CN114039006A - Light emitting device and display device - Google Patents
Light emitting device and display device Download PDFInfo
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- CN114039006A CN114039006A CN202111322479.7A CN202111322479A CN114039006A CN 114039006 A CN114039006 A CN 114039006A CN 202111322479 A CN202111322479 A CN 202111322479A CN 114039006 A CN114039006 A CN 114039006A
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- H10K50/00—Organic light-emitting devices
- H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
- H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
- H10K50/12—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers comprising dopants
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- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
- H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
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- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/10—OLED displays
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Abstract
The embodiment of the invention relates to the technical field of display, and discloses a light-emitting device and a display device. In the present invention, a light emitting device includes: the first electrode and the second electrode are oppositely arranged; a light emitting layer disposed between a first electrode and a second electrode, the light emitting layer including a first surface facing the first electrode and a second surface facing the second electrode; the light-emitting layer comprises a first host material, a first guest material and a second guest material; in a direction along the first electrode toward the second electrode, the doping concentration of the first guest material in the light emitting layer gradually decreases, and the doping concentration of the second guest material in the light emitting layer gradually increases. The light-emitting device and the display device provided by the invention can reduce the driving voltage of the light-emitting device, improve the light-emitting efficiency of the light-emitting device and prolong the service life of the light-emitting device.
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 device.
Background
With the development of Display technology, Organic Light Emitting Diode (OLED) Display panels gradually enter the market, and compared with conventional Thin Film transistor liquid Crystal Display (TFT LCD), the OLED Display panels have the advantages of low energy consumption, self-luminescence, wide viewing angle, fast response speed, and easy application to flexible Display technology. In the related art, the light emitting device in the OLED display panel generally forms a light emitting layer by doping a guest light emitting material in a host material.
The inventor finds that at least the following problems exist in the prior art: the light emitting device in the related art has a high driving voltage, resulting in low light emitting efficiency and a short service life of the light emitting device.
Disclosure of Invention
An object of embodiments of the present invention is to provide a light emitting device and a display device, which can reduce a driving voltage of the light emitting device, improve light emitting efficiency of the light emitting device, and extend a service life of the light emitting device.
To solve the above technical problem, an embodiment of the present invention provides a light emitting device including: the first electrode and the second electrode are oppositely arranged; a light emitting layer disposed between a first electrode and a second electrode, the light emitting layer including a first surface facing the first electrode and a second surface facing the second electrode; the light-emitting layer comprises a first host material, a first guest material and a second guest material; in a direction along the first electrode toward the second electrode, the doping concentration of the first guest material in the light emitting layer gradually decreases, and the doping concentration of the second guest material in the light emitting layer gradually increases.
An embodiment of the present invention also provides a display device including: such as the light emitting device described above.
Compared with the prior art, in the embodiment of the invention, since the light emitting layer includes the first guest material and the second guest material, the first guest material is an electron-bias type light emitting material, the second guest material is a hole-bias type light emitting material, and in the direction from the first surface to the second surface, the doping concentration of the first guest material in the light emitting layer gradually decreases, and the doping concentration of the second guest material in the light emitting layer gradually increases, that is, by being close to the first electrode, the doping concentration of the first guest material is higher, and the doping concentration of the second guest material is lower, so that the injection of electrons (or holes) is increased by the first guest material at the side close to the first electrode, and the injection of electrons (or holes) is not affected by the second guest material at the side close to the second electrode, the doping concentration of the second object material is high, and the doping concentration of the first object material is low, so that hole (or electron) injection is increased in the second object material at the side close to the second electrode, and the hole (or electron) injection cannot be influenced by the first object material, so that the carrier injection capacity is improved, the driving voltage of the light-emitting device is reduced, the light-emitting efficiency of the light-emitting device is improved, and the service life of the light-emitting device is prolonged.
