Thin film light emitting device, method of manufacturing the same, and display panel

Abstract

The present disclosure provides a thin film light-emitting device, a preparation method thereof and a display panel, and belongs to the technical field of display. The thin film light-emitting device comprises an anode, a hole transport layer, a light-emitting layer and a cathode which are sequentially stacked; wherein the hole transport layer comprises a hole transport material and an electron trap material; the LUMO energy level of the electron trap material is less than the LUMO energy level of the hole transport material. The thin film light-emitting device can improve the stability of the hole transport layer.

Description

Technical Field

[0001] This disclosure relates to the field of display technology, and more specifically, to a thin-film light-emitting device, a method for preparing the same, and a display panel. Background Technology

[0002] Quantum dot light-emitting diodes (LEDs) are a type of light-emitting display technology that has come very close to commercialization in recent years. The hole transport layer of quantum dot LEDs is generally made of organic semiconductor materials; however, these organic semiconductor materials are easily damaged, which leads to a decrease in the performance of quantum dot LEDs.

[0003] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide a thin-film light-emitting device, its preparation method, and a display panel to improve the stability of the hole transport layer.

[0005] According to one aspect of this disclosure, a thin-film light-emitting device is provided, comprising an anode, a hole transport layer, a light-emitting layer, and a cathode stacked sequentially; wherein the hole transport layer comprises a hole transport material and an electron trapping material; the LUMO energy level of the electron trapping material is lower than the LUMO energy level of the hole transport material.

[0006] According to one embodiment of this disclosure, the LUMO energy level of the electron trap material is not less than the LUMO energy level of the luminescent layer.

[0007] According to one embodiment of this disclosure, the electron trapping material has a mass content of no more than 10% in the hole transport layer.

[0008] According to one embodiment of this disclosure, the electron mobility of the electron trapping material is not greater than 1 × 10⁻⁶. -3 cm 2 V - 1 s -1 .

[0009] According to one embodiment of this disclosure, the electron trapping material captures electrons at a rate faster than the hole transport material captures electrons at a rate faster than the hole transport material captures electrons.

[0010] According to one embodiment of this disclosure, the electron trapping material captures electrons at a rate faster than the rate at which excitons and holes on the hole transport material are quenched.

[0011] According to one embodiment of this disclosure, the electron trapping material captures electrons within 1 nm at a rate faster than 1010. 9 / Second.

[0012] According to one embodiment of this disclosure, the electron trapping material captures electrons within 2 nm at a rate faster than 102. 9 / Second.

[0013] According to one embodiment of this disclosure, the electron trapping material that has trapped electrons extracts electrons at a rate greater than 10-10. 3 / Second.

[0014] According to one embodiment of this disclosure, the HOMO energy level of the electron trapping material is not higher than the HOMO energy level of the hole transport material.

[0015] According to one embodiment of this disclosure, the mass content of electron trapping material in the hole transport layer gradually decreases along the direction from the anode to the light-emitting layer.

[0016] According to one embodiment of this disclosure, the hole transport layer includes a plurality of sequentially stacked sublayers; the mass content of electron trapping material in the sublayer closest to the light-emitting layer is less than the mass content of electron trapping material in the sublayer furthest from the light-emitting layer.

[0017] According to one embodiment of this disclosure, the hole transport material and the electron trap material are cross-linked to form a polymer.

[0018] According to one embodiment of this disclosure, the electron trap material is connected to at least a portion of the hole transport material via chemical bonds or linking groups.

[0019] According to one embodiment of this disclosure, the electron trap material includes one or more of fullerenes, fullerene derivatives, small molecule semiconductor materials, and polymer semiconductor materials.

[0020] According to one embodiment of this disclosure, the electronic trap material is selected from the following materials:

[0021]

[0022] According to one embodiment of this disclosure, the hole transport material is an organic semiconductor material; the light-emitting layer is a quantum dot light-emitting layer or an organic light-emitting layer.

[0023] According to one embodiment of this disclosure, the thin-film light-emitting device is a blue light-emitting thin-film light-emitting device.

[0024] According to another aspect of this disclosure, a method for fabricating a thin-film light-emitting device is provided, for fabricating the aforementioned thin-film light-emitting device; the fabrication method includes fabricating an anode, a hole transport layer, a light-emitting layer, and a cathode;

[0025] The preparation of the hole transport layer includes:

[0026] The hole transport material and the electron trap material are dissolved in a solvent to obtain a precursor solution;

[0027] The hole transport layer is prepared using the precursor liquid through a coating process, screen printing process, or inkjet printing process.

[0028] According to another aspect of this disclosure, a method for fabricating a thin-film light-emitting device is provided, for fabricating the aforementioned thin-film light-emitting device; the fabrication method includes fabricating an anode, a hole transport layer, a light-emitting layer, and a cathode;

[0029] The preparation of the hole transport layer includes:

[0030] The monomers of the hole transport material and the monomers of the electron trap material are polymerized together to form a multifunctional polymer;

[0031] The multifunctional polymer is dissolved in a solvent to obtain a precursor solution;

[0032] The hole transport layer is prepared using the precursor liquid through a coating process, screen printing process, or inkjet printing process.

[0033] According to another aspect of this disclosure, a method for fabricating a thin-film light-emitting device is provided, for fabricating the aforementioned thin-film light-emitting device; the fabrication method includes fabricating an anode, a hole transport layer, a light-emitting layer, and a cathode;

[0034] The preparation of the hole transport layer includes:

[0035] The hole transport layer is formed by co-evaporation of the hole transport material and the electron trap material.

[0036] According to another aspect of this disclosure, a method for fabricating a thin-film light-emitting device is provided, for fabricating the aforementioned thin-film light-emitting device; the fabrication method includes fabricating an anode, a hole transport layer, a light-emitting layer, and a cathode;

[0037] The preparation of the hole transport layer includes:

[0038] Synthesize multifunctional materials, wherein the multifunctional material is a material formed by linking the hole transport material and the electron trap material through chemical bonds or linking groups;

[0039] The multifunctional material and the hole transport material are uniformly mixed to form a vapor-deposited material;

[0040] The hole transport layer is formed using the aforementioned vapor deposition material and a vapor deposition process.

