White organic electroluminescent device with double-excited-base compound as main body
Technical Field
The invention belongs to the technical field of organic electroluminescent devices, and particularly relates to a white organic electroluminescent device with a double-excited-group compound as a main body.
Background
An Organic Light Emitting Device (OLED) emits light by radiative recombination of carriers, that is, electrons and holes are recombined in a light emitting layer through an electron transport layer and a hole transport layer, respectively, to form excitons, which emit visible light when they return to a ground state by radiative recombination. Organic electroluminescent devices (OLEDs), which have many advantages not possessed by conventional illumination display technologies, have characteristics of full color display, self-luminescence, wide viewing angle, high response speed, high definition, high contrast, ultra-thinness, flexible display, simple preparation process, low cost, and the like, as compared to LCDs, and thus have attracted much attention. In recent years, more and more scientific research institutes and large companies have made a lot of capital investment and research on the OLED industry, and the technology has been applied to various fields in life such as smart phone screens, solid-state lighting, curved flat panel displays, and the like, and large-scale commercialization has been achieved. In order to make OLEDs better suited for solid-state lighting, further improvements in the efficiency of the devices at high brightness are essential, and their overall performance is further optimized.
In recent years, the new generation of Thermally Activated Delayed Fluorescence (TADF) organic electroluminescent materials has attracted a large number of researchers through the triplet state (T)1) To a singlet state (S)1) The inter-inversion system traversal (RISC) of (a) can achieve internal quantum efficiencies close to 100%. The exciplex has an exciton utilization rate close to 100% as an intermolecular TADF material, and the light emission mechanism thereof is that intermolecular charge transfer is carried out, namely, a hole at the HOMO energy level on an electron donor and an electron at the LUMO energy level on an acceptor form a new excited state-The energy band difference of the excited ground state is very small, so that the reverse system crossing from the triplet state to the singlet state can be realized, and the exciton utilization rate is close to 100%. The exciplex can emit light by itself or can be used as a main material of a luminescent material, and when the exciplex is used as the main material and is doped with the high-efficiency high-brightness luminescent material, the turn-on voltage of a device can be obviously reduced, the efficiency of the device is improved, and the high-performance device is prepared.
Since the discovery by Leonhardt and Weller in 1963 that pyrene molecules in an excited state and dimethylaniline molecules in a ground state can interact to form an exciplex, exciplex light emission has attracted much attention due to the importance and universality of its existence. In 2012, Adachi et al prepared OLED devices with an External Quantum Efficiency (EQE) of 5.4% using a molar ratio of m-MTDATA to 3TPYMB of 1: 1. In 2015, a green exciplex type fluorescent OLED with external quantum efficiency of 15.4% and an energy band difference (delta E) of exciplex is prepared by taking a hole transport material TAPC as a donor and taking an electron transport material DPTPCz as an acceptor in a mass ratio of 1:1ST) It was only 0.047eV, and exhibited a photoluminescence spectrum at 503 nm. In 2016, the same subject group of Jang-Joo Kim, mcbp and PO-T2T were mixed to form an exciplex, which was used as an exciplex type host material doped with a guest material, FIrPic, to obtain a phosphorescent device as high as 34.1%. Organic electroluminescent devices based on exciplex hosts have become a hotspot for the study of exciplexes. Meanwhile, the material structure for forming the exciplex is controllable, the cost is low, and the application prospect in the field of OLEDs is very wide.
Although devices based on exciplex hosts are capable of achieving internal quantum efficiencies of 100% in theory, many researchers have designed a large number of high efficiency, low drive voltage WOLEDs. But in practice the following problems still remain: (1) in a white light device prepared by taking an exciplex as a main body, a structure of double light emitting layers is generally adopted, but the number of general exciplex main bodies is small, different light emitting layers need different exciplex main bodies to realize white light, and the difference of potential barriers between different exciplex main bodies is considered, so that the turn-on voltage and the driving voltage of the device can be increased. (2) A white light device using an exciplex as a main body generally requires two or more kinds of light emitting materials, and meanwhile, the transmission balance of carriers in a light emitting layer affects the carrier recombination region, thereby affecting the spectral stability and the efficiency roll-off.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides an organic electroluminescent device with a double-exciplex as a main body, which not only realizes the organic electroluminescent device with high efficiency and low driving voltage, but also realizes the white light organic electroluminescent device with reduced efficiency, good color stability, simple structure and wide spectrum coverage by only adopting a single light-emitting layer structure of a light-emitting material.
