Fluorescence/phosphorescence mixed white light OLEDs based on AIE material and preparation method thereof
Technical Field
The invention belongs to the field of organic light emitting diodes, and particularly relates to fluorescence/phosphorescence mixed white light OLEDs based on an AIE material and a preparation method thereof.
Background
Electroluminescence is a phenomenon in which substances such as semiconductors emit light under the action of an electric field, and light emitting diodes developed using the electroluminescence phenomenon have been widely used in daily lighting systems and are an indispensable part of human production and life. In contrast, Organic Light-Emitting Diodes (OLEDs) made of Organic semiconductors are considered as a new generation of illumination Light source due to their advantages of being Light, thin, flexible, surface-Emitting, free of glare and blue Light hazards, and close to sunlight, and have a wide application prospect in the fields of home illumination, medical illumination, automobile illumination, museum illumination, and the like.
The color rendering index represents the color rendering capability of a light source on an object, and is an important index for measuring the illumination quality of an illumination device. In order to achieve a high color rendering index, a three-primary-color light emitting layer design is usually adopted, and a high-efficiency, low-efficiency roll-off and high-color rendering index white light OLEDs are prepared by designing a blue light emitting unit, a green light emitting unit and a red light emitting unit.
The materials currently used for preparing white light OLEDs mainly comprise three-generation material systems of fluorescence, phosphorescence and thermal activation delayed fluorescence. However, these materials all face serious aggregation to cause fluorescence quenching problem, which results in that their fluorescence quantum efficiency is low in the non-doped state, and the prepared device has serious exciton quenching phenomenon, often shows higher efficiency roll-off, and the disadvantage is more obvious especially in the aspect of short wavelength blue light materials. In addition, the conventional white light OLEDs generally require a complex doping process, which increases the process difficulty and greatly increases the manufacturing cost.
Disclosure of Invention
In view of the above disadvantages and shortcomings of the prior art, it is a primary object of the present invention to provide a fluorescent/phosphorescent hybrid white light OLEDs based on AIE materials. The OLEDs with the structure are mainly characterized in that non-doped Aggregation Induced Emission (AIE) materials are adopted in blue light and green light emitting layers, and a red light phosphorescent molecule doped hole transport main body is combined to serve as a red light emitting layer, so that the fluorescence/phosphorescence mixed white light OLEDs with high efficiency, low efficiency roll-off, high color rendering index and good spectral stability are successfully prepared, the device structure is greatly simplified, and the OLED has important application value.
The invention also aims to provide a preparation method of the fluorescence/phosphorescence mixed type white light OLEDs based on the AIE material.
The purpose of the invention is realized by the following technical scheme:
the light emitting layer of the OLEDs is composed of a phosphorescent guest doped host red light emitting layer, an undoped AIE green light emitting layer, a spacing layer and an undoped AIE blue light emitting layer in sequence from an anode to a cathode.
Further, the AIE-based fluorescence/phosphorescence hybrid white OLEDs sequentially include an ITO anode, a hole injection layer, a hole transport layer, an electron blocking layer, a light emitting layer, an electron transport layer, an electron injection layer, and a metal cathode.
Further, the thickness of the red light emitting layer is 5-8 nm, and the phosphorescent guest material in the red light emitting layer is Ir (dmdppr-mp)2(divm) (ACS Photonics 2019,6,767-778), the host material is TCTA (4,4' -tris (carbazole-9-yl) triphenylamine), and the mass concentration of the phosphorescent guest material doped in the host material is 2-5%.
Furthermore, the thickness of the undoped AIE green light emitting layer is 6-10 nm, the adopted AIE green light material is CP-BP-PXZ (Angew. chem. Int. Ed.2017,56, 12971-12976), and the molecular structure is shown as the following formula:
furthermore, the thickness of the spacing layer is 2-3 nm, and the material of the spacing layer is TCTA.
Further, the thickness of the non-doped AIE blue light emitting layer is 5-20 nm, the adopted AIE blue light material is TPB-AC (radial distance, 2017,196, 245-:
further, the hole injection layer is made of organic material or inorganic material, the organic material can be HAT-CN (2,3,6,7,10, 11-hexacyano-1, 4,5,8,9, 2-azabenzophenanthrene) or CuPc (copper phthalocyanine), and the inorganic material can be MoO3(molybdenum oxide) or ReO3(rhenium oxide), the thickness of the hole injection layer is preferably 5 to 10 nm.
