CN116322097A - Laminated organic electroluminescent device - Google Patents
Laminated organic electroluminescent device Download PDFInfo
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Abstract
The invention discloses a laminated organic electroluminescent device, which comprises an anode layer, at least two light-emitting units, a cathode layer and a connecting layer, wherein the anode layer, the at least two light-emitting units and the cathode layer are sequentially arranged from bottom to top; the first connecting layer and the fourth connecting layer are respectively and directly connected with two adjacent light-emitting units, the first connecting layer and the fourth connecting layer are gradient doped connecting layers, the gradient doped connecting layers are composed of a main body and doped objects, and in the first connecting layer, the mass percentage of the doped objects is lower at the side which is contacted with the light-emitting units and gradually increases towards the side which is not contacted with the light-emitting units; in the fourth connecting layer, the mass percentage of the doped object is higher at the side contacting the light-emitting unit and decreases towards the side not contacting the light-emitting unit; the laminated organic electroluminescent device has the characteristics of low driving voltage, high efficiency and long service life.
Description
Technical Field
The invention relates to the technical field of organic photoelectric materials and devices, in particular to a laminated organic electroluminescent device.
Background
An Organic Light-emitting Diode (OLED) technology is a technology of emitting Light under the action of an applied voltage, and has many advantages of flexibility, self-luminescence, lightness, thinness, low power consumption and the like, and has been widely applied to the fields of smart phones, wearable devices, vehicle-mounted displays and the like. The organic electroluminescent device structure and the preparation process thereof play a crucial role in representing the luminous performance of the OLED material, and are one of the key parts of OLED display and illumination technology. Therefore, the exploration of a new OLED device structure with low driving voltage, high luminous efficiency and long service life and the preparation process thereof become research hot spots in the current OLED technical field.
In order to improve the light-emitting brightness and the service life stability of the OLED device, a plurality of light-emitting units can be stacked to obtain a light-emitting element with a stacked structure through a connecting layer (Charge Generation Layer, CGL) structure. A light emitting cell typically comprises at least one light emitting layer, a hole transporting layer and an electron transporting layer. Compared with a single-light-emitting layer OLED device, the light-emitting brightness and the service life of the stacked device under the driving of the same current density are improved by times. That is, at the same brightness, the current density required for the stacked OLED is smaller than that of the conventional single-layer OLED, thereby achieving the effect of extending the lifetime; however, at constant current density the luminance of the stacked OLED is higher than that of a conventional single-layer OLED, and the voltage increases. Therefore, for stacked OLED devices, reducing the driving voltage drop of the connection layer between the light emitting units, and improving the stability of the connection layer are key to obtaining low driving voltage, high efficiency, and long life stacked OLED devices.
In terms of improving the performance of the connection layer, researchers and panel manufacturers have performed systematic optimization work, for example, in patent application CN114520301a, a stacked organic light emitting device is disclosed, a spacer layer structure is introduced between an n-type doped layer and a p-type doped layer, so that n-type dopants are prevented from easily diffusing into the p-type doped layer and an adjacent light emitting layer, and thus the driving voltage of the device is increased, and on the other hand, the injection and balance of carriers are improved by optimizing the collocation of a charge generating layer and an adjacent compound, so that the overall performance of the device is improved; for another example, in the patent application KR20170062938, the voltage is reduced, the efficiency is improved, and the lifetime is improved by optimizing the matching of the p-type charge generation layer and the hole transport layer in contact with the p-type charge generation layer in terms of energy level and hole mobility.
However, the existing researches on the performance of the connecting layer are less related to gradient doping, and cannot further reduce the energy level barrier between the connecting layer and the transmission layer of the light-emitting unit and improve the energy level matching between the connecting layer and the light-emitting unit, so that the driving voltage drop of the connecting layer in the laminated OLED device is reduced, and the efficiency and the service life stability of the device are improved.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a new stacked organic electroluminescent device, which effectively reduces the energy level barrier between the connection layer and the light emitting unit transmission layer and improves the energy level matching between the connection layer and the light emitting unit by providing a gradient doping process of the connection layer, and the prepared device has the characteristics of low driving voltage, high efficiency and long service life.
