Quantum dot light emitting diode based on self-assembled molecular hole injection layer and preparation method and application thereof

Abstract

The invention discloses a quantum dot light emitting diode based on a self-assembled molecular hole injection layer and a preparation method and application thereof. Relates to the technical field of optoelectronic devices. The quantum dot light-emitting diode comprises an indium tin oxide substrate, 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, and the component of the hole injection layer is 4-di (N-3-benzoic acid) triphenylamine. According to the quantum dot light emitting diode, the 4-di (N-3-benzoic acid) triphenylamine (DPDA) is used as a hole injection layer component, so that the comprehensive performance of a device is remarkably improved, and the external quantum efficiency (EQE) peak efficiency of the device can reach 20.96%.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic device technology, and in particular to a quantum dot light-emitting diode based on a self-assembled molecular hole injection layer, its preparation method, and its application. Background Technology

[0002] Quantum dot light-emitting diodes (QLEDs), as a novel optoelectronic device based on quantum dot materials, exhibit excellent color purity, high luminous efficiency, and solution-processable characteristics due to their unique quantum confinement effect. They possess irreplaceable application potential in the display and lighting fields and are widely recognized as a core competitive system for next-generation display technologies. Compared to the reliance on backlight modules in traditional liquid crystal displays (LCDs) and the short lifespan of organic light-emitting diodes (OLEDs), QLEDs offer comprehensive advantages in color saturation, energy efficiency, and adaptability to flexible substrates, making them a key technological path for achieving ultra-high resolution, flexible foldable, and transparent displays. However, the efficient and stable operation of QLED devices still faces core scientific challenges: based on the inherent optical advantages of quantum dot light-emitting layers (QDs), the dynamic balance between charge injection and transport plays a decisive role in device performance. The significant imbalance between holes and electrons in injection efficiency, migration ability, and interfacial recombination characteristics directly restricts the improvement of device efficiency and the extension of lifespan.

[0003] Typical QLED devices employ a multilayer heterostructure consisting of an anode / hole injection layer / hole transport layer / quantum dot emitting layer / electron transport layer / electron injection layer / cathode. The charge injection layer acts as a "bridge" connecting the electrodes and transport layers, and its energy level structure and interface characteristics directly determine the carrier injection efficiency and device interface stability. During device operation, electrons and holes are injected from the cathode / anode respectively, migrate through the transport layer to the quantum dot emitting layer, and undergo radiative recombination. However, electrons and holes differ significantly in key parameters: electron mobility is 1-2 orders of magnitude higher than hole mobility, and the electron injection barrier is much lower than the hole injection barrier. This discrepancy leads to an imbalance in charge accumulation within the device: an excess of electrons and a deficiency of holes in the quantum dot emitting layer, triggering a triple negative effect: First, excess electrons are easily captured by defects on the quantum dot surface, forming non-radiative recombination centers, resulting in a decrease in the quantum yield of light emission; second, at high brightness, Auger recombination occurs when excess electrons recombine with holes, causing a sharp roll-off in device efficiency; third, the charge imbalance causes electric field concentration at the interface, accelerating the photo-oxidation of the quantum dot material and the degradation of transport layer molecules, leading to a decline in device lifetime. Therefore, solving the charge injection imbalance problem is the core objective for optimizing the performance of QLED devices, and the hole injection layer, as a key functional layer for regulating hole injection efficiency, plays an irreplaceable role in improving the overall performance of the device through its energy level matching and interface engineering.

