WO2019218970A1 - Thermally-activated delayed fluorescent organic electroluminescent device - Google Patents

Abstract

A thermally-activated delayed fluorescent organic electroluminescent device, comprising a light-emitting layer. The light-emitting layer comprises at least one first organic compound and at least one second organic compound as host materials, and a phosphorescent compound or a fluorescent compound as a guest material. The organic electroluminescent device provided has high luminous efficiency and low roll-off.

Description

Thermally activated delayed fluorescent organic electroluminescent device Technical field

The present invention relates to the field of semiconductor technology, and in particular to an organic electroluminescent device.

Background technique

Organic electroluminescent devices based on thermally activated delayed fluorescent materials have become a hotspot of research and development due to their low material synthesis difficulty, no need to use precious metals, and high purity of luminescent color. It is considered to have great application potential in the field of next-generation flat panel display. In recent years, it has received extensive attention.

The basic structure of an organic electroluminescent device comprises an opposite cathode and an anode, and a light-emitting layer sandwiched between the cathode and the anode. Generally, in order to obtain higher device performance, the light-emitting layer generally requires the host material to be doped with a guest material to obtain more efficient energy transfer efficiency, and fully utilize the luminescent potential of the guest material.

Thermally activated delayed fluorescence (TADF) materials are the third generation of organic luminescent materials developed after organic fluorescent materials and organic phosphorescent materials. The thermally activated delayed fluorescent material has a small triplet state and a singlet energy difference, which facilitates the realization of anti-intersystem enthalpy, reduces the triplet exciton concentration, reduces the exciton quenching probability, and fully utilizes the single line formed under electrical excitation. For exciton and triplet excitons, the internal quantum efficiency of the device can reach 100%. At the same time, the material structure is controllable, the property is stable, the price is cheap, no precious metal is needed, and the application prospect in the field of OLEDs is broad.

Although TADF materials can theoretically achieve 100% exciton utilization, the following problems actually exist:

(1) For a thermally activated delayed fluorescent luminescent material, the smaller the triplet state and the singlet energy difference have a smaller radiation transition rate, it is difficult to have both high exciton utilization and high fluorescence radiation efficiency;

(2) Even though doped devices have been used to mitigate the T exciton concentration quenching effect, most devices of TADF materials are severely quenched at high current densities due to excessive exciton concentration, resulting in severe roll-off of the device at high current densities. .

In order to improve the efficiency and stability of organic electroluminescent devices, it is necessary to improve the structure of the device and the development of new materials in order to meet the needs of future panel companies and lighting companies.

Summary of the invention

In view of this, the present invention provides a high efficiency organic electroluminescent device in view of the problems existing in the prior art. The organic electroluminescent device provided by the invention can realize multi-channel energy transfer between host and guest, improve the utilization of excitons inside the device, reduce the probability of exciton quenching, and effectively improve the efficiency and stability of the organic electroluminescent device.

The technical solution of the present invention is as follows:

An organic electroluminescent device comprising a light-emitting layer comprising a host material and a guest material, the host material comprising at least one first organic compound and at least one second organic compound, the guest material being phosphorescent a compound or a fluorescent compound;

The difference between the singlet level and the triplet level of the first organic compound is not more than 0.2 eV, preferably not more than 0.15 eV, more preferably not more than 0.1 eV;

The difference between the singlet level and the triplet level of the second organic compound is not more than 0.2 eV, preferably not more than 0.15 eV, more preferably not more than 0.1 eV;

The singlet energy level of the first organic compound is smaller than the triplet energy level of the second organic compound, and the difference is not less than 0.1 eV, preferably not less than 0.15 eV, more preferably not less than 0.2 eV;

The difference between the HOMO level and the LUMO level of the second organic compound is not less than 2.8 eV, preferably not less than 3.0 eV, more preferably not less than 3.2 eV.

Preferably, the first organic compound is a compound having a D-A structure or a D-Π-A structure.

