CN110335954B - Efficient and stable white light organic electroluminescent device and preparation method thereof - Google Patents

Abstract

An efficient and stable white light organic electroluminescence device and a preparation method thereof belong to the technical field of organic semiconductor light-emitting devices. From bottom to top are the transparent substrate, anode, hole injection layer, hole transport layer, exciton blocking layer, light-emitting layer, electron transport layer, electron injection layer and cathode, wherein the light-emitting layer is a three-layer structure, from bottom to top The sequence is a yellow phosphorescent layer, a spacer layer and an undoped blue fluorescent layer; the yellow phosphorescent layer is composed of a green thermally activated delayed fluorescent host material doped with a yellow phosphorescent guest material. In the present invention, a thermally activated delayed fluorescent material is used as a parent to sensitize a yellow phosphorescent guest. The material has excellent carrier transport capability and can be used as a host for bipolar transport; and the triplet energy level is greater than that of the yellow phosphorescent guest material. level, which can prevent the return of energy from the object to the subject. Yellow light and blue light emission complement each other to form white light, thereby improving exciton utilization and improving device performance.

Description

An efficient and stable white light organic electroluminescent device and preparation method thereof

technical field

The invention belongs to the technical field of organic semiconductor light-emitting devices, in particular to an efficient and stable white light organic electroluminescent device and a preparation method thereof.

Background technique

White light organic electroluminescent diodes (OLEDs) are flat light sources with the advantages of flexibility, bendability, wide viewing angle, energy saving, and fast response speed. They can complement the shortcomings of inorganic OLED lighting technology and are the main force of next-generation lighting technology. In addition, in the display field, WOLED can be used as a backlight source for liquid crystal display technology, or as a sub-pixel to prepare high-standard RGBW-TV, that is, red/green/blue/white pixel TV.

According to the different types of light-emitting materials in the light-emitting layer, OLEDs can be divided into full-fluorescence, full-phosphorescence, and fluorescence/phosphorescence hybrid WOLEDs. For all-fluorescent WOLEDs, conventional fluorescent materials are used. Although they have a long life, the efficiency is generally low, less than 20lm/W. All-phosphorescent WOLEDs can utilize both singlet and triplet excitons simultaneously, resulting in high device efficiency. However, it is limited to the scarcity of heavy metal resources and the poor stability of blue phosphorescent materials, which is not conducive to commercial development. Therefore, the hybrid WOLED produced by mixing blue fluorescent material and complementary color phosphorescent materials such as green, yellow, and red can effectively combine the advantages of all-fluorescent and all-phosphorescent WOLEDs with the help of a reasonable device structure and material system. , is a very promising high-efficiency and stable white light device for commercial products.

In hybrid WOLEDs, singlet excitons and triplet excitons can be mutually quenched, which greatly reduces the efficiency of the device. With the help of designing appropriate device structures and suitable material systems, singlet excitons and triplet excitons can be adjusted, so that singlet excitons are utilized by blue fluorescent materials to generate blue light, and triplet excitons are utilized by phosphorescent materials. Each component was able to exhibit its own luminescence, and the complementary polychromatic spectra were performed to obtain white light emission. At present, although there are many reports of hybrid WOLED, the stability of the device is not good and the efficiency is low. In addition, the structures of these devices are generally complex, the fabrication process is very difficult, and the repeatability is poor, which is not conducive to commercial applications.

Therefore, developing a white light WOLED with simple process, low cost, high efficiency and stability is of great significance for promoting the commercialization of white light OLED.

SUMMARY OF THE INVENTION

In order to solve the above problems, the purpose of the present invention is to provide a high-efficiency and stable white light organic electroluminescent device and a preparation method thereof. As the host to sensitize the phosphorescent guest material, the singlet excitons are utilized by the blue fluorescent material to generate blue light, and the triplet excitons are utilized by the phosphorescent material, thereby improving the exciton utilization rate and improving the device performance. A white light organic electroluminescence device with simple device structure and fabrication process, low cost, high efficiency and stability is prepared, which is beneficial to commercial application.