In addition, in the light-emitting layer, a ratio of a maximum doping concentration of the first guest material to a minimum doping concentration of the first guest material is greater than or equal to 2; and/or, in the light emitting layer, a ratio of a maximum doping concentration of the second guest material to a minimum doping concentration of the second guest material is greater than or equal to 2.
In addition, the light emitting layer includes a first region near the first surface, and a second region near the second surface; in the first region, the doping concentration of the first guest material in the light emitting layer is greater than the doping concentration of the second guest material in the light emitting layer; in the second region, the doping concentration of the second guest material in the light emitting layer is greater than the doping concentration of the first guest material in the light emitting layer.
In addition, the light-emitting layer further comprises a second main body material, the first main body material is an electron-type main body material, the second main body material is a hole-type main body material, and the first main body material and the second main body material are uniformly distributed in the light-emitting layer. The organic light-emitting device comprises the hole type main body material and the electron type main body material, so that current carriers can be balanced, the light-emitting efficiency of the organic light-emitting device is improved, and the driving voltage of the light-emitting device is reduced.
In addition, the first electrode is arranged as a cathode layer, and the second electrode is arranged as an anode layer; the first guest material is a partial electron type luminescent material, and the second guest material is a partial hole type luminescent material.
In addition, the light-emitting layer further comprises a second host material, the first host material is an electron-type host material, and the second host material is a hole-type host material; the light emitting layer includes a first region adjacent to the first surface, and a second region adjacent to the second surface; in the first region, the doping concentration of the first host material in the light-emitting layer is greater than that of the second host material in the light-emitting layer; in the second region, the doping concentration of the second host material in the light emitting layer is greater than the doping concentration of the first host material in the light emitting layer. The doping concentration of the second main material at the side close to the second electrode is higher, so that the transmission of holes to the light-emitting layer is favorably realized, the charge accumulation of the first area of the light-emitting layer is favorably improved, the exciton recombination area is widened, the exciton quenching probability under large current is reduced, the exciton utilization efficiency is favorably improved, and the light-emitting efficiency of the light-emitting device is favorably improved; meanwhile, the doping concentration of the first main body material at the side close to the first electrode is higher, so that the holes can be effectively prevented from being continuously transmitted to the first electrode, the problems of quenching effect and color purity caused by the holes are solved, the damage effect of the holes on the interface of a relevant film layer between the light-emitting layer and the cathode is reduced, and the service life of the light-emitting device is prolonged while the light-emitting efficiency of the light-emitting device is improved.
In addition, an energy level difference of a highest occupied molecular orbital level of the second guest material and a highest occupied molecular orbital level of the first host material is less than or equal to 0.2 eV; and/or the energy level difference between the highest occupied molecular orbital level of the second host material and the highest occupied molecular orbital level of the first guest material is less than or equal to 0.2 eV. The HOMO energy level difference between the second guest material and the first host material is smaller, so that holes can be freely transmitted in the luminescent layer, the exciton composite area is widened, the possibility of exciton quenching under high current density is reduced, and the luminescent efficiency of the luminescent device is improved; by making the HOMO level difference between the second host material and the first guest material smaller, electrons can be more freely transmitted in the light emitting layer, thereby widening the exciton recombination region, and reducing the possibility of exciton quenching under high current density, thereby being beneficial to improving the light emitting efficiency of the light emitting device.
In addition, an energy level difference of a highest occupied molecular orbital level of the second guest material and a highest occupied molecular orbital level of the first host material is less than or equal to 0.2 eV; and/or the energy level difference between the highest occupied molecular orbital level of the first host material and the highest occupied molecular orbital level of the first guest material is less than or equal to 0.2 eV. The HOMO energy level difference between the second guest material and the first host material is smaller, so that holes can be freely transmitted in the luminescent layer, the exciton composite area is widened, the possibility of exciton quenching under high current density is reduced, and the luminescent efficiency of the luminescent device is improved; by making the HOMO level difference between the first host material and the first guest material smaller, electrons can be more freely transmitted in the light emitting layer, thereby widening the exciton recombination region, and reducing the possibility of exciton quenching under high current density, thereby being beneficial to improving the light emitting efficiency of the light emitting device.
