hole-blocking layers, electron-injecting layers.
- the first organic semiconductor layer may be an electron transport layer
- the second organic semiconductor layer may be a light-emitting layer.
- the functions of these layers are not strictly distinguished.
- the light-emitting layer which is the second organic semiconductor layer, may also function as a hole transport layer, and the hole blocking layer may function as an electron injection layer.
- the hole injection layer may be between the electron blocking layer and the hole transport layer, and the electron injection layer may It may be between the layer and the electron-transporting layer.
- Each layer in the organic EL element may contain a layer containing the same organic semiconductor material.
- the organic EL device may contain rubrene as the second organic semiconductor material in the second organic semiconductor layer (light emitting layer), it may have a hole blocking layer made of rubrene.
- the organic EL device of the present embodiment can be produced by conventionally known methods such as vacuum deposition, chemical vapor deposition, sputtering, vapor deposition polymerization, spin coating, blade coating, bar coating, dip coating, and lamination. It can be manufactured by forming the first and second organic semiconductor layers by a method such as a method. Specifically, for example, by laminating a first electrode, a first organic semiconductor layer, a second organic semiconductor layer, a second electrode, and any other layers on a substrate, the present embodiment of organic EL elements can be manufactured. The method for forming each organic semiconductor layer can be appropriately selected according to the compound.
- the substrate for example, a glass substrate, a quartz substrate, a sapphire substrate, a plastic substrate, a film substrate, or the like can be used.
- the thickness of the first and second organic semiconductor layers in the organic EL device of the present embodiment is not particularly limited, but is preferably 0.1 nm to 500 nm, more preferably 2 nm to 200 nm.
- Organic EL elements are expected to be applied to, for example, organic EL displays, organic EL lighting, digital signage, light sources for photosensors, laser light sources, and light sources for optical communication.
- the maximum wavelength (about 565 nm) of the PL spectrum of rubrene is the maximum wavelength (about 565 nm) of the ABS spectrum of PTCDI-C8 and C60 (first organic semiconductor material). 490 nm and 345 nm, respectively). Further, the maximum wavelength (about 605 nm) of the PL spectrum of DBP (third organic semiconductor material) is on the longer wavelength side than the maximum wavelength of the PL spectrum of rubrene. Further, as shown in FIG. 13, the maximum wavelength of the ABS spectrum of NDI-bis-HFI is about 305 nm, which is on the lower wavelength side than the maximum wavelength of the PL spectrum of rubrene.
- ⁇ Measurement of PL intensity> A single rubrene layer was prepared with no dopant (0% by volume) and DBP added as a dopant at 0.2% by volume, 0.5% by volume, 1% by volume, and 5% by volume with respect to the entire rubrene layer. , respectively, the emission intensity (PL intensity) was measured.
- the rubrene layer was formed by thermal evaporation on a quartz substrate under high vacuum ( ⁇ 10 ⁇ 5 Pa) in a vacuum deposition system. DBP was introduced by a co-evaporation method when the rubrene layer was deposited, and the mixture concentration was controlled by the ratio of deposition rates.
- the PL intensity was measured with an absolute PL quantum yield measuring device (Quantaurus-QY, Hamamatsu Photonics). The results are shown in FIG. As is clear from FIG. 5, when DBP was added as a dopant, light emission was confirmed around 605 nm derived from DBP, and energy transfer from rubrene to DBP was confirmed.
- Fluorescence quantum yield (PL QY) was measured using an absolute PL quantum yield measurement device (Quantaurus-QY, manufactured by Hamamatsu Photonics Co., Ltd.) for various rubrene layers prepared for the measurement of PL intensity. Table 1 shows the results.
- the fluorescence quantum yield is higher when the dopant (DBP) is added than when the dopant is not added, especially when the amount of DBP added is 0.5% by volume.
- the highest fluorescence quantum yield (72.6%) was obtained.
- MoO 3 hole injection layers (10 nm, 0.01 nm /s), a rubrene layer (50 nm, 0.1 nm/s), a PTCDI-C8 layer (50 nm, 0.1 nm/s), a LiF electron injection layer (0.2 nm, 0.001 nm/s) and an Al electrode (70 nm , 0.3 nm/s) were thermally evaporated in this order under high vacuum ( ⁇ 10 ⁇ 5 Pa) in a vacuum deposition system.