Preferably, the second organic compound is a compound having a D-A structure or a D-Π-A structure.

Preferably, the first organic compound is selected from one of the following compounds:

Preferably, the second organic compound is selected from one of the following compounds:

Preferably, the weight ratio of the first organic compound to the second organic compound is from 9:1 to 1:9, preferably from 7:3 to 3:7, more preferably from 6:4 to 4:6.

Preferably, the fluorescent compound comprises a thermally activated delayed fluorescent material, wherein the singlet state level and the triplet level difference of the thermally activated delayed fluorescent material are not more than 0.2 eV, preferably not more than 0.15 eV, more preferably not more than 0.1 eV.

Preferably, the singlet state energy level of the thermally activated delayed fluorescent material is smaller than the triplet energy level of the first organic compound, and the difference is not less than 0.1 eV, preferably not less than 0.15 eV.

Preferably, the weight of the guest material relative to the weight of the host material is from 0.5 to 20% by weight, preferably from 1 to 15% by weight, more preferably from 3 to 12% by weight, based on the weight of the host material.

Preferably, the organic electroluminescent device provided by the present application further includes a hole transporting region and an electron transporting region, the hole transporting region comprising one or more of a hole injecting layer, a hole transporting layer, and an electron blocking layer. Combining; the electron transporting region comprises a combination of one or more of an electron injecting layer, an electron transporting layer, and a hole blocking layer.

The application also provides an illumination or display element comprising an organic electroluminescent device as described above.

The beneficial technical effects of the present invention are:

In the organic electroluminescent device of the present invention, the host material of the light-emitting layer is composed of two materials, wherein the first compound is a thermally activated delayed fluorescent material having a small singlet-triplet level difference (ΔEst). The second organic compound is also a thermally activated delayed fluorescent material having a smaller singlet-triplet level difference ([Delta]Est). The thermally activated delayed fluorescent material can achieve effective reverse intersystem crossing, reduce the triplet exciton concentration of the host material, reduce the probability of triplet exciton quenching, and improve device stability.

Since the first organic compound and the second organic compound are both thermally activated delayed fluorescent materials, having a small triplet state and a singlet energy difference, the first organic compound can transfer energy from the triplet state to the singlet state through the anti-intersystem enthalpy. Then, from the singlet state, the Forster energy transfer is transferred to the singlet energy level of the guest material, and the triplet energy of the first organic compound can also be transferred to the triplet energy level of the guest material through the Dexter energy transfer. The exciton energy in the second organic compound can also be transitioned from the triplet state to the singlet state by the anti-systemic enthalpy, and then transmitted to the first organic compound and the singlet energy level of the guest material through the Forster energy transfer, while the second organic compound The triplet energy can also be transferred to the first organic compound and the triplet energy level of the guest material through Dexter energy transfer to achieve multi-channel energy transfer, as shown in Figure 1. The second compound in the present invention is a compound having a wider band gap, and the second organic compound having a wide band gap can dilute the first organic compound, reducing the quenching effect of the first organic compound due to agglomeration. At the same time, the T1 energy level of the second organic compound in the invention is higher than the S1 energy level of the first organic compound, which can effectively prevent energy return between the first organic compound and the second organic compound, improve energy utilization, and further improve The efficiency and stability of the device.

The invention provides that the light-emitting layer of the organic electroluminescent device can improve the efficiency of the organic electroluminescent device and reduce the roll-off of efficiency, and has good application effects and industrialization prospects.

DRAWINGS

Figure 1 is a schematic diagram of energy transfer between host and guest.

2 is a schematic view of an embodiment of an organic electroluminescent device, wherein: 1, a substrate layer; 2, an anode layer; 3, a hole injection layer 4, a hole transport layer; 5, an electron blocking layer; 7, hole blocking / electron transport layer; 8, electron injection layer; 9, cathode layer.

Fig. 3 is a graph showing changes in device voltage with time at an initial luminance of 5000 cd/m ² .