In addition, the sum of the doping concentration of the first guest material and the doping concentration of the second guest material is less than or equal to 30%. By the arrangement, on one hand, more holes and electrons can be ensured to freely enter the light-emitting layer, and the exciton recombination efficiency of the light-emitting device can be improved; on the other hand, excessive holes and electrons cannot enter the light-emitting layer, so that the phenomenon that the excessive holes are continuously transmitted to the first electrode side or the excessive electrons are continuously transmitted to the second electrode side and have adverse effects on the design of a subsequent film layer is avoided, the longer service life of the device is ensured, and the film layer optimization design of the light-emitting device is facilitated.
Drawings
One or more embodiments are illustrated by way of example in the accompanying drawings, which correspond to the figures in which like reference numerals refer to similar elements and which are not to scale unless otherwise specified.
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 graph comparing the light emitting efficiency of the light emitting device provided in this embodiment mode with that of a light emitting device doped with only one guest material.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, it will be appreciated by those of ordinary skill in the art that numerous technical details are set forth in order to provide a better understanding of the present application in various embodiments of the present invention. However, the technical solution claimed in the present application can be implemented without these technical details and various changes and modifications based on the following embodiments.
The inventors found that, due to poor conductivity of the guest light emitting material in the light emitting layer and the presence of carrier trapping in the related art, the driving voltage of the light emitting device is high, the light emitting efficiency of the light emitting device is low, and the service life is short.
A first embodiment of the present invention relates to a light emitting device, as shown in fig. 1 and 2, including: the organic light emitting diode comprises a first electrode 11, a second electrode 12 and a light emitting layer 13, wherein the second electrode 12 is arranged opposite to the first electrode 11, and the light emitting layer 13 is positioned between the first electrode 11 and the second electrode 12. The light-emitting layer 13 includes a first host material 131a, a first guest material 132a, and a second guest material 132 b.
The light-emitting layer 13 includes a first surface 133 facing the first electrode 11 and a second surface 134 disposed opposite to the first surface, and the doping concentration of the first guest material 132a in the light-emitting layer 13 is gradually decreased and the doping concentration of the second guest material 132b in the light-emitting layer 13 is gradually increased along a direction X in which the first surface 133 is directed to the second surface 134.
That is, by making the doping concentration of the first guest material 132a larger, the doping concentration of the second guest material 132b smaller, so that the first guest material 132a increases electron (or hole) injection at a side close to the first electrode 11 and the second guest material 132b does not affect the electron (or hole) injection, by making the doping concentration of the second guest material 132b larger, the doping concentration of the first guest material 132a smaller, so that the hole (or electron) injection is increased by the second guest material 132b at the side close to the second electrode 12 and the hole (or electron) injection is not affected by the first guest material 132a, thereby improving the carrier injection capability, and further, the driving voltage of the light-emitting device is reduced, the light-emitting efficiency of the light-emitting device is improved, and the service life of the light-emitting device is prolonged.
In this embodiment, the first electrode 11 may be configured as a cathode layer, the second electrode 12 may be configured as an anode layer, the first guest material 132a may be a biased electron type light emitting material, and the second guest material 132b may be a biased hole type light emitting material. By the doping concentration of the first guest material 132a being higher and the doping concentration of the second guest material 132b being lower on the side close to the first electrode 11, the electron injection is increased by the first guest material 132a on the side close to the first electrode 11 and the electron injection is not affected by the second guest material 132b, and by the doping concentration of the second guest material 132b being higher and the doping concentration of the first guest material 132a being lower on the side close to the second electrode 12, the hole injection is increased by the second guest material 132b on the side close to the second electrode 12 and the hole injection is not affected by the first guest material 132 a.
In practical applications, the doping concentrations of the first guest material 132a and the second guest material 132b in different regions in the light emitting layer can be changed by controlling the size of the opening of the angle limiting plate used by the evaporation source of the first guest material 132a and the evaporation source of the second guest material 132b when evaporating different regions.