In order to achieve the above purpose, the present invention provides the following technical solutions:
a laminated organic electroluminescent device comprises an anode layer, at least two light-emitting units, a cathode layer and a connecting layer, wherein the anode layer, the at least two light-emitting units and the cathode layer are sequentially arranged from bottom to top; the connecting layer comprises a first connecting layer, a second connecting layer, a third connecting layer and a fourth connecting layer;
the first connecting layer and the fourth connecting layer are respectively and directly connected with two adjacent light-emitting units, and the first connecting layer and the fourth connecting layer are gradient doped connecting layers; the gradient doped connecting layer consists of a host and a doped object;
the doping object of the first connecting layer is an n-type dopant material and is selected from at least one of lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, gold, silver, copper, iron, nickel, platinum, palladium, ruthenium, ytterbium, molybdenum trioxide, vanadium pentoxide, tungsten trioxide, cesium fluoride, cesium carbonate, lithium fluoride, lithium carbonate, 8-hydroxyquinolinate lithium, sodium chloride, ferric chloride and ferric oxide;
the doped object of the fourth connecting layer is p-type dopant material selected from MoO 3 、WO 3 、V 2 O 5 、MoO 2 、Co 3 O 4 And at least one of the following compounds (1-1) to (1-20):
the main body of the first connecting layer is an organic material with electron transport property and is selected from at least one of the following compounds (2-1) to (2-42):
the second connection layer is made of n-type dopant material and is selected from at least one of lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, gold, silver, copper, iron, nickel, platinum, palladium, ruthenium, ytterbium, molybdenum trioxide, vanadium pentoxide, tungsten trioxide, cesium carbonate, lithium carbonate, sodium chloride, ferric chloride and ferric oxide.
The third connecting layer is a p-type dopant material and is selected from MoO3, WO3, V2O5, moO2, co3O4 and at least one of the following compounds (4-1) to (4-20):
in the first connecting layer, the mass percentage of the doped object is lower at the side contacting the light emitting unit and gradually increases towards the side not contacting the light emitting unit; in the fourth connection layer, the mass percentage of the doped object is higher at the side contacting the light emitting unit and decreases toward the side not contacting the light emitting unit.
Further, the doped objects in the first connecting layer and the fourth connecting layer are doped in a gradient manner at a constant mass percentage change rate; in the first connecting layer, the mass percentage of the doped object is lower at the side which is contacted with the light-emitting unit, and the mass percentage of the doped object is larger than 0, and the doped object is gradually increased to the side which is not contacted with the light-emitting unit at a constant doping mass percentage change rate; in the fourth connection layer, the mass percentage of the doped object is higher at the side which is contacted with the light emitting unit, the change rate of the doping mass percentage is reduced to the side which is not contacted with the light emitting unit, and the mass percentage of the doped object is larger than 0.
The light emitting unit includes any one or a combination of a plurality of hole injection layer, hole transport layer, electron blocking layer, light emitting layer, hole blocking layer, electron transport layer and electron injection layer.
The thickness of the first connecting layer is 10-50 nm, the thicknesses of the second connecting layer and the third connecting layer are 1-20 nm, and the thickness of the fourth connecting layer is 5-50 nm.
In the first connecting layer, the mass percentage of doped objects is 1-70wt%; in the fourth connecting layer, the mass percentage of the doped object is 0.5-50wt%.
The number of the light-emitting units is 2-5.
