CN115020602A - Light emitting device, method of manufacturing the same, and display apparatus - Google Patents

Abstract

The invention provides a light emitting device, a method of manufacturing the same, and a display apparatus including the light emitting device. The light emitting device comprises a first electrode, a second electrode and a light emitting function layer positioned between the first electrode and the second electrode; the light-emitting functional layer comprises a light-emitting layer, a first barrier layer and a second barrier layer, wherein the first barrier layer is positioned between the light-emitting layer and the first electrode; and the light emitting layer includes a host material and a guest material; at least one of the first barrier layer and the second barrier layer is doped with the guest material. According to the light-emitting device, on the premise that no new material is introduced, by doping the light-emitting functional layer with the guest material, the exciton distribution area can be widened, the light-emitting efficiency of the light-emitting device is effectively improved, the phenomenon of efficiency roll-off is improved, and the service life of the device is prolonged.

Description

Light emitting device, method of manufacturing the same, and display apparatus

Technical Field

The invention belongs to the technical field of display, and particularly relates to a light-emitting device, a preparation method of the light-emitting device and a display device comprising the light-emitting device.

Background

Organic Light-Emitting diodes (OLEDs) have been widely used in the display technology field due to their excellent display properties, and have attracted much attention in the industry. OLEDs can be classified into fluorescent OLEDs, phosphorescent OLEDs, and Thermally Activated Delayed Fluorescence (TADF) OLEDs according to the light emitting material used, and currently, fluorescent OLEDs and phosphorescent OLEDs are commercially used more. In the electrically excited state, the organic luminescent material will generate 25% of singlet excitons and 75% of triplet excitons, based on the total number of excitons. According to the principle of conservation of spin, only 25% of singlet excitons of a fluorescent material are capable of generating photons by radiative transitions. Different from fluorescent materials, due to the spin-orbit coupling effect of heavy metals, triplet excitons of phosphorescent materials can emit photons through radiation transition, so that the maximum internal quantum efficiency of phosphorescent OLEDs can reach 100% theoretically, and the efficiency of devices is greatly improved.

However, triplet excitons have a longer lifetime than singlet excitons, and there is a certain probability of triplet-triplet annihilation (TTA) and triplet-polaron annihilation (TPA) occurring before the radiative transition occurs, which results in the loss of triplet excitons, which in turn results in a reduction in device efficiency. Compared with low brightness (or low current density), the triplet exciton and polaron concentration is higher at high brightness (or high current density), the TTA and TPA processes are more serious, and the device efficiency will be greatly reduced, which is a common problem faced by most phosphorescent OLEDs: and (4) efficiency roll-off. The heat generated by the TTA and TPA processes can reduce the lifetime of phosphorescent OLED devices, and a reduction in device efficiency can also lead to increased power consumption, both of which are detrimental to the commercial use of phosphorescent OLEDs.

For the same number of excitons and polarons in an OLED device, the wider the exciton recombination zone, the lower the exciton and polaron concentration within the recombination zone. Broadening the exciton recombination zone (the zone where electrons and holes recombine to form excitons) is an effective way to reduce exciton and polaron concentrations, improving the roll-off in efficiency of phosphorescent OLEDs. Early phosphorescent OLEDs, which mostly used Single-host structures (S-EMLs), generally had unbalanced capability of transporting holes and electrons, so the holes and electrons would recombine near the anode side (or near the cathode side) to form excitons, which had narrow recombination regions and severe efficiency roll-off. From the perspective of broadening the exciton recombination zone, researchers developed a range of phosphorescent OLED device structures including: a Double light emitting layer structure (Double EML, D-EML), a blended host light emitting layer structure (Mixed EML, M-EML), a gradient doped host light emitting layer structure (Graded EML, G-EML), and the like. However, the structures of the devices still have a plurality of problems, such as the narrow D-EML exciton recombination region and the serious efficiency roll-off; M-EML and G-EML relate to co-evaporation of main materials, and have complex preparation process, poor repeatability among different batches and the like.

In addition, from the viewpoint of material development, introduction of new host materials has been involved from S-EML using only one host material to D-EML, M-EML and G-EML using two host materials. The different guest materials require different host materials with different photoelectric properties, so that new different host materials need to be developed from S-EML to D-EML, M-EML and G-EML for different commercially used guest materials, which increases the development cost and difficulty.