The emission color of the first guest material 132a and the emission color of the second guest material 132b may be the same or different. For example, the emission color of the first guest material 132a and the emission color of the second guest material 132b may be both red, green, or blue, so that the light-emitting layer 13 exhibits red, green, or blue; alternatively, the emission color of the first guest material 132a and the emission color of the second guest material 132b are red and yellow, respectively, so that the light-emitting layer 13 appears orange.
The "partial hole type light-emitting material" refers to a light-emitting material in which hole mobility is higher than electron mobility or hole injection capability is higher than electron injection capability; "light-emitting material of the electron bias type" means a light-emitting material having an electron mobility larger than a hole mobility or an electron injecting ability larger than a hole injecting ability.
The "doping concentration of the first guest material 132 a/the second guest material 132 b" means a ratio of the volume of the first guest material 132 a/the second guest material 132b to the total volume of the light-emitting layer 13 at the time of vapor deposition, that is, the doping concentration of the first guest material 132a is 100% of the volume of the first guest material 132 a/the total volume of the light-emitting layer 13, and the doping concentration of the second guest material 132b is 100% of the volume of the second guest material 132 b/the total volume of the light-emitting layer 13. That is, the doping concentration of the first guest material 132a is a volume ratio of the first guest material 132a in the light-emitting layer 13 per unit volume, and the doping concentration of the second guest material 132b is a volume ratio of the second guest material 132b in the light-emitting layer 13 per unit volume.
In practical applications, the light emitting device may further include: a hole blocking layer 14(HBL) between the light emitting layer 13(EML) and the first electrode 11(Cathode), an electron transport layer 15(ETL) between the hole blocking layer 14 and the first electrode 11, an electron injection layer 16(EIL) between the electron transport layer 15 and the first electrode 11, an electron blocking layer 17(EBL) between the light emitting layer 13 and the second electrode 12, a hole transport layer 18(HTL) between the electron blocking layer 17 and the second electrode 12, and a hole injection layer 19(HIL) between the hole transport layer 18 and the second electrode 12. That is, the first surface 133 is a contact interface of the light emitting layer 13(EML) and the hole blocking layer 14(HBL), and the second surface 134 is a contact interface of the light emitting layer 13(EML) and the electron blocking layer 17 (EBL).
In order to further improve the carrier injection capability, in the present embodiment, in the light emitting layer 13, the ratio of the maximum doping concentration of the first guest material 132a to the minimum doping concentration of the first guest material 132a is greater than or equal to 2, and/or, in the light emitting layer 13, the ratio of the maximum doping concentration of the second guest material 132b to the minimum doping concentration of the second guest material 132b is greater than or equal to 2.
It is understood that the doping concentration of the first guest material 132a at the interface of the light emitting layer 13 and the hole blocking layer 14 is the maximum doping concentration of the first guest material 132a, and the doping concentration of the first guest material 132a at the interface of the light emitting layer 13 and the electron blocking layer 17 is the minimum doping concentration of the first guest material 132 a; the doping concentration at the interface of the light-emitting layer 13 and the electron blocking layer 17 is the maximum doping concentration of the second guest material 132b, and the doping concentration of the second guest material 132b at the interface of the light-emitting layer 13 and the hole blocking layer 14 is the minimum doping concentration of the second guest material 132 b.
Optionally, the light-emitting layer 13 includes a first region near the first surface 133 where the doping concentration of the first guest material 132a in the light-emitting layer 13 is greater than the doping concentration of the second guest material 132b in the light-emitting layer 13, and a second region near the second surface 134 where the doping concentration of the second guest material 132b in the light-emitting layer 13 is greater than the doping concentration of the first guest material 132a in the light-emitting layer 13.
The host material and the guest material of the light-emitting layer 13 will be specifically described below with reference to the drawings:
fig. 1 is a schematic structural diagram of a light-emitting device provided in this embodiment, and referring to fig. 1, a light-emitting layer 13 has a structure of dual hosts and dual guests.
