Carrier generation layer, series organic light-emitting device and display panel

Abstract

The invention discloses a carrier generation layer, a series organic light-emitting device and a display panel, the carrier generation layer comprises an N-type material layer, a P-type material layer and an energy level buffer layer, the energy level buffer layer is arranged between the N-type material layer and the P-type material layer, the LUMO energy level of the energy level buffer layer is located between the LUMO energy level of the N-type material layer and the LUMO energy level of the P-type material layer to form a step energy level, and the step energy level is located between the N-type material layer and the P-type material layer. The abrupt change of the LUMO energy level of the P-type material layer and the LUMO energy level of the N-type material layer is buffered, the potential barrier in the migration process of electrons from the P-type material layer to the N-type material layer is reduced, the composite heating of the electrons and holes at the interface from the P-type material layer to the N-type material layer is reduced, the problem that the service life of the series organic light-emitting device is shortened due to heat accumulation is avoided, and the service life of the series organic light-emitting device is prolonged. And the service life of the series organic light-emitting device is prolonged. In addition, the potential barrier of electrons in the migration process from the P-type material layer to the N-type material layer is reduced, the driving voltage of the series organic light-emitting device is reduced, and then the driving cost is reduced.

Description

Technical Field

[0001] The present invention relates to organic light - emitting display technology, and particularly to a carrier generation layer, a tandem organic light - emitting device, and a display panel. Background Art

[0002] A tandem organic light - emitting device (Tandem OLED) is a display technology formed by stacking two OLED devices together. Its working principle is based on the basic structure of an OLED, and a carrier generation layer (Carrier Generation Layer, CGL) is used to connect two OLED light - emitting layers in series. After holes and electrons in the first light - emitting layer recombine to emit light, the remaining holes and electrons pass through the carrier generation layer and recombine again in the second light - emitting layer to emit light.

[0003] An existing carrier generation layer adopts a composite structure formed by stacking an N - type material layer and a P - type material layer. During the operation of the tandem organic light - emitting device, the carriers generated by the P - type material layer migrate to both sides respectively. Among them, electrons migrate to the N - type material layer and continue to migrate to one of the light - emitting layers, where they recombine with holes to emit light. Correspondingly, holes migrate to the other light - emitting layer and recombine with electrons in this light - emitting layer to emit light.

[0004] However, due to the discontinuous LUMO (Lowest Unoccupied Molecular Orbital) energy levels of the N - type material layer and the P - type material layer, a potential barrier will be formed at the interface between the N - type material layer and the P - type material layer, which hinders the migration of electrons. The electrons accumulated at the interface will recombine with holes, generating Joule heat, resulting in large energy losses. The accumulated Joule heat will cause material degradation, and further reduce the service life of the device. In addition, in order to overcome the potential barrier at the interface between the N - type material and the P - type material, the driving voltage of the tandem organic light - emitting device (10V - 12V) is much higher than that of a single - layer organic light - emitting device (4V - 6V), increasing the driving cost. Summary of the Invention

[0005] A carrier generation layer, a tandem organic light - emitting device, and a display panel according to the present invention can improve the service life of the tandem organic light - emitting device and reduce the driving cost.

[0006] In a first aspect, the present invention provides a carrier generation layer, comprising:

[0007] An N - type material layer having a first LUMO energy level;

[0008] A P - type material layer having a second LUMO energy level, and the first LUMO energy level is greater than the second LUMO energy level;

[0009] An energy level buffer layer is provided between the N-type material layer and the P-type material layer, and the energy level buffer layer has a third LUMO energy level, which is located between the first LUMO energy level and the second LUMO energy level.

[0010] Optionally, the N-type material layer is formed by doping an electron transport layer with an N-type dopant, and the P-type material layer is formed by doping a hole transport layer with a P-type dopant.

[0011] Optionally, the N-type dopant includes an alkali metal compound, and the P-type dopant includes at least one of HAT-CN, F4-TCNQ, MoO3, and W2(hpp)4.

[0012] Optionally, the doping ratio of the N-type dopant is 10%-50%, and the doping ratio of the P-type dopant is 2%-15%.

[0013] Optionally, the material of the energy level buffer layer includes at least one of ZnO, lithium 8-hydroxyquinolate, and C 60 among others.