- the device was encapsulated with a glass substrate and an epoxy resin in a glove box to obtain an organic EL device.
- the obtained organic EL device has the following structure. ITO electrode/ MoO3 hole injection layer/rubrene layer (DBP doped)/PTCDI-C8 layer/LiF electron injection layer/Al electrode
- Example 1 An organic EL device was produced in the same manner as in Example 1, except that DBP was not added.
- the obtained organic EL device has the following structure. ITO electrode/ MoO3 hole injection layer/rubrene layer (undoped)/PTCDI-C8 layer/LiF electron injection layer/Al electrode
- Example 2 Insertion of hole blocking layer
- An organic EL device was fabricated in the same manner as in Example 1, except that a BCP layer (10 nm, 0.05 nm/s) was formed by thermal evaporation between the PTCDI-C8 layer and the LiF electron injection layer.
- This organic EL device has the following configuration. ITO electrode/MoO 3 hole injection layer/rubrene layer (DBP doped)/PTCDI-C8 layer/BCP layer/LiF electron injection layer/Al electrode.
- FIG. 7 shows the results of measuring the V-luminance characteristics together with the results of measuring the organic EL element (rubDBP) of Example 1.
- FIG. 7 shows the results of measuring the V-luminance characteristics together with the results of measuring the organic EL element (rubDBP) of Example 1.
- the insertion of the BCP layer improves the light emission luminance in the high voltage region.
- Example 3 Insertion of electron blocking layer
- a rubrene layer (10 nm, 0.1 nm/s) (Example 3A) or an NPD layer (10 nm, 0.1 nm/s) (Example 3B) is placed between the MoO3 hole injection layer and the rubrene layer (DBP-doped).
- BBP-doped rubrene layer
- Example 3A ITO electrode/MoO 3 hole injection layer/rubrene layer (undoped)/rubrene layer (DBP doped)/PTCDI-C8 layer/LiF electron injection layer/Al electrode
- Example 3B ITO electrode/ MoO3 hole injection layer/NPD layer/rubrene layer (DBP doped)/PTCDI-C8 layer/LiF electron injection layer/Al electrode
- FIG. 8 shows the results of measuring the V-luminance characteristics by the method described above together with the results of measuring the organic EL element (rubDBP) of Example 1. As is clear from FIG. 8, the insertion of the rubrene layer or the NPD layer improves the emission luminance in the high voltage region.
- Example 4 Examination of the first organic semiconductor layer
- PTCDI-C6 layer 50 nm, 0.1 nm / s
- PTCDI-C13 layer 50 nm, 0.1 nm / s
- C60 layer 50 nm , 0.1 nm/s
- Example 4A ITO electrode/ MoO3 hole injection layer/rubrene layer (undoped)/rubrene layer (DBP doped)/PTCDI-C6 layer/LiF electron injection layer/Al electrode
- Example 4B ITO electrode/ MoO3 hole injection layer/rubrene layer (undoped)/rubrene layer (DBP doped)/PTCDI-C13 layer/LiF electron injection layer/Al electrode
- Example 4C ITO electrode/MoO 3 hole injection layer/rubrene layer (undoped)/rubrene layer (DBP doped)/C60 layer/LiF electron injection layer/Al electrode. The results of measuring the external quantum yield (EQE) are shown in FIG.
- Example 9 together with the results of measuring the organic EL device of Example 3A.
- an organic EL device for comparison was produced by adopting a rubrene layer (undoped) with a thickness of 60 nm instead of the "rubrene layer (undoped)/rubrene layer (DBP doped)". and measured in the same way.
- the results are shown in FIG.
- no matter which electron transport layer is used the luminous efficiency is improved by about 10 times when the rubrene layer (DBP doping) is used, but the PTCDI-C8 layer is used. The luminous efficiency is highest when it is used.
- Example 5 Examination of dopant
- An organic EL device was fabricated in the same manner as in Example 3A except that DCJTB (0.5% by volume) was used as a dopant instead of DBP for the rubrene layer (DBP-doped).