[0004] To reduce the hole injection barrier and improve charge transport balance, existing technologies introduce a hole injection layer to achieve energy level transition between the anode and the hole transport layer (HTL). In traditional QLED devices, the transparent conductive anode is typically indium tin oxide (ITO), with a work function of approximately 4.7 eV, while the highest occupied molecular orbital (HOMO) energy level of commonly used hole transport materials is approximately 5.4 eV, resulting in a 0.7 eV injection barrier. According to the Richardson-Schottky hot electron emission model, for every 0.1 eV increase in barrier height, the carrier injection current density decreases by an order of magnitude. Therefore, this barrier severely restricts the effective injection of holes from ITO to the HTL. To address this issue, researchers have developed three typical hole injection material systems: The first category consists of conductive polymer materials, represented by poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). PEDOT:PSS, due to its high conductivity, tunable work function, and excellent solution processability, became the most widely used hole injection layer material in early QLED devices. Its working mechanism involves increasing the carrier concentration of PEDOT through doping with polystyrene sulfonate (PSS) and lowering the potential barrier between ITO and HTL using a surface dipole layer. The second category consists of inorganic metal oxide materials, including molybdenum trioxide (MoO3), vanadium pentoxide (V2O5), and tungsten oxide (WO3). These materials have high work functions, allowing them to form near-ohmic contacts with the HOMO level of HTL, significantly reducing the injection barrier. Simultaneously, metal oxides exhibit high chemical stability, effectively suppressing interfacial chemical reactions.

[0005] In contrast, self-assembled molecules offer a revolutionary solution for efficient hole injection layers in quantum dot light-emitting diodes (LEDs), combining superior chemical stability, simple solution processability, and high hole injection capability. These self-assembled molecules assemble on metal oxide anodes (e.g., indium tin oxide) via chemisorption-driven ordering, forming strong bonds with the oxide surface. Crucially, this bonding forms an interfacial dipole and modulates the work function of the anode, thereby minimizing the hole injection barrier. By modifying the terminal functional groups, the work function of the self-assembled molecule hole injection layer can be tuned to optimize hole injection from the hole injection layer to the hole transport layer. Based on these advantages and their proven performance in optoelectronic devices such as solar cells, advanced self-assembled molecule variants represent candidates for efficient hole injection layers in quantum dot LEDs.

[0006] While existing hole injection materials have improved the charge injection balance of QLED devices to some extent, their inherent limitations still restrict further performance enhancements: conductive polymer materials (such as PEDOT:PSS) exhibit significant chemical instability. PEDOT:PSS aqueous solutions are strongly acidic (pH=1-2), and during device fabrication and long-term use, the acidic PSS components easily diffuse to the ITO anode, leading to corrosion of the indium oxide layer on the ITO surface and increasing the anode sheet resistance. Simultaneously, the strong hygroscopic nature of PSS can cause interfacial delamination in humid environments, resulting in increased leakage current and ultimately shortened device lifespan. Furthermore, the work function tuning range of PEDOT:PSS is limited, making it difficult to match novel HTL materials with deep HOMO energy levels.

[0007] Inorganic metal oxide materials suffer from poor process compatibility. These materials typically require vacuum thermal evaporation or magnetron sputtering, which is incompatible with QLED solution processing techniques, increasing equipment costs and process complexity. Furthermore, the crystallinity of metal oxide films is difficult to control; for example, vapor-deposited MoO3 tends to form polycrystalline structures with surface roughness reaching 2-3 nm, leading to poor contact with the HTL interface, forming interface trap states that capture hole carriers and trigger nonradiative recombination. In addition, some metal oxides (such as V₂O₅) possess strong oxidizing properties and can undergo electron transfer reactions with HTL materials (such as NPB) to generate V₂O₅. 4+ The interaction with NPB cation radicals leads to a decrease in the conductivity of the HTL layer and an increase in the device turn-on voltage.

[0008] The hole transport performance and stability of self-assembled molecular materials (such as TCTA and α-NPD) still need optimization. Existing small-molecule hole injection materials generally have low hole mobility, lower than electron transport materials, leading to charge transport imbalance within the device and an efficiency roll-off exceeding 30% at high brightness. Simultaneously, small-molecule materials exhibit poor thermal stability, easily crystallizing during device operation, resulting in film morphology damage (needle-like crystals on the surface) and increased interfacial resistance. Furthermore, existing small-molecule materials lack sufficient solution processability, with most requiring vacuum evaporation, limiting their application in large-area flexible devices.

