OLED display panel and display device equipped therewith

Abstract

An OLED display panel comprising a first electrode (101, 201, 301) and a second electrode (102, 202, 302), at least one light-emitting layer (103, 203, 303, 503, 603) arranged between the first electrode (101, 201, 301) and the second electrode (102, 202, 302); a first functional layer (104, 204, 304) and a second functional layer (105, 205, 305) arranged on either side of the respective light-emitting layer; wherein the first functional layer (104, 204, 304) comprises at least one compound having hole transport capability; and the second functional layer (105, 205, 305) comprises at least one compound having electron transport capability; wherein in the at least one light-emitting layer (103, 203, 303, 503, 603) an organic light-emitting compound is doped with a thermally activated delayed fluorescence material in at least one of the light-emitting layers (103, 203, 303, 503, 603); where the lowest triplet energy level of the organic light-emitting compound (T H ) is higher than the lowest singlet energy level of the thermally activated material (S T ) delayed fluorescence; where the lowest triplet energy level of the compound with hole transport capability (T1) and the lowest triplet energy level of the organic light-emitting compound (T H ) satisfy the following formula (I): T 1 − TH > − 0.2 eV where the lowest triplet energy level of the compound with electron transport capability (T2) and the lowest triplet energy level of the organic light-emitting compound (T H ) satisfy the following formula (II): T 2 − TH > − 0.2 eV wherein the at least one light-emitting layer (103, 203, 303, 503, 603) comprises at least one blue light-emitting layer; wherein the blue light-emitting layer comprises at least one high-energy organic light-emitting compound, at least one low-energy organic light-emitting compound, and a thermally activated delayed fluorescence material doped therein; wherein the lowest singlet energy level of the high-energy organic light-emitting compound is higher than the lowest singlet energy level of the thermally activated delayed fluorescence material; where the lowest singlet energy level of the low-energy organic light-emitting compound is lower than the lowest singlet energy level of the thermally activated delayed fluorescence material.

Description

TECHNICAL FIELDThe present disclosure relates to the field of organic electroluminescent materials, and more specifically to an OLED display panel and a display device equipped therewith, and more particularly to a combination of a light emitting layer material and its application in an organic electroluminescent device.TECHNOLOGICAL BACKGROUNDCurrently, an organic electroluminescent device generally consists of an anode, an organic layer and a cathode, at least one of the organic layers having a luminescent function, and the light emitting layer of an OLED device generally needs to meet the requirement of emitting light beams of three wavelengths, a blue light (B), a green light (G) and a red light (R). Typically, the blue light-emitting material is a fluorescence-emitting material, a TTA light-emitting material, or a phosphorescence-emitting material; the green light-emitting material is a phosphorescence-emitting material; and the red light-emitting material is a phosphorescence-emitting material. The luminescence mechanism of fluorescence consists in the use of singlet excitons making up 25% of the total excitons generated after carrier recombination; the luminescence mechanism of TTA consists in the generation of a singlet exciton from two triplet excitons using 62.5% of the total excitons; and the luminescence mechanism of phosphorescence consists in the use of singlet excitons and triplet excitons generated after carrier recombination.When the blue light-emitting material is a fluorescent light-emitting material, the dopant is mainly perylene derivatives, oxadiazole derivatives, and anthracene derivatives, singlet excitons are used that make up 25% of total excitons, and the maximum external quantum yield is not more than 5%, which results in too high power consumption and also waste of energy. When the blue light-emitting material is a TTA material, the host material in the light-emitting layer is mainly used to complete the triplet-triplet annihilation process for luminescence, using 62.5% of the total excitons produced and this ratio is higher than that in fluorescence, but theoretically 100% utilization of the excitons produced cannot be achieved, thereby causing waste of energy. When the blue light-emitting material is a phosphorescence-emitting material, the dopant is mainly organic complexes of heavy metals such as iridium, platinum and ruthenium, and theoretically, 100% utilization of the excitons generated can be achieved, but due to the longer lifetime of the triplet excitons, a state in which the concentration of the excitons is too high occurs, causing extinction among the excitons, thereby causing energy deactivation, and thus the lifetime of the device is shorter.In 2011, Professor Adachi et al. reported a thermally activated delayed fluorescence (TADF) material with good light output by the University of Kyushu, Japan. The energy gap between state S 1 and state T 1 of such a material is smaller and the lifetime of the excitons in state T 1 is longer. Under certain temperature conditions, for the excitons in state T 1 the process T 1 → S 1 can be realized by reverse intersystem crossing (RISC), and then undergo radiation attenuation from state S 1 to ground state S 0. Therefore, the luminous efficiency