- This organic EL element has the following structure.
- Example 6 Examination of film thickness of electron transport layer
- An organic EL device was fabricated in the same manner as in Example 3A, except that the thickness of the PTCDI-C8 layer was changed from 50 nm to 20 nm.
- FIG. 11 shows the results of measuring the V-luminance characteristics of the obtained organic EL device by the method described above together with the measurement results of the organic EL device of Example 3A. As is clear from FIG. 11, the luminance is high even when the film thickness is 20 nm.
- Example 7 Examination of film thickness of light-emitting layer
- An organic EL device was fabricated in the same manner as in Example 3A, except that the thickness of the rubrene layer (doped with DBP) was changed from 50 nm to 20 nm, 100 nm, 150 nm or 200 nm.
- the results of measuring the V-luminance characteristics of the obtained organic EL device by the method described above are shown in FIG. 12(A) together with the measurement results of the organic EL device of Example 3A.
- FIG. 12B together with the measurement results of the organic EL element of Example 3A.
- the luminance is high regardless of the film thickness.
- the thicker the film (200 nm) the higher the EQE (maximum 2.91% @ 30 mA/cm 2 ).
- Example 8 Examination of first organic semiconductor layer 2
- An organic EL device was fabricated in the same manner as in Example 3A, except that an NDI-bis-HFI layer (50 nm) was formed by thermal evaporation instead of the PTCDI-C8 layer.
- This organic EL device has the following configuration. ITO electrode/ MoO3 hole injection layer/rubrene layer (undoped)/rubrene layer (DBP doped)/NDI-bis-HFI layer/LiF electron injection layer/Al electrode. , and V-luminance characteristics are shown in FIG. 14 together with the measurement results of the organic EL device of Example 3A. As is clear from FIG. 14, the organic EL device of Example 8 can achieve high luminance (380 cd/m) even at a low voltage (1.5 V).
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Abstract
Description
すなわち、本発明の有機EL素子は、
一対の電極間に挟持された複数の有機半導体層を備える有機EL素子であって、
有機半導体層が、第1の有機半導体材料を含む第1の有機半導体層と、第2の有機半導体材料及び第3の有機半導体材料を含む第2の有機半導体層とを有し、
