CN109768176B - Organic light-emitting diode and display panel - Google Patents
Organic light-emitting diode and display panel Download PDFInfo
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- CN109768176B CN109768176B CN201910023947.7A CN201910023947A CN109768176B CN 109768176 B CN109768176 B CN 109768176B CN 201910023947 A CN201910023947 A CN 201910023947A CN 109768176 B CN109768176 B CN 109768176B
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Abstract
The invention discloses an organic light emitting diode and a display panel. The organic light emitting diode includes an anode, an exciton separation layer, a first hole transport layer, an organic light emitting layer, and a cathode, which are stacked. Wherein the material of the exciton separation layer includes a host material having a lower LUMO level than that of the first hole transport layer and a hole transport limiting material. When the applied voltage of the organic light-emitting diode is lower, the exciton separation layer improves the transmission rate of the first hole transmission layer for transmitting holes to the organic light-emitting layer, reduces the driving voltage of the organic light-emitting diode and can improve the brightness of the organic light-emitting diode; when the applied voltage of the organic light-emitting diode is higher, the exciton separation layer improves the recombination balance of holes and electrons in the organic light-emitting layer, and the light-emitting performance of the organic light-emitting diode is enhanced; meanwhile, the increase rate of the current density when the voltage rises can be reduced, so that the service life of the organic light-emitting diode is prolonged.
Description
Technical Field
The embodiment of the invention relates to the technical field of display, in particular to an organic light emitting diode and a display panel.
Background
Organic Light-Emitting diodes (OLEDs) utilize a self-Emitting Light-Emitting mechanism, do not require a backlight, and when applied to a display panel and a display device, the overall thickness of the display panel and the display device is thin, which is beneficial to realizing a Light and thin design. Meanwhile, the organic light emitting diode has the advantages of high display brightness, wide viewing angle, high response speed and the like, and is widely applied to the display fields of mobile phones, PDAs, digital cameras and the like at present.
However, the conventional OLED has a problem of an increase in driving voltage, which causes a decrease in performance and a decrease in lifetime of the OLED.
Disclosure of Invention
The invention provides an organic light emitting diode and a display panel, which are used for reducing the influence of the increase of the driving voltage of an OLED on the performance of the OLED and prolonging the service life of the OLED.
In a first aspect, embodiments of the present invention provide an organic light emitting diode, including an anode, an exciton separation layer, a first hole transport layer, an organic light emitting layer, and a cathode, which are stacked;
wherein a material of the exciton separation layer includes a host material having a lower LUMO level than that of the first hole transport layer and a hole-transport limiting material.
Further, the hole transport limiting material is a metal material, preferably Al, Mg or Li.
Further, the main body material is tungsten oxide or molybdenum oxide.
Further, the mass ratio of the hole-transport-limiting material to the exciton-separating layer is greater than or equal to 1% and less than or equal to 20%.
Further, the exciton separation layer has a thickness of
Further, the distance from the surface of the exciton separation layer adjacent to the organic light emitting layer to the surface of the organic light emitting layer adjacent to the exciton separation layer is greater than or equal to
And is less than or equal to
Further, the LUMO level of the host material ranges from greater than or equal to-6 eV to less than or equal to-5 eV.
Further, the organic light emitting diode further includes a second hole transport layer;
the second hole transport layer is disposed between the anode and the exciton separation layer.
Further, the device also comprises an electron injection layer, an electron transport layer and a hole injection layer which are arranged in a stacked mode;
the electron injection layer is arranged between the organic light-emitting layer and the cathode, and the electron transport layer is arranged between the electron injection layer and the organic light-emitting layer; the hole injection layer is disposed between the exciton separation layer and the anode.
In a second aspect, embodiments of the present invention further provide a display panel, including the organic light emitting diode provided in any embodiment of the present invention.
According to the technical scheme, the organic light-emitting diode comprises an anode, an exciton separation layer, a first hole transport layer, an organic light-emitting layer and a cathode which are arranged in a stacked mode. Wherein the material of the exciton separation layer includes a host material having a lower LUMO level than that of the first hole transport layer and a hole transport limiting material. When the voltage applied to the organic light-emitting diode is lower (such as 0-4V), the transmission rate of the first hole transmission layer for transmitting holes to the organic light-emitting layer can be increased, so that the current density of the organic light-emitting diode is increased, and the light-emitting brightness of the organic light-emitting diode is improved. When the applied voltage of the organic light-emitting diode is higher (such as 4-9V), the difference value between the hole transmission rate and the electron transmission rate can be reduced, so that the recombination balance of holes and electrons in the organic light-emitting layer can be improved, and the light-emitting performance of the organic light-emitting diode is enhanced. Meanwhile, under the condition of the same voltage, the quantity of the holes transmitted to the cathode after being transmitted to the organic light-emitting layer is reduced, so that the increase rate of current density when the voltage is increased can be reduced, and the service life of the organic light-emitting diode is prolonged.