Specifically, the light-emitting layer 13 further includes a second host material 131b, that is, the light-emitting layer 13 includes a first host material 131a, a second host material 131b, a first guest material 132a and a second guest material 132b, the first host material 131a is an electron type host material, the second host material 131b is a hole type host material, the first guest material 132a is a biased electron type light-emitting material, and the second guest material 132b is a biased hole type light-emitting material, and the light-emitting layer 13 includes both the hole type host material and the electron type host material, so that carriers can be balanced, the light-emitting efficiency of the organic light-emitting device can be improved, and the driving voltage of the light-emitting device can be reduced.
Here, the "hole type host material" refers to a material having a hole mobility greater than an electron mobility or having a hole injection capability greater than an electron injection capability, and the "electron type host material" refers to a material having an electron mobility greater than a hole mobility or having an electron injection capability greater than a hole injection capability. That is, hole transport is fast and electron transport is slow in a hole-type host material; the hole transport in the electronic host material is slow, while the electron transport is fast. For example, the hole-type host material may be CBP and the electron-type host material may be BAlq.
Further, the first host material 131a and the second host material 131b can be uniformly distributed in the light-emitting layer 13, and in practical applications, the first host material 131a and the second host material 131b can be pre-mixed and then evaporated, that is, the first host material 131a and the second host material 131b are mixed in advance to form a host material evaporation source, so that the number of evaporation sources can be reduced, the complexity and cost of evaporation equipment can be reduced, the difficulty of an evaporation process can be reduced, the ratio of the first host material 131a to the second host material 131b can be easily controlled, and the problem of ratio imbalance can be avoided.
Of course, the first host material 131a and the second host material 131b may be unevenly distributed in the light-emitting layer 13, for example, in the first region, the doping concentration of the first host material 131a in the light-emitting layer 13 is higher than the doping concentration of the second host material 131b in the light-emitting layer 13, in the second region, the doping concentration of the second host material 131b in the light-emitting layer 13 is higher than the doping concentration of the first host material 131a in the light-emitting layer 13, that is, the first host material 131a and the second host material 131b are respectively evaporated by using the first evaporation source and the second evaporation source, and the doping concentrations of the first host material 131a and the second host material 131b in different regions in the light-emitting layer are changed by controlling the size of the opening of the angle limiting plate used for the first evaporation source and the second evaporation source when evaporating different regions.
The doping concentration of the second main material 131b on the side close to the second electrode 12 is higher, which is beneficial to realizing the transmission of holes to the light-emitting layer 13, thereby being beneficial to improving the charge accumulation of the first region of the light-emitting layer 13, widening the exciton recombination region, reducing the exciton quenching probability under large current, being beneficial to improving the exciton utilization efficiency, and being beneficial to improving the light-emitting efficiency of the light-emitting device; meanwhile, the doping concentration of the first main body material 131a on the side close to the first electrode 11 is higher, so that holes can be effectively prevented from being continuously transmitted to the first electrode 11, the problems of quenching effect and color purity caused by the holes are solved, the destructive effect of the holes on the interface of the relevant film layer between the light-emitting layer 13 and the cathode is reduced, and the light-emitting efficiency of the light-emitting device is improved while the service life of the light-emitting device is prolonged.
Alternatively, the difference in the Highest Occupied Molecular Orbital (HOMO) level of the second guest material 132b and the Highest Occupied Molecular orbital level of the first host material 131a may be less than or equal to 0.2eV (electron volt), and/or the difference in the Highest Occupied Molecular orbital level of the second host material 131b and the Highest Occupied Molecular orbital level of the first guest material 132a may be less than or equal to 0.2 eV. That is, the difference between the HOMO level of the second guest material 132b minus the HOMO level of the first host material 131a is less than or equal to 0.2eV (note that the difference may be less than 0), and/or the difference between the HOMO level of the second host material 131b minus the HOMO level of the first guest material 132a is less than or equal to 0.2eV (note that the difference may be less than 0).
