A white light OLED device using exciplexes and excimers and its application

Abstract

The present invention provides a white light OLED device utilizing exciplexes and excimers, comprising: a cathode, an anode, at least two light-emitting layers, and a blocking layer. The at least two light-emitting layers include a blue light-emitting layer and a low-energy light-emitting layer, the blue light-emitting layer containing an exciplex composed of two organic compounds, and the low-energy light-emitting layer containing a mixture of the exciplex and at least one excimer. Furthermore, the blocking layer is positioned between the blue light-emitting layer and the low-energy light-emitting layer. When a DC voltage exceeding its turn-on voltage is applied, the device emits white light composed of blue light from the exciplex and light from low-energy excimer monomers and aggregates. This white light OLED device achieves a high CRI using only a single emitter, eliminating the need for a blue light emitter.

Description

Technical Field

[0001] The invention relates to a novel white light organic electroluminescent device and application thereof. Background Art

[0002] Organic light-emitting diodes (OLEDs), as a next-generation display technology, offer a range of excellent properties, including self-luminescence, no need for a backlight module, high contrast and clarity, wide viewing angles, full curing, compatibility with flexible panels, excellent temperature characteristics, low power consumption, fast response speed, and low manufacturing costs. They have been widely used in industries such as flat panel displays, flexible displays, solid-state lighting, and automotive displays. However, achieving both high efficiency and a high color rendering index (CRI) has been a bottleneck and a hot topic in OLED research.

[0003] The mechanism of OLED luminescence is that, under the influence of an applied electric field, electrons and holes are injected from the positive and negative electrodes, respectively, and then migrate, recombine, and decay within the organic material, generating light. The typical structure of an OLED consists of a cathode layer, an anode layer, and an organic functional layer located between these two layers. The organic functional layer can include one or more of the following: an electron transport layer, a hole transport layer, and a light-emitting layer. The selection of organic functional layer materials is crucial in the preparation and optimization of OLEDs, and their properties are a key factor in determining device performance.

[0004] According to the different luminescence mechanisms, OLED materials can be divided into fluorescent materials, phosphorescent materials, triplet-triplet annihilation (TTA) materials and thermally activated delayed fluorescence (TADF) materials.

[0005] Chelates and organometallic compounds are used as functional materials in a wide variety of applications. In organic-based OLED devices, the use of organometallic complexes that exhibit phosphorescence rather than fluorescence has been increasingly discussed. Due to theoretical spin statistics, the use of organometallic compounds as phosphorescent emitters can quadruple energy and power efficiency. Their key advantages for practical applications include long operating lifetimes, high temperature and stress stability, and low operating and utilization voltages, making them suitable for mobile applications.

[0006] Metal complexes of Group 10 transition metals (Ni, Pd, Pt) are known to exhibit electroluminescence in the blue, red, and green regions. The central metal atom is bonded via two aromatic nitrogen atoms and two carbon atoms, or via two imine nitrogen atoms and two phenolic oxygen atoms, or via two aromatic nitrogen atoms and two basic nitrogen atoms.

[0007] However, there is still demand in the industry for white light OLED devices with high color rendering index (CRI), high efficiency and strong thermal stability. Summary of the Invention

[0008] Therefore, the object of the present invention is to provide a novel white light organic electroluminescent device using an exciplex and an excimer, and a preparation method and application thereof.

[0009] The present invention provides a white light OLED device using exciplexes and excimers, comprising: a cathode, an anode, and an organic functional layer, wherein the organic functional layer comprises at least two light-emitting layers and at least one barrier layer.

[0010] The at least two light-emitting layers include a blue light-emitting layer and a low-energy light-emitting layer, wherein the blue light-emitting layer comprises an exciplex composed of two organic compound main materials, wherein the wavelength of light emitted by the exciplex is between 460 and 500 nm; the low-energy light-emitting layer comprises the exciplex and at least one excimer; wherein the wavelength of light emitted in the monomeric state of the excimer is between 500 and 550 nm, and the wavelength of light emitted in the aggregated state is between 560 and 690 nm; and

[0011] The blocking layer is located between the blue light layer and the low-energy light-emitting layer. The function of the blocking layer is to partially block the passage of charges or carriers, thereby enabling the exciplex to emit blue light.

