CN110707227A - Light-emitting device and display panel - Google Patents
Light-emitting device and display panel Download PDFInfo
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- CN110707227A CN110707227A CN201910989460.4A CN201910989460A CN110707227A CN 110707227 A CN110707227 A CN 110707227A CN 201910989460 A CN201910989460 A CN 201910989460A CN 110707227 A CN110707227 A CN 110707227A
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
- H10K50/14—Carrier transporting layers
- H10K50/15—Hole transporting layers
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
- H10K50/14—Carrier transporting layers
- H10K50/15—Hole transporting layers
- H10K50/155—Hole transporting layers comprising dopants
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
- H10K50/14—Carrier transporting layers
- H10K50/16—Electron transporting layers
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
- H10K50/14—Carrier transporting layers
- H10K50/16—Electron transporting layers
- H10K50/165—Electron transporting layers comprising dopants
Abstract
The invention discloses a light emitting device and a display panel. The light-emitting device comprises an anode, a cathode, a light-emitting layer and a current carrier regulation and control layer, wherein the light-emitting layer and the current carrier regulation and control layer are positioned between the anode and the cathode; wherein the carrier regulation layer comprises a mixed material of a hole transport material and an electron transport material. The invention solves the problems of low luminous efficiency, efficiency roll-off and short service life of the light-emitting device by arranging the carrier regulation and control layer.
Description
Technical Field
The embodiment of the invention relates to the technical field of display, in particular to a light-emitting device and a display panel.
Background
The Organic Light-Emitting Diode (OLED) display technology has advantages of self-luminescence, wide viewing angle, high contrast, low power consumption, and high response speed, and is widely used in the display field.
However, the conventional OLED device has problems of low luminous efficiency, efficiency roll-off and short lifetime.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a light emitting device and a display panel, so as to solve the problems of low light emitting efficiency, efficiency roll-off and short lifetime of the light emitting device.
In order to achieve the purpose, the invention adopts the following technical scheme:
in one aspect, an embodiment of the present invention provides a light emitting device, including an anode, a cathode, and a light emitting layer and a carrier control layer located between the anode and the cathode, where in a thickness direction of the light emitting device, the carrier control layer is located on a surface of at least one side of the light emitting layer;
wherein the carrier regulation layer comprises a mixed material of a hole transport material and an electron transport material.
Optionally, the hole transport material comprises 4,4',4 ″ -tris (carbazol-9-yl) triphenylamine, 1, 3-dicarbazole-9-ylbenzene, or 4,4' -bis (9-carbazol) biphenyl; the electron transport material comprises 1,3, 5-tri (1-phenyl-1H-benzimidazol-2-yl) benzene or 4, 6-bis (3, 5-di (3-pyridyl) phenylphenyl) -2-methylpyrimidine.
Optionally, the mass ratio of the hole transport material to the electron transport material is 1:9 to 9: 1;
preferably, the mass ratio of the hole transport material to the electron transport material is from 3:7 to 7: 3.
Optionally, the carrier control layer includes a hole control layer on a surface of the light-emitting layer on a side close to the anode, and the hole control layer includes a mixed material of a first hole transport material and a first electron transport material.
Optionally, the LUMO level of the hole-regulating layer is higher than the LUMO level of the host material in the light-emitting layer;
preferably, the difference between the LUMO level of the hole-regulating layer and the LUMO level of the host material is greater than 0.2 eV;
preferably, the light-emitting device further includes a hole injection layer and a hole transport layer between the hole control layer and the anode, and the hole transport layer is located on the surface of the hole injection layer on the side close to the hole control layer.
Optionally, the carrier control layer includes an electron control layer, the electron control layer is located on a surface of the light emitting layer on a side close to the cathode, and the electron control layer includes a mixed material of a second hole transport material and a second electron transport material.