[0009] In summary, the shortcomings of existing hole injection materials in terms of chemical stability, process compatibility, or charge transport performance make it difficult for QLED devices to simultaneously achieve the comprehensive goals of high efficiency, high brightness, and long lifetime. Therefore, developing novel hole injection materials that combine precise energy level control, high mobility, solution processability, and interfacial stability has become crucial to overcoming the performance bottlenecks of QLED devices. Self-assembled molecular materials are considered the most promising solution due to their molecular design flexibility and energy level control potential; however, the current systems still have shortcomings in improving mobility, optimizing stability, and adapting to solution processing, requiring breakthroughs through molecular structure innovation and interface engineering strategies. Summary of the Invention

[0010] The purpose of this invention is to provide a quantum dot light-emitting diode with hole-injection components that combine high-efficiency charge injection, solution processability, and stability.

[0011] The first aspect of the present invention is: A quantum dot light-emitting diode is provided.

[0012] The second aspect of the present invention is: A method for fabricating quantum dot light-emitting diodes is provided.

[0013] The third aspect of the present invention is: Applications of quantum dot light-emitting diodes.

[0014] Specifically, the technical solution adopted according to the first aspect of the present invention is as follows: A quantum dot light-emitting diode includes an indium tin oxide substrate, 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. The hole injection layer is composed of 4-bis(N-3-benzoic acid)triphenylamine, and the hole transport layer is composed of at least one of N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine, poly(N-vinylcarbazole), and poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl).

[0015] According to embodiments of the present invention, one of the technical solutions has at least one of the following advantages or beneficial effects: The quantum dot light-emitting diode of this invention significantly improves the overall performance of the device by using 4-bis(N-3-benzoic acid)triphenylamine (DPDA) as the hole injection layer component, enabling the device to achieve a peak external quantum efficiency (EQE) of 20.96%, which is 75.1% higher than the structure without a hole injection layer. The maximum brightness reaches 38,560 cd / m², and the turn-on voltage is reduced from 5 V to 3 V. At the same time, it maintains stable efficiency output at high brightness (above 5,000 cd / m²), effectively alleviating the efficiency roll-off problem of traditional devices.

[0016] The reason is that the HOMO level of DPDA (-5.2 eV) lies between the HOMO level of indium tin oxide (ITO) substrates (approximately -4.7 eV) and the hole transport layer components (such as poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl) (TFB, HOMO level -5.3 eV), poly(N-vinylcarbazole) (PVK, HOMO level -5.8 eV), N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB, HOMO level -5.4 eV), forming a stepped energy level arrangement, which reduces the hole injection barrier from 0.7 eV in the traditional structure to 0.3 eV). Below eV, it promotes efficient hole injection; the triphenylamine group in the molecule has a high hole mobility, which can balance the electron-hole transport rate (the electron mobility is usually 1-2 orders of magnitude higher than that of the hole) and reduce the formation of non-radiative recombination centers in the quantum dot emitting layer; the benzoic acid group passivates the interface defect state and inhibits exciton quenching by forming hydrogen bonds with the hydroxyl groups on the ITO surface.

[0017] According to one embodiment of the present invention, the thickness of the indium tin oxide substrate is 70-75 nm.

[0018] According to one embodiment of the present invention, the thickness of the hole injection layer is 40-45 nm.

[0019] According to one embodiment of the present invention, the thickness of the hole transport layer is 30-35 nm.

[0020] According to one embodiment of the present invention, the thickness of the quantum dot light-emitting layer is 20-25 nm.

[0021] According to one embodiment of the present invention, the thickness of the electron transport layer is 40-45 nm.

[0022] According to one embodiment of the present invention, the hole transport layer is composed of poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl) or poly(N-vinylcarbazole).

[0023] According to one embodiment of the present invention, the indium tin oxide substrate is the anode of a quantum dot light-emitting diode.

[0024] According to one embodiment of the present invention, the quantum dot luminescent layer is composed of CdZnSe / ZnSeS / CdZnS core-shell quantum dots. Using core-shell quantum dots improves luminescence efficiency and stability; furthermore, the CdZnS shell can passivate surface defects of the quantum dots, reduce non-radiative recombination, and broaden the luminescence spectrum coverage.

[0025] According to one embodiment of the present invention, the electron transport layer is composed of ZnO. The electron mobility of ZnO is ~60 cm⁻¹. 2 The / V·s) is matched with the hole mobility of the DPDA to avoid efficiency roll-off caused by excessive electron injection.