[0012] According to the white light OLED device provided by the present invention, in a preferred embodiment, the exciplex is a complex of the CDBP compound shown in Formula I and the compound PO-T2T shown in Formula II:

[0013]

[0014] The molar ratio of CDBP:PO-T2T may be 1:0.5-2, preferably 1:0.8-1.5, and most preferably 1:1.

[0015] According to the white light OLED device provided by the present invention, the excimer can be any excimer known in the art that can emit light in the range of 500 to 550 nm in the monomeric state and in the range of 560 to 690 nm in the aggregated state. For example, in a preferred embodiment, the excimer is an organometallic complex represented by Formula III:

[0016]

[0017] Wherein M, CY1, CY2, Rn, Rm, R1, R2, R3, R4, R5 and R6 are defined as follows:

[0018] (a) M represents platinum Pt or palladium Pd;

[0019] (b) CY1 is selected from a pyridine ring, a 5-membered ring, a 6-membered ring, a nitrogen heterocycle or a sulfur heterocycle, or a derivative thereof;

[0020] (c) CY2 is selected from a 5-membered ring, a 6-membered ring, a nitrogen heterocycle or an oxygen bridge, or a derivative thereof;

[0021] (d) Rn and Rm are connected to the CY1 ring or CY2 functional group respectively; wherein Rn and Rm are selected from a linear or branched C 1～8 hydrocarbon group;

[0022] (e) R1, R2, R3, R4, R5 and R6 are each independently selected from hydrogen or C 1～20 Straight-chain or branched-chain alkyl.

[0023] More preferably, the organometallic complex is a compound Tetra-Pt-2 represented by Formula IV, wherein tBu represents tert-butyl:

[0024]

[0025] Wherein, based on the total weight of the exciplex and the excimer in the low-energy light-emitting layer, the content of the excimer may be 10 to 30 wt %, preferably 15 to 25 wt %.

[0026] According to the white light OLED device provided by the present invention, the material of the barrier layer can be any barrier layer material known in the art. For example, in a preferred embodiment, the material of the barrier layer is the MCP described in Formula V:

[0027]

[0028] According to the white light OLED device provided by the present invention, the thickness of the blue light layer can be 2 to 15 nm, preferably 5 to 10 nm. The thickness of the low-energy light-emitting layer can be 2 to 10 nm, preferably 5 to 8 nm. The thickness of the barrier layer can be 0.5 to 3 nm, preferably 1 to 3 nm.

[0029] In a preferred embodiment of the present invention, in addition to the blue light layer, the blocking layer, and the low-energy light-emitting layer, the organic functional layer may further include one or more of a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer. In a preferred embodiment, the hole injection layer is a compound HAT-CN represented by Formula VI. In a preferred embodiment, the hole transport layer is a compound TAPC represented by Formula VII.

[0030]

[0031] In some embodiments, the organic functional layer of the white light OLED device may further contain other organic compounds, metals or metal compounds as dopants.

[0032] According to the white light OLED device provided by the present invention, the positions of the two light-emitting layers (i.e., the blue light-emitting layer and the low-energy light-emitting layer) may be different for different device structures. In a preferred embodiment of the present invention, the blue light-emitting layer is close to the anode side, and the low-energy light-emitting layer is close to the cathode side.

[0033] The present invention also provides a method for preparing the above-mentioned white light OLED device, which comprises forming the blue light layer, the blocking layer and the low-energy light-emitting layer on a substrate by one or more methods selected from the group consisting of vacuum evaporation, spin coating, printing and the like.

[0034] The present invention further provides a light source device, wherein the light source device includes the white light OLED device provided by the present invention.