Optionally, the HOMO level of the electron-regulating layer is higher than the HOMO level of the host material in the light-emitting layer;
preferably, the difference between the HOMO level of the electron-regulating layer and the HOMO level of the host material is greater than 0.2 eV;
preferably, the light-emitting device further comprises an electron injection layer and an electron transport layer, which are located between the electron regulation layer and the cathode, and the electron transport layer is located on the surface of the electron injection layer on the side close to the electron regulation layer.
Optionally, an excited state energy level of the carrier control layer is higher than an excited state energy level of the host material in the light emitting layer.
Optionally, the excited state energy level comprises a singlet state energy level and/or a triplet state energy level.
In another aspect, embodiments of the present invention provide a display panel including the light emitting device provided in any embodiment of the present invention.
The invention has the beneficial effects that: according to the technical scheme provided by the embodiment of the invention, the injection and transmission capability (or transmission rate) of the current carrier at the corresponding side of the light-emitting layer is adjusted by arranging the current carrier regulation and control layer formed by blending the hole transmission material and the electron transmission material on the surface of at least one side of the light-emitting layer, so that the difference between the injection and transmission capability of the hole and the injection and transmission capability of the electron is reduced, the number of the hole and the electron reaching the light-emitting layer is balanced, the phenomenon that the surplus current carrier is quenched with excitons in the light-emitting layer is avoided, the light-emitting efficiency of the light-emitting device is effectively improved, and the; meanwhile, quenching of excitons is avoided, non-radiative energy is prevented from being generated, and heat generated by the light-emitting device is reduced, so that the service life of the light-emitting device is prolonged. Moreover, for light emitting devices with different structures, the technical scheme provided by the embodiment of the invention can balance the transmission of holes and electrons in the light emitting device only by adjusting the mixing ratio (such as mass ratio) of the hole transmission material and the electron transmission material in the carrier regulation layer, solves the problem of limited selection of the carrier blocking material and the main material of the light emitting layer, increases the selection space of the carrier blocking material and the main material of the light emitting layer, and reduces the manufacturing cost of the light emitting device.
Drawings
The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which:
fig. 1 is a schematic structural diagram of a light emitting device according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of another light-emitting device provided by an embodiment of the present invention;
fig. 3 is a schematic structural diagram of another light-emitting device provided by an embodiment of the present invention;
fig. 4 is a schematic structural diagram of a single electron transport device according to an embodiment of the present invention;
FIG. 5 is a schematic structural diagram of a single hole transport device according to an embodiment of the present invention;
fig. 6 is a schematic structural diagram of another light-emitting device provided by an embodiment of the present invention;
fig. 7 is a schematic structural diagram of another light-emitting device provided by an embodiment of the present invention;
fig. 8 is a schematic structural diagram of another light-emitting device provided in an embodiment of the present invention.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
As the OLED device mentioned in the background art has problems of low luminous efficiency, roll-off in efficiency, and short lifetime, the inventors have studied and found that the main reason for the low luminous efficiency, roll-off in efficiency, and short lifetime of the OLED device (light emitting device) is quenching between carriers and excitons in the light emitting layer, and the root cause for the quenching between carriers and excitons is imbalance between holes and electrons reaching the light emitting layer due to the difference between the injection transport capability of holes and the injection transport capability of electrons. Specifically, an OLED device includes at least an anode, a light-emitting layer, and a cathode in a stacked arrangement. When the OLED device works, electrons are injected into the light-emitting layer from the cathode, holes are injected into the light-emitting layer from the anode, the electrons and the holes are combined in the light-emitting layer to form excited-state excitons, the excited-state excitons are attenuated, energy is released in the form of light, and the light-emitting layer emits light. Because the injection transmission capability of the holes is different from that of the electrons and has a large difference, after the holes reaching the light-emitting layer are combined with the electrons, excess carriers (holes or electrons) exist, a part of the excess carriers are quenched with excitons formed by combination, so that the excitons cannot release light energy, the luminous efficiency of the OLED device is reduced, and the problem of efficiency roll-off occurs.