In summary, in order to improve the efficiency roll-off phenomenon of the phosphorescent device, improve the device efficiency, and prolong the device lifetime, it is necessary to design a simple and universal novel device structure

Disclosure of Invention

The invention provides a light-emitting device, a preparation method thereof and a display device comprising the light-emitting device, aiming at solving the problems in the related art, the technical scheme is as follows:

in a first aspect, the present invention provides a light emitting device comprising a first electrode, a second electrode, and a light emitting functional layer between the first electrode and the second electrode; the light-emitting functional layer comprises a light-emitting layer, a first barrier layer and a second barrier layer, wherein the first barrier layer is positioned between the light-emitting layer and the first electrode; and the light emitting layer includes a host material and a guest material; at least one of the first barrier layer and the second barrier layer is doped with the guest material.

According to a preferred embodiment, the first blocking layer is doped with a guest material when the electron mobility of the host material is greater than the hole mobility. Wherein the main body material is selected from one or more of (8-hydroxyquinoline aluminum), (1,3, 5-tri (1-phenyl-1H-benzimidazole-2-yl) benzene) and (3- (biphenyl-4-yl) -5- (4-tert-butylphenyl) -4-phenyl-4H-1, 2, 4-triazole).

According to another preferred embodiment, the second blocking layer is doped with a guest material when the electron mobility of the host material is smaller than the hole mobility. Wherein the main material is (4,4 '-bis (N-carbazolyl) -9,9' -spirobifluorene.

According to yet another preferred embodiment, the first and second blocking layers are doped with a guest material when the electron mobility and the hole mobility of the host material are substantially the same. Wherein the host is a blend of 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene and (4,4 '-bis (N-carbazolyl) -9,9' -spirobifluorene.

Preferably, the light emitting function layer further includes a first transport layer between the first barrier layer and the first electrode; wherein the first transport layer is doped with the guest material.

Further, the guest material is a metal iridium complex. Preferably, the metal iridium complex is one or more selected from bis (2- (2 '-benzothienyl) pyridine-N, C3') (acetylacetonato) iridium, tris (2-phenylpyridine) iridium, bis (2-phenylpyridine) iridium acetylacetonate and tris [2- (p-tolyl) pyridine ] iridium.

Preferably, the doping concentrations of the guest materials are 0.5 to 3%, respectively.

In a second aspect, the present invention provides a display apparatus comprising at least one sub-pixel including the light emitting device.

In a third aspect, the present invention provides a method for manufacturing a light emitting device, including sequentially forming a second electrode, a light emitting function layer, and a first electrode. The forming of the light-emitting function layer comprises sequentially forming a second barrier layer, a light-emitting layer and a first barrier layer, wherein the light-emitting layer comprises a host material and a guest material. The method further includes doping one or both of the first and second barrier layers with the guest material.

According to a specific embodiment, when the electron mobility of the host material is smaller than the hole mobility, doping the first blocking layer with the guest material;

when the electron mobility of the host material is larger than the hole mobility, doping a second barrier layer by using the guest material;

and when the electron mobility and the hole mobility of the host material are basically the same, doping the first barrier layer and the second barrier layer with the guest material.

Preferably, when the electron mobility and the hole mobility of the host material are substantially the same, forming the light emitting functional layer further includes forming a first transport layer between the first blocking layer and the first electrode;

the preparation method further comprises doping the first transfer layer with the guest material.

The advantages or beneficial effects of the above technical solution at least include:

under the condition of not introducing a new material, the exciton distribution area can be widened and the exciton concentration is reduced only by a method of doping an object material in the second blocking layer and/or the first blocking layer and the first transmission layer, so that the efficiency roll-off is improved, the device efficiency is improved, and the device service life is prolonged.

The foregoing summary is provided for the purpose of description only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the present application will be readily apparent by reference to the drawings and following detailed description.

Drawings

In the drawings, like reference numerals refer to the same or similar parts or elements throughout the several views unless otherwise specified. The figures are not necessarily to scale. It is appreciated that these drawings depict only some embodiments in accordance with the disclosure and are therefore not to be considered limiting of its scope.

FIG. 1 is a schematic structural diagram of a phosphorescent OLED device of the related art;

FIGS. 2 and 3 respectively show exciton distribution diagrams of a related art phosphorescent OLED device;

FIG. 4 illustrates the structure of materials that can be used for the functional layers in the present invention;

FIG. 5 shows a schematic exciton distribution of an OLED device after doping of an electron blocking layer according to an embodiment of the present invention;

FIG. 6 shows a schematic exciton distribution after doping of the hole blocking layer and the electron transport layer of an OLED device according to an embodiment of the present invention;

FIG. 7 shows a schematic exciton distribution after doping of the electron blocking layer, the hole blocking layer and the electron transport layer of an OLED device according to an embodiment of the present invention;

FIG. 8 is a schematic diagram of the exciton distribution area detected in the intercalation experiment;

fig. 9 is an exciton distribution diagram of the device before and after doping a guest material in a certain region of the electron blocking layer according to example 1 of the present invention;

fig. 10 is a graph of current efficiency versus luminance of the device before and after doping guest material in a certain region of the electron blocking layer according to example 1 of the present invention;

FIG. 11 is a normalized electroluminescence spectrum of the device before and after doping a guest material in a certain region of the electron blocking layer according to example 1 of the present invention;

fig. 12 is a schematic view of a pixel structure of a display device according to the present invention.