of an OLED device using such a light emitting layer material is comparable to that of a phosphorescence emitting material, and there is no need for a rare metal element, thereby reducing the material cost.There is still a need in the art to develop a method for improving the efficiency of a blue light emitting organic electroluminescent device by using a thermally activated delayed fluorescence (TADF) material and to provide an efficient and stable method for manufacturing an organic electroluminescent device.US 2015 / 0 115 225 A1 discloses an organic electroluminescent device comprising: a cathode; an anode; and an organic thin-film layer arranged between the cathode and the anode, wherein the organic thin-film layer has one or more layers including an emitting layer, wherein the emitting layer includes a first material and a second material in the form of a fluorescent doping material.WO 2016 / 194 604 A1 discloses an organic EL device with a low driving voltage, a high luminous efficiency and a long lifetime. The organic EL device is an organic electroluminescence device having a light emitting layer between an anode and a cathode that are opposed to each other, wherein: the light emitting layer contains a host material and a light emitting dopant; and the host material is a material obtained by mixing a first host selected from compounds in which each of a diphenyltriazinyl group is bonded to a nitrogen atom of an indolocarbazole ring and a phenyl group of the diphenyltriazinyl group is substituted with one or more phenyl groups, and a second host selected from compounds in which each of aromatic hydrocarbon groups is bonded to two nitrogen atoms of a biscarbazole ring and at least one of the aromatic hydrocarbon groups is a condensed aromatic hydrocarbon group.US 2012 / 0 241 732 A1 discloses a fluorescence-emitting material that improves the luminous efficiency of an organic light-emitting element such as an organic EL element or an organic PL element, and an organic light-emitting element using the fluorescence-emitting material. The fluorescence emitting material comprises a compound having an indolocarbazole skeleton.SUMMARY OF THE DISCLOSUREThe present invention provides an OLED display panel according to claim 1 and a display device according to claim 24 comprising the OLED display panel. Preferred embodiments are set out in the dependent claims.Compared with the prior art, the present disclosure has the following advantageous effects:In the present disclosure, a higher luminous efficiency is obtained by selecting a thermally activated delayed fluorescence material to dope it into an organic light emitting layer and a compound having a specific energy level cooperative therewith, thereby improving the luminous efficiency of an organic photo-electronic device.DESCRIPTION OF THE DRAWINGSFIG. 1 is a cross-sectional structural view of an OLED display panel provided in a specific embodiment of the present disclosure; FIG. 2 is a cross-sectional structural view of an OLED display panel provided in a specific embodiment of the present disclosure; FIG. 3 is a cross-sectional structural view of an OLED display panel provided in a specific embodiment of the present disclosure; FIG. 4 is a configuration diagram of a display device provided in an example of the present disclosure; FIG. 5 is a cross-sectional configuration diagram of the OLED display panels in an example 2 and a comparative example 2 when a function test is performed in the present disclosure; FIG. 6 is a cross-sectional configuration diagram of OLED display panels in Example 5 and Comparative Example 4 when function testing is performed in the present disclosure.SPECIFIC EMBODIMENTSFor the purpose of following the present disclosure, the following examples are given below in the present disclosure. It will be understood by those skilled in the art that the examples are merely illustrations of the present disclosure and are not to be construed as specific limitations of the present disclosure.In a specific embodiment of the present disclosure, with reference to FIG. 1, an OLED display panel is provided, comprising a first electrode 101 and a second electrode 102, at least one light emitting layer 103 arranged between the first electrode 101 and the second electrode 102; a first functional layer 104 and a second functional layer 105 arranged on both sides of a respective light emitting layer 103; wherein the first functional layer 104 comprises at least one compound having hole transportability; and the second functional layer 105 comprises at least one compound having electron transportability; wherein in the at least one light emitting layer an organic light emitting compound in at least one of the light emitting layers 103 is doped with a thermally activated material of delayed fluorescence; wherein the lowest triplet energy level of the organic light emitting compound (T H) is higher than the lowest singlet energy level of the thermally activated delayed fluorescence material (S T) ; wherein the lowest triplet energy level of the hole transportability compound (T 1) and the lowest triplet energy level of the organic light emitting compound (T H) satisfy the following formula (I): wherein the lowest triplet energy level of the electron transportability compound (T 2) and the lowest triplet energy level of the organic light emitting compound (T H) satisfy the following formula (II):Note that the OLED display panel according to the present disclosure may further include a plurality of light emitting layers, and FIG. 1 illustrates an example in which only one light emitting layer is