High-external-quantum-efficiency organic dark red / near-infrared light-emitting diode based on highly-oriented light-emitting layer

Abstract

The invention discloses a high-external-quantum-efficiency organic dark red / near-infrared light-emitting diode based on a strong-orientation light-emitting layer, and belongs to the technical field of diodes. The organic dark red / near-infrared light emitting diode with controllable wavelength and excellent performance is prepared at low cost by adjusting factors such as eccentric distance, sucker rotating speed and solvent system and adjusting the horizontal dipole molecular orientation ratio, and meanwhile, the performance of the device is remarkably improved. The light emitting range of the organic dark red / near-infrared light emitting diode is 600-850nm, and the external quantum efficiency of a device with optimal performance can be up to about 18%.

Description

Technical Field The invention relates to an organic deep red / near infrared light emitting diode with high external quantum efficiency based on a strongly oriented light emitting layer and a preparation method thereof, belonging to the technical field of organic light emitting diodes. Background Art

[0002] Organic deep red / near infrared light-emitting diodes have important applications in the fields of bio-imaging, infrared lighting, optical communications, environmental sensing, and food and product quality control. Organic small molecule devices are generally deposited by vacuum evaporation, but due to the limitation of the size of the vacuum cavity, it is difficult to prepare OLED devices with a large area, and it is difficult to accurately control the doping ratio, especially in the case of low concentration doping. In addition, the evaporation method has high power consumption and is prone to waste of materials and energy. Solution-processed organic light-emitting diodes have more advantages in the commercial production of low-cost, large-area and flexible displays. At present, the external quantum efficiency of organic light-emitting diodes in the blue, green and orange-red emission ranges has reached more than 20%, while the performance of organic deep red / near infrared light-emitting diodes with excellent biocompatibility has progressed slowly. In addition to the inherent limitation of the luminescence quantum yield caused by the narrow band gap, the difficulty lies in the lack of an effective method to construct high external quantum efficiency organic deep red / near infrared light-emitting diodes by solution processing.

[0003] In order to fine-tune the solid-state molecular arrangement of the active layer, people have conducted continuous research and a large number of optimization strategies. In recent years, by applying external forces to guide molecular arrangement and adjusting coating parameters to control film morphology and crystal phase, it has been used to manufacture organic field-effect transistors with significantly enhanced charge carrier mobility. In 2022, Oliveira et al. tried to use Langmur-Blodgett film to improve device performance. This method produced devices with significantly improved performance. However, this method is complicated to operate, the film-making equipment is expensive, and the technical requirements are very high.

[0004] The present invention proposes a strongly oriented light-emitting layer and a preparation method thereof for high external quantum efficiency organic deep red / near infrared light-emitting diodes. The invention controls the degree of orderly arrangement of molecules during the film formation process of the light-emitting layer to obtain an organic deep red / near infrared light-emitting diode with significantly improved light outcoupling output efficiency and external quantum efficiency. Summary of the invention

[0005] The invention provides a highly oriented light-emitting layer for organic deep red / near infrared LED and a preparation method thereof, which is achieved by the following steps:

[0006] Step A: accurately weighing PVK as the main material of the light-emitting layer and TPAAP as the guest material of the light-emitting layer, preparing the main and guest materials of the light-emitting layer into a light-emitting layer mixture solution, and dissolving them with a solvent;

[0007] Step B: spin coating a hole injection layer PEDOT:PSS on a pre-prepared ITO glass substrate, followed by annealing;

[0008] Step C: Then spin-coating the hole transport layer PVK on the hole injection layer PEDOT:PSS and performing annealing;

[0009] Step D: placing the substrate obtained in step C on a large turntable, with the distance between the substrate and the rotation center of the large turntable being 0.5-5 cm, and taking the light-emitting layer mixture solution in step A and rapidly spin-coating it into a film by eccentric spin coating;

[0010] Step E: annealing the film obtained in step D at 60-130° C. for 10-30 min, and removing the position to be covered by the anode after cooling;

[0011] Step F: The light-emitting layer obtained in step E except for the anode position is transferred into a vacuum deposition chamber, and an electron transport layer TmPyPB, an electron injection layer LiF, and a cathode Al are sequentially deposited on the light-emitting layer to obtain an organic deep red / near infrared light-emitting diode;

[0012] In the above invention, in step A, the mass ratio of the host to the guest is 0.5%-30% (preferably 7-9%); in addition, chlorobenzene is used for dissolution; 0.8-1.2 ml of chlorobenzene corresponds to every 7 g of PVK in the luminescent layer mixture solution.

