Thin-film light-emitting device and preparation method therefor, and display panel

Abstract

A thin-film light-emitting device and a preparation method therefor, and a display panel, relating 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. The hole transport layer comprises a hole transport material and an electron trap material, and 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

Thin film light emitting device and preparation method thereof, and display panel

[0001] Cross-references

[0002] The present disclosure claims priority to Chinese patent application number 202310960595.4 filed on August 1, 2023, entitled “Thin-Film Light-Emitting Device, Preparation Method Thereof, and Display Panel”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to the field of display technology, and in particular to a thin film light emitting device and a preparation method thereof, and a display panel. Background Art

[0004] Quantum-dot light-emitting diodes (QDs) are a type of light-emitting display technology that has been very close to commercialization in recent years. The hole transport layer of QDs typically uses organic semiconductor materials, but these materials are easily damaged, which can lead to performance degradation in QDs.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute prior art known to ordinary technicians in the field.

[0006] Summary of the Invention

[0007] The purpose of the present disclosure is to overcome the above-mentioned deficiencies of the prior art, provide a thin film light emitting device and a preparation method thereof, and a display panel, and improve the stability of the hole transport layer.

[0008] According to one aspect of the present disclosure, a thin film light-emitting device is provided, comprising an anode, a hole transport layer, a light-emitting layer and a cathode stacked in sequence; 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 lower than the LUMO energy level of the hole transport material.

[0009] According to one embodiment of the present disclosure, the LUMO energy level of the electron trap material is not less than the LUMO energy level of the light-emitting layer.

[0010] According to one embodiment of the present disclosure, the mass content of the electron trap material in the hole transport layer is no more than 10%.

[0011] According to one embodiment of the present disclosure, the electron mobility of the electron trap material is no greater than 1×10 -3 cm 2 V -1 s-1 .

[0012] According to one embodiment of the present disclosure, the rate at which the electron trap material captures electrons is faster than the rate at which holes in the hole transport material capture electrons.

[0013] According to one embodiment of the present disclosure, the rate at which the electron trap material captures electrons is faster than the rate at which excitons on the hole transport material are quenched with holes.

[0014] According to one embodiment of the present disclosure, the electron trap material captures electrons within 1 nm faster than 10 9 / Second.

[0015] According to one embodiment of the present disclosure, the electron trap material captures electrons within 2 nm faster than 10 9 / Second.

[0016] According to one embodiment of the present disclosure, the electron trap material that captures electrons can extract electrons faster than 10 3 / Second.

[0017] According to one embodiment of the present disclosure, the HOMO energy level of the electron trap material is not higher than the HOMO energy level of the hole transport material.

[0018] According to one embodiment of the present disclosure, the mass content of the electron trap material in the hole transport layer gradually decreases along the direction from the anode to the light-emitting layer.

[0019] According to one embodiment of the present disclosure, the hole transport layer includes a plurality of sequentially stacked sublayers; the mass content of the electron trap material in the sublayer closest to the light-emitting layer is less than the mass content of the electron trap material in the sublayer farthest from the light-emitting layer.

[0020] According to one embodiment of the present disclosure, the hole transport material and the electron trap material are cross-linked to form a polymer.

[0021] According to one embodiment of the present disclosure, the electron trap material is connected to at least a portion of the hole transport material via a chemical bond or a connecting group.

[0022] According to one embodiment of the present disclosure, the electron trap material includes one or more of fullerene, fullerene derivatives, small molecule semiconductor materials, and polymer semiconductor materials.

[0023] According to one embodiment of the present disclosure, the electron trap material is selected from the following materials:

[0024] According to one embodiment of the present disclosure, the hole transport material is an organic semiconductor material; and the light-emitting layer is a quantum dot light-emitting layer or an organic light-emitting layer.

[0025] According to one embodiment of the present disclosure, the thin film light emitting device is a blue thin film light emitting device.

[0026] According to another aspect of the present disclosure, a method for preparing a thin film light emitting device is provided, for preparing the above-mentioned thin film light emitting device; the preparation method comprises preparing an anode, a hole transport layer, a light emitting layer and a cathode;

[0027] The preparation of the hole transport layer comprises:

[0028] dissolving the hole transport material and the electron trap material in a solvent to obtain a precursor solution;

[0029] The hole transport layer is prepared using the precursor liquid by a coating process, a screen printing process or an inkjet printing process.

[0030] According to another aspect of the present disclosure, a method for preparing a thin film light emitting device is provided, for preparing the above-mentioned thin film light emitting device; the preparation method comprises preparing an anode, a hole transport layer, a light emitting layer and a cathode;

[0031] The preparation of the hole transport layer comprises:

[0032] performing a polymerization reaction on the monomer of the hole transport material and the monomer of the electron trap material to form a multifunctional polymer;

[0033] dissolving the multifunctional polymer in a solvent to obtain a precursor solution;

[0034] The hole transport layer is prepared using the precursor liquid by a coating process, a screen printing process or an inkjet printing process.

[0035] According to another aspect of the present disclosure, a method for preparing a thin film light emitting device is provided, for preparing the above-mentioned thin film light emitting device; the preparation method comprises preparing an anode, a hole transport layer, a light emitting layer and a cathode;

[0036] The preparation of the hole transport layer comprises:

[0037] The hole transport material and the electron trap material are co-evaporated to form the hole transport layer.

[0038] According to another aspect of the present disclosure, a method for preparing a thin film light emitting device is provided, for preparing the above-mentioned thin film light emitting device; the preparation method comprises preparing an anode, a hole transport layer, a light emitting layer and a cathode;

[0039] The preparation of the hole transport layer comprises:

[0040] synthesizing a multifunctional material, wherein the multifunctional material is a material formed by connecting the hole transport material and the electron trap material via a chemical bond or a connecting group;

[0041] uniformly mixing the multifunctional material and the hole transport material to form an evaporation material;

[0042] The hole transport layer is formed by using the evaporation material and adopting an evaporation process.

