White organic light-emitting diodes based on ultra-thin phosphorescent layers

Abstract

The present invention relates to a white light organic light emitting diode based on a phosphorescent ultra-thin layer, wherein the light emitting layer unit is composed of an electron donor material layer and an electron acceptor material layer of the same number arranged alternately, an interface exciplex is formed between any two adjacent electron donor material layers and electron acceptor material layers, and a phosphorescent ultra-thin layer with complementary luminescent colors is embedded between each electron donor material layer and electron acceptor material layer, and the phosphorescent ultra-thin layer is sensitized by the interface exciplex to achieve complementary light emission of the phosphorescent ultra-thin layer, and white light emission is formed by compounding. The present invention utilizes the effective energy transfer from the interface exciplex to the phosphorescent ultra-thin layer, and simplifies the device structure and preparation process under the premise of achieving efficient white light emission.

Description

Technical Field

[0001] The invention belongs to the technical field of organic optoelectronic devices and relates to an organic light emitting diode, in particular to a white light organic light emitting diode which emits light through an interface excimer complex sensitized phosphorescent ultra-thin layer. Background Art

[0002] White organic light-emitting diodes (OLEDs) are a type of surface light source that are flexible, thin, light-weight, have soft light colors, and are free of blue pollution. They are known as a new generation of low-power, green lighting technology and have become a research hotspot in academia and industry in recent years.

[0003] In order to achieve white light emission, it is necessary to introduce multiple complementary color luminescent materials into the same device. These complementary luminescent materials are usually a combination of blue and yellow luminescent materials, or a combination of blue, green and red luminescent materials, or a combination of blue, green, yellow and red luminescent materials.

[0004] The color rendering index is an important indicator for evaluating the color quality of white light OLEDs. The higher the color rendering index of white light, the stronger its ability to restore the color of the object itself.

[0005] In order to obtain white light emission with a high color rendering index, the white light needs to have a wide and continuous spectrum. This requires the design of a reasonable device structure, the introduction of more complementary luminescent materials in the same device, and the adjustment of the relative luminous intensity of luminescent materials of different colors. Therefore, the device structure of white light OLEDs is more complicated than that of monochromatic light devices.

[0006] Phosphorescent materials have become the commonly used luminescent materials for the development of white light OLEDs in recent years due to their high exciton utilization rate. The luminescent layer prepared by host-guest doping can effectively suppress the high-concentration exciton quenching problem of phosphorescent materials, making the host-guest doped luminescent layer the mainstream technology for the development of white light OLEDs in recent years. However, the host-guest doped luminescent layer usually involves complex doping technology, which has very demanding requirements on equipment and preparation process.

[0007] The complex device structure and device preparation process will lead to low yield and high preparation cost of white OLEDs, which greatly restricts the low-cost and large-scale industrialization and promotion of white OLEDs. In addition, white OLEDs also face problems such as high power consumption caused by high driving voltage, color stability and color quality that need to be improved. These factors also restrict the industrialization process of white OLED lighting panels to a certain extent.

[0008] When the exciplex is used as the main body of the phosphorescent material, its barrier-free injection property can effectively reduce the driving voltage of the device. When the exciplex with thermally activated delayed fluorescence (TADF) characteristics is used as the main body, it can also enhance the effective energy transfer from the exciplex to the phosphorescent material, inhibit the quenching of triplet excitons in the main body of the exciplex, and improve the utilization rate of excitons inside the device, that is, realize the sensitization effect of the exciplex on the phosphorescent material.

[0009] Compared with bulk exciplexes formed by co-doping of donor and acceptor materials, interfacial exciplexes can avoid the doping process during co-deposition of materials and simplify the device structure and preparation process.

[0010] At the same time, the energy level difference at the interface of the electron donor material layer / electron acceptor material layer of the interfacial exciplex can limit the carriers and excitons at the interface, which is beneficial to the regulation of the spectrum of white light OLEDs. For example, researchers have found that when a layer of organic functional layer material within 7nm is introduced between the electron donor material layer and the electron acceptor material layer of the interfacial exciplex, it does not affect the formation of exciplexes between the electron donor material and the electron acceptor material on both sides.

[0011] Compared with the traditional doped phosphorescent light-emitting layer, the phosphorescent ultra-thin light-emitting layer can not only simplify the device structure and preparation process of white light OLEDs, but also reduce the use of expensive phosphorescent materials and increase the flexibility of device design. The thickness of the phosphorescent ultra-thin layer is less than 1nm, and when it is introduced into the interface exciplex donor / acceptor interface, it will not affect the formation of exciton emission, which makes it possible to design ultra-simple, low-drive and high-efficiency white light OLEDs by combining the interface exciplex and the phosphorescent ultra-thin layer. Summary of the invention

[0012] The purpose of the present invention is to provide a white light organic light emitting diode based on a phosphorescent ultra-thin layer, which utilizes the combination of an interfacial excited radical complex and a phosphorescent ultra-thin layer to achieve the preparation of a low-drive, high-performance white light organic light emitting diode through a simple device structure and preparation process.