Drawings
Fig. 1 is a schematic cross-sectional structure diagram of an organic light emitting diode according to an embodiment of the present invention;
fig. 2 is a schematic diagram illustrating electron-hole movement when a low voltage is applied to an organic light emitting diode according to an embodiment of the present invention;
fig. 3 is a schematic diagram of an internal electric field formed when a high voltage is applied to an organic light emitting diode according to an embodiment of the present invention;
fig. 4 is a schematic cross-sectional view of another organic light emitting diode according to an embodiment of the present invention;
fig. 5 is a schematic cross-sectional view of another organic light emitting diode according to an embodiment of the invention;
fig. 6 is a schematic structural diagram of a display panel according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. 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.
In the prior art, an organic light emitting diode includes at least an anode, an organic light emitting layer, and a cathode, which are stacked. In the light emitting process of the organic light emitting diode, when a driving current is supplied to the organic light emitting diode, electrons are injected from the cathode into the organic light emitting layer, holes are injected from the anode into the organic light emitting layer, the electrons and the holes are recombined in the organic light emitting layer to form excitons in an excited state, the excitons in the excited state are attenuated, and energy is released in the form of light, so that the organic light emitting layer emits light. The energy levels of different layers of the organic light emitting diode are different, so that holes and electrons can encounter potential barriers between different layers in the transmission process of different layers, and the existence of the potential barriers can cause the phenomenon that the driving voltage is gradually increased along with the use of the OLED, so that the luminous performance of the OLED is reduced. The transmission rate of holes in the organic light emitting diode is greater than that of electrons, the number of the holes in the organic light emitting layer is greater than that of the electrons along with the increase of the driving voltage, too many holes cannot be compounded, the part of the holes which cannot be compounded can be continuously transmitted to the cathode side, the current density of the OLED can be increased in a J-shape mode, and therefore the heat generated by the OLED is increased, the efficiency is reduced, and the service life is shortened.
In view of the above problems, embodiments of the present invention provide an organic light emitting diode. Fig. 1 is a schematic cross-sectional structure diagram of an organic light emitting diode according to an embodiment of the present invention, and as shown in fig. 1, the organic light emitting diode 10 includes an anode 11, an exciton separation layer 12, a first hole transport layer 13, an organic light emitting layer 14, and a cathode 15, which are stacked. Among them, the material of the exciton separation layer 12 includes a host material having a LUMO level higher than that of the first hole transport layer 13 and a hole-transport-limiting material.
Specifically, the material of the anode 11 may be Indium Tin Oxide (ITO). The material of the cathode 15 may be a metal material, such as a conductive material with a low work function, for example, aluminum (Al), gold (Au), silver (Ag), or a metal alloy including Ag. The organic light-emitting layer 14 may include a light-emitting host material and a light-emitting guest material. Illustratively, the light emitting host material may be 8-hydroxyquinoline aluminum (Alq3), 9, 10-bis (1-naphthyl) Anthracene (ADN), or 4,4' -bis (9H-carbazol-9-yl) biphenyl (CBP), and the light emitting guest material may be 2-tert-butyl-4- (dicyanomethylene) -6- [2- (1,1,7, 7-tetramethyljulolidin-9-yl) vinyl ] -4H-pyran (DCJTB), which is red corresponding to the emission color of the organic light emitting diode 10; alternatively, the light emitting guest material may be N, N '-Dimethylquinacridone (DMQA), N' -Dibutylquinacridone (DBQA), 5, 12-dibutyl-1, 3,8, 10-Tetramethylquinacridone (TMDBQA), or coumarin 545T (C545T), which corresponds to the light emitting color of the organic light emitting diode 10 being green; alternatively, the light-emitting guest material may be 4,4 '-bis (9-ethyl-3-carbazolenyl) -1,1' -biphenyl (BCzVBi), 4 '-bis [4- (di-p-tolylamino) styryl ] biphenyl (DPAVBi), 1, 4-bis [4- (di-p-tolylamino) styryl ] benzene (DPAVB), or 3,3' - (1, 4-phenylbis-2, 1-vinyl) bis (9-ethyl-9H-carbazole) (BCZVB) which is blue in correspondence to the light emission color of the organic light-emitting diode 10. The first hole transport layer 13 may be NPB or TPD. The materials described above are merely exemplary, and the materials of the anode 11, the hole transport layer 13, the organic light emitting layer 14, and the cathode 15 are not limited in the present invention.