exemplified. If a plurality of light-emitting layers are contained, the first functional layer and second functional layer are arranged on both sides of each corresponding light-emitting layer.The thermally activated delayed fluorescence (TADF) material is a material in which excited triplet excitons can be converted to the singlet state by reverse intersystem crossing at room temperature when the energy gap between the triplet state and singlet state is small. When a TADF material is used in the blue light emitting layer, a blue light emitting organic electroluminescent device capable of converting triplet excitation energy into fluorescence with a theoretical quantum efficiency of 100% can be provided. The TADF material is used directly as a doping material, and the luminescence process is achieved by a radiation transition of the singlet excitons generated to the ground state. The TADF material transfers the energy of the singlet excitons generated to the ordinary fluorescent dopant material, and the dopant material emits fluorescence through the radiation transition.In a reference example, the at least one light emitting layer comprises at least one blue light emitting layer; wherein the blue light emitting layer has at least one high-energy organic light emitting compound and a delayed fluorescence thermally activated material doped therein; wherein in the blue light emitting layer, the lowest singlet energy level of the high-energy organic light emitting compound is higher than the lowest singlet energy level of the delayed fluorescence thermally activated material.When the light emitting layer is doped with a thermally activated delayed fluorescence material, an organic compound having a high energy state is selected for the host material, and the luminescent type further includes the transition from the triplet state to the singlet state of the thermally activated delayed fluorescence material, in addition to the transition from the singlet state of the high energy organic compound to the singlet state of the thermally activated delayed fluorescence material.When the blue light emitting layer comprises at least one high energy organic light emitting compound and a delayed fluorescence thermally activated material doped therein, in the light emitting layer doped with the delayed fluorescence thermally activated material, the volume fraction of the delayed fluorescence thermally activated material is preferably ≤50%, for example 48%, 46%, 44%, 42%, 38%, 35%, 33%, 28%, 24%, 21%, 18%, 15%, 13%, 11%, 8% and 6%, etc., more preferably ≤25%, and most preferably ≤15%.The volume fraction of the thermally activated delayed fluorescence material in the light emitting layer determines the concentration of excitons and a sufficiently high energy transfer, wherein by a volume fraction of 50% or less, it can be ensured that the energy is sufficient without causing too high concentration of excitons, which results in extinction of excitons, which reduces the efficiency and the lifetime of the device.According to the invention, the at least one light emitting layer comprises at least one blue light emitting layer; wherein the blue light emitting layer comprises at least one high-energy organic light emitting compound, at least one low-energy organic light emitting compound and a delayed fluorescence thermally activated material doped therein; wherein the lowest singlet energy level of the high-energy organic light emitting compound is higher than the lowest singlet energy level of the delayed fluorescence thermally activated material; wherein the lowest singlet energy level of the low-energy organic light emitting compound is lower than the lowest singlet energy level of the delayed fluorescence thermally activated material.When the light emitting layer is doped with a thermally activated delayed fluorescence material, an organic compound having a high energy state and an organic compound having a low energy state are simultaneously selected for the host material, and the luminescent type further comprises the transition from the triplet state to the singlet state of the thermally activated delayed fluorescence material, in addition to the transition from the singlet state of the high energy organic compound to the singlet state of the low energy organic compound (including the direct transition from the singlet state of the high energy organic compound to the singlet state of the low energy organic compound, and the transition first from the singlet state of the high energy organic compound to the singlet state of the thermally activated delayed fluorescence material and then to the singlet state of the low energy organic compound). As a result, with the "blue light emitting layer having at least one high-energy organic light emitting compound, at least one low-energy organic light emitting compound, and a delayed fluorescence thermally activated material doped therein", excellent energy transfer can be realized and the object of high efficiency can be achieved.When the blue light-emitting layer has at least one high-energy organic light-emitting compound, at least one low-energy organic light-emitting compound, and a thermally activated material doped therein with delayed fluorescence, in the blue light-emitting layer, the volume proportion of the high-energy organic light-emitting compound is preferably ≥50%, for example, 52%, 55%, 57%, 59%, 61%, 63%, 67%, 69%, 72%, 74%, 76%, 78%, 82%, 85%, 88%, 92%, and 95%, etc.When the blue light-emitting layer has at least one high-energy organic light-emitting compound, at least one low-energy organic light-emitting