The high-efficiency and stable white light organic electroluminescent device described in the present invention includes, from bottom to top, a transparent substrate, an anode, a hole injection layer, a hole transport layer, an exciton blocking layer, a light-emitting layer, an electron transport layer, and an electron transport layer. The injection layer and the cathode, wherein the light-emitting layer has a three-layer structure, and from bottom to top are a yellow phosphorescent layer, a spacer layer and an undoped blue fluorescent layer; the yellow phosphorescent layer is doped with a green thermally activated delayed fluorescent host material Yellow phosphorescent guest material.

In the above white light organic electroluminescence device, the thermally activated delayed fluorescence host material has a small energy level difference between the singlet state and the triplet state, and the reverse intersystem crossing of the triplet excitons to the singlet state can occur at room temperature, reducing the triplet state. The concentration of state excitons slows down the TTA process and reduces the efficiency roll-off. In this white light device, singlet excitons are utilized by blue fluorescent materials to generate blue light, triplet excitons are utilized by yellow phosphorescent materials to generate yellow light, and yellow light and blue light emission complement each other to form white light, thereby realizing white light emission.

Further, the thickness of the yellow phosphorescent layer is 0.1-30 nm, the thickness of the spacer layer is 1-10 nm, the thickness of the undoped blue fluorescent material layer is 0.1-40 nm, and the thickness of the remaining layers is ≤40 nm.

Further, the non-doped blue fluorescent material is N,N-diphenyl-4-(10-(4-(1,2,2-triphenylene)phenyl)anthracene-9-yl) Aniline (TPAATPE, CN109608403A) is an excellent aggregation-induced luminescent material with high luminous efficiency and good stability.

Further, the spacer layer material is composed of hole-type 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline] (TAPC) and electron-type bis(2-( At least one of 2-hydroxyphenyl)-pyridine) beryllium (Bepp ₂ ). The triplet energy level of the spacer layer material is larger than that of the green thermally activated delayed fluorescence host material and the yellow phosphorescent guest material, which can better prevent the energy transfer between the fluorescent material and the phosphorescent material, and effectively utilize the triplet state excitons generated by the device. singlet excitons, thus ensuring high device efficiency.

Further, the spacer layer material can be hole-type TAPC or electron-type Bepp ₂ , or a combination of the two in any ratio; the present invention has fully tried the mass dosage of TAPC, Bepp ₂ and TAPC: Bepp ₂ alone The ratio is 3:7, 5:5, 7:3 the effect of different composition of the spacer layer on the device effect.

Further, the green thermally activated delayed fluorescence host material is 10-(4-(diphenylboron)phenyl)-10H-phenothiazine (PTZMes ₂ B, Front.Chem.2019,7,373, which is the same as the traditional parent Compared with other materials, thermally activated delayed fluorescent materials have a small energy level difference between the singlet state and the triplet state, and the inverse intersystem crossing of triplet excitons to singlet states can occur at room temperature, reducing the concentration of triplet excitons and slowing down The TTA process reduces the efficiency roll-off. In addition, the material has excellent carrier transport capability and can be used as a host for ambipolar transport to sensitize phosphorescent materials; and the triplet energy level is larger than that of red/yellow phosphorescent guest materials. The state energy level, which can prevent the return of energy from the object to the host.

Further, the yellow phosphorescent guest material is (acetylacetone)bis[2-(thieno[3,2-c]pyridin-4-yl)phenyl]iridium(III)(PO-01), which has low The triplet level can better capture the triplet excitons in the device, thereby improving the device efficiency; the light-emitting layer is prepared by the host-guest doping technology. The excitons generated by the composite of the delayed fluorescent matrix material are utilized by the yellow phosphorescent material to generate yellow light, and the yellow light and the blue light emission complement each other to form white light, thereby realizing dual-color white light emission.

Further, the doping amount of the yellow phosphorescent guest material is 0.1-30% of the mass sum of the host material and the guest material, preferably 1-20%.

Further, the substrate is transparent conductive glass, the anode is indium tin oxide (ITO), and the hole injection layer is 2,3,6,7,10,11-hexacyano-1,4,5, 8,9,12-hexaazatriphenylene (HATCN), the hole transport layer is TAPC, and the exciton blocking layer is tris(4-carbazole-9-phenyl)amine (TCTA).