[0013] Specifically, the white light organic light emitting diode based on the phosphorescent ultra-thin layer described in the present invention introduces multiple interface exciplexes into the same device by alternating the electron donor material layer and the electron acceptor material layer, and then embeds the complementary phosphorescent ultra-thin layer at the electron donor material layer / electron acceptor material layer interface that forms the interface exciplex. The interface exciplex is used as the host and the phosphorescent ultra-thin layer is used as the guest. The interface exciplex host sensitizes the phosphorescent ultra-thin layer guest to achieve complementary light emission of the phosphorescent ultra-thin layer, and the white light emission is formed by compounding.

[0014] Based on the above-mentioned luminescence mechanism, the white light organic light emitting diode based on the phosphorescent ultra-thin layer described in the present invention is firstly the same as a conventional organic light emitting diode, and at least includes an anode, a cathode and a light emitting layer unit necessary for constituting an organic light emitting diode.

[0015] But the difference is that in the light-emitting layer unit described in the present invention, first, it includes no less than 2 layers of electron donor material layers, and the same number of electron acceptor material layers arranged alternately with the electron donor material layers, and at the same time, an interface excimer complex can be formed between any two adjacent electron donor material layers and electron acceptor material layers.

[0016] Secondly, the luminescent layer unit also includes a phosphorescent ultra-thin layer, and the phosphorescent ultra-thin layer is embedded between each adjacent electron donor material layer and electron acceptor material layer, and at the same time, the luminescent colors of the phosphorescent ultra-thin layer are complementary.

[0017] That is to say, the light-emitting layer unit of the white light organic light-emitting diode based on the phosphorescent ultra-thin layer of the present invention is composed of n electron donor material layers and n electron acceptor material layers arranged alternately, and 2n-1 phosphorescent ultra-thin layers embedded between the electron donor material layers and the electron acceptor material layers, and finally the light-emitting layer of the present invention is composed of the formed multiple interface exciplexes and the complementary phosphorescent ultra-thin layers. Among them, the number of n is at least 2.

[0018] The outermost electron donor material layer is located on the anode side, and the outermost electron acceptor material layer is located on the cathode side.

[0019] Therefore, the white light organic light emitting diode based on the phosphorescent ultra-thin layer described in the present invention uses the formed interface exciplex as the main body of the light-emitting layer, and the phosphorescent ultra-thin layer as the guest of the light-emitting layer, and realizes the luminescence of the phosphorescent ultra-thin layer through the direct carrier capture mechanism and the sensitization mechanism of the interface exciplex to the phosphorescent ultra-thin layer. Therefore, in the present invention, the triplet energy level of the formed interface exciplex should be higher than the triplet energy level of the phosphorescent ultra-thin layer material, so that the multi-channel energy transfer of the interface exciplex to the phosphorescent ultra-thin layer can be realized, the quenching of the triplet excitons in the phosphorescent ultra-thin layer can be reduced, and the sensitization effect of the interface exciplex main body on the phosphorescent ultra-thin layer guest can be realized.

[0020] Therefore, the phosphorescent ultra-thin layer of the present invention emits light after being sensitized by the interface exciplex, and the light colors of each phosphorescent ultra-thin layer are complementary and recombined, eventually forming white light emission.

[0021] In the light-emitting layer unit of the present invention that utilizes a multi-interface exciplex host to sensitize a phosphorescent ultra-thin layer guest, the electron donor material and the electron acceptor material are conventional electron donor materials and electron acceptor materials, and the present invention has no special requirements for them.

[0022] Among them, generally, the selected electron donor material usually has strong hole transport performance and a relatively high highest occupied molecular orbital (HOMO) energy level; specifically, the electron donor material may include but is not limited to mCP, TCTA, TAPC, m-MTDATA, HAT-CN and other materials.

[0023] The electron acceptor material generally has strong electron transport performance and a relatively low lowest unoccupied molecular orbital (LUMO) energy level. Specifically, the electron acceptor material may include but is not limited to PO-T2T, B3PYMPM, 3P-T2T, TmPyPB, TPBi and other materials.

[0024] Furthermore, when the formed interfacial exciplex has a very small singlet-triplet energy level difference, it will exhibit strong thermally activated delayed fluorescence (TADF) characteristics, which can convert non-radiative triplet excitons into singlet excitons through up-conversion, reduce the quenching of triplet excitons in the main body of the exciplex, and thus improve the exciton utilization rate of the device.

[0025] The n electron donor material layers of the present invention can be the same material, and can be matched with n electron acceptor material layers composed of the same material to form an exciplex with a triplet energy level higher than the triplet energy level of all phosphorescent ultra-thin layers.

[0026] Furthermore, the present invention can also be that the n electron donor material layers are the same, i.e., one material, and are matched with n electron acceptor material layers composed of different materials, wherein the triplet energy level of all the donor / acceptor exciplexes formed is higher than the triplet energy level of the phosphorescent ultra-thin layer embedded in its interface.

[0027] Similarly, the n electron acceptor material layers described in the present invention can be the same material, and can be matched with n electron donor material layers composed of the same material to form an exciplex with a triplet energy level higher than the triplet energy level of all phosphorescent ultra-thin layers.

[0028] Furthermore, the present invention may also be that the n electron donor material layers are the same, i.e., one material, and are matched with n electron acceptor material layers composed of different materials, wherein the triplet energy levels of all donor / acceptor excited complexes formed are higher than the triplet energy level of the phosphorescent ultra-thin layer embedded in its interface.