compound, and a thermally activated material doped therein with delayed fluorescence, in the blue light-emitting layer, the volume proportion of the low-energy organic light-emitting compound is ≤ 10%, for example, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2% and 1%, etc.In a preferred specific embodiment, the difference in energy level between the lowest singlet state S T and the lowest triplet state T T of the thermally activated delayed fluorescence material is ΔE st= E ST- E TT ≤ 0.30 eV, for example 0.29 eV, 0.28 eV, 0.27 eV, 0.26 eV, 0.25 eV, 0.24 eV, 0.23 eV, 0.22 eV, 0.21 eV, 0.20 eV, 0.19 eV, 0.18 eV, 0.16 eV, 0.14 eV, 0.13 eV, 0.12 eV, 0.11 eV, 0.10 eV, 0.09 eV, 0.08 eV, 0.07 eV, 0.06 eV, 0.05 eV, 0.04 eV, 0.03 eV, 0.02 eV and 0.01 eV, etc. When ΔE st > 0.30 eV, the fluorescence retarding effect of the compound is not evident.The compound preferably has a ΔE st ≤ 0.25 eV; more preferably the compound has a ΔE st ≤ 0.15 eV; even more preferably the compound has a ΔE st ≤ 0.10 eV; even more preferably the compound has a ΔE st ≤ 0.05 eV; most preferably the compound has a ΔE st ≤ 0.02 eV; and most preferably the compound has a ΔE st ≤ 0.01 eV.The present disclosure is not particularly limited to a specific thermally activated delayed fluorescence material, and any thermally activated delayed fluorescence material that can be obtained by those skilled in the art may be used in the OLED display panel according to the present disclosure.In the first aspect of the specific embodiments, the thermally activated delayed fluorescence material is any one or a combination of at least two materials selected from the group consisting of the compounds having the structure represented by formula (S-1); wherein A a1, A a2, A a3, A a4, A a5, A a6, A a7, A a8 i A a9 and Aa10in formula (S-1) are each independently selected from a hydrogen atom, a nitrile group or a functional group having a structure according to formula (II); and A a1, A a2, A a3, A a4, A a5, A a6, A a7, A a8, A a9 and A a10 is at least one nitrile group and at least one group having a structure of the formula (S-1a); wherein R a1, R a2, R a3, R a4, R a5, R a5, R a7 and R a8 in formula (S-1a) are each independently selected from a hydrogen atom, a deuterium atom or a C 6-30- aromatic group or a C_NER58 heterocyclic aromatic group.The thermally activated delayed fluorescence material described in any of the specific embodiments includes, for example, or In the second aspect of the specific embodiments, the thermally activated delayed fluorescence material is any one or a combination of at least two materials selected from the group consisting of the compounds having the structure represented by formula (S-2); wherein A b1, A b2, A b3 and A b4 in formula (S-2) are each independently selected from a hydrogen atom or a functional group having a structure of formula (S-2b), and at least one of A b1, A b2, A b3 and A b4 is a functional group having a structure of formula (S-2b); wherein R b1 and R b2 are each independently selected from a hydrogen atom, a deuterium atom, a C 1- C 30- alkyl, a C 6-30- aromatic group, or a C 2-30- heterocyclic aromatic group; wherein Y b1 and Y b2 are each independently selected from a substituted or unsubstituted carbon or nitrogen; wherein X in formula (S-2b) is any compound selected from the group consisting of an oxy group, a thio group, a substituted or unsubstituted imino group, a substituted or unsubstituted methylene group, a substituted or unsubstituted silicolene group; wherein R b3, R b4, R b5, R b6, R b7, R b8, R b9 and R b10 are each independently selected from a hydrogen atom, a deuterium atom, a C 1- C 30 alkyl group, a C6-30aromatic group or a C2-30heterocyclic aromatic group.The thermally activated delayed fluorescence material described in any of the specific embodiments includes, for example: one of and The thermally activated delayed fluorescence material according to the present disclosure may also be selected from any thermally activated delayed fluorescence materials known to those skilled in the art, for example, the following: In a further specific embodiment, with reference to FIG. 2, an OLED display panel has, by way of example, the structure as shown in FIG. 2, which comprises a first electrode 201 and a second electrode 202, at least one light-emitting layer 203 arranged between the first electrode 201 and second electrode 202; a first functional layer 204 and a second functional layer 205 arranged on both sides of a respective light-emitting layer 203; a third functional layer 206 arranged between the first electrode 201 and the first functional layer 204, wherein the third functional layer has at least one hole transport connection having a structure according to formula (K-1); wherein R k1 R k2, R k3, R k4, R k5 and R k6 in formula (K-1) are each independently selected from the group consisting of hydrogen, an unsubstituted phenyl or a phenyl group having a C1-C6alkyl substituent; wherein R K5 and R k6 are each independently selected from the group consisting of hydrogen, an unsubstituted C1-C6alkyl, fluorine and chlorine.The third functional layer has a function of transporting holes and adjusting the length of the optical cavity.In a specific embodiment, the hole transport compound having a structure according to formula (K-1) comprises and / or In a further specific embodiment, with reference to FIG. 3, an OLED display panel has, by way of example, the structure as shown in FIG. 3, which comprises a first electrode 301 and a second electrode 302, at least one light-emitting layer 303 arranged between the first electrode 301 and