第1の有機半導体層と第2の有機半導体層とが接合面を形成し、
第1の有機半導体材料のHOMO準位は、第2の有機半導体材料のHOMO準位より低く、且つ第1の有機半導体材料のLUMO準位は、第2の有機半導体材料のLUMO準位より低く、
第2の有機半導体材料は、三重項-三重項消滅を生じる材料であり、
第2の有機半導体材料の励起三重項準位T1は、第2の有機半導体材料のHOMO準位及び第1の有機半導体材料のLUMO準位のエネルギー差より小さく、
第2の有機半導体材料のHOMO準位及び第1の有機半導体材料のLUMO準位のエネルギー差は、第2の有機半導体材料のHOMO準位とLUMO準位のエネルギー差よりも0.5eV以上小さく、
第2の有機半導体層において、第2の有機半導体材料はホスト材料であり、第3の有機半導体材料はドーパントであり、
第2の有機半導体材料の発光スペクトルの最大波長が、第1の有機半導体材料の吸収スペクトルの最大波長よりも長波長側にある。
ルブレン、PTCDI-C8、C60又はDBPを、真空蒸着システム内で、高真空下(~10-5Pa)で、石英基板上に熱蒸着して、単層の薄膜を形成した。層の厚さは、それぞれ約50nmであった。ルブレン及びDBPの薄膜についてPLスペクトルを、PTCDI-C8及びC60の薄膜についてABSスペクトルを、それぞれ測定した。その結果を図4に示す。また、NDI-bis-HFIについてABSスペクトルを測定した結果を図13に示す。
吸収スペクトルは、分光計(V-570、Jasco社製)で測定した。
発光スペクトルは、分光蛍光光度計(Fluorolog, HORIBA社製)で測定した。
単層のルブレン層について、ドーパントなし(0体積%)、ドーパントとしてDBPをルブレン層全体に対して0.2体積%、0.5体積%、1体積%、5体積%添加したものを準備し、それぞれについて、発光強度(PL強度)を測定した。ルブレン層は、真空蒸着システム内で、高真空下(~10-5Pa)で、石英基板上に熱蒸着することで形成した。DBPはルブレン層を蒸着する際に共蒸着法によって導入し、混合濃度は蒸着速度の比率で制御した。PL強度の測定は、絶対PL量子収率測定装置(Quantaurus-QY, 浜松ホトニクス社製)で測定した。その結果を図5に示す。図5から明らかであるように、ドーパントとしてDBPを添加した場合には、DBP由来の約605nm付近に発光が確認され、ルブレンからDBPへのエネルギー移動が確認できた。
上記PL強度の測定で準備した各種ルブレン層について、絶対PL量子収率測定装置(Quantaurus-QY,浜松ホトニクス社製)を用いて、蛍光量子収率(PL QY)を測定した。その結果を表1に示す。
インジウムスズ酸化物(ITO)でコーティングされたガラス基板(ITOの厚さ:150nm、シート抵抗:10.3Ω-1、テクノプリント社製)上に、MoO3正孔注入層(10nm、0.01nm/s)、ルブレン層(50nm、0.1nm/s)、PTCDI-C8層(50nm、0.1nm/s)、LiF電子注入層(0.2nm、0.001nm/s)及びAl電極(70nm、0.3nm/s)を、この順で、真空蒸着システム内で、高真空下(~10-5Pa)で熱蒸着した。デバイスを、グローブボックス内で、ガラス基板及びエポキシ樹脂によって封入して、有機EL素子を得た。なお、ルブレン層に、ドーパントとしてDBPを、ルブレン層全体に対して0.5体積%添加した。DBPはルブレン層を蒸着する際に共蒸着法によって導入し、混合濃度は蒸着速度の比率で制御した。
得られた有機EL素子は、以下の構成を有する。
ITO電極/MoO3正孔注入層/ルブレン層(DBPドープ)/PTCDI-C8層/LiF電子注入層/Al電極
DBPを添加しなかった他は、実施例1と同様にして、有機EL素子を作製した。得られた有機EL素子は、以下の構成を有する。
ITO電極/MoO3正孔注入層/ルブレン層(ドープなし)/PTCDI-C8層/LiF電子注入層/Al電極
実施例1及び比較例1の有機EL素子のV-輝度特性を、ソースメジャーユニット(B2902A Keysight Technologies社製)、輝度計(BM-9 Topcom社製)を用いて測定した。その結果を図6(A)に示す。
実施例1及び比較例1の有機EL素子の外部量子収率(EQE)を、校正済みの高感度・広帯域分光器(AvaSpec-UV/VIS/NIR、Avantes社製)を用いて測定した。その結果を図6(B)に示す。
図6(A)及び(B)から明らかであるように、ドーパントがある場合(実施例1)はない場合(比較例1)と比較して、同一電圧条件下で発光輝度が最大9.89倍、同一電流密度条件下で外部量子収率(EQE)が最大28.9倍、最小3.19倍、それぞれ向上した。
PTCDI-C8層とLiF電子注入層との間に、BCP層(10nm、0.05nm/s)を熱蒸着により形成した他は、実施例1と同様にして、有機EL素子を作製した。この有機EL素子は、以下の構成を有する。
ITO電極/MoO3正孔注入層/ルブレン層(DBPドープ)/PTCDI-C8層/BCP層/LiF電子注入層/Al電極