[0029] Furthermore, the present invention preferably has the triplet energy levels of the electron donor material and the electron acceptor material on both sides of all the phosphorescent ultra-thin layers among the n electron donor material layers and the electron acceptor material layers higher than the triplet energy level of the phosphorescent ultra-thin layer embedded in its interface.

[0030] Thus, the phosphorescent ultra-thin layers embedded in the interfaces of 2n-1 donor / acceptor layers emit complementary colors. The emission of the phosphorescent ultra-thin layers is achieved through direct carrier capture by the phosphorescent ultra-thin layers and energy transfer from the interface excited radical complex to the phosphorescent ultra-thin layers, and complementary lights of different colors are combined to form white light.

[0031] In the white light organic light emitting diode based on the phosphorescent ultra-thin layer described in the present invention, the performance and efficiency of the white light device can be adjusted by changing the number of interface exciplexes and corresponding phosphorescent ultra-thin layers in the light-emitting unit constructed by sensitizing the phosphorescent ultra-thin layer guest with the multi-interface exciplex host, and by adjusting the arrangement order of the phosphorescent ultra-thin layers.

[0032] The present invention can reasonably select and arrange the phosphorescent ultra-thin layer so that the phosphorescent ultra-thin layer forms two-color white light emission in the light-emitting unit where the multi-interface exciplex host sensitizes the phosphorescent ultra-thin layer guest.

[0033] Specifically, it is preferred that the phosphorescent ultra-thin layers are respectively composed of a phosphorescent material that emits blue light and a phosphorescent material that emits yellow light, and the blue light and yellow light emitted by the multiple phosphorescent ultra-thin layers are combined to form white light, thereby achieving blue-yellow two-color white light emission.

[0034] If the number of blue phosphorescent ultra-thin layers is x, the number of yellow phosphorescent ultra-thin layers is 2n-1-x, and vice versa. The embedding order of 2n-1 blue and yellow phosphorescent ultra-thin layers can be combined at will, for example: blue-blue-yellow, blue-yellow-blue, yellow-blue-yellow, blue-yellow-blue-yellow-blue and other combinations of phosphorescent ultra-thin layer emission units.

[0035] Similarly, the present invention can also reasonably select and arrange the phosphorescent ultra-thin layer so that in the light-emitting unit where the multi-interface exciplex host sensitizes the phosphorescent ultra-thin layer guest, the phosphorescent ultra-thin layer can form three-color white light emission.

[0036] Specifically, the phosphorescent ultra-thin layer is preferably composed of three phosphorescent materials, namely, a phosphorescent material emitting red light, a phosphorescent material emitting green light or yellow light, and a phosphorescent material emitting blue light, and the number of phosphorescent ultra-thin layers of each color is at least 1, and the total number of all embedded phosphorescent ultra-thin layers is 2n-1.

[0037] Similarly, the embedding order of three different phosphorescent ultra-thin layers of red, green or yellow and blue can also be combined at will. For example, when using red, green and blue phosphorescent ultra-thin layers, they can be combined into blue-green-red, red-green-blue, blue-red-green, red-blue-green, green-red-blue, green-blue-red and blue-green-red-green-blue, green-blue-green-red-blue and other phosphorescent ultra-thin layer emission units; if using red, yellow and blue phosphorescent ultra-thin layers, they can be combined into blue-yellow-red, red-yellow-blue, blue-red-yellow, red-blue-yellow, yellow-red-blue, yellow-blue-red and blue-yellow-red-yellow-blue, yellow-blue-yellow-red-blue and other phosphorescent ultra-thin layer emission units. The blue light, green light and red light (or blue light, yellow light and red light) emitted by 2n-1 phosphorescent ultra-thin layers are combined to form white light emission.

[0038] Similarly, the present invention can also reasonably select and arrange the phosphorescent ultra-thin layer so that in the light-emitting unit where the multi-interface exciplex host sensitizes the phosphorescent ultra-thin layer guest, the phosphorescent ultra-thin layer can form four-color white light emission.

[0039] Likewise, the number of phosphorescent ultra-thin layers of each color is at least 1, and the total number of all embedded phosphorescent ultra-thin layers is 2n-1.

[0040] Specifically, the phosphorescent ultra-thin layer is preferably composed of four phosphorescent materials, namely, a phosphorescent material that emits red light, a phosphorescent material that emits yellow light, a phosphorescent material that emits green light, and a phosphorescent material that emits blue light. The embedding order of the four different phosphorescent ultra-thin layers can also be combined at will. The embedding order of the phosphorescent ultra-thin layers can be adjusted to form phosphorescent ultra-thin layer emission units with various combinations such as blue-green-yellow-red-blue, blue-red-yellow-green-blue, and blue-green-red-yellow-blue. The red, green, yellow and blue lights emitted by the 2n-1 phosphorescent ultra-thin layers complement each other and form white light.

[0041] In addition, in the light-emitting layer unit of the white light organic light-emitting diode based on the ultra-thin phosphorescent layer described in the present invention, the device performance can be adjusted by adjusting the thickness of the electron donor material layer and the electron acceptor material layer in the multi-interface excimer complex body.

[0042] Preferably, the present invention generally sets the thickness of the outermost electron donor material layer and electron acceptor material layer in the light-emitting layer unit to be thicker, 3-100nm, and the thickness of the electron donor material layer and electron acceptor material layer between the two is set to be thinner, generally 1-20nm.

