White phosphorescent organic light emitting diode with simple structure

Abstract

The present application relates to a white phosphorescent organic light emitting diode with simple structure, which has an organic light emitting unit composed of a pair of electron donor material layer / electron acceptor material layer capable of forming an exciplex at the interface and several light color complementary phosphorescent ultra-thin layers embedded in the interface of the electron donor material layer / electron acceptor material layer and stacked together. Through the sensitization of the interface exciplex host to the phosphorescent ultra-thin layer guest, the complementary light emission of the phosphorescent ultra-thin layer is realized, and the white light emission is formed by combination. The present application utilizes the simple preparation process of the interface exciplex and the phosphorescent ultra-thin layer, effectively simplifies the device structure and the preparation process, and stabilizes the luminescence spectrum of the white light device through the limiting effect of the interface exciplex on the carriers and excitons.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of organic optoelectronic devices, and relates to an organic light-emitting diode, in particular to a white phosphorescent organic light-emitting diode with a simple structure. BACKGROUND

[0002] White organic light-emitting diodes (OLEDs) are a new light-emitting technology that is expected to be widely applied in the field of solid-state lighting, and have been widely and deeply researched and developed in the academic and industrial circles due to their advantages such as no blue hazard, surface light emission, light weight, high efficiency, low power consumption and flexible preparation.

[0003] After more than twenty years of development, white OLEDs have gradually matured in terms of device structure design and working mechanism, and the device performance has also been greatly improved. For example, the device efficiency of the full phosphorescent and thermally activated delayed fluorescent white OLEDs reported in many documents exceeds that of a fluorescent lamp.

[0004] However, for many reasons, white OLED technology has not been widely applied in the lighting market. On the one hand, white OLEDs have not been mass-produced, making the cost of white OLED lighting panels relatively high and not competitive in the market; on the other hand, white OLEDs still have some problems and deficiencies, such as complex device structure and device preparation process in industrialized white OLEDs, high power consumption at actual lighting brightness, and color stability and color quality that need to be further improved.

[0005] Currently, the light-emitting materials used to realize white OLEDs mainly include the first generation of conventional fluorescent light-emitting materials, the second generation of phosphorescent light-emitting materials, and the third generation of thermally activated delayed fluorescent materials (TADF) widely reported in recent years.

[0006] According to statistical rules, 25% of singlet excitons and 75% of triplet excitons are simultaneously generated in the device under electrical excitation. Due to the spin-forbidden effect, only 25% of singlet excitons are used for light emission in the device of the first generation of conventional fluorescent light-emitting materials, making the overall device efficiency low. In the third generation of TADF materials, due to the very small singlet-triplet energy level difference (ΔEST) Δ E ST <0.1eV), triplet excitons can also be easily converted into singlet excitons at room temperature to obtain delayed fluorescent emission, significantly improving the utilization rate of triplet excitons, so that OLEDs based on TADF materials can theoretically achieve nearly 100% exciton utilization.

[0007] However, the requirements for TADF materials in molecular design and synthesis are very demanding, and it is still a major challenge to develop a series of mature high-performance TADF materials that can be used in white OLEDs.

[0008] In contrast, the second generation of organic-metal complex-based phosphorescent light-emitting materials containing heavy metal elements are relatively mature, and there are more high-performance materials to choose from, which have become the first choice for the academic and industrial communities to develop high-efficiency, high-color quality, and low-power white OLEDs.

[0009] In such light-emitting materials, the spin-orbital coupling effect is greatly enhanced, so that the spin prohibition of triplet excitons is weakened, and singlet excitons can easily convert to triplet excitons through intersystem crossing processes, and then be used for radiation emission. Therefore, in OLEDs prepared from such light-emitting materials, 25% of singlet excitons and 75% of triplet excitons can be utilized under electrical excitation, thereby achieving 100% internal quantum efficiency.

[0010] However, phosphorescent light-emitting materials generally have a high concentration of exciton quenching effect. In order to achieve high device efficiency, in phosphorescent OLEDs, the light-emitting layer is usually composed of a non-emitting host material doped with a phosphorescent light-emitting material. Therefore, suitable host materials are crucial to the design of phosphorescent OLEDs and their device performance. This is because under electrical excitation, a suitable host material can prevent the concentration quenching effect of phosphorescent light-emitting materials and avoid energy loss; a suitable host material can also prevent reverse energy transfer from phosphorescent light-emitting materials to host materials due to mismatched energy levels between the host and the guest.

[0011] So far, as host materials for phosphorescent light-emitting materials, they can be mainly summarized into the following three categories: the first category is host materials with electron or hole transport ability and suitable energy level; the second category is host materials with bipolar transport characteristics and suitable energy level; and the third category is exciplex host materials with suitable energy level formed by electron donor materials and electron acceptor materials.

[0012] The use of the first two categories of host materials greatly improves OLEDs, but there are still some problems in the use of these two categories of host materials for device development, such as unbalanced carrier transport, narrow carrier recombination region, and high device turn-on voltage, etc.