Figure 4 shows the variation of the EQE of the device at different temperatures.

Detailed ways

In the context of the present invention, unless otherwise stated, HOMO means the highest occupied orbital of a molecule, and LUMO means the lowest unoccupied orbital of a molecule. Further, the "HOMO level and LUMO level difference" referred to in the present specification means the difference of the absolute values of each energy value. Furthermore, in the context of the present invention, the HOMO and LUMO energy levels are represented by absolute values, and the comparison between energy levels is also the magnitude of the absolute value thereof, and those skilled in the art know that the greater the absolute value of the energy level, the energy The lower the energy of the stage.

In the context of the present invention, "not greater than" in the present invention means less than or equal to, unless otherwise stated, "not less than" means greater than or equal to, and there are no upper and lower limits.

In the context of the present invention, unless otherwise stated, the singlet (S1) level means the singlet state of the lowest excited state level of the molecule, and the triplet (T1) level means the lowest excited level of the triplet state of the molecule. Further, the "triplet level difference" and "single line state and triplet level difference" referred to in the present specification mean the difference of the absolute values of each energy value. In addition, the difference between the energy levels is expressed in absolute values. Furthermore, the singlet and triplet levels can be measured by fluorescence and phosphorescence spectroscopy, respectively, as is well known to those skilled in the art.

In the present invention, the selection of the first organic compound and the second organic compound constituting the host material is not particularly limited as long as the singlet and triplet energy levels thereof and the LUMO level and the HOMO level difference satisfy the above conditions.

In a particularly preferred embodiment, the first organic compound is selected from the group consisting of compounds of the formula:

In a particularly preferred embodiment, the second organic compound is selected from the group consisting of compounds of the formula:

In the present invention, the weight ratio of the first organic compound to the second organic compound constituting the host material is not particularly limited. There is no particular restriction on the choice of guest materials. There is no particular limitation on the weight ratio of the constituent host material to the guest material. In a preferred embodiment, the guest material is selected from compounds having the formula:

Generally, in an organic light-emitting device, electrons are injected from a cathode and transported to a light-emitting layer, and holes are injected from an anode and transmitted to a light-emitting layer.

In one embodiment, the first electrode can be an anode and the second electrode can be a cathode.

In a preferred embodiment, the anode comprises a metal, a metal oxide or a conductive polymer. For example, the anode can have a work function in the range of about 3.5 to 5.5 eV. Illustrative examples of conductive materials include carbon, aluminum, vanadium, chromium, copper, zinc, silver, gold, other metals, and alloys thereof; zinc oxide, indium oxide, tin oxide, indium tin oxide (ITO), indium zinc oxide, and others. Similar metal oxides; and mixtures of oxides and metals, such as ZnO:Al and SnO ₂ :F. Both transparent and non-transparent materials can be used as the anode material. For structures that emit light to the anode, a transparent anode can be formed. Herein, the transparency means the extent to which light emitted from the organic material layer is permeable, and the light transmittance is not particularly limited.

For example, when the organic light-emitting device of the present specification is of a top emission type, and an anode is formed on a substrate before the organic material layer and the cathode are formed, not only a transparent material but also a non-transparent material having excellent light reflectivity can be used as the anode material. . In another embodiment, when the organic light-emitting device of the present specification is of a bottom emission type, and the anode is formed on the substrate before the organic material layer and the cathode are formed, a transparent material is required as the anode material, or the non-transparent material needs to be formed as A film that is thin enough to be transparent.

In a preferred embodiment, as the cathode, a material having a small work function is preferable as the cathode material so that electron injection can be easily performed.

For example, in the present specification, a material having a work function ranging from 2 eV to 5 eV can be used as the cathode material. The cathode may comprise a metal such as magnesium, calcium, sodium, potassium, titanium, indium, lanthanum, lithium, lanthanum, aluminum, silver, tin and lead or alloys thereof; a material having a multilayer structure such as LiF/Al or LiO ₂ / Al, etc., but is not limited to this.