At present, a carrier blocking layer, such as a hole blocking layer and an electron blocking layer, is usually prepared by using a material with low electron mobility, a singlet state energy level and a triplet state energy level (referred to as a carrier blocking material in the embodiments of the present invention), and the carrier blocking layer is used to limit the injection and transportation capability of a corresponding carrier, thereby balancing the transmission of holes and electrons. However, the carrier transport performance of each carrier blocking material is fixed, and for light emitting devices with different structures, the carrier injection transport capacity of the light emitting devices is likely to be different, so that different carrier blocking materials need to be selected, and even new carrier blocking materials are required to optimize the carrier injection transport capacity, which greatly limits the selection of the carrier blocking materials. In addition, a bipolar material, that is, a material which can achieve both hole transport and electron transport is generally used as a host material of the light-emitting layer, and the bipolar material is provided to optimize the injection transport capability of carriers. In summary, in the conventional light emitting device capable of balancing the hole and electron transport, the selection of the carrier blocking material and the host material of the light emitting layer is limited, and the manufacturing cost of the light emitting device is increased.
Based on the above technical problem, the present embodiment provides the following solutions:
fig. 1 is a schematic structural diagram of a light emitting device provided in an embodiment of the present invention, where the composite anode can be applied to an electroluminescent device, and is suitable for a case where holes and electrons reaching a light emitting layer in the electroluminescent device are balanced. Specifically, as shown in fig. 1, the light-emitting device provided in the present embodiment includes an anode 10, a cathode 30, and a light-emitting layer 21 and a carrier-adjusting layer 22 located between the anode 10 and the cathode 30, and the carrier-adjusting layer 22 is located on a surface of at least one side of the light-emitting layer 21 in a thickness direction of the light-emitting device; the carrier control layer 22 includes a mixed material of a hole transport material and an electron transport material.
In the embodiment, the hole transport material is a partial hole type material, so that the mobility of holes can be improved, the hole transport is facilitated, and a certain blocking effect on electrons is achieved; correspondingly, the electron transport material is a partial electron type material, can improve the mobility of electrons, is beneficial to the transport of the electrons, and has a certain blocking effect on holes. Based on this, in the present embodiment, the carrier control layer 22 is formed by mixing the hole transport material and the electron transport material, so that the injection transport capability of the carrier control layer 22 for carriers (holes or electrons) is between the injection transport capability of the hole transport material for carriers and the injection transport capability of the electron transport material for carriers, and further the injection transport capability of at least one carrier can be adjusted by adjusting the mixing ratio (for example, mass ratio) of the hole transport material and the electron transport material, so as to reduce the difference between the injection transport capability of holes and the injection transport capability of electrons, thereby balancing the number of holes and electrons reaching the light emitting layer, avoiding the excess carriers and excitons from being quenched, and improving the light emitting efficiency. Meanwhile, the carrier control layer 22 designed in this embodiment can completely replace a carrier blocking layer, that is, the problem of unbalanced hole and electron transmission can be solved without providing a carrier blocking layer in the light emitting device; the hole transport material and the electron transport material can be fixed two materials, and the transmission of holes and electrons can be balanced only by adjusting the mixing ratio of the hole transport material and the electron transport material, so that the problem of high manufacturing cost of a light-emitting device caused by balancing the transmission of the holes and the electrons by selecting a new carrier blocking material and a main body material of a light-emitting layer in the prior art is solved.