[0041] According to another aspect of this disclosure, a display panel is provided, including the thin-film light-emitting device described above.

[0042] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0043] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0044] Figure 1 This is a schematic diagram of the structure of a thin-film light-emitting device in one embodiment.

[0045] Figure 2 This is a schematic diagram of the structure of a thin-film light-emitting device in one embodiment.

[0046] Figure 3 This is a schematic diagram of the structure of a thin-film light-emitting device in one embodiment.

[0047] Figure 4 This is a schematic diagram of the structure of a thin-film light-emitting device in one embodiment.

[0048] Figure 5 This is a schematic diagram of the structure of a thin-film light-emitting device in one embodiment.

[0049] Figure 6 The luminescence intensity curves of each thin film are shown in the first verification example.

[0050] Figure 7 In the second verification example, the driving voltage-current density curves and driving voltage-brightness curves of each device are shown.

[0051] Figure 8 In the second verification example, the driving voltage-current efficiency curves and driving voltage-external quantum efficiency curves of each device are shown.

[0052] Figure 9 The T90 lifetime curve and voltage variation curve are for the control device.

[0053] Figure 10 The T90 lifetime curve and voltage variation curve of the first verification device are shown. Detailed Implementation

[0054] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore detailed descriptions of them will be omitted. Furthermore, the drawings are merely illustrative of this disclosure and are not necessarily drawn to scale.

[0055] Although relative terms such as "up" and "down" are used in this specification to describe the relative relationship of one component of an icon to another, these terms are used only for convenience, such as according to the orientation of the examples shown in the accompanying drawings. It is understood that if the device of the icon is flipped upside down, the component described as "up" will become the component described as "down." When a structure is "up" of another structure, it may mean that the structure is integrally formed on the other structure, or that the structure is "directly" mounted on the other structure, or that the structure is "indirectly" mounted on the other structure through another structure.

[0056] The terms “a,” “one,” “the,” “the,” and “at least one” are used to indicate the presence of one or more elements / components / etc.; the terms “including” and “having” are used to indicate an open-ended inclusion and to mean that there may be other elements / components / etc. in addition to the listed elements / components / etc.; the terms “first,” “second,” and “third,” etc., are used only as markers and are not a limitation on the number of objects.

[0057] This disclosure provides a thin-film light-emitting device and a display panel using the thin-film light-emitting device. See also Figure 1 The thin-film light-emitting device includes an anode (AE) and a cathode (CE) stacked together, and a light-emitting functional layer (EFU) sandwiched between the anode (AE) and the cathode (CE). See also Figure 1 The light-emitting functional layer (EFU) comprises at least a hole transport layer (HTL) and a light-emitting layer, with the HTL located on the side of the light-emitting layer closest to the anode (AE). The anode and cathode respectively supply electrons and holes to the EFU, enabling the light-emitting layer to emit light. It is understood that the materials and film layers of the EFU vary depending on the type of thin-film light-emitting device.

[0058] For example, see Figure 2When the thin-film light-emitting device is an OLED (Organic Light-Emitting Diode), the light-emitting functional layer (EFU) may include an organic light-emitting layer (EML) as the light-emitting layer, and may include one or more of the following: a hole injection layer, a hole transport layer (HTL), an electron blocking layer (EBL), an electron transport layer (ETL), and an electron injection layer (EIL), and at least includes a hole transport layer (HTL). Furthermore, the organic light-emitting layer (EML) may include a host material and a guest material, wherein the guest material may be a fluorescent dopant or a phosphorescent dopant, and particularly may be a thermally activated delayed fluorescence material. See also... Figure 4 When the OLED adopts a stacked structure, a charge generation layer CGL can also be set in the light-emitting functional layer EFU.

[0059] For another example, see Figure 8 When the thin-film light-emitting device is a QLED (quantum dot light-emitting diode), the light-emitting functional layer (EFU) may include a quantum dot light-emitting layer (QDL) as the light-emitting layer, and may include one or more of the following: a hole injection layer, an electron transport layer (ETL), an electron blocking layer (EBL), a hole blocking layer (HBL), an electron transport layer (ETL), and an electron injection layer (EIL), and at least includes a hole transport layer (HTL). The quantum dot light-emitting layer may have quantum dots. Furthermore, the quantum dots can be interconnected through surface modification groups. See also... Figure 5 When the QLED adopts a stacked structure, a charge generation layer CGL can also be set in the light-emitting functional layer EFU.

[0060] In this disclosure, see Figures 2-5 The light-emitting functional layer (EFU) can include a single light-emitting stacked structure (ELS) or multiple layers of light-emitting stacked structures (ELS). When the EFU includes multiple layers of light-emitting stacked structures (ELS), a charge-generating layer (CGL) can be disposed between adjacent layers of light-emitting stacked structures (ELS). Each layer of light-emitting stacked structure (ELS) has one or more light-emitting layers, which can be either organic light-emitting layers or quantum dot light-emitting layers.

[0061] exist Figure 2 and Figure 3 In the example, the light-emitting functional layer (EFU) has a single layer of light-emitting stacked structure (ELS). See also Figure 2 and Figure 3The thin-film light-emitting device includes an anode (AE), a light-emitting stacked structure (ELS), and a cathode (CE) stacked sequentially. The ELS includes a hole modulation section, a light-emitting layer (e.g., an organic light-emitting layer (EML) or a quantum dot light-emitting layer (QDL), and an electron modulation section stacked sequentially. The hole modulation section is located on the side of the light-emitting layer closer to the anode, and the electron modulation section is located on the side of the light-emitting layer closer to the cathode. The anode is used to inject holes into the light-emitting layer through the hole modulation section, and the cathode is used to inject electrons into the light-emitting layer through the electron modulation section. The hole modulation section and the electron modulation section are used to adjust the injection efficiency and injection rate of holes and electrons injected into the light-emitting layer, and to adjust the energy levels of the injected electrons and holes, respectively, to improve the balance between hole and electron injection, thereby improving the performance of the light-emitting functional layer (EFU), such as improving the luminous efficiency of the thin-film light-emitting device, increasing the device lifetime of the thin-film light-emitting device, and reducing the power supply voltage of the thin-film light-emitting device, or one or more of these improvements.