[0043] According to yet another aspect of the present disclosure, a display panel is provided, comprising the above-mentioned thin film light-emitting device.

[0044] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings are incorporated into and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification, are used to explain the principles of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0046] FIG1 is a schematic structural diagram of a thin film light emitting device in one embodiment.

[0047] FIG2 is a schematic structural diagram of a thin film light emitting device in one embodiment.

[0048] FIG3 is a schematic structural diagram of a thin film light emitting device in one embodiment.

[0049] FIG4 is a schematic structural diagram of a thin film light emitting device in one embodiment.

[0050] FIG5 is a schematic structural diagram of a thin film light emitting device in one embodiment.

[0051] FIG6 is a luminous intensity curve of each thin film in the first verification example.

[0052] FIG. 7 shows a driving voltage-current density curve and a driving voltage-luminance curve of each device in the second verification example.

[0053] FIG8 shows the driving voltage-current efficiency curve and the driving voltage-external quantum efficiency curve of each device in the second verification example.

[0054] FIG9 is a T90 lifespan curve and a voltage variation curve of a control device.

[0055] FIG10 is a T90 lifetime curve and a voltage variation curve of the first verification device. DETAILED DESCRIPTION

[0056] Example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art. Like reference numerals in the figures represent identical or similar structures, and thus their detailed descriptions will be omitted. Furthermore, the figures are merely schematic illustrations of the present disclosure and are not necessarily drawn to scale.

[0057] Although relative terms such as "upper" and "lower" are used in this specification to describe the relationship of one illustrated component to another, these terms are used herein for convenience only, such as in accordance with the orientation of the illustrations in the accompanying drawings. It will be understood that if the illustrated device were flipped upside down, the component described as "upper" would become the component "lower." When a structure is referred to as "on" another structure, this may mean that the structure is integrally formed with the other structure, that the structure is "directly" disposed on the other structure, or that the structure is "indirectly" disposed on the other structure via the other structure.

[0058] The terms "a", "an", "the", "said" 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 express open-ended inclusion and mean that additional elements / components / etc. may be present in addition to the listed elements / components / etc.; the terms "first", "second" and "third" etc. are used only as labels and are not intended to limit the quantity of their objects.

[0059] The embodiments of the present disclosure provide a thin film light emitting device and a display panel using the thin film light emitting device. Referring to FIG1 , the thin film light emitting device includes a stacked anode AE ​​and a cathode CE, and a light emitting functional layer EFU sandwiched between the anode AE ​​and the cathode CE. Referring to FIG1 , the light emitting functional layer EFU includes at least a hole transport layer HTL and a light emitting layer, and the hole transport layer HTL is located on the side of the light emitting layer close to the anode AE. The anode and the cathode respectively provide electrons, holes and other carriers to the light emitting functional layer EFU, so that the light emitting layer of the light emitting functional layer EFU emits light. It can be understood that the type of thin film light emitting device is different, and the material and film layer of the light emitting functional layer EFU are different.

[0060] For example, referring to FIG2 , when the thin-film light-emitting device is an OLED (organic electroluminescent diode), the light-emitting functional layer EFU may include an organic light-emitting layer EML as a light-emitting layer, and may include one or more of a hole injection layer, a hole transport layer HTL, 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 the hole transport layer HTL. Furthermore, the organic light-emitting layer EML may include a light-emitting layer host material and a light-emitting layer guest material, and the light-emitting layer guest material may be a fluorescent dopant or a phosphorescent dopant, in particular, a thermally activated delayed fluorescent material. Referring to FIG4 , when the OLED adopts a stacked structure, a charge generation layer CGL may also be provided in the light-emitting functional layer EFU.

[0061] For another example, referring to FIG8 , 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 a light-emitting layer, and may include one or more of 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 may be connected to each other through surface modification groups. Referring to FIG5 , when the QLED adopts a stacked structure, a charge generation layer CGL may also be provided in the light-emitting functional layer EFU.

[0062] In the embodiments of the present disclosure, referring to Figures 2 to 5 , the light-emitting functional layer EFU may include a single light-emitting stacked structure ELS, or may include a stack of multiple light-emitting stacked structures ELS. When the light-emitting functional layer EFU includes multiple light-emitting stacked structures ELS, a charge generation layer CGL may be provided between two adjacent light-emitting stacked structures ELS. Each light-emitting stacked structure ELS is provided with one or more light-emitting layers, which may be either an organic light-emitting layer or a quantum dot light-emitting layer.

[0063] In the examples shown in Figures 2 and 3, the light-emitting functional layer (EFU) comprises a light-emitting stacked structure (ELS). Referring to Figures 2 and 3, the thin-film light-emitting device comprises an anode (AE), a light-emitting stacked structure (ELS), and a cathode (CE) stacked in sequence. The light-emitting stacked structure (ELS) comprises a hole regulation unit, a light-emitting layer (e.g., an organic light-emitting layer (EML) or a quantum dot light-emitting layer (QDL), and an electron regulation unit stacked in sequence. The hole regulation unit is located on the side of the light-emitting layer near the anode, and the electron regulation unit is located on the side of the light-emitting layer near the cathode. The anode is used to inject holes into the light-emitting layer via the hole regulation unit, while the cathode is used to inject electrons into the light-emitting layer via the electron regulation unit. The hole regulation unit and the electron regulation unit are respectively used to adjust the injection efficiency and injection rate of holes and electrons into the light-emitting layer, as well as the energy levels of the injected electrons and holes, thereby improving the balance between hole and electron injection and thereby improving the performance of the light-emitting functional layer (EFU), such as increasing the luminous efficiency of the thin-film light-emitting device, increasing the device lifespan of the thin-film light-emitting device, and reducing the power supply voltage of the thin-film light-emitting device.