[0014] Optionally, the energy level buffer layer is a three-layer stacked structure, and the three-layer stacked structure includes a stacked structure of lithium 8-hydroxyquinolate, ZnO, and lithium 8-hydroxyquinolate, and a stacked structure of lithium 8-hydroxyquinolate, C 60 and lithium 8-hydroxyquinolate.

[0015] Optionally, the thickness range of the energy level buffer layer is 2 nm - 10 nm, and the surface roughness of the energy level buffer layer is less than or equal to 1 nm.

[0016] Optionally, the energy level buffer layer is prepared by evaporation or atomic layer deposition.

[0017] In a second aspect, the present invention further provides a tandem organic light-emitting device, including the carrier generation layer provided in the first aspect of the present invention, and further including:

[0018] A first light-emitting layer, which is provided on the side of the N-type material layer of the carrier generation layer away from the energy level buffer layer;

[0019] A first hole transport layer, which is provided on the side of the first light-emitting layer away from the carrier generation layer;

[0020] A hole injection layer, which is provided on the side of the first hole transport layer away from the first light-emitting layer;

[0021] An anode, which is provided on the side of the hole injection layer away from the first hole transport layer;

[0022] A second hole transport layer, which is disposed on a side of the P-type material layer of the carrier generation layer away from the energy level buffer layer;

[0023] A second light-emitting layer, which is disposed on a side of the second hole transport layer away from the carrier generation layer;

[0024] An electron transport layer, which is disposed on a side of the second light-emitting layer away from the second hole transport layer;

[0025] A cathode, which is disposed on a side of the electron transport layer away from the second light-emitting layer.

[0026] In a third aspect, the present invention further provides a display panel, including the tandem organic light-emitting device provided in the second aspect of the present invention.

[0027] The carrier generation layer provided by the present invention includes an N-type material layer, a P-type material layer, and an energy level buffer layer. The N-type material layer has a first LUMO energy level, the P-type material layer has a second LUMO energy level, the first LUMO energy level is greater than the second LUMO energy level. The energy level buffer layer is disposed between the N-type material layer and the P-type material layer, and the energy level buffer layer has a third LUMO energy level. The third LUMO energy level is located between the first LUMO energy level and the second LUMO energy level, forming a stepped energy level, buffering the mutation of the LUMO energy level of the P-type material layer and the LUMO energy level of the N-type material layer, reducing the potential barrier during the migration of electrons from the P-type material layer to the N-type material layer, reducing the recombination heat generation of electrons and holes at the interface between the P-type material layer and the N-type material layer, avoiding the problem of reduced service life of the tandem organic light-emitting device caused by heat accumulation, and improving the service life of the tandem organic light-emitting device. In addition, the potential barrier during the migration of electrons from the P-type material layer to the N-type material layer is reduced, reducing the driving voltage of the tandem organic light-emitting device, and thus reducing the driving cost. Description of the Drawings

[0028] The present invention will be further described in detail below with reference to the drawings and embodiments.

[0029] Figure 1 It is a schematic structural diagram of a carrier generation layer provided by the present invention;

[0030] Figure 2 It is an energy level relationship diagram between layers in a carrier generation layer provided by the present invention;

[0031] Figure 3 It is a schematic structural diagram of a tandem organic light-emitting device provided by the present invention;

[0032] Figure 4 It is an energy level relationship diagram between layers in the tandem organic light-emitting device provided by the present invention;

[0033] Figure 5 It is the voltage-current density-luminance (I-V-L) characteristic curve graph of device A;

[0034] Figure 6 It is the luminance-current efficiency relationship graph of device A;

[0035] Figure 7 It is the lifetime curve graph of device A at an initial luminance of 5000 cd / m 2 ;

[0036] Figure 8 It is the voltage-current density-luminance (I-V-L) characteristic curve graph of device B;

[0037] Figure 9 It is the luminance-current efficiency relationship graph of device B;

[0038] Figure 10 It is the lifetime curve graph of device B at an initial luminance of 5000 cd / m 2 ;

[0039] Figure 11 It is the voltage-current density-luminance (I-V-L) characteristic curve graph of device C;

[0040] Figure 12 It is the luminance-current efficiency relationship graph of device C;

[0041] Figure 13 It is the lifetime curve graph of device C at an initial luminance of 5000 cd / m 2 ;