[0062] The hole regulation section may include one or more of the following films: a hole injection layer, a hole transport layer (HTL), and an electron blocking layer (EBL), and at least includes a hole transport layer (HTL). The hole injection layer, hole transport layer (HTL), and electron blocking layer (EBL) are stacked sequentially from the anode to the light-emitting layer. It is understood that in some examples, one or more of the following films may be configured as a multilayer structure; for example, the hole transport layer (HTL) may include a first type of hole transport layer and a second type of hole transport layer stacked together.

[0063] The electronic conditioning unit may include one or more films such as an electron injection layer (EIL), an electron transport layer (ETL), and a hole blocking layer (HBL), wherein the electron injection layer (EIL), the electron transport layer (ETL), and the hole blocking layer (HBL) are stacked sequentially along the direction from the cathode to the light-emitting layer. It is understood that in some examples, one or more of the electron injection layer (EIL), the electron transport layer (ETL), and the hole blocking layer (HBL) may be configured as a multilayer stacked structure; for example, the electron transport layer (ETL) may include a first type of electron transport layer and a second type of electron transport layer stacked together.

[0064] exist Figure 4 and Figure 5 In the example, the light-emitting functional layer (EFU) has a multi-layered light-emitting stack structure (ELS). Figure 4 and Figure 5 The example illustrates a two-layer light-emitting stacked structure (ELS). See also... Figure 4 and Figure 5The thin-film light-emitting device includes an anode, a multi-layered light-emitting stacked structure (ELS), and a cathode, all stacked sequentially. Each layer of the ELS includes a hole modulation section, a light-emitting layer (e.g., an organic light-emitting layer or a quantum dot light-emitting layer), and an electron modulation section, all stacked sequentially. The hole modulation section is located on the side of the light-emitting layer closest to the anode, and the electron modulation section is located on the side of the light-emitting layer closest to the cathode.

[0065] Optionally, the light-emitting functional layer (EFU) may further include a charge generation layer (CGL) located between two adjacent light-emitting stacked structures (ELS) to improve the efficiency of injecting electrons and holes into the two adjacent ELS. For example, the charge generation layer (CGL) includes an N-type charge generation layer (NCGL) and a P-type charge generation layer (PCGL) stacked between two adjacent ELS. The N-type charge generation layer (NCGL) is adjacent to the electron conditioning section of one of the ELS and is used to inject electrons into that ELS; the P-type charge generation layer (PCGL) is adjacent to the hole conditioning section of the other ELS and is used to inject holes into that ELS. In other words, the P-type charge generation layer (PCGL) is located on the side of the N-type charge generation layer (NCGL) away from the anode. Of course, it is understood that in other examples, the charge generation layer (CGL) may also include other structures.

[0066] It is understood that in some other embodiments of this disclosure, the electronic conditioning section of the light-emitting stacked structure ELS may be omitted, or it may have other structures besides the electron injection layer EIL, the electron transport layer ETL, and the hole blocking layer HBL.

[0067] It is understandable that when multiple light-emitting layers are set in the light-emitting stack structure ELS, the colors of the multiple light-emitting layers can be the same or different, and the types of the multiple light-emitting layers can be the same or different.

[0068] It is understandable that any light-emitting stacked ELS can include a light-emitting layer (e.g., a quantum dot light-emitting layer or an organic light-emitting layer), and one or more of the following: a hole injection layer, a hole transport layer (HTL), an electron blocking layer (EBL), an electron transport layer (ETL), and an electron injection layer (EIL), or other layers can be added as needed. Of course, one or more of the following can also be omitted from the light-emitting stacked ELS: the hole injection layer, the electron blocking layer (EBL), the electron transport layer (ETL), and the electron injection layer (EIL). For two light-emitting stacked ELS structures of the same thin-film light-emitting device, the layer structures of the two ELS structures can be the same or different.

[0069] The hole transport material in the hole transport layer is an organic semiconductor material, such as a small organic molecule semiconductor or a polymer semiconductor. Damage to the hole transport material leads to a decrease in device performance. Electrons leaking from the emissive layer into the hole transport layer are one of the key factors in the damage to the hole transport material. After leaking from the emissive layer to the hole transport layer, electrons can damage the hole transport material through various pathways. For example, hot electrons in an excited state directly damage the hole transport material, or electrons are captured by holes to form excitons, which then damage the hole transport material through a thermal energy state generated by a nonlinear quenching process.

[0070] In this embodiment, an electron trapping material is introduced into the hole transport layer. The LUMO level of this electron trapping material is lower than that of the hole transport material. Therefore, electrons leaking into the hole transport layer (which may be referred to herein as leak electrons) can be captured by the electron trapping material, for example, by directly capturing the leak electrons or by capturing electrons from the hole transport material incorporating the leak electrons. In this way, leak electrons entering the hole transport layer from the emitting layer can be at least partially captured by the electron trapping material, avoiding damage to the hole transport material caused by these leak electrons.

[0071] In one embodiment of this disclosure, the thin-film light-emitting device is a blue thin-film light-emitting device. Compared to red and green thin-film light-emitting devices, the hole transport layer of a blue thin-film light-emitting device is more easily damaged; therefore, introducing an electron trapping material into the hole transport layer of the blue thin-film light-emitting device to improve its lifespan can more effectively mitigate the limitation imposed by the blue thin-film light-emitting device on the lifespan of the display panel or light-emitting panel.

[0072] In one embodiment of this disclosure, the thin-film light-emitting device is a QLED, meaning the light-emitting layer is a quantum dot light-emitting layer. In this embodiment, the electron transport layer can be made of an inorganic semiconductor material, such as zinc oxide or magnesium oxide; the hole transport material is an organic semiconductor material. This makes the hole transport layer the most easily damaged layer in the QLED, thus limiting the device's lifetime. In this embodiment, by adding an electron trapping material to the hole transport layer to improve its stability, the lifetime of the QLED can be improved.

