A stacked organic electroluminescent device and a preparation method and application thereof

Abstract

The application discloses a laminated organic electroluminescent device and a preparation method and application thereof. The composition of the charge generation layer in the laminated organic electroluminescent device comprises an electron transport layer, a doped metal oxide layer and a hole transport layer which are sequentially laminated, the doped metal oxide layer is a low work function metal doped transition metal oxide layer, the work function of the low work function metal in the doped metal oxide layer is less than 3.8 eV, the reducing property of the low work function metal in the doped metal oxide layer is stronger than that of the transition metal ion contained in the transition metal oxide in the doped metal oxide layer, and the doped metal oxide layer is made by vacuum co-evaporation of the low work function metal and the transition metal oxide. The laminated organic electroluminescent device has the advantages of low working voltage, high luminous efficiency, good long-term stability and the like, and is suitable for smart phones, tablet computers, notebook computers, displays, televisions, vehicle-mounted display devices and the like.

Description

Technical Field

[0001] This invention relates to the field of organic electroluminescence technology, specifically to a multilayer organic electroluminescent device, its fabrication method, and its application. Background Technology

[0002] Tandem organic light-emitting diodes (OLEDs) are a special type of OLED device that connects multiple light-emitting units through a charge generation layer (CGL). They achieve higher brightness and longer lifespan at the same current density, representing a crucial direction in current OLED technology development. The charge generation layer is the core component of the OLED, and its performance directly affects the overall efficiency and operating voltage of the device. Metal oxides (e.g., molybdenum trioxide (MoO3), tungsten trioxide (WO3), vanadium pentoxide (V2O5), etc.) have high work functions (MoO3: 6.7eV~6.9eV; WO3: 6.5eV~6.7eV; V2O5: 6.4eV~6.6eV). They can form a good match with the HOMO energy levels of organic materials to constitute the CGL. Under electric field driving, they can effectively generate and separate electron-hole pairs through defect energy levels, injecting corresponding charge carriers into adjacent light-emitting units. These materials are widely used in OLEDs.

[0003] However, traditional metal oxide-based charge generation layers have the following problems: 1) Limited charge generation efficiency: When pure metal oxides are used as charge generation layers, the separation and transport efficiency of internal charges is not high, which leads to the need for higher operating voltages in stacked organic light-emitting devices; 2) Poor interface energy level matching: There is an energy level difference between metal oxides and commonly used hole transport layer materials (e.g., NPB), which affects the effective injection and transport of charges, and ultimately affects the luminous efficiency of stacked organic light-emitting devices; 3) Insufficient stability: Under high current density operating conditions, metal oxide-based charge generation layers are prone to performance degradation, which affects the long-term stability of stacked organic light-emitting devices; 4) Fixed and unadjustable work function: The work function of metal oxides is relatively fixed and it is difficult to adjust flexibly according to the needs of different hole transport layer materials, making it difficult for stacked organic light-emitting devices to achieve high efficiency at low voltages.

[0004] To address the above problems, researchers have taken the following improvement measures, but the actual results are relatively limited: CN104051659 A discloses a stacked organic electroluminescent device and its fabrication method, which improves hole injection and transport capabilities by using a mixture of metal oxide and conductive metal element (one of silver, aluminum, platinum and gold), but the work function of the dopant element is relatively high, the control effect is relatively limited, and the transmittance of the charge generation layer is significantly affected; CN104037344 A discloses a stacked organic electroluminescent device and its fabrication method, which improves hole transport efficiency and suppresses the crystallization of polycrystalline hole transport materials by doping metal oxide with organic transport materials, but does not change the inherent properties of the metal oxide in the charge generation layer.

[0005] Therefore, it is of great significance to develop a multilayer organic electroluminescent device with low operating voltage, high luminous efficiency, and good long-term stability by improving the charge generation layer. Summary of the Invention

[0006] The purpose of this invention is to provide a multilayer organic electroluminescent device, its preparation method, and its application.

[0007] The technical solution adopted in this invention is: A stacked organic electroluminescent device, wherein the charge generation layer comprises an electron transport layer (ETL), a doped metal oxide layer, and a hole transport layer (HTL) stacked sequentially. The doped metal oxide layer is a transition metal oxide layer doped with a low work function metal. The work function of the low work function metal in the doped metal oxide layer is <3.8 eV. The reducing power of the low work function metal in the doped metal oxide layer is stronger than that of the transition metal ions contained in the transition metal oxide in the doped metal oxide layer. The doped metal oxide layer is formed by vacuum co-evaporation of the low work function metal and the transition metal oxide.