[0064] The hole regulation unit may include one or more layers of film layers such as a hole injection layer, a hole transport layer HTL, and an electron blocking layer EBL, and at least includes a hole transport layer HTL. Among them, the hole injection layer, the hole transport layer HTL, the electron blocking layer EBL, etc. are stacked in sequence along the direction from the anode to the light-emitting layer. It is understood that in some examples, one or more of the film layers such as the hole injection layer, the hole transport layer HTL, and the electron blocking layer EBL can be set as a multi-layer stacked structure. For example, the hole transport layer HTL can include a first hole transport layer and a second hole transport layer stacked, etc.

[0065] The electron regulation unit may include one or more layers of film layers 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, the hole blocking layer HBL, etc. are stacked in sequence along the direction from the cathode to the light-emitting layer. It is understood that in some examples, one or more of the film layers such as the electron injection layer EIL, the electron transport layer ETL, and the hole blocking layer HBL may be configured as a multi-layer stacked structure, for example, the electron transport layer ETL may include a first electron transport layer and a second electron transport layer stacked, etc.

[0066] In the examples of Figures 4 and 5, the light-emitting functional layer EFU has a multi-layer stacked light-emitting stack structure ELS (Figures 4 and 5 illustrate a two-layer light-emitting stack structure ELS). Referring to Figures 4 and 5, the thin-film light-emitting device includes an anode, a multi-layer stacked light-emitting stack structure ELS, and a cathode stacked in sequence. Any layer of the light-emitting stack structure ELS includes a hole regulation unit, a light-emitting layer (e.g., an organic light-emitting layer or a quantum dot light-emitting layer), and an electron regulation unit stacked in sequence, wherein the hole regulation unit is located on the side of the light-emitting layer close to the anode, and the electron regulation unit is located on the side of the light-emitting layer close to the cathode.

[0067] Optionally, the light-emitting functional layer EFU may further include a charge generation layer CGL located between two adjacent light-emitting stack structures ELS to improve the efficiency of injecting electrons and holes into the two adjacent light-emitting stack structures 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 light-emitting stack structures ELS. The N-type charge generation layer NCGL is arranged adjacent to the electron regulation portion of one of the light-emitting stack structures ELS, and is used to inject electrons into the electron regulation portion of the light-emitting stack structure ELS; the P-type charge generation layer PCGL is arranged adjacent to the hole regulation portion of the other light-emitting stack structure ELS, and is used to inject holes into the hole regulation portion of the light-emitting stack structure ELS. In other words, the P-type charge generation layer PCGL is arranged on the side of the N-type charge generation layer NCGL away from the anode. Of course, it can be understood that in other examples, the charge generation layer CGL may also include other structures.

[0068] It is understood that in some other embodiments of the present disclosure, the electron regulation portion of the light emitting stacked structure ELS may be omitted, or may have other structures in addition to the electron injection layer EIL, the electron transport layer ETL, and the hole blocking layer HBL.

[0069] It is understandable that when multiple light-emitting layers are provided in the light-emitting stack structure ELS, the colors of the multiple light-emitting layers may be the same or different, and the types of the multiple light-emitting layers may be the same or different.

[0070] It is understandable that, for any light-emitting stacked structure ELS, it may be provided with a light-emitting layer (such as a quantum dot light-emitting layer or an organic light-emitting layer), and may be provided with one or more of a hole injection layer, a hole transport layer HTL, an electron blocking layer EBL, a hole blocking layer HBL, an electron transport layer ETL and an electron injection layer EIL, or other film layers may be added as needed. Of course, in the light-emitting stacked structure ELS, one or more of the hole injection layer, the electron blocking layer EBL, the hole blocking layer HBL, the electron transport layer ETL and the electron injection layer EIL may also be omitted. For two light-emitting stacked structures ELS of the same thin-film light-emitting device, the film layer structures of the two light-emitting stacked structures ELS may be the same or different.

[0071] The hole transport material in the hole transport layer is an organic semiconductor material, such as an organic small molecule semiconductor material or a polymer semiconductor material. Damage to the hole transport material can lead to reduced device performance. Electrons leaking from the light-emitting layer into the hole transport layer are one of the key factors in damaging the hole transport material. After electrons leak from the light-emitting layer into the hole transport layer, they can damage the hole transport material through a variety of different pathways. For example, hot electrons in an excited state can directly damage the hole transport material, or electrons can be captured by holes to form excitons, which then destroy the hole transport material through the thermal energy state generated by the nonlinear quenching process.

[0072] In an embodiment of the present disclosure, an electron trap material is introduced into the hole transport layer. The LUMO energy level of the electron trap material is lower than the LUMO energy level of the hole transport material. Therefore, the electrons that leak into the hole transport layer (hereinafter referred to as leakage electrons) can be captured by the electron trap material, for example, directly capturing the leakage electrons, or capturing electrons from the hole transport material combined with the leakage electrons. In this way, the leakage electrons that enter the hole transport layer from the light-emitting layer can be at least partially captured by the electron trap material, thereby avoiding damage to the hole transport material caused by these leakage electrons.

[0073] In one embodiment of the present 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 susceptible to damage. Therefore, introducing an electron trap material into the hole transport layer of the blue thin-film light-emitting device to increase the lifespan of the blue thin-film light-emitting device can more effectively alleviate the restriction of the blue thin-film light-emitting device on the lifespan of the display panel or light-emitting panel.

[0074] In one embodiment of the present disclosure, the thin-film light-emitting device is a QLED, where 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, while the hole transport material is an organic semiconductor material. This makes the hole transport layer the most vulnerable layer in this QLED, limiting the device's lifespan. In this embodiment of the present disclosure, the lifetime of the QLED can be extended by adding an electron-trapping material to the hole transport layer to improve its stability.