The cathode can be formed using the same material as the anode. In this case, the cathode can be formed using an anode material as described above. Additionally, the cathode or anode can comprise a transparent material.

The organic light-emitting device of the present invention may be of a top emission type, a bottom emission type, or a two-side emission type depending on the material used.

In a preferred embodiment, the organic light-emitting device of the present invention comprises a hole transport layer. The hole transport layer may preferably be interposed between the hole injection layer and the light-emitting layer or between the anode and the light-emitting layer. The hole transport layer is formed of a hole transport material known to those skilled in the art. The hole transporting material is preferably a material having a high hole mobility capable of transferring holes from the anode or the hole injecting layer to the light emitting layer. Specific examples of the hole transporting material include, but are not limited to, an aromatic amine-based organic material, a conductive polymer, and a block copolymer having a joint portion and a non-joining portion.

In a preferred embodiment, the organic light-emitting device of the present invention further comprises an electron blocking layer. The electron blocking layer may preferably be disposed between the hole transport layer and the light emitting layer, or between the hole injection layer and the light emitting layer, or between the anode and the light emitting layer. The electron blocking layer is formed of an electron blocking material known to those skilled in the art, such as TCTA.

In a preferred embodiment, the organic light-emitting device of the present invention comprises an electron injecting layer. The electron injecting layer may preferably be placed between the cathode and the luminescent layer. The electron injecting layer is formed of an electron injecting material known to those skilled in the art. The electron injecting layer can be formed using, for example, an electron accepting organic compound. Here, as the electron accepting organic compound, a known optional compound can be used without particular limitation. As such an organic compound, a polycyclic compound such as p-terphenyl or tetraphenyl or a derivative thereof; a polycyclic hydrocarbon compound such as naphthalene, naphthacene, anthracene, hexabenzobenzene, fluorene, fluorene, or the like can be used. Phenylhydrazine or phenanthrene, or a derivative thereof; or a heterocyclic compound, for example, phenanthroline, phenanthroline, phenanthridine, acridine, quinoline, quinoxaline or phenazine, or a derivative thereof. It may also be formed using inorganic materials including, but not limited to, for example, magnesium, calcium, sodium, potassium, titanium, indium, lanthanum, lithium, lanthanum, aluminum, silver, tin, and lead or alloys thereof; LiF, LiO ₂ , LiCoO ₂ , NaCl, MgF ₂ , CsF, CaF ₂ , BaF ₂ , NaF, RbF, CsCl, Ru ₂ CO ₃ , YbF _{3 ,} etc.; and a material having a multilayer structure such as LiF/Al or LiO ₂ /Al.

In a preferred embodiment, the organic light emitting device of the present invention comprises an electron transport layer. The electron transport layer may preferably be disposed between the electron injecting layer and the light emitting layer, or between the cathode and the light emitting layer. The electron transport layer is formed of an electron transport material known to those skilled in the art. The electron transporting material is a material capable of easily receiving electrons from the cathode and transferring the received electrons to the light emitting layer. Materials having high electron mobility are preferred. Specific examples of the electron transporting material include, but are not limited to, an 8-hydroxyquinoline aluminum complex; a composite containing Alg ₃ ; an organic radical compound; and a hydroxyflavone metal complex; and TPBi.

In a preferred embodiment, the organic light-emitting device of the present invention further comprises a hole blocking layer. The hole blocking layer may preferably be disposed between the electron transport layer and the light emitting layer, or between the electron injecting layer and the light emitting layer, or between the cathode and the light emitting layer. The hole blocking layer is a layer that prevents the injected holes from passing through the light emitting layer to the cathode, and can be generally formed under the same conditions as the hole injection layer. Specific examples thereof include, but are not limited to, oxadiazole derivatives, triazole derivatives, phenanthroline derivatives, BCP, aluminum complexes and the like.

