A method for preparing a luminescent device based on an exciplex

Abstract

This invention relates to the field of chemical technology and discloses a method for preparing a light-emitting device based on an exciton complex, comprising the following steps: dissolving BCzPh and PO-T2T separately in chromatographic grade dichloromethane under an inert gas atmosphere to obtain corresponding solutions; pouring the PO-T2T solution and BCzPh solution into a container and stirring under an inert gas atmosphere at room temperature to obtain a mixed solution of the exciton complex; and initially preparing a light-emitting device based on the BCzPh:PO-T2T exciton complex. The electroluminescence (EL) wavelength of the device prepared by this invention is a pure green TADF-OLED with a wavelength of 511 nm, and the device has a wavelength of 117011 cd / m². ‑2 The device exhibits high brightness and a high external quantum yield (EQE) of 13.36%. Simultaneously, the balanced carrier transport environment within the device significantly enhances its spectral stability. The method is simple to operate, time-efficient, energy-saving, and has simple process requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemistry, and in particular to a preparation method of a luminescent device based on an excimer. BACKGROUND

[0002] Thermally activated delayed fluorescence (TADF) light-emitting diodes have attracted wide attention in both academia and industry as a new generation of organic light-emitting diodes (OLEDs). According to a self-selected statistics, the electrons and holes injected in the OLED emission layer (EML) will cause recombination, and then generate singlet and triplet excitons in a ratio of 25:75. For traditional fluorescent OLEDs, only singlet excitons can be utilized, while phosphorescent OLEDs have high cost and uncertain toxicity of noble metal resources. In comparison, due to the small singlet-triplet energy difference (EST) of TADF emitters, triplet excitons can return to singlet energy levels through reverse intersystem crossing, and the emitters are mostly metal-free organic molecules, so TADF OLEDs have excellent characteristics of high exciton utilization, low cost, low toxicity, and simple manufacturing process.

[0003] Many methods have been applied to develop TADF emitters, such as designing organic molecules with high intramolecular charge transfer characteristics to achieve a reduction in the singlet-triplet energy difference (EST). However, this dramatically increases the manufacturing cost of emitters and increases the complexity of the synthesis process. Moreover, most organic molecules rely on thermal evaporation to form a stable nanometer-thick emission layer, which further reduces the utilization of raw materials, as a large amount of raw materials are wasted in the large volume of evaporation chamber rather than deposited on the pre-designed conductive substrate.

[0004] In order to avoid the above technical problems, it is necessary to use existing materials to form a complex with TADF emission characteristics as an OLED emitter to meet the needs of actual production, and to take advantage of the good solubility of most organic molecules in common organic solvents to achieve solvent method manufacturing, to achieve large-area printing with a low concentration of spin-coating solvent, to further improve the utilization of raw materials, to strictly control the time and economic costs, and to solve the actual production problems. SUMMARY

[0005] The purpose of the present application is to solve the problems existing in the prior art, and to provide a preparation method of a luminescent device based on an excimer.

[0006] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0007] A preparation method of a luminescent device based on an excimer, comprising the following steps:

[0008] Step 1: BCzPh and PO-T2T are dissolved in chromatographic grade dichloromethane under inert gas atmosphere to obtain corresponding solutions;

[0009] Step 2: The PO-T2T solution and the BCzPh solution are poured into a container and stirred under normal temperature inert gas environment to obtain a mixed solution of exciplexes;

[0010] Step 3: A light-emitting device of BCzPh: PO-T2T exciplex is prepared;

[0011] The ITO conductive glass is cleaned with soap, deionized water, ethanol, chloroform, acetone and isopropanol in sequence, and is subjected to ultraviolet ozone treatment;

[0012] The PEDOT: PSS solution (Baytron PVP Al 4083) is spin-coated on the treated ITO conductive glass through a filter head, and then is subjected to annealing treatment. Then the ITO conductive glass is transferred into a glove box filled with inert gas, and PVK dissolved in chlorobenzene solution is spin-coated on the PEDOT: PSS film, and then is subjected to annealing treatment, finally forming a PEDOT: PSS / PVK layer, which serves as a hole injection layer and a hole transport layer;

[0013] The mixed solution of exciplexes prepared in step 2 is spin-coated on the PEDOT: PSS / PVK layer as a light-emitting layer;

[0014] Step 4: The product obtained in step 3 is transferred into a vacuum chamber, and TPBi, LiF and Al layers are sequentially deposited by thermal evaporation, wherein the TPBi layer serves as an electron transport layer and a hole blocking layer, and the LiF and Al layers serve as a top electrode; thus a light-emitting device based on exciplexes is obtained.

[0015] Preferably, in step 2, the addition ratio of the PO-T2T solution to the BCzPh solution is 1:1.

[0016] Preferably, in step 2, the stirring time under normal temperature inert gas environment is 5 min, and the stirring speed is 600-1000 r / min.

[0017] Preferably, in step 1, the concentration ratio of BCzPh to PO-T2T is 1:1, and the volume ratio is 1:1.

[0018] Preferably, the inert gas in steps 1-3 is nitrogen.