[0075] In one embodiment of the present disclosure, the LUMO energy level of the electron trap material is no less than the LUMO energy level of the light-emitting layer. This prevents the LUMO energy level of the electron trap material from being too low, thereby forming a significant electron leakage path. Of course, in other embodiments of the present disclosure, the LUMO energy level of the electron trap material may also be lower than the LUMO energy level of the light-emitting layer, but it should not be too much lower. For example, the LUMO energy level of the electron trap material cannot be lower than the LUMO energy level of the light-emitting layer by more than 1.5 eV.

[0076] In one embodiment of the present disclosure, the mass content of the electron trap material in the hole transport layer is no more than 10%. This prevents the formation of significant leakage paths due to excessive concentrations of the electron trap material in the hole transport layer. Furthermore, the mass content of the electron trap material in the hole transport layer is no more than 5%, for example, 1%, 2%, 3%, 4%, or 5%.

[0077] In one embodiment of the present disclosure, the electron mobility of the electron trap material is no greater than 1×10 -3 cm 2 V -1 s -1 In this way, the electron trap material can be prevented from forming a significant leakage channel in the hole transport layer.

[0078] In one embodiment of the present disclosure, the mass content of the electron-trapping material in the hole transport layer gradually decreases along the direction from the anode to 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 of electricity from the light-emitting layer to the hole transport layer through the electron-trapping material.

[0079] In another embodiment of the present disclosure, the hole transport layer comprises multiple sequentially stacked sublayers; the mass content of the electron-trapping material in the sublayer closest to the light-emitting layer is lower than the mass content of the 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 minimizing leakage from the light-emitting layer to the hole transport layer through the electron-trapping material.

[0080] In one example, the hole transport layer may include a first sublayer and a second sublayer stacked sequentially from the anode to the light-emitting layer. The mass content of the electron trap material in the second sublayer is lower than the mass content of the electron trap material in the first sublayer. For example, the mass content of the electron trap material in the second sublayer is no more than half the mass content of the electron trap material in the first sublayer, such as 10%, 20%, 30%, 40%, or 50% of the mass content of the electron trap material in the first sublayer.

[0081] Of course, in other embodiments of the present 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 to reduce the electron leakage from the light emitting layer to the hole transport layer.

[0082] Of course, in other embodiments of the present disclosure, other means may be used to configure the hole transport layer to reduce the electron leakage channels that may be generated by the electron trap material. For example, the electron trap materials may be designed to be discontinuous to avoid the formation of continuous electron leakage channels.

[0083] In one embodiment of the present disclosure, the electron trapping material captures electrons at a faster rate than the hole transport material captures electrons. This allows the electron trapping material to capture electrons more quickly and efficiently, reducing the proportion of excitons formed by recombination between leaked electrons and holes in the hole transport material, thereby more effectively reducing the damage caused by leaked electrons to the hole transport material.

[0084] In one embodiment of the present disclosure, the rate at which the electron trap material captures electrons is faster than the rate at which the excitons on the hole transport material are quenched with holes. When the holes in the hole transport material capture leaked electrons to form excitons, the excitons can quench with other holes to release / transfer energy, which may result in the risk of damage to the hole transport material. In an embodiment of the present disclosure, the rate at which the electron trap material captures electrons is greater than the rate at which the excitons on the hole transport material are quenched with holes, which may increase the probability that the hole transport material that has captured the leaked electrons will transfer electrons to the electron trap material, thereby reducing the risk of damage to the hole transport material due to quenching of the excitons on the hole transport material.

[0085] In one example, the rate at which the electron trap material captures electrons is faster than the rate at which holes in the hole transport material capture electrons, and faster than the rate at which excitons on the hole transport material quench with holes.

[0086] In one embodiment of the present disclosure, the electron trap material captures electrons within 1 nm faster than 10 9 / second. This allows the electron trap material to efficiently capture leaked electrons and provide effective protection for the hole transport material. Furthermore, the electron trap material captures electrons within 2nm faster than 10 9 In this way, the ability of the electron trap material to capture leaked electrons can be further improved, further enhancing the protection effect of the hole transport material.

[0087] In the embodiment of the present disclosure, the electron trap material captures electrons within 1 nm faster than 10 9 / second means that when the leakage electrons enter the range of 1nm around the electron trap material, the rate at which the leakage electrons are captured by the electron trap material is faster than 10 9 / sec. The electron trap material captures electrons within 2nm faster than 10 9 / second means that when the leakage electrons enter the range of 2nm around the electron trap material, the rate at which the leakage electrons are captured by the electron trap material is faster than 10 9 / Second.

[0088] In one embodiment of the present disclosure, the electron trap material that has captured electrons extracts electrons at a rate faster than 10 3 / second. This ensures that the electron-trapping material can quickly remove the leaked electrons after capturing them. For example, the captured electrons can quickly recombine with holes in the hole transport material or holes in the electron-trapping material, thereby allowing the electron-trapping material to regain its ability to capture electrons. Because the electron-trapping material has a low LUMO energy level, it is less likely to damage the hole transport layer when removing electrons.

[0089] In one example, the rate at which the electron trap material captures electrons is faster than the rate at which holes in the hole transport material capture electrons, and faster than the rate at which excitons and holes on the hole transport material are quenched; the rate at which the electron trap material that has captured electrons extracts electrons is faster than 10 3 In this way, the electron trap material can quickly capture electrons to protect the hole transport material, and can quickly and safely extract electrons, which enables the electron trap material to provide long-lasting protection for the hole transport layer.

[0090] In one embodiment of the present disclosure, the HOMO energy level of the electron trap material is not higher than the HOMO energy level of the hole transport material. In this way, the electron trap material in the hole transport layer does not generate significant hole traps, thereby avoiding affecting the hole transport performance of the hole transport layer. Of course, in other embodiments of the present disclosure, the HOMO energy level of the electron trap material can also be appropriately higher than the HOMO energy level of the hole transport material, which is 0.1eV, 0.2eV or 0.3eV higher than the HOMO energy level of the hole transport material.