[0073] In one embodiment of this disclosure, the LUMO energy level of the electron trapping material is not lower than the LUMO energy level of the emitting layer. This avoids the formation of a significant electron leakage channel due to an excessively low LUMO energy level in the electron trapping material. Of course, in other embodiments of this disclosure, the LUMO energy level of the electron trapping material can also be lower than the LUMO energy level of the emitting layer, but it should not be excessively lower; for example, the LUMO energy level of the electron trapping material should not be 1.5 eV lower than the LUMO energy level of the emitting layer.

[0074] In one embodiment of this disclosure, the electron trapping material has a mass content of no more than 10% in the hole transport layer. This avoids the formation of significant leakage paths due to excessive electron trapping material content in the hole transport layer. Further, the mass content of the electron trapping material in the hole transport layer is no more than 5%, for example, 1%, 2%, 3%, 4%, or 5%.

[0075] In one embodiment of this disclosure, the electron mobility of the electron trap material is not greater than 1×10⁻⁶. - 3 cm 2 V -1 s -1 In this way, significant leakage paths can be avoided in the electron trap material within the hole transport layer.

[0076] In one embodiment of this disclosure, the mass content of electron trapping material in the hole transport layer gradually decreases along the direction from the anode to the light-emitting layer. This results in less electron trapping material near the light-emitting layer, particularly reducing the electron trapping material at the interface between the hole transport layer and the light-emitting layer, thereby reducing leakage current from the light-emitting layer to the hole transport layer through the electron trapping material.

[0077] In another embodiment of this disclosure, the hole transport layer comprises a plurality of sequentially stacked sublayers; the mass content of electron trapping material in the sublayer closest to the light-emitting layer is less than the mass content of electron trapping material in the sublayer furthest from the light-emitting layer. This reduces the amount of electron trapping material near the light-emitting layer, particularly at the interface between the hole transport layer and the light-emitting layer, thereby reducing leakage current from the light-emitting layer to the hole transport layer through the electron trapping material.

[0078] In one example, the hole transport layer may include a first sublayer and a second sublayer stacked sequentially along the direction from the anode to the light-emitting layer. The mass content of the electron trapping material in the second sublayer is lower than the mass content of the electron trapping material in the first sublayer. For example, the mass content of the electron trapping material in the second sublayer is no more than half the mass content of the electron trapping material in the first sublayer, such as 10%, 20%, 30%, 40%, or 50% of the mass content of the electron trapping material in the first sublayer.

[0079] Of course, in other embodiments of this disclosure, other means may be used to reduce the mass content of the electron trap material at the interface between the hole transport layer and the light-emitting layer, so as to reduce the electron leakage from the light-emitting layer to the hole transport layer.

[0080] Of course, in other embodiments of this disclosure, other means can be used to configure the hole transport layer to reduce electron leakage channels that may be generated by the electron trapping material. For example, the electron trapping materials can be designed to be discontinuous to avoid the formation of continuous electron leakage channels.

[0081] In one embodiment of this disclosure, the electron trapping material traps electrons at a rate faster than the hole transport material traps electrons at a rate faster. This allows the electron trapping material to trap electrons more quickly and efficiently, reducing the proportion of excitons formed by the recombination of leaked electrons with holes in the hole transport material, and thus more effectively minimizing the damage caused by leaked electrons to the hole transport material.

[0082] In one embodiment of this disclosure, the electron trapping material captures electrons at a rate faster than the rate at which excitons and holes quench each other on the hole transport material. When a hole in the hole transport material captures a leaking electron to form an exciton, this exciton can quench with other holes, releasing / transferring energy, which can lead to the risk of damage to the hole transport material. In this embodiment, the electron trapping material captures electrons at a rate greater than the rate at which excitons and holes quench each other on the hole transport material. This increases the probability of the hole transport material, which has captured a leaking electron, transferring electrons to the electron trapping material, thereby reducing the risk of exciton quenching on the hole transport material damaging it.

[0083] In one example, the electron trapping material traps electrons at a rate faster than the hole transport material traps electrons at a rate faster than the excitons on the hole transport material quench holes.

[0084] In one embodiment of this disclosure, the electron trapping material captures electrons within 1 nm at a rate faster than 10-1. 9 / second. This allows the electron trapping material to efficiently capture leaked electrons, providing effective protection for hole transport materials. Furthermore, the electron trapping material captures electrons within 2nm at a rate faster than 10-1. 9 / second. This further enhances the ability of electron trap materials to capture leaky electrons, thus further strengthening the protective effect against hole transport materials.

[0085] In this embodiment of the disclosure, the electron trapping material traps electrons within 1 nm at a rate faster than 10n. 9 / second refers to the rate at which leakage electrons are captured by the electron trapping material when they enter a 1nm radius around the material, exceeding 10-10. 9 / second. Electron trapping materials trap electrons within 2nm at a rate faster than 10-10. 9 / second refers to the rate at which leakage electrons are captured by the electron trapping material when they enter a 2nm radius around the material, exceeding 10-10. 9 / Second.

[0086] In one embodiment of this disclosure, the electron-trapping material that has trapped electrons extracts electrons at a rate greater than 10-10. 3 / second. This ensures that the electron trapping material can quickly export the leaked electrons after capturing them, for example, by rapidly recombinating the captured electrons with holes in the hole transport material or the electron trapping material itself, thereby allowing the electron trapping material to regain its ability to trap electrons. Because the electron trapping material has a low LUMO energy level, it is less likely to damage the hole transport layer when exporting electrons.

[0087] In one example, the electron trapping material traps electrons at a rate faster than the hole transport material traps electrons at a rate faster than the rate at which excitons and holes quench each other on the hole transport material; the electron trapping material with trapped electrons extracts electrons at a rate faster than 10. 3 / second. In this way, the electron trapping material can quickly trap electrons to protect the hole transport material and can quickly and safely export electrons, which enables the electron trapping material to provide long-lasting protection for the hole transport layer.

[0088] In one embodiment of this disclosure, the HOMO energy level of the electron trapping material is not higher than the HOMO energy level of the hole transport material. Thus, the electron trapping material in the hole transport layer will not generate significant hole traps, avoiding any impact on the hole transport performance of the hole transport layer. Of course, in other embodiments of this disclosure, the HOMO energy level of the electron trapping material can also be appropriately higher than the HOMO energy level of the hole transport material, preferably by 0.1 eV, 0.2 eV, or 0.3 eV higher.

