Pure blue light organic light-emitting device with triple alternating deposition light-emitting layer structure

Abstract

The invention discloses a pure blue light organic light-emitting device with a triple alternating deposition light-emitting layer structure, and belongs to the technical field of organic light-emitting devices. The device is sequentially composed of a substrate, an anode, a hole transport layer, a light-emitting layer, an electron transport layer and a cathode. Wherein the organic light-emitting layer is of a light-emitting layer structure formed by alternately depositing a donor material layer of an interface exciplex, a sensitizer ultrathin layer and an acceptor material doped blue light dye layer. The acceptor material is doped with the blue light dye layer according to a certain proportion. Due to the fact that the light-emitting layer adopts a triple alternating deposition light-emitting layer structure and the sensitizer is introduced, Dexter energy transfer loss can be fully reduced, the exciton utilization rate is effectively improved, and therefore the device efficiency is improved. In addition, by alternately depositing exciplexes, the interface can be increased, and more excitons can be generated.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic electroluminescent devices, and in particular, relates to a pure blue light organic electroluminescent device with a triple alternately deposited light-emitting layer structure. Background Art

[0002] Organic light-emitting diodes (OLEDs) have become a new generation of display products after liquid crystal displays (LCDs), and have great potential advantages and broad application prospects in solid-state lighting. The advantages of OLEDs are mainly reflected in thin thickness, light weight, high efficiency, high brightness, bendability, wide viewing angle, low voltage, simple manufacturing process, high temperature controllability, wide material sources, and no need for backlight. After nearly 30 years of efforts by domestic and foreign scientific researchers, OLEDs have gradually entered the industrialization stage from the basic research stage, and the development prospects in the lighting field are optimistic about the industry. According to the 2017 OLED Lighting Annual Report released by market research organization UBI Research, the OLED lighting market will grow from US$6.4 million to US$2.11 billion from 2017 to 2025, with an average annual growth rate of 107%. Although OLED lighting has huge market potential, there are still some common key technologies that need to be broken through in the industrial development. In particular, the design of efficient pure blue light organic electroluminescent devices remains a challenge.

[0003] In order to prepare high-quality display light sources to meet market needs, research on blue OLEDs is particularly necessary. Some studies have made significant progress in addressing this challenge, especially in terms of efficiency and lifetime extension, which is mainly due to the improvement of device structure and the development of new luminescent materials [Adv. Mater. 2013, 25, P1455-1459; Adv. Mater. 2014, 25, P1612-1616; J. Mater. Chem. C. 2018, 6, P5012–5017; ACS Appl. Mater. Interfaces. 2017, 9, P37864–37872].

[0004] So far, the device structure using the exciplex formed by intermolecular charge transfer as the main body has been favored by many researchers due to its bipolar transmission ability and wide band gap, and is regarded as an ideal host for luminescent materials such as phosphorescence, fluorescence, and thermally activated delayed fluorescence (TADF). In addition, most exciplexes have a small ΔEst and exhibit TADF process through reverse intersystem crossing at room temperature, in which triplet excitons can be effectively upconverted to singlet excitons, promoting the energy transfer from Dexter to the singlet exciton. The change of energy transfer mechanism can further improve the efficiency of the device. These advantages have greatly promoted the development of devices based on exciplexes.