Further, the cathode is an Al thin film, the electron injection layer is lithium fluoride (LiF), and the electron transport layer is 3,3",5,5"-4(3-pyridyl)-1,1':3 ',1"-terphenyl (BmPyPB).

Compared with the prior art, the beneficial effects of the present invention are:

In the high-efficiency and stable white light organic electroluminescent device of the present invention, an aggregation-induced luminescent material with excellent performance is selected as the blue light layer, and a high-efficiency thermally activated delayed fluorescent material is used as the main body, which can simultaneously capture singlet and triplet excitons to generate Hybridizing the phosphorescent guest material enables singlet excitons to be utilized by blue fluorescent materials to generate blue light, and triplet excitons to be utilized by phosphorescent materials, thereby improving exciton utilization and improving device performance. A white light organic electroluminescence device with simple device structure and fabrication process, low cost, high efficiency and stability is prepared, which is beneficial to commercial application.

In addition, the structure and material of the white light organic electroluminescence device are also optimized, and a white light organic electroluminescence device with simple device structure and fabrication process, low cost, high efficiency and stability is prepared.

The raw materials mentioned in the present invention are all commercially available or prepared according to known documents or patents, and the molecular structural formula is as follows:

Description of drawings

1 is a schematic structural diagram of the white light organic electroluminescent devices of Examples 1 to 5;

Fig. 2 is the performance curve diagram of the white light organic electroluminescent device of embodiment 1;

Fig. 3 is the performance curve diagram of the white light organic electroluminescent device of embodiment 1 under different brightness;

Fig. 4 is the performance curve diagram of the white light organic electroluminescent device of embodiment 2;

Fig. 5 is the performance curve diagram of the white light organic electroluminescent device of embodiment 3;

Fig. 6 is the performance curve diagram of the yellow-white light organic electroluminescent device of embodiment 4;

7 is a performance curve diagram of the yellow light organic electroluminescent device of Example 5;

Detailed ways

The present invention will be further described below with reference to the accompanying drawings, so as to facilitate the understanding of the present invention by those skilled in the art. Obviously, the described embodiments are only a part of this experiment, not all of the embodiments. Those skilled in the art, based on the above-mentioned content of the invention, make non-essential modifications, equivalent replacements and improvements to the present invention, etc., should be Included in the protection scope of the present invention. The raw materials mentioned below are all commercially available or prepared according to known documents or patents, and the unmentioned process steps and preparation methods are those well known to those skilled in the art.

Example 1

A white light organic electroluminescence device W1, the structure of the device W1 is: ITO/HATCN(5nm)/TAPC(35nm)/TCTA(5nm)/PTZMes ₂ B:PO-01(12nm, 10%)/TAPC: Bepp ₂ (4 nm, 5:5)/TPAATPE (8 nm)/BmPyPB (40 nm)/LiF (1 nm)/Al.

First, the mass doping concentration ratio of TAPC:Bepp ₂ in the spacer layer is selected to be 5:5, that is, the hole-type TAPC and the electron-type Bepp ₂ in the spacer layer are each 50%. As shown in Figure 1, the structure of the device W1 is stacked from bottom to top by the following functional layers: substrate, anode, hole injection layer, hole transport layer, exciton blocking layer, yellow phosphorescent layer, spacer layer, blue Color phosphor layer, electron transport layer, electron injection layer and cathode. The preparation method is as follows:

ITO sheets were prepared by sputtering on the base conductive glass as the anode; the ITO conductive glass was successively cleaned with deionized water, isopropanol, acetone, toluene, acetone, and isopropanol in an ultrasonic bath for 20 minutes, and placed in an oven. Dry in medium. After 40 minutes of surface treatment on the ITO glass in a UV-ozone cleaning machine, it was moved into a vacuum evaporation device; on the anode ITO conductive glass, a hole injection layer HATCN was vacuum-evaporated with a thickness of 5 nm; on the HATCN, vacuum evaporation A hole transport layer TAPC was deposited with a thickness of 35nm; on TAPC, an exciton blocking layer TCTA was deposited with a thickness of 5nm; on TCTA, a luminescent layer was deposited: the luminescent layer was a yellow phosphorescent layer PTZMes ₂ B: PO-01 (12nm, PTZMes ₂ B is a host fluorescent material, PO-01 is a guest phosphorescent material, and the mass doping concentration of the guest material is 10%), spacer layer TAPC: Bepp ₂ (4nm, preliminary selection TAPC: The mass doping concentration ratio of Bepp ₂ is 5:5), the undoped blue fluorescent layer TPAATPE (8nm); on the light-emitting layer, the electron transport layer BmPyPB is vapor-deposited with a thickness of 40 nm; on the BmPyPB, vapor-deposited The electron injection layer LiF has a thickness of 1 nm; on the LiF, the cathode Al is vapor-deposited with a thickness of 100 nm.