[0013] In contrast, the use of the third category of host materials for device preparation can achieve excellent carrier transport balance, wide carrier recombination region, and low turn-on voltage, etc. In particular, exciplexes with TADF characteristics as host materials can effectively improve the exciton utilization rate.

[0014] The phosphorescent OLEDs developed by using the above three kinds of host materials inevitably introduce a doping process, which is not conducive to simplifying the preparation process of the device, and is contrary to the requirement of simple structure and preparation process for realizing the industrialization of white OLEDs.

[0015] The phosphorescent super-thin layer instead of the phosphorescent doping layer can effectively solve the above-mentioned complex doping process problem. It has been proved in some documents that introducing a spacer layer with a certain thickness (less than 7 nm) at the interface of the interface exciplex formed by the donor / acceptor will not affect the formation of the interface exciplex, which provides a new idea for the design of white OLEDs.

[0016] Therefore, the present application combines the phosphorescent super-thin layer and the interface exciplex to design white OLEDs, directly stacks and embeds the complementary phosphorescent super-thin layer into the interface of the donor / acceptor of the interface exciplex, realizes the design and development of high-performance white OLEDs through a simple device structure and preparation process, and promotes the industrialization process of white OLEDs. SUMMARY

[0017] The purpose of the present application is to provide a white phosphorescent organic light-emitting diode with a simple structure, which combines the interface exciplex and the phosphorescent super-thin layer, and realizes the preparation of low-drive high-performance white organic light-emitting diode through a simple device structure and preparation process.

[0018] Specifically, the white phosphorescent organic light-emitting diode with a simple structure according to the present application is at least composed of a cathode, an anode, and an organic light-emitting unit between the anode and the cathode, like a conventional organic light-emitting diode.

[0019] However, the organic light-emitting unit of the white phosphorescent organic light-emitting diode with a simple structure according to the present application is composed of a pair of electron donor material layer / electron acceptor material layer and a plurality of layers of light color complementary phosphorescent super-thin layers.

[0020] The interface exciplex can be formed at the interface of the electron donor material layer / electron acceptor material layer, and the plurality of layers of light color complementary phosphorescent super-thin layers are stacked together and embedded between the interfaces of the electron donor material layer / electron acceptor material layer.

[0021] Meanwhile, in order to ensure that the embedded phosphorescent super-thin layer does not affect the formation of the interface exciplex of the electron donor material layer / electron acceptor material layer, the total thickness of the phosphorescent super-thin layer should be less than 5 nm.

[0022] Furthermore, the electron donor material layer also serves as the hole transport layer of the organic light-emitting diode, and the electron acceptor material layer also serves as the electron transport layer of the organic light-emitting diode, so that the device structure of the organic light-emitting diode is as simple as possible.

[0023] The white phosphorescent organic light-emitting diode of the present application uses an interface exciplex as a host of a phosphorescent ultra-thin layer, and the phosphorescent ultra-thin layer as a guest, and a plurality of phosphorescent ultra-thin layers with complementary colors realize light emission of the phosphorescent ultra-thin layer through a direct carrier trapping mechanism and a sensitization mechanism of the interface exciplex to the phosphorescent ultra-thin layer, and combine to form white light emission.

[0024] Further, in the white phosphorescent organic light-emitting diode of the present application, the total thickness of the phosphorescent ultra-thin layer is preferably 0.01-5 nm, and the thickness of each single-layer phosphorescent ultra-thin layer is 0.01-1 nm.

[0025] In the organic light-emitting unit of the white phosphorescent organic light-emitting diode of the present application, the triplet energy level of the formed interface exciplex host can be higher than the triplet energy level of all the phosphorescent ultra-thin layer guests, to realize complete energy transfer of the interface exciplex to the phosphorescent ultra-thin layer.

[0026] In the organic light-emitting unit of the white phosphorescent organic light-emitting diode of the present application, the triplet energy level of the formed interface exciplex host can also be higher than the triplet energy level of part of the phosphorescent ultra-thin layer guests, to realize incomplete energy transfer of the interface exciplex to the phosphorescent ultra-thin layer.

[0027] Both of the above two modes can realize the sensitization of the interface exciplex host to the phosphorescent ultra-thin layer guest, reduce the quenching of triplet excitons in the phosphorescent ultra-thin layer, and improve the device performance.

[0028] Further, if the formed interface exciplex has TADF characteristics, the non-radiative triplet excitons in the host can be converted into singlet excitons through upconversion, further reducing the quenching of triplet excitons, and further improving the exciton utilization rate of the device. In addition, the conversion of triplet excitons into singlet excitons through upconversion can also enhance the Förster energy transfer from the interface exciplex host to the phosphorescent ultra-thin layer, further improve the energy transfer efficiency from the host to the guest, and be beneficial to improving the electroluminescent efficiency of the device.

[0029] In the white phosphorescent organic light-emitting diode of the present application, the electron donor material as an electron donor material layer generally has strong hole transport performance and a relatively high highest occupied molecular orbital (HOMO) energy level. Specifically, the electron donor material can include but is not limited to materials such as mCP, TCTA, TAPC, m-MTDATA, HAT-CN, etc.