The technical scheme of the invention is as follows: the application provides a white organic electroluminescent device with a main body of a double-exciplex. The white organic electroluminescent device structure of the invention sequentially comprises a substrate, an anode, a hole injection layer, a hole transport layer, an organic luminescent layer, an electron transport layer, an electron injection layer and a cathode, the organic luminous layer is formed by mixing two donor materials, an acceptor material and an orange-red luminous material, wherein the donor material is a hole-transport organic micromolecule material, the acceptor material is an electron-transport organic micromolecule material, wherein a double-exciplex formed by two donor materials and one acceptor material is used as a main material of the luminescent layer, the mixing ratio is 1:1:1, but not limited to this ratio, the orange-red luminescent material is a doping object and the doping concentration is below 0.3 wt%, so as to ensure incomplete energy transfer of the host and the object and realize a three-color white light device with the double-exciplex emitting blue light and green light and the dye emitting red light. Meanwhile, the formed double-exciplex has efficient reverse intersystem crossing behavior, the triplet state energy level of the double-exciplex is higher than that of the luminescent material, the energy transfer efficiency of the host and the guest is higher, the triplet state energy level of the double-exciplex is lower than that of the hole transport material and the electron transport material, and excitons are effectively limited in the luminescent layer. The two donor materials and the acceptor material can generate two exciplex emissions under the condition of light excitation or electric field excitation after being mixed, and the emission spectrum of the exciplex and the absorption spectrum of the luminescent material have overlap on the side of the longest wavelength.
In the above-mentioned double-exciplex host, the blue exciplex can be selected as the exciplex whose emission peak is located at 430-500nm, and the green exciplex can be selected as the exciplex whose emission peak is located at 500-550nm, but it is ensured that two donor materials and one acceptor material or one donor material and two acceptor materials can both form the exciplex. The orange-red luminescent material can be selected from fluorescent materials, phosphorescent materials, TADF materials and the like with emission peaks at 580-630 nm.
The substrate may be a rigid substrate (such as glass or silicon), or a flexible substrate (such as polyethylene terephthalate or polymethyl methacrylate);
the anode may be made of a transparent metal oxide Indium Tin Oxide (ITO), a metal oxide FTO, or a high work function metal such as Ag, Au, or Cu.
The cathode may be formed by depositing 100nm of Al as a cathode material by thermal deposition, or may be formed of a metal having a low work function such as Ca or Ba.
A plurality of organic functional layers are arranged between the anode and the cathode, and the organic functional layers comprise a hole injection layer, a hole transport layer, an organic light-emitting layer, an electron transport layer and an electron injection layer. The hole injection material is preferably MoO 32,3,6,7,10, 11-hexacyano-1, 4,5,8,9, 12-hexaazatriphenylene (1,4,5,8,9,11-hexaazatriphenylene hexacarbonie, HAT-CN) can also be used; the hole transport material is preferably 1,3-Di-9-carbazolylbenzene (1,3-Di-9-carbazolylbenzene, MCP), or 4,4' -cyclohexylbis [ N, N-bis (4-methylphenyl) aniline](di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexoxane, TAPC), 4',4 ″ -Tris (carbazol-9-yl) triphenylamine (4,4',4 ″ -Tris (carbazol-9-yl) -triphenylamine, TCTA), N ' -diphenyl-N, N ' -Bis (3-methylphenyl) -1,1' -biphenyl-4, 4' -diamine (N, N ' -Bis (3-methylphenyl) -N, N ' -Bis (phenyl) benzidine, TPD), N ' -diphenyl-N, N ' - (1-naphthyl) -1,1' -biphenyl-4,4' -diamine (N, N ' -Bis- (1-aminophenyl) -N, N ' -Bis-phenyl- (1,1' -biphenyl) -4,4' -diamine, NPB), 4',4 ″ -Tris (N-3-methylphenyl-N-phenylamino) triphenylamine (4,4',4 ″ -Tris (N-3-methylphenyl-N-phenylamino) triphenylamine, m-MTDATA); the thickness of the luminescent layer is 0-100nm, 1,3-Di-9-carbazolylbenzene (1,3-Di-9-carbazolylbenzene, MCP), 4 '-Tris (carbazol-9-yl) triphenylamine (4,4' -Tris (carbazol-9-yl) -triphenylamine, TCTA) and 4,6-bis (3, 5-bis (pyridin-4-yl) phenyl) -2-phenylpyrimidine (4,6-bis (3,5-Di (pyridine-4-yl) phenyl) -2-phenylpyrimidine, B4PyPPM) are doped in a molar mass ratio of 1:1:1 (not limited to 1:1:1) to form a host of the double-exciplex, the luminescent material can be selected from phosphorescent materials, fluorescent luminescent materials and TADF materials, the phosphorescent material is preferably (acetylacetone) bis (2-methyl dibenzo [ f, h ]]Quinoxaline) Iridium (bis (2-methylidenzo [ f, h ]]quinoxaline)(acetylacetonate)iridium(III),Ir(MDQ)2(acac)), the yellow light material bis (4-phenyl-thiophene [3,2-c ] acetylacetonate may also be used]pyridine-C2, N iridium (Iridium (III) bis (4-phenylthieno [3, 2-C))]pyridinato-N, C2') acetyl-acetate, PO-01); the electron transport material is preferably 4,6-bis (3,5-di (pyridin-4-yl) phenyl) -2-phenylpyrimidine (4,6-bis (3,5-di (pyridine-4-yl) phenyl) -2-phenylpyrimidine, B4PyPPM), or 1,3,5-tris [ (3-pyridyl) -3-phenylpyrimidine]Benzene (1,3,5-Tri [ (3-pyridol) -phen-3-yl)]benzene, Tmpypb), 4,7-diphenyl-1,10-Phenanthroline (4,7-diphenyl-1,10-Phenanthroline, Bphen), 1,3,5-Tris (1-phenyl-1H-benzimidazol-2-yl) benzene (1,3,5-Tris (1-phenyl-1H-benzimidazol-2-yl) -benzene, TPBi), 1,3-bis (3, 5-bis (pyridin-3-yl) phenyl]Benzene (1,3-Bis [3,5-di (pyridine-3-yl) phenyl)]benzene, BmPyPhB), Tris (8-hydroxyquinoline) Aluminum (Aluminum Tris (8-hydroxyquinoline), Alq3), 2, 9-Dimethyl-4, 7-biphenyl-1, 10-phenanthroline (2, 9-Dimethyl-4, 7-diphenyl-1, 10-phenanholine, BCP); the electron injection material is preferably 8-hydroxyquinoline-lithium (8-hydroxyquinoline, Liq), and LiF may be used.
The above-mentioned materials are all available from commercial materials companies.
The invention has the beneficial effects that: the embodiment of the invention provides a preparation method of a white organic electroluminescent device with a double-exciplex as a main body, which is characterized in that the double-exciplex is prepared by blending three functional materials, and the double-exciplex is used as a main body doped with an ultra-low-concentration red light material or a yellow light material to obtain a white light emitting device, so that low driving voltage, low efficiency roll-off, good spectrum stability and wide spectrum coverage are realized. The invention achieves white light device emission with a single light emitting layer structure using only one light emitting material. The donor material and the acceptor material of the double-exciplex formed by the invention have very matched energy levels, so that the injection potential barrier of a current carrier is effectively reduced, the transmission capability of the current carrier is improved, the number of the current carrier is increased, good current carrier balance is realized, the starting and driving voltage of a device is obviously reduced, the efficiency of the device is improved, the quenching effect of the concentration of the current carrier is reduced, and the problem of efficiency roll-off is obviously improved. The invention not only realizes the organic electroluminescent device with high efficiency and low driving voltage, but also realizes the white light organic electroluminescent device with reduced efficiency, good color stability, high color rendering index and simple structure of a single light-emitting layer structure based on the double-exciplex main body.
Drawings
FIG. 1: the structure schematic diagram of the organic electroluminescent device taking the novel blue exciplex as the main body is shown;
wherein 1 is a substrate, 2 is an anode, 3 is a hole injection layer, 4 is a hole transport layer, 5 is a luminescent layer, 6 is an electron transport layer, 7 is an electron injection layer, and 8 is a cathode;
FIG. 2: the invention relates to a light-emitting schematic diagram of a white light organic electroluminescent device with a double-exciplex main body doped with ultra-low concentration dye;
FIG. 3: the current density-voltage curve of the white organic electroluminescent device realized based on the double-exciplex main body is shown in the specification;
FIG. 4: the invention relates to a normalized spectrum diagram of a white light organic electroluminescent device realized based on a double-exciplex main body.