[0026] Specifically, the technical solution adopted according to the second aspect of the present invention is as follows: A method for preparing the quantum dot light-emitting diode includes the following steps: A hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode are sequentially deposited on the surface of an indium tin oxide substrate to obtain the quantum dot light-emitting diode.

[0027] According to one embodiment of the present invention, the method further includes a pretreatment step of the indium tin oxide substrate, wherein the pretreatment is ultraviolet-ozone treatment for 5-20 min. Ultraviolet-ozone pretreatment can introduce -OH groups onto the indium tin oxide substrate, increasing the surface work function of ITO and reducing the implantation barrier of DPDA.

[0028] According to one embodiment of the present invention, the hole injection layer is prepared by processing a solution containing 4-bis(N-3-benzoic acid)triphenylamine, wherein the concentration of the 4-bis(N-3-benzoic acid)triphenylamine solution is 0.01-0.2 mmol / mL. At a concentration of 0.01-0.1 mmol / mL, DPDA molecules form conductive channels through π-π stacking; concentrations exceeding 0.1 mmol / mL lead to increased interface defects due to molecular aggregation, while concentrations below 0.01 mmol / mL are too low to achieve the desired effect. Preferably, the concentration of the 4-bis(N-3-benzoic acid)triphenylamine solution is 0.05-0.1 mmol / mL. At 0.1 mmol / mL, the interfacial contact resistance between DPDA and adjacent layers is minimized, and the carrier injection balance is maximized.

[0029] According to one embodiment of the present invention, the hole injection layer is prepared by spin coating process, with a spin coating speed of 2000-4000 rpm and a spin coating time of 20-40 s.

[0030] According to one embodiment of the present invention, after spin coating, the process further includes an annealing step of the hole injection layer, wherein the annealing temperature is 60-120°C.

[0031] According to one embodiment of the present invention, the annealing time is 5-10 min. Annealing can remove solvent residue and improve the crystallinity of the DPDA film.

[0032] Another aspect of the present invention provides a display device, comprising a quantum dot light-emitting diode as described in the first aspect embodiment above. Since this application employs all the technical solutions of the aforementioned quantum dot light-emitting diode, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments.

[0033] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the discovery. Attached Figure Description

[0034] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the molecular structure of 4-bis(N-3-benzoic acid)triphenylamine.

[0035] Figure 2 This is a schematic diagram of the quantum dot light-emitting diode of Example 1.

[0036] Figure 3Electroluminescence test images of the quantum dot light-emitting diodes prepared in Example 1 and the comparative example.

[0037] Figure 4 The current density-voltage-brightness characteristics of the quantum dot light-emitting diodes prepared in Example 1 and the comparative example are shown in the test graph.

[0038] Figure 5 The current efficiency-brightness characteristics of the quantum dot light-emitting diodes prepared in Example 1 and the comparative example are shown in the test graph.

[0039] Figure 6 The current efficiency-brightness characteristics of the quantum dot light-emitting diodes prepared in Examples 1-4 are shown in the test graphs.

[0040] Figure 7 The external quantum efficiency-luminance characteristics of the quantum dot light-emitting diodes prepared in Example 1 and the comparative example are shown in the test graph.

[0041] Figure 8 The external quantum efficiency-luminance characteristics of the quantum dot light-emitting diodes prepared in Examples 1-4 are shown in the test diagram.

[0042] Figure 9 External quantum efficiency-luminance characteristics test diagrams for quantum dot light-emitting diodes prepared in Examples 1 and 5. Detailed Implementation

[0043] The terms "preferred," "more preferred," etc., used in this invention refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this invention.

[0044] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of the present invention.

[0046] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0047] In this embodiment, the indium tin oxide substrate of the quantum dot light-emitting diode has a thickness of 70 nm, the hole injection layer has a thickness of 40 nm, the hole transport layer has a thickness of 30 nm, the quantum dot light-emitting layer has a thickness of 20 nm, and the electron transport layer has a thickness of 40 nm.

[0048] Example 1 A quantum dot light-emitting diode, the structural schematic diagram of which is shown below. Figure 2 As shown, the quantum dot light-emitting diode consists of an indium tin oxide substrate, 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.