Generally, the injection transport capability of holes of most light emitting devices (about 90% of light emitting devices) is greater than that of electrons, and the injection transport capability of electrons of the other small light emitting devices is greater than that of holes, and the carrier control layer is specifically positioned according to actual conditions in the embodiment. When the injection transmission capability of holes in the light-emitting device is larger than that of electrons, the carrier regulation and control layer is arranged on one side of the light-emitting layer close to the anode, so that the injection transmission capability of the holes is reduced; when the injection transmission capability of electrons in the light-emitting device is larger than that of holes, the carrier regulation and control layer is arranged on one side of the light-emitting layer close to the cathode, so that the injection transmission capability of the electrons is reduced; in addition, in the embodiment, the injection and transportation capacity of the holes and the electrons is not considered, the carrier regulation and control layers are arranged on the two sides of the light-emitting layer, and the quantity of the holes and the electrons reaching the light-emitting layer is balanced by regulating the injection and transportation capacity of the holes and the electrons at the same time.
Illustratively, as shown in fig. 1, the carrier regulating layer 22 includes a hole regulating layer 221, the hole regulating layer 221 is located on a surface of the light emitting layer 21 on a side close to the anode 10, and the hole regulating layer 221 includes a mixed material of a first hole transporting material and a first electron transporting material. At this time, for a light emitting device in which the injection transport capability of holes is larger than that of electrons, by adjusting the mixing ratio of the first hole transport material and the first electron transport material, the injection transport capability of holes can be reduced, and the transport of holes and electrons can be optimized. As shown in fig. 2, the carrier regulation layer 22 includes an electron regulation layer 222, the electron regulation layer 222 is located on a surface of the light emitting layer 21 on a side close to the cathode 30, and the electron regulation layer 222 includes a mixed material of a second hole transport material and a second electron transport material. At this time, for a light emitting device in which the injection transport ability of electrons is greater than that of holes, by adjusting the mixing ratio of the second hole transport material and the second electron transport material, the injection transport ability of electrons can be reduced, and the transport of holes and electrons can be optimized. In addition, as shown in fig. 3, the carrier regulation layer 22 includes a hole regulation layer 221 and an electron regulation layer 222, the hole regulation layer 221 is located on a surface of the light-emitting layer 21 on a side close to the anode 10, the electron regulation layer 222 is located on a surface of the light-emitting layer 21 on a side close to the cathode 30, the hole regulation layer 221 includes a mixed material of a first hole transport material and a first electron transport material, and the electron regulation layer 222 includes a mixed material of a second hole transport material and a second electron transport material. At this time, with any of the light-emitting devices described above, the transport of holes and electrons can be optimized by simultaneously adjusting the mixing ratio of the first hole transport material to the first electron transport material and the mixing ratio of the second hole transport material to the second electron transport material.
In the above light emitting device, one of the anode and the cathode includes a reflective electrode and/or a transparent electrode, and the other includes a transparent electrode, for example, the anode includes a reflective electrode in which case the material of the reflective electrode includes silver or copper, or the like, or the anode includes a stacked structure of a transparent electrode-reflective electrode-transparent electrode in which case the material of the transparent electrode includes a metal oxide such as indium tin oxide, indium oxide, gallium oxide, indium zinc oxide, or the like, and the material of the reflective electrode includes silver or copper, or the like; the cathode includes a transparent electrode, and in this case, the material of the transparent electrode includes a magnesium-silver alloy, a metal oxide, or the like. In addition, the light emitting device provided in this embodiment may be an electroluminescent device, specifically, an Organic Light Emitting Diode (OLED) light emitting device or a quantum dot light emitting device, and accordingly, the light emitting layer is an organic light emitting layer or a quantum dot light emitting layer, and the light emitting device may emit white light, red light, green light, or blue light.