[0091] In one embodiment of the present disclosure, in the hole transport layer, the hole transport material and the electron trap material are two independent materials, that is, there is no strong chemical bond such as a covalent bond between the two. The electron trap material is uniformly dispersed in the hole transport layer. In one example, a solution containing a hole transport material and an electron trap material can be used as a raw material to form a hole transport layer by a solution process such as coating, spin coating, printing or inkjet printing. In another example, the hole transport material and the electron trap material can be co-evaporated to form a hole transport layer, and the evaporation rate of the hole transport material and the electron trap material determines the content of the electron trap material in the hole transport layer.

[0092] In one example, the hole transport layer can be prepared by the following method:

[0093] dissolving the hole transport material and the electron trap material in a solvent to obtain a precursor solution;

[0094] The hole transport layer is prepared using the precursor liquid by a coating process, a screen printing process or an inkjet printing process.

[0095] In this example, the hole transport material, electron trap material, and solvent need to be selected so that the hole transport material and the electron trap material can be evenly and non-aggregatedly distributed in the solution, thereby facilitating the formation of a film layer (such as a hole transport layer) with uniform thickness.

[0096] In another example, the hole transport layer can be prepared by the following method:

[0097] The hole transport material and the electron trap material are co-evaporated to form the hole transport layer.

[0098] For example, a hole transport material and an electron trap material can be placed in evaporation pools 1 and 2, respectively. The evaporation rate of the hole transport material is controlled between 0.1 angstroms and 10 nanometers per minute, and the evaporation rate of the electron trap material is controlled between 0.1 angstroms and 10 nanometers per minute. In this way, the evaporation rate ratio of the hole transport material to the electron trap material can be controlled between 1:1 and 1000:1, depending on the doping design. In this example, the melting point of the electron trap material can be controlled below 800°C to ensure efficient evaporation.

[0099] In another embodiment of the present disclosure, the hole transport material and the electron trap material are cross-linked to form a multifunctional polymer, so that the multifunctional polymer has both a hole transport segment and an electron trap segment. For example, the general chemical formula of the multifunctional polymer is [A] x [B] y A represents a monomer of a hole-transporting conductive polymer, and B represents an electron-trapping material or a monomer thereof. x represents the number of repeating units of A, and y represents the number of repeating units of the electron-trapping material or a monomer thereof. The polymer may be a random dimer, a diblock polymer, or an alternating polymer.

[0100] In this way, the multifunctional polymer can directly serve as the hole transport layer, integrating both the hole transport material and the electron trapping material into the multifunctional polymer. This ensures a uniform ratio and distribution of the electron trapping material within the hole transport layer. Compared to direct mixing, the compositional distribution of the film produced using this polymer is more stable, and the distribution of the electron trapping material does not change over time, annealing conditions, or other factors. This minimizes changes in the electrical properties of the hole transport layer caused by diffusion of the electron trapping material, and reduces the negative effects of the electron trapping material on adjacent layers.

[0101] Optionally, A can be a TFB monomer, a PVK (English name: Poly(N-vinyl carbazole), Chinese name: Poly(N-vinyl carbazole)) monomer, a TPD (English name: (N,N'-bis(3-methylphenyl)-N,N'-diphenyl-benzidine); Chinese name: N,N'-diphenyl-N,N'-di(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine)) monomer, or other monomers.

[0102] It can be understood that in the polymer, B can be directly a monomer of the electron trap material, or it can be a modified electron trap material, and the modified electron trap material is an electron trap material monomer with a condensation functional group (such as a double bond, isocyanate, etc.) introduced to enable the modified electron trap material to polymerize with A.

[0103] In one example, the electron trap material can be linked to a polymer serving as a hole transport material through chemical synthesis to form a new polymer.

[0104] In another example, the monomers of the electron trap material and the monomers of the hole transport material may be polymerized together to generate a desired polymer.

[0105] In one example, the hole transport layer can be prepared by the following method:

[0106] The preparation of the hole transport layer comprises:

[0107] performing a polymerization reaction on the monomer of the hole transport material and the monomer of the electron trap material to form a multifunctional polymer;

[0108] dissolving the multifunctional polymer in a solvent to obtain a precursor solution;

[0109] The hole transport layer is prepared using the precursor liquid by a coating process, a screen printing process or an inkjet printing process.

[0110] In other embodiments, the electron trap material is connected to at least part of the hole transport material through a chemical bond or a linking group. In this embodiment, a multifunctional material can be synthesized first, and the multifunctional material is a material formed by connecting the hole transport material and the electron trap material through a chemical bond or a linking group; for example, the structure of the multifunctional material is a structure formed by directly connecting the hole transport material and the electron trap material through a chemical bond (such as a single bond), or a structure formed by connecting the hole transport material and the electron trap material through a linking group (such as a methylene group, a phenylene group, etc.). It can be understood that it is not necessarily required to use the hole transport material and the electron trap material as raw materials to synthesize the required multifunctional material, and the structure of the synthesized material is based on the interconnection of the multifunctional material as the hole transport material and the electron trap material. The multifunctional material has both hole transport function and electron capture function. 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) is co-evaporated to form the hole transport layer.

[0111] For example, consider the hole transport material A, the electron trap material B, and the multifunctional material AB. When depositing the hole transport layer via evaporation, the evaporation source material is A with a mass content x, and AB with a mass content 1-a. x is a positive number less than 1. By adjusting a, the mass content of the electron trap material in the hole transport layer can be adjusted.

[0112] It is understood that one multifunctional material may be connected to one electron trap material or multiple electron trap materials.

[0113] In one example, the hole transport layer can be prepared by the following method:

[0114] synthesizing a multifunctional material, wherein the multifunctional material is a material formed by connecting the hole transport material and the electron trap material via a chemical bond or a connecting group;

[0115] uniformly mixing the multifunctional material and the hole transport material to form an evaporation material;

[0116] The hole transport layer is formed by using the evaporation material and adopting an evaporation process.

