Light emitting device

Abstract

The present disclosure provides a light-emitting device, belonging to the technical field of optoelectronic manufacturing. The light-emitting device comprises an anode layer, an organic functional layer, a composite cathode layer and an encapsulation layer which are sequentially stacked; the composite cathode layer comprises an electron injection layer, a metal oxide layer and a transparent conductive layer which are sequentially stacked on the organic functional layer, and the electron injection layer is doped with rare earth metal atoms. The present disclosure can improve the injection efficiency of carriers and improve the light-emitting effect of the organic light-emitting diode.

Description

Technical Field

[0001] This disclosure relates to the field of optoelectronic manufacturing technology, and in particular to a light-emitting device. Background Technology

[0002] Organic light-emitting diodes (OLEDs), also known as organic electroluminescent diodes, are a display and lighting technology that uses organic semiconductor materials to emit light under the drive of an electric field. OLEDs have significant advantages such as self-illumination, high contrast, flexibility, fast response speed, and wide viewing angle, and are widely used in display fields such as smartphones, tablets, televisions, and wearable devices.

[0003] In related technologies, organic light-emitting diodes (OLEDs) typically consist of an anode layer, an organic functional layer, a cathode layer, and an encapsulation layer stacked sequentially. When a voltage is applied, electrons and holes are injected from the cathode and anode layers, respectively, and recombine in the organic functional layer to form excitons. These excitons then undergo radiative transitions to emit light. Therefore, the injection efficiency, transport efficiency, and carrier balance of electrons and holes are the core factors determining the photoelectric performance of OLEDs (such as luminous efficiency, brightness, and lifetime), while the water and oxygen barrier properties of the encapsulation layer directly affect the long-term stability of the device.

[0004] In existing technologies, the cathode layer mostly adopts traditional structures such as Yb composite Mg / Ag and Mg:Ag, and the encapsulation layer is mostly a single material structure. This results in problems such as high electron injection barrier, poor interface stability, and weak water and oxygen barrier, leading to insufficient electron injection efficiency and carrier imbalance, which in turn affects the luminous effect and long-term reliability of OLEDs, limiting their further application in the high-end display field. Summary of the Invention

[0005] This disclosure provides a light-emitting device that improves carrier injection efficiency and enhances the light-emitting effect of organic light-emitting diodes. The technical solution is as follows: This disclosure provides a light-emitting device comprising an anode layer, an organic functional layer, and a composite cathode layer stacked sequentially on the organic functional layer; the composite cathode layer comprises an electron injection layer, a metal oxide layer, and a transparent conductive layer stacked sequentially on the organic functional layer, wherein the electron injection layer is doped with rare earth metal atoms.

[0006] In one implementation of this disclosure, the anode layer includes at least one of a Ti layer, an Al layer, and an Ag layer.

[0007] In another implementation of this disclosure, the thickness of the anode layer is 50 nm to 200 nm.

[0008] In another implementation of this disclosure, the rare earth metal atoms include at least one of Yb and Sm, and the mass percentage of rare earth metal atoms doped in the electron-injected layer is 0.5% to 10%.

[0009] In another implementation of this disclosure, the thickness of the electron injection layer is 5 nm to 30 nm.

[0010] In another implementation of this disclosure, the metal oxide layer is a single-layer structure, which is a MoO3 layer, a WO3 layer, or a V2O5 layer. Alternatively, the metal oxide layer may be a multilayer structure, which may include at least two of the following: a MoO3 layer, a WO3 layer, and a V2O5 layer.

[0011] In another implementation of this disclosure, the thickness of the metal oxide layer is 0.5 nm to 3 nm.

[0012] In another implementation of this disclosure, the transparent conductive layer is at least one of indium zinc oxide, indium tin oxide, or aluminum zinc oxide.

[0013] In another implementation of this disclosure, the thickness of the transparent conductive layer is 50 nm to 200 nm.

[0014] In another implementation of this disclosure, the light-emitting device further includes an encapsulation layer located on the surface of the composite cathode layer away from the organic functional layer. The encapsulation layer comprises alternating layers of silicon nitride and aluminum oxide, and the water vapor transmission rate of the encapsulation layer is ≤10%. -6 g / (m 2 ·day).