[0042] Figure 14 It is the voltage-current density-luminance (I-V-L) characteristic curve graph of device D;

[0043] Figure 15 It is the luminance-current efficiency relationship graph of device D;

[0044] Figure 16 It is the lifetime curve graph of device D at an initial luminance of 5000 cd / m 2 ;

[0045] Figure 17 It is the voltage-current density-luminance (I-V-L) characteristic curve graph of device E;

[0046] Figure 18 It is the luminance-current efficiency relationship graph of device E;

[0047] Figure 19 It is the lifetime curve graph of device E at an initial luminance of 5000 cd / m 2 ; Detailed Implementation Modes

[0048] To make the technical problems solved by the present invention, the technical solutions adopted, and the achieved technical effects clearer, the technical solutions of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0049] In the description of the present invention, unless otherwise clearly defined and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0050] In the present invention, unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may include the direct contact of the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through other features therebetween. Moreover, the first feature being "above", "above", and "on" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the first feature is at a higher horizontal height than the second feature. The first feature being "below", "below", and "under" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the first feature is at a lower horizontal height than the second feature. In addition, the terms "first" and "second" are only used for distinction in description and do not have special meanings.

[0051] Figure 1 FIG. [X] is a schematic structural diagram of a carrier generation layer provided by the present invention. Figure 2 FIG. [Y] is an energy level relationship diagram between layers in a carrier generation layer provided by the present invention. As Figure 1 、 2 shown, the carrier generation layer includes:

[0052] An N-type material layer 101, and the N-type material layer 101 has a first LUMO energy level.

[0053] A P-type material layer 102, and the P-type material layer 102 has a second LUMO energy level, and the first LUMO energy level is greater than the second LUMO energy level.

[0054] The energy level buffer layer 103 is disposed between the N-type material layer 101 and the P-type material layer 102, and the energy level buffer layer 103 has a third LUMO energy level, and the third LUMO energy level is located between the first LUMO energy level and the second LUMO energy level.

[0055] As Figure 2 shown, exemplarily, during the operation of the tandem organic light-emitting device prepared with the carrier generation layer, carriers are generated and separated at the interface of the P-type material layer 102 far from the energy level buffer layer 103. Among them, electrons migrate to the energy level buffer layer 103 and the N-type material layer 101 in sequence, and continue to migrate to one of the light-emitting layers, where they recombine with holes to emit light. Since the LUMO energy level of the energy level buffer layer 103 is located between the LUMO energy levels of the P-type material layer 102 and the N-type material layer 101, forming a stepped energy level, buffering the abrupt change of the LUMO energy levels of the P-type material layer 102 and the N-type material layer 101, reducing the potential barrier during the migration of electrons from the P-type material layer 102 to the N-type material layer 101, reducing the recombination heat generation of electrons and holes at the interface between the P-type material layer 102 and the N-type material layer 101, avoiding the problem of reducing the service life of the tandem organic light-emitting device caused by heat accumulation, and improving the service life of the tandem organic light-emitting device. In addition, the potential barrier during the migration of electrons from the P-type material layer 102 to the N-type material layer 101 is reduced, reducing the driving voltage of the tandem organic light-emitting device, and thus reducing the driving cost.

[0056] The carrier generation layer provided by the present invention includes an N-type material layer, a P-type material layer, and an energy level buffer layer. The N-type material layer has a first LUMO energy level, the P-type material layer has a second LUMO energy level, the first LUMO energy level is greater than the second LUMO energy level, the energy level buffer layer is disposed between the N-type material layer and the P-type material layer, and the energy level buffer layer has a third LUMO energy level, and the third LUMO energy level is located between the first LUMO energy level and the second LUMO energy level, forming a stepped energy level, buffering the abrupt change of the LUMO energy levels of the P-type material layer and the N-type material layer, reducing the potential barrier during the migration of electrons from the P-type material layer to the N-type material layer, reducing the recombination heat generation of electrons and holes at the interface between the P-type material layer and the N-type material layer, avoiding the problem of reducing the service life of the tandem organic light-emitting device caused by heat accumulation, and improving the service life of the tandem organic light-emitting device. In addition, the potential barrier during the migration of electrons from the P-type material layer to the N-type material layer is reduced, reducing the driving voltage of the tandem organic light-emitting device, and thus reducing the driving cost.