Further, TAPC (4,4' -cyclohexyl bis [ N, N-bis (4-methylphenyl) aniline ]) can be adopted as the hole transport layer, and the thickness is preferably 40-50 nm; the electron blocking layer can adopt TCTA (4,4' -tris (carbazole-9-yl) triphenylamine), and the thickness is preferably 5-10 nm.
Furthermore, TmPyPB (3,3'- [5' - [3- (3-pyridyl) phenyl ] [1,1':3',1 '-terphenyl ] -3, 3' -diyl ] bipyridine) can be adopted as the electron transport layer, and the thickness is preferably 40-50 nm.
Further, the electron injection layer may employ LiF (lithium fluoride), and a thickness of 1nm is preferable.
Furthermore, the metal cathode can adopt an aluminum cathode, and the thickness is preferably 100-150 nm.
The preparation method of the fluorescence/phosphorescence mixed white light OLEDs based on the AIE material comprises the following preparation steps:
and (3) sequentially evaporating a hole injection layer, a hole transport layer, an electron blocking layer, a light emitting layer, an electron transport layer, an electron injection layer and a metal cathode after the ITO anode is pretreated to obtain the fluorescence/phosphorescence mixed white light OLEDs based on the AIE material.
The fluorescence/phosphorescence mixed white light OLEDs of the AIE material of the invention have the following advantages and beneficial effects:
(1) the invention adopts the undoped AIE blue light material as the blue light emitting layer and the undoped AIE green light material as the green light emitting layer, thereby greatly simplifying the structure and the process of the device. Meanwhile, by introducing the spacing layer between the blue light emitting layer and the green light emitting layer, exciton quenching is eliminated, the efficiency is improved, and the spectral stability of the device is also obviously improved, so that the prepared white light OLEDs simultaneously have the advantages of high efficiency, low efficiency roll-off, high color rendering index and good spectral stability;
(2) the invention can realize white light emission with different qualities by simply adjusting the thickness of each light-emitting layer and the spacing layer, and has wide application value.
Drawings
FIG. 1 is a schematic structural diagram of a fluorescence/phosphorescence mixed white light OLEDs based on an aggregation-induced emission material in an embodiment of the present invention.
FIG. 2 is a graph showing the electroluminescence spectra of the fluorescence/phosphorescence mixed white OLEDs device W1 based on aggregation inducing luminescent material in example 1 of the present invention under different brightness.
FIG. 3 is a graph showing the electroluminescence spectra of the fluorescence/phosphorescence mixed white OLEDs device W2 based on aggregation inducing luminescent material in example 2 of the present invention under different brightness.
FIG. 4 is a graph showing current density-luminance-voltage characteristics of fluorescence/phosphorescence hybrid white OLEDs based on aggregation inducing luminescent materials in examples 1 and 2 of the present invention.
FIG. 5 is a graph showing power efficiency-external quantum efficiency-luminance characteristics of fluorescence/phosphorescence hybrid type white OLEDs based on aggregation inducing luminescent materials in examples 1 and 2 of the present invention.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.
The schematic structure of the OLEDs in the following examples is shown in fig. 1. Wherein 1 represents an ITO anode, 2 represents a hole injection layer, 3 represents a hole transport layer, 4 represents an electron blocking layer, 5 represents a light emitting layer, 6 represents an electron transport layer, 7 represents an electron injection layer, 8 represents a metal cathode, 9 represents a red light emitting layer, 10 represents a green light emitting layer, 11 represents a spacer layer, and 12 represents a blue light emitting layer.
Example 1
In this example, the fluorescence/phosphorescence mixed white light OLEDs (device W1) based on aggregation induced emission material uses ITO as anode, HAT-CN as hole injection layer, TAPC as hole transport layer, and TCTA as electronA barrier layer made of Ir (dmdppr-mp)2(divm) guest-doped TCTA host is a red light emitting layer (the guest doping concentration is 3 mass%), CP-BP-PXZ is a green light emitting layer, TCTA is a spacer layer, TPB-AC is a blue light emitting layer, TmPyPB is an electron transport layer, LiF is an electron injection layer, and metal Al is a cathode. The device structure is as follows:
device W1 ITO/HAT-CN (5nm)/TAPC (50nm)/TCTA (5nm)/TCTA 3 wt% Ir (dmppr-mp)2(divm)(8nm)/CP-BP-PXZ(6nm)/TCTA(2nm)/TPB-AC(10nm)/TmPyPB(40nm)/LiF(1nm)/Al(120nm)。
The preparation steps of the device W1 are as follows:
(1) ultrasonically cleaning the ITO glass by using a cleaning agent for 60 minutes, then ultrasonically cleaning the ITO glass by using deionized water for 20 minutes, blow-drying by using nitrogen, then drying the ITO glass in an oven at 120 ℃ for 30 minutes, and finally carrying out plasma treatment on the ITO surface for 4 minutes.