In a preferred embodiment, the hole blocking layer can be the same layer as the electron transport layer.

Further, according to an embodiment of the present specification, the organic light emitting device may further include a substrate. Specifically, in the organic light emitting device, the first electrode or the second electrode may be provided on the substrate. There is no particular limitation on the substrate. The substrate can be a rigid substrate, such as a glass substrate, or a flexible substrate, such as a flexible film-shaped glass substrate, a plastic substrate, or a film-shaped substrate.

The organic light-emitting device of the present invention can be produced using the same materials and methods known in the art. For example, the organic light-emitting device of the present invention can be fabricated by sequentially depositing a first electrode, one or more organic material layers, and a second electrode on a substrate. Specifically, the organic light emitting device can be produced by depositing a metal, a conductive metal oxide or an alloy thereof on a substrate using a physical vapor deposition (PVD) method (for example, sputtering or electron beam evaporation) to form an anode; An organic material layer including a hole injection layer, a hole transport layer, an electron blocking layer, a light emitting layer, and an electron transport layer is formed on the anode; a material that can be used to form a cathode is then deposited thereon. Further, the organic light-emitting device can also be fabricated by sequentially depositing a cathode material, one or more organic material layers, and an anode material on a substrate. Further, during the manufacture of the organic light-emitting device, in addition to the physical vapor deposition method, the organic light-emitting composite material of the present invention may be formed into an organic material layer using a solution coating method. As used in the specification, the term "solution coating method" means spin coating, dip coating, blade coating, inkjet printing, screen printing, spray coating, roll coating, and the like, but is not limited thereto.

Regarding the thickness of each layer, there is no particular limitation, and those skilled in the art can decide as needed and specific circumstances.

In a preferred embodiment, the thickness of the light-emitting layer and optionally the hole injection layer, the hole transport layer, the electron block layer, and the electron transport layer, the electron injection layer are each from 0.5 to 150 nm, preferably from 1 to 100 nm.

In a preferred embodiment, the luminescent layer has a thickness of from 20 to 80 nm, preferably from 30 to 50 nm.

An organic electroluminescent device comprising the organic light-emitting composite material of the present invention has an advantage in that the device is more efficient and has a longer life.

The present invention is specifically described below in conjunction with FIG. 2 and the examples, but the scope of the present invention is not limited by these preparation examples.

Example 1:

The structure of the organic electroluminescent device prepared in Example 1 is shown in FIG. 2, and the specific preparation process of the device is as follows:

The ITO anode layer 2 on the transparent glass substrate layer 1 was cleaned, ultrasonically washed with deionized water, acetone, and ethanol for 15 minutes, respectively, and then treated in a plasma cleaner for 2 minutes; the ITO glass substrate was dried and placed in a vacuum. In the cavity, the vacuum degree is less than 2*10 ^-6 Torr, and 10 nm thick HAT-CN is deposited on the ITO anode layer 2, and the layer is used as the hole injection layer 3; then 80 nm of HT1 is evaporated, and the layer is empty. The hole transport layer 4, then vapor-deposited 20 nm thick EB1, the layer serves as the electron blocking layer 5; further, vapor-deposited 30 nm light-emitting layer 6: the main material and the doping material are selected as shown in Table 1, by a film thickness meter Rate control; on the luminescent layer 6, further evaporation of ET1 and Liq having a thickness of 40 nm, the mass ratio of the two is 1:1, this layer of organic material acts as a hole blocking/electron transport layer 7; Above the electron transport layer 7, a vacuum deposition thickness of 1 nm LiF is used, which is an electron injection layer 8; on the electron injection layer 8, a cathode Al (80 nm) is vacuum-deposited, and this layer is a cathode electrode layer 9.

Examples 2 to 60:

The methods for preparing the organic electroluminescent device of Examples 2 to 60 were similar to those of Example 1, and the materials used were as shown in Table 1.

