Hybrid white organic light-emitting diode based on solution processing and preparation method thereof

Abstract

The invention relates to the technical field of organic light-emitting devices, in particular to a hybrid white-light organic light-emitting diode based on solution processing and a preparation method thereof.The device sequentially comprises an ITO glass substrate, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer and a cathode, the luminescent layer is composed of high triplet state energy level double host materials mCBP and DPEPO, a blue light TADF object, a green light phosphorescence or TADF object, and a red light fluorescence or phosphorescence object, chlorobenzene is used as a solvent for solution processing, and the luminescent layer is prepared through a spin coating technology. The method comprises the steps of ITO substrate cleaning, spin coating of functional layers, high-temperature annealing treatment and vacuum evaporation of an electron transport layer, an electron injection layer and a cathode, high external quantum efficiency, low efficiency roll-off, high color rendering index and stable white light emission are achieved by optimizing material selection and the technological process, and the method has remarkable technical advantages and wide application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of organic electroluminescent devices, in particular to a hybrid white light organic light emitting diode based on solution processing and a preparation method thereof. Background Art

[0002] As a new generation of planar light source technology, white organic light-emitting diodes have become a core research direction in the field of full-color display and solid-state lighting due to their self-luminescence, low power consumption and flexible bendability. Although vacuum-evaporated WOLEDs devices have excellent performance, their high cost and low material utilization have seriously hindered the widespread application of the technology. In contrast, the low-cost and simple preparation process of solution processing technology can meet the production needs of large-scale and promote the industrialization of WOLEDs devices. However, white organic light-emitting diodes (S-WOLEDs) prepared by solution method usually adopt a multi-doped single-light-emitting layer structure. Due to multiple factors such as solvent limitations, film quality and charge carrier aggregation at the interface, the development of efficient and stable WOLEDs is hindered. Summary of the Invention

[0003] (1) Technical problems solved

[0004] In view of the deficiencies in the prior art, the present invention provides a hybrid white organic light emitting diode based on solution processing and a preparation method thereof.

[0005] (2) Technical solution

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A hybrid white light organic light-emitting diode based on solution processing of the present invention comprises an ITO glass substrate, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer and a cathode arranged in sequence; the light-emitting layer is composed of a dual host material and a three-color light-emitting guest, and the three-color light-emitting guest comprises a blue light TADF guest, a green light phosphorescent or TADF guest, and a red light fluorescent or phosphorescent guest.

[0007] Preferably, the dual host system includes high triplet energy level mCBP and DPEPO as host materials in a mass ratio of 1:1.

[0008] Further preferably, the blue light TADF guest is DMAC-DPS with a doping concentration of 20 wt%; the green light emitting guest is the TADF material 4CzIPN or the phosphorescent material Ir(ppy)2(acac) with a doping concentration of 0.5 wt%; and the red light emitting guest is the fluorescent material DBP or the phosphorescent material RD071 with a doping concentration of 0.2 wt%.

[0009] Again preferably, the hole injection layer is PEDOT:PSS with a thickness of 30-50 nm; the hole transport layer is PVK with a thickness of 50-80 nm; the electron transport layer is TmPyPb with a thickness of 40-60 nm; the electron injection layer is Liq with a thickness of 1-3 nm; and the cathode is metallic aluminum with a thickness of 100-150 nm.

[0010] Preferably, the light-emitting layer is solution-processed using chlorobenzene as a solvent, and the hole transport layer and the light-emitting layer are both prepared by spin coating, wherein the hole transport layer is spin-coated with a 7 mg ml-1 PVK chlorobenzene solution at 4000 rpm, and the light-emitting layer is spin-coated with a 10 mg ml-1 light-emitting layer chlorobenzene solution at 2000 rpm.

[0011] Further preferably, the triplet energy level of the dual host material mCBP is 2.7 eV, the triplet energy level of DPEPO is 2.8 eV, and the triplet energy level of the blue light TADF material DMAC-DPS is 2.6 eV, which have a high reverse intersystem crossing rate.