[0015] The beneficial effects of the technical solutions provided in this disclosure include at least the following: In the light-emitting device provided in this embodiment, rare-earth metal atoms are doped into the electron injection layer of the composite cathode layer. Utilizing the low work function of rare-earth metals, the injection barrier from the cathode to the organic functional layer is significantly reduced, enhancing the electron injection capability and significantly improving the electron injection efficiency.

[0016] Simultaneously, in the composite cathode layer, the rare-earth metal atoms doped in the electron injection layer can undergo interfacial reduction reactions with adjacent metal oxide layers, partially reducing high-valence metal ions in the metal oxide to low-valence states and releasing some oxygen atoms from the metal oxide. These vacancies left behind after the release of oxygen atoms are called oxygen vacancies. Oxygen vacancies can form high-density donor defect states within the material's bandgap, effectively improving the conductivity of the metal oxide layer, constructing an efficient electron transport pathway, accelerating electron migration rate, and further optimizing electron transport efficiency.

[0017] For example, rare earth metal atoms include Yb or Sm, and the metal oxide layer includes a MoO3 layer, a WO3 layer, or a V2O5 layer. During the evaporation process, the metal oxide layer undergoes an in-situ interfacial reaction with the Yb in the electron-injected layer.

[0018] This process involves the transfer of electrons from the metal to the oxide, resulting in the partial reduction of the oxide and the generation of oxygen-vacancy-rich and low-valence metal ions (Mo). 5+ W 5+ V 4+ The non-stoichiometric phase of MoO 3-x WO 3-x V2O 5-x ).

[0019] The specific reaction mechanism is as follows: Metal oxidation: Yb loses electrons to form Yb³. + (Yb→Yb³) + +3e - Oxide reduction: The oxide captures electrons, accompanied by the formation of oxygen vacancies (MoO3 + xe). - +xO² - →MoO 3-x +Oxygen vacancy).

[0020] This reduced phase introduces a high density of defect states in the band gap, improving the material's electrical conductivity. More importantly, it creates a low-barrier, high-mobility electron transport channel between the low-work-function electron-injected layer (ET:Yb) and the high-work-function transparent conductive layer. This channel effectively bridges the energy level mismatch between the two, thus achieving efficient electron injection.

[0021] In addition, the dense metal oxide layer can block the penetration of oxygen and water molecules in the environment, preventing rare earth metals from failing due to oxidation and reducing injection efficiency; its chemical stability is also better than that of pure metal cathodes, significantly improving the reliability of light-emitting devices. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the structure of a light-emitting device provided in an embodiment of this disclosure.

[0024] The markings in the diagram are explained as follows: 10. Anode layer; 20. Organic functional layer; 21. Hole transport layer; 22. Emissive layer; 23. Electron transport layer; 30. Composite cathode layer; 31. Electron injection layer; 32. Metal oxide layer; 33. Transparent conductive layer; 40. Encapsulation layer. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this disclosure clearer, the embodiments of this disclosure will be described in further detail below with reference to the accompanying drawings.

[0026] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” “third,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms “an” or “a” and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “comprising” or “including” and similar terms mean that the elements or objects preceding “comprising” or “including” encompass the elements or objects listed following “comprising” or “including” and their equivalents, and do not exclude other elements or objects. The terms “connected” or “linked” and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The terms “upper,” “lower,” “left,” “right,” “top,” and “bottom,” etc., are used only to indicate relative positional relationships, and these relative positional relationships may change accordingly when the absolute position of the described objects changes.

[0027] Figure 1 This is a schematic diagram of the structure of a light-emitting device provided in an embodiment of this disclosure. Figure 1 As shown, the light-emitting device includes an anode layer 10, an organic functional layer 20, and a composite cathode layer 30 stacked sequentially.

[0028] like Figure 1 As shown, the composite cathode layer 30 includes an electron injection layer 31, a metal oxide layer 32, and a transparent conductive layer 33, which are sequentially stacked on the organic functional layer 20.