Detailed Description

In the following, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present application. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

A related art phosphorescent OLED device structure is shown in fig. 1. The OLED device structure comprises a first electrode (cathode), a first injection layer (electron injection layer), a first transmission layer (electron transmission layer), a first barrier layer (hole barrier layer), a light-emitting layer, a second barrier layer (electron barrier layer), a second transmission layer (hole transmission layer), a second injection layer (hole injection layer) and a second electrode (anode) which are sequentially stacked. The area where the holes and the electrons meet and are combined to form excitons is called an exciton recombination zone, and the width of the exciton recombination zone is mainly determined by the hole and electron transport performance of the light-emitting layer material.

As shown in fig. 2 and 3, the light emitting layer material generally has a better ability to transport electrons than holes (or a better ability to transport holes than electrons), and thus, electrons and holes generally meet and recombine to form excitons in a narrow region of the light emitting layer near the electron blocking layer (or the hole blocking layer), and the exciton distribution region is narrow, the exciton concentration is high, the TTA and TPA effects are severe, and the roll-off phenomenon is also severe.

The technical solution of the present invention and how to solve the above technical problems will be described in detail with specific embodiments below.

The device structure according to the present invention comprises, in order, a first electrode (which may be, for example, a cathode), a second electrode (which may be, for example, an anode), and a light-emitting functional layer between the first electrode and the second electrode. The light-emitting function layer comprises a light-emitting layer, a first blocking layer (hole blocking layer) positioned between the light-emitting layer and the first electrode, and a second blocking layer positioned between the light-emitting layer and the second electrode.

Further, the device structure of the present invention may further include a first transport layer (electron transport layer) between the first blocking layer (hole blocking layer) and the first electrode (cathode), and may further include a first injection layer (electron injection layer) between the first transport layer (electron transport layer) and the first electrode (cathode), a second transport layer (hole transport layer) between the second blocking layer (electron blocking layer) and the second electrode (anode), and a second injection layer (hole injection layer) between the second transport layer (hole transport layer) and the second electrode (anode).

According to a specific embodiment, the second electrode is formed on the substrate base plate, and the second injection layer, the second transport layer, the second barrier layer, the light-emitting layer, the first barrier layer, the first transport layer, the first injection layer, and the first electrode are sequentially stacked on a surface of the second electrode on a side facing away from the substrate.

In particular, the second electrode may be a transparent conductive layer, such as an Indium Tin Oxide (ITO) film layer, deposited on the substrate base plate.

The light-emitting layer can comprise a host material and a doping body of a guest material, and the doping concentration of the guest material can be regulated and controlled according to the performance of the device, such as 0.5-3%. As described above, the host material may have a difference or substantial balance between the transport capabilities for electrons and the transport capabilities for holes (i.e., the electron transport capabilities may be better than the hole transport capabilities, or the hole transport capabilities may be better than the electron transport capabilities, or the electron transport capabilities may be substantially balanced with the hole transport capabilities).

In the light emitting device of the present invention, the host material, the electron blocking material and the hole blocking material should have higher triplet energy levels than the light emitting guest material, the electron blocking material should have higher hole mobility and lower electron mobility, and the hole blocking material should have higher electron mobility and lower hole mobility.

According to one embodiment, as shown in FIG. 4, a host material with electron mobility greater than hole mobility useful in the present invention may be (8-hydroxyquinoline aluminum) (Alq) ₃ ) One or more of (1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene) (TPBi) and (3- (biphenyl-4-yl) -5- (4-tert-butylphenyl) -4-phenyl-4H-1, 2, 4-triazole) (TAZ 1). At this time, inIn the light emitting device including the light emitting layer of the above host material, excitons are mainly distributed in a narrow portion of the light emitting layer near the electron blocking layer, so that the concentration of excitons in the portion of the light emitting layer is high, and the TTA and TPA phenomena are easily generated.

The guest material which can be doped with the above host material may be a metal iridium complex, and may be, for example, (bis (2- (2 '-benzothienyl) pyridine-N, C3') (acetylacetonato) iridium) (Btp) ₂ Ir (acac), tris (2-phenylpyridine) iridium, bis (2-phenylpyridine) iridium acetylacetonate and tris [2- (p-tolyl) pyridine]One or more of iridium.