second electrode 302; a first functional layer 304 and a second functional layer 305 arranged on both sides of a respective light-emitting layer 303; a third functional unit arranged between the first electrode 301 and the first functional layer 304, wherein the third functional unit has a third functional layer 306 and additional functional layers 3071 and 3072 arranged on both sides of the third functional layer 306. The additional functional layer comprises a hole transport compound having a structure of formula (K-1) and a dopant having a structure of formula (C-1) doped into the hole transport compound having the structure of formula (K-1); wherein R C1 in formula (C-1) comprises a fluorine substituted aromatic ring group.The additional functional layer has the function of assisting in the injection of holes from the anode into the hole transport layer.In a specific embodiment, the dopant having a structure according to formula (C-1) comprises: In a specific embodiment, the second functional layer comprises a host material having a structure according to formula (D-1) and a dopant dispersed in the host material, wherein the dopant comprises a metal and / or a metal compound; wherein R D1 R D2, R D3 and R D4 in formula D-1 are each independently selected from hydrogen, an alkyl group, a substituted or unsubstituted aromatic group; wherein a metallic element in the metal and / or the metal compound comprises an alkali metal, an alkaline earth metal and / or a rare earth metal.By selecting a host material having a structure according to formula (D-1) and a dopant dispersed in the host material so as to obtain a second functional layer, high electron mobility and good electron injection can be achieved.In a specific embodiment, the host material having a structure according to formula (D-1) comprises: In a specific embodiment, the metallic element in the metal and / or the metal compound comprises lithium, calcium, ytterbium or magnesium.Preferably, the metallic element in the metal and / or the metal compound is lithium.In a specific embodiment, the second electrode includes silver or a silver alloy; an alloying element of the silver alloy includes any one element or a combination of at least two of an alkali metal element, an alkaline earth metal element, and a rare earth metal element.The alloying element of the silver alloy preferably comprises any element or a combination of at least two of the elements lithium, calcium, ytterbium and magnesium.In a specific embodiment, the first electrode has at least two functional layers, and the at least two functional layers include a reflective film and a conductive transparent thin film.The reflective film preferably comprises silver.The conductive transparent thin film preferably comprises an ITO film or an IZO film.In a specific embodiment, the second electrode comprises a magnesium-silver alloy, a silver metal, a silver-ytterbium alloy or a silver-rare earth metal alloy.In a specific embodiment, a light beam from the OLED display panel is emitted from the second electrode.In a specific embodiment, the present disclosure also provides a display device including the OLED display panel as described above in any of the embodiments. The display device may be a mobile phone as shown in FIG. 4, but may be a computer, a television, and a smart portable device, etc., but the examples of the present disclosure are not particularly limited thereto.Functional tests are also carried out for a series of examples and comparative examples provided by the present disclosure within the scope of the present disclosure, wherein the test method is as follows:A Keithley 2365A digital nanovoltmeter is used to test the currents of the organic photo-electronic devices manufactured in the examples and comparative examples at different voltages, and then to determine the current densities of the organic photo-electronic devices at different voltages by dividing the currents by the light emitting area. The luminance and radiant energy flux density of the organic photo-electronic devices prepared in Test Examples and Comparative Examples were tested at different voltages with a Konicaminolta CS-2000 spectroradiometry luminance meter. According to the current density and luminance of the organic photo-electronic devices at different voltages, the current efficiency (Cd / A) and the external quantum efficiency EQE at an identical current density (0.1 mA / cm 2) were obtained.Examples 1, 3, 4, 6, 7, 9, 10, 11 and 12 and Comparative Examples 1 and 3 have the structure as shown in FIG. 3, which has the following in detail:a substrate 1, an ITO electrode 301, a first doping layer 3071 (thickness: 10 nm), a third functional layer 306 (thickness: 60 nm), a second doping layer 3072 (thickness: 10 nm), a first hole transport layer 304 (thickness: 30 nm), a light emitting layer 303 (thickness: 30 nm), a first electron transport layer 305 (thickness: 30 nm) and a silver electrode 302 (thickness: 100 nm).Example 2 and Comparative Example 2 have the structure shown in FIG. 5, which specifically includes:a substrate 1, an ITO electrode 501, a first doping layer 5071 (thickness: 10 nm), a third functional layer 506 (thickness: 60 nm), a first hole transport layer 504 (thickness: 30 nm), a light emission layer 503 (thickness: 30 nm), a first electron transport layer 505 (thickness: 30 nm), and a silver electrode 502 (thickness: 100 nm).Example 5 and Comparative Example 4 have the structure as shown in FIG. 6, which specifically includes:a substrate 1, an ITO electrode 601, a third functional layer 606 (thickness: 60 nm), a second doping layer 6072 (thickness: 10 nm), a first hole transport layer 604 (thickness: 30 nm), a light emission layer 603 (thickness: 30 nm), a first electron transport layer 605 (thickness: 30 nm), and a silver electrode 602 (thickness: 100 nm).Example 8 and Comparative Example 6 have the structure as shown in FIG. 1, which specifically includes:a substrate 1, a first electrode 101 (an ITO electrode), a first functional layer 104 (a hole transport layer) (thickness: 30 nm), a light emission layer 503 (thickness: 30 nm), a second functional layer 105 (an electron transport layer) (thickness: 30 nm), and a second electrode 102 (a silver electrode) (thickness: 100 nm).The materials selected for the respective layers of the OLED display panels in Examples 1-6 are shown in Table 1-1 and Table 1-2: Table 1-1: Selected materials for the respective layers of the OLED display panels in Examples 1-6 Table 1-1: Selected materials for the respective layers of the OLED display panels in Examples 1 to 6First Doping LayerK:C (1:100)K:C (1:100)K:C (1:100)K:C (1:100)K:C (1:100)Third Functional LayerK. KK. KK. KK. KK. KK. KSecond doping layerK:C (1:100)K:C (1:100)K:C (1:100)K:C (1:100)K:C (1:100)First Hole Transport LayerHT1HT1HT1HT1HT1HT1Light-emitting LayerMaterialsBH:S1:BDBH:S1:BDBH:S1:BDBH:S1BH:S1BH:S1:BDDoping Ratio(80:15:5)(80:15:5)(80:15:5)(90:10)(90:10)(90:1:9)First Electron Transport LayerET1:Yb (100:1)ET1:Yb (100:1)ET1:Yb (100:1)ET1:Yb (100:1)ET1:Yb (100:1)ET2:Yb (100:1)Silver electron layerAg AgAg AgMgAg alloyAg AgAg AgAg AgTable 1-2: Selected materials for the respective layers of the OLED display panels in Examples 7 to 12Table 1-2: Selected materials for the respective layers of the OLED display panels in Examples 7 to 12First Doping LayerK:C (1:100)K:C (1:100)K:C (1:100)K:C (1:100)K:C (1:100)Third Functional LayerK. K-K. KK. KK. KK. KSecond doping layerK:C (1:100)K:C (1:100)K:C (1:100)K:C (1:100)K:C (1:100)First Hole Transport LayerHT1HT1HT1HT1HT1HT1Light-emitting LayerMaterialsBH:S1:BDBH:S1:BDBH:S2:BDBH:S3:BDBH:S4:BDBH:S5:BDDoping Ratio(45:50:5)(80:15:5)(80:15:5)(80:15:5)(80:15:5)(80:15:5)First Electron Transport LayerET2:Yb (100:1)ET1:Yb (100:1)ET1:YbET1:YbET1:YbET1:YbSilver electron layerAg AgAg AgAg AgAg AgAg AgAg AgTable 1-3: Selected materials for the respective layers of the OLED display panels in the Comparative ExamplesTable 1-3: Selected materials for the respective layers of the OLED display panels in the Comparative ExamplesFirst Doping LayerK:C (1:100)K:C (1:100)K:C (1:100)-K:C (1:100)-Third Functional LayerK. KK. KK. KK. KK. K--Second doping layerK:C (1:100)-K:C (1:100)K:C (1:100)K:C (1:100)-First Hole Transport LayerHT1HT1HT1HT1--HT1Light-emitting LayerBH:BD (95:5)BH:BD (95:5)BH:BD (95:5)BH:BD (95:5)BH:BD (95:5)BH:BD (95:5)First Electron Transport LayerET1:Yb (100:1)ET1:Yb (100:1)ET1:Yb (100:1)ET1:Yb (100:1)ET1:Yb (100:1)ET2: Yb (100:1)Silver electrode layerAg AgAg AgMgAg alloyAg AgAg AgAg AgThe meaning of the respective code designations in Tables 1-1, 1-2 and 1-3 is explained in Table 2. Table 2: Chemical formula for the respective code designations in Tables 1-1 and 1-2 Table 2: Chemical formula for the respective code designations in Tables 1-1 and 1-2K. K S2C. C S3NPB S4HT1 S5BH (High Energy Organic Light Emitting Compound) ET1BD (Low Energy Organic Light Emitting Compound) ET2S1The results of the functional tests for the OLED display panels provided in the examples and comparative examples are shown in Table 3. Table 3: Results of the functional tests for the OLED display panels provided in Examples and Comparative Examples Table 3: Results of the functional tests for the OLED display panels provided in Examples and Comparative ExamplesExample 13,3 V7 %Example 23,2 V6,3 %Example 33,3 V6,5 %Example 43,3 V12,2 %Example 55,6 V4,7 %Example 67,6 V6,2 %Example 77,7 V5,8 %Example 86,6 V3,8 %Example 93,2 V7,2 %Example 103,4 V7,1 %Example 113,3 V6,8 %Example 123,3 V6,9 %Comparative Example 13,2 V6,0 %Comparative Example 23,3 V5,7 %Comparative Example 33,3 V5,2 %Comparative Example 45,5 V2,5 %Comparative Example 57,5 V2,0 %Comparative Example 66,1 V1,0 %As is apparent from Tables 1 to 3, the luminous efficiency can be improved by using the thermally activated delayed fluorescence material by appropriate arrangement of the structure of the apparatus. In particular, the external quantum efficiency (EQE) of the OLED display panel can be significantly improved by using, as a dopant, a thermally activated delayed material for admixture with the host material, provided that the voltage does not greatly change, the voltages in Examples 1 to 4 were, for example, in the range of 3.2-3.3 V and the external quantum efficiency was greater than 6.5%; on the other hand, the voltage in Comparative Examples 1 to 3 was in the range of 3.2-3.3 V and the external quantum efficiency was less than 6.0%. As can be seen from the results of Examples 2 and 5 and Example 1, by the arrangement of the third functional layer and by the cooperation with the thermally activated delayed material, the external quantum efficiency of the OLED device can be effectively improved. As is apparent from the results of Examples 1, 6 and 7, the OLED device had the highest external quantum efficiency when the doping amount of the thermally activated delayed material was 15%. However, as is apparent from the results of Comparative Examples 1 to 6 and Examples, the external quantum efficiency of the corresponding device can be improved only when the thermally activated delayed material was doped therein, irrespective of the presence of the third functional layer and the structure of the third functional unit.