[0005] However, this approach also has the following inherent problems: (1) The traditional multi-doped structure mixes the host material with the dye molecules, and the spatial distance between the host molecules and the dye molecules is small, which greatly enhances the Dexter energy transfer phenomenon between the molecules and causes a large roll-off in the device efficiency. (2) The single emitting layer based on the main structure of the exciplex needs to be doped with a donor material, an acceptor material, and at least two luminescent guest materials, and the preparation process is relatively complicated. (3) The trap effect of the dye molecules makes it easy for the carriers to be directly captured by the dye, thereby directly recombining and radiating light on the dye molecules. This phenomenon reduces the transmission efficiency of the carriers in the device and affects the device performance. (4) The mixed doping form of the donor and acceptor allows some carriers to cross the potential barrier between the donor and the acceptor and then directly recombine in the donor material or the acceptor material, resulting in an increase in the singlet excitation energy of the device and an increase in the turn-on voltage burden of the device. (5) Most OLED devices using exciplexes as the main body are limited to sky blue, green, yellow, and red light, while pure blue and deep blue devices are very rare. This is because it is very difficult to develop high-energy hosts whose high triplet energy can prevent the reverse energy transfer from the blue triplet emitter to the exciplex host, thereby improving the device efficiency and stability. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a pure blue light organic electroluminescent device with a triple alternating deposition light-emitting layer structure, which can fully reduce the Dexter energy transfer loss, effectively improve the exciton utilization rate, and thus improve the device efficiency; it can also increase the interface by alternately depositing the exciton complex to generate more excitons.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A pure blue light organic electroluminescent device with a triple alternately deposited light-emitting layer structure comprises a substrate, an anode, a hole transport layer, a total light-emitting layer, an electron transport layer and a cathode; the organic light-emitting layer between the hole transport layer and the electron transport layer comprises a plurality of alternately deposited single light-emitting layers, and the total thickness of the organic light-emitting layer is 20-50 nm.

[0009] According to an embodiment of the present invention, the thickness of a single organic light-emitting layer is 10-15 nm.

[0010] For example, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm or any value between any two of the above value ranges.

[0011] According to an embodiment of the present invention,

[0012] According to an embodiment of the present invention, the ultra-thin layer of the sensitizer is 0.5 nm;

[0013] According to an embodiment of the present invention, the doping concentration of the blue organic light-emitting dye in the acceptor material-doped blue light-emitting dye layer is 1 wt % to 5 wt %.

[0014] According to an embodiment of the present invention, the organic light-emitting layer comprises three single light-emitting layers deposited alternately.

[0015] According to an embodiment of the present invention, the thickness of each donor material layer forming the interfacial exciplex may be the same or different, and independently be 3-8 nm, and may be 3, 4, 5, 6, 7, or 8 nm.

[0016] According to an embodiment of the present invention, the thickness of each acceptor material doped blue light dye layer may be the same or different, and independently be 5-15 nm, and may be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 nm.

[0017] According to an embodiment of the present invention, the thickness of each ultra-thin layer of the sensitizer may be the same or different, and independently be 0.3-0.7 nm; and may be 0.3, 0.4, 0.5, 0.6, 0.7 nm. Preferably 0.5 nm

[0018] According to an embodiment of the present invention, the total thickness of the total light-emitting layer is 25-45 nm.

[0019] For example, 20, 25, 30, 35, 40, 45, 50nm.

[0020] According to an embodiment of the present invention, the donor material of the interfacial exciplex is located on the hole transport layer side, and the acceptor material is located on the electron transport layer side.

[0021] According to an embodiment of the present invention, the difference between the HOMO energy level of the donor material and the HOMO energy level of the acceptor material is greater than or equal to 0.4 eV, and the difference between the LUMO energy level of the donor material and the LUMO energy level of the acceptor material is greater than or equal to 0.4 eV.

[0022] According to an embodiment of the present invention, the interface formed by the donor material and the acceptor material generates an interface exciplex under light excitation or electric field excitation, and the emission spectrum of the formed exciplex overlaps with the absorption spectrum of the blue light dye on the longest wavelength side.

[0023] In order to ensure good energy transfer between the host, sensitizer and dye, the emission wavelength of the interface exciplex is less than or equal to 430nm and the CIE coordinate y value is less than or equal to 0.08. In order to reduce the capture effect of the dye on carriers, the acceptor material of the interface exciplex is used as the host, and the LUMO energy level of the dye is shallower than the LUMO energy level of the acceptor material.

[0024] According to an embodiment of the present invention, the blue light emitting material and the sensitizer are both blue TADF materials, so as to maintain good efficiency while ensuring good color purity.

[0025] According to an embodiment of the present invention, the emission peak of the blue light TADF material is located at 460-480nm, the doping concentration of the blue light TADF material in the acceptor material doped blue light dye layer is greater than or equal to 1wt% and the half maximum full width is less than or equal to 28nm.