[0013] In the above invention content, in step B, the ITO glass substrate is cleaned and then ultrasonicated twice using deionized water, acetone and ethanol respectively, and the ultrasonication time is 15-30 minutes. The obtained PEDOT:PSS layer is annealed at 140-170° C. for 15 minutes.

[0014] In step C of the above invention, after the hole injection layer PEDOT:PSS layer is annealed, it is immediately transferred into a vacuum glove box, and the PVK layer is prepared after cooling. The PVK layer is annealed at 100-130° C. for 15 min.

[0015] In the above invention content step D, the rotation speed is controlled between 1500-4000rpm. If the rotation speed is too low, the organic molecules in the film cannot be effectively arranged, and if the rotation speed is too high, the solvent evaporates too quickly, which will cause the molecules to form a film before they can be arranged under force, affecting the horizontal dipole orientation ratio. The substrate size is preferably (14-16)cm*(13-14)cm in length and width, preferably 15.5cm in length and 13.5cm in width, and the corresponding volume of the luminescent layer mixture solution is 20-30 microliters.

[0016] In step E of the above invention content, the present invention can prepare multiple diodes at one time, and the position covered by the anode corresponding to each diode is gently scraped off with a scraper, or wiped off with an organic solvent chlorobenzene.

[0017] In the above invention, in step F, the vacuum degree is lower than 3*10 -4 The evaporation was carried out under Pa conditions, and the maximum evaporation rate of each layer was controlled at the following.

[0018] The organic deep red / near infrared light emitting diode has a light emission range of 600-850nm, and the external quantum efficiency of the best performance device can be as high as about 18%. The organic molecules in the prepared light emitting layer are arranged to reach a horizontal dipole orientation ratio of more than 70%, and the light outcoupling output efficiency of the prepared organic deep red / near infrared light emitting diode is significantly improved, which has certain application prospects in the fields of information storage, medical equipment and imaging technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the eccentric spin coating device of the present invention;

[0020] Figure 2 is a device structure diagram of an organic deep red / near infrared light emitting diode in the present invention;

[0021] Figure 3 It is the current density-radiance-voltage diagram of Examples 1-3. The leakage current of the device prepared by eccentric spin coating is significantly reduced at low current, which reduces the loss and is beneficial to the improvement of device performance. As the voltage increases, the radiance of the device prepared by eccentric spin coating is also significantly increased. The comparison sample is a diode obtained by normal spin coating of the light-emitting layer (without eccentricity).

[0022] Figure 4 The external quantum efficiency-voltage diagram of Examples 1-3 shows that the external quantum efficiency of the device prepared by eccentric spin coating is significantly improved, and the maximum external quantum efficiency is also improved compared with the device prepared by evaporation of the luminescent material in the literature. The comparison sample is a diode obtained by normal spin coating of the luminescent layer (without eccentricity). DETAILED DESCRIPTION

[0023] The present invention is described in detail below in conjunction with embodiments, but the present invention is not limited to these manufacturing examples.