[0049] The component of the aforementioned hole injection layer is 4-bis(N-3-benzoic acid)triphenylamine (DPDA), and its molecular structure diagram is shown below. Figure 1 As shown.

[0050] The hole transport layer described above is composed of poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl) (TFB, CAS 223569-31-1).

[0051] The composition of the aforementioned quantum dot luminescent layer is CdZnSe / ZnSeS / CdZnS core-shell quantum dots (QDR).

[0052] The electron transport layer described above is composed of ZnO.

[0053] A method for preparing the above-mentioned quantum dot light-emitting diode includes the following steps: S1 uses laser marking to etch a transparent indium tin oxide (ITO) conductive glass substrate into the desired shape. Then, it is placed in a beaker containing detergent / acetone / ethanol for ultrasonic cleaning for 1-2 hours, and then placed in a beaker containing deionized water for cleaning 4 times, 10 minutes each time. The treated indium tin oxide substrate is placed on a heating stage to dry the moisture and then subjected to ultraviolet-ozone treatment for 10 minutes. S2 dissolved the self-assembled molecule DPDA in dimethyl sulfoxide (DMSO) to obtain a DPDA solution with a concentration of 0.1 mmol / mL; dissolved TFB in chlorobenzene (CB) to obtain a TFB solution with a concentration of 8 mg / mL; dissolved QDR in n-octane solution to obtain a QDR quantum dot solution with a concentration of 15 mg / mL; and dissolved ZnO particles in anhydrous ethanol to obtain a ZnO solution with a concentration of 20 mg / mL. S3 Preparation of hole injection layer: 0.1 mmol / mL DPDA solution was spin-coated onto an indium tin oxide substrate using a spin coater at a speed of 3000 rpm for 30 s. Immediately after spin coating, annealing was performed at a temperature of 120℃ for 10 min. S4 Preparation of hole transport layer: 8 mg / mL TFB solution prepared with chlorobenzene was spin-coated onto the hole injection layer using a spin coater at a speed of 3000 rpm for 30 s. After spin coating, annealing was performed immediately at a temperature of 120℃ for 10 min. S5 was used to prepare the quantum dot light-emitting layer. A 15 mg / mL QDR solution prepared with n-octane was spin-coated onto the hole transport layer using a spin coater. The spin-coating speed was 3000 rpm and the spin-coating time was 30 s. Immediately after spin-coating, the layer was annealed at 60℃ for 5 min. S6 Preparation of electron transport layer: A 20 mg / mL ZnO solution prepared with anhydrous ethanol was spin-coated onto the quantum dot light-emitting layer using a spin coater. The spin-coating speed was 3000 rpm and the spin-coating time was 30 s. After spin-coating, annealing was performed immediately at a temperature of 60 ℃ for 10 min. S7 Preparation of Metal Cathode: A 120nm Al electrode is deposited on the electron transport layer using a thermal evaporation machine to obtain a quantum dot light-emitting diode.

[0054] A light-emitting device, the preparation method of which is as follows: The quantum dot light-emitting diodes described above are encapsulated with a glass sheet to obtain the light-emitting device described above.

[0055] Example 2 The difference between Example 2 and Example 1 is that the concentration of the DPDA solution in Example 2 is 0.2 mmol / mL.

[0056] Example 3 The difference between Example 3 and Example 1 is that the concentration of the DPDA solution in Example 3 is 0.05 mmol / mL.

[0057] Example 4 The difference between Example 4 and Example 1 is that the concentration of the DPDA solution in Example 4 is 0.01 mmol / mL.

[0058] Example 5 The difference between Example 5 and Example 1 is that the hole transport layer in the quantum dot light-emitting diode in Example 5 is composed of poly(N-vinylcarbazole) (PVK).

[0059] Comparative Example The difference between the comparative example and Example 1 is that the quantum dot light-emitting diode in the comparative example does not contain a hole injection layer.