[0008] Preferably, the molar ratio of the low work function metal to the transition metal oxide in the doped metal oxide layer is 0.1 to 0.8:1.

[0009] Preferably, the low work function metal in the doped metal oxide layer is at least one of ytterbium (Yb), calcium (Ca), magnesium (Mg), strontium (Sr), barium (Ba), europium (Eu), and samarium (Sm).

[0010] Preferably, the transition metal oxide in the doped metal oxide layer is one of MoO3, WO3, and V2O5.

[0011] Preferably, the thickness of the doped metal oxide layer is 3 nm to 20 nm.

[0012] Preferably, the multilayer organic electroluminescent device comprises a first electrode, a first light-emitting unit, a charge-generating layer, a second light-emitting unit, and a second electrode stacked sequentially.

[0013] Preferably, the first electrode is one of an ITO electrode or an ITO / Ag / ITO electrode.

[0014] Preferably, the first light-emitting unit (1) st The -EML consists of a hole injection layer (HIL), a hole transport layer (HTL), an electron blocking layer (EBL), an emissive layer (EML), and a hole blocking layer (HBL) stacked sequentially.

[0015] Preferably, the second light-emitting unit (2) nd The electron transport layer (EML) consists of an electron blocking layer, a light emitting layer, a hole blocking layer, and an electron transport layer (ETL) stacked sequentially.

[0016] Preferably, the second electrode is one of an Al electrode, an Ag electrode, or a Mg-Ag alloy electrode.

[0017] A method for fabricating a multilayer organic electroluminescent device as described above includes the following steps: preparing each layer using a vacuum evaporation process to obtain the multilayer organic electroluminescent device.

[0018] Application of the stacked organic electroluminescent device as described above in the fabrication of smartphones, tablets, laptops, monitors, televisions, or automotive display devices.

[0019] The principle of this invention: During vacuum co-evaporation of a low work function metal and a transition metal oxide, the low work function metal, due to its stronger reducing power than the transition metal ions contained in the transition metal oxide, preferentially reacts with active oxygen to form the corresponding stable oxide. Simultaneously, it injects electrons into the lattice of the transition metal oxide, accompanied by the generation of oxygen vacancies, and causes the transition metal in the transition metal oxide to transition from a high valence state to a low valence state, enriching the defect energy levels. This systematically reduces the work function of the transition metal oxide and improves charge separation efficiency, without causing defects similar to those found in Li. + The high mobility risk ultimately makes multilayer organic electroluminescent devices have characteristics such as low operating voltage, high luminous efficiency, and good long-term stability.

[0020] The beneficial effects of the present invention are: the multilayer organic electroluminescent device of the present invention has the advantages of low operating voltage, high luminous efficiency and good long-term stability, and is suitable for use in smartphones, tablets, laptops, monitors, televisions, automotive display devices, etc., and its preparation process is simple and the production cost is low, making it suitable for large-scale industrial production and application. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of a stacked organic electroluminescent device.

[0022] Figure 2 The curve showing the current density / luminous intensity-voltage relationship of device A is shown.

[0023] Figure 3 The curve showing the relationship between current efficiency / power efficiency and luminous intensity for device A is shown.

[0024] Figure 4 The curve showing the current density / luminous intensity-voltage relationship of device B is shown.

[0025] Figure 5 The curve showing the relationship between current efficiency / power efficiency and luminous intensity for device B is shown.

[0026] Figure 6 The curve shows the current density / luminous intensity-voltage relationship of device C.

[0027] Figure 7 The curve showing the relationship between current efficiency / power efficiency and luminous intensity for device C is shown.

[0028] Figure 8 The curve showing the current density / luminous intensity-voltage relationship of device D is shown.

[0029] Figure 9 The curve showing the relationship between current efficiency / power efficiency and luminous intensity for device D is shown.

[0030] Figure 10 The curve shows the current density / luminous intensity-voltage relationship of device E.

[0031] Figure 11 The curve showing the relationship between current efficiency / power efficiency and luminous intensity for device E is shown.

[0032] Figure 12 The curve showing the current density / luminous intensity-voltage relationship of device F is shown.

[0033] Figure 13 The curve showing the relationship between current efficiency / power efficiency and luminous intensity for device F is shown.

[0034] Figure 14 The curve showing the current density / luminous intensity-voltage relationship of device G is shown.

[0035] Figure 15 The curve showing the relationship between the current efficiency / power efficiency and the luminous intensity of device G is shown.