[0029] Among them, the electron injection layer 31 is doped with rare earth metal atoms.

[0030] Optionally, the anode layer includes at least one of a Ti layer, an Al layer, and an Ag layer.

[0031] For example, the thickness of the anode layer is 50 nm to 200 nm.

[0032] Optionally, the rare earth metal atoms include at least one of Yb and Sm, and the mass percentage of rare earth metal atoms doped in the electron-injected layer is 0.5% to 10%.

[0033] In this embodiment, rare-earth metal Yb is doped into the electron injection layer. Yb atoms donate electrons to the electron transport matrix (such as Bphen), forming an n-type doping effect that significantly lowers the Fermi level of the composite material. Compared to traditional LiF / Al or Mg:Ag cathode systems (effective work function approximately 3.0–3.7 eV), this Yb-doped system has a lower effective electron injection barrier, making it easier for electrons to be injected into the organic functional layer 20 from the cathode side, thus becoming a highly efficient electron injection source and significantly improving electron injection efficiency.

[0034] When the mass percentage of Yb doping is less than 0.5%, the number of Yb atoms is insufficient, and its extremely low work function of 2.6 eV cannot be effectively utilized to reduce the electron injection barrier, resulting in limited improvement in electron injection efficiency and difficulty in playing a core role. At the same time, the interfacial reaction between a small amount of Yb and the metal oxide layer 32 is weak, the generated oxygen vacancy density is insufficient, and the improvement in conductivity is not significant.

[0035] When the mass percentage concentration of Yb doped is higher than 10%, Yb tends to aggregate in the organic matrix, which can damage the uniformity of the film, leading to local charge accumulation and increased leakage current. Furthermore, excessive Yb can over-reduce the metal oxide layer 32, generating too many defect states, which can exacerbate exciton nonradiative quenching and reduce luminescence efficiency.

[0036] For example, the electron injection layer can be a phenanthroline compound (such as Bphen) or a triazine compound (such as TmPyPB, Tris-PCz). These matrix materials are selected from electron transport materials and have excellent compatibility with rare earth metals (Yb, Sm) and n-type doping efficiency.

[0037] For example, the thickness of the electron-injected layer is 5 nm to 30 nm.

[0038] When the thickness of the electron injection layer is less than 5 nm, the thinner layer may not be able to form a continuous and dense film, resulting in uneven electron injection and even leakage current. When the thickness of the electron injection layer is greater than 30 nm, the excessive thickness of the electron injection layer will increase the series resistance and driving voltage of the device, because electrons need to pass through a longer, low-mobility organic layer to reach the light-emitting layer.

[0039] For example, the thickness of the electron-injected layer is 8 nm.

[0040] Optionally, the metal oxide layer is a single-layer structure.

[0041] For example, the single-layer structure is a MoO3 layer, a WO3 layer, or a V2O5 layer.

[0042] Optionally, the metal oxide layer has a multilayer structure.

[0043] For example, the multilayer structure includes at least two of the following: a MoO3 layer, a WO3 layer, and a V2O5 layer.

[0044] In this embodiment, the MoO3, WO3, and V2O5 layers undergo an in-situ interface reaction with the underlying Yb-doped electron-injected layer 31. Yb acts as a strong reducing agent, removing high-valence metal atoms (such as Mo) from the metal oxide. 6+ W 6+ Partially reduced to a lower valence state (e.g., Mo) 5+ W 5+ At the same time, oxygen atoms are released to form oxygen vacancies.

[0045] This process transforms the metal oxide layer 32 into a reduced phase rich in oxygen vacancies and low-valence metal atoms. Oxygen vacancies, acting as donor states, introduce high-density defect states into the band gap, enhancing the material's electrical conductivity and creating efficient electron transport channels. Furthermore, the synergistic effect of the low-valence metal atoms and Yb further enhances electron mobility, achieving a seamless transition from electron injection to transport.

[0046] For example, the thickness of the metal oxide layer is 0.5 nm to 3 nm.