Compared with the prior art, the invention has the beneficial effects that:
(1) According to the invention, the n-type doping agent is adopted in the first connecting layer, the p-type doping agent is adopted in the fourth connecting layer, and the gradient doping technology is adopted in both the first connecting layer and the fourth connecting layer, so that the LUMO energy level of the first connecting layer is more matched with the LUMO energy level of the electron transport layer of the adjacent light-emitting unit, the HOMO energy level of the fourth connecting layer is more matched with the HOMO energy level of the hole transport layer of the adjacent light-emitting unit, the injection barrier of carriers injected into the transport layer is reduced, the driving voltage of a laminated device is reduced, and the power efficiency is improved;
(2) The mass concentration of the n-type dopant in the first connecting layer is gradually reduced, so that the n-type dopant is prevented from diffusing to the light-emitting layer adjacent to the light-emitting unit, and the problems of quenching of light-emitting excitons and reduction of the service life of the device are avoided; on the other hand, the first connecting layer is arranged between the electron transport layer adjacent to the light-emitting unit and the second connecting layer, so that the damage to the electron transport layer of the light-emitting unit caused by the higher preparation temperature of the n-type dopant material in the second connecting layer can be avoided;
(3) A second connecting layer and a third connecting layer are arranged between the first connecting layer and the fourth connecting layer, so that rapid separation of electrons and holes is realized under the action of an external electric field, and injection of electrons to the first connecting layer and injection of holes to the fourth connecting layer are realized, thereby obtaining efficient carrier generation effect; and meanwhile, as the first connecting layer is doped with the n-type dopant and the fourth connecting layer is doped with the p-type dopant, the injection barrier of electrons injected into the first connecting layer and holes injected into the fourth connecting layer is reduced, thereby being beneficial to reducing the driving voltage of a laminated device and improving the power efficiency.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the following description will briefly explain the drawings used in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 shows a schematic structure of a stacked organic electroluminescent device of the present invention;
fig. 2 shows a graph of current density versus voltage for example 1 and comparative example 20 of the present invention;
fig. 3 shows a device lifetime characteristic diagram of example 1 and comparative example 21 of the present invention.
In the figure: 100. an anode layer; 101. a hole injection layer; 102. a first hole transport layer; 103. a second hole transport layer; 104. a first light emitting layer; 105. a second electron transport layer; 106. a first electron transport layer; 107. a first connection layer; 108. a second connection layer; 109. a third connection layer; 110. a fourth connection layer; 111. a third hole transport layer; 112. a fourth hole transport layer; 113. a second light emitting layer; 114. a fourth electron transport layer; 115. a third electron transport layer; 116. an electron injection layer; 117. and a cathode layer.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present disclosure more apparent, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present disclosure. It will be apparent that the described embodiments are some, but not all, of the embodiments of the present disclosure. All other embodiments, which can be made by one of ordinary skill in the art without the benefit of the present disclosure, are intended to be within the scope of the present invention based on the described embodiments.
It is to be understood that any and all embodiments of the invention may be combined with any other embodiment or features of multiple other embodiments to yield yet further embodiments without conflict. The present invention includes such combinations resulting in additional embodiments.
In this specification, groups and substituents thereof can be selected by one skilled in the art to provide stable moieties and compounds. When substituents are described by conventional formulas written from left to right, the substituents also include chemically equivalent substituents obtained when writing formulas from right to left.
The section headings used in this specification are for organizational purposes only and are not to be construed as limiting the subject matter described. All documents or portions of documents cited in this disclosure, including but not limited to patents, patent applications, articles, books, operating manuals, and treatises, are hereby incorporated by reference in their entirety.
Unless otherwise specified, all technical and scientific terms used herein have the standard meaning of the art to which the claimed subject matter belongs. In case there are multiple definitions for a term, the definitions herein control.
As used herein, the singular forms "a", "an", and "the" are understood to include plural referents unless the context clearly dictates otherwise. Furthermore, the term "comprising" is an open-ended limitation and does not exclude other aspects, i.e. it includes the content indicated by the invention.
The invention provides a laminated organic electroluminescent device, which consists of a substrate, an anode layer, at least two light-emitting units, a cathode layer and a connecting layer for connecting two adjacent light-emitting units, wherein the light-emitting units comprise any one or a combination of a plurality of hole injection layers, hole transport layers, electron blocking layers, light-emitting layers, hole blocking layers, electron transport layers and electron injection layers.