[0043] Furthermore, in the light-emitting layer unit of the white organic light-emitting diode based on the ultra-thin phosphorescent layer described in the present invention, the spectrum and performance of the device can be adjusted by adjusting the thickness of the ultra-thin phosphorescent layer.

[0044] The thickness of the complementary phosphorescent ultra-thin layers may be the same or different. Preferably, the thickness of each phosphorescent ultra-thin layer is 0.01-1 nm.

[0045] In the white organic light emitting diode based on the phosphorescent ultra-thin layer described in the present invention, a hole transport layer and an electron transport layer may be provided on both sides of the light emitting layer unit.

[0046] Furthermore, the material of the hole transport layer can be selected to be the same as the material of the outermost electron donor material layer close to the anode side; similarly, the material of the electron transport layer can also be selected to be the same as the material of the outermost electron acceptor material layer close to the cathode side.

[0047] Furthermore, the present invention may further provide a layer of hole transport material different from the outermost electron donor material layer close to the anode side on the outer side of the hole transport layer to form a second hole transport layer.

[0048] In the present invention, a layer of electron transport material different from the outermost electron acceptor material layer close to the cathode side may be arranged outside the electron transport layer to form a second electron transport layer.

[0049] The provision of the additional hole transport layer and electron transport layer further balances the overall electron or hole injection and transport to the light-emitting unit region of the device, thereby further improving the white light emission color stability and device efficiency of the white light organic light-emitting diode of the present invention.

[0050] In addition, the present invention can also set a hole injection layer inside the anode of the white light organic light emitting diode based on the ultra-thin phosphorescent layer and an electron injection layer inside the cathode to further improve the device's anode injection hole capability and cathode injection electron capability.

[0051] In the white light organic light emitting diode based on the phosphorescent ultra-thin layer of the present invention, holes and electrons are respectively injected from the anode and cathode into the hole transport layer and the electron transport layer through the hole and electron injection layers, and then the hole transport layer and the electron transport layer respectively transmit the holes and electrons in opposite directions to the light emitting layer unit constructed by the interface excimer complex and the phosphorescent ultra-thin layer, forming two-color, three-color or four-color phosphorescent emission in the light emitting area, and finally compounding to form white light emission.

[0052] The uniqueness of the present invention lies in that the main body of the light-emitting layer unit is composed of electron donor material layers and electron acceptor material layers that are alternately arranged and can form interfacial exciplexes; except for the electron donor material layer closest to the anode, the other electron donor material layers can form interfacial exciplexes with the electron acceptor material layers on both sides; except for the electron acceptor material layer closest to the cathode, the other electron acceptor material layers can form interfacial exciplexes with the electron donor material layers on both sides.

[0053] The feature of alternating arrangement of electron donor and electron acceptor materials in the above-mentioned host-guest light-emitting layer unit, on the one hand, introduces multiple interface exciton complexes into the same device through clever design and simple structure, solving the current problem of difficulty in introducing multiple interface exciton complexes into the same device; on the other hand, it also confines the carriers and excitons in the light-emitting layer unit to the interface between the electron donor and the electron acceptor, improving the stability of white light color quality and device efficiency.

[0054] The white light organic light emitting diode device structure and preparation process of the present invention, which is formed by sensitizing the phosphorescent ultra-thin layer through the multi-interface excimer complex, are simple and have good repeatability, and are conducive to the commercialization and promotion of white light OLEDs. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a schematic diagram of the light-emitting layer structure of the white light organic light-emitting diode based on the phosphorescent ultra-thin layer of the present invention.

[0056] Figure 2 It is the normalized electroluminescence spectrum and current efficiency-brightness curve of the monochromatic light device in Example 1.

[0057] Figure 3 It is a normalized electroluminescence spectrum and current efficiency-brightness curve of the two-color white light device of Example 2.

[0058] Figure 4 It is a normalized electroluminescence spectrum and current efficiency-brightness curve of the three-color white light device in Example 3.

[0059] Figure 5 It is a normalized electroluminescence spectrum, current efficiency-brightness curve and current density-voltage-brightness curve of the four-color white light device of Example 4. DETAILED DESCRIPTION

[0060] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solution of the present invention so that those skilled in the art can well understand and utilize the present invention, rather than limiting the scope of protection of the present invention.

[0061] The names and abbreviations of the experimental methods, production processes, instruments and equipment involved in the embodiments of the present invention are all conventional names in the field and are very clear and unambiguous in the relevant application fields. Technicians in the field can understand the conventional process steps and apply the corresponding equipment according to the names and implement them according to conventional conditions or conditions recommended by the manufacturer.

[0062] The directional terms such as "upper", "lower", "left", "right", "middle", etc. involved in the embodiments of the present invention are only for the convenience of description and are not intended to limit the scope of the present invention. Changes or adjustments to their relative relationships should be regarded as within the scope of the present invention without substantially changing the technical content.

[0063] The various raw materials or reagents used in the examples of the present invention are not particularly limited in their sources, and are all conventional products that can be purchased commercially, or can be prepared according to conventional methods well known to those skilled in the art.