[0026] According to an embodiment of the present invention, the doping concentration of the blue organic light-emitting dye in the acceptor material-doped blue light-emitting dye layer is 1 wt % to 5 wt %.

[0027] According to an embodiment of the present invention, the emission wavelength of the TADF sensitizer is less than or equal to 460 nm, and the emission spectrum and the absorption spectrum of the blue light dye overlap on the longest wavelength side.

[0028] According to an embodiment of the present invention, a hole transport type bipolar host material 4,4′-N,N′-dicarbazole biphenyl (CBP) is used, but the present invention is not limited thereto.

[0029] According to an embodiment of the present invention, an organic compound 2-(9,9'-spirobi[fluorene]-3-yl)-4,6-diphenyl-1,3,5-triazine (SF3-TRZ) having electron transport properties is used, but is not limited thereto.

[0030] According to an embodiment of the present invention, the anode is a transparent metal oxide ITO, FTO, or a high work function metal Ag, Au, Cu, etc., and any anode material can also be used. An anode buffer layer can be inserted between the anode and the light-emitting unit layer to improve the injection of holes. The anode buffer layer can be MoO 3 , WO 3 、V 2 O 5 wait;

[0031] According to an embodiment of the present invention, the hole injection layer material is 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT-CN).

[0032] According to an embodiment of the present invention, the hole transport layer material is an organic material with high hole mobility, which may be 4,4',4"-tri(carbazole-9-yl)triphenylamine, (TCTA), 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline] (TAPC), N,N'-diphenyl-N,N'-(1-naphthyl)1,1'-biphenyl-4,4'-diamine (NPB), etc.

[0033] According to an embodiment of the present invention, the electron transport layer material adopts an organic material with high electron mobility, which may be 4,6-bis(3,5-di(4-pyridyl)phenyl)-2-phenylpyrimidine (B4PyPPM), 1,3,5-tri(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), di[2-((oxy)diphenylphosphino)phenyl]ether (DPEPO), 2,4,6-tri[3-(diphenylphosphinoyl)phenyl]-1,3,5-triazole (PO-T2T), etc.

[0034] According to an embodiment of the present invention, the electron injection layer material is LiF, Liq or the like.

[0035] According to an embodiment of the present invention, the thickness of the electron injection layer material is generally less than 2 nm.

[0036] According to an embodiment of the present invention, the cathode is a metal such as Al, Ca, Ba, etc. having a low work function.

[0037] According to an embodiment of the present invention, the organic light-emitting dye adopts TADF blue light-emitting material, including but not limited to N7, N7, N13, N13, 5, 9, 11, 1-octaphenyl-5H, 9H, 11H, 15H-[1, 4] benzazaborolino [2, 3, 4-kl][1, 4] benzazaborolino [4', 3', 2': 4, 5][1, 4] benzazaborolino [3, 2-b] dibenzoazaborolin-7, 13-diamine (v-DABNA), 2, 12-di-tert-butyl-5, 9-bis (4- (tert-butyl) phenyl) -5, 9-dihydro-5, 9-diaza-13b-boronaphthalene [3,2,1-de]anthracene (t-DABNA), N7,N7,N13,N13,5,15-hexaphenyl-9,11-bis(4-(tert-butyl)phenyl)-5,9,11,15-tetrahydro-5,9,11,15-tetraaza-19b,20b-diboronaphthalene [3,2,1-de:1',2',3'-jk]pentaphenyl-7,13-diamine (t-Bu-ν-DABNA), 5,9-diphenyl-5H,9H-[1,4]benzhaborano[2,3,4-kl]benzhaborane (DNBNA-1), any high-efficiency TADF blue emitting dye can be used.

[0038] According to an embodiment of the present invention, the sensitizer is 9-(5'-(4,6-diphenyl-1,3,5-triazine-2-yl)-[1,1':3',1"-terphenyl]-2'-yl)-3,6-diphenyl-9H-carbazole (PPCzTrz), but is not limited thereto. Any TADF sensitizer that meets the requirements can be used.