[0012] Preferably, a method for preparing a hybrid white organic light-emitting diode based on solution processing comprises the following steps:

[0013] (a) ITO substrate cleaning and surface ozone treatment;

[0014] (b) sequentially spin-coating a hole injection layer, a hole transport layer, and a light-emitting layer on the treated substrate;

[0015] (c) placing the substrate on a high-temperature annealing table for annealing;

[0016] (d) sequentially depositing an electron transport layer, an electron injection layer, and a cathode under a vacuum environment;

[0017] (e) Encapsulate the device.

[0018] Further preferably, in the step (b), the hole injection layer is a PEDOT:PSS aqueous solution, which is filtered through a 0.45 μm filter and then spin-coated on the substrate at a spin-coating speed of 4000 rpm for 30 seconds.

[0019] Again preferably, in the step (c), when the hole transport layer is prepared, the annealing temperature is 150° C. and the time is 30 min; when the hole injection layer is prepared, the annealing temperature is 100° C. and the time is 20 min.

[0020] Preferably, in step (d), the electron transport layer is The rate of evaporation is 40nm, and the electron injection layer is The rate of evaporation is 2nm, and the cathode is The deposition rate was 120 nm.

[0021] (3) Beneficial effects

[0022] Compared with the prior art, the present invention provides a hybrid white organic light-emitting diode based on solution processing and a preparation method thereof, which has the following beneficial effects:

[0023] Efficient and stable white-light emission: The dual-host materials, mCBP and DPEPO, with high triplet energy levels, are combined with the blue TADF guest DMAC-DPS, the green phosphorescent or TADF guest 4CzIPN / Ir(ppy)2(acac), and the red fluorescent or phosphorescent guest DBP / RD071 to create a highly efficient energy transfer pathway. This design not only improves exciton utilization but also achieves a high color rendering index (CRI>80) and stable white-light emission.

[0024] High external quantum efficiency and low efficiency roll-off: The blue TADF material DMAC-DPS has a high reverse intersystem crossing rate (K RISC ), can effectively utilize singlet and triplet excitons, thereby significantly improving the external quantum efficiency (EQE) of the device. Experimental results show that the maximum EQE can reach 17.2% at 3000cd / m 2 The EQE of 15.2% is still maintained at low brightness, showing a lower efficiency roll-off.

[0025] Simple solution processing: The luminescent layer is solution-processed using chlorobenzene as the solvent, and the hole transport layer and luminescent layer are prepared by spin coating, ensuring film quality and uniformity. Compared to traditional vacuum evaporation technology, solution processing offers advantages such as low cost and ease of large-scale fabrication, significantly reducing production costs and complexity.

[0026] Excellent carrier balance and stability: Through the rational design of each functional layer (such as PEDOT:PSS as a hole injection layer, PVK as a hole transport layer, TmPyPB as an electron transport layer, etc.), good carrier balance is achieved, the quenching of excitons at the interface is reduced, and the overall stability and service life of the device are improved.

[0027] Modular structural design and convenient operation process: The preparation method of this invention includes steps such as ITO substrate cleaning, spin coating of various functional layers, high-temperature annealing, and vacuum evaporation of the electron transport layer, electron injection layer, and cathode. It is simple to operate and highly reproducible. In particular, precise control of annealing temperature and time further improves the crystallinity and stability of the film.

[0028] Broad Applicability and Application Prospects: This invention is suitable for a variety of display and lighting applications, particularly in full-color displays and solid-state lighting. Its high efficiency, low cost, and excellent color reproduction make it an ideal choice for future smart displays and energy-efficient lighting. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the structure of the layers of the present invention arranged in sequence and the main materials of the light-emitting layer.

[0030] Figure 2 1 is a current density-voltage-brightness characteristic curve of the present invention.

[0031] Figure 3 This is a current efficiency-current density-power efficiency characteristic curve of the present invention.

[0032] Figure 4 This is a graph showing the external quantum efficiency-current density characteristic of the present invention.

[0033] Figure 5 The light emitting layer of the present invention adopts (W1) material at 1000 cd m -2 , 2000cd m -2 and 3000cd m -2 Electroluminescence spectrum at brightness.