According to the technical scheme provided by the embodiment, the injection and transmission capability (or transmission rate) of the current carrier at the corresponding side of the light-emitting layer is adjusted by arranging the current carrier regulation and control layer formed by blending the hole transmission material and the electron transmission material on the surface of at least one side of the light-emitting layer, so that the difference between the injection and transmission capability of the hole and the injection and transmission capability of the electron is reduced, the number of the hole and the electron reaching the light-emitting layer is balanced, the phenomenon that the surplus current carrier is quenched with excitons in the light-emitting layer is avoided, the light-emitting efficiency of the light-emitting device is effectively improved, and the; meanwhile, quenching of excitons is avoided, non-radiative energy is prevented from being generated, and heat generated by the light-emitting device is reduced, so that the service life of the light-emitting device is prolonged. Moreover, for light emitting devices with different structures, the technical scheme provided by the embodiment of the invention can balance the transmission of holes and electrons in the light emitting device only by adjusting the mixing ratio (such as mass ratio) of the hole transmission material and the electron transmission material in the carrier regulation layer, solves the problem of limited selection of the carrier blocking material and the main material of the light emitting layer, increases the selection space of the carrier blocking material and the main material of the light emitting layer, and reduces the manufacturing cost of the light emitting device.
Alternatively, in the above embodiments, the hole transport material may include 4,4',4 ″ -tris (carbazol-9-yl) triphenylamine (TCTA), 1, 3-dicarbazol-9-ylbenzene (mCP), or 4,4' -bis (9-Carbazol) Biphenyl (CBP); the electron transport material may comprise 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene (TPBi) or 4, 6-bis (3, 5-bis (3-pyrid) ylphenyl) -2-methylpyrimidine (B)3PYMPM). The hole transport material and the electron transport material in this embodiment are not limited, and may be any of the hole transport materials and the electron transport materials that are conventionally used.
Optionally, the mass ratio of the hole transport material to the electron transport material is from 1:9 to 9: 1. Thus, by setting the mass ratio of the hole transport material to the electron transport material to 1:9 to 9:1, the transport of holes and electrons can be effectively balanced. Preferably, the mass ratio of the hole transport material to the electron transport material is 3:7 to 7:3, so as to be suitable for a mixed arrangement of a common hole transport material and an electron transport material, wherein the common hole transport material and the electron transport material can be the specific hole transport material and the specific electron transport material.
Specifically, when the carrier control layer includes a hole control layer, the proportion of the first electron transport material should be not greater than the proportion of the first hole transport material in order to ensure the number of holes provided while limiting the injection transport capability of holes, and at this time, the mass ratio of the first hole transport material to the first electron transport material is 1:1 to 9:1, preferably 1:1 to 7: 3. When the carrier control layer comprises an electron control layer, the proportion of the second hole transport material is not more than the proportion of the second electron transport material to ensure the quantity of the provided electrons while limiting the injection transport capability of the electrons, and at this time, the mass ratio of the second hole transport material to the second electron transport material is 1:9-1:1, preferably 3:7-1: 1.
Generally, for a light emitting device with the same structure, if a hole transport material is different from an electron transport material, the mass ratio of the hole transport material to the electron transport material is also different; however, for light emitting devices of different structures, even if the hole transport material is the same as the electron transport material, the mass ratio of the hole transport material to the electron transport material in the different structures may be different. Therefore, the specific mass ratio of the hole transport material to the electron transport material in the carrier control layer should be determined depending on the actual situation.