The relative height of the LUMO energy level of each film layer in the present invention is understood to be that the ionized state energy level (the energy level with the lowest energy is called the ground state, and the other energy levels are called the excited states, and the state in which electrons are no longer attracted by atomic nuclei when they are "far away" from the atomic nuclei is called the ionized state, and the ionized state energy level is 0) is used as the reference energy level, the energy level closer to the reference energy level is a relatively higher energy level, and the energy level farther from the reference energy level is a relatively lower energy level. Since the value of each energy level is a negative value, the absolute value of a relatively high energy level is small. The exciton separation layer 12 is disposed between the anode 11 and the first hole transport layer 13, and its material includes a host material having a lower LUMO level than that of the first hole transport layer 13. I.e., the absolute value of the LUMO level of the host material is greater than the absolute value of the LUMO level of the first hole transport layer 13, it is possible to achieve that the exciton separation layer 12 pulls electrons from the first hole transport layer 13 into the exciton separation layer 12. In general, the LUMO level of the host material may be set close to the HOMO level of the first hole transport layer 13, and the ability of the exciton separation layer 12 to pull electrons from the first hole transport layer 13 into the exciton separation layer 12 may be further improved.
The light emitting principle of the organic light emitting diode 10 mainly includes four processes of carrier (the carrier may be an electron or a hole) injection, carrier transport, carrier recombination, and exciton de-excitation light emission. Specifically, when a certain voltage is applied to the organic light emitting diode 10 (which can also be understood as providing a driving current), holes of the anode 11 and electrons of the cathode 15 are respectively injected into the organic light emitting layer 14 (this is a carrier injection process); the injected electrons and holes are transported under the action of an electric field (this is a carrier transport process); electrons and holes recombine in the organic light-emitting layer 14 by coulomb action, generating excitons (this is a carrier recombination process); the excitons return from the excited state to the ground state while releasing photons to emit light (this is an exciton de-excitation light emission process).
In this embodiment, holes provided by the anode 11 need to be transmitted to the organic light emitting layer 14 through the exciton separation layer 12 and the first hole transport layer 13, and electrons provided by the cathode 15 can be directly transmitted to the organic light emitting layer 14. Also, the density of holes supplied from the anode 11 and electrons supplied from the cathode 15 increases as the voltage applied to the organic light emitting diode 10 increases.
It should be noted that the transport of the holes in the organic light emitting diode 10 is apparent transport, which is essentially hole immobilization, and since the anode provides the holes, valence electrons in adjacent covalent bonds easily skip to fill the holes, so that the holes are transferred to the adjacent covalent bonds, and then new holes are filled by their adjacent valence electrons, and this process continues, which is equivalent to the movement of the holes. In the present invention, the transport of holes is understood to mean the apparent transport of holes.
Fig. 2 is a schematic diagram of electron-hole movement when a low voltage is applied to an organic light emitting diode according to an embodiment of the present invention. As shown in fig. 2, when the voltage (which may also be understood as providing a driving current) is applied to the organic light emitting diode 10 and the voltage between the anode 11 and the cathode 15 is relatively small, the transport rate of holes provided by the anode 11 and the transport rate of electrons generated by the cathode 15 are relatively small. Excitons in the exciton separation layer 12 are continuously separated by excitons under the action of a driving voltage to form electrons and holes. Since the LUMO level of the host material of the exciton separation layer 12 is lower than that of the first hole transport layer 13, electrons in the first hole transport layer 13 easily transition, the exciton separation layer 12 may pull electrons from the first hole transport layer 13 into the exciton separation layer 12, the electrons move in the a direction in fig. 2 and recombine with holes in the exciton separation layer 12, and the holes in the first hole transport layer 13 are reversely transported to the organic emission layer 14 with respect to the electrons pulled into the exciton separation layer 12, and the holes move in the B direction in fig. 2. Therefore, the exciton separation layer 12 facilitates the transport of holes in the first hole transport layer 13 to the organic light emitting layer 14, increasing the transport rate of holes. Under the condition of the same voltage, compared with the organic light emitting diode without the exciton separation layer 12, the current density formed by the organic light emitting diode 10 provided by the scheme is increased, so that the light emitting brightness of the organic light emitting diode 10 can be improved. Alternatively, compared to an organic light emitting diode without the exciton separation layer 12, the driving voltage required for the organic light emitting diode 10 is lower when the turn-on voltage of the organic light emitting diode 10 is low, that is, when the density of carriers in the organic light emitting diode 10 reaches the turn-on condition of the organic light emitting diode. In addition, the LUMO energy level of the host material is close to the HOMO energy level of the first hole transport layer 13, and the exciton separation layer 12 can more easily pull electrons from the first hole transport layer 13 into the exciton separation layer 12, which is more favorable for transporting holes in the first hole transport layer 13 to the organic light emitting layer 14, and thus the transport rate of the holes is increased.