[0034] Figure 6 The light emitting layer of the present invention adopts (W2) material at 1000cd m -2 , 2000cd m -2 and 3000cd m -2 Electroluminescence spectrum at brightness; DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] See also Figure 1-3 The present invention provides a hybrid white light organic light emitting diode based on solution processing, comprising an ITO glass substrate, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer and a cathode arranged in sequence; the light emitting layer is composed of a dual host material and a three-color light emitting guest, and the three-color light emitting guest includes a blue light TADF guest, a green light phosphorescent or TADF guest, and a red light fluorescent or phosphorescent guest.

[0037] This technical solution provides a solution-processed hybrid white organic light-emitting diode (S-WOLED). Its core lies in the design of a dual-host system and a three-color luminescent guest to achieve efficient and stable white light emission. The following is the working principle of each component:

[0038] ITO glass substrate: acts as a transparent conductive layer, providing a current input path.

[0039] Hole injection layer (PEDOT:PSS): Improves the injection efficiency of holes from the ITO electrode to the hole transport layer and reduces the interface barrier.

[0040] Hole transport layer (PVK): effectively transports holes to the light-emitting layer, balances the carrier concentration, and prevents exciton quenching at the interface.

[0041] Luminous layer:

[0042] Dual host material (mCBP:DPEPO): Using mCBP and DPEPO with high triplet energy levels as host materials, a single light-emitting layer is formed through physical mixing. This dual host strategy helps balance carrier transport and broaden the exciton distribution area.

[0043] Three-color luminescent objects:

[0044] The blue-light TADF guest DMAC-DPS has a high reverse intersystem crossing rate (K RISC ), which can effectively utilize singlet and triplet excitons to improve luminescence efficiency.

[0045] Green phosphorescent or TADF guests (such as 4CzIPN or Ir(ppy)2(acac)) and red fluorescent or phosphorescent guests (such as DBP or RD071) are responsible for the emission of green and red light, respectively, and together construct white light emission with a full color range.

[0046] Electron transport layer (TmPyPB): promotes the transfer of electrons to the light-emitting layer while suppressing the leakage of electrons to the hole transport layer, further optimizing the carrier balance.

[0047] Electron injection layer (Liq): reduces the interface barrier between the cathode and the electron transport layer and improves the electron injection efficiency.

[0048] Cathode (metal aluminum): acts as a reflective electrode to enhance light output coupling.

[0049] Principle of synergy of dual-agent system

[0050] Carrier balance mechanism:

[0051] The host material, mCBP (triplet energy level = 2.7eV), has excellent hole transport capabilities, while DPEPO (triplet energy level = 2.8eV) excels at electron transport. The two, in a 1:1 mass ratio, form a complementary network. The highest occupied molecular orbital (HOMO) of mCBP matches the hole transport layer, PVK, while the lowest unoccupied molecular orbital (LUMO) of DPEPO matches the electron transport layer, TmPyPb. This creates a uniform carrier distribution within the luminescent layer, broadening the exciton recombination zone to the center of the luminescent layer and preventing efficiency roll-off caused by charge accumulation at the interface.

[0052] Energy level matching mechanism:

[0053] The high triplet energy level of the dual host (triplet energy level > 2.6 eV) is higher than that of the blue light TADF guest DMAC-DPS (triplet energy level = 2.6 eV), ensuring that excitons can be efficiently transferred from the host to the guest, avoiding competition for energy with the host's spontaneous emission.

[0054] Principle of cascade exciton energy transfer

[0055] Triplet state recovery of blue-light TADF guests:

[0056] DMAC-DPS is a blue-light TADF material with high reverse intersystem crossing rate (K RISC ) converts triplet excitons (T1) into singlet excitons (S1), achieving 100% exciton utilization. Its S1 energy level (2.7 eV) matches that of mCBP / DPEPO, ensuring positive energy transfer to the guest.

[0057] Energy relay of green / red light objects:

[0058] Green TADF guest (such as 4CzIPN, triplet energy level = 2.5eV): After receiving the singlet energy of the blue guest, it emits light through fluorescence radiation. At the same time, its triplet energy level is higher than that of the red guest, and it can further transfer energy to the red material.

[0059] Green phosphorescent guest (such as Ir(ppy)2(acac), triplet energy level = 2.5eV): directly captures triplet excitons and emits light through phosphorescence radiation, avoiding triplet state waste.

