D-f transition rare earth complex non-doped device

Abstract

An electroluminescent material and a non-doped electroluminescent device manufactured using the electroluminescent material. The electroluminescent device comprises a cathode, an anode, and a light-emitting layer between the cathode and the anode, the light-emitting layer consisting of a light-emitting d-f transition Ce(III) complex or Eu(II) complex; the light-emitting d-f transition Ce(III) complex has one or more Ce 3+ ions as central light-emitting ions and forms coordination bonds with Ce 3+ ions, and a first coordination layer around the Ce 3+ ions has 3-15 coordination atoms including one or more of C, N, O, F, Cl, Br, and I. The non-doped device has better electroluminescent performance than equivalent doped devices, while being less expensive to manufacture.

Description

Technical Field

[0001] This invention belongs to the field of organic electroluminescence. In particular, this invention relates to a mixed Ce(III) complex and its application as an undoped electroluminescent material. Background Technology

[0002] Organic light-emitting diodes (OLEDs) are a novel technology with numerous advantages in both lighting and display fields, and have already begun to be applied in the commercial market. Compared to traditional organic small-molecule fluorescent and transition metal complex phosphorescent materials, rare-earth complexes with df transitions have the following characteristics: 1. 100% theoretical exciton utilization, resulting in higher device efficiency; 2. Short excited-state lifetime, leading to better theoretical device stability; 3. The d-orbital energy is easily affected by ligands, allowing for adjustable emission color and easy achievement of full-color displays from red to blue; 4. The abundance of rare earth elements in the Earth's crust far exceeds that of expensive transition metals (iridium, platinum, etc.), making them significantly cheaper.

[0003] For OLED devices, undoped devices with a single-component light-emitting layer offer numerous advantages. Compared to doped devices, undoped devices have simpler structures, use less material, are easier to fabricate, and are less expensive. However, in practical applications, most light-emitting materials, including small organic molecules and transition metal complexes, exhibit concentration quenching, where luminous efficiency decreases with increasing concentration. These materials are unsuitable for direct use as the light-emitting layer in OLEDs, necessitating the introduction of a host material to mitigate the concentration quenching problem. Therefore, addressing the concentration quenching issue has become a crucial challenge for undoped devices. Summary of the Invention

[0004] The inventors of this invention have discovered that, compared to other luminescent materials, the concentration quenching problem of rare-earth complexes in df transitions is less severe, and the concentration quenching of some rare-earth complexes in df transitions is even unobservable. Therefore, it has great application potential in high-efficiency undoped devices.

[0005] This invention addresses the shortcomings of existing technologies by providing an electroluminescent material having any one of the following structures: Formula 1, Formula 2, Formula 3, Formula 4, Formula 5, Formula 6, Formula 7, or Formula 8.

[0006]

[0007] R1-R6 are independently selected from hydrogen, alkyl, halogen-substituted alkyl, alkoxy, alkenyl, halogen-substituted alkenyl, alkynyl, halogen-substituted alkynyl, aryl, substituted aryl, O, N, S heteroaryl, and alkyl containing O, N, or S coordination sites; X is a monovalent ion, such as trifluoromethanesulfonate, halogen, pseudohalogen, tetrafluoroborate, hexafluorophosphate, etc.

[0008] Preferably, R1-R6 are independently selected from hydrogen, alkyl, aryl, substituted aryl, O, N, and S heteroaryl; more preferably, R1-R6 are independently selected from hydrogen, methyl, phenyl, substituted phenyl, arylamino, pyridine, phenylpyridine, carbazole, substituted carbazole, phenylphosphino, benzimidazole, and phenyltriazine; more preferably, X is a monovalent ion, such as trifluoromethanesulfonate or halogen.

[0009] More preferably, R1-R6 are independently selected from hydrogen, methyl, carbazole, and substituted carbazole;

[0010] Preferably, R1 is carbazole or carbazole with a molecular weight not exceeding 1000, preferably not exceeding 400, alkyl, aryl, halogen, or cyano substituted, R2, R3, and R5 are methyl, and R4 and R6 are hydrogen.