[0035] The present invention also provides a device comprising the white light OLED device of the present invention, the device comprising a fixed visual display unit, a mobile visual display unit, a lighting unit, a keyboard, clothing, furniture and wallpaper. The device can be a fixed visual display unit, a mobile visual display unit, a lighting unit, a keyboard, clothing, furniture and wallpaper. The mobile visual display unit can be a tablet computer, a mobile phone, a laptop computer, a digital camera, a music player, a visual display unit in a vehicle, and a destination display on or in a bus or train. Preferably, the fixed visual display unit is a visual display unit in an information panel. Preferably, the mobile visual display unit is a visual display unit of a smartphone.

[0036] The white-light OLED device provided by the present invention emits blue light from an exciplex formed from two components, while low-energy light is emitted from the exciplex. When a DC voltage exceeding its turn-on voltage is applied, the device emits white light composed of blue light from the exciplex and low-energy light from monomeric and aggregated excimer states. The white-light OLED device of the present invention achieves a very high CRI (CRI>80) by utilizing only a single luminescent material in combination with a host material, without requiring a blue emitter. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, in which:

[0038] Figure 1 The device with MCP barrier layer thickness of 2nm prepared in Example 1 of the present invention has a 100cd / m 2 , 1000cd / m 2 and 5000cd / m2 Normalized EL spectrum at brightness of ;

[0039] Figure 2 The device with MCP barrier layer thickness of 4nm prepared in Example 1 of the present invention has a power density of 100cd / m 2 , 1000cd / m 2 and 5000cd / m 2 Normalized EL spectrum at brightness of ;

[0040] Figure 3 The device with MCP barrier layer thickness of 6nm prepared in Example 1 of the present invention has a 100cd / m 2 , 1000cd / m 2 and 5000cd / m 2 Normalized EL spectrum at brightness of ;

[0041] Figure 4 The device prepared in comparative example 1 was 100 cd / m 2 , 1000cd / m 2 and 5000cd / m 2 Normalized EL spectrum at brightness of ;

[0042] Figure 5 The device prepared in comparative example 2 was 100 cd / m 2 , 1000cd / m 2 and 5000cd / m 2 Normalized EL spectrum at brightness of . DETAILED DESCRIPTION

[0043] The present invention will be further described in detail below in conjunction with specific embodiments. The examples given are only for illustrating the present invention, not for limiting the scope of the present invention.

[0044] Example 1

[0045] A white OLED device with multiple emitting layers (EML) was fabricated using a SPECTROS vacuum evaporation system from Kurt J. Lesker. The device structure is as follows:

[0046] Substrate ITO / HAT-CN (5nm) / TAPC (50nm) / CDBP (10nm) / CDBP:PO-T2T:20wt%Tetra-Pt-2 (6nm) / MCP (2nm, 4nm, or 6nm) / CDBP:PO-T2T (10nm) / PO-T2T (50nm) / LiF (1.2nm) / Al (100nm)

[0047] Among them, CDBP:PO-T2T=1:1, and the MCP layer is a blocking layer located between the two light-emitting layers.

[0048] Performance Testing

[0049] The performance of the white OLED devices with MCP thickness of 2nm, 4nm and 6nm prepared in this embodiment was tested using Keithley 2400 power supply and Hamamatsu Photonics C9920-12 OLED test system. Figure 1-3 The OLED performance data are listed in Table 1.

[0050] Table 1

[0051]

[0052] Note: CIE = Commission Internationale de l'Eclairage, i.e., International Commission on Illumination; the turn-on voltage refers to the brightness of 1 cd / m 2 Voltage when CRI = Color Rendering Index

[0053] exist Figure 1 In the experiment, when the thickness of MCP was 2 nm, the blue emission of the exciplex CDBP:PO-T2T was greatly enhanced, and low-energy emission was also obvious. This indicates that electrons can be partially blocked by the MCP layer, and some excitons can be generated and captured in the emitting layer of CDBP:PO-T2T, which can then enhance the blue emission of the exciplex CDBP:PO-T2T. As a result, the 1000 cd / m2 in the warm white region of the CIE chromaticity diagram was 2 At the brightness of , the CIE coordinates are (0.44,0.49). Figure 2 When the thickness of MCP increases to 4 nm, the blue light emitted by the exciplex is much stronger, but the low-energy emission is greatly suppressed and the intensity is too low, so the CIE coordinates are (0.29, 0.47) and the brightness is 1000 cd / m 2 , located in the yellow-green area of ​​the CIE chromaticity diagram. Figure 3 This situation is more serious when the thickness of MCP is 6nm. 2 At brightness of , the CIE coordinates are (0.28, 0.46).