(2) Transferring the pretreated ITO glass into a vacuum cavity of a vacuum evaporation instrument, and vacuumizing the instrument by adopting an oil pump and a molecular pump until the vacuum degree reaches 5 multiplied by 10-4And when the power is less than pa, starting the sample table to rotate at the rotating speed of 10 revolutions per minute, and then sequentially coating films on the ITO glass according to the structure of the device W1 to prepare each functional layer.
(3) Firstly, depositing a hole injection layer HAT-CN on an ITO substrate by a vacuum evaporation mode, and controlling the deposition speed to be
The thickness was 5 nm.
(4) Then, a hole transport layer TAPC is deposited on the hole injection layer, with the deposition rate controlled at
The thickness was 50 nm.
(5) Then, an electron blocking layer TCTA is deposited on the hole transport layer at a controlled deposition rate
The thickness was 5 nm.
(6) Then, a phosphorescent guest Ir (dmdppr-mp) was deposited on the electron blocking layer
2The red light emitting layer of (divm) doped TCTA main body is controlled in deposition speed
The thickness is 8nm, and the mass concentration of the doped object is 3%.
(7) Then, an AIE green light emitting layer CP-BP-PXZ was deposited on the red light emitting layer at a controlled deposition rate
The thickness was 6 nm.
(8) Then, a spacer layer TCTA is deposited on the AIE green light emitting layer with the deposition rate controlled at
The thickness was 2 nm.
(9) Then, an AIE blue light emitting layer TPB-AC is deposited on the spacer layer at a deposition rate controlled to
The thickness was 10 nm.
(10) Then, an electron transport layer TmPyPB is deposited on the light emitting layer at a deposition rate controlled
The thickness was 40 nm.
(11) Then, an electron injection layer LiF is deposited on the electron transport layer, and the deposition speed is controlled at
The thickness was 1 nm.
(12) Finally, depositing Al cathode on the electron injection layer, and controlling the deposition speed at
The thickness was 120nm, the device fabrication was completed, and then taken out and tested.
The electroluminescence spectra of the white light device W1 prepared in this example at different brightnesses are shown in fig. 2.
The current density-luminance-voltage characteristic curve of the white light device W1 prepared in this example is shown in fig. 4.
The power efficiency-quantum efficiency-luminance characteristic curve of the white light device W1 prepared in this example is shown in fig. 5.
Example 2
In this example, a fluorescence/phosphorescence mixed white light OLEDs (device W2) based on aggregation inducing luminescent material is different from example 1 only in the thickness of the red light emitting layer, the spacer layer and the green light emitting layer, and the device structure is as follows:
device W2 ITO/HAT-CN (5nm)/TAPC (50nm)/TCTA (5nm)/TCTA 3 wt% Ir (dmppr-mp)2(divm)(5nm)/CP-BP-PXZ(10nm)/TCTA(3nm)/TPB-AC(10nm)/TmPyPB(40nm)/LiF(1nm)/Al(120nm)。
The electroluminescence spectrum of the white light device W2 prepared in this example at different luminances is shown in fig. 3, the current density-luminance-voltage characteristic curve is shown in fig. 4, and the power efficiency-quantum efficiency-luminance characteristic curve is shown in fig. 5.
The electroluminescent property data of the white light devices W1 and W2 prepared in examples 1 and 2 above are shown in table 1:
TABLE 1
aIn the order of maximum and 1000cd m-2The value at the luminance of the light beam,bat 1000cd m-2The value at brightness.
As can be seen from the results of Table 1 and FIGS. 2 to 5, the fluorescence/phosphorescence mixed white light OLEDs based on the aggregation-induced emission material have the characteristics of high efficiency, low efficiency roll-off and high color rendering index, and the highest power efficiency can reach 50.5lm W-1The external quantum efficiency can reach 20.5 percent and is 1000cd m-2The power efficiency at luminance is still maintained at 32.9lm W-1The external quantum efficiency is as high as 18.9%, and the high color rendering index is 1237-15907 cd m-2Greater than 90 at brightness. In addition, the white light device with adjustable light colors can be prepared by simply adjusting the thicknesses of the light-emitting layer and the spacing layer, the color coordinate is adjusted from warm white (0.46,0.49) to pure white (0.35,0.33), the color rendering index is up to 97 at most, and the important application value is displayed.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.