[0011] Preferably, R1 is an aryl-substituted carbazole, R2, R3, and R5 are methyl groups, and R4 and R6 are hydrogen groups;

[0012] In a further preferred embodiment, R1 is phenylcarbazole with the phenyl group attached to the pyrazole ring and the carbazole group located at the para position of the pyrazole group, R2, R3, and R5 are methyl groups, and R4 and R6 are hydrogen groups.

[0013] According to one embodiment of the present invention, for example, the electroluminescent material is selected from at least one of the following compounds: Ce-dmpz-CZ1, Ce-dmpz-CZ2, and Ce-dmpz-CZ3.

[0014]

[0015]

[0016] An embodiment of the present invention also provides an electroluminescent device, the electroluminescent device comprising a cathode, an anode, and a light-emitting layer located between the cathode and the anode, the light-emitting layer being composed of a df transition rare earth complex;

[0017] Preferably, the df transition rare earth complex is a df transition Ce(III) complex;

[0018] More preferably, the df transition rare earth complex is a luminescent df transition Ce(III) complex;

[0019] More preferably, the luminescent df transition Ce(III) complex has one or more Ce... 3+ Ions as central luminescent ions and with Ce 3+ The ions form ligands with coordinate bonds, and these Ce 3+ The first coordination layer surrounding the ion has 3-15 coordinating atoms, which include one or more of C, N, O, F, Cl, Br, and I.

[0020] Preferably, the formula weight of the ligands in the Ce(III) complex is less than 1000, more preferably less than 500, wherein it does not contain a conjugated system or contains only a small conjugated system. The ligands include C and H atoms, and one or more of B, N, O, P, S, F, Cl, Br, and I atoms. The small conjugated system refers to: a single pentagonal or hexagram conjugated ring, or several pentagonal or hexagram conjugated rings connected non-conjugated to each other, or two rings directly connected in the same plane or ring-co-linked.

[0021] According to one embodiment of the present invention, for example, the ligand of the df transition Ce(III) complex includes at least one of the following substituents: phenyl, substituted phenyl, aromatic amino, pyridine, phenylpyridine, carbazole, substituted carbazole, phenylphosphoxy, benzimidazole and phenyltriazine.

[0022] According to one embodiment of the present invention, for example, the df transition Ce(III) complex comprises an electroluminescent material as described above.

[0023] According to one embodiment of the present invention, for example, the electroluminescent device further includes an electron transport layer located between the cathode and the light-emitting layer, the electron transport layer comprising...

[0024] TmPyPB(1,3,5-tris[(3-pyridyl)-3-phenyl]benzene, 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene),

[0025] DPEPO (bis[2-((oxo)diphenylphosphino)phenyl]ether, bis-(2-(diphenyl phosphino)phenyl)ether oxide),

[0026] Bphen(4,7-diphenyl-1,10-phenanthroline, Bathophenanthroline),

[0027] TSPO1 (diphenylphosphine oxide-4-(triphenylsilyl)phenyl),

[0028] POT2T (2,4,6-tris[3-(diphenylphosphinoyl)phenyl]-1,3,5-triazine,2,4,6-tris[m-(diphenylphosphinoyl)phenyl]-1,3,5-triazine),

[0029] and / or

[0030] TPBi(1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, 1,3,5-tris(N-phenylbenzimidazol-2-yl)-benzene);

[0031] Preferably, the electroluminescent device further includes a hole transport layer located between the anode and the light-emitting layer; preferably, the hole transport layer includes:

[0032] PCzAc(9,9-dimethyl-10-(9-phenyl-9H-carbazol-3-yl)-9,10-dihydroacridine),

[0033] mCP(N,N-diazolyl-3,5-benzene,N,N-dicarbazolyl-3,5-benzene),

[0034] mCBP(3,3-di(9H-carbazol-9-yl)biphenyl),

[0035] m-MTDATA(4,4',4”-tris[phenyl(m-tolyl)amino]triphenylamine, 4,4',4”-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine),