The light-emitting layer of the organic electroluminescent device is mainly used for generating excitons by combining holes and electrons injected into the light-emitting layer, and the excitons complete the electro-optic conversion process in a radiation transition mode. The material constituting the light-emitting layer may be an undoped light-emitting compound composed of only the first compound, may be a binary light-emitting composition composed of the first compound and the third compound, or may be a ternary light-emitting composition composed of the first compound, the second compound, and the third compound. As the first compound, a fluorescent material, a phosphorescent material, a thermally activated delayed fluorescent material, or the like, which is selected according to a light emission mechanism, is preferable, and a phosphorescent material containing a coordinated metal such as iridium, platinum, or the like, a thermally activated delayed fluorescent material containing a boron nitrogen derivative, a boron oxygen derivative, an indolocarbazole derivative, or a boron fluorine derivative, and a fluorescent material containing a fluoranthene derivative, a pyrene derivative, or an imidazole derivative are preferable. The second compound preferably contains a benzonitrile derivative, a triazine derivative, a pyrimidine derivative, a pyridine derivative, a pyrazine derivative, an imidazole derivative, a derivative of benzothiophene oxide, a phenanthroline derivative, a benzonitrile derivative, a thermally activated delayed fluorescence material of a phosphorus oxide derivative as the second compound.
The anode layer of the organic electroluminescent device mainly has the function of injecting holes into the hole transport layer or the luminescent layer, and anode layer materials with the work function of more than 4.5eV are preferentially used. The anode layer material is preferably selected from Indium Tin Oxide (ITO), tin oxide (NESA), indium Gallium Zinc Oxide (IGZO), silver, and the like. The anode layer may be formed as an anode layer film by a thermal vapor deposition method, a sputtering method, or the like. The light transmittance of the visible region of the anode is preferably made greater than 80%. In addition, the sheet resistance of the anode layer is preferably 500 Ω/cm -1 Hereinafter, the film thickness is preferably selected in the range of 10 to 200nm.
The cathode layer of the organic electroluminescent device mainly functions to inject electrons into the electron injection layer, the electron transport layer or the light emitting layer, preferably a material having a small work function. The cathode material is not particularly limited, but is preferably selected from aluminum, magnesium, silver, magnesium-silver alloy, magnesium-aluminum alloy, aluminum-lithium alloy, and the like. The cathode layer may be formed as a cathode layer thin film by a thermal vapor deposition method, a sputtering method, or the like, and the cathode layer film thickness is preferably selected in the range of 10 to 200nm. Further, light emission may be extracted from the cathode side as needed.
The organic electroluminescent element of the present invention preferably has an electron injection layer at an interface region between the cathode layer and the electron transport layer or the light emitting layer. The electron injection layer is mainly used for promoting electron injection from the cathode layer to the electron transport layer or the light-emitting layer, so that the light-emitting brightness and the service life of the organic electroluminescent device are improved. The electron injection layer material is a material having a work function of 3.8eV or less, and may preferably be selected from lithium, cesium, barium, ytterbium, cesium fluoride, cesium carbonate, lithium fluoride, lithium carbonate, lithium 8-hydroxyquinolinate, barium oxide, and the like. The electron injection layer may form electrons by thermal evaporationInjection layer film, vapor deposition rate is preferably
The thickness of the cathode layer thus produced is preferably selected in the range of 0.1 to 15 nm.
The electron transport layer of the organic electroluminescent device is an organic layer formed between the light emitting layer and the cathode layer (or electron injection layer), and mainly serves to transport electrons from the cathode to the light emitting layer. The electron transport layer may be composed of a layer of organic layer material, defined as a first electron transport layer; it is also possible to consist of two organic layers, the organic layer on the side close to the cathode layer being defined as a first electron transport layer and the organic layer on the side close to the light-emitting layer being defined as a second electron transport layer. The electron transport material used for the electron transport layer is preferably an aromatic heterocyclic compound having 1 or more hetero atoms in the molecule, and particularly preferably a nitrogen-containing ring derivative. The nitrogen-containing ring derivative is preferably an aromatic ring having a nitrogen-containing six-membered ring or five-membered ring skeleton or a condensed aromatic ring having a nitrogen-containing six-membered ring or five-membered ring skeleton.