As shown in fig. 2, when the light emitting device includes the light emitting layer formed of the above host material and guest material having electron mobility greater than hole mobility, excitons may be concentrated in a certain region of the light emitting layer adjacent to the second blocking layer (electron blocking layer). As shown in fig. 5, in order to reduce the exciton concentration in the light emitting layer, the present inventors doped the above guest material in a certain region of the second blocking layer (electron blocking layer), preferably in a region adjacent to the light emitting layer, so that the excitons at high concentration at the interface of the second blocking layer (electron blocking layer) and the light emitting layer transfer the energy in the light emitting layer to the guest material doped in the electron blocking layer through energy transfer (or it can be understood that the excitons at high concentration at the interface of the electron blocking layer and the light emitting layer can diffuse into the electron blocking layer doped with the guest material), thereby reducing the exciton concentration in the light emitting layer, reducing TTA and TPA effects, and improving the efficiency roll-off of the device.

Preferably, the light-emitting guest material is doped in a region of the second blocking layer (electron blocking layer) near the light-emitting layer, wherein the doping thickness may be 20nm or less. The concentration of the doped guest material can be adjusted according to the actual device effect, and the doping concentration can be 0.5-3%, such as 0.5%, 1%, 2%, 3%, and the like.

With further reference to fig. 4, in the light emitting device structure of the present invention, the anode can be Indium Tin Oxide (ITO); the hole injection material may be one or more of copper (II) phthalocyanine (CuPc) and 2,3,5, 6-tetrafluoro-7, 7',8,8' -tetracyanoquinodimethane (F4-TCNQ). The hole transport material may be one or more of N, N '-diphenyl-N, N' - (1-naphthyl) -1,1 '-biphenyl-4, 4' -diamine (NPB) and 2,2',7,7' -tetrakis- (diphenylamino) -spirobifluorene (spiro-TAD). The electron blocking material may be one or more of 5,10, 15-Triphenyltriandole (TPDI) and 5,10, 15-Tribenzyltriandole (TBDI). The hole blocking material may be one or more of 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (BCP) and tris-2, 3,5, 6-trimethylphenylboron (TPbB). The electron transport material may be one or more of 3,3' - [5' - [3- (3-pyridyl) phenyl ] [1,1':3', 1' -terphenyl ] -3, 3' -diyl ] bipyridine (TmPyPB) and 2, 7-bis (diphenylphosphinyl) -9,9' -spirobifluorene (SPPO 13). The electron injecting material may be lithium fluoride (LiF) or ytterbium (Yb) metal. The cathode may be a metallic magnesium (Mg) and/or silver (Ag) alloy.

According to another embodiment, as shown in fig. 4, a host material having an electron mobility less than a hole mobility that may be used in the present invention may be 4,4 '-bis (N-carbazolyl) -9,9' -spirobifluorene (CFL), and a guest material may be as described above. At this time, in the light emitting device including the light emitting layer containing the above host material, excitons are mainly distributed in a narrow portion of the light emitting layer near the first blocking layer (hole blocking layer) (as shown in fig. 3), so that the exciton concentration in this portion of the light emitting layer is high, and the TTA and TPA phenomena are easily generated.

When the light emitting device includes the light emitting layer formed of the above host material and guest material having electron mobility less than hole mobility, as shown in fig. 6, in order to reduce exciton concentration in the light emitting layer, the present inventors doped the above guest material in a certain region of the first blocking layer (hole blocking layer) and the first transport layer (electron transport layer), preferably a region adjacent to the hole blocking layer, such that the excitons of high concentration at the interface of the first blocking layer (hole blocking layer) and the light emitting layer transfer energy in the light emitting layer to the guest material doped in the first blocking layer (hole blocking layer) and the first transport layer (electron transport layer) through energy transfer (or it can be understood that the excitons of high concentration at the interface of the hole blocking layer and the light emitting layer can be diffused into the hole blocking layer and the electron transport layer doped with the guest material), thereby reducing exciton concentration in the light emitting layer, the TTA and TPA effects are reduced, and the efficiency roll-off of the device is improved.

Preferably, the light-emitting guest material is doped in the regions of the hole blocking layer and the electron transport layer near the hole blocking layer, wherein the doping thickness of the hole blocking layer may be 5nm or less and the doping thickness of the electron transport layer may be 15nm or less. The concentration of the doped guest material can be adjusted and controlled according to the actual device effect, and the doping concentration can be respectively 0.5-3%, such as 0.5%, 1%, 2%, 3% and the like.