Claims

OLED display panel, comprising a first electrode (101, 201, 301) and a second electrode (102, 202, 302), at least one light-emitting layer (103, 203, 303, 503, 603) arranged between the first electrode (101, 201, 301) and the second electrode (102, 202, 302); a first functional layer (104, 204, 304) and a second functional layer (105, 205, 305) arranged on both sides of the respective light-emitting layer; wherein the first functional layer (104, 204, 304) comprises at least one compound having a hole transport capability; and the second functional layer (105, 205, 305) comprises at least one compound having an electron transport capability; wherein in the at least one light emitting layer (103, 203, 303, 503, 603), an organic light emitting compound in at least one of the light emitting layers (103, 203, 303, 503, 603) is doped with a delayed fluorescence thermally activated material; wherein the lowest triplet energy level of the organic light emitting compound (T H) is higher than the lowest singlet energy level of the delayed fluorescence thermally activated material (S T) ; wherein the lowest triplet energy level of the hole transportability compound (T 1) and the lowest triplet energy level of the organic light emitting compound (T H) satisfy the following formula (I): T 1-T H>-0.2 eV wherein the lowest triplet energy level of the electron transportability compound (T 2) and the lowest triplet energy level of the organic light emitting compound (T H) satisfy the following formula (II): T 2-T H>-0.2 eV wherein the at least one light emitting layer (103, 203, 303, 503, 603) comprises at least one blue light emitting layer; wherein the blue light emitting layer comprises at least one high energy organic light emitting compound, at least one low energy organic light emitting compound, and a delayed fluorescence thermally activated material doped therein; wherein the lowest singlet energy level of the high energy organic light emitting compound is higher than the lowest singlet energy level of the delayed fluorescence thermally activated material; wherein the lowest singlet energy level of the low energy organic light emitting compound is lower than the lowest singlet energy level of the delayed fluorescence thermally activated material.The OLED display panel according to claim 1, wherein in the light emitting layer (103, 203, 303, 503, 603) doped with the thermally activated delayed fluorescence material, the volume fraction of the thermally activated delayed fluorescence material is ≤ 50%.The OLED display panel according to claim 1, wherein in the light emitting layer (103, 203, 303, 503, 603) doped with the thermally activated delayed fluorescence material, the volume fraction of the thermally activated delayed fluorescence material is ≤ 25%.The OLED display panel according to claim 1, wherein in the light emitting layer (103, 203, 303, 503, 603) doped with the thermally activated delayed fluorescence material, the volume fraction of the thermally activated delayed fluorescence material is ≤ 15%.The OLED display panel according to claim 1, wherein in the blue light emitting layer, the volume fraction of the high energy organic light emitting compound is ≥ 50%.The OLED display panel according to claim 1, wherein in the blue light emitting layer, the volume fraction of the low-energy organic light emitting compound is ≤ 10%.The OLED display panel of claim 1, wherein the difference in energy level between the lowest singlet state S T and the lowest triplet state T T of the thermally activated delayed fluorescence material is ΔE st= E ST- E TT ≤ 0.30 eV.The OLED display panel according to claim 7, wherein the thermally activated delayed fluorescence material is any one or a combination of at least two materials selected from the group consisting of the compounds having the structure represented by formula (S-1); wherein A a1, A a2, A a3, A a4, A a5, A a6, A a7, A a8, A a9 and Aa10in formula (S-1) are each independently selected from a hydrogen atom, a nitrile group or a functional group having a structure according to formula (II); and A a1, A a2, A a3, A a4, A a5, A a6, A a7, A a8, A a9 and A a10 is at least one nitrile group and at least one group having a structure of the formula (S-1a); wherein R al1 R a2, R a3, R a4, R a5, R a6, R a7 and R a8 in formula (S-1a) are each independently selected from a hydrogen atom, a deuterium atom or a C 6-30- aromatic group or a C_NER45 heterocyclic aromatic group.The OLED display panel according to claim 7, wherein the thermally activated delayed fluorescence material is any one or a combination of at least two materials selected from the group consisting of the compounds having the structure represented by formula (S-2); wherein A b1, A