In one embodiment of the present invention, a scheme for determining a mass ratio of a hole transport material to an electron transport material in a carrier control layer is devised. This embodiment will be described by taking a case where the carrier control layer includes a hole control layer as an example. The present embodiment provides a single electron transport device and a single hole transport device. As shown in fig. 4, the single electron transport device includes a first anode 11, a first mixed layer 201 including a mixed material of an electron transport material and an electron injection material, a first light emitting layer 211, a first electron transport layer 202, a first electron injection layer 203, and a first cathode 31, which are sequentially stacked. As shown in fig. 5, the single hole transport device includes a second anode 12, a first hole injection layer 204, a first hole transport layer 205, a hole regulation layer 221, a second light emitting layer 212, a second mixed layer 206, and a second cathode 32, which are sequentially stacked, wherein the second mixed layer 206 includes a mixed material of a hole transport material and a hole injection material. Specifically, this embodiment designs the single electron transport device and the single hole transport device according to the structure of the actually required light emitting device, the first anode 11 and the second anode 12 are anodes in the required light emitting device, the first cathode 31 and the second cathode 32 are cathodes in the required light emitting device, the first light emitting layer 211 and the second light emitting layer 212 are light emitting layers in the required light emitting device, and the first electron transport layer 202, the first electron injection layer 203, the first hole injection layer 204, and the first hole transport layer 205 are an electron transport layer, an electron injection layer, a hole injection layer, and a hole transport layer in the required light emitting device, respectively. Based on the method, a first current density-voltage curve of the single electron transmission device is measured; then testing a second current density-voltage curve of the single-hole transmission device, comparing the second current density-voltage curve with the first current density-voltage curve, and adjusting the mass ratio of the first hole transmission material to the first electron transmission material in the hole control layer 221 to enable the second current density-voltage curve to be close to the first current density-voltage curve, so as to determine a better range of the mass ratio of the first hole transmission material to the first electron transmission material; and finally, in the preferable range of the mass ratio, keeping the mass of one of the first hole transport material and the first electron transport material unchanged, adjusting the mass of the other one of the first hole transport material and the first electron transport material within the range of 10 percent from top to bottom, applying the adjusted hole regulation and control layer to a required light-emitting device, and determining the light-emitting device with the optimal performance by comparing the luminous efficiency, the efficiency roll-off or the service life. Therefore, the mass ratio of the hole transport material to the electron transport material in the carrier control layer is determined through the design scheme, so that the effect of balancing hole and electron transport is optimal.
It should be noted that fig. 4 and fig. 5 are only schematic illustrations, and the film layer structures of the actual single electron transport device and the actual single hole transport device are designed according to the film layer structure of the desired light emitting device, for example, when there is no hole injection layer in the desired light emitting device, the first hole injection layer 204 does not need to be disposed in the single hole transport device, and when there is no electron injection layer in the desired light emitting device, the first electron injection layer 203 does not need to be disposed in the single electron transport device. In addition, the thickness of the carrier control layer obtained by the above design is 30 to 200 angstroms.
Alternatively, based on the above-described embodiments, in another embodiment of the present invention, the LUMO level of the carrier-regulating layer is higher than the LUMO level of the host material in the light-emitting layer, or the HOMO level of the carrier-regulating layer is higher than the HOMO level of the host material in the light-emitting layer, so that carriers reaching the light-emitting layer are prevented from being transported further to the anode or the cathode through the light-emitting layer.
Illustratively, as shown in fig. 6, the carrier regulating layer 22 includes a hole regulating layer 221, the hole regulating layer 221 is located on a surface of the light emitting layer 21 on a side close to the anode 10, and the hole regulating layer 221 includes a mixed material of a first hole transporting material and a first electron transporting material. Wherein the LUMO level of the hole-regulating layer 221 is higher than the LUMO level of the host material in the light-emitting layer 21.
In the present embodiment, the host material in the light-emitting layer 21 may include CBP, Alq3, mCBP, Bepp2, and the like. By setting the LUMO level of the hole control layer 221 to be higher than the LUMO level of the host material in the light emitting layer 21, a barrier for blocking electron transmission is formed between the hole control layer 221 and the light emitting layer 21, electrons reaching the light emitting layer 21 can be limited in the light emitting layer 21, and on the basis of balancing the number of holes and electrons reaching the light emitting layer 21, the electrons reaching the light emitting layer can be ensured to be combined with the holes, so that the light emitting efficiency of the light emitting device is further improved. Preferably, the difference between the LUMO level of the hole regulating layer and the LUMO level of the host material is greater than 0.2eV, thereby effectively confining electrons in the light emitting layer 21. Illustratively, the first hole transporting material is mCP having a LUMO level of-2.4 eV, the first electron transporting material is TPBi having a LUMO level of-2.4 eV, and the host material is CBP having a LUMO level of-2.9 eV.