[0036] TCTA (tris(4-(9-carbazolyl)phenyl)amine, 4′,4″,4″′-tris-(N-carbazolyl)-triphenylamine),

[0037] CzSi(9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole, 9-(4-tertbutylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole),

[0038] and / or

[0039] TAPC (4,4′-cyclohexylbis[N,N-di(4-methylphenyl)aniline], 1,1-bis[4-[N,N'-di(ptolyl)amino]phenyl]cyclohexane);

[0040] Preferably, the electroluminescent device further includes an electron transport layer located between the cathode and the light-emitting layer, and a hole transport layer located between the anode and the light-emitting layer;

[0041] Preferably, the hole transport layer includes mCP, and the electron transport layer includes Bphen.

[0042] According to one embodiment of the present invention, for example, the thickness of the light-emitting layer is 1-100nm, preferably 1-80nm, preferably 1-60nm, preferably 1-40nm, preferably 1-30nm, preferably 10-25nm, and most preferably 20nm. Attached Figure Description

[0043] Figure 1 These are the photophysical test results of the three complexes Ce-dmpz-Cz1, Ce-dmpz-Cz2, and Ce-dmpz-Cz3 prepared in the embodiments of the present invention; wherein a) is the dichloromethane solution (10) of Ce-dmpz-Cz1, Ce-dmpz-Cz2, and Ce-dmpz-Cz3. - 3 M) shows the ultraviolet absorption spectrum (dashed line) and room temperature emission spectrum (solid line); b) shows the excited-state lifetime decay curves of Ce-dmpz-Cz1, Ce-dmpz-Cz2, and Ce-dmpz-Cz3 dichloromethane solutions; c) and d) show the room temperature emission spectra and excited-state lifetime decay curves of Ce-dmpz-Cz1, Ce-dmpz-Cz2, and Ce-dmpz-Cz3 solid powders.

[0044] Figure 2 This is a diagram showing the current density of single-hole devices prepared with different Ce(III) complexes according to embodiments of the present invention.

[0045] Figure 3 These are the current efficiency-luminance-external quantum efficiency curves of electroluminescent devices prepared using Ce-dmpz, Ce-dppz, and Ce-dmpz-Cz2. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. However, those skilled in the art will understand that this invention is not limited to the accompanying drawings and the following embodiments.

[0047] The rare earth complexes shown below were prepared in the embodiments of the present invention:

[0048]

[0049] The photoluminescence quantum yields of the above compounds in solution and solid powder states were tested, and the results are shown in Table 1. Currently, the rare-earth complexes with df transitions synthesized in the embodiments of this invention all exhibit very high quantum yields in the solid powder state. This indicates that this type of luminescent material basically does not exhibit concentration quenching in the solid state, which is a necessary condition for fabricating high-performance undoped devices.

[0050] Table 1 Quantum yields of df transition rare earth complexes in solution and solid powder

[0051]

[0052]

[0053] a Dichloromethane solution, concentration 1*10 -5 mol / L; b The compound has poor solubility in dichloromethane, and the solution quantum yield was not measured.

[0054] Embodiments of the present invention have explored undoped devices using Ce-dmpz, Ce-dppz, Ce-1, Ce-2, Eu-1, and EuBr2-N8 as luminescent material complexes. The device structure is shown below:

[0055] D1 ITO / MoO3(2nm) / mCP:MoO3(20wt%,40nm) / mCP(10nm) / Ce-dmpz(4nm) / Bphen(40nm) / LiF(0.7nm) / Al(100nm)

[0056] D2 ITO / MoO3(2nm) / mCP:MoO3(20wt%,40nm) / mCP(10nm) / Ce-dppz(4nm) / Bphen(40nm) / LiF(0.7nm) / Al(100nm)

[0057] D3 ITO / MoO3(2nm) / CzSi:MoO3(20wt%,30nm) / CzSi(10nm) / Ce-1(5nm) / TSPO1(10nm) / Bphen(40nm) / LiF(0.7nm) / Al(100nm)