[0039] According to an embodiment of the present invention, the hole transport layer material may be the same as or different from the interfacial exciplex donor material; the electron transport layer material may be the same as or different from the interfacial exciplex acceptor material.

[0040] Beneficial effects of the present invention:

[0041] The present invention can fully reduce the Dexter energy transfer loss and effectively improve the exciton utilization rate, thereby improving the device efficiency, because the light-emitting layer adopts a triple alternating deposition light-emitting layer structure and introduces a sensitizer. In addition, by alternately depositing the exciton complex, the interface can be increased and more excitons can be generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic structural diagram of a single-layer white light organic electroluminescent device based on an interfacial exciplex of the present invention;

[0043] Figure 2 The voltage-current density curve of the pure blue light organic electroluminescent device based on the triple alternating deposition light-emitting layer structure of the present invention;

[0044] Figure 3 The voltage-current efficiency curve of the pure blue light organic electroluminescent device based on the triple alternating deposition light-emitting layer structure of the present invention;

[0045] Figure 4 It is the normalized electroluminescence spectrum of the pure blue light organic electroluminescent device based on the triple alternating deposition light-emitting layer structure of the present invention.

[0046] Figure numerals: 01 - anode and hole injection layer; 02 - hole transport layer; 03 - electron blocking layer; 04 - total organic light-emitting layer; 05 - electron transport layer; 06 - electron injection layer and cathode. DETAILED DESCRIPTION

[0047] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments and accompanying drawings. It should be understood that the following embodiments are only exemplary illustrations and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope of protection that the present invention is intended to protect.

[0048] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available.

[0049] ITO: Indium Tin Oxide, used as a transparent anode.

[0050] HAT-CN: 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene, a hole injection material, is conducive to the injection of holes.

[0051] TAPC: 4,4'-cyclohexylbis[N,N-di(4-methylphenyl)aniline], hole transport material.

[0052] TCTA: 4,4',4"-tri(carbazol-9-yl)triphenylamine, used as a blocking layer to block electrons from entering the hole transport layer.

[0053] CBP: 4,4′-N,N′-dicarbazole biphenyl, used as the donor material of the interfacial excited complex.

[0054] v-DABNA: N7,N7,N13,N13,5,9,11,1-octaphenyl-5H,9H,11H,15H-[1,4]benzazaboro[2,3,4-kl][1,4]benzazaboro[4',3',2':4,5][1,4]benzazaboro[3,2-b]dibenzazaborane-7,13-diamine, a high-efficiency blue light TADF luminescent material; the emission peak at 471nm is limited to the emission peak protection range of 460nm-480nm of the blue light material; the half-peak width is 21nm, which is limited to the half-peak width less than or equal to 28nm in the claims.

[0055] SF3-TRZ: 2-(9,9'-spirobi[fluorene]-3-yl)-4,6-diphenyl-1,3,5-triazine, an electron transport material and an acceptor material for an interfacial excited complex.

[0056] PPCzTrz: 9-(5'-(4,6-diphenyl-1,3,5-triazine-2-yl)-[1,1':3',1"-terphenyl]-2'-yl)-3,6-diphenyl-9H-carbazole, sensitizer.

[0057] Liq: 8-hydroxyquinoline-lithium, cathode buffer layer (ie, electron injection layer material), is beneficial to electron injection.

[0058] Al: Aluminum, thickness 100nm, used as cathode.

[0059] Example 1

[0060] The preparation of organic light-emitting devices can be carried out in a multi-source organic molecular vapor deposition system. The detailed process is as follows:

[0061] The substrate used in the experiment is ITO conductive glass. First, the front and back sides of the ITO glass are repeatedly scrubbed with acetone, anhydrous ethanol, and deionized water to remove surface impurities and metal ions.

[0062] The cleaned ITO substrate was ultrasonically treated with acetone, ethanol and deionized water for 10 minutes in sequence, and then dried and subjected to UV treatment for 10 minutes.