The electron transport layer of the organic electroluminescent device of the present invention is preferably selected from the following compounds but is not limited to the following structures:
the thickness of the electron transport layer is not particularly limited, and is preferably 10 to 100nm. Wherein when the electron transport layer of the organic electroluminescent device is composed of the first electron transport layer, the film thickness of the first electron transport layer is preferably 10-100 nm; when the electron transport layer of the organic electroluminescent device is composed of a first electron transport layer and a second electron transport layer, the film thickness of the first electron transport layer is preferably 9 to 70nm, and the film thickness of the second electron transport layer is preferably 1 to 30nm.
The hole transport layer of the organic electroluminescent device is an organic layer formed between the light emitting layer and the anode layer (or hole injection layer), and mainly serves to transport holes from the anode to the light emitting layer. The hole transport layer may be composed of a layer of organic layer material, defined as a first hole transport layer; it is also possible to consist of two layers of organic layer material, the organic layer on the side close to the anode layer being defined as a first hole transport layer and the organic layer on the side close to the light-emitting layer being defined as a second hole transport layer. As the hole transporting material for the hole transporting layer, an aromatic amine compound, for example, an aromatic amine derivative represented by the following formula (70), is preferably used.
In the above formula (70), ar 1 ～Ar 4 An aromatic hydrocarbon group having 6 to 50 (preferably 6 to 30, more preferably 6 to 20, still more preferably 6 to 12) or a condensed aromatic hydrocarbon group having 6 to 50 (preferably 6 to 30, more preferably 6 to 20, still more preferably 6 to 12) ring-forming carbon atoms which may have a substituent, an aromatic heterocyclic group having 5 to 50 (preferably 5 to 30, more preferably 5 to 20, still more preferably 5 to 12) or a condensed aromatic heterocyclic group having 5 to 50 (preferably 5 to 30, more preferably 5 to 20, still more preferably 5 to 12) ring-forming carbon atoms which may be substituted, or a group in which these aromatic hydrocarbon groups or condensed aromatic hydrocarbon groups are bonded to an aromatic heterocyclic group or a condensed aromatic heterocyclic group.
In Ar 1 With Ar 2 Between and at Ar 3 With Ar 4 And may form a ring therebetween. In addition, anotherIn the above formula (70), L represents a substituted or unsubstituted aromatic hydrocarbon group having 6 to 50 (preferably 6 to 30, more preferably 6 to 20, still more preferably 6 to 12) ring-forming carbon atoms, or a substituted or unsubstituted condensed aromatic hydrocarbon group having 6 to 50 (preferably 6 to 30, more preferably 6 to 20, still more preferably 6 to 12) ring-forming carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 5 to 50 (preferably 5 to 30, more preferably 5 to 20, still more preferably 5 to 12) ring-forming carbon atoms, or a substituted or unsubstituted condensed aromatic heterocyclic group having 5 to 50 (preferably 5 to 30, more preferably 5 to 20, still more preferably 5 to 12) ring-forming carbon atoms.
As the hole transporting material for the hole transporting layer, another aromatic amine compound, for example, an aromatic amine derivative represented by the following formula (71), is preferably used.
Ar in the above formula (71) 1 ～Ar 3 Ar of formula (70) 1 ～Ar 4 Is the same as defined in the following.
The hole transport layer of the organic electroluminescent device of the present invention, the compound according to formulae (70) and (71) is preferably selected from the following compounds, but is not limited to the following structures:
the thickness of the hole transport layer is not particularly limited, and is preferably 20 to 200nm. Wherein when the hole transport layer of the organic electroluminescent device is composed of the first hole transport layer, the film thickness of the first hole transport layer is preferably 20 to 200nm; when the hole transport layer of the organic electroluminescent device is composed of a first hole transport layer and a second hole transport layer, the film thickness of the first hole transport layer is preferably 19 to 150nm, and the film thickness of the second hole transport layer is preferably 1 to 50nm.