[0036] Figure 16 The curve showing the current density / luminous intensity-voltage relationship of device H is shown.

[0037] Figure 17 The curve showing the relationship between current efficiency / power efficiency and luminous intensity for device H is shown.

[0038] Figure 18 The curve showing the current density / luminous intensity-voltage relationship of device I is shown.

[0039] Figure 19 The curve showing the relationship between current efficiency / power efficiency and luminous intensity for device I is shown.

[0040] Figure 20 The curve showing the current density / luminous intensity-voltage relationship of device J is shown.

[0041] Figure 21 The curve showing the relationship between current efficiency / power efficiency and luminous intensity for device J is shown.

[0042] Figure 22 The curve shows the current density / luminous intensity-voltage relationship of device K.

[0043] Figure 23 The curve showing the relationship between current efficiency / power efficiency and luminous intensity for device K is shown. Detailed Implementation

[0044] The present invention will be further explained and described below with reference to specific embodiments.

[0045] Comparative Example 1: A stacked organic electroluminescent device (structural schematic diagram shown) Figure 1 As shown; denoted as device A; a green light stacked device, it is composed of a first electrode, a first light-emitting unit, a charge-generating layer, a second light-emitting unit, and a second electrode stacked sequentially from bottom to top (each layer is prepared using a vacuum evaporation process), the specific structure of which is as follows: First electrode: ITO electrode; First light-emitting unit: NPB:F4-TCNQ (100nm, 4%) / NPB (20nm) / TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%) / Bebq2 (15nm); Charge generation layer: Bphen:Li (10nm, 3%) / MoO3 (10nm) / NPB (15nm); Second luminescent unit: TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%)Bebq2 (15nm) / Bphen:Li (10nm, 3%); Second electrode: Al electrode.

[0046] Example 1: A stacked organic electroluminescent device (structural schematic diagram shown) Figure 1 As shown; denoted as device B; a green light stacked device, it is composed of a first electrode, a first light-emitting unit, a charge-generating layer, a second light-emitting unit, and a second electrode stacked sequentially from bottom to top (each layer is prepared using a vacuum evaporation process), the specific structure of which is as follows: First electrode: ITO electrode; First light-emitting unit: NPB:F4-TCNQ (100nm, 4%) / NPB (20nm) / TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%) / Bebq2 (15nm); Charge generation layer: Bphen:Li (10nm, 3%) / Yb:MoO3 (10nm, 0.4:1) / NPB (75nm); Second luminescent unit: TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%)Bebq2 (15nm) / Bphen:Li (10nm, 3%); Second electrode: Al electrode.

[0047] Example 2: A stacked organic electroluminescent device (structural schematic diagram shown) Figure 1 As shown; denoted as device C; a green light stacked device, it is composed of a first electrode, a first light-emitting unit, a charge-generating layer, a second light-emitting unit, and a second electrode stacked sequentially from bottom to top (each layer is prepared using a vacuum evaporation process), the specific structure of which is as follows: First electrode: ITO electrode; First light-emitting unit: NPB:F4-TCNQ (100nm, 4%) / NPB (20nm) / TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%) / Bebq2 (15nm); Charge generation layer: Bphen:Li (10nm, 3%) / Ca:MoO3 (10nm, 0.4:1) / NPB (75nm); Second luminescent unit: TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%)Bebq2 (15nm) / Bphen:Li (10nm, 3%); Second electrode: Al electrode.

[0048] Example 3: A stacked organic electroluminescent device (structural schematic diagram shown) Figure 1As shown; denoted as device D; a green light stacked device, it is composed of a first electrode, a first light-emitting unit, a charge-generating layer, a second light-emitting unit, and a second electrode stacked sequentially from bottom to top (each layer is prepared using a vacuum evaporation process), the specific structure of which is as follows: First electrode: ITO electrode; First light-emitting unit: NPB:F4-TCNQ (100nm, 4%) / NPB (20nm) / TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%) / Bebq2 (15nm); Charge generation layer: Bphen:Li (10nm, 3%) / Mg:MoO3 (10nm, 0.4:1) / NPB (75nm); Second luminescent unit: TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%)Bebq2 (15nm) / Bphen:Li (10nm, 3%); Second electrode: Al electrode.