Comparative examples 1 to 18:

The methods for preparing the organic electroluminescent device of Comparative Examples 1 to 18 were similar to those of Example 1, and the materials used were as shown in Table 1.

Table 1

The structural formula of the raw materials referred to in Table 1 is as follows:

The energy level relationship of each substance is:

HI1: HOMO is 5.9 eV, LUMO is 3.0 eV, S1 is 2.79 eV, and T1 is 2.72 eV;

HI2: HOMO is 5.82 eV, LUMO is 2.8 eV, S1 is 2.82 eV, and T1 is 2.77 eV;

HI5: HOMO is 5.65 eV, LUMO is 2.84 eV, S1 is 2.76 eV, and T1 is 2.74 eV;

HI13: HOMO is 5.86eV, LUMO is 3.09eV, S1 is 2.78eV, and T1 is 2.71eV;

HI16: HOMO is 5.63 eV, LUMO is 2.82 eV, S1 is 2.79 eV, and T1 is 2.71 eV;

HII12: HOMO is 5.68 eV, LUMO is 2.66 eV, S1 is 2.89 eV, and T1 is 2.88 eV;

HII16: HOMO is 6.48eV, LUMO is 2.89eV, S1 is 3.06eV, and T1 is 2.89eV;

HII23: HOMO is 5.79 eV, LUMO is 2.52 eV, S1 is 3.05 eV, and T1 is 2.97 eV;

HII24: HOMO is 5.95 eV, LUMO is 2.85 eV, S1 is 3.02 eV, and T1 is 2.92 eV;

DP-1: HOMO is 5.41 eV, LUMO is 2.71 eV, S1 is 2.62 eV, and T1 is 2.45 eV;

DP-2: HOMO is 5.51 eV, LUMO is 2.9 eV, S1 is 2.61 eV, and T1 is 2.48 eV;

The organic electroluminescent devices prepared in Examples 1 to 60 and Comparative Examples 1 to 18 were tested for performance. The test method was as follows: the HOMO level was measured by an IPS-3 ionization energy measurement system, and the measurement steps were as follows: on ITO full glass. The sample film was vapor-deposited at 60 nm; the sample was placed in the sample stage of the IPS-3 ionization energy test system, and vacuum was applied to 5×10 ^-2 Pa; a voltage was applied to the sample, and electrons were emitted from the surface of the sample to be fed back in the form of current; The fitting obtains the ionization energy of the electron, which is the HOMO value of the sample.

The LUMO energy level is calculated by indirectly measuring the sample band gap. The measurement steps are as follows: the sample film is vapor-deposited on a blank glass at 60 nm, the absorption of the sample is measured by an ultraviolet-visible spectrophotometer, and the absorption wavelength of the sample is obtained by absorbing the cutoff edge, and then passed. E=1240/λ converts the band gap of the sample, and the LUMO value of the sample can be obtained by the difference between the HOMO level and the sample band gap.

The S1 level and the T1 level are obtained by measuring the sample normal temperature and the low temperature PL spectrum. The measurement steps are as follows: a mixed single film of the above materials is prepared in a vacuum evaporation chamber, and then the normal temperature PL spectrum and the low temperature PL spectrum of the above single film are respectively measured. The normal temperature PL spectrum is irradiated onto the surface of the sample by a 325 nm laser light source, and the emitted light is detected to obtain the peak wavelength of the excitation spectrum. The low-temperature PL spectrum was obtained by cooling the sample to 35 K, and irradiating the surface of the sample with a laser light source of 325 nm to detect the emitted light to obtain the peak wavelength of the excitation spectrum. Then, S1 and T1 are converted by the formula E=1240/λ, and the value of ΔEst is obtained.

The results obtained by the above method tests are shown in Table 2.