The performance of the device W1 prepared above is tested, and FIG. 2 is a performance diagram of the white light organic electroluminescence device W1 of this embodiment. It can be seen from the figure that when the mass ratio of the spacer layer TAPC:Bepp ₂ is 5:5, the efficiency of the device is very high, the maximum external quantum efficiency (EQE) is as high as 25.2%, and the CIE coordinates are (0.44, 0.44) , which is very efficient compared to the white light electroluminescent devices reported so far. Moreover, the stability of the device is very good, when the brightness is increased to 1000cd/ ^m2 , the efficiency of the device only drops by 10%. In addition, as shown in Figure 3, when the brightness increases from 384cd/m ² to 5211cd/m ² , the CIE coordinates only change from (0.44, 0.44) to (0.43, 0.43), indicating that the device has high stability.

Example 2

Keeping the device structure and preparation materials of the white light device W1 unchanged, and changing the mass ratio of the spacer layer TAPC:Bepp ₂ , the white light device W2 was prepared. The structure of the device is: ITO/HATCN(5nm)/TAPC(35nm)/TCTA( 5nm)/ _PTZMes2B :PO-01(12nm, 10%)/TAPC: _Bepp2 (4nm, 7:3)/TPAATPE(8nm)/BmPyPB(40nm)/LiF(1nm)/Al.

FIG. 4 is a performance diagram of the white light organic electroluminescent device W2 of this embodiment. Compared with device W1, this device ensures that the mass doping concentration of PTZMes ₂ B+PO-01 occupied by PO-01 remains unchanged at 10%, which reduces the mass of the electron transport layer Bepp _2. When the mass ratio of TAPC: Bepp ₂ When the ratio is 7:3, the electron migration ability of the spacer layer decreases, so that the recombination region of excitons moves from the yellow light layer to the blue light layer, quenching the triplet excitons, and the efficiency of the device decreases, and the maximum EQE reaches 24.1% , the CIE coordinates are (0.43, 0.43).

Example 3

Keeping the device structure and preparation materials of the white light device W1 unchanged, and continuing to change the mass doping concentration ratio of the spacer layer TAPC:Bepp ₂ , the white light device W3 was prepared. The structure of the device is: ITO/HATCN(5nm)/TAPC(35nm) )/TCTA(5nm)/ _PTZMes2B :PO-01(12nm,10%)/TAPC: _Bepp2 (4nm,1:0)/TPAATPE(8nm)/BmPyPB(40nm)/LiF(1nm)/Al.

FIG. 5 is a performance diagram of the white light organic electroluminescent device W3 of this embodiment. Compared with device W1, this device ensures that the mass doping concentration of PTZMes ₂ B+PO-01 occupied by PO-01 remains unchanged at 10%, which continues to reduce the mass of the electron transport layer Bepp _2. When TAPC: the mass of Bepp ₂ When the ratio is 1:0, that is, the spacer layer is all composed of hole-type TAPC. The electron migration ability of the spacer layer is very weak, so that the recombination area of the excitons continues to move from the yellow light layer to the blue light layer, which seriously quenches the triplet excitons and reduces the efficiency of the device. The maximum EQE is only 17.1%, and the CIE The coordinates are (0.41, 0.41). However, under the illumination-related luminance of 1000cd m ^-2 , the EQE of the device remains at 16.8% with almost no attenuation, indicating that the device still has high stability.