[0117] Optionally, the electron trap material includes one or more of fullerene, fullerene derivatives, small molecule semiconductor materials, and polymer semiconductor materials.

[0118] For example, the electron trap material is selected from the following materials:

[0119] Among them, the LUMO energy levels 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] The fullerene materials listed in Table 1 possess rapid electron-accepting capabilities, resulting in a high electron capture rate. However, fullerene materials have low LUMO energy levels, which can lead to a significant risk of leakage. Therefore, when using fullerene materials as electron-trapping materials, it is necessary to balance various performance factors to minimize the risk of leakage from the light-emitting layer through the electron-trapping material, or to pair them with more suitable hole-transporting materials.

[0122] For example, the HOMO energy level of TFB is -5.4 eV, and the LUMO energy level is -2.8 eV. The HOMO energy level of fullerene is relatively low, deeper than -5.4 eV.

[0123] When TFB is used as a hole transport material and fullerene is used as an electron trapping material, the fullerene has a relatively good electron trapping ability, and its HOMO energy level is deep enough to not form significant hole traps. However, its LUMO energy level is too small, which can easily cause leakage in the light-emitting layer and lead to efficiency loss.

[0124] In addition, the LUMO energy levels and HOMO energy levels of some of the above materials are shown in Table 2:

[0125] Table 2: HOMO and LUMO energy levels of some organic semiconductor materials

[0126] Table 2 shows that the HOMO energy levels of these organic semiconductor materials are not significantly higher than TFB, and their LUMO energy levels are lower than TFB and relatively close to TFB. Therefore, from the perspective of HOMO and LUMO energy levels, these organic semiconductor materials can form a better energy level match with TFB when used as electron trap materials.

[0127] It is understood that in the embodiments of the present disclosure, the electron trap material is not limited to the above materials.

[0128] The disclosed embodiments also provide a verification example to verify the protective effect of adding an electron trap material to the hole transport material on the hole transport material.

[0129] First verification example:

[0130] The hole transport material used is the polymer TFB (Poly(9,9-dioctylfluorene-alt-N-(4-sec-butylphenyl)-diphenylamine), and the electron trap material is PCBM. The hole transport material and electron trap material are co-dissolved in chlorobenzene to obtain a hole transport layer precursor solution.

[0131] An ITO-patterned glass substrate was UV-treated and ozone-treated. PEDOT:PSS was then spin-coated at 3000 rpm for 1 minute. This was followed by annealing at 150°C in air for 30 minutes to form a hole injection layer. The device was then transferred to an inert ring and spin-coated with the aforementioned hole transport layer precursor solution at a concentration of 12 mg / mL (hole transport material + electron trap material). The spin-coating speed was 2000 rpm for 1 minute, followed by annealing at 120°C for 10 minutes to obtain a hole transport layer film for testing.

[0132] In this demonstration example, a first, second, third, and fourth verification films were prepared. The first verification film contained 2% by weight of the electron trap material; the second verification film contained 5% by weight of the electron trap material; the third verification film contained 10% by weight of the electron trap material; and the fourth verification film contained 20% by weight of the electron trap material.

[0133] The first verification film, the second verification film, the third verification film and the fourth verification film are irradiated with detection light (low intensity), aging light (high intensity) and detection light (low intensity) in turn, and the wavelength of the irradiation light is 405 nanometers. At the same time, the intensity of the light emitted by the hole transport material after being excited is detected, and the light intensity can reflect the degree of damage to the hole transport material. The stronger the light intensity, the less damage to the hole transport material, and the better the protection effect of the electron trap material on the hole transport material. Among them, the hole transport material generates photoexcitons (electron-hole pairs) after being irradiated with light. The electron trap material can protect the hole transport material by capturing the electrons of the photoexcitons, reducing a series of damages to the hole transport material caused by the electrons generated by the photoexcitons. The verification test results are shown in Figure 6.

[0134] As shown in Figure 6, when the film is irradiated with a relatively low intensity test light, all four films are excited and emit light under the light. However, it is obvious that when the mass content of the electron trap material is between 5% and 20%, the stability of the film is better. This shows that the electron trap material has a good protective effect on the hole transport material. When the film is irradiated with a higher intensity aging light, the luminescence intensity of the four films is ranked from large to small: 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 film added with the electron trap material under strong light is greatly improved, and the stability of the film is correlated with the amount of electron trap material added. Within a certain content range, the more electron trap material is added, the better the stability of the hole transport material.

[0135] Second verification example

[0136] A control device and three verification devices (a first verification device, a second verification device, and a third verification device) were prepared as follows.

[0137] 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.

[0138] 2) UV treatment and ozone treatment are performed on the patterned ITO substrate (ITO layer + glass layer).

[0139] 3) Spin coating PEDOT:PSS at a rotation speed of 3000 rpm for 1 minute, followed by annealing at 150° C. in air for 30 minutes to form a hole injection layer.

[0140] 4) The device was transferred to an inert environment, and a hole transport layer precursor solution was spin-coated at a rotation speed of 2000 rpm for 1 minute; then, the device was annealed at 120° C. for 10 minutes to form a hole transport layer.

[0141] 5) Spin coating a quantum dot liquid with a quantum dot content of 20 mg / mL, a rotation speed of 2000 rpm, and a spinning time of 1 minute; then annealing at 100° C. for 10 minutes to form a quantum dot light-emitting layer.

[0142] 6) Spin-coating a zinc oxide precursor solution at a rotation speed of 2000 rpm for 1 minute; then annealing at 100° C. for 10 minutes to obtain an electron transport layer.

[0143] 7) Evaporated cathode, made of aluminum with a thickness of 100 nm.

[0144] The resulting thin-film light-emitting device includes an anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode, stacked in sequence. 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 an electron-trapping material (except for the control device); the electron transport layer is made of zinc oxide; and the cathode is made of aluminum.