[0060] Performance testing: The quantum dot light-emitting diodes prepared in Example 1 and the comparative example were subjected to electroluminescence testing. The test results are as follows: Figure 3 As shown. From Figure 3 It is known that the electroluminescence spectra of the two sets of devices (the quantum dot light-emitting diode of Example 1 (containing a DPDA hole injection layer) and the comparative quantum dot light-emitting diode (without a DPDA hole injection layer)) did not show significant differences in emission peak position and full width at half maximum (FWHM) parameters. After introducing the self-assembled molecule DPDA as a hole injection layer, the spectral characteristic peak position of the quantum dot light-emitting diode of Example 1 did not shift, and the FWHM value remained constant. Therefore, Figure 3 The electroluminescence test results show that the introduction of the DPDA hole injection layer does not change the intrinsic luminescence characteristics of the quantum dot light-emitting layer. Based on this, it can be inferred that no new light-emitting centers or energy transfer paths are generated during the operation of the quantum dot light-emitting diode.

[0061] The quantum dot light-emitting diodes prepared in Example 1 and the comparative example were subjected to current density-voltage-brightness characteristic tests. The test results are as follows: Figure 4 As shown. From Figure 4 It is known that, under the same driving voltage conditions, the brightness of the quantum dot light-emitting diode (including the DPDA hole injection layer) in Example 1 is significantly improved (maximum brightness reaches 38560 cd / m²). 2 The current density increases accordingly, indicating that the introduction of the DPDA hole injection layer effectively optimizes the carrier injection balance; while the comparative quantum dot light-emitting diode, lacking a hole injection layer, has a significantly reduced brightness (maximum brightness reaches 6809 cd / m²). 2 From an application perspective, the quantum dot light-emitting diode of Example 1 achieves high brightness output characteristics while maintaining a compact device structure, meeting the technical requirements of the micro-display field for high-efficiency devices. Further analysis revealed that the turn-on voltage of the quantum dot light-emitting diode of Example 1 (defined as the device's luminous intensity reaching 1 cd / m²) is... 2 The driving voltage (at that time) is reduced to 3 V, while the turn-on voltage of the comparative quantum dot light-emitting diode is 5 V. This improvement in electrical performance stems from the optimized energy level matching between the DPDA molecule and the adjacent functional layer. Its HOMO energy level and the valence band of the quantum dot light-emitting layer form a stepped energy level arrangement, effectively reducing the hole injection barrier.

[0062] The quantum dot light-emitting diodes prepared in Example 1 and the comparative example were subjected to current efficiency-luminance characteristic tests, and the test results are as follows: Figure 5 As shown. Test results indicate that in the low-brightness region (1~100 cd / m²), 2Both types of quantum dot LEDs exhibited a non-linear increase in current efficiency with increasing brightness. The highest current efficiency of the quantum dot LED in Example 1 reached 28.78 cd / A, a significant improvement over the comparative example (16.48 cd / A). When the brightness reached the high-brightness region (1000~10000 cd / m²), the efficiency remained high. 2 At 5000 cd / m², the efficiency degradation rate of Example 1 was significantly lower than that of the comparative example, especially at 5000 cd / m². 2 In the high-brightness range described above, a significant efficiency roll-off phenomenon is observed in the comparative example. Furthermore, the quantum dot LED of Example 1 maintains superior efficiency stability across the entire brightness range. This performance difference stems from the optimization effect of the DPDA hole injection layer on the device's electrical characteristics. Therefore, the introduction of self-assembled DPDA molecules as a hole injection layer not only significantly improves the device's current efficiency but also achieves enhanced efficiency stability at high brightness levels through energy level engineering optimization, providing a feasible solution for extending the operating life of QLED devices.