In addition, optionally, the light-emitting device further includes a hole injection layer 23 and a hole transport layer 24 between the hole regulation layer 221 and the anode 10, and the hole transport layer 24 is located on the surface of the hole injection layer 23 on the side close to the hole regulation layer 221. The inventors have found that, if the hole control layer 221 is formed by directly doping the first electron transport material in the hole transport layer 24 of the light emitting device, a large injection barrier is formed between the hole injection layer 23 and the hole control layer 221, and holes are difficult to inject into the hole control layer 221, which causes an "overshoot" problem for holes, and not only does not play a role in balancing hole and electron transport, but also greatly reduces the number of holes reaching the light emitting layer, so that the light emitting efficiency of the light emitting device is lower than that of the conventional light emitting device. Therefore, in this embodiment, the number of holes reaching the light-emitting layer is ensured by separately providing a hole control layer 221 on the side of the hole transport layer 24 close to the light-emitting layer 21 to reduce the injection barrier from the hole injection layer 23 to the hole control layer 221.
Illustratively, as shown in fig. 7, the carrier regulation layer 22 includes an electron regulation layer 222, the electron regulation layer 222 is located on a surface of the light-emitting layer 21 on a side close to the cathode 30, and the electron regulation layer 222 includes a mixed material of a second hole transport material and a second electron transport material. Wherein the HOMO level of the electron-regulating layer is higher than the HOMO level of the host material in the light-emitting layer.
In this embodiment, by setting the HOMO energy level of the electron regulation layer 222 to be higher than the HOMO energy level of the host material in the light emitting layer 21, a barrier for blocking hole transmission is formed between the electron regulation layer 222 and the light emitting layer 21, so that holes reaching the light emitting layer 21 can be limited in the light emitting layer 21, and on the basis of balancing the number of holes and electrons reaching the light emitting layer 21, the holes reaching the light emitting layer can be ensured to be combined with electrons, thereby further improving the light emitting efficiency of the light emitting device. Preferably, the difference between the HOMO level of the electron regulation layer and the HOMO level of the host material is greater than 0.2eV, thereby effectively confining holes in the light emitting layer 21.
In addition, optionally, the light-emitting device further includes an electron injection layer 25 and an electron transport layer 26 between the electron regulation layer 222 and the cathode 30, and the electron transport layer 26 is located on a surface of the electron injection layer 25 close to the electron regulation layer 222. Similarly, in the present embodiment, by separately providing the electron control layer 222 on the side of the electron transport layer 26 close to the light emitting layer 21, the number of transported electrons can be prevented from being excessively reduced, and the number of electrons reaching the light emitting layer can be ensured.
Illustratively, as shown in fig. 8, the structure shown in fig. 8 is different from the structures shown in fig. 6 and 7 in that, in fig. 8, the carrier regulation layer 22 includes a hole regulation layer 221 and an electron regulation layer 222, and the LUMO level of the hole regulation layer 221 is higher than the LUMO level of the host material in the light emitting layer 21, and the HOMO level of the electron regulation layer is higher than the HOMO level of the host material in the light emitting layer, whereby both holes and electrons reaching the light emitting layer 21 can be confined in the light emitting layer 21, so that the holes and electrons in the light emitting layer 21 are completely recombined, thereby further improving the light emitting efficiency of the light emitting device.
Alternatively, on the basis of the above embodiments, in a further embodiment of the present invention, the excited state energy level of the carrier regulation layer is higher than the excited state energy level of the host material in the light emitting layer. In this embodiment, holes and electrons in the light emitting layer are combined to form excited excitons, and since the excited state energy level of the carrier control layer is higher than the excited state energy level of the host material in the light emitting layer, the excitons on the excited state energy level of the host material cannot jump to the excited state energy level of the carrier control layer, so that the excitons are limited in the light emitting layer, thereby preventing the excitons from passing through the light emitting layer to be quenched, solving the problem of energy return, and improving the light emitting efficiency of the light emitting device.