[0057] In some embodiments of the present invention, the N-type material layer is formed by doping an N-type dopant into an electron transport layer, and the P-type material layer is formed by doping a P-type dopant into a hole transport layer.

[0058] In some embodiments of the present invention, the material of the electron transport layer may be Bphen (4,7-diphenyl-1,10-phenanthroline), and the N-type dopant includes alkali metal compounds, including but not limited to Li, Liq (lithium 8-hydroxyquinoline), Cs2CO3 (cesium carbonate), CsN3 (cesium azide), KHB4 (potassium tetrahydroborate), Rb2CO3 (rubidium carbonate), RbF (rubidium fluoride), and Rb2S (rubidium sulfide).

[0059] In some embodiments of the present invention, the material of the hole transport layer may be NPB (N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine), and the P-type dopant includes at least one of HAT-CN (2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene), F4-TCNQ (2,3,5,6-tetrafluoro-7,7',8,8'-tetracyanoquinodimethane), MoO3 (molybdenum trioxide), and W2(hpp)4.

[0060] In some embodiments of the present invention, the doping ratio of the N-type dopant is 10% - 50%. Exemplarily, in a specific embodiment of the present invention, the doping ratios of the N-type dopant are 10%, 11%, 12%, 13%, 14%, and 15%.

[0061] In some embodiments of the present invention, the doping ratio of the P-type dopant is 2% - 15%. Exemplarily, in a specific embodiment of the present invention, the doping ratios of the P-type dopant are 2%, 5%, 8%, 10%, 12%, and 15%.

[0062] In some embodiments of the present invention, the material of the energy level buffer layer 103 includes at least one of ZnO, lithium 8-hydroxyquinoline, and C 60 Exemplarily, the energy level buffer layer 103 can be prepared from one of the materials of ZnO, lithium 8-hydroxyquinoline, and C 60 or prepared by mixing and doping two or three of the materials of ZnO, lithium 8-hydroxyquinoline, and C 60 or formed into a composite stacked structure of two or three of the materials of ZnO, lithium 8-hydroxyquinoline, and C, which is not limited in the present invention. 60 It should be noted that the materials of the N-type material layer, P-type material layer, and energy level buffer layer in the embodiments of the present invention are exemplary descriptions of the present invention. In other embodiments of the present invention, other materials may also be used as long as the functions and effects of the present invention can be achieved, which is not limited in the present invention.

[0063] It should be noted that the materials of the N-type material layer, P-type material layer, and energy level buffer layer in the embodiments of the present invention are exemplary descriptions of the present invention. In other embodiments of the present invention, other materials may also be used as long as the functions and effects of the present invention can be achieved, which is not limited in the present invention.

[0064] In some embodiments of the present invention, the energy level buffer layer is a three-layer stacked structure. The three-layer stacked structure includes a stacked structure of lithium 8-hydroxyquinoline, ZnO, and lithium 8-hydroxyquinoline, and a stacked structure of lithium 8-hydroxyquinoline, C 60 and a stacked structure of lithium 8-hydroxyquinoline. By wrapping ZnO or C 60 between two layers of lithium 8-hydroxyquinoline, it is possible to avoid direct contact between ZnO or C 60 and the organic layers (such as the light-emitting layer and the hole-transporting layer) of the tandem organic light-emitting device, which may cause degradation of the material interface, and improve the service life of the tandem organic light-emitting device. It is also possible to reduce the problem that direct contact between ZnO or C 60 and the organic layers (such as the light-emitting layer and the hole-transporting layer) of the tandem organic light-emitting device leads to an increase in contact resistance, thereby reducing the energy loss during the carrier transport process. In addition, the three-layer stacked structure forms a continuous LUMO energy level, further reducing the potential barrier during the electron transport process, and thus reducing the energy loss during the carrier transport process.

[0065] In some embodiments of the present invention, the thickness range of the energy level buffer layer 103 is 2 nm - 10 nm, and the surface roughness of the energy level buffer layer 103 is less than or equal to 1 nm. Exemplarily, in a specific embodiment of the present invention, the thickness of the energy level buffer layer 103 can be 2 nm, 5 nm, 8 nm, 10 nm, and the surface roughness can be 0.2 nm, 0.5 nm, 0.8 nm, 1 nm.