[0030] Likewise, the electron acceptor material as the electron acceptor material layer generally has strong electron transport performance and a relatively low lowest unoccupied molecular orbital (LUMO) energy level. Specifically, the electron acceptor material can include, but is not limited to, PO-T2T, B3PYMPM, B4PYMPM, 3P-T2T, TmPyPB, TPBi, and the like.

[0031] The combinations of the electron donor materials and the electron acceptor materials include, but are not limited to, mCP:PO-T2T, mCP:B3PYMPM, mCP:B4PYMPM, and the like, and are capable of forming an excited complex with TADF characteristics.

[0032] Preferably, the thickness of the electron donor material layer and the electron acceptor material layer in the organic light-emitting unit is 3-100 nm, and the thickness of the two layers can be the same or different.

[0033] In the white phosphorescent organic light-emitting diode, the several layers of light color complementary phosphorescent ultra-thin layers can be composed of at least one layer of blue light emitting phosphorescent material and at least one layer of yellow light emitting phosphorescent material, and the blue light and yellow light emitted by different phosphorescent ultra-thin layers are combined to form two-color complementary white light. For example, the following combinations can be included, but are not limited to: blue-yellow, blue-blue-yellow, blue-yellow-blue, yellow-blue-yellow, blue-yellow-blue-yellow-blue, and the like.

[0034] In the white phosphorescent organic light-emitting diode, the several layers of light color complementary phosphorescent ultra-thin layers can also be composed of at least one layer of red light emitting phosphorescent material, at least one layer of green light emitting phosphorescent material, and at least one layer of blue light emitting phosphorescent material, and the red light, green light, and blue light emitted by different phosphorescent ultra-thin layers are combined to form three-color white light. That is, the number of layers of each color of phosphorescent ultra-thin layer is at least 1, and can be combined with 1 or more layers of phosphorescent ultra-thin layer of other colors to form complementary white light emitting phosphorescent ultra-thin layers.

[0035] Alternatively, the several layers of light color complementary phosphorescent ultra-thin layers can also be composed of at least one layer of red light emitting phosphorescent material, at least one layer of yellow light emitting phosphorescent material, and at least one layer of blue light emitting phosphorescent material, and the red light, yellow light, and blue light emitted by different phosphorescent ultra-thin layers are combined to form three-color white light. That is, the number of layers of each color of phosphorescent ultra-thin layer is at least 1, and can be combined with 1 or more layers of phosphorescent ultra-thin layer of other colors to form complementary white light emitting phosphorescent ultra-thin layers.

[0036] The white phosphorescent organic light emitting diode of the present application, the several layers of the phosphorescent ultra-thin layer with complementary colors can also be composed of at least one layer of red light emitting phosphorescent material, at least one layer of yellow light emitting phosphorescent material, at least one layer of green light emitting phosphorescent material and at least one layer of blue light emitting phosphorescent material, and the red light, green light, yellow light and blue light emitted by the plurality of phosphorescent ultra-thin layers are combined to form four-color white light. Similarly, the number of layers of each color of the phosphorescent ultra-thin layer is at least 1, which can be combined with one or more layers of other colors of the phosphorescent ultra-thin layer to form a complementary white light emitting phosphorescent ultra-thin layer.

[0037] The white phosphorescent organic light emitting diode of the present application, the several layers of the phosphorescent ultra-thin layer with complementary colors can also be composed of at least one layer of red light emitting phosphorescent material, at least one layer of yellow light emitting phosphorescent material, at least one layer of green light emitting phosphorescent material and at least one layer of blue light emitting phosphorescent material, and the red light, green light, yellow light and blue light emitted by the plurality of phosphorescent ultra-thin layers are combined to form four-color white light. Similarly, the number of layers of each color of the phosphorescent ultra-thin layer is at least 1, which can be combined with one or more layers of other colors of the phosphorescent ultra-thin layer to form a complementary white light emitting phosphorescent ultra-thin layer.

[0038] The white phosphorescent organic light emitting diode of the present application, the several layers of the phosphorescent ultra-thin layer with complementary colors can also be composed of at least one layer of red light emitting phosphorescent material, at least one layer of yellow light emitting phosphorescent material, at least one layer of green light emitting phosphorescent material and at least one layer of blue light emitting phosphorescent material, and the red light, green light, yellow light and blue light emitted by the plurality of phosphorescent ultra-thin layers are combined to form four-color white light. Similarly, the number of layers of each color of the phosphorescent ultra-thin layer is at least 1, which can be combined with one or more layers of other colors of the phosphorescent ultra-thin layer to form a complementary white light emitting phosphorescent ultra-thin layer.

[0039] In addition, the white phosphorescent organic light emitting diode can also adjust the combination of the interface exciplex electron donor material layer and the electron acceptor material layer to realize the adjustment of the performance of the white light emitting device.