[0047] By controlling the thickness of the metal oxide within the aforementioned range, it is possible to effectively diffuse Yb atoms from the lower layer to the interface, where they undergo an in-situ reduction reaction with the metal oxide, generating a highly conductive reduced phase rich in oxygen vacancies and low-valence metal atoms. Furthermore, this thickness ensures that the conductive channels generated by the reaction are sufficiently continuous, providing an effective path for electron injection.

[0048] Meanwhile, the thickness of the metal oxide layer within the aforementioned range is sufficient to form a dense physical barrier layer, effectively isolating water and oxygen in the environment and protecting the underlying Yb-doped layer from oxidation, thereby maintaining its low work function characteristics. Simultaneously, the extremely thin thickness of the metal oxide layer also ensures optical transmittance, avoiding any impact on the light output of the device.

[0049] Optionally, the transparent conductive layer is at least one of an indium zinc oxide (IZO) layer, an indium tin oxide (ITO) layer, or an aluminum zinc oxide (AZO) layer.

[0050] For example, the transparent conductive layer may be an ITO layer.

[0051] Optionally, the thickness of the transparent conductive layer is from 50 nm to 200 nm.

[0052] For example, the thickness of the transparent conductive layer is 100 nm.

[0053] Optionally, such as Figure 1 As shown, the light-emitting device also includes an encapsulation layer 40, which is located on the surface of the composite cathode layer 30 away from the organic functional layer 20.

[0054] Encapsulation layer 40 comprises alternating layers of silicon nitride and aluminum oxide, and the water vapor transmission rate of encapsulation layer 40 is ≤10%. -6 g / (m 2 ·day).

[0055] Among them, g / m 2 / day refers to the number of grams of water vapor that permeates per square meter per day.

[0056] Because the organic functional layers of OLEDs are extremely sensitive to water and oxygen, they will rapidly oxidize and degrade upon contact, leading to dark spots, decreased brightness, or even screen failure. An encapsulation layer formed by alternating deposition of silicon nitride and aluminum oxide layers can effectively block water and oxygen.

[0057] The water vapor transmission rate of the encapsulation layer provided in this embodiment is less than or equal to 10. -6 g / m 2 / day. It is evident that the performance in preventing moisture penetration far surpasses that of related light-emitting devices; therefore, this encapsulation layer effectively isolates the device from environmental corrosion.

[0058] Optionally, such as Figure 1 As shown, the organic functional layer 20 includes a hole transport layer 21, a light-emitting layer 22, and an electron transport layer 23 stacked sequentially.

[0059] The hole transport layer plays a crucial role in efficiently transporting holes injected from the anode to the light-emitting layer. It also acts as an electron blocking layer, preventing electrons from the cathode from directly passing through the light-emitting layer to the anode. This confines the electron-hole recombination region within the light-emitting layer, away from the electrode interface, thus preventing exciton quenching by the metal electrodes and improving the device's luminous efficiency.

[0060] For example, the materials used to prepare the hole transport layer include small molecule materials (such as NPB and TCTA).

[0061] For example, the thickness of the hole transport layer is less than or equal to 60 nm.

[0062] If the hole transport layer 21 is too thin, it may result in excessive hole injection or poor blocking effect; if the hole transport layer 21 is too thick, it will increase the device resistance and driving voltage.

[0063] The luminescent layer is the core functional layer of an organic electroluminescent device. Its function is to receive holes from the hole transport layer and electrons from the electron transport layer, allowing them to recombine and form excitons. The excitons then emit visible light through radiation attenuation. Therefore, the characteristics of the luminescent material directly determine the device's emission color, efficiency, and lifespan.

[0064] For example, the materials used to prepare the light-emitting layer can be small molecule light-emitting materials and metal complex light-emitting materials. For example, green light materials are Ir(ppy)3 and Alq3; blue light materials are DPBVBi, tBu-PBD, and DABNA-1; and red light materials are Ir(pq)2(acac).

[0065] For example, the thickness of the light-emitting layer is 10 nm to 100 nm.