[0063] The quantum dot light-emitting diodes prepared in Examples 1-4 were used to test their current efficiency and brightness characteristics. The test results are as follows: Figure 6As shown in the figure, the curve with 0.1 mmol / mL corresponds to Example 1 (0.1 mmol / mL DPDA), the curve with 0.2 mmol / mL corresponds to Example 2 (0.2 mmol / mL DPDA), the curve with 0.05 mmol / mL corresponds to Example 3 (0.05 mmol / mL DPDA), and the curve with 0.01 mmol / mL corresponds to Example 4 (0.01 mmol / mL DPDA). The test results show that within the concentration range of 0.01~0.1 mmol / mL, the peak current efficiency of the quantum dot LED device exhibits a non-monotonic change with increasing DPDA concentration. The test results show that the peak efficiency of Example 4 (0.01 mmol / mL) is 23.09 cd / A, Example 3 (0.05 mmol / mL) increases to 24.55 cd / A, and Example 1 (0.1 mmol / mL) reaches the optimal value of 28.87 cd / A. However, when the DPDA concentration was further increased to 0.2 mmol / mL (Example 2), the peak efficiency significantly decreased to 17.52 cd / A. Efficiency-concentration analysis showed that within the 0.01–0.1 mmol / mL range, increasing the DPDA concentration effectively optimized the interfacial contact characteristics between the hole injection layer and the quantum dot emitting layer. DPDA molecules at appropriate concentrations (0.05–0.1 mmol / mL) formed continuous conductive channels through π-π stacking, reducing the hole injection barrier. Furthermore, when the DPDA concentration exceeded 0.1 mmol / mL, the device performance exhibited a sharp decline. This anomaly stemmed from the molecular aggregation effect caused by high concentrations; excessive DPDA molecules formed cluster structures, disrupting the uniformity of the interfacial layer; or excessive hole injection led to carrier injection imbalance, exacerbating the Auger recombination process. Therefore, at a DPDA concentration of 0.1 mmol / mL, the device achieved optimal carrier transport balance and recombination efficiency matching, resulting in improved current efficiency compared to other concentration groups. The experimental results confirm that DPDA concentration regulation has a dual effect on the performance of QLED devices: an appropriate concentration optimizes the interfacial electrical properties, while an excessive concentration induces a negative aggregation effect, providing experimental basis for optimizing the concentration of hole injection layer materials.

[0064] The quantum dot light-emitting diodes prepared in Example 1 and the comparative example were subjected to external quantum efficiency-luminosity characteristic tests. The test results are as follows: Figure 7 As shown. Test results indicate that within the range of 100~1000 cd / m³ 2 In the mid-to-high brightness range, the external quantum efficiency (EQE) of the quantum dot light-emitting diode in Example 1 exhibits a significant advantage, with a peak efficiency of 20.96%, a 75.1% improvement compared to the comparative example (11.97%). This is particularly evident at approximately 5000 cd / m². 2At operating brightness, the EQE of Example 1 is significantly better than that of the comparative example, and no obvious efficiency roll-off phenomenon is observed. Efficiency characteristic analysis shows that the EQE advantage of Example 1 stems from the optimization of the device's electrical characteristics by the DPDA hole injection layer. Theoretically, firstly, DPDA molecules form a stepped energy level arrangement with the quantum dot valence band through their HOMO energy levels, reducing the hole injection barrier and effectively alleviating the problem of insufficient hole injection. Secondly, the transport characteristics of the DPDA layer achieve carrier mobility matching, improving the carrier balance within the device. Finally, the interface dipole modulation between the light-emitting layer and the DPDA layer reduces the surface defect state density of the quantum dot layer, lowering the nonradiative recombination rate. Test results show that the comparative quantum dot light-emitting diode, lacking a hole injection layer, exhibits typical efficiency decay characteristics in its test curve, reaching approximately 5000 cd / m². 2 After reaching a certain brightness, the EQE (Electrical Quenching Effect) decreases sharply, attributed to carrier injection imbalance caused by restricted hole injection and exciton quenching induced by interface defect states. Therefore, the introduction of a DPDA (Dielectric Power Distribution Amplifier) ​​hole injection layer, through mechanisms such as energy level engineering, carrier dynamics modulation, and interface defect passivation, enables the device to operate at 100–10000 cd / m². 2 The external quantum efficiency under brightness was significantly improved.