[0040] The white phosphorescent organic light emitting diode of the present application, the several layers of the phosphorescent ultra-thin layer with complementary colors can also be composed of at least one layer of red light emitting phosphorescent material, at least one layer of yellow light emitting phosphorescent material, at least one layer of green light emitting phosphorescent material and at least one layer of blue light emitting phosphorescent material, and the red light, green light, yellow light and blue light emitted by the plurality of phosphorescent ultra-thin layers are combined to form four-color white light. Similarly, the number of layers of each color of the phosphorescent ultra-thin layer is at least 1, which can be combined with one or more layers of other colors of the phosphorescent ultra-thin layer to form a complementary white light emitting phosphorescent ultra-thin layer.

[0041] Further, the present application can further provide a second hole transport layer outside the electron donor material layer and a second electron transport layer outside the electron acceptor material layer.

[0042] The above-mentioned additional second hole transport layer and second electron transport layer can further balance the injection and transmission of electrons or holes to the light emitting unit region of the whole device, and further improve the color stability and device efficiency of the white light emitting organic light emitting diode of the present application.

[0043] In addition, the present application can further introduce a hole injection layer inside the anode and an electron injection layer inside the cathode of the white phosphorescent organic light emitting diode to further improve the ability of the anode to inject holes and the ability of the cathode to inject electrons.

[0044] The white phosphorescent organic light emitting diode with simple structure has the advantages that the holes and the electrons are injected into the hole transport layer and the electron transport layer from the anode and the cathode through the hole injection layer and the electron injection layer, the holes and the electrons are transmitted to the interface of the electron donor material layer and the electron acceptor material layer from the hole transport layer and the electron transport layer respectively, the blue-yellow double color, the blue-green-red or the blue-yellow-red three color and the blue-green-yellow-red four color phosphorescent emission is formed at the interface, and the white light emission is formed finally by the combination.

[0045] The organic light emitting unit is composed of a pair of interface exciplex and complementary phosphorescent ultrathin layer, the complementary phosphorescent ultrathin layer is introduced into the interface of the electron donor material layer and the electron acceptor material layer of the interface exciplex through a simple direct layering mode, the device does not involve a doping process, and the light emission is realized through the sensitization of the exciplex host to the phosphorescent ultrathin layer guest.

[0046] The white phosphorescent organic light emitting diode with simple structure has the advantages that the electron donor material and the electron acceptor material are used as the hole transport layer and the electron transport layer respectively, the carrier injection barrier is reduced while the device structure is simplified, the carriers and the excitons in the organic light emitting unit are limited at the interface of the electron donor layer and the electron acceptor layer, and the stability of the white light color quality and the device efficiency are improved.

[0047] The white phosphorescent organic light emitting diode device structure and the preparation process are simple, the repeatability is good, and the commercialization popularization of the white light OLEDs is facilitated. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 It is a device structure schematic diagram of the white phosphorescent organic light emitting diode with simple structure.

[0049] Figure 2 It is the normalized electroluminescence spectrum of the double color, the three color and the four color white light organic light emitting diode with the blue / yellow, the blue / green / red and the blue / green / yellow phosphorescent ultrathin layer combination embedded in the interface of the exciplex in Example 1.

[0050] Figure 3 It is the normalized electroluminescence spectrum and the electroluminescence performance curve diagram of the blue-yellow double color white light organic light emitting diode with different phosphorescent ultrathin layer thicknesses in Example 2.

[0051] Figure 4 It is the normalized electroluminescence spectrum and the electroluminescence performance curve diagram of the blue-green-red three color white light organic light emitting diode with different phosphorescent ultrathin layer thicknesses in Example 3.

[0052] Figure 5Normalized electroluminescence spectra of blue-green-yellow-red four-color white organic light-emitting diodes with different color phosphor ultra-thin layer arrangement sequences in Example 4. DETAILED DESCRIPTION

[0053] The specific embodiments of the present application are described in further detail below in conjunction with the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present application, so that those skilled in the art can well understand and utilize the present application, and are not intended to limit the protection scope of the present application.

[0054] The experimental methods, production processes, instruments and equipment involved in the embodiments of the present application are all conventional names in the art, and are very clear and explicit in the relevant application fields. Those skilled in the art can understand the conventional process steps and apply the corresponding equipment according to the conventional conditions or the conditions recommended by the manufacturer.

[0055] The orientation terms such as "upper", "lower", "left", "right", "middle" and the like involved in the embodiments of the present application are only for the convenience of clear description, and are not intended to limit the scope of the present application. Changes or adjustments of the relative relationship without substantial changes in technical content are also considered as the scope of the present application.

[0056] The various raw materials or reagents used in the embodiments of the present application are not limited in terms of origin, and are all conventional products that can be obtained by market purchase. They can also be prepared according to conventional methods well known to those skilled in the art.

[0057] The monochromatic or white light organic light-emitting diode devices involved in the embodiments of the present application 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, which is purchased from Shenzhen Huayu Joint Science and Technology Co., Ltd., and the surface resistance is 15 Ω / sq.

[0058] Except that high-purity aluminum wire is purchased from Beijing Cui Bailing Non-ferrous Metal Technology Development Center Co., Ltd., all other organic and inorganic functional materials are purchased from Shanghai Hanfeng Chemical Technology Co., Ltd., and are not subjected to any purification treatment before use.