[0066] The electron transport layer is responsible for receiving and efficiently transporting electrons from the electron injection layer to the emissive layer. Simultaneously, it needs to possess a certain hole-blocking capability to prevent holes from the anode from directly passing through the emissive layer, effectively confining the recombination process of electrons and holes within the emissive layer. This helps improve the generation efficiency and utilization rate of excitons.

[0067] For example, the materials used to prepare the electron transport layer include Bphen and TPBi.

[0068] For example, the thickness of the electron transport layer is less than or equal to 80 nm.

[0069] An excessively thick electron transport layer increases series resistance, leading to a rise in driving voltage; an excessively thin electron transport layer may fail to effectively block holes or result in excessive electron injection, disrupting carrier balance.

[0070] To verify the technical effectiveness of the composite cathode layer and encapsulation layer of this disclosure, Example 1 and Comparative Example 1 are provided for comparison. The light-emitting device in Example 1 uses the composite cathode layer and encapsulation layer of this disclosure, while Comparative Example 1 uses the cathode structure and encapsulation structure of a conventional light-emitting device.

[0071] Example 1: Anode layer 10: adopts a Ti / Al stacked structure, wherein the thickness of the Ti adhesion layer is 5nm, the thickness of the Al conductive reflective layer is 115nm, and the total thickness is 120nm.

[0072] The anode layer can be prepared by DC magnetron sputtering with a sputtering power of 150W, a working pressure of 0.3Pa, and an argon flow rate of 50sccm, ensuring that the sheet resistance of the anode layer 10 is ≤8Ω / □.

[0073] Organic functional layer 20: Hole transport layer 21 (NPB, 40nm), light-emitting layer 22 (CBP:Ir(ppy)3, doping mass ratio 8%, 30nm), and electron transport layer 23 (TPBi, 35nm) are deposited sequentially by vacuum thermal evaporation; the evaporation rate is controlled at 0.1~0.3nm / s, and the vacuum degree is ≤1×10 -5 Pa.

[0074] Composite cathode layer 30: (1) Electron injection layer 31: TPBi is used as the substrate material, doped with Yb atoms, the mass percentage of Yb doping is 5%, and the layer thickness is 15nm.

[0075] The electron-injected layer was prepared using a dual-source co-evaporation process, monitored in real time by a quartz crystal oscillator. The evaporation rate ratio of TPBi to Yb was calibrated to correspond to the target doping ratio, and the vacuum degree was ≤5×10⁻⁶. -6 Pa.

[0076] (2) Metal oxide layer 32: A single layer of MoO3 with a thickness of 1.5 nm was used. The vacuum thermal evaporation rate was 0.02 nm / s. After deposition, it was annealed in situ at 60 °C for 30 min to improve the density.

[0077] (3) Transparent conductive layer 33: ITO material is selected, with a thickness of 120nm, prepared by radio frequency magnetron sputtering, with a power of 120W, a gas pressure of 0.2Pa, an O2 / Ar mixing ratio of 2%, a sheet resistance of ≤15Ω / □, and a light transmittance of ≥90%.

[0078] Encapsulation layer 40: Composed of alternating silicon nitride and aluminum oxide layers, a total of 4 layers (2 cycles). The single cycle structure is: 100nm silicon nitride layer (plasma-enhanced chemical vapor deposition process, 80℃) / 20nm aluminum oxide layer (atomic layer deposition process, 90℃, TMA / H2O precursor).

[0079] The encapsulation layer 40 has a total thickness of 240 nm, and its water vapor permeability was tested to be 6.2 × 10⁻⁶. -7 g / (m 2 ·day), satisfying ≤10 -6 g / (m 2 Requirements for using day.

[0080] Comparative Example 1: To verify the technical effectiveness of the composite cathode layer and encapsulation structure disclosed herein, this comparative example provides a light-emitting device using a conventional cathode structure, the fabrication process and structural parameters of which are as follows: Anode layer 10': It adopts the same Ti / Al stacked structure as in Example 1 (Ti 5nm / Al 115nm), and the preparation process and parameters are completely identical.