得られた有機EL素子(rubDBP/BCP)について、上述の方法で、V-輝度特性を測定した結果を、実施例1の有機EL素子(rubDBP)の測定結果と合わせて図7に示す。図7から明らかであるように、BCP層を挿入することにより、高電圧領域での発光輝度が向上する。
MoO3正孔注入層とルブレン層(DBPドープ)との間に、ルブレン層(10nm、0.1nm/s)(実施例3A)又はNPD層(10nm、0.1nm/s)(実施例3B)を熱蒸着により形成した他は、実施例1と同様にして、2種の有機EL素子を作製した。これらの有機EL素子は、以下の構成を有する。
実施例3A:
ITO電極/MoO3正孔注入層/ルブレン層(ドープなし)/ルブレン層(DBPドープ)/PTCDI-C8層/LiF電子注入層/Al電極
実施例3B:
ITO電極/MoO3正孔注入層/NPD層/ルブレン層(DBPドープ)/PTCDI-C8層/LiF電子注入層/Al電極
得られた2種の有機EL素子(rub/rubDBP,NPD/rubDPB)について、上述の方法で、V-輝度特性を測定した結果を、実施例1の有機EL素子(rubDBP)の測定結果と合わせて図8に示す。図8から明らかであるように、ルブレン層又はNPD層を挿入することにより、高電圧領域での発光輝度が向上する。
PTCDI-C8層に代えて、PTCDI-C6層(50nm、0.1nm/s)(実施例4A)、PTCDI-C13層(50nm、0.1nm/s)(実施例4B),C60層(50nm、0.1nm/s)(実施例4C)を熱蒸着により形成した他は、実施例3Aと同様にして、3種の有機EL素子を作製した。これらの有機EL素子は、以下の構成を有する。
実施例4A:
ITO電極/MoO3正孔注入層/ルブレン層(ドープなし)/ルブレン層(DBPドープ)/PTCDI-C6層/LiF電子注入層/Al電極
実施例4B:
ITO電極/MoO3正孔注入層/ルブレン層(ドープなし)/ルブレン層(DBPドープ)/PTCDI-C13層/LiF電子注入層/Al電極
実施例4C:
ITO電極/MoO3正孔注入層/ルブレン層(ドープなし)/ルブレン層(DBPドープ)/C60層/LiF電子注入層/Al電極
得られた3種の有機EL素子について、上述の方法で、外部量子収率(EQE)を測定した結果を、実施例3Aの有機EL素子の測定結果と合わせて図9に示す。また、実施例3A及び4A~4Cについて、「ルブレン層(ドープなし)/ルブレン層(DBPドープ)」に代えて厚さ60nmのルブレン層(ドープなし)を採用した比較用の有機EL素子を作製し、同様に測定を行った。その結果を図9に示す。図9から明らかであるように、どの電子輸送層を採用した場合であっても、ルブレン層(DBPドープ)を採用したときの方が10倍程度発光効率が向上するが、PTCDI-C8層を使用したときが最も発光効率が高い。
ルブレン層(DBPドープ)について、DBPに代えてDCJTB(0.5体積%)をドーパントとして採用した他は実施例3Aと同様にして、有機EL素子を作製した。この有機EL素子は、以下の構造を有する。
ITO電極/MoO3正孔注入層/ルブレン層(ドープなし)/ルブレン層(DCJTBでドープ)/PTCDI-C8層/LiF電子注入層/Al電極
得られた有機EL素子(DCJTB)について、高感度・広帯域分光器(AvaSpec-UV/VIS/NIR、Avantes社製)を用いてEL発光スペクトルを測定した結果を、実施例3Aの有機EL素子(DBP)及び比較例1(rub)の測定結果と合わせて図10(A)に示す。この結果から明らかであるように、ドーパント(DBP又はDCJTB)を用いた場合には、ルブレンからDBP又はDCJTBへのエネルギー移動が起こることで、ルブレンの発光が消光し、DBP又はDCJTB由来の発光が観測された。
また、得られ有機EL素子(DCJTB)について、上述の方法で、V-輝度特性を測定した結果を、実施例3Aの有機EL素子(DBP)の測定結果と合わせて図10(B)に示す。図10(B)から明らかであるように、DBPでドープした場合の方が発光輝度が高い。
PTCDI-C8層の厚さを50nmから20nmに代えた他は、実施例3Aと同様にして、有機EL素子を作製した。
得られた有機EL素子について、上述の方法で、V-輝度特性を測定した結果を、実施例3Aの有機EL素子の測定結果と合わせて図11に示す。図11から明らかであるように、膜厚を20nmとした場合であっても発光輝度は高い。
ルブレン層(DBPでドープ)の厚さを50nmから20nm、100nm、150nm又は200nmに代えた他は、実施例3Aと同様にして、有機EL素子を作製した。
得られた有機EL素子について、上述の方法で、V-輝度特性を測定した結果を、実施例3Aの有機EL素子の測定結果と合わせて図12(A)に、外部量子収率(EQE)を測定した結果を、実施例3Aの有機EL素子の測定結果と合わせて図12(B)に示す。図12(A)から明らかであるように、いずれの膜厚でも発光輝度は高い。図12(B)から明らかであるように、膜厚が厚い(200nm)方がEQEが大きい(最大2.91%@30mA/cm2).