[0049] Example 4: A stacked organic electroluminescent device (structural schematic diagram shown) Figure 1 As shown; denoted as device E; a green light stacked device, it is composed of a first electrode, a first light-emitting unit, a charge-generating layer, a second light-emitting unit, and a second electrode stacked sequentially from bottom to top (each layer is prepared using a vacuum evaporation process), the specific structure of which is as follows: First electrode: ITO electrode; First light-emitting unit: NPB:F4-TCNQ (100nm, 4%) / NPB (20nm) / TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%) / Bebq2 (15nm); Charge generation layer: Bphen:Li (10nm, 3%) / Yb:MoO3 (10nm, 0.2:1) / NPB (75nm); Second luminescent unit: TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%)Bebq2 (15nm) / Bphen:Li (10nm, 3%); Second electrode: Al electrode.

[0050] Example 5: A stacked organic electroluminescent device (structural schematic diagram shown) Figure 1 As shown; denoted as device F; a green light stacked device, it is composed of a first electrode, a first light-emitting unit, a charge-generating layer, a second light-emitting unit, and a second electrode stacked sequentially from bottom to top (each layer is prepared using a vacuum evaporation process), the specific structure of which is as follows: First electrode: ITO electrode; First light-emitting unit: NPB:F4-TCNQ (100nm, 4%) / NPB (20nm) / TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%) / Bebq2 (15nm); Charge generation layer: Bphen:Li (10nm, 3%) / Yb:MoO3 (10nm, 0.6:1) / NPB (75nm); Second luminescent unit: TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%)Bebq2 (15nm) / Bphen:Li (10nm, 3%); Second electrode: Al electrode.

[0051] Performance testing: The current density / luminous intensity-voltage relationship curves and the current efficiency / power efficiency-luminous intensity relationship curves of devices A to F are shown below. Figures 2-13 As shown in the table below, the performance comparison data is as follows: Table 1 Performance comparison data of devices A to F

[0052] Depend on Figures 2-13 As shown in Table 1, compared with device A, devices B to F incorporate Yb, Ca, or Mg into the metal oxide. The resulting stacked light-emitting devices exhibit a significant decrease in driving voltage at the same brightness, while also improving power efficiency and increasing device lifespan.

[0053] Comparative Example 2: A single-layer organic electroluminescent device (denoted as device G; green single-layer device) is composed of a first electrode, a light-emitting unit, and a second electrode stacked sequentially from bottom to top (each layer is prepared by vacuum evaporation process), and its specific structure is as follows: First electrode: ITO electrode; Light-emitting units: NPB:F4-TCNQ (100nm, 4%) / NPB (20nm) / TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%) / Bebq2 (15nm) / Bphen:Li (10nm, 3%); Second electrode: Al electrode.

[0054] Comparative Example 3: A single-layer organic electroluminescent device (denoted as device H; red light single-layer device) is composed of a first electrode, a light-emitting unit, and a second electrode stacked sequentially from bottom to top (each layer is prepared by vacuum evaporation process), and its specific structure is as follows: First electrode: ITO electrode; Light-emitting units: NPB:F4-TCNQ (95nm, 4%) / NPB (15nm) / TCTA (5nm) / Bepp2:Ir(piq)3 (30nm, 5%) / Bebq2 (15nm) / Bphen:Li (15nm, 3%); Second electrode: Al electrode.

[0055] Example 6: A stacked organic electroluminescent device (structural schematic diagram shown) Figure 1 As shown; denoted as Device I; a red light stacked device, it is composed of a first electrode, a first light-emitting unit, a charge-generating layer, a second light-emitting unit, and a second electrode stacked sequentially from bottom to top (each layer is prepared using a vacuum evaporation process), the specific structure of which is as follows: First electrode: ITO electrode; First light-emitting unit: NPB:F4-TCNQ (95nm, 4%) / NPB (15nm) / TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%) / Bebq2 (15nm); Charge generation layer: Bphen:Li (15nm, 3%) / Yb:MoO3 (10nm, 0.4:1) / NPB (110nm); Second luminescent unit: TCTA (5nm) / Bepp2:Ir(ppy)3 (30nm, 5%)Bebq2 (15nm) / Bphen:Li (15nm, 3%); Second electrode: Al electrode.

[0056] Comparative Example 4: A single-layer organic electroluminescent device (denoted as device J; blue light single-layer device) is composed of a first electrode, a light-emitting unit, and a second electrode stacked sequentially from bottom to top (each layer is prepared by vacuum evaporation process), and its specific structure is as follows: First electrode: ITO electrode; Light-emitting unit: NPB:F4-TCNQ (55nm, 4%) / NPB (15nm) / TCTA (5nm) / TPBi∶FIrpic (25nm, 5%) / Bepp2:LiQ (25nm, 1:0.7); Second electrode: Al electrode.