It should be noted that, because the voltage applied to the organic light emitting diode 10 is relatively small, for example, the voltage applied to the organic light emitting diode 10 is 0 to 4V, at this time, the transport rate of the holes generated by the anode 11 is relatively small, the effect of increasing the transport rate of the holes through the exciton separation layer 12 is obvious, and the turn-on voltage of the organic light emitting diode 10 is relatively small, so that the organic light emitting diode provided in this embodiment can apply a smaller driving voltage in the turn-on stage compared to the existing organic light emitting diode.
Fig. 3 is a schematic diagram of an internal electric field formed when a high voltage is applied to an organic light emitting diode according to an embodiment of the present invention. As shown in fig. 3, as the voltage applied to the organic light emitting diode 10 increases, the hole transport rate generated at the anode 11 is relatively high, and at this time, the exciton separation layer 12 generates a relatively large amount of excitons and a relatively large amount of formed electrons and holes. And exciton-separating layer 12 continues to pull electrons from first hole-transporting layer 13 into exciton-separating layer 12, thus forming an electric field at the interface of exciton-separating layer 12 and first hole-transporting layer 13, as shown by C in fig. 3. The exciton separation layer 12 continuously consumes electrons of the first hole transport layer 13, and thus the number of holes in the first hole transport layer 13 is greater than the number of electrons. And the holes generated by exciton separation in exciton separation layer 12 are recombined with the electrons pulled in first hole transport layer 13, so that the number of electrons in exciton separation layer 12 is greater than that of holes. Therefore, the direction of the electric field formed at the interface of the exciton separation layer 12 and the first hole transport layer 13 is opposite to the direction of the electric field applied to the organic light emitting diode 10, as indicated by the arrows in fig. 3. Therefore, at the interface of exciton separation layer 12 and first hole transport layer 13, the electric field formed by exciton separation layer 12 and first hole transport layer 13 reduces the voltage loaded on the holes, and thus the transport rate of the holes can be reduced. Meanwhile, since the exciton separation layer 12 includes the hole-transport-limiting material, the hole-transport-limiting material can provide free electrons under the action of voltage, and the free electrons in the hole-transport-limiting material are limited from moving in the opposite direction of the electric field. The hole transport material is thus confined to facilitate electron injection into anode 11. Therefore, electrons in the exciton separation layer 12 are more easily recombined with holes generated in the anode 11, thereby blocking the path of holes from the anode 11 to the organic light emitting layer 14 and reducing the amount of holes transmitted to the organic light emitting layer 14. Meanwhile, due to the action of an external voltage of the organic light emitting diode 10, a large number of holes are generated by the anode 11, the exciton separation layer 12 cannot completely block and combine all the holes, part of the holes enter the organic light emitting layer 14, and the exciton separation layer 12 continuously performs an exciton separation process, the exciton separation layer 12 can continuously pull electrons from the first hole transmission layer 13 to enter the exciton separation layer 12, so that the transmission rate of the holes in the first hole transmission layer 13 to enter the organic light emitting layer 14 can be ensured, and the holes required by normal light emitting of the organic light emitting diode 10 are ensured. But the transport rate of holes into the organic light-emitting layer 14 is still reduced overall due to the blocking and recombination action of the exciton separation layer 12 on the holes generated by the anode. Since the hole transport rate in the conventional organic light emitting diode is greater than the electron transport rate, the difference between the hole transport rate and the electron transport rate can be reduced by reducing the hole transport rate through the exciton separation layer 12, so that the recombination balance of the holes and the electrons in the organic light emitting layer 14 can be realized, and the light emitting performance of the organic light emitting diode 10 is enhanced. Meanwhile, the transport rate of holes is reduced by the exciton separation layer 12, and the number of holes transported to the cathode 15 after being transported to the organic light emitting layer 14 is reduced under the same voltage condition, so that the increase rate of current density when the voltage is increased can be reduced, thereby prolonging the service life of the organic light emitting diode 10.
It should be noted that when a relatively high voltage is applied to the organic light emitting diode 10, for example, the voltage applied to the organic light emitting diode 10 is 4V to 9V, and the transport rate of holes generated by the anode 11 is large, the exciton separation layer 12 is mainly used to block the transport of holes to the organic light emitting layer 14, thereby reducing the transport rate of holes.