[0064] The monochromatic or white-light organic light-emitting diode devices involved in the embodiments of the present invention are all realized by high vacuum evaporation process. All monochromatic or white-light organic light-emitting diode devices are prepared on a pre-patterned ITO (indium tin oxide) glass substrate purchased from Shenzhen Huayu United Technology Co., Ltd., with a surface resistance of 15Ω / sq.

[0065] Except for high-purity aluminum wire purchased from Beijing Cuibailin Nonferrous Metals Technology Development Center Co., Ltd., all other organic and inorganic functional materials were purchased from Shanghai Hanfeng Chemical Technology Co., Ltd. and did not undergo any purification treatment before use.

[0066] The preparation methods of all the monochromatic and white light organic light emitting diode devices involved in the embodiments of the present invention are as follows.

[0067] 1. Cleaning of ITO glass substrate.

[0068] After cleaning the oil stains on the surface of the ITO glass substrate with cleaning powder, the ITO glass substrate was repeatedly rinsed with tap water until a complete water film was formed, and then the ITO glass substrate was placed in deionized water and acetone in turn, and ultrasonically cleaned for 20 minutes each.

[0069] 2. Drying of ITO glass substrate.

[0070] The cleaned ITO glass substrate was taken out from acetone, dried with a nitrogen gun, and placed in a constant temperature oven at 80°C for 2 h.

[0071] 3. UV treatment of ITO glass substrate.

[0072] Before evaporation, the dried ITO glass substrate was taken out from the oven and irradiated with ultraviolet light for 20 minutes to further remove organic matter adhering to the ITO glass substrate and improve the surface work function of ITO.

[0073] 4. Cavity filling of ITO glass substrate.

[0074] The ITO glass substrate is taken out from the UV box, placed on the mask plate loaded with the ITO glass, and the mask plate loaded with the ITO glass substrate is introduced into the cavity of the high vacuum coating machine.

[0075] 5. Vacuum the equipment.

[0076] Turn on the power supply, mechanical pump and molecular pump of the high vacuum coating machine in sequence to evacuate the vacuum chamber.

[0077] 6. Thermal evaporation preparation of organic light emitting diodes.

[0078] When the vacuum degree in the high vacuum coating machine chamber is lower than 5×10 -4 Pa, the thermal evaporation sources containing functional materials such as hole and electron injection layer materials and hole and electron transport layer materials and luminescent materials in the cavity are heated separately, and various functional layers are thermally deposited on the ITO glass substrate in sequence according to the designed device structure.

[0079] Finally, the mask plate with the ITO glass substrate is rotated to align the mask position for depositing the aluminum cathode with the ITO glass substrate, and the thermal evaporation source with aluminum wire is heated to deposit the aluminum cathode, thereby finally preparing a complete organic light-emitting diode.

[0080] During the thermal evaporation process, the evaporation rate and film thickness of the material are monitored by a quartz crystal frequency meter connected to the outside of the vacuum chamber. The evaporation rate of the phosphorescent ultra-thin layer material is 0.06Å / s, the evaporation rate of other organic functional layer materials is 1.00Å / s, and the evaporation rate of the inorganic material MoO 3 The evaporation rates of LiF and Al are approximately 0.3Å / s, 0.1Å / s, and 7.0Å / s, respectively.

[0081] The overlapping part of the ITO glass and the aluminum cathode is taken as the effective light-emitting area of ​​the device, and the effective light-emitting area of ​​the device is 3.0 mm×3.0 mm.

[0082] The present invention specifically tests the performance of the organic light emitting diode in the embodiment according to the following method.

[0083] The prepared organic light-emitting diode was taken out from the vacuum chamber, and the current density, current efficiency and brightness of the device were obtained using a computer-integrated ST-900M photometer and a Keithley 2400 digital source meter. The electroluminescence spectrum, color coordinates and color rendering index of the device at different voltages were obtained using a computer-integrated Spectra Scan PR655 spectroradiometer.

[0084] The specific compound names corresponding to the abbreviations of the chemical substances involved in the following embodiments of the present invention are as follows.

[0085] mCP: 1,3-di-9-carbazolylbenzene.

[0086] TCTA:4,4′,4”-tris(carbazol–9-yl)triphenylamine。

[0087] TAPC:4,4′-cyclohexylidenebis[N,N-bis(p-tolyl)aniline]。

[0088] m-MTDATA:4,4′,4”-Tris[phenyl(m-tolyl)amino]triphenylamine。

[0089] HAT-CN:2,3,6,7,10,11-Hexaazatriphenylenehexacabonitrile。

[0090] PO-T2T:2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine。

[0091] B3PYMPM:4,6-Bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine。

[0092] 3P-T2T:2,4,6-tris(2-(1H-pyrazol-1-yl)phenyl)-1,3,5-triazine。

[0093] TmPyPB:1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene。

[0094] TPBi:1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene。

[0095] FIrpic:bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III)。

[0096] Ir(ppy) 3 :tris[2-(p-tolyl)pyridine-C2,N)]iridium(III)。

[0097] Ir(bt) 2(acac): iridium(III)bis(2-phenylbenzothiozolato-N,C20)acetylacetonate.

[0098] Ir(piq) 2 (acac):bis(1-phenyliso-quinoline)(acetylacetonate)iridium(III).

[0099] Example 1.