[0058] D4 ITO / MoO3(2nm) / mCBP:MoO3(20wt%,40nm) / mCBP(10nm) / Ce-2(20nm) / TmPyPB(40nm) / LiF(0.7nm) / Al(100nm)

[0059] D5 ITO / MoO3(2nm) / mCP:MoO3(20wt%,30nm) / mCP(10nm) / Eu-1(10nm) / POT2T(40nm) / LiF(0.7nm) / Al(100nm)

[0060] D6 ITO / MoO3(2nm) / mCP:MoO3(20wt%,30nm) / mCP(10nm) / EuBr2-N8(10nm) / POT2T(40nm) / LiF(0.7nm) / Al(100nm)

[0061] Table 2 Summary of the performance of devices D1-D6

[0062]

[0063] a Light-up voltage, device brightness is 1 cd m -2 Voltage at that time; b Maximum EQE of the device; c Maximum current efficiency of the device; d Maximum brightness of the device; e The device brightness is 20 cd m. -2 The color coordinates at that time.

[0064] Devices D1-D6 use Ce-dmpz, Ce-dppz, Ce-1, Ce-2, Eu-1, and EuBr2-N8 as luminescent materials, respectively. The specific performance of these devices is summarized in Table 2. Overall, the current efficiency and external quantum efficiency of these six devices are relatively low, as are their maximum brightness. Their performance is significantly different from their corresponding doped devices, failing to meet expectations. This indicates that there is still considerable room for improvement in undoped devices prepared using rare-earth complexes with df transitions.

[0065] The inventors of this invention recognized that the reason why the performance of the above-mentioned devices did not meet expectations might be that the carrier transport performance of such materials is relatively poor and the carrier transport is unbalanced, which affects the final device performance. Therefore, in order to improve the electroluminescence performance of the above-mentioned materials, the molecular structure of Ce-dmpz was further improved. By introducing carrier transport groups onto the dimethylpyrazole anion of Ce-dmpz, three Ce(III) complexes emitting sky blue light, Ce-dmpz-Cz1, Ce-dmpz-Cz2 and Ce-dmpz-Cz3 (their structures are shown in the reaction formula below), were obtained, and their photophysical properties were characterized.

[0066] Synthesis and Characterization:

[0067]

[0068] The synthetic routes for the complexes are shown above. The pyrazole ligands used in Ce-dmpz-Cz1 and Ce-dmpz-Cz3 were obtained by Suzuki coupling, and the pyrazole ligand used in Ce-dmpz-Cz2 was obtained by Ullmann coupling. The obtained pyrazoles were dehydrogenated with sodium tert-butoxide and then mixed with cerium trifluoromethanesulfonate and potassium tris(3,5-dimethyl)pyrazoleborane in THF to obtain the corresponding complexes.

[0069] The photophysical properties of the above-mentioned complexes were further characterized below.

[0070] Figure 1 These are the photophysical test results of the three complexes Ce-dmpz-Cz1, Ce-dmpz-Cz2, and Ce-dmpz-Cz3 prepared in the embodiments of the present invention; wherein a) is the dichloromethane solution (10) of Ce-dmpz-Cz1, Ce-dmpz-Cz2, and Ce-dmpz-Cz3. - 3 M) shows the UV absorption spectrum (dashed line) and room temperature emission spectrum (solid line); b) shows the excited-state lifetime decay curves of Ce-dmpz-Cz1, Ce-dmpz-Cz2, and Ce-dmpz-Cz3 dichloromethane solutions; c) and d) show the room temperature emission spectra and excited-state lifetime decay curves of Ce-dmpz-Cz1, Ce-dmpz-Cz2, and Ce-dmpz-Cz3 solid powders. Figure 1 As shown, the dichloromethane homogenates of the three complexes exhibit strong sky-blue light emission, with photoluminescence quantum efficiencies (PLQY) all reaching 100%. Their ultraviolet absorption spectra are as follows: Figure 1As shown in a), the df transition absorption peaks of Ce(III) ions in Ce-dmpz-Cz1, Ce-dmpz-Cz2, and Ce-dmpz-Cz3 are located at 389 nm, 395 nm, and 392 nm, respectively. The absorption of the corresponding pyrazole sodium salts corresponds to a strong and broad absorption peak below 365 nm, originating from the pyrazole ligand. Their PL spectra are almost identical in dichloromethane solution and powder states, which can be attributed to their similar coordination modes. This is because the ground state of Ce(III) has two similar energy levels. 2 F 5 / 2 and 2 F 7 / 2 Therefore, the emission of the complex exhibits bimodal emission characteristics. In addition, the excited-state lifetimes of Ce-dmpz-Cz1, Ce-dmpz-Cz2, and Ce-dmpz-Cz3 solutions are 93 ns, 55 ns, and 45 ns, respectively, while the excited-state lifetimes of the solid powders are 131 ns, 60 ns, and 85 ns, respectively. The shorter excited-state lifetimes are also consistent with the parity-allowed df transition luminescence properties of Ce(III).