[0089] In one embodiment of this disclosure, the hole transport material and the electron trapping material are two independent materials in the hole transport layer, meaning they are not connected by strong chemical bonds such as covalent bonds. The electron trapping material is uniformly dispersed in the hole transport layer. In one example, a solution containing both the hole transport material and the electron trapping material can be used as a raw material, and the hole transport layer can be formed through solution processes such as coating, spin coating, printing, or inkjet printing. In another example, the hole transport material and the electron trapping material can be co-deposited to form the hole transport layer, and the deposition rate of the hole transport material and the electron trapping material determines the content of the electron trapping material in the hole transport layer.

[0090] In one example, the hole transport layer can be prepared using the following method:

[0091] The hole transport material and the electron trap material are dissolved in a solvent to obtain a precursor solution;

[0092] The hole transport layer is prepared using the precursor liquid through a coating process, screen printing process, or inkjet printing process.

[0093] In this example, the hole transport material, electron trapping material, and solvent are selected so that the hole transport material and electron trapping material can be uniformly and non-aggregated in the solution, which is conducive to the formation of a film layer with uniform thickness (e.g., a hole transport layer).

[0094] In another example, the hole transport layer can be prepared using the following method:

[0095] The hole transport layer is formed by co-evaporation of the hole transport material and the electron trap material.

[0096] For example, hole transport materials and electron trapping materials can be placed in evaporation tank 1 and evaporation tank 2, respectively. The evaporation rate of the hole transport material is controlled at 0.1 Å to 10 nm / min, and the evaporation rate of the electron trapping material is controlled at 0.1 Å to 10 nm / min. Thus, the ratio of the evaporation rates of the hole transport material and the electron trapping material can be controlled between 1:1 and 1000:1 according to different doping designs. In this example, the melting point of the electron trapping material can be made less than 800°C to ensure effective evaporation.

[0097] In another embodiment of this disclosure, the hole transport material and the electron trapping material are cross-linked to form a multifunctional polymer, which simultaneously possesses segments for hole transport and segments for electron trapping. For example, the general chemical formula of this multifunctional polymer is [A]. x [B] y A represents the monomer of the hole-transporting conductive polymer, and B represents the electron-trapping material or its monomer. x represents the number of repeating units of A, and y represents the number of repeating units of the electron-trapping material or its monomer. The polymer can be a random dimer, a diblock polymer, or an alternating polymer.

[0098] Thus, the multifunctional polymer can be directly used as a hole transport layer, in which both the hole transport material and the electron trap material are integrated into the multifunctional polymer, ensuring the material ratio of the electron trap material and the uniformity of its distribution in the hole transport layer. Compared with the direct mixing scheme, the component distribution of the film layer prepared with this polymer is more stable, and the distribution of the electron trap material will not change with time, annealing conditions, etc., thus minimizing the change in the electrical properties of the hole transport layer caused by the diffusion of the electron trap material and reducing the negative effects of the electron trap material on adjacent layers, etc.

[0099] Optionally, A can be a TFB monomer, a PVK (Poly(N-vinyl carbazole)) monomer, a TPD ((N,N'-bis(3-methylphenyl)-N,N'-diphenyl-benzidine); N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine)) or other monomers.

[0100] It can be understood that in this polymer, B can be directly the monomer of the electron trap material or a modified electron trap material, and the modified electron trap material is obtained by introducing a condensation functional group (such as a double bond, an isocyanide group, etc.) onto the electron trap material monomer to enable the modified electron trap material to polymerize with A.

[0101] In one example, through chemical synthesis, the electron trap material can be linked to the polymer serving as the hole transport material to form a new polymer.

[0102] In another example, the monomers of the electron trap material and the hole transport material can be made to undergo a polymerization reaction together to generate the required polymer.

[0103] In one example, the following method can be used to prepare the hole transport layer:

[0104] Preparing the hole transport layer includes:

[0105] Polymerizing the monomers of the hole transport material and the electron trap material together to form a multifunctional polymer;

[0106] Dissolving the multifunctional polymer in a solvent to obtain a precursor solution; <000027​​​​In other embodiments, the electron trapping material is linked to at least a portion of the hole transport material via chemical bonds or linking groups. In this embodiment, a multifunctional material can be synthesized first, which is a material formed by linking the hole transport material and the electron trapping material via chemical bonds or linking groups; for example, the structure of the multifunctional material is a structure formed by directly linking the hole transport material and the electron trapping material via chemical bonds (e.g., single bonds), or a structure formed by linking the hole transport material and the electron trapping material via linking groups (e.g., methylene, phenylene, etc.). It is understood that it is not necessarily required to use the hole transport material and the electron trapping material as raw materials to synthesize the desired multifunctional material; the key is that the synthesized material structurally presents a multifunctional material in which the hole transport material and the electron trapping material are interconnected. This multifunctional material simultaneously possesses hole transport and electron trapping functions. When preparing the hole transport layer, the hole transport material and the multifunctional material can be used as raw materials. For example, a mixture of the hole transport material and the multifunctional material (evaporation material) can be used for co-evaporation to form the hole transport layer.

[0109] For example, the hole transport material is A, the electron trapping material is B, and the multifunctional material is AB. When preparing the hole transport layer using a vapor deposition process, the evaporation source material is A with a mass content of x, and AB with a mass content of 1-a. x is a positive number less than 1. By adjusting a, the mass content of the electron trapping material in the hole transport layer can be adjusted.

[0110] It is understandable that a multifunctional material can be connected to one electronic trap material or multiple electronic trap materials.

[0111] In one example, the hole transport layer can be prepared using the following method:

[0112] Synthesize multifunctional materials, wherein the multifunctional material is a material formed by linking the hole transport material and the electron trap material through chemical bonds or linking groups;

[0113] The multifunctional material and the hole transport material are uniformly mixed to form a vapor-deposited material;

[0114] The hole transport layer is formed using the aforementioned vapor deposition material and a vapor deposition process.

[0115] Optionally, the electron trap material includes one or more of fullerenes, fullerene derivatives, small molecule semiconductor materials, and polymer semiconductor materials.