[0063] The treated ITO glass is placed face down in a multi-source organic metal molecular vapor deposition system through a glove box. (See Chinese Patent: ZL03110977.2, "Pot-type evaporation source for organic electroluminescent coating machine"). The evaporation table contains 8 organic evaporation sources and 2 metal electrode evaporation sources. Four devices can be evaporated at a time. The evaporation sources do not affect each other, thus avoiding contamination between materials. During the device preparation process, the multi-source organic molecular vapor deposition system starts to grow materials when the vacuum degree is about 3×10-4Pa, and the vacuum degree of the system can reach up to 10-5Pa. The thickness and growth rate of the material growth are controlled by a film thickness controller. The growth rate of the organic material is controlled at The electroluminescence spectrum and color coordinates of the device were measured by a spectrometer PR655, and the brightness-voltage and current-voltage characteristics were measured by combining the spectrometer with a programmable ammeter Keithley 2450. All tests were completed in room temperature atmosphere.

[0064] The structure of the pure blue organic electroluminescent device based on the triple alternating deposition light-emitting layer structure is as follows:

[0065] On an ITO glass substrate, a 10nm hole injection layer HAT-CN, a 20nm hole transport layer TAPC, a 5nm electron blocking layer TCTA, a 5nm interface exciplex donor material CBP, a 0.5nm sensitizer ultra-thin layer PPCzTrz, a 5nm acceptor material for doped dyes, the acceptor material is SF3-TRZ, and doped v-DABNA, wherein the interface exciplex acceptor material SF3-TRZ serves as the main body of the doped dye, the doping concentration of v-DABNA is 5%, a 5nm interface exciplex donor material CBP, a 0.5nm sensitizer ultra-thin layer, a 5nm acceptor material for doped dyes, a 35nm electron transport layer SF3-TRZ, a 0.8nm electron injection layer Liq, and a 100nm Al cathode are sequentially deposited.

[0066] That is, its structure is ITO / HAT-CN (10nm) / TAPC (20nm) / TCTA (5nm) / CBP (5nm) / PP CzTrz (0.5nm) / SF3-TRZ:5% v-DABNA (10nm) / CBP (5nm) / PPCzTrz (0.5nm) / SF 3 –TRZ:5%v-DABNA(10nm) / CBP(5nm) / PPCzTrz(0.5nm) / SF3-TRZ:5%v-DABNA(10nm) / SF 3-TRZ (35nm) / Liq (0.8nm) / Al, 5nm of the donor material of the interfacial excited complex, 0.5nm of the ultra-thin layer of the sensitizer and 10nm of the acceptor material doped with the dye form a single light-emitting layer, and then two identical light-emitting layers are deposited.

[0067] Comparative Example 1

[0068] The device is a conventional co-doped device, and the preparation process is the same as that of Example 1, except that the organic light-emitting layer is:

[0069] The organic light-emitting layer in Comparative Example 1 was changed to a main body CBP: SF3-TRZ doped with a blue dye, excluding the ultra-thin layer of sensitizer PPCzTrz, and a 5 nm CBP blocking layer was inserted in front of the light-emitting layer to prevent TCTA from reacting with the exciplex receptor.

[0070] Its structure is ITO / HAT-CN (10nm) / TAPC (20nm) / TCTA (5nm) / CBP (5nm) / CBP: SF3-TRZ: 5% v-DABNA (35nm) / SF3-TRZ (35nm) / Liq (0.8nm) / Al.

[0071] Figure 2-Figure 4 The current density-voltage curve, current efficiency-voltage curve and normalized electroluminescence spectrum of the devices prepared in Example 1 and Comparative Example 1 are shown respectively. It can be seen from the figure that the pure blue light organic electroluminescent device based on the triple alternating deposition light-emitting layer structure has good photoelectric performance, and the maximum current efficiency can reach 31cd / A. When the dye is doped in the acceptor material, one of the carriers can directly reach the interface between the donor and the acceptor material through the transport layer; conversely, due to the appropriate energy level matching, there is an injection barrier between the host and the dye, thereby effectively confining the other carrier in the host material for transmission. Therefore, the light-emitting layer designed by the present invention can effectively improve the transmission efficiency of the carrier in the device.