[0066] In some embodiments of the present invention, the energy level buffer layer 103 is prepared by evaporation or atomic layer deposition. Exemplarily, taking the energy level buffer layer 103 as ZnO as an example, a film can be formed by thermal evaporation. The ZnO material is high-purity powder (purity ≥ 99.99%), the evaporation temperature < 1300 °C, and during the evaporation process, the substrate temperature is ensured to be ≤ 80 °C. Exemplarily, taking the energy level buffer layer 103 as a mixture of ZnO and lithium 8-hydroxyquinoline, or C 60 and lithium 8-hydroxyquinoline as an example, co-evaporation can be used for co-blending, and the co-blending ratio is 1:1 to 1:9. Exemplarily, taking the energy level buffer layer 103 as ZnO as an example, a film can be formed by atomic layer deposition (Atomic Layer Deposition, ALD). The ZnO precursor is diethylzinc (DEZ) and H2O, the number of cyclic depositions is 50 - 150 times, and the thickness of a single cyclic deposition is During the deposition process, the temperature in the chamber is maintained at 80 °C - 120 °C, the precursor pulse time is DEZ 0.1 s / H2O 0.05 s, and the purge time ≥ 5 s. In one pulse time, atomized precursors are blown into the chamber to deposit on the substrate. After a period of time, the atomized precursors in the chamber for this time are purged clean, and the next cycle is entered.

[0067] The present invention also provides a tandem organic light-emitting device. Figure 3 FIG. Figure 3 is a schematic structural diagram of a tandem organic light-emitting device provided by the present invention. Figure 4 FIG. Figure 4 is an energy level relationship diagram of each layer in the tandem organic light-emitting device provided by the present invention. As shown in FIGS. Figure 3 and 4 , the tandem organic light-emitting device includes: Figure 3 , 4 The tandem organic light-emitting device includes:

[0068] A charge generation layer 100, which includes an N-type material layer 101, a P-type material layer 102, and an energy level buffer layer 103. The N-type material layer 101 has a first LUMO energy level, the P-type material layer 102 has a second LUMO energy level, the first LUMO energy level is greater than the second LUMO energy level, the energy level buffer layer 103 is disposed between the N-type material layer 101 and the P-type material layer 102, and the energy level buffer layer 103 has a third LUMO energy level, and the third LUMO energy level is located between the first LUMO energy level and the second LUMO energy level. Specifically, for the specific structure, materials, and parameters of the charge generation layer 100, reference can be made to the foregoing embodiments, and the present invention will not elaborate herein.

[0069] A first light-emitting layer 110, which is disposed on a side of the N-type material layer 101 of the charge generation layer 100 away from the energy level buffer layer 103. Electrons generated by the charge generation layer 100 migrate to the first light-emitting layer 110, and recombine with holes in the first light-emitting layer 110 to generate photons and emit light. Exemplarily, the material of the first light-emitting layer 110 may be Bepp2-doped Ir(ppy)3. Bepp2 is beryllium bis(2-(2-phenolyl)pyridine), and Ir(ppy)3 is tris(2-phenylpyridine)iridium.

[0070] A first hole transport layer 120, which is disposed on a side of the first light-emitting layer 110 away from the charge generation layer 100. The first hole transport layer 120 is used to transport holes from the hole injection layer 130 to the first light-emitting layer 110, so that they recombine with electrons in the first light-emitting layer 110 to emit light. Exemplarily, the material of the first hole transport layer 120 may be NPB, that is, N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine.

[0071] A hole injection layer 130, which is disposed on a side of the first hole transport layer 120 away from the first light-emitting layer 110. The hole injection layer 130 is used to facilitate the smooth entry of holes from the anode 140 into the first hole transport layer 120. The material of the hole injection layer 130 may be NPB doped with F4-TCNQ (2,3,5,6-tetrafluoro-7,7',8,8'-tetracyanoquinodimethane).

[0072] Anode 140 is disposed on the side of the hole injection layer 130 away from the first hole transport layer 120. The anode 140 is used to inject holes into the hole injection layer 130. Exemplarily, the anode material can be ITO (indium tin oxide).

[0073] The second hole transport layer 150 is disposed on the side of the P-type material layer 102 of the carrier generation layer 100 away from the energy level buffer layer 103. During the operation of the tandem organic light-emitting device, carriers are generated and separated at the interface between the P-type material layer 102 and the second hole transport layer 150. The second hole transport layer 150 is used to transport the generated holes to the second light-emitting layer 160. Exemplarily, the material of the second hole transport layer 150 can be NPB.