[0116] For example, the electron trap material is selected from the following materials:

[0117]

[0118]

[0119] The LUMO and HOMO energy levels of some of the above materials are shown in Table 1:

[0120] Table 1: HOMO and LUMO energy levels of some fullerene materials

[0121] PCBM <![CDATA[PC 71 BM]]> Bis-PCBM ICBA ICTA C60 C70 LUMO(eV) -4.2 -4.2 -3.6 -4.0 -3.36 -4.1 -3.7 HOMO(eV) -6.0 -6.1 -6.0 -5.9 -5.80 -6.3 -6.3

[0122] The fullerene materials in Table 1 exhibit rapid electron acceptance, enabling them to trap electrons effectively. However, fullerenes have a low LUMO energy level, posing a significant risk of leakage. Therefore, when using fullerenes as electron trapping materials, a comprehensive balance of various performance aspects is necessary to reduce the risk of leakage from the emitting layer through the electron trapping material, or to pair them with more suitable hole transport materials.

[0123] For example, the HOMO level of TFB is -5.4 eV, and the LUMO level is -2.8 eV. Fullerenes have relatively low HOMO levels, deeper than -5.4 eV.

[0124] When TFB is used as the hole transport material and fullerene is used as the electron trapping material, the fullerene exhibits good electron trapping capability, and its HOMO level is deep enough to avoid significant hole trapping. However, its LUMO level is too small, which can easily cause leakage current in the emitting layer and result in efficiency loss.

[0125] The LUMO and HOMO energy levels of some of the above materials are shown in Table 2:

[0126] Table 2: HOMO and LUMO energy levels of some organic semiconductor materials

[0127] IDIC-4CI PM6 (3) (4) (5) LUMO(eV) -3.83 -3.65 -3.37 -3.4 -3.17 HOMO(eV) -5.72 -5.45 -5.39 -7.0 -5.70

[0128] As shown in Table 2, the HOMO energy levels of these organic semiconductor materials are not significantly higher than those of TFB, and their LUMO energy levels are lower than those of TFB but quite close to them. Therefore, from the perspective of HOMO and LUMO energy levels, these organic semiconductor materials, when used as electron trapping materials, can achieve better energy level matching with TFB.

[0129] It is understood that, in the embodiments of this disclosure, the electronic trap material is not limited to the materials described above.

[0130] This disclosure also provides verification examples to verify the protective effect of adding electron trap materials to hole transport materials.

[0131] First verification example:

[0132] The hole transport material was the polymer TFB (Poly(9,9-dioctylfluorene-alt-N-(4-sec-butylphenyl)-diphenylamine), and the electron trapping material was PCBM. The hole transport material and the electron trapping material were co-dissolved in chlorobenzene to obtain the hole transport layer precursor solution.

[0133] ITO patterned glass substrates were subjected to UV and ozone treatment. Then, PEDOT:PSS was spin-coated at 3000 rpm for 1 minute; followed by annealing in air at 150°C for 30 minutes to form a hole injection layer. The device was transferred to an inert ring, and the aforementioned hole transport layer precursor solution was spin-coated at a concentration of 12 mg / mL (hole transport material + electron trap material) at 2000 rpm for 1 minute, followed by annealing at 120°C for 10 minutes to obtain the hole transport layer film for testing.

[0134] In this verification example, a first verification film, a second verification film, a third verification film, and a fourth verification film were prepared. Specifically, the electron trapping material comprised 2% of the mass of the first verification film; 5% of the mass of the electron trapping material in the second verification film; 10% of the mass of the electron trapping material in the third verification film; and 20% of the mass of the electron trapping material in the fourth verification film.

[0135] The first, second, third, and fourth verification films were sequentially irradiated with detection light (low intensity), aging light (high intensity), and detection light (low intensity) at a wavelength of 405 nm. Simultaneously, the intensity of the light emitted after the hole transport material was excited was measured; this intensity reflects the degree of damage to the hole transport material. Higher intensity indicates less damage to the hole transport material and better protection from the electron trapping material. Specifically, the hole transport material generates photoexcitons (electron-hole pairs) upon irradiation. The electron trapping material can protect the hole transport material by trapping the electrons in these photoexcitons, reducing the damaging effects of the electrons generated by the photoexcitons. The verification test results are presented below. Figure 6 middle.

[0136] See Figure 6When the films were irradiated with low-intensity detection light, all four films were excited and emitted light. However, it was evident that the films exhibited better stability when the mass content of the electron trapping material was between 5% and 20%. This indicates that the electron trapping material provides good protection for the hole transport material. When the films were irradiated with high-intensity aging light, the luminescence intensity of the four films, from highest to lowest, was: the third verification film C13, the fourth verification film C14, the second verification film C12, and the first verification film C11. This shows that the stability of the films with added electron trapping material is significantly improved under strong light, and the stability of the films is correlated with the amount of electron trapping material added. Within a certain content range, the higher the amount of electron trapping material added, the better the stability of the hole transport material.

[0137] Second verification example

[0138] The control device and three verification devices (first verification device, second verification device and third verification device) were prepared according to the following method.

[0139] 1) TFB (as a hole transport material) and PC71BM (as an electron trap material) were dissolved in chlorobenzene to obtain a hole transport layer precursor solution; the total mass concentration of TFB and PC71BM in the precursor solution was 12 mg / mL.

[0140] 2) Perform UV treatment and ozone treatment on the patterned ITO substrate (ITO layer + glass layer).

[0141] 3) Spin-coat PEDOT:PSS at 3000 rpm for 1 minute, then anneal in air at 150°C for 30 minutes to form a hole injection layer.

[0142] 4) Transfer the device to an inert environment, spin-coat the hole transport layer precursor liquid at a speed of 2000 rpm for 1 minute; then anneal at 120°C for 10 minutes to form the hole transport layer.

[0143] 5) Spin-coating quantum dot solution with a quantum dot content of 20 mg / mL, a spin speed of 2000 rpm, and a spin time of 1 minute; then annealing at 100℃ for 10 minutes to form a quantum dot luminescent layer.

[0144] 6) Spin-coat the zinc oxide precursor solution at a speed of 2000 rpm for 1 minute; then anneal at 100°C for 10 minutes to obtain the electron transport layer.