[0081] Organic functional layer 20': Hole transport layer 21' (NPB, 40nm), light-emitting layer 22' (CBP:Ir(ppy)3, doping mass ratio 8%, 30nm), and electron transport layer 23' (TPBi, 35nm) are deposited sequentially by vacuum thermal evaporation; the evaporation rate, vacuum degree and other process parameters of each layer are consistent with those in Example 1.

[0082] Cathode layer 30': A traditional Mg:Ag alloy cathode is used, in which the mass ratio of Mg to Ag is 1:9, and the total thickness is 12nm.

[0083] The cathode layer 30' was prepared using a dual-source co-evaporation process, with the evaporation rate ratio monitored by a quartz crystal oscillator, and the deposition vacuum degree ≤5×10⁻⁶. -6 Pa. This cathode structure is an electron injection scheme commonly used by those skilled in the art.

[0084] Encapsulation layer 40': adopts a single-layer silicon nitride (SiNx) structure with a thickness of 800nm.

[0085] The encapsulation layer 40' was prepared using plasma-enhanced chemical vapor deposition (PECVD) at a deposition temperature of 80°C. The resulting encapsulation layer had a water vapor permeability of approximately 8.5 × 10⁻⁶ as measured by MOCON. -5 g / (m 2 (day), with relatively weak water and oxygen barrier properties.

[0086] Performance comparison test The devices prepared in Example 1 and Comparative Example 1 were characterized for photoelectric performance under exactly the same test conditions (25°C, nitrogen glove box environment, Keithley 2400 source meter with PR-655 spectroradiometer). The key indicators are compared as follows:

[0087] The above is not intended to limit this disclosure in any way. Although this disclosure has been disclosed above through embodiments, it is not intended to limit this disclosure. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the technical solution of this disclosure. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of this disclosure without departing from the content of the technical solution of this disclosure shall still fall within the scope of the technical solution of this disclosure.

Claims

1. A light-emitting device, characterized in that, The light-emitting device includes an anode layer (10), an organic functional layer (20), and a composite cathode layer (30) stacked sequentially. The composite cathode layer (30) includes an electron injection layer (31), a metal oxide layer (32) and a transparent conductive layer (33) sequentially stacked on the organic functional layer (20), wherein the electron injection layer (31) is doped with rare earth metal atoms.

2. The light-emitting device according to claim 1, characterized in that, The anode layer (10) includes at least one of a Ti layer, an Al layer, and an Ag layer.

3. The light-emitting device according to claim 1, characterized in that, The thickness of the anode layer (10) is 50 nm to 200 nm.

4. The light-emitting device according to any one of claims 1 to 3, characterized in that, The rare earth metal atoms include at least one of Yb and Sm, and the mass percentage of rare earth metal atoms doped in the electron injection layer (31) is 0.5% to 10%.

5. The light-emitting device according to claim 4, characterized in that, The thickness of the electron injection layer (31) is 5 nm to 30 nm.

6. The light-emitting device according to any one of claims 1 to 3, characterized in that, The metal oxide layer (32) is a single-layer structure, which is a MoO3 layer, a WO3 layer or a V2O5 layer; or, the metal oxide layer (32) is a multi-layer structure, which includes at least two of the MoO3 layer, the WO3 layer and the V2O5 layer.

7. The light-emitting device according to claim 6, characterized in that, The thickness of the metal oxide layer (32) is 0.5 nm to 3 nm.

8. The light-emitting device according to any one of claims 1 to 3, characterized in that, The transparent conductive layer (33) is at least one of indium zinc oxide layer, indium tin oxide layer or aluminum zinc oxide layer.

9. The light-emitting device according to claim 8, characterized in that, The thickness of the transparent conductive layer (33) is 50 nm to 200 nm.

10. The light-emitting device according to any one of claims 1 to 9, characterized in that, The light-emitting device further includes an encapsulation layer (40), which is located on the surface of the composite cathode layer (30) away from the organic functional layer (20). The encapsulation layer (40) comprises alternating layers of silicon nitride and aluminum oxide, and the water vapor transmission rate of the encapsulation layer (40) is ≤10%. -6 g / (m 2 ·day).

Images