[0024] Example 1

[0025] Use a ten-thousandth analytical balance to accurately weigh two bottles of PVK7 mg and one bottle of TPAAP4.8 mg. Gently loosen the bottle cap and transfer it into the glove box. Add 1 mL of chlorobenzene to one bottle of PVK and use it as a hole transport layer after it is fully dissolved. Add 1 mL of chloroform to each of the other two bottles. After fully dissolving, take 416 μL of PVK and 80 μL of TPAAP and add them to a new bottle and mix them evenly as the light-emitting layer solution (the mass ratio of PVK and TPAAP in the light-emitting layer solution is 7.6%, and 1 ml of chlorobenzene is corresponding to every 7 g of PVK). Spin coat the PEDOT:PSS layer on the pre-prepared ITO glass substrate (15.5 cm long and 13.5 cm wide) and anneal at 160°C for 15 min. After annealing, immediately transfer it into a vacuum glove box, spin coat the PVK layer after cooling, and anneal at 120°C for 15 min. After cooling again, place the substrate 2 cm away from the center of rotation, take 26 μL of solution and use eccentric spin coating to prepare the light-emitting layer film, and the rotation speed is controlled at 2900 rpm. The obtained film was annealed at 120°C for 15 min. After cooling, the covered area of ​​the anode was gently wiped off with chlorobenzene and transferred into the vacuum deposition chamber. -4 Under the condition of Pa, the electron transport layer TmPyPB, the electron injection layer LiF, and the cathode Al are sequentially evaporated. The maximum rate corresponding to each layer during evaporation is controlled at Organic deep red / near infrared light emitting diodes can be obtained.

[0026] Example 2

[0027] Use a ten-thousandth analytical balance to accurately weigh two bottles of PVK7 mg and one bottle of TPAAP4.8 mg. Gently loosen the bottle cap and transfer it into the glove box. Add 1 mL of chlorobenzene to one bottle of PVK and fully dissolve it as a hole transport layer. Add 1 mL of chloroform to each of the other two bottles. After fully dissolving, take 520 μL of PVK and 50 μL of TPAAP and add them to a new bottle and mix them evenly as the light-emitting layer solution (the mass ratio of PVK and TPAAP in the light-emitting layer solution is 15%, and 1 ml of chlorobenzene is corresponding to every 7 g of PVK). Spin coat the PEDOT:PSS layer on the pre-prepared ITO glass substrate (15.5 cm long and 13.5 cm wide) and anneal at 150°C for 20 min. After annealing, immediately transfer it into a vacuum glove box, spin coat the PVK layer after cooling, and anneal at 120°C for 20 min. After cooling again, place the substrate 3 cm away from the center of rotation, take 28 μL of solution and use eccentric spin coating to prepare the light-emitting layer film, and the rotation speed is controlled at 2100 rpm. The obtained film was annealed at 110°C for 20 min. After cooling, the covered area of ​​the anode was gently wiped off with chlorobenzene and transferred into the vacuum deposition chamber. -4Pa, the electron transport layer TmPyPB, the electron injection layer LiF, and the cathode Al were sequentially deposited, and the maximum rates were controlled at Organic deep red / near infrared light emitting diodes can be obtained.

[0028] Example 3

[0029] Use a ten-thousandth analytical balance to accurately weigh two bottles of PVK7 mg and one bottle of TPAAP4.8 mg. Gently loosen the bottle cap and transfer it into the glove box. Add 1 mL of chlorobenzene to one bottle of PVK and fully dissolve it as a hole transport layer. Add 1 mL of chloroform to each of the other two bottles. After fully dissolving, take 720 μL of PVK and 200 μL of TPAAP and add them to a new bottle and mix them evenly as the light-emitting layer solution (the mass ratio of PVK and TPAAP in the light-emitting layer solution is 5.3%, and 1 ml of chlorobenzene is corresponding to every 7 g of PVK). Spin coat the PEDOT:PSS layer on the pre-prepared ITO glass substrate (15.5 cm long and 13.5 cm wide) and anneal at 160°C for 10 min. After annealing, immediately transfer it into a vacuum glove box, spin coat the PVK layer after cooling, and anneal at 120°C for 10 min. After cooling again, place the substrate 4 cm away from the center of rotation, take 25 μL of solution and use eccentric spin coating to prepare the light-emitting layer film, and the rotation speed is controlled at 1600 rpm. The obtained film was annealed at 130°C for 10 min. After cooling, the covered area of ​​the anode was gently wiped off with chlorobenzene and transferred into the vacuum deposition chamber. -4 Pa, the electron transport layer TmPyPB, the electron injection layer LiF, and the cathode Al were sequentially deposited, and the maximum rates were controlled at Organic deep red / near infrared light emitting diodes can be obtained.