[0054] In Table 1, when the thickness of MCP is 2 nm, EQE max The color resolution is 12.2%, the CRI is 74, and the maximum brightness is 11380cd / m 2 However, when the thickness of MCP increases to 4nm or 6nm, the EQEmax is greatly reduced, only 4.8% and 4.2% respectively. As mentioned above, the emission color is not even white. This means that the blocking layer of MCP (4nm or 6nm) is too thick, so that most excitons are prevented from migrating into the low-energy EML of CDBP:PO-T2T:tetra-Pt-2. Therefore, the low-energy emission is greatly suppressed, and the emission of the device is in the yellow-green region in the CIE chromaticity diagram. The hole / electron balance is much worse, and the EQE max Greatly reduced.

[0055] In summary, the 2 nm thick barrier layer helps enhance the blue emission of the exciplex CDBP:PO-T2T, with an EQEmax of 12.2%, a CRI of 74, and a warm white color.

[0056] Comparative Example 1

[0057] The device was prepared in the same manner as in Example 1, except that no barrier layer was provided. The device structure is as follows:

[0058] Substrate: ITO / HAT-CN (5nm) / TAPC (50nm) / CDBP (10nm) / CDBP:PO-T2T:20wt% tetra-Pt-2 (6nm) / CDBP:PO-T2T (10nm) / PO-T2T (50nm) / LiF (1.2nm) / Al (100nm) (Device 1)

[0059] Among them, CDBP:PO-T2T=1:1.

[0060] Comparative Example 2

[0061] The device was prepared in the same manner as in Comparative Example 1, except that two CDBP:PO-T2T blue EMLs were designed to enhance blue light emission. The device structure is as follows:

[0062] Substrate: ITO / HAT-CN (5nm) / TAPC (50nm) / CDBP (10nm) / CDBP:PO-T2T (6nm) / CDBP:PO-T2T:20wt%tetra-Pt-2 (6nm) / CDBP:PO-T2T (10nm) / PO-T2T (50nm) / LiF (1.2nm) / Al (100nm) (Device 2)

[0063] Among them, CDBP:PO-T2T=1:1.

[0064] Performance Testing

[0065] The performance of the OLED devices prepared in Comparative Examples 1 and 2 was tested in the same manner as in Example 1. Figure 4 and 5 The OLED performance data are listed in Table 2.

[0066] Table 2

[0067]

[0068] Note: CIE = Commission Internationale de l'Eclairage, i.e., International Commission on Illumination; the turn-on voltage refers to the brightness of 1 cd / m 2 Voltage when CRI = Color Rendering Index

[0069] For both devices 1 and 2, the blue emission in the 450-500 nm band is too weak, likely due to energy transfer from the blue EML to the CDBP:PO-T2T:20 wt% tetraPt-2 EML. As a result, the low-energy emission in the 500-800 nm range is much stronger than the blue emission. Therefore, the CRI of these two devices is too low (CRI = 64 for device 1; CRI = 62 for device 2). At 1000 cd / m 2 Under brightness, the CIE coordinates of these two devices are (0.43, 0.51) and (0.44, 0.52), respectively, which are located in the yellow area of ​​the CIE chromaticity diagram. In addition, the efficiency of these two devices is very low, with a maximum EQE of max are 8.6% and 8.3%, respectively. In addition, the dual blue EML in device 2 does not enhance the blue emission, as Figure 5 shown.

[0070] Comparing the results of Comparative Examples 1 and 2 with Example 1, it can be seen that the 2 nm thick MCP blocking layer between the two light-emitting layers has an excellent effect of partially blocking charge overflow, thereby retaining some charges in the CDBP:PO-T2T blue light layer to emit blue light. If the thickness is too thick, it will seriously affect the quantum efficiency and device power efficiency of the device.