Example 4

Keeping the device structure and preparation materials of the white light device W1 unchanged, and continuing to change the mass doping concentration ratio of the spacer layer TAPC:Bepp ₂ , the yellow-white light device W4 was prepared. The structure of the device is: ITO/HATCN(5nm)/TAPC (35nm)/TCTA(5nm)/PTZMes ₂ B:PO-01(12nm,10%)/TAPC:Bepp ₂ (4nm,3:7)/TPAATPE(8nm)/BmPyPB(40nm)/LiF(1nm)/ Al.

As shown in Fig. 6, when the mass doping concentration ratio of TAPC:Bepp ₂ is 3:7, due to the reduction of TAPC, the hole transport ability of the spacer layer is weakened, making it easier for electrons to reach the yellow light layer, and excitons can be realized. The full utilization of the device improves the efficiency of the device, and the maximum EQE reaches 25.8%, but the CIE coordinates of the device are at (0.48, 0.47), which is already in the yellow-white light region.

Example 5

Keeping the device structure and preparation materials of the white light device W1 unchanged, and continuing to change the mass ratio of the spacer layer TAPC:Bepp ₂ , the yellow light device W5 was prepared. The structure of the device is: ITO/HATCN(5nm)/TAPC(35nm)/ TCTA(5nm)/ _PTZMes2B :PO-01(12nm,10%)/TAPC: _Bepp2 (4nm,0:1)/TPAATPE(8nm)/BmPyPB(40nm)/LiF(1nm)/Al.

As shown in Figure 7, since the spacer layer is full of Bepp ₂ , all triplet excitons reach the yellow light layer, resulting in almost no blue light component. The CIE coordinates are (0.49, 0.49), which has deviated from the white light region, but the device The efficiency reached the highest with an EQE of 27.1%.

For the devices prepared in Examples 4 and 5, almost only yellow light is produced, and no blue light is produced, so the devices do not belong to white light devices. In conclusion, when TAPC accounts for 50-100% of the mass sum of TAPC and Bepp ₂ , the device of the present invention can be prepared.

Detailed electroluminescence performance data for the devices of all examples of the present invention are listed in Table 1.

Table 1: Electroluminescence performance data of 5 devices W1～W6

The above-mentioned embodiments are preferred embodiments of the present invention, and those skilled in the art, without departing from the technical principles of the present invention, make non-essential modifications, equivalent replacements and improvements, etc., should be included in the present invention. within the scope of protection.

Claims (2)

1. an efficient and stable white light organic electroluminescent device is characterized in that: from bottom to top, it is a transparent substrate, an anode, a hole injection layer, a hole transport layer, an exciton blocking layer, a light-emitting layer, an electron transport layer, Electron injection layer and cathode, wherein, the light-emitting layer has a three-layer structure, and from bottom to top are a yellow phosphorescent layer, a spacer layer and an undoped blue fluorescent layer; It is composed of phosphorescent guest material, and the thickness of the yellow phosphorescent layer is 0.1-30 nm; the undoped blue fluorescent material is N,N-diphenyl-4-(10-(4-(1,2,2-triphenylene) Phenyl)anthracene-9-yl)aniline, the thickness of the undoped blue fluorescent layer is 0.1-40nm; the material of the spacer layer is made of hole-type 4,4'-cyclohexylbis[N,N-bis(4- Methylphenyl)aniline] and electronic form of bis(2-(2-hydroxyphenyl)-pyridine) beryllium, 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl) Aniline] accounts for 50-100% of the mass sum of 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline] and bis(2-(2-hydroxyphenyl)-pyridine) beryllium , the thickness of the spacer layer is 1-10 nm; the green thermally activated delayed fluorescence host material is 10-(4-(diphenylboron)phenyl)-10H-phenothiazine, and the yellow phosphorescent guest material is (acetylacetone)di[ 2-(thieno[3,2-c]pyridin-4-yl)phenyl]iridium, the doping amount of the yellow phosphorescent guest material is 0.1-30% of the mass sum of the green thermally activated delayed fluorescence host material and the yellow phosphorescent guest material . 2. A kind of high-efficiency and stable white light organic electroluminescence device as claimed in claim 1, it is characterized in that: the doping amount of yellow phosphorescent guest material is 1/1 of the mass sum of green thermally activated delayed fluorescence host material and yellow phosphorescent guest material. ~20%.

Images