[0059] The preparation method of all white light organic light-emitting diode devices involved in the embodiments of the present application is as follows.

[0060] I. Cleaning of ITO glass substrate

[0061] After cleaning the ITO glass substrate surface with detergent powder to remove oil stains, the ITO glass substrate is repeatedly rinsed with tap water until a complete water film is formed. Then the ITO glass substrate is sequentially placed in deionized water and acetone, and each is ultrasonically cleaned for 20 min.

[0062] II. Drying of ITO glass substrate

[0063] The cleaned ITO glass substrate was taken out of the acetone and dried by nitrogen gun, and then put into a constant temperature oven at 80°C for 2h.

[0064] III. Ultraviolet treatment of ITO glass substrate

[0065] Before evaporation, the dried ITO glass substrate was taken out of the oven and treated by ultraviolet lamp for 20min to further remove the organic matter adhered to the ITO glass substrate and improve the work function of the ITO surface.

[0066] IV. Loading of ITO glass substrate

[0067] The ITO glass substrate was taken out of the ultraviolet box, put into the mask loaded with ITO glass substrate, and then introduced into the cavity of the high vacuum coating machine.

[0068] V. Vacuum pumping of the equipment

[0069] The power supply, mechanical pump and molecular pump of the high vacuum coating machine were turned on in sequence to pump the vacuum cavity.

[0070] VI. Thermal evaporation preparation of organic light-emitting diode

[0071] When the vacuum degree in the cavity of the high vacuum coating machine was lower than 5x10 -4 Pa, the heating of the thermal evaporation source loaded with functional materials and light-emitting materials such as hole and electron injection layer materials, hole and electron transport layer materials, etc. in the cavity was started, and various functional layers were sequentially deposited on the ITO glass substrate according to the designed device structure.

[0072] Finally, the mask loaded with ITO glass substrate was rotated to align the mask position of the deposited aluminum cathode with the ITO glass substrate, the thermal evaporation source loaded with aluminum wire was heated, and the aluminum cathode was deposited to finally prepare a complete organic light-emitting diode.

[0073] During the thermal evaporation process, the evaporation rate of the materials and the thickness of the film layer were monitored by a quartz crystal frequency meter connected outside the vacuum cavity. Among them, the evaporation rate of the phosphorescent ultra-thin layer material was 0.06Å / s, the evaporation rate of other organic functional layer materials was 1.00Å / s, and the evaporation rates of inorganic materials MoO3, LiF and aluminum were about 0.3Å / s, 0.1Å / s and 7.0Å / s, respectively.

[0074] The overlapping part of ITO glass and aluminum cathode was used as the effective light-emitting area of the device, and the effective light-emitting area of the device was 3.0mmx3.0mm.

[0075] The performance of the organic light emitting diode in the examples is tested according to the following method.

[0076] The prepared organic light emitting diode is taken out from the vacuum cavity, and the current density, current efficiency and brightness of the device are obtained by using a computer integrated control ST-900M photometer and a Keithley 2400 digital source meter; the electroluminescence spectrum, color coordinates and color rendering index of the device under different voltages are obtained by using a computer integrated control Spectra Scan PR655 spectral radiometer.

[0077] Example 1.

[0078] In this example, the interface exciplex formed by the electron donor material mCP and the electron acceptor material PO-T2T is used as the host, and the light color complementary phosphorescent ultrathin layer is selected as the guest, and a white light device structure of "electron donor material layer / ultrathin phosphorescent light emitting layer / electron acceptor material layer" as shown in Figure 1 is constructed, and a simple structure blue-yellow bicolor, blue-green-red tricolor and blue-green-yellow-red four-color white light organic light emitting diode is prepared, and the specific device structures of the three white light devices are given below.

[0079] Blue-yellow bicolor white light device W10: ITO / MoO3 (3nm) / mCP (40nm) / FIrpic (0.35nm) / Ir(bt)2(acac) (0.01nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0080] Blue-green-red tricolor white light device W20: ITO / MoO3 (3nm) / mCP (40nm) / FIrpic (0.35nm) / Ir(ppy)3 (0.02nm) / Ir(pq)2(acac) (0.01nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0081] Blue-green-yellow-red four-color white light device W30: ITO / MoO3 (3nm) / mCP (40nm) / Ir(ppy)3 (0.02nm) / Ir(bt)2(acac) (0.02nm) / Ir(piq)2(acac) (0.01nm) / FIrpic (0.35nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0082] In each of the above white organic light-emitting diodes, the 3 nm thick MoO3 thin layer is a hole injection layer, the 1 nm thick LiF is an electron injection layer. The 40 nm thick mCP is simultaneously a hole transport layer and an electron donor layer forming an interface exciplex, and the 50 nm thick PO-T2T is simultaneously an electron transport layer and an electron acceptor layer forming an interface exciplex. The Ir(piq)2(acac) thin layer and the Ir(pq)2(acac) thin layer are red phosphorescent ultrathin layers, the Ir(bt)2(acac) thin layer is a yellow phosphorescent ultrathin layer, the Ir(ppy)3 thin layer is a green phosphorescent ultrathin layer, and the FIrpic thin layer is a blue phosphorescent ultrathin layer. ITO is an anode, and the 100 nm thick Al film is a cathode.