[0100] In this embodiment, a main structure of "electron donor material layer / electron acceptor material layer / electron donor material layer / electron acceptor material layer" is constructed by alternately depositing electron donor material mCP and acceptor material PO-T2T, and a phosphorescent ultra-thin layer is introduced at the interface between each electron donor material layer and the electron acceptor material layer to prepare red, yellow, green and blue OLEDs with multi-interface excited radical complex-sensitized phosphorescent ultra-thin layers. The specific device structures of the four devices are given below.

[0101] Red light device R: ITO / MoO 3 (3nm) / mCP (40nm) / Ir(piq) 2 (acac) (0.18nm) / PO-T2T(3nm) / Ir(piq) 2 (acac) (0.18nm) / mCP (3nm) / Ir(piq) 2 (acac) (0.18nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0102] Yellow light device Y: ITO / MoO 3 (3nm) / mCP (40nm) / Ir(bt) 2 (acac) (0.21nm) / PO-T2T(3nm) / Ir(bt) 2 (acac) (0.21nm) / mCP (3nm) / Ir(bt) 2 (acac) (0.21nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0103] Green light device G: ITO / MoO 3 (3nm) / mCP (40nm) / Ir(ppy) 3(0.22nm) / PO-T2T(3nm) / Ir(ppy) 3 (0.22nm) / mCP (3nm) / Ir(ppy) 3 (0.22nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0104] Blue light device B: ITO / MoO 3 (3nm) / mCP (40nm) / FIrpic (0.35nm) / PO-T2T (3nm) / FIrpic (0.35nm) / mCP (3nm) / FIrpic (0.35nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0105] In the above monochromatic OLEDs, the 3nm thick MoO 3 The 1nm thick LiF layer is the hole injection layer, and the 40nm thick mCP layer is the hole transport layer and the electron donor layer of the interface exciplex. The 50nm thick PO-T2T layer is the electron transport layer and the electron acceptor layer of the interface exciplex. The 0.18nm Ir(piq) 2 (acac) thin layer is red phosphorescent layer, 0.21nm Ir(bt) 2 (acac) thin layer is yellow phosphorescent layer, 0.22nm Ir(ppy) 3 The thin layer is a green phosphorescent layer, and the 0.35nm FIrpic thin layer is a blue phosphorescent layer; the 3nm thick mCP layer is an electron donor layer of the interface exciplex, and is also a spacer between the ultra-thin phosphorescent layers; the 3nm thick PO-T2T layer is an electron acceptor layer of the interface exciplex, and is also a spacer between the ultra-thin phosphorescent layers. ITO is the anode, and the 100nm thick Al film is the cathode.

[0106] Figure 2 It is the normalized electroluminescence spectrum and current efficiency-brightness curve of four monochromatic light devices R, Y, G and B at a driving voltage of 5V.

[0107] Among them, it can be seen from the normalized electroluminescence spectrum of the device in (a) that the four devices have only one luminescence peak, which is located at 628nm in the red light region, 564nm in the yellow light region, 512nm in the green light region and 475nm in the blue light region, and the color coordinates are (0.68, 0.32), (0.51, 0.48), (0.33, 0.61) and (0.17, 0.38), respectively, achieving excellent red, yellow, green and blue light emission.

[0108] No luminescence peaks of the excited complex and its single component appear in the spectra of the four devices, indicating complete energy transfer from the interface excited complex host to the phosphorescent ultra-thin layer guest, and further illustrating the rationality and feasibility of the device design based on the main structure of "electron donor material layer / electron acceptor material layer / electron donor material layer / electron acceptor material layer" of the present invention.

[0109] In the current efficiency-brightness curve diagram (b), the maximum current efficiencies of the above four monochromatic light devices R, Y, G and B reached 7.4, 50.0, 48.7 and 32.3 cd / A, respectively, which are close to the efficiencies of reported doped phosphorescent devices.

[0110] However, the device structure and preparation process of the multi-interface exciton complex-sensitized phosphorescent ultra-thin layer OLEDs of the present invention are simpler and can reduce the use of expensive phosphorescent materials, proving the feasibility and universal applicability of the multi-interface exciton complex-sensitized phosphorescent ultra-thin layer structure for monochromatic light devices.

[0111] Example 2.

[0112] In order to prove the feasibility of the present invention to achieve white light emission, this example combines blue (FIrpic), yellow (Ir(bt) 2 A (acac)) complementary color phosphorescent ultra-thin layer was introduced into the interface of the exciplex to prepare a blue-yellow dual-color white light device, and the performance of the white light devices with different numbers of interface exciplexes was compared.

[0113] Device W11: ITO / MoO 3 (3nm) / mCP (40nm) / FIrpic (0.35nm) / PO-T2T (3nm) / Ir(bt) 2 (acac) (0.06nm) / mCP (3nm) / FIrpic (0.35nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0114] Device W12: ITO / MoO 3 (3nm) / mCP (40nm) / FIrpic (0.35nm) / PO-T2T (3nm) / Ir(bt) 2 (acac) (0.06nm) / mCP (3nm) / FIrpic (0.35nm) / PO-T2T (3nm) / Ir(bt) 2(acac)(0.06nm) / mCP (3nm) / FIrpic (0.35nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0115] Figure 3 The following are the normalized electroluminescence spectra and current efficiency-brightness curves of devices W11 and W12 at a driving voltage of 5V. It can be seen that both devices have successfully achieved complementary white light emission. Their normalized electroluminescence spectra (a) contain two obvious emission peaks, located in the blue light region and the yellow light region respectively. The emission peak in the blue light region originates from the emission of the FIrpic phosphorescent ultra-thin layer; the emission peak in the yellow light region originates from Ir(bt) 2 (acac) phosphorescent ultrathin layer emission, blue light emitted by FIrpic phosphorescent ultrathin layer and Ir(bt) 2 The yellow light emitted by the (acac) phosphorescent ultrathin layer is recombined to form white light emission.