The organic electroluminescent element of the invention is preferably doped with n-type dopant in the electron transport layer and p-type dopant in the hole transport layer, wherein the n-type dopant and the p-type dopant have the main functions of improving the transmissibility of the electron transport layer and the hole transport layer respectively and reducing the driving voltage of the organic electroluminescent device. Here, the n-type dopant is preferably lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, gold, silver, copper, iron, nickel, platinum, palladium, ruthenium, ytterbium, molybdenum trioxide, vanadium pentoxide, tungsten trioxide, cesium fluoride, cesium carbonate, lithium fluoride, lithium carbonate, lithium 8-hydroxyquinolinate, sodium chloride, ferric oxide, or the like; the p-type dopant is preferably MoO 3 、WO 3 、V 2 O 5 、MoO 2 、Co 3 O 4 And at least one of the following compounds (HI-1) to (HI-20):
when the hole transport layer contains the p-type dopant and the hole transport material, the doping concentration of the p-type dopant is preferably 0.1 to 50.0wt%; when the hole transport layer contains the n-type dopant and the electron transport material, the doping concentration of the n-type dopant is preferably 1.0 to 90.0wt%.
Specifically, as shown in fig. 1, the organic electroluminescent device includes a substrate, an anode layer 100, a first light emitting unit, a connection layer, a second light emitting unit and a cathode layer 117 that are sequentially stacked from bottom to top, where the first light emitting unit sequentially includes any one or more combinations of a hole injection layer 101, a first hole transport layer 102, a second hole transport layer 103, a first light emitting layer 104, a second electron transport layer 105 and a first electron transport layer 106, and the second light emitting unit sequentially includes any one or more combinations of a third hole transport layer 111, a fourth hole transport layer 112, a second light emitting layer 113, a fourth electron transport layer 114, a third electron transport layer 115 and an electron injection layer 116, and the connection layer sequentially includes a first connection layer 107, a second connection layer 108, a third connection layer 109 and a fourth connection layer 110.
The specific preparation process of the laminated organic electroluminescent device comprises the following steps:
examples 1 to 6
(1) A glass substrate having an ITO transparent electrode (anode layer 10, film thickness of ITO: 95 nm) with a thickness of 30 mm. Times.30 mm. Times.0.7 mm was subjected to ultrasonic cleaning in acetone, a washing liquid, ultrapure water (3 times), and isopropanol in this order, and the ultrasonic cleaning time was 10 minutes for each step. Placing the cleaned ITO glass substrate in an oven at 80 ℃ for baking for 3 hours;
(2) Vacuum plasma cleaning treatment is carried out on the baked ITO glass substrate for 10 minutes;
(3) The glass substrate after plasma treatment is mounted on a substrate holder of a vacuum vapor deposition apparatus, and first, a compound HATCN is deposited on a surface of a side on which transparent electrode lines are formed so as to cover the transparent electrodes, thereby forming a hole injection layer 101 having a film thickness of 10 nm;
(4) Evaporating a compound HT-10 on the hole injection layer 101 to form a first hole transport layer 102 with a film thickness of 30 nm;
(5) Evaporating a compound HT-48 on the first hole transport layer 102 to form a second hole transport layer 103 with a film thickness of 10 nm;
(6) Third compound RH and first compound RD were co-evaporated on second hole transport layer 103 to form first light-emitting layer 104 having a film thickness of 25nm, and the concentration of first compound RD in first light-emitting layer 104 was set to 4wt%, and the structures of third compound RH and first compound RD used were as follows:
(7) Evaporating ET-15 on the first light-emitting layer 104 to form a second electron transport layer 105 with a film thickness of 10 nm;
(8) Evaporating ET-4 on the second electron transport layer 105 to form a first electron transport layer 106 with a film thickness of 10 nm;
(9) Co-evaporating n-type doped object and electron-transporting compound on the first electron transport layer 106 by gradient doping to form a first connection layer 107 having a film thickness of 20 nm;
(10) Depositing an n-type dopant material ytterbium on the first connection layer 107 to form a second connection layer 108 with a film thickness of 3 nm;
(11) Evaporating p-type dopant material 4-7 on the second connection layer 108 to form a third connection layer 109 with a film thickness of 3 nm;
(12) Co-evaporating p-type doped object and hole-transporting compound on the third connection layer 109 by gradient doping to form a fourth connection layer 110 with a film thickness of 20 nm;
(13) Evaporating a compound HT-10 on the fourth connection layer 110 to form a third hole transport layer 111 with a film thickness of 20 nm;
(14) Evaporating a compound HT-48 on the third hole transport layer 111 to form a fourth hole transport layer 112 with a film thickness of 10 nm;
(15) Co-evaporating a third compound RH and a first compound RD on the fourth hole transport layer 112 to form a second light emitting layer 113 having a film thickness of 25nm, wherein the concentration of the first compound RD in the second light emitting layer 113 is set to 4wt%;
(16) Evaporating ET-15 on the second light-emitting layer 113 to form a fourth electron transport layer 114 with a film thickness of 10 nm;
(17) Evaporating ET-4 on the fourth electron transport layer 114 to form a third electron transport layer 115 with a film thickness of 30 nm;
(18) Evaporating Liq on the third electron transport layer 115 to form an electron injection layer 116 with a film thickness of 3 nm;
(19) Metal Al was deposited on the electron injection layer 116 to form a cathode layer 117 having a film thickness of 100nm.