[0065] The quantum dot light-emitting diodes prepared in Examples 1-4 were subjected to external quantum efficiency-luminosity characteristic tests, and the test results are as follows: Figure 8 As shown in the figure, the curve with 0.1 mmol / mL corresponds to Example 1 (0.1 mmol / mL DPDA), the curve with 0.2 mmol / mL corresponds to Example 2 (0.2 mmol / mL DPDA), the curve with 0.05 mmol / mL corresponds to Example 3 (0.05 mmol / mL DPDA), and the curve with 0.01 mmol / mL corresponds to Example 4 (0.01 mmol / mL DPDA). The test results show that the EQE of the quantum dot LED device in Example 1 reaches a peak of 20.96%, significantly better than that in Example 4 (16.18%) and Example 3 (17.33%). Concentration effect analysis shows that DPDA concentration has a dual regulatory effect on device efficiency. Within the concentration range of 0.01~0.1 mmol / mL, EQE increases monotonically with increasing concentration. Example 1 shows a significant improvement in efficiency compared to Example 4. When the DPDA concentration exceeds 0.1 mmol / mL, the device performance exhibits an inflection point decline.

[0066] The quantum dot light-emitting diodes prepared in Examples 1 and 5 were subjected to external quantum efficiency-luminosity characteristic tests. The test results are as follows: Figure 9As shown. The test results show that the quantum dot light-emitting diode (LED) fabricated using PVK as a component of the hole transport layer (Example 5) has a maximum external quantum efficiency of only 12.65%, which is much lower than that of the quantum dot LED fabricated using PVK as a component of the hole transport layer (maximum external quantum efficiency of 20.96%, Example 1). This indicates that although both PVK and TFB can be used as components of the hole transport layer, combining TFB with DPDA, a component of the hole injection layer, has more advantages. The reasons are twofold. First, TFB and DPDA have better energy level matching. The HOMO level of TFB (-5.3 eV) and the HOMO level of DPDA (-5.2 eV) form a stepped energy level structure, with an injection barrier of only 0.1 eV, allowing holes to be efficiently injected into the hole transport layer through thermal excitation. In contrast, the HOMO level of PVK is higher (-5.8 eV), forming a larger barrier of 0.5 eV with DPDA, which hinders hole injection and causes a large number of charge carriers to accumulate at the interface, forming nonradiative recombination centers. Second, the fluorene units in the TFB molecular chain have a good planar conjugated structure, which can form a continuous conductive channel with the triphenylamine group of DPDA through π-π stacking. The carbazole group in the PVK molecule has greater steric hindrance and is prone to forming disordered stacking during film formation.

[0067] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A quantum dot light-emitting diode, characterized in that: The device comprises an indium tin oxide substrate, 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. The hole injection layer is composed of 4-bis(N-3-benzoic acid)triphenylamine, and the hole transport layer is composed of at least one of N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine, poly(N-vinylcarbazole), and poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl).

2. The quantum dot light-emitting diode according to claim 1, characterized in that: The hole transport layer is composed of poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl) or poly(N-vinylcarbazole).

3. The quantum dot light-emitting diode according to claim 1, characterized in that: The quantum dot luminescent layer is composed of CdZnSe / ZnSeS / CdZnS core-shell structured quantum dots.

4. The quantum dot light-emitting diode according to claim 1, characterized in that: The electron transport layer is composed of ZnO.

5. A method for preparing a quantum dot light-emitting diode as described in any one of claims 1 to 4, characterized in that: Includes the following steps: A hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode are sequentially deposited on the surface of an indium tin oxide substrate to obtain the quantum dot light-emitting diode.

6. The method according to claim 5, characterized in that: It also includes a step of pretreating the indium tin oxide substrate, wherein the pretreating is ultraviolet-ozone treatment for 5-20 min.

7. The method according to claim 5, characterized in that: The hole injection layer is prepared by processing a solution containing 4-bis(N-3-benzoic acid)triphenylamine, wherein the concentration of the 4-bis(N-3-benzoic acid)triphenylamine solution is 0.01-0.2 mmol / mL.

8. The method according to claim 7, characterized in that: The hole injection layer is prepared by spin coating, with a spin coating speed of 2000-4000 rpm and a spin coating time of 20-40 s.

9. The method according to claim 8, characterized in that: After spin coating, the process further includes an annealing step for the hole injection layer, wherein the annealing temperature is 60-120℃.

10. A display device, characterized in that: Including the quantum dot light-emitting diode as described in any one of claims 1 to 4.

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