[0145] 7) Evaporated cathode, made of aluminum, with a thickness of 100nm.

[0146] Thus, the fabricated thin-film light-emitting device comprises an anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode, which are sequentially stacked. In this example, the anode is made of ITO; the hole transport layer is made of PEDOT:PSS; the hole transport layer is made of a mixture of TFB and electron trapping materials (except for the control device); the electron transport layer is made of zinc oxide; and the cathode is made of aluminum.

[0147] In the control device, the hole transport layer does not contain electron trapping material. In the first verification device, the electron trapping material accounts for 5% of the mass of the hole transport layer; in the second verification device, the electron trapping material accounts for 10% of the mass of the hole transport layer; and in the third verification device, the electron trapping material accounts for 20% of the mass of the hole transport layer.

[0148] Performance tests were performed on each of the above devices. The current density and brightness of each device were tested under different voltages, and the test results are shown below. Figure 7 The current efficiency and external quantum efficiency of various devices were tested at different voltages, and the test results are presented in [the table / document / etc.]. Figure 8 According to Figure 7 and Figure 8 It can be seen that doping the hole transport layer with electron trap materials leads to a certain loss of efficiency.

[0149] The test control device had an initial luminance of 1000 cd / m². 2 The T90 lifetime curve under certain conditions and the voltage change curve under constant current density are shown in the test results. Figure 9 In the middle. The first verification device was tested at an initial brightness of 1000 cd / m². 2 The T90 lifetime curve under certain conditions and the voltage change curve under constant current density are shown in the test results. Figure 10 According to Figure 9 and Figure 10 It can be seen that by doping the hole transport layer with 5% mass content of PC71BM, the T90 lifetime of the device can be extended from 5.5 hours to 33 hours, significantly improving the device performance. According to Figures 7-10 It can be seen that doping the hole transport layer with 5% PC71BM can effectively improve the stability of the hole transport layer and increase the lifetime of thin-film light-emitting devices.

[0150] The following examples, using multiple embodiments, illustrate the structure, materials, and fabrication methods of the thin-film light-emitting devices in the embodiments of this disclosure.

[0151] Example 1

[0152] The thin-film light-emitting device comprises an anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode, which are stacked sequentially. In this example, the anode is made of ITO; the hole transport layer is made of PEDOT:PSS; the hole transport layer is made of a mixture of TFB and PCBM; the electron transport layer is made of zinc oxide; and the cathode is made of aluminum.

[0153] The following method can be used to prepare this thin-film light-emitting device.

[0154] 1) TFB and PCBM were dissolved in chlorobenzene to obtain a hole transport layer precursor solution; the total mass concentration of TFB and PCBM in the precursor solution was 12 mg / mL; the mass percentage of PCBM in the film-forming material (UV-1084+TFB) was 2% to 20%.

[0155] 2) Perform UV treatment and ozone treatment on the patterned ITO substrate (ITO layer + glass layer).

[0156] 3) Spin-coat PEDOT:PSS at 3000 rpm for 1 minute, then anneal in air at 150°C for 30 minutes to form a hole injection layer.

[0157] 4) Transfer the device to an inert environment, spin-coat the hole transport layer precursor liquid at a speed of 2000 rpm for 1 minute; then anneal at 120°C for 10 minutes to form the hole transport layer.

[0158] 5) Spin-coating quantum dot solution with a quantum dot content of 20 mg / mL, a spin speed of 2000 rpm, and a spin time of 1 minute; then annealing at 100℃ for 10 minutes to form a quantum dot luminescent layer.

[0159] 6) Spin-coat the zinc oxide precursor solution at a speed of 2000 rpm for 1 minute; then anneal at 100°C for 10 minutes to obtain the electron transport layer.

[0160] 7) Evaporated cathode, made of aluminum, with a thickness of 100nm.

[0161] Example 2

[0162] The thin-film light-emitting device comprises an anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode, which are sequentially stacked. In this example, the anode is made of ITO; the hole transport layer is made of PEDOT:PSS; the electron transport layer is made of zinc oxide; and the cathode is made of aluminum. The hole transport layer is made of the following multifunctional polymer:

[0163]

[0164] Where x represents the number of repeating units in the TFB monomer, which is 200; y represents the number of repeating units in the cyclooctatetraene derivative monomer, which is 2.

[0165] In this example, hole transport materials and electron trapping materials are crosslinked to form a polymer, such that the multifunctional polymer has segments for hole transport and segments for electron trapping.

[0166] In this embodiment, the thin-film light-emitting device can be prepared by referring to the preparation method of Example 1, the only difference being that the multifunctional polymer of this embodiment is used as the film-forming material when preparing the hole transfer precursor solution. The mass concentration of the film-forming material in the hole transfer precursor solution is 12 mg / mL.

[0167] Example 3

[0168] The thin-film light-emitting device comprises an anode, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode, which are stacked sequentially. In this example, the anode is made of molybdenum oxide / silver; the hole transport layer is made of C70-doped CBP; the electron transport layer is made of zinc oxide; and the cathode is made of ITO.

[0169] The structure of CBP is as follows:

[0170]

[0171] The following method can be used to prepare this thin-film light-emitting device.

[0172] 1) Perform UV and ozone treatment on a patterned ITO substrate (ITO layer + glass layer).

[0173] 2) Spin-coat zinc oxide precursor solution at 2000 rpm for 1 minute; then anneal at 100°C for 10 minutes to obtain the electron transport layer.

[0174] 3) Spin-coating quantum dot solution with a quantum dot content of 20 mg / mL, a spin speed of 2000 rpm, and a spin time of 1 minute; then annealing at 100℃ for 10 minutes to form a quantum dot luminescent layer.

[0175] 4) A stable hole transport layer is formed by co-evaporation process. Source 1 uses CBP (evaporation rate of 1nm / min) and source 2 uses C70 (evaporation rate of 0.1nm / min), and 50nm is co-evaporated.

[0176] 5) Evaporated cathode, material is molybdenum oxide / silver, thickness is 3nm / 100nm.