b2, A b3 and A b4 in formula (S-2) are each independently selected from a hydrogen atom or a functional group having a structure of formula (S-2b), and at least one of A b1, A b2, A b3 and A b4 is a functional group having a structure of formula (S-2b); wherein R b1 and R b2 are each independently selected from a hydrogen atom, a deuterium atom, a C 1-30- alkyl, a C 6-30- aromatic group, or a C 2-30- heterocyclic aromatic group; wherein Y b1 and Y b2 are each independently selected from a substituted or unsubstituted carbon or nitrogen; wherein, in formula (S-2b), X is any compound selected from the group consisting of an oxy group, a thio group, a substituted or unsubstituted imino group, a substituted or unsubstituted methylene group, a substituted or unsubstituted silicolene group; wherein R b3, R b4, R b5, R b6, R b7, R b8, R b9 and R b10 are each independently selected from a hydrogen atom, a deuterium atom, a C 1- C 30- alkyl group, a C6-30aromatic group or a C2-30heterocyclic aromatic group.The OLED display panel of claim 1, wherein a third functional layer (206, 306, 506, 606) is disposed between the first electrode (201, 301) and the first functional layer (204, 304), and the third functional layer (206, 306, 506, 606) comprises at least one hole transport compound having a structure according to formula (K-1): wherein R k1, R k2, R k3, R k4, R k5 and R k6 in formula (K-1) are each independently selected from the group consisting of hydrogen, an unsubstituted phenyl, or a phenyl group having a C1-C6 alkyl substituent; wherein R K5 and R k6 are each independently selected from the group consisting of hydrogen, an unsubstituted C1-C6alkyl, fluorine and chlorine.The OLED display panel of claim 10, wherein the hole transport compound having the structure according to formula (K-1) comprises: and / or The OLED display panel of claim 10, wherein both sides of the third functional layer (306) are each independently provided with an additional functional layer (3071, 3072), wherein the additional functional layer (3071, 3072) comprises a hole transport compound having a structure of formula (K-1) and a dopant having a structure of formula (C-1) doped into the hole transport compound having the structure of formula (K-1); wherein R C1 in formula (C-1) comprises a fluorine-substituted aromatic ring group.The OLED display panel of claim 12, wherein the dopant having a structure according to formula (C-1) comprises: The OLED display panel of claim 1, wherein the second functional layer (105, 205, 305) comprises a host material having a structure according to formula (D-1) and a dopant dispersed in the host material, wherein the dopant comprises a metal and / or a metal compound; wherein R D1, R D2, R D3 and R D4 in formula (D-1) are each independently selected from hydrogen, an alkyl group, a substituted or unsubstituted aromatic group; wherein a metallic element in the metal and / or the metal compound comprises an alkali metal, an alkaline earth metal and / or a rare earth metal.The OLED display panel of claim 14, wherein the host material having a structure according to formula (D-1) comprises: The OLED display panel of claim 14, wherein the metallic element in the metal and / or the metal compound comprises lithium, calcium, ytterbium or magnesium.The OLED display panel of claim 14, wherein the metal element in the metal and / or the metal compound is lithium.The OLED display panel of claim 1, wherein the second electrode (102, 202, 302) comprises silver or a silver alloy; wherein an alloying element of the silver alloy comprises any one or a combination of at least two of an alkali metal element, an alkaline earth metal element, and a rare earth metal element.The OLED display panel of claim 18, wherein the alloying element of the silver alloy comprises any one or a combination of at least two of lithium, calcium, ytterbium, and magnesium.The OLED display panel of claim 1, wherein the first electrode (101, 201, 301) comprises at least two functional layers, and the at least two functional layers comprise a reflective film and a conductive transparent thin film.The OLED display panel of claim 20, wherein the reflective film comprises silver; wherein the conductive transparent thin film comprises an ITO film or an IZO film.The OLED display panel of claim 1, wherein the second electrode (102, 202, 302) comprises a magnesium-silver alloy, a silver metal, a silver-ytterbium alloy, or a silver-rare earth metal alloy.The OLED display panel of claim 1, wherein the OLED display panel is configured to emit light from the second electrode (102, 202, 302).A display device comprising the OLED display panel according to any one of claims 1 to 23.

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