[0072] At the same time, due to the large potential barriers between the HOMO and LUMO of the donor material and the acceptor material, a large number of excitons are recombined at the interface between the donor and the acceptor material to form an interfacial exciplex, which inhibits the direct recombination of carriers on the donor material or the acceptor material. At the same time, the interfacial exciplex and the TADF sensitizer can produce two RISC processes, converting triplet excitons into singlet excitons, and realizing efficient cascade energy transfer from the host to the sensitizer and the fluorescent dopant ν-DABNA.

[0073] At the same time, due to the RISC characteristics of the dopant ν-DABNA itself, there are three RISC processes in the whole process. It can be seen that due to the existence of three RISC processes, triplet excitons are effectively utilized. Therefore, the efficiency of the manufactured OLED device is greatly improved.

[0074] The above is only a preferred application implementation of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A blue light organic electroluminescent device with a triple alternating deposition light-emitting layer structure, comprising a substrate, an anode, a hole transport layer, an organic light-emitting layer, an electron transport layer and a cathode in sequence; characterized in that: The organic light-emitting layer comprises a plurality of alternately deposited single light-emitting layers, and the total thickness of the organic light-emitting layer is 20-50 nm; The single organic light-emitting layer is composed of a donor material layer for forming an interface exciplex, an ultra-thin sensitizer layer, and an acceptor material doped blue light dye layer deposited in three layers in an alternating manner.

2. The blue organic electroluminescent device according to claim 1, characterized in that: The thickness of a single organic light-emitting layer is 10-15 nm; Preferably, the ultra-thin layer of sensitizer is 0.5 nm; Preferably, the donor material of the interfacial exciplex is located on the hole transport layer side, and the acceptor material is located on the electron transport layer side.

3. The blue organic electroluminescent device according to claim 1, characterized in that: The emission wavelength of the interface exciplex is less than or equal to 430 nm and the CIE coordinate y value is less than or equal to 0.

08.

4. The blue organic electroluminescent device according to claim 1, characterized in that: The acceptor material of the interfacial exciplex is the main body, and the LUMO energy level of the dye is shallower than the LUMO energy level of the acceptor material; Preferably, the difference between the HOMO energy level of the donor material and the HOMO energy level of the acceptor material is greater than or equal to 0.4 eV; the difference between the LUMO energy level of the donor material and the LUMO energy level of the acceptor material is greater than or equal to 0.4 eV; Preferably, the interface formed by the donor material and the acceptor material generates an interface exciplex under light excitation or electric field excitation, and the emission spectrum of the formed exciplex and the absorption spectrum of the blue light dye overlap on the longest wavelength side.

5. The blue organic electroluminescent device according to claim 1, characterized in that: The blue light emitting material and the sensitizer are both TADF materials.

6. The blue organic electroluminescent device according to claim 5, characterized in that: The emission peak of the blue light TADF material is located at 460-480nm, the doping concentration of the blue light TADF material in the light-emitting layer is greater than or equal to 1wt% and the half-peak width is less than or equal to 28nm; Preferably, the doping concentration of the blue organic light-emitting dye in the acceptor material-doped blue light-emitting dye layer is 1 wt % to 5 wt %.

7. The blue organic electroluminescent device according to claim 5, characterized in that: The emission wavelength of the TADF sensitizer is less than or equal to 460 nm, and the emission spectrum and the absorption spectrum of the blue light dye overlap on the longest wavelength side.

8. The blue organic electroluminescent device according to claim 1, characterized in that: The donor material is a hole transport type bipolar host material 4,4′-N,N′-dicarbazole biphenyl.

9. The blue organic electroluminescent device according to claim 1, characterized in that: The acceptor material is an organic compound 2-(9,9'-spirobi[fluorene]-3-yl)-4,6-diphenyl-1,3,5-triazine having electron transport properties.

10. The blue organic electroluminescent device according to any one of claims 1 to 9, characterized in that: The hole transport layer material is the same as or different from the interface exciplex donor material; the electron transport layer material is the same as or different from the exciplex acceptor material.

Images