[0083] Figure 2 The normalized electroluminescence spectra, color rendering index (CRI), color coordinates (CIE) and correlated color temperature (CCT) of the devices W10-W30 under a driving voltage of 4-6 V are shown respectively.

[0084] Figure 2 In a, the electroluminescence spectrum of the white light device W10 contains two obvious emission peaks, corresponding to the emission of the blue FIrpic and the yellow Ir(bt)2(acac) phosphorescent ultrathin layer respectively, and the white light is formed by the combination. There is no emission from the exciplex and the donor material mCP and the acceptor material PO-T2T forming the exciplex in the electroluminescence spectrum of the device W10, which proves that the device structure of the application can effectively limit the carriers at the interface of the exciplex and completely transfer the energy from the interface exciplex to the phosphorescent ultrathin layer, which makes the two-color white light device W10 also achieve high spectral stability.

[0085] From Figure 2 It can be seen from b that when the blue (FIrpic), green (Ir(ppy)3) and red (Ir(pq)2(acac)) phosphorescent ultrathin layers are embedded into the mCP / PO-T2T exciplex interface, the corresponding device W20 realizes three-color white light emission. In the device W20, the electroluminescence spectrum contains three emission peaks, which are located in the blue, green and red light regions, corresponding to the emission of FIrpic, Ir(ppy)3 and Ir(piq)2(acac), and there is no other impurity peak in the spectrum, and it exhibits high color stability, which proves the feasibility and superiority of the application in constructing a three-color white light device.

[0086] Figure 2In c, when the blue (FIrpic), green (Ir(ppy)3), yellow (Ir(bt)2(acac)) and red (Ir(piq)2(acac)) four-color phosphorescent ultrathin layers are simultaneously embedded into the mCP / PO-T2T exciton complex interface, the corresponding device W30 realizes more ideal white light emission, and the electroluminescent spectrum contains four emission peaks in the blue, green, yellow and red light regions, corresponding to the emission of FIrpic, Ir(ppy)3, Ir(bt)2(acac) and Ir(piq)2(acac). Under the driving voltage of 5V, the CRI of device W30 reaches 90, the CCT is 3004K, and the color quality is extremely high, which belongs to an ideal lighting source. And with the change of driving voltage, the device W30 also shows extremely high spectral stability. The realization of high-performance four-color white light devices further proves the feasibility, universality and superiority of the application in constructing white light devices.

[0087] In addition, the above three white light devices also achieve high power efficiency, which are 27.8 lm W -1 , 40.6 lm W -1 and 21.4 lm W -1 .

[0088] Example 2.

[0089] To prove that changing the thickness of the phosphorescent ultrathin layer can easily realize the adjustment of the spectrum and electroluminescent performance of the white light device, this embodiment changes the thickness of the yellow phosphorescent ultrathin layer (Ir(bt)2(acac)) while keeping the host structure, functional layer materials and thickness of the blue-yellow two-color white light device W10 in Example 1 unchanged, and prepares the following device structure: ITO / MoO3(3nm) / mCP (40nm) / FIrpic (0.35nm) / Ir(bt)2(acac) ( X nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm), wherein X =0.02, 0.03, 0.04, corresponding to devices W11, W12 and W13, respectively.

[0090] Figure 3 a gives the normalized electroluminescent spectrum, CRI, CIE and CCT of devices W11-W13 under the driving voltage of 6V. It can be seen that with the increase of the thickness of the yellow phosphorescent ultrathin layer, the intensity of the blue light peak in the device electroluminescent spectrum gradually weakens, realizing the adjustment from cool white light to warm white light. The color coordinates of the three devices W11, W12 and W13 under the driving voltage of 6V are (0.40, 0.48), (0.42, 0.48) and (0.43, 0.48), respectively.

[0091] Furthermore, the electroluminescence performance curves of the three devices ( Figure 3 (b), (c), and (d) also clearly show that the electroluminescence performance of the device gradually improves with the increase of the thickness of the yellow phosphorescent ultrathin layer. In particular, when the thickness of the yellow phosphorescent ultrathin layer Ir(bt)2(acac) is 0.04 nm, the corresponding device W13 achieves the highest device performance, with its maximum current efficiency, power efficiency, and external quantum efficiency reaching 41.7 cd A. -1 48.5lm W -1 and 14.6%.

[0092] Therefore, the spectral and luminescent properties of the device can be adjusted by simply changing the thickness of the phosphorescent ultrathin layer.

[0093] Example 3.