By making the HOMO level difference between the second guest material 132b and the first host material 131a smaller, holes can be more freely transmitted in the light-emitting layer 13, thereby widening the exciton recombination region and reducing the possibility of exciton quenching under a large current density, which is beneficial to improving the light-emitting efficiency of the light-emitting device; by making the HOMO level difference between the second host material 131b and the first guest material 132a smaller, electrons can be more freely transmitted in the light emitting layer 13, thereby widening the exciton recombination region, and reducing the possibility of exciton quenching under a large current density, which is beneficial to improving the light emitting efficiency of the light emitting device.
Fig. 2 is a schematic structural diagram of a light-emitting device provided in this embodiment, and referring to fig. 2, a light-emitting layer 13 has a single-host and dual-guest structure. At this time, the first host material 131a is a material having hole mobility and electron mobility in the same order of magnitude, and the hole injection capability and the electron injection capability are substantially equivalent.
Specifically, the energy level difference of the highest occupied molecular orbital level of the second guest material 132b and the highest occupied molecular orbital level of the first host material 131a is less than or equal to 0.2eV, and/or the energy level difference of the highest occupied molecular orbital level of the first host material 131a and the highest occupied molecular orbital level of the first guest material 132a is less than or equal to 0.2 eV. That is, the difference between the HOMO level of the second guest material 132b minus the HOMO level of the first host material 131a is less than or equal to 0.2eV (note that the difference may be less than 0), and/or the difference between the HOMO level of the first host material 131a minus the HOMO level of the first guest material 132a is less than or equal to 0.2eV (note that the difference may be less than 0).
By making the HOMO level difference between the second guest material 132b and the first host material 131a smaller, holes can be more freely transmitted in the light-emitting layer 13, thereby widening the exciton recombination region and reducing the possibility of exciton quenching under a large current density, which is beneficial to improving the light-emitting efficiency of the light-emitting device; by making the HOMO level difference between the first host material 131a and the first guest material 132a smaller, electrons can be more freely transmitted in the light emitting layer 13, thereby widening the exciton recombination region, and reducing the possibility of exciton quenching under a large current density, which is beneficial to improving the light emitting efficiency of the light emitting device.
In practical applications, the sum of the doping concentration (volume ratio) of the first guest material 132a and the doping concentration (volume ratio) of the second guest material 132b is less than or equal to 30%, so that on one hand, more holes and electrons can be ensured to freely enter the light-emitting layer 13, which is beneficial to improving the exciton recombination efficiency of the light-emitting device; on the other hand, excessive holes and electrons do not enter the light-emitting layer 13, so that the excessive holes are prevented from being continuously transmitted to the first electrode 11 side or the excessive electrons are prevented from being continuously transmitted to the second electrode 12 side, the design of a subsequent film layer is adversely affected, the long service life of the device is ensured, and the film layer optimization design of the light-emitting device is facilitated.
As shown in fig. 3, fig. 3 is a graph comparing the luminous efficiency of the light-emitting device provided in this embodiment mode with that of a light-emitting device doped with only one guest material.
In this embodiment, a curve 1 is a graph of a change in luminous efficiency of the light-emitting device according to the current density, and a curve 2 is a graph of a change in luminous efficiency of the light-emitting device doped with only one guest material according to the current density, both of which are schematic diagrams of emitting green light. As can be seen from the figure, the efficiency of the light-emitting device provided in this embodiment mode is improved by about 20% compared with the efficiency of the light-emitting device doped with only one guest material.