[0074] The second light-emitting layer 160 is disposed on the side of the second hole transport layer 150 away from the carrier generation layer 100. The holes from the carrier generation layer 100 recombine with electrons in the second light-emitting layer 160 to emit light. Exemplarily, the material of the second light-emitting layer 160 can be Bepp2-doped Ir(ppy)3.

[0075] The electron transport layer 170 is disposed on the side of the second light-emitting layer 160 away from the second hole transport layer 150. The electron transport layer 170 is used to transport the electrons generated by the cathode 180 into the second light-emitting layer 160, so that they recombine with holes in the second light-emitting layer 160 to emit light. Exemplarily, the material of the electron transport layer 170 can be Bphen-doped lithium 8-hydroxyquinoline.

[0076] The cathode 180 is disposed on the side of the electron transport layer 170 away from the second light-emitting layer 160. The cathode 180 is used to generate electrons. Exemplarily, the material of the cathode 180 is Al.

[0077] It should be noted that the materials of each layer in the tandem organic light-emitting device in the embodiments of the present invention are exemplary descriptions of the present invention. In other embodiments of the present invention, other materials can also be used as long as the functions and effects of the present invention can be achieved. The present invention is not limited herein.

[0078] In addition, in some other embodiments of the present invention, an electron transport layer can also be disposed between the N-type material layer 101 and the first light-emitting layer 110 to promote the transport of electrons from the N-type material layer 101 to the first light-emitting layer 110. An electron injection layer can also be disposed between the electron transport layer 170 and the cathode 180 to help electrons be smoothly injected from the cathode 180 into the electron transport layer 170.

[0079] In the embodiments of the present invention, in order to verify the effects of the present invention, a plurality of tandem organic light-emitting devices were prepared as test devices for testing experiments.

[0080] The test devices are as follows:

[0081] Device A: ITO / NPB:F4-TCNQ(50nm, 4%) / NPB(20nm) / Bepp2:Ir(ppy)3(30nm, 5%) / Bphen:Liq(30nm, 70%) / NPB:F4TCNQ(50nm, 4%) / NPB(20nm) / Bepp2:Ir(ppy)3(30nm, 5%) / Bphen:Liq(30nm, 70%) / Al(200nm). The meaning it represents is: The carrier generation layer in Device A is of a conventional structure and does not include an energy level buffer layer. The anode is ITO; the hole injection layer 130 is NPB doped with F4-TCNQ, with a doping ratio of 4% and a thickness of 50nm; the first hole transport layer 120 is NPB with a thickness of 20nm; the first light-emitting layer 110 is Bepp2 doped with Ir(ppy)3, with a doping ratio of 5% and a thickness of 30nm; the N-type material layer 101 is Bphen doped with Liq, with a doping ratio of 70% and a thickness of 30nm; the P-type material layer 102 is NPB doped with F4-TCNQ, with a doping ratio of 4% and a thickness of 50nm; the second hole transport layer 150 is NPB with a thickness of 20nm; the second light-emitting layer 160 is Bepp2 doped with Ir(ppy)3, with a doping ratio of 5% and a thickness of 30nm; the electron transport layer 170 is Bphen doped with Liq, with a doping ratio of 70% and a thickness of 30nm; the cathode is 200nm thick Al.

[0082] Device B: ITO / NPB:F4-TCNQ(50nm, 4%) / NPB(20nm) / Bepp2:Ir(ppy)3(30nm, 5%) / Bphen:Liq(30nm, 70%) / ZnO(2nm) / NPB:F4-TCNQ(50nm, 4%) / NPB(20nm) / Bepp2:Ir(ppy)3(30nm, 5%) / Bphen:Liq(30nm, 70%) / Al(200nm). In this device, a 2nm thick ZnO is added between the N-type material layer 101 and the P-type material layer 102 as the energy level buffer layer 103, and the others are the same as Device A.