[0060] Red light guest (such as DBP fluorescent material or RD071 phosphorescent material): is excited through singlet or triplet energy transfer, eventually forming a cascade transmission path of "blue light → green light → red light" to achieve full-color luminescence balance.

[0061] Solution Processing Film Formation Principle

[0062] Solvent selection and film quality:

[0063] Chlorobenzene, with its boiling point of 131°C, is a solvent that is highly compatible with the solute and evaporates rapidly during spin coating, forming a uniform film. The hole-transport layer, PVK (7 mg / mL), is spin-coated at 4000 rpm, forming a dense layer 50-80 nm thick. The luminescent layer (10 mg / mL) is spin-coated at 2000 rpm to avoid high-speed aggregation of guest molecules and ensure uniform luminescence.

[0064] Annealing treatment effect:

[0065] The hole injection layer (PEDOT:PSS) was annealed at 150°C for 20 minutes to remove solvent residues and improve conductivity; the hole transport layer (PVK) was annealed at 150°C for 30 minutes to promote orderly arrangement of molecular chains and reduce trap state density; the light-emitting layer was annealed at 100°C for 20 minutes to optimize molecular stacking and reduce non-radiative recombination centers.

[0066] Working principle of the optimal technical solution

[0067] Dual-host system: mCBP and DPEPO with high triplet energy levels are mixed in a 1:1 mass ratio, ensuring good carrier transport properties and a broad exciton recombination zone, which is conducive to efficient energy transfer.

[0068] Blue light TADF material DMAC-DPS: Its triplet energy level is 2.6eV, with high K RISC properties, making it possible to efficiently convert excitons into photons even under low excitation conditions.

[0069] Spin coating process: Using chlorobenzene as a solvent for solution processing ensures the quality and uniformity of the film. In particular, the hole transport layer and the light-emitting layer are both spin-coated to ensure the consistency of the film thickness and good optical properties.

[0070] Annealing treatment: By precisely controlling the annealing temperature and time, the solvent residue in the film can be removed, the crystallinity and stability of the film layer can be improved, and the overall performance of the device can be optimized.

[0071] like Figure 1The light-emitting layer shown uses a combination of two materials, W1 and W2, where W1 includes dual host materials mCBP and DPEPO (mass ratio 1:1), blue light TADF guest material DMAC-DPS, and a doping concentration of 20wt%; the green light-emitting guest is the TADF material Ir(ppy)2(acac), and the doping concentration is 0.5wt%; the red light-emitting guest is the fluorescent material DBP, and the doping concentration is 0.2wt%; W2 includes dual host materials mCBP and DPEPO (mass ratio 1:1), blue light TADF guest material DMAC-DPS, and a doping concentration of 20wt%; the green light-emitting guest is the TADF material 4CzIPN, and the doping concentration is 0.5wt%; the red light-emitting guest is the phosphorescent material RD071, and the doping concentration is 0.2wt%.

[0072] Detailed workflow

[0073] ITO substrate cleaning: The patterned ITO glass substrate was sequentially subjected to conventional ultrasonic cleaning with deionized water, isopropyl alcohol, ethanol, and isopropyl alcohol for 15 minutes. The cleaned substrate was then blown dry with a nitrogen gun and placed in an ultraviolet ozone machine for surface ozone treatment for 20 minutes.

[0074] Device preparation: adsorb the treated substrate on the turntable of the spin coater placed in the fume hood, filter the low-temperature stored PEDOT:PSS aqueous solution with a 0.45μm aqueous filter, take 100μL with a pipette and drop it on the glass substrate, turn on the spin coater and spin at 4000rpm for 30s. After the spin coating is completed, place the substrate on a high-temperature annealing table with a pre-set annealing temperature of 150℃ and anneal for 20min. After the annealing is completed, move the substrate to a glove box with a nitrogen environment. Spin coat 7mg ml at 4000rpm. -1 PVK chlorobenzene solution was prepared and then annealed at 150 °C for 30 min. 10 mg ml was spin-coated at 2000 rpm. -1 The chlorobenzene solution of the light-emitting layer was annealed at 100℃ for 20min, and then the electrode was wiped with a cotton swab dipped in alcohol until the electrode was exposed. Finally, the spin-coated substrate was transferred to a high vacuum evaporator and sequentially 40nm TmPyPB was evaporated at a rate of 2nm of Liq was evaporated at a rate of 120nm of electrode Al was evaporated at a rate of , and the device was completed.