Table 2

As can be seen from the data in the table, in Examples 1 to 60, compared with Comparative Examples 1 to 18, a separate thermally activated delayed fluorescent material was used as a host material, and a conventional phosphorescent material and a thermally activated delayed fluorescent material were used as a guest material. Compared with the dual heat-activated delayed fluorescent material, the prepared device has the highest device efficiency, and under high brightness, the efficiency roll-off is more serious and the device stability is poor. It can be seen from the attenuation ratio data that in the examples, the TADF double body was used as the host material, the efficiency attenuation ratio was substantially less than 15% at 1000 cd/m ² and 5000 cd/m ² , and the TADF was used as the host material alone in the comparative example. At a luminance of 1000 cd/m ² and 5000 cd/m ² , the attenuation ratios are all large, both approaching or exceeding 10%. The main reason for this is because the triplet excitons are quenched by the easy aggregation of the fluorescent material with a single thermal activation. At the same time, at a higher current density, there is only a single energy transfer channel between the host and the guest, which tends to result in higher exciton concentration and severe exciton quenching, which seriously affects the efficiency and stability of the device under high brightness.

By using two kinds of thermally activated delayed fluorescent materials, the first organic compound and the second organic compound are mixed to form a host material, and the first organic compound can transfer energy from the triplet state to the singlet state through the anti-systemic enthalpy, and then pass through the singlet state through the Forster Energy transfer is transferred to the guest material. At the same time, the second organic compound excitons can also transition from the triplet state to the singlet state through the inter-system enthalpy, and then pass through the Forster energy transfer to the first organic compound and the guest material to achieve multi-channel energy transfer. The second compound in the present invention is a compound having a wider band gap, and the second organic compound having a wide band gap can dilute the first organic compound, suppressing the Dexter energy transfer between the first organic compound and the guest material, and reducing the first organic compound due to The quenching effect brought about by agglomeration. At the same time, the T1 energy level of the second organic compound in the invention is higher than the S1 energy level of the first organic compound, which can effectively prevent energy return between the first organic compound and the second organic compound, improve energy utilization, and further improve The efficiency and stability of the device.

To further verify the stability under a high luminance of the device, the present invention was tested at an initial luminance of 5000cd / m ^2, the voltage change over time of the device, the device of Comparative Example 1, Example 1, Comparative Example 5, Example 15 Comparative example 7,

Example 37, Comparative Example 14, and Example 50 were tested. The results are shown in Table 3 and Figure 3.

table 3

Time (h)	0	50	100	150	200	250	300
Voltage change	△V	△V	△V	△V	△V	△V	△V
Comparative example 1	0	0.03	0.06	0.15	0.24	0.36	0.66
Example 1	0	0.03	0.05	0.08	0.10	0.11	0.11
Comparative example 5	0	0.02	0.06	0.12	0.36	0.56	0.71
Example 15	0	0.03	0.04	0.06	0.06	0.08	0.10
Comparative example 7	0	0.02	0.05	0.14	0.33	0.54	0.75
Example 37	0	0.02	0.02	0.03	0.04	0.06	0.12
Comparative example 14	0	0.02	0.06	0.13	0.25	0.46	0.86
Example 50	0	0.03	0.05	0.08	0.08	0.12	0.13

It can be found from the above Table 3 and FIG. 3 that the device applied in the present invention changes the device voltage at about 300 volts at 5000 cd/m ² over time, and the device in the comparative example is in the comparative example. When the voltage is over 300 hours, the variation exceeds 0.6V or even higher, indicating that the stability of the device is better at higher brightness.