PTCDI-C8層に代えて、NDI-bis-HFI層(50nm)を熱蒸着により形成した他は、実施例3Aと同様にして、有機EL素子を作製した。この有機EL素子は、以下の構成を有する。
ITO電極/MoO3正孔注入層/ルブレン層(ドープなし)/ルブレン層(DBPドープ)/NDI-bis-HFI層/LiF電子注入層/Al電極
得られた有機EL素子について、上述の方法で、V-輝度特性を測定した結果を、実施例3Aの有機EL素子の測定結果と合わせて図14に示す。図14から明らかであるように、実施例8の有機EL素子は、低電圧(1.5V)であっても高発光輝度(380cd/m)を達成することができる。
Claims (4)
- 一対の電極間に挟持された複数の有機半導体層を備える有機EL素子であって、
前記有機半導体層が、第1の有機半導体材料を含む第1の有機半導体層と、第2の有機半導体材料及び第3の有機半導体材料を含む第2の有機半導体層とを有し、
第1の有機半導体層と第2の有機半導体層とが接合面を形成し、
第1の有機半導体材料のHOMO準位は、第2の有機半導体材料のHOMO準位より低く、且つ第1の有機半導体材料のLUMO準位は、第2の有機半導体材料のLUMO準位より低く、
第2の有機半導体材料は、三重項-三重項消滅を生じる材料であり、
第2の有機半導体材料の励起三重項準位T1は、第2の有機半導体材料のHOMO準位及び第1の有機半導体材料のLUMO準位のエネルギー差より小さく、
第2の有機半導体材料のHOMO準位及び第1の有機半導体材料のLUMO準位のエネルギー差は、第2の有機半導体材料のHOMO準位とLUMO準位のエネルギー差よりも0.5eV以上小さく、
第2の有機半導体層において、第2の有機半導体材料はホスト材料であり、第3の有機半導体材料はドーパントであり、
第2の有機半導体材料の発光スペクトルの最大波長が、第1の有機半導体材料の吸収スペクトルの最大波長よりも長波長側にある、有機EL素子。 - 第1の有機半導体材料のHOMO準位と第2の有機半導体材料のHOMO準位との差が0.5eV以上である、請求項1に記載の有機EL素子。
- 第1の有機半導体材料のLUMO準位と第2の有機半導体材料のLUMO準位との差が0.5eV以上である、請求項1又は2に記載の有機EL素子。
- 第2の有機半導体材料の励起三重項準位T1と、第2の有機半導体材料のHOMO準位及び第1の有機半導体材料のLUMO準位のエネルギー差との差が、0.8eV未満である、請求項1~3のいずれか一項に記載の有機EL素子。
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CN202280025771.9A CN117158124A (zh) | 2021-04-01 | 2022-03-31 | 有机el元件 |
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Citations (3)
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JP2008535266A (ja) * | 2005-03-31 | 2008-08-28 | ザ、トラスティーズ オブ プリンストン ユニバーシティ | 三重項状態への直接注入を利用するoled |
JP2013157552A (ja) * | 2012-01-31 | 2013-08-15 | Canon Inc | 有機発光素子 |
JP2019505091A (ja) * | 2016-04-28 | 2019-02-21 | エルジー・ケム・リミテッド | 有機発光素子 |
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JP2008535266A (ja) * | 2005-03-31 | 2008-08-28 | ザ、トラスティーズ オブ プリンストン ユニバーシティ | 三重項状態への直接注入を利用するoled |
JP2013157552A (ja) * | 2012-01-31 | 2013-08-15 | Canon Inc | 有機発光素子 |
JP2019505091A (ja) * | 2016-04-28 | 2019-02-21 | エルジー・ケム・リミテッド | 有機発光素子 |
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