[0071] Under the same device structure, embodiments of the present invention prepared single-carrier device evaluation materials for the above three complex materials to transport hole carriers.

[0072] The structure is ITO / MoO3(2nm) / mCP(40nm) / Ce(III) complex(4nm) / mCP(40nm) / MoO3(2nm) / Al(100nm). ITO is the anode, Al is the cathode, MoO3 is the hole injection layer, and mCP is the hole transport layer. Figure 2 This is a diagram showing the current density of single-hole devices prepared with different Ce(III) complexes according to embodiments of the present invention.

[0073] like Figure 2 As shown, introducing a carbazole group with good hole transport capability onto the pyrazole group significantly improved the current of the single-hole device corresponding to the complex. This indicates that the introduced carbazole can effectively enhance the hole migration capability of the material. Among them, Ce-dmpz-Cz2 showed the most significant improvement.

[0074] To examine the electroluminescence performance of the complexes after introducing carbazole groups into the ligands, the efficiency performance of three materials—Ce-dmpz-Cz2, Ce-dmpz, and Ce-dppz—is compared below.

[0075] Figure 3The figures show the current efficiency-luminosity-external quantum efficiency curves of electroluminescent devices fabricated using Ce-dmpz, Ce-dppz, and Ce-dmpz-Cz2. An electroluminescent device was fabricated using Ce-dmpz-Cz2 as the luminescent material; the device structure is as follows:

[0076] The device is configured as follows: D7 ITO / MoO3(2nm) / mCP:MoO3(20wt%, 40nm) / mCP(10nm) / Ce-dmpz-Cz2(4nm) / Bphen(40nm) / LiF(0.7nm) / Al(100nm), where ITO is the anode and Al is the cathode; MoO3 serves as the hole injection layer, mCP:MoO3 is the p-type doped hole transport layer, mCP is the hole transport layer, BPhen is the electron transport layer, and LiF is the electron injection layer. The device performance is listed in Table 3.

[0077] Table 3 Summary of the performance of D7 and D8 devices

[0078]

[0079] a Light-up voltage, device brightness is 1 cd m -2 Voltage at that time; b Maximum EQE of the device; c Maximum current efficiency of the device; d Maximum brightness of the device; e The device brightness is 20 cd m. -2 The color coordinates at that time.

[0080] Depend on Figure 3 The results show that, under the condition that all emitting layers are undoped, the efficiency of the Ce-dmpz-Cz2 device is significantly improved compared to the Ce-dmpz and Ce-dppz devices. At the same current density, the Ce-dmpz-Cz2 device exhibits higher luminance, and at the same luminance, its EQE is also higher. This can be attributed to the improved hole mobility and better control of the carrier recombination region resulting from the improved material structure.

[0081] For ease of comparison, Ce-dmpz-doped device D8 was fabricated in BCPO as the host material, using the same implantation and transport layers as D7. The device performance is listed in Table 3.