Further, in order to verify the stability under the change of the ambient temperature of the device, in the present invention, when the luminance was 100 cd/A, Comparative Example 3, Example 13, Example 15, Example 17, Comparative Example 8, and Example 37 were tested. The variation of the EQE of the device at different temperatures in Example 39 and Example 43 is shown in Table 4 and Figure 4:

Table 4

Category (h) / temperature °C	-10	10	20	30	40	50	60	70	80
Comparative example 3	10.2%	10.5%	10.5%	10.3%	9.2%	8.3%	7.6%	6.3%	5.4%
Example 13	18.2%	18.2%	18.2%	18.2%	18.0%	17.8%	17.4%	16.8%	16.8%
Example 15	19.6%	19.8%	19.8%	19.8%	19.65	19.4%	19.4%	19.3%	19.3%
Example 17	18.0%	18.1%	18.0%	18.1%	18.0%	18.0%	17.8%	17.8%	17.6%
Comparative example 8	9.2%	9.2%	9.0%	8.8%	8.4%	7.8%	7.2%	6.4%	6.0%
Example 37	17.6%	17.6%	17.6%	17.6%	17.4%	17.4%	17.0%	17.2%	17.2%
Example 39	17.6%	17.8%	17.6%	17.4%	17.4%	17.2%	17.0%	17.0%	16.8%
Example 43	17.8%	17.8%	17.8%	17.8%	17.6%	17.2%	17.2%	17.2%	17.0%

It can be found from the above Table 4 and FIG. 4 that the device to which the present invention is applied has a small change in device EQE at different temperatures compared with the conventional device, and at a relatively high temperature, the device EQE has almost no The change indicates that the device with the structure of the present application has better device stability.

Claims (10)

1. An organic electroluminescent device comprising a light-emitting layer comprising a host material and a guest material, the host material comprising at least one first organic compound and at least one second organic compound, the guest material being phosphorescent a compound or a fluorescent compound characterized in that

   The difference between the singlet level and the triplet level of the first organic compound is not more than 0.2 eV, preferably not more than 0.15 eV, more preferably not more than 0.1 eV;

   The difference between the singlet level and the triplet level of the second organic compound is not more than 0.2 eV, preferably not more than 0.15 eV, more preferably not more than 0.1 eV.
2. The organic electroluminescent device according to claim 1, wherein the first organic compound has a singlet energy level smaller than a triplet energy level of the second organic compound, and the difference is not less than 0.1 eV, preferably not less than 0.15 eV. More preferably not less than 0.2 eV;

   The difference between the HOMO level and the LUMO level of the second organic compound is not less than 2.8 eV, preferably not less than 3.0 eV, more preferably not less than 3.2 eV.
3. The organic electroluminescent device according to claim 1, wherein the first organic compound and the second organic compound are each independently a compound having a D-A structure or a D-Π-A structure.
4. The organic electroluminescent device according to claim 1, 2 or 3, wherein the first organic compound is one selected from the group consisting of:

   

   

   
5. The organic electroluminescent device according to claim 1, 2 or 3, wherein the second organic compound is one selected from the group consisting of:

   

   
6. The organic electroluminescent device according to claim 1, wherein the weight ratio of the first organic compound to the second organic compound is from 9:1 to 1:9, preferably from 7:3 to 3:7, more preferably : 4 to 4:6.
7. The organic electroluminescent device according to claim 1, wherein the fluorescent compound comprises a thermally activated delayed fluorescent material, wherein a difference between a singlet level and a triplet level of the thermally activated delayed fluorescent material is not more than 0.2 eV. Preferably, it is not more than 0.15 eV, more preferably not more than 0.1 eV.
8. The organic electroluminescent device according to claim 1 or 6, wherein the singlet state level of the thermally activated delayed fluorescent material is smaller than the triplet level of the first organic compound, and the difference is not less than 0.1 eV. It is preferably not less than 0.15 eV.
9. The organic electroluminescent device according to claim 1, wherein the weight of the guest material relative to the weight of the host material is from 0.5 to 20% by weight, preferably from 1 to 15% by weight, more preferably from 3 to 12% by weight, based on the weight of the host material .
10. The organic electroluminescent device according to claim 1, further comprising a hole transporting region and an electron transporting region, wherein the hole transporting region comprises a hole injecting layer, a hole transporting layer, and an electron blocking layer a combination of one or more; the electron transporting region comprising a combination of one or more of an electron injecting layer, an electron transporting layer, and a hole blocking layer.

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