Optionally, the excited state energy level comprises a singlet state energy level and/or a triplet state energy level. Generally, excitons in an excited state in the light emitting layer are singlet excitons and triplet excitons, and thus, setting the singlet energy level and/or triplet energy level of the carrier regulating layer higher than that of the host material in the light emitting layer can confine most of the excitons in the light emitting layer, ensuring the light emitting efficiency of the light emitting device.
In addition, the embodiment of the invention also provides a display panel, and the display panel comprises the light-emitting device provided by any embodiment of the invention.
The display panel provided by the embodiment of the invention can be applied to display equipment with a display function, such as mobile phones, computers, intelligent wearable equipment and the like, and the embodiment of the invention is not limited to the display equipment.
The display panel provided by the embodiment of the invention comprises the light-emitting device provided by the embodiment of the invention, has the same functions and effects, and is not described again here.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A light-emitting device is characterized by comprising an anode, a cathode, a light-emitting layer and a carrier regulation layer, wherein the light-emitting layer and the carrier regulation layer are positioned between the anode and the cathode;
wherein the carrier regulation layer comprises a mixed material of a hole transport material and an electron transport material.
2. The light-emitting device according to claim 1, wherein the hole-transporting material comprises 4,4',4 ″ -tris (carbazol-9-yl) triphenylamine, 1, 3-dicarbazol-9-ylbenzene, or 4,4' -bis (9-carbazol) biphenyl; the electron transport material comprises 1,3, 5-tri (1-phenyl-1H-benzimidazol-2-yl) benzene or 4, 6-bis (3, 5-di (3-pyridyl) phenylphenyl) -2-methylpyrimidine.
3. The light-emitting device according to claim 1, wherein a mass ratio of the hole transport material to the electron transport material is 1:9 to 9: 1;
preferably, the mass ratio of the hole transport material to the electron transport material is from 3:7 to 7: 3.
4. The light-emitting device according to claim 1, wherein the carrier control layer comprises a hole control layer on a surface of the light-emitting layer on a side close to the anode, and wherein the hole control layer comprises a mixed material of a first hole-transporting material and a first electron-transporting material.
5. The light-emitting device according to claim 4, wherein the LUMO level of the hole-regulating layer is higher than the LUMO level of the host material in the light-emitting layer;
preferably, the difference between the LUMO level of the hole-regulating layer and the LUMO level of the host material is greater than 0.2 eV;
preferably, the light-emitting device further includes a hole injection layer and a hole transport layer between the hole control layer and the anode, and the hole transport layer is located on the surface of the hole injection layer on the side close to the hole control layer.
6. The light-emitting device according to claim 1, 4 or 5, wherein the carrier adjusting layer comprises an electron adjusting layer on a surface of the light-emitting layer on a side close to the cathode, and wherein the electron adjusting layer comprises a mixed material of a second hole-transporting material and a second electron-transporting material.
7. The light-emitting device according to claim 6, wherein the HOMO level of the electron-regulating layer is higher than that of the host material in the light-emitting layer;
preferably, the difference between the HOMO level of the electron-regulating layer and the HOMO level of the host material is greater than 0.2 eV;
preferably, the light-emitting device further comprises an electron injection layer and an electron transport layer, which are located between the electron regulation layer and the cathode, and the electron transport layer is located on the surface of the electron injection layer on the side close to the electron regulation layer.
8. The light-emitting device according to claim 1, wherein an excited state energy level of the carrier regulation layer is higher than an excited state energy level of a host material in the light-emitting layer.
9. The light-emitting device according to claim 8, wherein the excited state level comprises a singlet state level and/or a triplet state level.
10. A display panel comprising the light-emitting device according to any one of claims 1 to 9.
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| CN201910989460.4A CN110707227A (en) | 2019-10-17 | 2019-10-17 | Light-emitting device and display panel |
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Application publication date: 20200117 |