[0075] Device packaging: Apply UV curing glue around the package cover, place the substrate material surface on the package cover, and irradiate with UV light for 2 minutes to cure.

[0076] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A solution-processed hybrid white organic light-emitting diode, characterized in that: It includes an ITO glass substrate, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer and a cathode arranged in sequence; the light-emitting layer is composed of a dual-host material and a three-color light-emitting guest, and the three-color light-emitting guest includes a blue light TADF guest, a green light phosphorescent or TADF guest, and a red light fluorescent or phosphorescent guest.

2. The solution-processed hybrid white organic light-emitting diode according to claim 1, characterized in that: The dual-host system includes high triplet energy level mCBP and DPEPO as host materials with a mass ratio of 1:

1.

3. The solution-processed hybrid white organic light-emitting diode according to claim 2, characterized in that: The blue light TADF guest is DMAC-DPS with a doping concentration of 20 wt %; the green light emitting guest is the TADF material 4CzIPN or the phosphorescent material Ir(ppy)2(acac) with a doping concentration of 0.5 wt %; the red light emitting guest is the fluorescent material DBP or the phosphorescent material RD071 with a doping concentration of 0.2 wt %.

4. The solution-processed hybrid white organic light-emitting diode according to claim 1, characterized in that: The hole injection layer is PEDOT:PSS with a thickness of 30-50nm; the hole transport layer is PVK with a thickness of 50-80nm; the electron transport layer is TmPyPb with a thickness of 40-60nm; the electron injection layer is Liq with a thickness of 1-3nm; and the cathode is metal aluminum with a thickness of 100-150nm.

5. The solution-processed hybrid white organic light-emitting diode according to claim 1, characterized in that: The light-emitting layer was solution-processed using chlorobenzene as a solvent, and the hole transport layer and the light-emitting layer were both prepared using a spin coating process, wherein the hole transport layer was spin-coated with a 7 mg ml-1 PVK chlorobenzene solution at 4000 rpm, and the light-emitting layer was spin-coated with a 10 mg ml-1 light-emitting layer chlorobenzene solution at 2000 rpm.

6. The solution-processed hybrid white organic light-emitting diode according to claim 3, characterized in that: The triplet energy level of the dual-host material mCBP is 2.7 eV, the triplet energy level of DPEPO is 2.8 eV, and the triplet energy level of the blue light TADF material DMAC-DPS is 2.6 eV, all of which have a high reverse intersystem crossing rate.

7. A method for preparing a hybrid white organic light-emitting diode based on solution processing, characterized in that: The preparation method for application of a hybrid white organic light-emitting diode based on solution processing according to any one of claims 1 to 7 comprises the following steps: (a) ITO substrate cleaning and surface ozone treatment; (b) sequentially spin-coating a hole injection layer, a hole transport layer, and a light-emitting layer on the treated substrate; (c) placing the substrate on a high-temperature annealing table for annealing; (d) sequentially depositing an electron transport layer, an electron injection layer, and a cathode under a vacuum environment; (e) Encapsulate the device.

8. The method for preparing a hybrid white organic light emitting diode based on solution processing according to claim 7, characterized in that: In the step (b), the hole injection layer is a PEDOT:PSS aqueous solution, which is filtered through a 0.45 μm filter and then spin-coated on the substrate at a spin-coating speed of 4000 rpm for 30 seconds.

9. The method for preparing a hybrid white organic light-emitting diode based on solution processing according to claim 7, characterized in that: In the step (c), when the hole transport layer is prepared, the annealing temperature is 150° C. and the time is 30 minutes. When the hole injection layer is prepared, the annealing temperature is 100° C. and the time is 20 minutes.

10. The method for preparing a hybrid white organic light emitting diode based on solution processing according to claim 7, characterized in that: In the step (d), the electron transport layer is The rate of evaporation is 40nm, and the electron injection layer is The rate of evaporation is 2nm, and the cathode is The deposition rate was 120 nm.

Images