[0116] At the same time, similar to the monochromatic device, the luminescence peak of the main body of the exciplex does not appear in the spectrum, achieving complete energy transfer from the main body to the guest. Under a driving voltage of 5V, the color coordinates of the two devices are (0.36, 0.44) and (0.36, 0.43), respectively, both located in the white light emission region, proving the feasibility of the present invention to achieve dual-color white light emission.

[0117] It can be clearly seen from the current efficiency-brightness curves of the two devices (b) that increasing the number of interface exciton complexes introduced and sensitizing the phosphorescent ultra-thin layer with more interface exciton complexes can significantly improve the performance of the white light device. For example, the maximum current efficiencies of the two devices mentioned above reached 48.2 and 51.9 cd / A, respectively.

[0118] Example 3.

[0119] In order to prove the universal applicability of the present invention in achieving white light emission, based on the white light device W11 in Example 2, this example introduces blue (FIrpic), yellow (Ir(bt) 2 (acac)) and red (Ir(piq) 2 The blue-yellow-red white light device was prepared by placing a (acac)-colored ultra-thin phosphorescent layer at the interface of the exciplex. At the same time, the arrangement order of the different colored ultra-thin phosphorescent layers embedded in the interface exciplex was changed to study its effect on the device performance.

[0120] Device W21: ITO / MoO 3 (3nm) / mCP (40nm) / Ir(bt) 2(acac) (0.06nm) / PO-T2T(3nm) / FIrpic (0.35nm) / mCP (3nm) / Ir(piq) 2 (acac) (0.04nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0121] Device W22: ITO / MoO 3 (3nm) / mCP (40nm) / Ir(bt) 2 (acac) (0.06nm) / PO-T2T(3nm) / Ir(piq) 2 (acac) (0.04nm) / mCP (3nm) / FIrpic (0.35nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0122] Device W23: ITO / MoO 3 (3nm) / mCP (40nm) / Ir(piq) 2 (acac) (0.04nm) / PO-T2T(3nm) / Ir(bt) 2 (acac) (0.06nm) / mCP (3nm) / FIrpic (0.35nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0123] Figure 4 The normalized electroluminescence spectra and current efficiency-brightness curves of the three devices of this embodiment at a driving voltage of 5V are given. It can be seen from the normalized electroluminescence spectra of (a), (b), and (c) that all three devices achieve good white light emission. Specifically, the normalized electroluminescence spectra of the three-color devices contain three obvious emission peaks, which are located in the blue light region, the yellow light region, and the red light region, respectively, which are attributed to the 0.35nm FIrpic blue phosphorescent ultra-thin layer, the 0.06nm Ir(bt) 2 (acac) Yellow phosphorescent ultra-thin layer and 0.04nm Ir(piq) 2 (acac) red phosphorescent ultra-thin layer emission. The three light colors of phosphorescent ultra-thin layer emission compound to form white light, the color coordinates at 5V are (0.55, 0.38), (0.39, 0.38) and (0.41, 0.41), all located in the white light emission region. The above results prove the feasibility of the present invention to achieve three-color white light emission and the universal applicability of achieving white light emission.

[0124] But at the same time, it can be clearly seen that by changing the embedding order of ultra-thin layers of phosphorescent light of different colors, the spectra of the corresponding three white light devices are significantly different, and device W23 achieves a more balanced white light emission.

[0125] In addition, from the current efficiency-brightness curves (d) of the three three-color white light devices, it can be seen that the embedding order of different color phosphorescent ultra-thin layers affects the efficiency of the device at the same time. Device W22 achieved the highest current efficiency of 22.5cd / A. It is proved that by simply changing the arrangement order of different color phosphorescent ultra-thin layers embedded in the interface exciplex, the spectrum and electroluminescence performance of the white light device can also be adjusted and optimized.

[0126] Example 4.

[0127] Based on the three-color white light device in Example 3, this example further prepared two blue (FIrpic)-green (Ir(ppy) 3 )-yellow(Ir(bt) 2 (acac))-Red(Ir(piq) 2 (acac)) four-color white light device. The main difference between the two white light devices is that the embedding order of the green, yellow and red phosphor ultra-thin layers is exactly opposite.