Table 1 shows an organic light emitting diode and a display device according to an embodiment of the present inventionThere is a table comparing hole transport rates of organic light emitting diodes. As shown in Table 1, the voltage is the driving voltage for driving the OLED, and the voltage is in V, and the OLED1 is the current density of the OLED provided by the embodiment of the invention at different voltages, and the unit is mA/cm2The OLED2 is the current density of the organic light emitting diode provided by the prior art under different voltages, and the unit is mA/cm2. By comparing the current densities of the OLED1 and the OLED2 under the same voltage condition, it can be seen that when the voltage is in the range of 0.3V to 2.7V, the value of the OLED1 is greater than that of the OLED2, i.e., the current density of the organic light emitting diode provided by the embodiment of the present invention is greater than that of the organic light emitting diode provided by the prior art, i.e., at a low voltage, the current density of the organic light emitting diode provided by the embodiment of the present invention is increased compared to that of the organic light emitting diode without the exciton separation layer, so that the light emitting luminance of the organic light emitting diode can be improved. Or compared with an organic light emitting diode without an exciton separation layer, the organic light emitting diode provided by the scheme has low turn-on voltage, namely when the density of carriers in the organic light emitting diode reaches the turn-on condition of the organic light emitting diode, the driving voltage required by the organic light emitting diode provided by the scheme is lower. When the voltage is in the range of 3.3V to 5.7V, the value of the OLED1 is smaller than that of the OLED2, that is, the current density of the organic light emitting diode provided by the embodiment of the present invention is smaller than that of the organic light emitting diode provided by the prior art, that is, at a high voltage, the exciton separation layer reduces the hole transport rate, and the difference between the hole transport rate and the electron transport rate can be reduced, so that the recombination balance of holes and electrons in the organic light emitting layer can be realized, and the light emitting performance of the organic light emitting diode can be enhanced. Meanwhile, the transport rate of holes is reduced through the exciton separation layer, and the quantity of the holes transported to the cathode after being transported to the organic light-emitting layer is reduced under the condition of the same voltage, so that the increase rate of current density when the voltage is increased can be reduced, and the service life of the organic light-emitting diode is prolonged.
Table 1 comparison table of hole transport rates of the organic light emitting diode of the present invention and the conventional organic light emitting diode
| Voltage (V) | 0.3 | 0.9 | 1.5 | 2.1 | 2.7 | 3.3 | 3.9 | 4.5 | 5.1 | 5.7 |
| OLED1 | 4.39E-4 | 2.69E-4 | 1.23E-4 | 2.96E-4 | 5.03E-2 | 0.97966 | 4.9892 | 15.5318 | 37.033 | 75.266 |
| OLED2 | 7.91E-5 | 9.68E-5 | 6.62E-5 | 2.13E-4 | 4.53E-2 | 1.05804 | 6.28636 | 22.3657 | 59.9934 | 135.479 |
In the technical solution of this embodiment, the organic light emitting diode includes an anode, an exciton separation layer, a first hole transport layer, an organic light emitting layer, and a cathode, which are stacked. Wherein the material of the exciton separation layer includes a host material having a lower LUMO level than that of the first hole transport layer and a hole transport limiting material. When the voltage applied to the organic light-emitting diode is lower (such as 0-4V), the exciton separation layer can pull electrons from the first hole transport layer to enter the exciton separation layer, so that the transmission rate of the holes transmitted by the first hole transport layer to the organic light-emitting layer can be increased, the current density of the organic light-emitting diode is increased, and the light-emitting brightness of the organic light-emitting diode is improved. When the applied voltage of the organic light-emitting diode is higher (such as 4-9V), the exciton separation layer blocks a path of a hole generated by the anode to enter the organic light-emitting layer, meanwhile, an electron is continuously pulled from the first hole transmission layer to enter the exciton separation layer, the speed of the first hole transmission layer for transmitting the hole to enter the organic light-emitting layer is ensured, the transmission speed of the hole to enter the organic light-emitting layer is reduced through the exciton separation layer, and the difference value between the hole transmission speed and the electron transmission speed is reduced, so that the recombination balance of the hole and the electron in the organic light-emitting layer can be improved, and the light-emitting performance of the organic light-emitting diode is enhanced. Meanwhile, the transport rate of holes is reduced through the exciton separation layer, and the quantity of the holes transported to the cathode after being transported to the organic light-emitting layer is reduced under the condition of the same voltage, so that the increase rate of current density when the voltage is increased can be reduced, and the service life of the organic light-emitting diode is prolonged.
On the basis of the above technical solution, the hole transport limiting material may be a metal material, and preferably may be Al, Mg or Li.