Wherein the combination of the compounds and the gradient doping process used in forming the first connection layer 107 and the fourth connection layer 110 in step (9) and step (12) are shown in examples 1 to 6 of table 1 below.
TABLE 1
Examples 7 to 12
The n-type dopant materials used in forming the second connection layer 107 and the p-type dopant materials used in forming the third connection layer 109 in the step (10) and the step (11) of the stacked organic electroluminescent devices prepared in examples 7 to 12 were combined as shown in table 2 below. An organic electroluminescent device was produced in the same manner as in example 1, except that the organic electroluminescent device was used.
TABLE 2
Comparative examples 20 to 24
The structure of the connection layer of the laminated organic electroluminescent devices prepared in comparative examples 20 to 24 was changed to the structure described in table 3 below. An organic electroluminescent device was produced in the same manner as in example 1, except that the organic electroluminescent device was used.
TABLE 3 Table 3
Evaluation of organic electroluminescent device Performance
The organic electroluminescent devices prepared in examples 1 to 12 and comparative examples 20 to 24 were measured using a spectroradiometer CS-2000 (Konica Minolta) and a digital source meter 2420 (Keithley) at a current density of 10mA/cm 2 Driving voltage, external Quantum Efficiency (EQE) and CIE1931 chromaticity coordinates (x, y) when driving the prepared organic electroluminescent device; measurement of 50mA/cm current density using device lifetime test 2 When the prepared organic electroluminescent device is driven, the brightness of the device is attenuated to the life (T95) of 95% of the initial brightness; the results of evaluation of the device properties of examples 1 to 12 and comparative examples 20 to 24 are shown in Table 4 below.
TABLE 4 Table 4
Comparing the device performance results of examples 1 and 3 and comparative examples 20 and 22 in table 4, it can be seen that the doping object in the first connection layer and the fourth connection layer adopts the graded doping process, which is favorable for reducing the driving voltage, and improving the lifetime of the device, and the lifetime improvement range is more than 30%. On one hand, due to the gradient doping effect, the first connecting layer is more matched with the electron transmission layer of the adjacent light-emitting unit, and the fourth connecting layer is more matched with the hole transmission layer of the adjacent light-emitting unit in energy level, so that the injection barrier of carriers is reduced, and the device driving voltage is reduced; on the other hand, the gradient doping process enables the concentration of the n-type dopant material on one side of the adjacent light-emitting unit to be low, so that the device is prevented from being aged rapidly due to the fact that a doping object enters the light-emitting layer. Further, as can be seen from comparing the device performance results of examples 1 and 3 with those of comparative examples 21, 23 and 24 in table 4, setting the second connection layer and the third connection layer between the first connection layer and the fourth connection layer can effectively reduce the driving voltage of the device, since the second connection layer and the third connection layer have good charge generation effect, the driving voltage drop of the device at the connection layer is reduced, thereby achieving the effect of reducing the driving voltage of the device. As can be seen from comparing the device performances of examples 1 to 12 and comparative examples 20 to 24 in table 4, after further replacing the combination of the compounds used for the first connection layer, the second connection layer, the third connection layer and the fourth connection layer, the device driving voltages and the device lives of examples 1 to 12 are both better than those of comparative examples 20 to 24, which indicates that the connection layer structures described in the present application are generally better than those of the connection layer structures in comparative examples for improving the performance of the stacked organic electroluminescent device.