Detailed Description
The meanings of the abbreviations used in the examples are as follows:
ITO: indium tin oxide; used as transparent anode
MoO3: the hole injection material is used for anode modification, so that the injection of holes is facilitated;
MCP: 1, 3-di-9-carbazolylbenzene; a hole-transporting material for transporting holes and serving as a donor material for forming an exciplex;
TCTA: 4,4',4 "-tris (carbazol-9-yl) triphenylamine; a donor material for forming an exciplex;
Ir(MDQ)2(acac): (Acetylacetone) bis (2-methyldibenzo [ f, h ]]Quinoxaline) iridium, high-efficiency orange-red phosphorescent materials;
b4 PyPPM: 4,6-bis (3, 5-bis (pyridin-4-yl) phenyl) -2-phenylpyrimidine, an electron transport material, an acceptor material for forming an exciplex;
liq: 8-hydroxyquinoline-lithium; the cathode buffer layer is beneficial to the injection of electrons;
al: aluminum, 100nm thick, as a cathode.
Example 1:
the preparation of the organic light-emitting device can be carried out in a multi-source organic molecule vapor deposition system, and the detailed process is as follows:
ITO conductive glass is selected as a substrate in the experiment. Firstly, repeatedly scrubbing an ITO glass substrate by using acetone and ethanol to remove impurities on the surface, and washing the ITO glass substrate by using deionized water to remove cotton balls stuck in the scrubbing process;
putting the cleaned ITO substrate into a clean beaker, sequentially performing ultrasonic treatment on the cleaned ITO substrate for 10 minutes by using acetone, ethanol and deionized water, then putting the cleaned ITO substrate into an oven for drying, and finally performing ultraviolet treatment on the dried ITO glass substrate for 10 minutes;
and (3) placing the processed substrate in a multi-source organic molecule vapor deposition system, wherein a vacuum cavity of the evaporation system is provided with 10 organic material evaporation sources and 3 metal evaporation sources. The vacuum degree of the evaporation system can reach 10
-5Pa, maintaining the vacuum degree of the system at
3X 10 during the film growth process
-4Pa or so. The material being grownThe thickness and the growth rate are controlled by an American IL-400 type film thickness controller, and the growth rate of the organic material is controlled in
The electroluminescence spectrum, brightness and current-voltage characteristics of the device are synchronously measured by a test system consisting of a spectrometer PR655, a current meter Keithley-2400 and a computer. All tests were performed in room temperature atmosphere.
In the white light device structure based on the double-excited-base compound main body in the embodiment, a hole injection layer MoO with the thickness of 3nm is sequentially evaporated on an ITO glass substrate3A 45nm hole transport layer MCP, a 25nm organic light emitting layer made of MCP, TCTA, B4PyPPM, Ir (MDQ)2acac, wherein MCP, TCTA, B4PyPPM are mixed at a molar ratio of 1:1:1 molar mass ratio as exciplex host, Ir (MDQ)2acac is red light dye with the doping proportion of 0.1 wt%; a 35nm electron transport layer B4PyPPM, a 0.8nm electron injection layer Liq, a 100nm Al cathode, and the structure of the device is ITO/MoO3(3 nm)/MCP(45nm)/MCP:TCTA:B4PyPPM:Ir(MDQ)2acac (25nm)/B4PyPPM (35nm)/Liq (0.8 nm)/Al (100 nm). Incomplete host-guest energy transfer is realized through a low-concentration doping mode, three-color white light device emission is realized by emitting blue light and green light by an exciplex host and emitting red light by a guest, and the proportion of a light-emitting layer is controlled by monitoring and adjusting the growth rate through an American IL-400 type film thickness controller.
Fig. 2 shows the principle diagram of the luminescence of the present example, from which the energy transfer process of the exciton can be seen. Fig. 3 shows a current density-voltage characteristic curve of the present example. Fig. 4 shows a normalized spectrum chart of an example of the present invention, and it is obvious from the graph that there are three emission peaks, which are respectively located at about 450nm, 520nm, and 610nm, and the coverage of the spectrum is large. Meanwhile, the white light device is 1000cd/m2Has a luminance lower color coordinate of (0.43,0.40), a Color Rendering Index (CRI) of up to 89, and a color temperature (CCT) of 3010.
Although the invention has been described with reference to examples, it is not limited to the examples and the drawings described above, and modifications may be made by a person skilled in the art within the scope of the claims.