Under the action of an external electric field, the hole-migration-limiting material in the exciton separation layer can provide free electrons, so that electrons in the exciton separation layer can be injected into the anode and can be recombined with holes, and therefore the hole-migration-limiting material is mainly used for driving the electrons in the exciton separation layer to move towards the anode and realize the recombination with the holes, so that the paths of the holes entering the organic light-emitting layer are blocked, and the quantity of the holes transmitted to the organic light-emitting layer is reduced. In order to achieve better injection of electrons of the exciton separation layer into the anode by the hole-transport-limiting material, the hole-transport-limiting material may be a metal material, preferably an active metal material, such as Al, Mg or Li, may be selected. The active metals can jump more free electrons under lower voltage and are transmitted to the anode direction under the action of an external electric field, so that the active metals can be compounded with more holes, the path that the holes generated by the anode enter the organic light-emitting layer can be better blocked, the quantity of the holes transmitted to the organic light-emitting layer is reduced, the compound balance of the holes and the electrons in the organic light-emitting layer is improved, and the light-emitting performance of the organic light-emitting diode is enhanced. Meanwhile, the transport rate of holes is reduced through the exciton separation layer, and the quantity of the holes transported to the cathode after being transported to the organic light-emitting layer is reduced under the condition of the same voltage, so that the increase rate of current density when the voltage is increased can be reduced, and the service life of the organic light-emitting diode is prolonged. The metal material is an example, but not limited to, metal.
In addition, the mass ratio of the hole transport material to the exciton separation layer is restricted to 1% or more and 20% or less.
In particular, limiting the mass ratio of hole transporting material to exciton separating layer affects the performance of the exciton separating layer. Illustratively, when the hole transport material is restricted to an active metal, if the mass ratio of the active metal material to the exciton separation layer is too small, i.e., the active metal material is relatively small with respect to the exciton separation layer, the free electrons provided by the active metal material are relatively small with respect to the exciton separation layer, and the capability of the exciton separation layer to enhance electron transport is reduced, so that the capability of the exciton separation layer to increase electron transport rate is reduced. If the mass ratio of the active metal material to the exciton separation layer is too large, that is, if the active metal material is more than the exciton separation layer, the excessive active metal material may affect the light emitting performance of the organic light emitting layer, and the excessive active metal material may reduce the light transmittance of the exciton separation layer. Therefore, the mass ratio of the active metal material to the exciton separation layer is limited to be more than or equal to 1% and less than or equal to 20%, the capability of the exciton separation layer for increasing the electron transmission rate can be ensured, the active metal material in the exciton separation layer is prevented from influencing the luminous performance of the organic light emitting layer too much, the light transmittance of the exciton separation layer can be ensured, and the light transmittance effect of the display panel is prevented from being influenced.
The exciton separation layer includes a hole-transport limiting material and a host material, and the hole-transport limiting material may be doped in the host material. In the process of forming the exciton separation layer, a process of double-source co-evaporation may be employed. The dual sources may be point sources or line sources. One of the dual sources is used for placing the hole transport limiting material and the other is used for placing the host material. In the dual source co-evaporation process, controlling the mass ratio of the hole-transport-limiting material to the exciton-separating layer can be achieved by controlling the deposition rate of the hole-transport-limiting material deposited in the dual source co-evaporation and the deposition rate of the host material deposited. Therefore, the speed of depositing the limited hole transport material and the speed of the main body material are respectively controlled by the double sources, so that the limited hole transport material and the main body material can be simultaneously deposited, the density of the exciton separation layer formed by evaporation is good, the effect of controlling the transmission speed of holes by the exciton separation layer is improved, the mass ratio of the hole transport material to the exciton separation layer can be controlled, and the performance of the exciton separation layer is ensured.
On the basis of the technical scheme, exciton separationThe distance from the surface of the layer adjacent to the organic light-emitting layer to the surface of the organic light-emitting layer adjacent to the exciton separation layer is greater than or equal to
And is less than or equal to
So as to prevent the metal material in the exciton separation layer from influencing the light emitting performance of the organic light emitting layer.
Specifically, since the exciton separation layer includes a hole transport-limiting material therein, illustratively, a metal material, and the metal atom easily causes decomposition of the polymer of the organic light-emitting layer, quenching the polymer of the organic light-emitting layer. The distance from the exciton separation layer to the organic light-emitting layer therefore needs to be greater than or equal to
The metal in the exciton separation layer is prevented from influencing the luminescence of the organic luminescent layer. Meanwhile, the too large distance from the exciton separation layer to the organic light emitting layer may result in too large thickness of the organic light emitting diode, which may cause the organic light emitting diode not to emit light normally, and therefore, the distance from the exciton separation layer to the organic light emitting layer should be limited to be less than or equal to
In general, the distance from the exciton separation layer to the organic light-emitting layer may be set
The organic light emitting diode can not only ensure that the metal material in the exciton separation layer does not influence the light emission of the organic light emitting layer, but also avoid the phenomenon that the exciton separation layer is too far away from the organic light emitting layer, so that the thickness of the organic light emitting diode is too large.
On the basis of the technical schemes, the main material is tungsten oxide or molybdenum oxide.