[0083] Device C: ITO / NPB:F4-TCNQ(50 nm, 4%) / NPB(20 nm) / Bepp2:Ir(ppy)3(30 nm, 5%) / Bphen:Liq(30 nm, 70%) / LiQ:ZnO(5 nm, 50%) / NPB:F4-TCNQ(50 nm, 4%) / NPB(20 nm) / Bepp2:Ir(ppy)3(30 nm, 5%) / Bphen:Liq(30 nm, 70%) / Al(200 nm). Compared with Device B, the difference of this device is that the energy level buffer layer 103 uses a mixed dopant of LiQ and ZnO, the doping ratio is 50%, and the thickness of the energy level buffer layer 103 is 5 nm.

[0084] Device D: ITO / NPB:F4-TCNQ(50 nm, 4%) / NPB(20 nm) / Bepp2:Ir(ppy)3(30 nm, 5%) / Bphen:Liq(30 nm, 70%) / C 60 (5 nm) / NPB:F4-TCNQ(50 nm, 4%) / NPB(20 nm) / Bepp2:Ir(ppy)3(30 nm, 5%) / Bphen:Liq(30 nm, 70%) / Al(200 nm). Compared with Device B, the difference of this device is that the energy level buffer layer 103 uses 5 nm thick C 60 .

[0085] Device E: ITO / NPB:F4-TCNQ(50 nm, 4%) / NPB(20 nm) / Bepp2:Ir(ppy)3(30 nm, 5%) / Bphen:Liq(30 nm, 70%) / Liq:C 60 (5 nm, 50%) / NPB:F4-TCNQ(50 nm, 4%) / NPB(20 nm) / Bepp2:Ir(ppy)3(30 nm, 5%) / Bphen:Liq(30 nm, 70%) / Al(200 nm). Compared with Device B, the difference of this device is that the energy level buffer layer 103 uses a mixed dopant of Liq and C 60 with a doping ratio of 50%, and the thickness of the energy level buffer layer 103 is 5 nm.

[0086] The test results are as follows:

[0087] Figure 5 is the voltage-current density-luminance (I-V-L) characteristic curve graph of Device A, Figure 6 is the luminance-current efficiency relationship graph of Device A, Figure 7 is the lifetime curve graph of Device A at an initial luminance of 5000 cd / m 2 ², Figure 8It is the voltage-current density-luminance (I-V-L) characteristic curve graph of device B, Figure 9 It is the luminance-current efficiency relationship graph of device B, Figure 10 It is the lifetime curve graph of device B at an initial luminance of 5000 cd / m 2 below, Figure 11 It is the voltage-current density-luminance (I-V-L) characteristic curve graph of device C, Figure 12 It is the luminance-current efficiency relationship graph of device C, Figure 13 It is the lifetime curve graph of device C at an initial luminance of 5000 cd / m 2 below, Figure 14 It is the voltage-current density-luminance (I-V-L) characteristic curve graph of device D, Figure 15 It is the luminance-current efficiency relationship graph of device D, Figure 16 It is the lifetime curve graph of device D at an initial luminance of 5000 cd / m 2 below, Figure 17 It is the voltage-current density-luminance (I-V-L) characteristic curve graph of device E, Figure 18 It is the luminance-current efficiency relationship graph of device E, Figure 19 It is the lifetime curve graph of device E at an initial luminance of 5000 cd / m 2 below. Table 1 is the performance summary table of each test device in Figures 5 - 19 as shown in Table 1. From the data comparison, devices B, C, D, and E are superior to device A in terms of turn-on voltage, driving voltage, and lifetime. Specifically, for the turn-on voltage optimization: the turn-on voltages of devices B and D are the lowest (4.7 V), which is 0.5 V lower than that of device A (5.2 V); the turn-on voltages of device C (4.8 V) and E (4.9 V) are also reduced by 0.4 V and 0.3 V respectively. At a luminance of 1000 cd / m 2 the driving voltages of devices B, C, D, and E are 6.0 - 6.1 V, which is 0.5 - 0.6 V lower than that of device A (6.6 V). The lifetime is significantly extended: at an initial luminance of 5000 cd / m 2 below, the lifetime of device C is the longest (463 hours), which is 50.3% higher than that of device A (308 hours); at the same time, compared with device A, the lifetimes of devices B (434 hours), E (387 hours), and D (355 hours) are also increased by 41.0%, 25.6%, and 15.3% respectively.