[0145] The control device contained no electron-trapping material in its hole transport layer. In the first verification device, the electron-trapping material accounted for 5% by weight of the hole transport layer; in the second verification device, the electron-trapping material accounted for 10% by weight of the hole transport layer; and in the third verification device, the electron-trapping material accounted for 20% by weight of the hole transport layer.

[0146] Performance tests were conducted on each of the aforementioned devices. The current density and luminance of each device were measured at different voltages, and the test results are shown in Figure 7. The current efficiency and external quantum efficiency of each device were also measured at different voltages, and the test results are shown in Figure 8. Figures 7 and 8 show that doping the hole transport layer with electron-trapping materials results in a certain efficiency loss.

[0147] The control device was tested at an initial brightness of 1000 cd / m 2 The T90 life curve under the condition of , and the voltage change curve under constant current density, the test results are shown in Figure 9. The first verification device was tested at an initial brightness of 1000cd / m 2 The T90 lifetime curve under the condition of constant current density and the voltage change curve under constant current density are shown in Figure 10. As shown in Figures 9 and 10, by doping the hole transport layer with 5% PC71BM by weight, the T90 lifetime of the device can be extended from 5.5 hours to 33 hours, significantly improving device performance. As shown in Figures 7 to 10, 5% PC71BM doping in the hole transport layer can significantly improve the stability of the hole transport layer and extend the lifetime of the thin-film light-emitting device.

[0148] The following describes the structure, materials, and preparation method of the thin-film light-emitting device in the embodiment of the present disclosure by taking multiple embodiments as examples.

[0149] Example 1

[0150] A thin-film light-emitting device includes an anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode, stacked in sequence. 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.

[0151] The thin film light emitting device can be prepared by the following method.

[0152] 1) Dissolving TFB and PCBM in chlorobenzene to obtain a hole transport layer precursor solution; the total mass concentration of TFB and PCBM in the precursor solution is 12 mg / mL; and the mass proportion of PCBM in the film-forming material (UV-1084+TFB) is 2% to 20%.

[0153] 2) UV treatment and ozone treatment are performed on the patterned ITO substrate (ITO layer + glass layer).

[0154] 3) Spin coating PEDOT:PSS at a rotation speed of 3000 rpm for 1 minute, followed by annealing at 150° C. in air for 30 minutes to form a hole injection layer.

[0155] 4) The device was transferred to an inert environment, and a hole transport layer precursor solution was spin-coated at a rotation speed of 2000 rpm for 1 minute; then, the device was annealed at 120° C. for 10 minutes to form a hole transport layer.

[0156] 5) Spin coating a quantum dot liquid with a quantum dot content of 20 mg / mL, a rotation speed of 2000 rpm, and a spinning time of 1 minute; then annealing at 100° C. for 10 minutes to form a quantum dot light-emitting layer.

[0157] 6) Spin-coating a zinc oxide precursor solution at a rotation speed of 2000 rpm for 1 minute; then annealing at 100° C. for 10 minutes to obtain an electron transport layer.

[0158] 7) Evaporated cathode, made of aluminum with a thickness of 100 nm.

[0159] Example 2

[0160] A thin-film light-emitting device includes an anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode, stacked in sequence. 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 polymers:

[0161] Wherein, x represents the number of repeating units of the TFB monomer, which is 200; y represents the number of repeating units of the cyclooctatetraene derivative monomer, which is 2.

[0162] In this example, the hole transport material and the electron trap material are cross-linked to form a polymer, so that the multifunctional polymer has a hole transport segment and an electron trap segment.

[0163] In this embodiment, a thin-film light-emitting device can be prepared by referring to the preparation method of Example 1, except that the multifunctional polymer of this embodiment is used as the film-forming material when preparing the hole transport layer precursor solution. The mass concentration of the film-forming material in the hole transport layer precursor solution is 12 mg / mL.

[0164] Example 3

[0165] The thin-film light-emitting device includes an anode, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode, stacked in sequence. In this example, the anode is made of molybdenum oxide / silver; the hole transport layer is made of CBP doped with C70; the electron transport layer is made of zinc oxide; and the cathode is made of indium tin oxide (ITO).

[0166] The structure of CBP is as follows:

[0167] The thin film light emitting device can be prepared by the following method.

[0168] 1) UV treatment and ozone treatment were performed on a patterned ITO substrate (ITO layer + glass layer).

[0169] 2) Spin coating a zinc oxide precursor solution at a rotation speed of 2000 rpm for 1 minute; and then annealing at 100° C. for 10 minutes to obtain an electron transport layer.

[0170] 3) Spin coating a quantum dot liquid, wherein the quantum dot content in the quantum dot liquid is 20 mg / mL, the rotation speed is 2000 rpm, and the rotation time is 1 minute; then annealing at 100° C. for 10 minutes to form a quantum dot light-emitting layer.

[0171] 4) A stable hole transport layer was formed by co-evaporation process. Source 1 used CBP (evaporation rate was 1 nm / min) and source 2 used C70 (evaporation rate was 0.1 nm / min), and the co-evaporation thickness was 50 nm.

[0172] 5) Evaporated cathode, the material is molybdenum oxide / silver, with a thickness of 3nm / 100nm.

[0173] Example 4

[0174] The thin-film light-emitting device includes an anode, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode, stacked in sequence. In this example, the anode is made of molybdenum oxide / silver; the hole transport layer is a mixture of CPB and C60-modified CPB; the electron transport layer is made of zinc oxide; and the cathode is made of indium tin oxide (ITO).

[0175] The structure of C60-modified CPB is as follows:

[0176] The thin film light emitting device can be prepared by the following method.

[0177] 1) UV treatment and ozone treatment were performed on a patterned ITO substrate (ITO layer + glass layer).