Specifically, an exciton separation layer is disposed between the anode and the first hole transport layer, and in order to achieve pulling of electrons in the first hole transport layer into the exciton separation layer, the LUMO level of the exciton separation layer is lower than the LUMO level of the first hole transport layer. In addition, in order that the exciton separation layer 12 may more easily pull electrons from the first hole transport layer 13 into the exciton separation layer 12, more facilitate the transport of holes in the first hole transport layer 13 to the organic light emitting layer 14, and increase the transport rate of holes, the LUMO level of the host material may be selected to be close to the HOMO level of the first hole transport layer 13. Therefore, the host material of the exciton separation layer should be selected to have a relatively deep LUMO level, and may be, for example, tungsten oxide or molybdenum oxide, so that the exciton separation layer easily pulls electrons from the first hole transport layer into the exciton separation layer. In general, the HOMO level of the first hole transport layer 13 ranges from-6 eV to-5 eV, and therefore, the LUMO level of the host material ranges from greater than or equal to-6 eV to less than or equal to-5 eV. Illustratively, the HOMO level of the first hole transport layer 13 may range from-6.0 eV to-5.5 eV, and preferably-5.7 eV, in which case the LUMO level of the exciton separation layer may be set to-5.6 eV.
On the basis of the above technical solutions, the thickness of the exciton separation layer can be set as
In particular, the thickness of the exciton separation layer directly affects the performance of the organic light emitting diode. When the exciton separation layer is thin, the exciton separation layer has a small effect, that is, the exciton separation layer does not have a significant effect of increasing the hole transfer rate at a low voltage and decreasing the hole transfer rate at a high voltage, and thus the driving voltage of the organic light emitting diode cannot be effectively decreased and the lifespan of the organic light emitting diode cannot be effectively extended. Therefore, the exciton separation layer needs to have a certain thickness, and when the thickness of the exciton separation layer is
The effect of the exciton separation layer can be embodied, so that the minimum thickness of the exciton separation layer is set to
And when the exciton separation layer is thick,the exciton separation layer affects the performance of the whole organic light emitting diode, and affects the light emission of the organic light emitting diode, and exemplarily, the thickness of the exciton separation layer is
When the organic light emitting diode emits light, the light emitting effect of the organic light emitting diode is decreased. Thus, the exciton separation layer may have a thickness of
Fig. 4 is a schematic cross-sectional view of another organic light emitting diode according to an embodiment of the present invention, and as shown in fig. 4, the organic light emitting diode 10 further includes a second hole transport layer 16. A second hole transport layer 16 is disposed between the anode 11 and the exciton separation layer 12.
Specifically, the first hole transport layer 13 and the second hole transport layer 16 may be made of the same material, and this embodiment may be understood as inserting the exciton separation layer 12 into the hole transport layer. In general, the sum of the thicknesses of the first hole transport layer 13 and the second hole transport layer 16 is a constant value, that is, the thickness of the hole transport layer is relatively constant. In order to adjust the distance from the exciton separation layer 12 to the organic light emitting layer 14 according to the volume ratio of the metal material in the exciton separation layer 12 and to control the hole transport rate of the exciton separation layer 12, the exciton separation layer 12 may be disposed in a hole transport layer, and the hole transport layer may be divided into a first hole transport layer 13 and a second hole transport layer 16, the thickness of the first hole transport layer 13 is the distance from the exciton separation layer 12 to the organic light emitting layer 14, and the distance from the exciton separation layer 12 to the organic light emitting layer 14 may be adjusted by disposing the thickness of the first hole transport layer 13.
Note that the distance from the exciton separation layer 12 to the organic light-emitting layer 14 can be adjusted according to the volume ratio of the metal material in the exciton separation layer 12. In general, the larger the volume ratio of the metal material, the larger the distance from the exciton separation layer 12 to the organic light-emitting layer 14, the thicker the thickness of the first hole transport layer 13, and the thinner the thickness of the second hole transport layer 16.
Fig. 5 is a schematic cross-sectional view of another organic light emitting diode according to an embodiment of the present invention, and as shown in fig. 5, the organic light emitting diode 10 may further include an electron injection layer 17, an electron transport layer 18, and a hole injection layer 19, which are stacked. An electron injection layer 17 is disposed between the cathode 15 and the organic light-emitting layer 14, an electron transport layer 18 is disposed between the organic light-emitting layer 14 and the electron injection layer 17, and a hole injection layer 19 is disposed between the exciton separation layer 12 and the anode 11. When the organic light emitting diode includes the second hole transport layer 16, the hole injection layer 19 is disposed between the second hole transport layer 16 and the anode 11. By providing the electron injection layer 17, the potential barrier between the cathode 15 and the organic layer can be reduced, so that the driving voltage of the organic light emitting diode can be reduced, and the light emitting efficiency of the organic light emitting diode can be improved. The material of the electron injection layer 17 may be LiF. The electron transport layer 18 can increase the electron transport rate, thereby enhancing the recombination of holes and electrons of the organic light emitting diode and improving the light emitting efficiency of the organic light emitting diode. The material of the electron transport layer 18 may be Alq 3. The hole injection layer 19 is in direct contact with the anode 11, so that the potential barrier between the anode 11 and the hole transport layer 182 can be reduced, the capability of injecting holes output by the anode 11 into the second hole transport layer 16 can be improved, and the material of the hole injection layer 19 can be copper phthalocyanine (CuPC) or titanyl phthalocyanine (TiOPC), and the like.