[0177] Example 4

[0178] The thin-film light-emitting device comprises an anode, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode, which are sequentially stacked. In this example, the anode is made of molybdenum oxide / silver; the hole transport layer is made of a mixture of CPB and C60-modified CPB; the electron transport layer is made of zinc oxide; and the cathode is made of ITO.

[0179] The structure of C60-modified CPB is as follows:

[0180]

[0181] The following method can be used to prepare this thin-film light-emitting device.

[0182] 1) Perform UV and ozone treatment on a patterned ITO substrate (ITO layer + glass layer).

[0183] 2) Spin-coat zinc oxide precursor solution at 2000 rpm for 1 minute; then anneal at 100°C for 10 minutes to obtain the electron transport layer.

[0184] 3) Spin-coating quantum dot solution with a quantum dot content of 20 mg / mL, a spin speed of 2000 rpm, and a spin time of 1 minute; then annealing at 100℃ for 10 minutes to form a quantum dot luminescent layer.

[0185] 4) A stable hole transport layer is formed by vapor deposition process. The source material is a mixture of CBP and C60 modified CPB (1:1). The vapor deposition rate is 1nm / min, and a total of 50nm is vapor deposited.

[0186] 5) Evaporated cathode, material is molybdenum oxide / silver, thickness is 3nm / 100nm.

[0187] This disclosure also provides a display panel that includes any of the thin-film light-emitting devices described in the above-described embodiments. The display panel can be a smartphone screen, a smartwatch screen, or other types of display screen. Since this display panel has any of the thin-film light-emitting devices described in the above-described embodiments, it has the same beneficial effects, which will not be repeated here.

Claims

1. A thin-film light-emitting device, comprising an anode, a hole transport layer, a light-emitting layer, and a cathode sequentially stacked; wherein, The hole transport layer comprises a hole transport material and an electron trapping material; the LUMO energy level of the electron trapping material is lower than that of the hole transport material; the LUMO energy level of the electron trapping material is not lower than that of the LUMO energy level of the luminescent layer; the electron mobility of the electron trapping material is not greater than 1 × 10⁻⁶. -3 cm 2 V -1 s -1 The electron trapping material captures electrons at a faster rate than the hole transport material captures electrons at a faster rate; the electron trapping material captures electrons at a faster rate than the exciton-hole quenching rate on the hole transport material; the electron trapping material captures electrons within 2 nm at a faster rate than 10 nm. 9 / second; electron trapping materials that trap electrons extract electrons at a rate faster than 10^65 volts per second. 3 / Second; The HOMO energy level of the electron trap material is not higher than the HOMO energy level of the hole transport material.

2. The thin-film light-emitting device according to claim 1, wherein, The electron trap material has a mass content of no more than 10% in the hole transport layer.

3. The thin-film light-emitting device according to claim 1 or 2, wherein, Along the direction from the anode to the light-emitting layer, the mass content of the electron trapping material in the hole transport layer gradually decreases.

4. The thin-film light-emitting device according to claim 1 or 2, wherein, The hole transport layer comprises multiple sublayers stacked sequentially; the mass content of electron trapping material in the sublayer closest to the light-emitting layer is less than the mass content of electron trapping material in the sublayer furthest from the light-emitting layer.

5. The thin-film light-emitting device according to claim 1 or 2, wherein, The hole transport material and the electron trap material crosslink to form a polymer.

6. The thin-film light-emitting device according to claim 1 or 2, wherein, The electron trap material is connected to at least a portion of the hole transport material via chemical bonds or linking groups.

7. The thin-film light-emitting device according to claim 1 or 2, wherein, The electron trap material includes one or more of fullerenes, fullerene derivatives, small molecule semiconductor materials, and polymer semiconductor materials.

8. The thin-film light-emitting device according to claim 1 or 2, wherein, The electron trap material is selected from the following materials: 。 9. The thin-film light-emitting device according to claim 1 or 2, wherein, The hole transport material is an organic semiconductor material; the light-emitting layer is a quantum dot light-emitting layer or an organic light-emitting layer.

10. The thin-film light-emitting device according to claim 1 or 2, wherein, The thin-film light-emitting device is a blue light-emitting thin-film light-emitting device.

11. A method for fabricating a thin-film light-emitting device, used to fabricate the thin-film light-emitting device according to any one of claims 1-4 and 7-10; the fabrication method includes fabricating an anode, a hole transport layer, a light-emitting layer, and a cathode; The preparation of the hole transport layer includes: The hole transport material and the electron trap material are dissolved in a solvent to obtain a precursor solution; The hole transport layer is prepared using the precursor liquid through a coating process, screen printing process, or inkjet printing process.

12. A method for fabricating a thin-film light-emitting device, used to fabricate the thin-film light-emitting device according to any one of claims 1-5 and 7-10; the fabrication method includes fabricating an anode, a hole transport layer, a light-emitting layer, and a cathode; The preparation of the hole transport layer includes: The monomers of the hole transport material and the monomers of the electron trap material are polymerized together to form a multifunctional polymer; The multifunctional polymer is dissolved in a solvent to obtain a precursor solution; The hole transport layer is prepared using the precursor liquid through a coating process, screen printing process, or inkjet printing process.

13. A method for fabricating a thin-film light-emitting device, used to fabricate the thin-film light-emitting device according to any one of claims 1-4 and 7-10; the fabrication method includes fabricating an anode, a hole transport layer, a light-emitting layer, and a cathode; The preparation of the hole transport layer includes: The hole transport layer is formed by co-evaporation of the hole transport material and the electron trap material.

14. A method for fabricating a thin-film light-emitting device, used to fabricate the thin-film light-emitting device according to any one of claims 1-4 and 6-10; the fabrication method includes fabricating an anode, a hole transport layer, a light-emitting layer, and a cathode; The preparation of the hole transport layer includes: Synthesize multifunctional materials, wherein the multifunctional material is a material formed by linking the hole transport material and the electron trap material through chemical bonds or linking groups; The multifunctional material and the hole transport material are uniformly mixed to form a vapor-deposited material; The hole transport layer is formed using the aforementioned vapor deposition material and a vapor deposition process.

15. A display panel comprising the thin-film light-emitting device according to any one of claims 1 to 10.

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