[0088] In summary, while reducing the working voltage (turn-on voltage and driving voltage), devices B, C, D, and E also have significantly better lifetimes than device A. The main reason for this is that a layer of energy level buffer layer is added in the middle of the carrier generation layer composed of the n-type material layer / p-type material layer to achieve a gradient energy level, reduce the carrier injection barrier, and optimize the energy loss.

[0089] Table 1

[0090]

[0091] The present invention also provides a display panel, including the series-connected organic light-emitting device provided in the aforementioned embodiment. The display panel is used as a display panel for a smart phone, a television, a tablet computer, a desktop display, etc., and the present invention is not limited thereto.

[0092] In the description of this article, it is necessary to understand that the terms "up", "down", "left", "right", and other orientations or positional relationships are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of description and simplification of operation, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0093] In the description of this specification, the description with reference to the terms "an embodiment", "example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example.

[0094] In addition, it should be understood that although this specification is described according to implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0095] The technical principle of the present invention is described above in conjunction with specific embodiments. These descriptions are only for explaining the principle of the present invention and cannot be interpreted as limiting the scope of protection of the present invention in any way. Based on the explanations herein, those skilled in the art can associate other specific implementations of the present invention without paying creative labor, and these methods will fall within the scope of protection of the present invention.

Claims

1. A carrier generation layer, characterized in that: include: An N-type material layer, wherein the N-type material layer has a first LUMO energy level; A P-type material layer, wherein the P-type material layer has a second LUMO energy level, and the first LUMO energy level is greater than the second LUMO energy level; An energy level buffer layer is disposed between the N-type material layer and the P-type material layer, and the energy level buffer layer has a third LUMO energy level, and the third LUMO energy level is located between the first LUMO energy level and the second LUMO energy level.

2. The carrier generation layer according to claim 1, characterized in that: The N-type material layer is formed by doping the electron transport layer with an N-type dopant, and the P-type material layer is formed by doping the hole transport layer with a P-type dopant.

3. The carrier generation layer according to claim 2, characterized in that: The N-type dopant includes an alkali metal compound, and the P-type dopant includes at least one of HAT-CN, F4-TCNQ, MoO3, and W2(hpp)4.

4. The carrier generation layer according to claim 2, characterized in that: The doping ratio of the N-type dopant is 10%-50%, and the doping ratio of the P-type dopant is 2%-15%.

5. The carrier generation layer according to any one of claims 1 to 4, characterized in that: The material of the energy level buffer layer includes ZnO, 8-hydroxyquinoline lithium and C 60 At least one of .

6. The carrier generation layer according to claim 5, characterized in that: The energy level buffer layer is a three-layer stacked structure, which includes a stacked structure of 8-hydroxyquinoline lithium, ZnO and 8-hydroxyquinoline lithium, and a stacked structure of 8-hydroxyquinoline lithium, C 60 and 8-hydroxyquinolate lithium stacking structure.

7. The carrier generation layer according to claim 5, characterized in that: The thickness of the energy level buffer layer is in the range of 2nm-10nm, and the surface roughness of the energy level buffer layer is less than or equal to 1nm.

8. The carrier generation layer according to claim 5, characterized in that: The energy level buffer layer is prepared by evaporation or atomic layer deposition.

9. A tandem organic light-emitting device, characterized in that: The method comprises the carrier generation layer as claimed in any one of claims 1 to 8, further comprising: A first light-emitting layer, wherein the first light-emitting layer is disposed on a side of the N-type material layer of the carrier generation layer away from the energy level buffer layer; A first hole transport layer, wherein the first hole transport layer is disposed on a side of the first light-emitting layer away from the carrier generating layer; A hole injection layer, wherein the hole injection layer is disposed on a side of the first hole transport layer away from the first light-emitting layer; an anode, the anode being disposed on a side of the hole injection layer away from the first hole transport layer; A second hole transport layer, the second hole transport layer is arranged on a side of the P-type material layer of the carrier generation layer away from the energy level buffer layer; A second light-emitting layer, wherein the second light-emitting layer is disposed on a side of the second hole transport layer away from the carrier generation layer; An electron transport layer, wherein the electron transport layer is disposed on a side of the second light-emitting layer away from the second hole transport layer; A cathode is disposed on a side of the electron transport layer away from the second light-emitting layer.

10. A display panel, characterized in that: Comprising the tandem organic light emitting device as claimed in claim 9.

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