[0057] Example 7: A stacked organic electroluminescent device (structural schematic diagram shown) Figure 1As shown; denoted as device K; a blue light-emitting multilayer device, it is composed of a first electrode, a first light-emitting unit, a charge-generating layer, a second light-emitting unit, and a second electrode stacked sequentially from bottom to top (each layer is prepared using a vacuum evaporation process), the specific structure of which is as follows: First electrode: ITO electrode; First light-emitting unit: NPB:F4-TCNQ (55nm, 4%) / NPB (15nm) / TCTA (5nm) / TPBi∶FIrpic (25nm, 5%) / Bepp2:LiQ (25nm, 1:0.7); Charge generation layer: Bphen:Li (10nm, 3%) / Yb:MoO3 (10nm, 0.4:1) / NPB (35nm); Second light-emitting unit: TCTA (5nm) / TPBi∶FIrpic (25nm, 5%) / Bepp2:LiQ (25nm, 1:0.7); Second electrode: Al electrode.

[0058] Performance testing: The current density / luminous intensity-voltage relationship curves and the current efficiency / power efficiency-luminous intensity relationship curves of devices G to K are shown below. Figures 14-23 As shown in the table below, the performance comparison data for devices B and G~K are as follows: Table 2 Performance comparison data of devices B and G~K

[0059] Depend on Figures 4-5 , Figures 14-23 As shown in Table 2, devices B, I, and K are green, red, and blue multilayer light emission devices with two identical light-emitting units, respectively, and all use a Yb:MoO (10nm, 0.4:1) metal oxide-based charge generation layer. When compared with devices G, H, and J (green, red, and blue single-layer light emission devices with a single light-emitting unit, respectively) (e.g., device B compared with device G), the current efficiency and lifetime are significantly improved, and the power efficiency is also increased. This indicates that the doped metal oxide-based charge generation layer in this invention can be applied to multilayer light emission devices of different colors and has universality.

[0060] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A stacked organic electroluminescent device, characterized in that, The charge generation layer comprises an electron transport layer, a doped metal oxide layer, and a hole transport layer stacked sequentially; the doped metal oxide layer is a transition metal oxide layer doped with a low work function metal; the work function of the low work function metal in the doped metal oxide layer is <3.8 eV; the reducing power of the low work function metal in the doped metal oxide layer is stronger than that of the transition metal ions contained in the transition metal oxide in the doped metal oxide layer; the doped metal oxide layer is formed by vacuum co-evaporation of the low work function metal and the transition metal oxide.

2. The stacked organic electroluminescent device according to claim 1, characterized in that: The molar ratio of low work function metal to transition metal oxide in the doped metal oxide layer is 0.1 to 0.8:

1.

3. The stacked organic electroluminescent device according to claim 1, characterized in that: The low work function metal in the doped metal oxide layer is at least one of ytterbium, calcium, magnesium, strontium, barium, europium, and samarium.

4. The stacked organic electroluminescent device according to claim 1, characterized in that: The transition metal oxide in the doped metal oxide layer is one of MoO3, WO3, and V2O5.

5. The stacked organic electroluminescent device according to claim 1, characterized in that: The thickness of the doped metal oxide layer is 3 nm to 20 nm.

6. The stacked organic electroluminescent device according to any one of claims 1 to 5, characterized in that: The stacked organic electroluminescent device comprises a first electrode, a first light-emitting unit, a charge-generating layer, a second light-emitting unit, and a second electrode, which are stacked sequentially.

7. The stacked organic electroluminescent device according to claim 6, characterized in that: The first light-emitting unit comprises a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, and a hole blocking layer stacked sequentially; and / or, the second light-emitting unit comprises an electron blocking layer, a light-emitting layer, a hole blocking layer, and an electron transport layer stacked sequentially.

8. The stacked organic electroluminescent device according to claim 6, characterized in that: The first electrode is one of an ITO electrode or an ITO / Ag / ITO electrode; and / or the second electrode is one of an Al electrode, an Ag electrode, or a Mg-Ag alloy electrode.

9. A method for fabricating a multilayer organic electroluminescent device as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Each layer was prepared using a vacuum evaporation process to obtain a stacked organic electroluminescent device.

10. The application of a multilayer organic electroluminescent device as described in any one of claims 1 to 8 in the fabrication of smartphones, tablets, laptops, displays, televisions, or automotive display devices.

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