Claims

1. A method for preparing a high external quantum efficiency organic deep red / near infrared light-emitting diode based on a strongly oriented light-emitting layer, characterized in that: The following steps are involved: Step A: accurately weighing PVK as the main material of the light-emitting layer and TPAAP as the guest material of the light-emitting layer, preparing the main and guest materials of the light-emitting layer into a light-emitting layer mixture solution, and dissolving them with a solvent; Step B: spin coating a hole injection layer PEDOT:PSS on a pre-prepared ITO glass substrate, followed by annealing; Step C: Then spin-coating the hole transport layer PVK on the hole injection layer PEDOT:PSS and performing annealing; Step D: placing the substrate obtained in step C on a large turntable, with the distance between the substrate and the rotation center of the large turntable being 0.5-5 cm, and taking the light-emitting layer mixture solution in step A and rapidly spin-coating it into a film by eccentric spin coating; Step E: annealing the film obtained in step D at 60-130° C. for 10-30 min, and removing the position to be covered by the anode after cooling; Step F: The light-emitting layer obtained in step E except for the anode position is transferred into a vacuum evaporation chamber, and an electron transport layer TmPyPB, an electron injection layer LiF, and a cathode Al are sequentially evaporated on the light-emitting layer to obtain an organic deep red / near infrared light-emitting diode.

2. A method for preparing a high external quantum efficiency organic deep red / near infrared light-emitting diode based on a strongly oriented light-emitting layer according to claim 1, characterized in that: In the above invention, in step A, the mass ratio of the host to the guest is 0.5%-30% (preferably 7-9%); in addition, chlorobenzene is used for dissolution; 0.8-1.2 ml of chlorobenzene corresponds to every 7 g of PVK in the luminescent layer mixture solution.

3. A method for preparing a high external quantum efficiency organic deep red / near infrared light-emitting diode based on a strongly oriented light-emitting layer according to claim 1, characterized in that: In step B, the ITO glass substrate is cleaned and ultrasonicated twice with deionized water, acetone, and ethanol respectively, and the ultrasonication time is 15-30 minutes. The obtained PEDOT:PSS layer is annealed at 140-170°C for 15 minutes. In step C, after the annealing of the hole injection layer PEDOT:PSS layer is completed, it is immediately transferred into a vacuum glove box, and the PVK layer is prepared after cooling. The PVK layer is annealed at 100-130°C for 15 minutes.

4. A method for preparing a high external quantum efficiency organic deep red / near infrared light-emitting diode based on a strongly oriented light-emitting layer according to claim 1, characterized in that: In step D, the rotation speed is controlled between 1500-4000rpm. If the rotation speed is too low, the organic molecules in the film cannot be effectively arranged, and if the rotation speed is too high, the solvent evaporates too quickly, which will cause the molecules to form a film before they can be arranged under force, affecting the horizontal dipole orientation ratio. The substrate size is preferably (14-16) cm*(13-14) cm in length and width, preferably 15.5 cm in length and 13.5 cm in width, and the corresponding volume of the luminescent layer mixture solution is 20-30 microliters.

5. A method for preparing a high external quantum efficiency organic deep red / near infrared light-emitting diode based on a strongly oriented light-emitting layer according to claim 1, characterized in that: In step E, multiple diode arrays are prepared at one time, and the position covered by the anode corresponding to each diode is gently scraped off with a scraper, or wiped off with an organic solvent chlorobenzene.

6. A method for preparing a high external quantum efficiency organic deep red / near infrared light-emitting diode based on a strongly oriented light-emitting layer according to claim 1, characterized in that: In step F, the vacuum degree is less than 3*10 -4 The evaporation was carried out under Pa conditions, and the maximum evaporation rate of each layer was controlled at the following.

7. An organic deep red / near infrared light-emitting diode with high external quantum efficiency based on a strongly oriented light-emitting layer, prepared according to the method described in any one of claims 1 to 6.

8. Application of an organic deep red / near infrared light-emitting diode with high external quantum efficiency based on a strongly oriented light-emitting layer prepared by the method according to any one of claims 1 to 6 in the fields of information storage, medical equipment and imaging technology.

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