[0178] 2) Spin coating a zinc oxide precursor solution at a rotation speed of 2000 rpm for 1 minute; and then annealing at 100° C. for 10 minutes to obtain an electron transport layer.

[0179] 3) Spin coating a quantum dot liquid, wherein the quantum dot content in the quantum dot liquid is 20 mg / mL, the rotation speed is 2000 rpm, and the rotation time is 1 minute; then annealing at 100° C. for 10 minutes to form a quantum dot light-emitting layer.

[0180] 4) A stable hole transport layer was formed by evaporation process. The source material was a mixture of CBP and C60-modified CPB (1:1) at an evaporation rate of 1 nm / min, and a total evaporation thickness of 50 nm.

[0181] 5) Evaporated cathode, the material is molybdenum oxide / silver, with a thickness of 3nm / 100nm.

[0182] The present disclosure also provides a display panel comprising any of the thin-film light-emitting devices described in the aforementioned thin-film light-emitting device embodiments. The display panel can be a smartphone screen, a smartwatch screen, or another type of display screen. Because the display panel comprises any of the thin-film light-emitting devices described in the aforementioned thin-film light-emitting device embodiments, it exhibits the same beneficial effects and is not further detailed herein.

Claims

1. A thin film light emitting device, comprising an anode, a hole transport layer, a light emitting layer and a cathode stacked in sequence; 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 lower than the LUMO energy level of the hole transport material.

2. The thin film light emitting device according to claim 1, wherein: The LUMO energy level of the electron trap material is not less than the LUMO energy level of the light emitting layer.

3. The thin film light emitting device according to claim 1, wherein: The mass content of the electron trap material in the hole transport layer is not higher than 10%.

4. The thin film light emitting device according to claim 1, wherein: The electron mobility of the electron trap material is no greater than 1×10 -3 cm 2 V -1 s -1 .

5. The thin film light emitting device according to claim 1, wherein: The electron trap material captures electrons at a faster rate than the holes of the hole transport material capture electrons.

6. The thin film light emitting device according to claim 1, wherein: The electron trap material captures electrons faster than the rate at which excitons on the hole transport material quench with holes.

7. The thin film light emitting device according to claim 1, wherein: The electron trap material captures electrons within 1 nm faster than 10 9 / Second.

8. The thin film light emitting device according to claim 7, wherein: The electron trap material captures electrons within 2nm faster than 10 9 / Second.

9. The thin film light emitting device according to claim 1, wherein: The electron trap material that captures electrons releases electrons faster than 10 3 / Second.

10. The thin film light emitting device according to claim 1, wherein: The HOMO energy level of the electron trap material is not higher than the HOMO energy level of the hole transport material.

11. The thin film light emitting device according to any one of claims 1 to 10, wherein: Along the direction from the anode to the light-emitting layer, the mass content of the electron trap material in the hole transport layer gradually decreases.

12. The thin film light emitting device according to any one of claims 1 to 10, wherein: The hole transport layer includes a plurality of sequentially stacked sublayers; the mass content of the electron trap material in the sublayer closest to the light-emitting layer is less than the mass content of the electron trap material in the sublayer farthest from the light-emitting layer.

13. The thin film light emitting device according to any one of claims 1 to 10, wherein: The hole transport material and the electron trap material are cross-linked to form a polymer.

14. The thin film light emitting device according to any one of claims 1 to 10, wherein: The electron trap material is connected to at least a portion of the hole transport material via a chemical bond or a connecting group.

15. The thin film light emitting device according to any one of claims 1 to 10, wherein: The electron trap material includes one or more of fullerene, fullerene derivatives, small molecule semiconductor materials, and polymer semiconductor materials.

16. The thin film light emitting device according to any one of claims 1 to 10, wherein: The electron trap material is selected from the following materials:

17. The thin film light emitting device according to any one of claims 1 to 10, 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.

18. The thin film light emitting device according to any one of claims 1 to 10, wherein: The thin film light emitting device is a blue light thin film light emitting device.

19. A method for preparing a thin film light emitting device, used for preparing the thin film light emitting device according to any one of claims 1 to 12 and claims 15 to 18; the preparation method comprises preparing an anode, a hole transport layer, a light emitting layer and a cathode; The preparation of the hole transport layer comprises: Dissolving the hole transport material and the electron trap material in a solvent to obtain a precursor solution; The hole transport layer is prepared using the precursor liquid by a coating process, a screen printing process or an inkjet printing process.

20. A method for preparing a thin film light emitting device, used for preparing the thin film light emitting device according to any one of claims 1 to 13 and claims 15 to 18; the preparation method comprises preparing an anode, a hole transport layer, a light emitting layer and a cathode; The preparation of the hole transport layer comprises: The monomer of the hole transport material and the monomer of the electron trap material are polymerized together to form a multifunctional polymer; dissolving the multifunctional polymer in a solvent to obtain a precursor solution; The hole transport layer is prepared using the precursor liquid by a coating process, a screen printing process or an inkjet printing process.

21. A method for preparing a thin film light emitting device, used for preparing the thin film light emitting device according to any one of claims 1 to 12 and claims 15 to 18; the preparation method comprises preparing an anode, a hole transport layer, a light emitting layer and a cathode; The preparation of the hole transport layer comprises: The hole transport material and the electron trap material are co-evaporated to form the hole transport layer.

22. A method for preparing a thin film light emitting device, used for preparing the thin film light emitting device according to any one of claims 1 to 12 and claims 14 to 18; the preparation method comprises preparing an anode, a hole transport layer, a light emitting layer and a cathode; The preparation of the hole transport layer comprises: Synthesizing a multifunctional material, wherein the multifunctional material is a material formed by connecting the hole transport material and the electron trap material via a chemical bond or a connecting group; uniformly mixing the multifunctional material and the hole transport material to form an evaporation material; The hole transport layer is formed by using the evaporation material and an evaporation process.

23. A display panel comprising the thin film light emitting device according to any one of claims 1 to 18.

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