Although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. The laminated organic electroluminescent device is characterized by comprising an anode layer, at least two light-emitting units, a cathode layer and a connecting layer, wherein the anode layer, the at least two light-emitting units and the cathode layer are sequentially arranged from bottom to top;
the connecting layer comprises a first connecting layer, a second connecting layer, a third connecting layer and a fourth connecting layer; the first connecting layer and the fourth connecting layer are respectively and directly connected with two adjacent light-emitting units, the first connecting layer and the fourth connecting layer are gradient doped connecting layers, and the gradient doped connecting layers consist of a main body and a doped object;
the doping object of the first connecting layer is an n-type dopant material and is selected from at least one of lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, gold, silver, copper, iron, nickel, platinum, palladium, ruthenium, ytterbium, molybdenum trioxide, vanadium pentoxide, tungsten trioxide, cesium fluoride, cesium carbonate, lithium fluoride, lithium carbonate, 8-hydroxyquinolinate lithium, sodium chloride, ferric chloride and ferric oxide;
the doped object of the fourth connecting layer is p-type dopant material selected from MoO 3 、WO 3 、V 2 O 5 、MoO 2 、Co 3 O 4 And at least one of the following compounds (1-1) to (1-20):
2. the laminated organic electroluminescent device according to claim 1, wherein the host of the first connection layer is an organic material having an electron transporting property, and is selected from at least one of the following compounds (2-1) to (2-42):
3. the stacked organic electroluminescent device of claim 1, wherein the second connection layer is an n-type dopant material selected from at least one of lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, gold, silver, copper, iron, nickel, platinum, palladium, ruthenium, ytterbium, molybdenum trioxide, vanadium pentoxide, tungsten trioxide, cesium carbonate, lithium carbonate, sodium chloride, ferric chloride, and ferric oxide.
4. The laminated organic electroluminescent device of claim 1, wherein the third connection layer is a p-type dopant material selected from MoO 3 、WO 3 、V 2 O 5 、MoO 2 、Co 3 O 4 And at least one of the following compounds (4-1) to (4-20):
5. the laminated organic electroluminescent device according to claim 1, wherein in the first connection layer, the mass percentage of the doped object is lower at a side contacting the light emitting unit, and the mass percentage of the doped object is greater than 0 and increases toward a side not contacting the light emitting unit; in the fourth connection layer, the mass percentage of the doped object is higher at the side contacting the light emitting unit and decreases gradually towards the side not contacting the light emitting unit, and the mass percentage of the doped object is more than 0%.
6. The laminated organic electroluminescent device of claim 5, wherein doping objects in the first and fourth connection layers are graded at a constant mass percent rate of change; in the first connecting layer, the mass percentage of the doped object is lower at the side which is contacted with the light-emitting unit, and the doped object is gradually increased to the side which is not contacted with the light-emitting unit at a constant doping mass percentage change rate; in the fourth connection layer, the mass percentage of the doped object is higher at the side contacting the light emitting unit, and decreases at a constant doping mass percentage change rate toward the side not contacting the light emitting unit.
7. The laminated organic electroluminescent device according to claim 1, wherein the light emitting unit comprises any one or a combination of more of a hole injection layer, a hole transport layer, an electron blocking layer, a light emitting layer, a hole blocking layer, an electron transport layer, and an electron injection layer.
8. The laminated organic electroluminescent device according to claim 1, wherein the thickness of the first connection layer is 10 to 50nm, the thicknesses of the second connection layer and the third connection layer are each 1 to 20nm, and the thickness of the fourth connection layer is 5 to 50nm.
9. The laminated organic electroluminescent device according to claim 1, wherein the mass percentage of the doped guest in the first connection layer is 1-70 wt%; in the fourth connecting layer, the mass percentage of the doped object is 0.5-50wt%.
10. The laminated organic electroluminescent device according to claim 1, wherein the number of the light emitting units is 2 to 5.
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