According to yet another embodiment, the present invention may employ a host material having a substantial balance of electron mobility and hole mobility, and the guest material may be as described above. At this time, in the light emitting device including the light emitting layer containing the above host material, excitons will be distributed throughout the entire light emitting layer. Such host materials may be a blend of 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene and (4,4 '-bis (N-carbazolyl) -9,9' -spirobifluorene in a mass ratio of 5: 5.

Referring to fig. 7, the light emitting device according to this embodiment dopes a guest material in a certain region of the second blocking layer (electron blocking layer), the first blocking layer (hole blocking layer), and the first transport layer (electron transport layer), and then the high concentration of excitons in the light emitting layer transfers energy to the guest material doped in the second blocking layer (electron blocking layer), the first blocking layer (hole blocking layer), and the first transport layer (electron transport layer) through energy transfer (i.e., the high concentration of excitons in the light emitting layer may diffuse into the electron blocking layer, hole blocking layer, and electron transport layer doped with the guest material), thereby reducing the exciton concentration, reducing TTA and TPA effects, and improving the efficiency roll-off of the device.

Preferably, the light-emitting guest material is doped in a region of the electron blocking layer adjacent to the light-emitting layer, a region of the hole blocking layer and a region of the electron transport layer adjacent to the hole blocking layer, wherein the doping thickness of the electron blocking layer may be 10nm or less, the doping thickness of the hole blocking layer may be 5nm or less, and the doping thickness of the electron transport layer may be 5nm or less. The concentration of the doped guest material can be adjusted and controlled according to the actual device effect, and the doping concentration can be respectively 0.5-3%, such as 0.5%, 1%, 2%, 3% and the like.

The invention also provides a display device comprising the light-emitting device. The display device can be a mobile phone, a computer, a television, a display or other devices with display functions.

Referring to fig. 12 in particular, the display device generally comprises three sub-pixels of red light, green light and blue light, and the device efficiency of the three sub-pixels gradually decreases as the service time of the display device increases, but the reduction rates of the device efficiency of the three sub-pixels of red light, green light and blue light are generally not consistent, which causes the color cast phenomenon of the display device after the display device is used for a period of time. If the red sub-pixel efficiency is reduced faster and the green and blue sub-pixels efficiency is reduced slower, the display device will turn green after a period of time. If the efficiency of the blue sub-pixel is reduced faster and the efficiency of the red and green sub-pixels is reduced slower, the display device will turn yellow after a period of time. The light-emitting device structure provided by the invention can be used for pertinently solving the problem of color cast caused by the fact that the service life of a sub-pixel device corresponding to one or a plurality of light-emitting colors in a display device is low, for example, if the service life of a red light sub-pixel is low, an exciton distribution area can be widened by doping guest materials in an electron blocking layer and/or a hole blocking layer and an electron transmission layer of a red light device, the service life of the device is prolonged, and the like.

The invention also provides a preparation method of the light-emitting device, which comprises the steps of sequentially forming a second electrode, a light-emitting functional layer and a first electrode, and doping one or both of the first barrier layer and the second barrier layer by adopting the guest material.

The forming of the light-emitting function layer comprises sequentially forming a second barrier layer, a light-emitting layer and a first barrier layer, wherein the light-emitting layer comprises a host material and a guest material.

Specifically, when the electron mobility of the host material is smaller than the hole mobility, the first barrier layer is doped with a guest material;

when the electron mobility of the host material is larger than the hole mobility, doping the second barrier layer with a guest material;

and when the electron mobility and the hole mobility of the host material are basically the same, doping the first barrier layer and the second barrier layer by adopting a guest material.

Forming the light emitting functional layer further includes forming a first transport layer between the first blocking layer and the first electrode when the electron mobility and the hole mobility of the host material are substantially the same; the preparation method further comprises doping the first transmission layer with a guest material.

In the preparation method of the invention, the doping concentration of the guest material in each layer is 0.5-3%.

According to a specific embodiment, the preparation method of the present invention may further include a conventional pretreatment step, that is, may include cleaning the substrate base, for example, ultrasonic cleaning, isopropyl alcohol cleaning, acetone cleaning, and drying may be sequentially performed.

Each of the electrode layer and the light emitting functional layer may be formed using a deposition method that is conventional in the art.