Claims

1. A white light OLED device using an exciplex and an exciplex, comprising: a cathode, an anode, and an organic functional layer, wherein the organic functional layer includes at least two light-emitting layers and at least one blocking layer, The at least two light-emitting layers include a blue light-emitting layer and a low-energy light-emitting layer, wherein the blue light-emitting layer comprises an exciplex composed of two organic compound host materials, wherein the wavelength of light emitted by the exciplex is between 460-500 nm; the low-energy light-emitting layer comprises the exciplex and at least one excimer; wherein the wavelength of light emitted in the monomeric state of the excimer is between 500-550 nm, and the wavelength of light emitted in the aggregated state is between 560-690 nm; and The blocking layer is located between the blue light layer and the low-energy light-emitting layer, and its function is to partially block the passage of charges or carriers, thereby causing the exciplex to emit blue light. The exciplex includes but is not limited to a complex of the CDBP compound shown in Formula I and the compound PO-T2T shown in Formula II: 。 2. The white light OLED device according to claim 1, wherein: The molar ratio of CDBP:PO-T2T is 1:0.5-2.

3. The white light OLED device according to claim 1, wherein: The molar ratio of CDBP:PO-T2T is 1:0.8-1.

5.

4. The white light OLED device according to claim 1, wherein: The excimer complex is an organometallic complex represented by formula III: Wherein M, CY1, CY2, Rn, Rm, R1, R2, R3, R4, R5 and R6 are defined as follows: (a) M is Pt or Pd; (b) CY1 is selected from a pyridine ring, a 5-membered ring, a 6-membered ring, a nitrogen heterocycle or a sulfur heterocycle, or a derivative thereof; (c) CY2 is selected from a 5-membered ring, a 6-membered ring, a nitrogen heterocycle or an oxygen bridge, or a derivative thereof; (d) Rn and Rm are connected to the CY1 ring or the CY2 functional group respectively; wherein Rn and Rm are selected from a linear or branched C 1-8 hydrocarbon group; (e) R1, R2, R3, R4, R5 and R6 are each independently selected from hydrogen or C 1-20 Straight-chain or branched-chain alkyl.

5. The white light OLED device according to claim 4, wherein: The organometallic complex is a compound Tetra-Pt-2 represented by formula IV, wherein tBu represents a tert-butyl group: 。 6. The white light OLED device according to claim 1, wherein: Based on the total weight of the exciplex and the excimer in the low-energy light-emitting layer, the content of the excimer is 10-30 wt %.

7. The white light OLED device according to claim 6, wherein: Based on the total weight of the exciplex and the excimer in the low-energy light-emitting layer, the content of the excimer is 15-25 wt %.

8. The white light OLED device according to claim 1, wherein: The material of the barrier layer includes but is not limited to the MCP shown in Formula V: 。 9. The white light OLED device according to claim 1, wherein: The thickness of the blocking layer is 0.5-3 nm, the thickness of the blue light layer is 2-15 nm, and the thickness of the low-energy light-emitting layer is 2-10 nm.

10. The white light OLED device according to claim 9, wherein: The thickness of the blocking layer is 1-3 nm, the thickness of the blue light layer is 5-10 nm, and the thickness of the low-energy light-emitting layer is 5-8 nm.

11. A method for preparing the white light OLED device according to any one of claims 1 to 10, comprising forming the blue light layer, the blocking layer and the low-energy light-emitting layer on a substrate by one or more methods selected from the group consisting of vacuum evaporation, spin coating, printing and printing.

12. A light source device, wherein: The light source device comprises the white light OLED device according to any one of claims 1 to 10.

13. A device comprising the white light OLED device according to any one of claims 1 to 10, the device comprising a fixed visual display unit, a mobile visual display unit, a lighting unit, a keyboard, clothing, furniture and wallpaper.

14. The device according to claim 13, wherein The mobile visual display unit is one of a tablet computer, a mobile phone, a laptop computer, a digital camera, a music player, a visual display unit in a vehicle, and a destination display on or in a bus and a train; preferably, the fixed visual display unit is a visual display unit in an information panel; preferably, the mobile visual display unit is a visual display unit of a smartphone.

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