[0082] D8:ITO / MoO3(2nm) / mCP:MoO3(20wt%,40nm) / mCP(10nm) / BCPO:Ce-dmpz(10wt%,20nm) / Bphen(40nm) / LiF(0.7nm) / Al(100nm)

[0083] As shown in Table 3, the undoped device D7, prepared from the improved material Ce-dmpz-Cz2, exhibits superior performance compared to the doped device D8. The D7 device has a lower turn-on voltage and surpasses D8 in maximum EQE, highest current efficiency, and maximum luminance. Furthermore, the D7 fabrication process omits the use of the host material BCPO, simplifying the selection of the host material and the host-guest doping process, resulting in a simpler and lower-cost process.

Claims

1. An electroluminescent material, characterized in that, The electroluminescent material is selected from at least one of the following compounds: Ce-dmpz-CZ1, Ce-dmpz-CZ2, and Ce-dmpz-CZ3.

2. An electroluminescent device, the electroluminescent device comprising a cathode, an anode, and a light-emitting layer located between the cathode and the anode, characterized in that, The light-emitting layer is composed of the electroluminescent material as described in claim 1.

3. The electroluminescent device according to claim 2, characterized in that, The electroluminescent device further includes an electron transport layer located between the cathode and the light-emitting layer, the electron transport layer comprising TmPyPB (1,3,5-tris[(3-pyridyl)-3-phenyl]benzene), DPEPO (bis[2-((oxo)diphenylphosphino)phenyl]ether), Bphen (4,7-diphenyl-1,10-phenanthroline), TSPO1 (diphenylphosphine oxide-4-(triphenylsilyl)phenyl), POT2T (2,4,6-tris[3-(diphenylphosphino)phenyl]-1,3,5-triazine) and / or TPBi (1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene).

4. The electroluminescent device according to claim 2 or 3, characterized in that, The thickness of the light-emitting layer is 1-100 nm.

5. The electroluminescent device according to claim 3, characterized in that, The electroluminescent device further includes a hole transport layer located between the anode and the light-emitting layer; the hole transport layer includes PCzAc(9,9-dimethyl-10-(9-phenyl-9H-carbazol-3-yl)-9,10-dihydroacridine), mCP(N,N-dicarbazolyl-3,5-benzene), mCBP(3,3-di(9H-carbazol-9-yl)biphenyl), and m-MTDATA(4,4',4”-tris[phenyl(m-tolyl)amino]triphenylamine). -tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine), TCTA (tris(4-(9-carbazolyl)phenyl)amine, 4′,4″,4″′-tris-(N-carbazolyl)-triphenylamine), CzSi (9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole, 9-(4-tertbutylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole) and / or TAPC (4,4′-cyclohexylbis[N,N-di(4-methylphenyl)aniline], 1,1-bis[4-[N,N'-di(ptolyl)amino]phenyl]cyclohexane).

6. The electroluminescent device according to claim 5, characterized in that, The electroluminescent device further includes an electron transport layer located between the cathode and the light-emitting layer, and a hole transport layer located between the anode and the light-emitting layer; The hole transport layer includes mCP, and the electron transport layer includes Bphen.

7. The electroluminescent device according to claim 2 or 3, characterized in that, The thickness of the light-emitting layer is 1-80 nm.

8. The electroluminescent device according to claim 2 or 3, characterized in that, The thickness of the light-emitting layer is 1-60 nm.

9. The electroluminescent device according to claim 2 or 3, characterized in that, The thickness of the light-emitting layer is 1-50 nm.

10. The electroluminescent device according to claim 2 or 3, characterized in that, The thickness of the light-emitting layer is 1-40 nm.

11. The electroluminescent device according to claim 2 or 3, characterized in that, The thickness of the light-emitting layer is 1-30 nm.

12. The electroluminescent device according to claim 2 or 3, characterized in that, The thickness of the light-emitting layer is 2-25 nm.

13. The electroluminescent device according to claim 2 or 3, characterized in that, The thickness of the light-emitting layer is 4 nm.

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