The invention can effectively improve the device efficiency of the luminescent device, especially the phosphorescent luminescent device, and improve the efficiency roll-off only by doping guest materials in the electron blocking layer and/or the hole blocking layer and the electron transport layer under the condition of not introducing new materials. Compared with the structure of the undoped light-emitting device, the highest current efficiency of the light-emitting device with the electron blocking layer doped with the guest material can be improved by 2 percent and is 1000cd/m ² The current efficiency can be improved by 3% under the brightness, and the current efficiency can be improved by 10000cd/m ² The current efficiency can be improved by 6% under the brightness; at 1000cd/m ² The efficiency roll-off can be reduced by 0.6% under the brightness and is 10000cd/m ² The efficiency roll-off can be reduced by 2.5% at brightness. At 15mA/cm ² The time for the luminance of the light emitting device to decay to 98% of the initial luminance can be improved by 6% at the current density.

Compared with the method for improving the efficiency roll-off by using a Double-luminescent-layer structure (Double EML, D-EML), a blended host luminescent-layer structure (Mixed EML, M-EML), a gradient doped host luminescent-layer structure (Graded EML, G-EML), a short exciton life guest material and the like, the technical scheme of the invention does not relate to the introduction of a new material, so that the development cost and the development difficulty can be reduced.

The invention will be further illustrated by the following examples, but is not limited thereto.

The materials used in the following examples and comparative examples were:

anode: ITO (indium tin oxide)

Hole injection material: copper (II) phthalocyanine (CuPc)

Hole transport material: n, N '-diphenyl-N, N' - (1-naphthyl) -1,1 '-biphenyl-4, 4' -diamine (NPB)

Electron blocking material: 5,10, 15-Triphenyltriandole (TPDI)

Main material: 8-Hydroxyquinoline aluminum (Alq) ₃ ) 4,4 '-bis (N-carbazolyl) -9,9' -spirobifluorene (CFL), guest material: bis (2- (2 '-benzothienyl) pyridine-N, C3') (acetylacetonato) iridium (Btp) ₂ Ir(acac))

Hole blocking material: 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (BCP)

Electron transport material: 3,3'- [5' - [3- (3-pyridyl) phenyl ] [1,1':3',1 '-terphenyl ] -3, 3' -diyl ] bipyridine (TmPyPB)

Electron injection material: LiF

Cathode: mg (magnesium)

Wherein "/" denotes a laminated structure and ": denotes doping or mixing.

Example 1

The light emitting Device (Device 2) of the present embodiment includes, sequentially formed on a substrate base: anode (190 μm)/hole injection layer (10 nm)/hole transport layer (120 nm)/electron blocking layer (65 nm)/electron blocking layer guest material (1%) (20 nm)/light emitting layer (host material: material, 2%, 45 nm)/hole blocking layer (5 nm)/electron transport layer (30 nm)/electron injection layer (2 nm)/cathode (14nm), wherein the host material is (8-hydroxyquinoline aluminum).

The preparation method of the light-emitting device comprises the following steps:

pretreating a glass substrate, comprising: and (2) putting the glass substrate into deionized water containing a detergent for ultrasonic cleaning, then sequentially carrying out ultrasonic cleaning by using isopropanol and acetone for 20 minutes, and then blowing the glass substrate by using nitrogen.

Sputtering an ITO film layer on the surface of the glass substrate subjected to the pretreatment in vacuum to form an anode;

vacuum evaporating a hole transport material layer on the surface of the anode to form a hole transport layer with the thickness of 120 nm;

vacuum evaporating an electron blocking material on the surface of the hole transport layer to form an electron blocking layer with the thickness of 65 nm;

doping the electron blocking layer by adopting a guest material to form the electron blocking layer, wherein the doping concentration of the guest material is 1%, and the thickness of the guest material is 20 nm;

vacuum evaporating a host material and a guest material on the surface of the electron blocking layer and the guest material to form a light emitting layer (the host material and the guest material) with the thickness of 5 nm;

vacuum evaporating a hole blocking material on the surface of the light emitting layer to form a hole blocking layer with the thickness of 5 nm;

vacuum evaporating an electron transport material on the surface of the hole blocking layer to form an electron transport layer with the thickness of 30 nm;

vacuum evaporating an electron injection material on the surface of the electron transport layer to form an electron injection layer with the thickness of 2 nm;

a cathode metal material was vacuum-deposited on the surface of the electron injection layer to form a cathode having a thickness of 14 nm.

Comparative example 1

The structure of the light emitting Device (Device 1) of the present comparative example includes: anode/hole injection layer (10 nm)/hole transport layer (120 nm)/electron blocking layer (85 nm)/light-emitting layer (host material: guest material, 2%, 45 nm)/hole blocking layer (5 nm)/electron transport layer (30 nm)/electron injection layer (2 nm)/cathode (14 nm).

A light emitting device was fabricated by the same method as example 1, except that the electron blocking layer doping step was not performed.

Comparative experiment method

The exciton distribution area condition of the device is tested through an intercalation experiment.