It should be noted that the materials of the electron injection layer 17, the electron transport layer 18, and the hole injection layer 19 are merely an example, and are not limited thereto.
Fig. 6 is a schematic structural diagram of a display panel according to an embodiment of the present invention, and as shown in fig. 6, the display panel 20 includes a substrate 21 and a plurality of pixel units 22 located on one side of the substrate 21. The pixel unit 22 includes an organic light emitting diode according to any embodiment of the present invention. The display panel 20 provided in the embodiment of the invention includes any of the above-mentioned organic light emitting diodes, and therefore, the display panel 20 also has the beneficial effects of the above-mentioned organic light emitting diodes, which can be referred to above and will not be described herein again.
The substrate 21 may be an array substrate, and is used to drive the pixel unit 22 to emit light.
Exemplarily, fig. 6 shows a row direction X and a column direction Y (a plane of the row direction X and the column direction Y shown in fig. 6 is a plane of the substrate base 21), and shows pixel units 22 arranged in 7 columns and 4 rows, each pixel unit 22 may include one blue sub-pixel 221, one red sub-pixel 222, and one green sub-pixel 223; meanwhile, the sub-pixels in each pixel unit 22 are arranged in the order of the blue sub-pixel 221, the red sub-pixel 222, and the green sub-pixel 223 along the column direction Y, and the arrangement of the pixels is only an exemplary illustration and not a limitation of the display panel 20 provided by the embodiment of the present invention. In other embodiments, the array arrangement of the pixel units 22, and the number and arrangement of the blue sub-pixel 221, the red sub-pixel 222, and the green sub-pixel 223 in each pixel unit 22 may be set according to the actual requirement of the display panel 20, which is not limited in the embodiments of the present invention.
It should be noted that the specific type of the display panel 20 is not limited in the embodiment of the present invention, and the technical solution proposed in the embodiment of the present invention can be applied to any display panel related to the transmission process of electrons and holes, and an exemplary display panel can be an OLED display panel, a Quantum Dot Light Emitting Diodes (QLED) display panel, or other display panels known to those skilled in the art.
The display panel can be applied to display devices with display functions, such as mobile phones, computers, smart wearable devices, and the like, and the embodiment of the invention is not limited thereto.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (9)
1. An organic light emitting diode comprising an anode, an exciton separation layer, a first hole transport layer, an organic light emitting layer and a cathode, which are arranged in a stacked manner; the exciton separation layer is disposed between the anode and the first hole transport layer;
wherein the material of the exciton separation layer comprises a host material and a hole-transporting-limiting material, the hole-transporting-limiting material being doped in the host material, the host material having a lower LUMO level than the LUMO level of the first hole transport layer; the hole migration limiting material is a metal material; the organic light emitting diode further comprises a second hole transport layer; the second hole transport layer is disposed between the anode and the exciton separation layer; wherein the larger the volume ratio of the metal material in the exciton separation layer, the thicker the thickness of the first hole transport layer, and the thinner the thickness of the second hole transport layer.
2. The organic light-emitting diode of claim 1, wherein the metal material is Al, Mg or Li.
3. The oled of claim 1, wherein the host material is tungsten oxide or molybdenum oxide.
4. The organic light-emitting diode of claim 1, wherein the mass ratio of the hole-transport-limiting material to the exciton-separating layer is greater than or equal to 1% and less than or equal to 20%.
5. The OLED of claim 1, wherein the exciton separation layer has a thickness of
6. Root of herbaceous plantThe organic light-emitting diode of claim 1, wherein the distance from the surface of the exciton separation layer adjacent to the organic light-emitting layer to the surface of the organic light-emitting layer adjacent to the exciton separation layer is greater than or equal to
And is less than or equal to
7. The organic light-emitting diode of claim 1, wherein the host material has a LUMO level in a range from greater than or equal to-6 eV to less than or equal to-5 eV.
8. The organic light-emitting diode according to claim 1, further comprising an electron injection layer and an electron transport layer, which are disposed in a stack, and a hole injection layer;
the electron injection layer is arranged between the organic light-emitting layer and the cathode, and the electron transport layer is arranged between the electron injection layer and the organic light-emitting layer; the hole injection layer is disposed between the exciton separation layer and the anode.
9. A display panel comprising the organic light emitting diode according to any one of claims 1 to 8.
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