Compared with the prior art, in the embodiment of the invention, the first guest material 132a is a biased electron type light emitting material, the doping concentration of the first guest material 132a is higher and the doping concentration of the second guest material 132b is lower on the side close to the first electrode 11, so that the electron injection is increased by the first guest material 132a on the side close to the first electrode 11, and the electron injection is not influenced by the second guest material 132b, and the hole injection is increased by the second guest material 132b on the side close to the second electrode 12, and the hole injection is not influenced by the first guest material 132a by the second guest material 132b being a biased hole type light emitting material, so that the carrier injection capability is improved, and the driving voltage of the light emitting device is reduced, the luminous efficiency of the light-emitting device is improved, and the service life of the light-emitting device is prolonged.
The invention also provides a display device which comprises the light-emitting device and a driving circuit for controlling the light-emitting device to work. The related technical details mentioned in the foregoing light emitting device are still valid here, and are not described here again in order to reduce repetition.
It will be understood by those of ordinary skill in the art that the foregoing embodiments are specific examples for carrying out the invention, and that various changes in form and details may be made therein without departing from the spirit and scope of the invention in practice.
Claims (10)
1. A light emitting device, comprising:
the first electrode and the second electrode are oppositely arranged;
a light emitting layer disposed between a first electrode and a second electrode, the light emitting layer including a first surface facing the first electrode and a second surface facing the second electrode;
the light-emitting layer comprises a first host material, a first guest material and a second guest material;
in a direction along the first electrode toward the second electrode, the doping concentration of the first guest material in the light emitting layer gradually decreases, and the doping concentration of the second guest material in the light emitting layer gradually increases.
2. The light-emitting device according to claim 1, wherein in the light-emitting layer, a ratio of a maximum doping concentration of the first guest material to a minimum doping concentration of the first guest material is greater than or equal to 2;
and/or, in the light emitting layer, a ratio of a maximum doping concentration of the second guest material to a minimum doping concentration of the second guest material is greater than or equal to 2.
3. The light-emitting device according to claim 1, wherein the light-emitting layer comprises a first region adjacent to the first surface, and a second region adjacent to the second surface;
in the first region, the doping concentration of the first guest material in the light emitting layer is greater than the doping concentration of the second guest material in the light emitting layer;
in the second region, the doping concentration of the second guest material in the light emitting layer is greater than the doping concentration of the first guest material in the light emitting layer.
4. The light-emitting device according to claim 1, wherein the light-emitting layer further comprises a second host material, wherein the first host material is an electron-type host material, wherein the second host material is a hole-type host material, and wherein the first host material and the second host material are uniformly distributed in the light-emitting layer.
5. A light emitting device according to claim 1, wherein the first electrode is provided as a cathode layer and the second electrode is provided as an anode layer;
the first guest material is a partial electron type luminescent material, and the second guest material is a partial hole type luminescent material.
6. The light-emitting device according to claim 5, wherein the light-emitting layer further comprises a second host material, the first host material is an electron-type host material, and the second host material is a hole-type host material;
the light emitting layer includes a first region adjacent to the first surface, and a second region adjacent to the second surface;
in the first region, the doping concentration of the first host material in the light-emitting layer is greater than that of the second host material in the light-emitting layer;
in the second region, the doping concentration of the second host material in the light emitting layer is greater than the doping concentration of the first host material in the light emitting layer.
7. The light-emitting device according to claim 6, wherein an energy level difference between a highest occupied molecular orbital level of the second guest material and a highest occupied molecular orbital level of the first host material is less than or equal to 0.2 eV;
and/or the energy level difference between the highest occupied molecular orbital level of the second host material and the highest occupied molecular orbital level of the first guest material is less than or equal to 0.2 eV.
8. The light-emitting device according to claim 5, wherein an energy level difference between a highest occupied molecular orbital level of the second guest material and a highest occupied molecular orbital level of the first host material is less than or equal to 0.2 eV;
and/or the energy level difference between the highest occupied molecular orbital level of the first host material and the highest occupied molecular orbital level of the first guest material is less than or equal to 0.2 eV.
9. The light-emitting device according to claim 1, wherein a sum of a doping concentration of the first guest material and a doping concentration of the second guest material is less than or equal to 30%.
10. A display device, comprising: a light emitting device as claimed in any one of claims 1 to 9.
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