Intercalation experiments intercalation materials were placed at different positions in the luminescent layer as shown in fig. 8. The intercalation material has lower singlet and triplet energy levels than the emissive guest material, and the excitons near the intercalation material will transfer energy to the intercalation material, so the electroluminescent intensity of the intercalation material is proportional to the exciton concentration at the location of the intercalation material.

As shown in fig. 9, the experimental results show that: the Device 2 (example 1) obtained by doping a guest material in a certain region of the electron blocking layer can widen the exciton distribution region and reduce the exciton concentration in the light emitting layer, compared with the undoped reference light emitting Device 1 (comparative example 1).

As shown in fig. 10 and table 1, by doping a guest material in the electron blocking layer, the efficiency of the phosphorescent light emitting device can be effectively improved, the efficiency roll-off can be improved, and the lifetime of the device can be prolonged. The experimental results show that: the maximum current efficiency of the light emitting Device 2 of example 1 was improved by 2% at 1000cd/m compared to the undoped light emitting Device 1 ² The current efficiency is improved by 3 percent under the brightness and is 10000cd/m ² The current efficiency is improved by 6% under the brightness; at 1000cd/m ² The efficiency roll-off is reduced by 0.6% under the brightness and is 10000cd/m ² The efficiency roll-off is reduced by 2.5% under the brightness; at 15mA/cm ² When the Device lifetime was tested at current density, the time for the luminance decay of Device 2 of comparative example 1 to 98% of the initial luminance increased by 6% compared to Device 1.

As shown in fig. 11, the light emitting Device 2 of example 1 has an electroluminescence spectrum substantially uniform with that of the undoped light emitting Device 1.

TABLE 1 comparison of device Performance before and after doping of guest materials in certain regions of the electron blocking layer

Example 2

The light emitting Device (Device 3) structure of the present embodiment includes: anode/hole injection layer (10 nm)/hole transport layer (120 nm)/electron blocking layer (85 nm)/light-emitting layer (host material: guest material, 2%, 45 nm)/hole blocking layer: guest material (1%) (5 nm)/electron transport layer: guest material (1%) (15 nm)/electron transport layer (15 nm)/electron injection layer (2 nm)/cathode (14 nm). Namely, a light-emitting object material is doped in a hole blocking layer with the thickness of 5nm and an electron transport layer with the thickness of 15nm, which are close to a light-emitting layer, and the doping concentration is 1 percent respectively.

A light emitting device was manufactured by the same method as example 1, except that the host material was 4,4 '-bis (N-carbazolyl) -9,9' -spirobifluorene (CFL).

Comparative example 2

A light emitting Device (Device 4) was fabricated by the same method as comparative example 1, except that the host material was 4,4 '-bis (N-carbazolyl) -9,9' -spirobifluorene (CFL).

The experimental results show that: the maximum current efficiency of the light emitting Device 3 of example 2 was improved by 1% at 1000cd/m compared to the undoped light emitting Device 4 ² The current efficiency is improved by 2 percent under the brightness and is 10000cd/m ² The current efficiency is improved by 4% under the brightness; at 1000cd/m ² The efficiency roll-off is reduced by 1.1% under the brightness and is 10000cd/m ² The efficiency roll-off is reduced by 2.1% under the brightness; at 15mA/cm ² When the Device lifetime was tested at current density, the time for the luminance of Device 3 of example 2 to decay to 98% of the initial luminance increased by 5% compared to Device 4 of comparative example 2.

TABLE 2 comparison of device performance before and after doping of guest materials in certain regions of hole blocking layer and electron transport layer

Example 3

The light emitting Device (Device 5) structure of the present embodiment includes: anode (190 μm)/hole injection layer (10 nm)/hole transport layer (120 nm)/electron blocking layer (75 nm)/electron blocking layer guest material (1%) (10 nm)/light-emitting layer (host material: guest material, 2%, 45 nm)/hole blocking layer guest material (1%) (5 nm)/electron transport layer (25 nm)/electron injection layer (2 nm)/cathode (14 nm). Wherein, the main material is: the blend of 1,3, 5-tri (1-phenyl-1H-benzimidazole-2-yl) benzene and 4,4 '-bis (N-carbazolyl) -9,9' -spirobifluorene has a blending mass ratio of 5: 5. Namely, a light-emitting object material is doped in a hole blocking layer with the thickness of 5nm and an electron transport layer with the thickness of 15nm, which are close to a light-emitting layer, and the doping concentration is 1 percent respectively.

A light-emitting device was produced by the same method as in example 1, except that the host materials were 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene and 4,4 '-bis (N-carbazolyl) -9,9' -spirobifluorene.