[0094] To further demonstrate the feasibility of adjusting the spectrum and performance of white light devices by simply changing the thickness of the phosphorescent ultrathin layer, based on the blue-green-red three-color white light device W20 in Example 1 above, the thickness of the green phosphorescent ultrathin layer Ir(ppy)3 was changed to prepare a three-color white light device with the following structure: ITO / MoO3 (3nm) / mCP (40nm) / FIrpic (0.35nm) / Ir(ppy)3 ( Z nm) / Ir(pq)2(acac) (0.01nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm), where, Z =0.01, 0.03 and 0.04, corresponding to devices W21, W22 and W23.

[0095] Figure 4 a) presents the normalized electroluminescence spectra of all three-color white light devices W21, W22, and W23 in this embodiment at a driving voltage of 6V. It can be seen that all three devices achieve excellent white light emission. Specifically, the normalized electroluminescence spectra of the devices contain three distinct emission peaks, located in the blue, green, and red light regions, respectively, and attributed to the 0.35nm FIRPIC blue phosphorescent ultrathin layer, ... Z The emission of light from the 0.01 nm Ir(ppy)3 green phosphorescent ultrathin layer and the 0.01 nm Ir(pq)2(acac) red phosphorescent ultrathin layer, combined with the emission of the three phosphorescent ultrathin layers, forms white light.

[0096] But at the same time, it can be seen that with the increase of the thickness of the green phosphorescent ultrathin layer, the green emission intensity in the electroluminescence spectrum of the corresponding device is obviously enhanced, which leads to the significant difference in the electroluminescence spectrum of the three devices, so that the CIE of the three devices W21, W22 and W23 also exhibits significant difference under the same driving voltage of 6V, which are (0.48, 0.42), (0.42, 0.47) and (0.38, 0.50) respectively.

[0097] In addition, from the electroluminescence performance curves of the three devices Figure 4 b、c and d, it can also be seen that with the increase of the thickness of the green phosphorescent ultrathin layer, the device efficiency shows an increasing trend, and when the thickness of Ir(ppy)3 is 0.04nm, the corresponding device W23 achieves the highest device efficiency, and the maximum current efficiency, power efficiency and external quantum efficiency reach 38.9cd A -1 , 45.3lm W -1 and 14.3% respectively.

[0098] The related results further prove the universal applicability of the adjustment of the spectrum and performance of the white light device by simply changing the thickness of the phosphorescent ultrathin layer.

[0099] Example 4.

[0100] In order to prove that by simply changing the arrangement order of different color phosphorescent ultrathin layers, the adjustment of the spectrum of the white light device can be realized, this embodiment selects a blue-green-yellow-red four-color white light device as the research object, and four four-color white light devices with different arrangement orders of different color phosphorescent ultrathin layers in the following device structure are prepared.

[0101] Device W30: ITO / MoO3(3nm) / mCP(40nm) / FIrpic(0.35nm) / Ir(ppy)3(0.02nm) / Ir(bt)2(acac)(0.02nm) / Ir(piq)2(acac)(0.01nm) / PO-T2T(50nm) / LiF(1nm) / Al(100nm).

[0102] Device W31: ITO / MoO3(3nm) / mCP(40nm) / Ir(ppy)3(0.02nm) / Ir(bt)2(acac)(0.02nm) / Ir(piq)2(acac)(0.01nm) / FIrpic(0.35nm) / PO-T2T(50nm) / LiF(1nm) / Al(100nm).

[0103] Device W32: ITO / MoO3(3nm) / mCP (40nm) / Ir(bt)2(acac) (0.02nm) / Ir(piq)2(acac) (0.01nm) / FIrpic (0.35nm) / Ir(ppy)3 (0.02nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0104] Device W33: ITO / MoO3(3nm) / mCP (40nm) / Ir(piq)2(acac) (0.01nm) / FIrpic (0.35nm) / Ir(ppy)3 (0.02nm) / Ir(bt)2(acac) (0.02nm) / PO-T2T (50nm) / LiF (1nm) / Al (100nm).

[0105] Figure 5 Normalized electroluminescence spectra of the four-color white light devices W30, W31, W32 and W33 of the present example under driving voltage of 4-7V and CRI, CIE and CCT.

[0106] It can be seen that all the normalized electroluminescence spectra of the four-color white light devices contain four obvious emission peaks, respectively located in the blue light region, the green light region, the yellow light region and the red light region. But it can be seen that after simply changing the stacking order of the phosphor super-thin layers of different colors at the exciton complex interface, the emission intensity of different wavebands in the four devices changes obviously, and the spectrum of the device is effectively adjusted.

[0107] Among them, the device W31 realizes the most ideal white light emission, the CRI reaches 90 under the driving voltage of 5V, the CCT is 3004K, and the color quality is extremely high, which belongs to an ideal illumination light source.

[0108] The above results prove the feasibility of the present application for adjusting the spectrum of the white light device by changing the stacking order of the phosphor super-thin layers of different colors at the exciton complex interface.

[0109] The above embodiments of the present application do not describe all the details, nor limit the present application to only the above described embodiments. Various changes, modifications, replacements and variations of the embodiments made by those skilled in the art without departing from the principles and purposes of the present application shall be included in the protection scope of the present application.

[0110] The specific compound names corresponding to the abbreviations of the chemical substances involved in the present application are as follows.