[0128] Device W31: ITO / MoO 3 (3nm) / mCP (40nm) / FIrpic (0.35nm) / PO-T2T (3nm) / Ir(piq) 2 (acac) (0.06nm) / mCP (3nm) / Ir(bt) 2 (acac) (0.06nm) / PO-T2T (3nm) / Ir(ppy) 3 (0.18nm) / mCP (3nm) / FIrpic (0.35nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0129] Device W32: ITO / MoO 3 (3nm) / mCP (40nm) / FIrpic (0.35nm) / PO-T2T (3nm) / Ir(ppy) 3 (0.18nm) / mCP (3nm) / Ir(bt) 2 (acac) (0.06nm) / PO-T2T (3nm) / Ir(piq) 2(acac) (0.06nm) / mCP (3nm) / FIrpic (0.35nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0130] Figure 5 The normalized electroluminescence spectra and current efficiency-brightness curves of the two four-color white light devices of this embodiment at a driving voltage of 5V are given. It can be seen that both four-color white light devices achieve good white light emission, and the luminescence spectra clearly contain four emission peaks ( Figure 5 a and 5b), which are located in the blue, green, yellow and red light regions, respectively, and are attributed to the 0.35nm FIrpic blue phosphorescent ultra-thin layer, the 0.18nm Ir(ppy) 3 Green phosphorescent ultra-thin layer, 0.06nm Ir(bt) 2 (acac) Yellow phosphorescent ultra-thin layer and 0.06nm Ir(piq) 2 (acac) Emission of red phosphorescent ultra-thin layer. The light emitted by the four phosphorescent ultra-thin layers is combined to form white light emission, and the color coordinates at 5V are (0.43, 0.44) and (0.43, 0.42), respectively, which are located in the white light emission region.

[0131] Although the spectra of the two four-color white light devices achieve wide coverage in the visible light region, with a half-peak width of nearly 200nm and a color rendering index greater than 80, which can meet the needs of indoor lighting, there are also obvious differences in the spectra of the two devices. For example, the yellow light emission intensity in the spectrum of device W31 is stronger, resulting in a better correlated color temperature. The correlated color temperature of device W31 reaches 3481K, which is significantly higher than the 3262K of device W32.

[0132] Furthermore, from the current efficiency-brightness curve ( Figure 5 c) and current density-voltage-brightness curve ( Figure 5 d) It can be seen that device W31 has achieved higher brightness and current efficiency, reaching 11060cd / m 2 and 33.4 cd / A. The feasibility of the present invention in achieving four-color white light emission and the universal applicability of achieving white light emission are demonstrated.

[0133] The above embodiments of the present invention do not describe all the details in detail, nor limit the present invention to the above embodiments. Various changes, modifications, substitutions and variations made by ordinary technicians in this field without departing from the principles and purpose of the present invention should be included in the protection scope of the present invention.

Claims

1. A white light organic light emitting diode based on a phosphorescent ultra-thin layer, comprising an anode, a cathode and a light emitting layer unit, in, The light-emitting layer unit comprises at least two electron donor material layers and the same number of electron acceptor material layers arranged alternately with the electron donor material layers, and an interface exciplex is formed between any two adjacent electron donor material layers and electron acceptor material layers; It also includes a phosphorescent ultra-thin layer embedded between each electron donor material layer and the electron acceptor material layer, and the luminescent colors of the phosphorescent ultra-thin layer are complementary; The triplet energy level of the formed interface exciplex is higher than the triplet energy level of the phosphorescent ultra-thin layer material. Through the direct carrier capture mechanism and the sensitization mechanism of the interface exciplex to the phosphorescent ultra-thin layer, the phosphorescent ultra-thin layer emits light and forms white light emission by compounding. The thickness of the phosphorescent ultra-thin layer is 0.01-1 nm, the thickness of the outermost electron donor material layer and the electron acceptor material layer is 3-100 nm, and the thickness of the electron donor material layer and the electron acceptor material layer between the two is 1-20 nm.

2. The white organic light emitting diode based on the phosphorescent ultra-thin layer according to claim 1, characterized in that The outermost electron donor material layer is located on the anode side, and the outermost electron acceptor material layer is located on the cathode side.

3. The white organic light emitting diode based on the phosphorescent ultra-thin layer according to claim 1, characterized in that The phosphorescent ultra-thin layers are respectively composed of phosphorescent materials that emit blue light and phosphorescent materials that emit yellow light, and the blue light and yellow light emitted by the multiple phosphorescent ultra-thin layers are combined to form white light.

4. The white organic light emitting diode based on the phosphorescent ultra-thin layer according to claim 1, characterized in that The phosphorescent ultra-thin layers are respectively composed of phosphorescent materials emitting red light, phosphorescent materials emitting green light or yellow light, and phosphorescent materials emitting blue light. The red light, green light or yellow light emitted by the multiple phosphorescent ultra-thin layers are combined with the blue light to form white light.

5. The white organic light emitting diode based on the phosphorescent ultra-thin layer according to claim 1, characterized in that The phosphorescent ultra-thin layers are respectively composed of phosphorescent materials emitting red light, yellow light, green light and blue light. The red light, green light, yellow light and blue light emitted by the multiple phosphorescent ultra-thin layers are combined to form white light.

6. The white organic light emitting diode based on the phosphorescent ultra-thin layer according to claim 1, characterized in that It also includes a hole transport layer and an electron transport layer arranged on both sides of the light-emitting layer unit.

7. The white organic light emitting diode based on the phosphorescent ultra-thin layer according to claim 6, characterized in that The hole transport layer material is the same as the electron donor material layer near the anode side, and the electron transport layer material is the same as the electron acceptor material layer near the cathode side.

8. The white organic light emitting diode based on the phosphorescent ultra-thin layer according to claim 1, characterized in that It also includes a hole injection layer located on the inner side of the anode and / or an electron injection layer located on the inner side of the cathode.

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