Comparative example 3

A light emitting Device (Device 6) was prepared using the same method as in comparative example 1, except that the host material was a blend of 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene and 4,4 '-bis (N-carbazolyl) -9,9' -spirobifluorene, and the blending mass ratio was 5: 5.

The exciton distribution area condition of the device was tested using the above intercalation experiments. The experimental results show that: the maximum current efficiency of the light emitting Device5 of example 3 was improved by 1% at 1000cd/m compared to the undoped light emitting Device 6 ² The current efficiency is improved by 1% under the brightness and is 10000cd/m ² The current efficiency is improved by 2% under the brightness; at 1000cd/m ² The efficiency roll-off is reduced by 0.4% under the brightness and is 10000cd/m ² The efficiency roll-off is reduced by 1.1% under the brightness; at 15mA/cm ² When Device lifetime was tested at current density, the time for the luminance of Device5 of example 3 to decay to 98% of the initial luminance increased by 3% compared to Device 6 of comparative example 3.

TABLE 3 Performance ratio of device before and after doping guest materials in electron blocking layer, hole blocking layer and electron transport layer

The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive various changes or substitutions within the technical scope of the present application, and these should be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims (15)

1. A light emitting device includes a first electrode, a second electrode, and a light emitting functional layer between the first electrode and the second electrode;

the light-emitting functional layer comprises a light-emitting layer, a first barrier layer and a second barrier layer, wherein the first barrier layer is positioned between the light-emitting layer and the first electrode; and is

The light-emitting layer includes a host material and a guest material;

it is characterized in that the preparation method is characterized in that,

at least one of the first barrier layer and the second barrier layer is doped with the guest material.

2. The light emitting device of claim 1, wherein the first blocking layer is doped with a guest material when the electron mobility of the host material is less than the hole mobility.

3. The light-emitting device according to claim 2, the host material being (4,4 '-bis (N-carbazolyl) -9,9' -spirobifluorene.

4. The light emitting device of claim 1, wherein the second blocking layer is doped with a guest material when the electron mobility of the host material is greater than the hole mobility.

5. The light emitting device of claim 4, the host material is selected from one or more of (8-hydroxyquinolinoaluminum), (1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene), and (3- (biphenyl-4-yl) -5- (4-tert-butylphenyl) -4-phenyl-4H-1, 2, 4-triazole).

6. The light emitting device of claim 1, the first and second blocking layers being doped with a guest material when the electron mobility and the hole mobility of the host material are substantially the same.

7. The light emitting device of claim 6, the host material being a blend of 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene and (4,4 '-bis (N-carbazolyl) -9,9' -spirobifluorene.

8. The light-emitting device according to claim 6, the light-emitting functional layer further comprising a first transport layer between the first barrier layer and the first electrode;

wherein the first transport layer is doped with the guest material.

9. The light-emitting device according to any one of claims 1 to 8, wherein the guest material is one or more metal iridium complexes selected from bis (2- (2 '-benzothienyl) pyridine-N, C3') (acetylacetonate) iridium, tris (2-phenylpyridine) iridium, bis (2-phenylpyridine) iridium acetylacetonate and tris [2- (p-tolyl) pyridine ] iridium.

10. The light-emitting device according to any one of claims 1 to 7, wherein the guest materials are doped at concentrations of 0.5 to 3%, respectively.

11. A display apparatus comprising at least one sub-pixel comprising a light emitting device according to any one of claims 1 to 10.

12. A method for preparing a light-emitting device comprises sequentially forming a second electrode, a light-emitting functional layer and a first electrode;

the forming of the light-emitting functional layer comprises sequentially forming a second barrier layer, a light-emitting layer and a first barrier layer, wherein the light-emitting layer comprises a host material and a guest material;

characterized in that the preparation method further comprises doping one or both of the first barrier layer and the second barrier layer with the guest material.

13. The manufacturing method according to claim 12, wherein when the electron mobility of the host material is smaller than the hole mobility, the first barrier layer is doped with the guest material;

when the electron mobility of the host material is larger than the hole mobility, doping the second barrier layer with the guest material;

and when the electron mobility and the hole mobility of the host material are basically the same, doping the first barrier layer and the second barrier layer with the guest material.

14. The production method according to claim 13, wherein when the electron mobility and the hole mobility of the host material are substantially the same, forming the light-emitting functional layer further comprises forming a first transport layer between the first blocking layer and a first electrode; and is

The preparation method further comprises doping the first transfer layer with the guest material.

15. The production method according to any one of claims 12 to 14, wherein the guest materials are doped at concentrations of 0.5 to 3%, respectively.

Images