[0111] mCP: 1,3-di-9-carbazolylbenzene.

[0112] TCTA: 4,4',4"-tris(carbazol-9-yl)triphenylamine.

[0113] TAPC: 4,4'-cyclohexylidenebis[N,N-bis(p-tolyl)aniline].

[0114] m-MTDATA: 4,4',4"-Tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine.

[0115] HAT-CN: Dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile.

[0116] PO-T2T: 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine.

[0117] B3PYMPM: 4,6-Bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine.

[0118] B4PYMPM: 4,6-Bis(3,5-di(pyridin-4-yl)phenyl)-2-methylpyrimidine.

[0119] 3P-T2T: 2,4,6-tris(2-(1H-pyrazol-1-yl)phenyl)-1,3,5-triazine.

[0120] TmPyPB: 1,3,5-Tri[(3-pyridyl)-phen-3-yl]benzene.

[0121] TPBi: 2,2',2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H[1]benzimidazole).

[0122] FIrpic: bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III).

[0123] Ir(ppy)3: tris[2-(p-tolyl)pyridine-C2,N)]iridium(III).

[0124] Ir(bt)2(acac): iridium(III) bis(2-phenylbenzothiozolato-N,C20) acetylacetonate.

[0125] Ir(pq)2(acac): bis(l-phenylisoquinoline)(acetylacetonate) iridium(III).

[0126] Ir(piq)2(acac): bis(l-phenyliso-quinoline)(acetylacetonate) iridium(III).

Claims

1. A white phosphorescent organic light emitting diode with simple structure, comprising an anode, a cathode and an organic light emitting unit between the anode and the cathode; The organic light emitting unit comprises a pair of electron donor material layer / electron acceptor material layer forming an interfacial exciplex, and a plurality of light color complementary phosphorescent ultrathin layers embedded between the electron donor material layer / electron acceptor material layer interface and stacked together, the complementary phosphorescent ultrathin layers are introduced into the interface of the electron donor material layer / electron acceptor material layer forming an interfacial exciplex by a simple direct stacking method, the device does not involve a doping process, the total thickness of the phosphorescent ultrathin layers is 0.01-5 nm, and the thickness of each single phosphorescent ultrathin layer is 0.01-1 nm; wherein The electron donor material layer simultaneously serves as a hole transport layer, and the electron acceptor material layer simultaneously serves as an electron transport layer, and the thickness of the electron donor material layer and the electron acceptor material layer is 3-100 nm; The organic light emitting unit uses the interfacial exciplex as a host of the phosphorescent ultrathin layers, and the phosphorescent ultrathin layers as guests, and the plurality of light color complementary phosphorescent ultrathin layers realize the light emission of the phosphorescent ultrathin layers through a direct carrier trapping mechanism and a sensitization mechanism of the interfacial exciplex to the phosphorescent ultrathin layers, and form white light emission by combination.

2. The white phosphorescent organic light emitting diode according to claim 1, characterized in that The triplet energy level of the formed interfacial exciplex host is higher than the triplet energy level of all the phosphorescent ultrathin layer guests or the triplet energy level of part of the phosphorescent ultrathin layer guests.

3. The white phosphorescent organic light emitting diode according to claim 1, characterized in that The phosphorescent ultrathin layers are composed of at least one layer of blue light emitting phosphorescent material and at least one layer of yellow light emitting phosphorescent material, and the blue light and yellow light emitted by different phosphorescent ultrathin layers form two-color complementary white light by combination.

4. The white phosphorescent organic light emitting diode according to claim 1, characterized in that The phosphorescent ultrathin layers are composed of at least one layer of red light emitting phosphorescent material, at least one layer of green light emitting phosphorescent material and at least one layer of blue light emitting phosphorescent material, and the red light, green light and blue light emitted by multiple phosphorescent ultrathin layers form three-color white light by combination.

5. The white phosphorescent organic light emitting diode according to claim 1, characterized in that The phosphorescent ultrathin layers are composed of at least one layer of red light emitting phosphorescent material, at least one layer of yellow light emitting phosphorescent material and at least one layer of blue light emitting phosphorescent material, and the red light, yellow light and blue light emitted by multiple phosphorescent ultrathin layers form three-color white light by combination.

6. The white phosphorescent organic light emitting diode according to claim 1, characterized in that The phosphorescent ultrathin layers are composed of at least one layer of red light emitting phosphorescent material, at least one layer of yellow light emitting phosphorescent material, at least one layer of green light emitting phosphorescent material and at least one layer of blue light emitting phosphorescent material, and the red light, green light, yellow light and blue light emitted by multiple phosphorescent ultrathin layers form four-color white light by combination.

7. The white phosphorescent organic light emitting diode according to claim 1, characterized in that A second hole transport layer and a second electron transport layer are respectively arranged outside the electron donor material layer and the electron acceptor material layer.

8. The white phosphorescent organic light emitting diode according to claim 1, characterized in that A hole injection layer inside the anode and / or an electron injection layer inside the cathode are further included.

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