[0019] Preferably, in step 3, the rotation speed of spin-coating PEDOT: PSS is 2000 r / min, the rotation speed of spin-coating PVK is 2000 r / min, and the rotation speed of spin-coating the exciplex solution on the PEDOT: PSS / PVK layer is 1500 r / min.

[0020] Preferably, in step 3, the annealing treatment of the PEDOT: PSS is specifically annealing at a temperature of 170℃ for 30 min, and the annealing treatment of the PVK is specifically annealing at a temperature of 150℃ for 15 min.

[0021] The beneficial effects of the present application are:

[0022] The present application provides a preparation method of an exciplex-based light-emitting device, in the preparation process, an efficient green-emitting exciplex is prepared by using an electron donor material PO-T2T and an electron acceptor material BCzPh, the exciplex has high solubility in various organic solvents and high steric hindrance, so that the nanometer thin film obtained by solvent method spin-coating has high luminous intensity and luminous uniformity, and the photoluminescence quantum yield (PLQY) reaches 53%. Further, the exciplex is used as an emitting layer to prepare a pure green TADF-OLED with an electroluminescence (EL) wavelength of 511 nm, and the device has a high brightness of 117011 cd m -2 and a high external quantum efficiency (EQE) of 13.36%. At the same time, the balanced carrier transport environment in the device greatly improves the spectral stability of the device.

[0023] The preparation method of the exciplex-based light-emitting device provided by the present application has the advantages of simple operation, short time consumption, low energy consumption and simple process requirement; the TADF exciplex prepared by the method has good film-forming property, high photoluminescence quantum yield, high color purity and good device stability. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the molecular structural formula of the electron donor material PO-T2T and the electron acceptor material BCzPh;

[0025] Figure 2 is the intrinsic photoluminescence spectrum of the electron acceptor material BCzPh and the electron donor PO-T2T, and the photoluminescence spectrum of the exciplex BCzPh: PO-T2T;

[0026] Figure 3 is the thin film transient photoluminescence spectrum (TRPL) and the corresponding photoluminescence lifetime of adjusting the total concentration of BCzPh and PO-T2T;

[0027] Figure 4The variable-temperature transient photoluminescence spectra of the optimized BCzPh:PO-T2T exciplex film;

[0028] Figure 5 The two-dimensional and three-dimensional atomic force microscope images of the optimized BCzPh:PO-T2T exciplex film;

[0029] Figure 6 The scanning electron microscope images (SEM) of the BCzPh:PO-T2T exciplex film at different concentrations;

[0030] Figure 7 The energy level structure diagram of the TADF-OLED based on the BCzPh:PO-T2T exciplex;

[0031] Figure 8 The electroluminescence spectrum (EL) of the optimized BCzPh:PO-T2T exciplex;

[0032] Figure 9 The luminance-voltage-current density curve of the TADF-OLED of the optimized BCzPh:PO-T2T exciplex;

[0033] Figure 10 The external quantum efficiency (EQE), current power (CE), and power efficiency-luminance curve (PE) of the TADF-OLED of the optimized BCzPh:PO-T2T exciplex. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments.

[0035] In one embodiment, a method for preparing a high-efficiency green-emitting BCzPh:PO-T2T exciplex using an electron donor PO-T2T and an electron acceptor BCzPh, and preparing a light-emitting device based on the prepared exciplex, is provided, which comprises the following steps:

[0036] 1) First, 5 mg of PO-T2T and 5 mg of BCzPh are respectively dissolved in 1.0 ml of chromatographically pure dichloromethane solution, and ultrasonic treatment is performed under an inert gas atmosphere until the solids are dissolved, i.e., a precursor solution is obtained.

[0037] 2) Secondly, 5mg / ml of PO-T2T solution and 5mg / ml of BCzPh solution were sealed with sealing glue, transferred to the stirring table for vigorous stirring for 10 minutes, then transferred to the ultrasonic cleaner for ultrasonic treatment, which lasted for five minutes, and then stood for five minutes to form a spin-coating solution with stable composition and uniform distribution.

[0038] 3) Preparation of BCzPh:PO-T2T exciton complex TADF-OLED;

[0039] The ITO conductive glass was cleaned with soap, deionized water, ethanol, chloroform, acetone and isopropanol in turn, and was treated with ultraviolet ozone;

[0040] The PEDOT: PSS solution (Baytron PVP Al 4083) was spin-coated on the treated ITO glass through the filter head at a speed of 2000r / min for 30 seconds, and then annealed at a temperature of 170℃ for 30 minutes; then the substrate was transferred to the glove box filled with N2 gas, and PVK dissolved in chlorobenzene solution was spin-coated on the PEDOT: PSS film at a speed of 3000r / min for 50 seconds, and then continued to be annealed at a temperature of 100℃ for 10 minutes, finally forming a PEDOT: PSS / PVK layer, which served as a hole injection layer and a hole transport layer;

[0041] 4) The BCzPh:PO-T2T solution prepared in step 2) was spin-coated on the PEDOT: PSS / PVK layer as a light-emitting layer;

[0042] 5) The product obtained in step 4) was finally transferred to the vacuum chamber, and TPBi, LiF and Al layers were deposited in turn by thermal evaporation, in which the TPBi layer served as an electron transport layer and a hole blocking layer, and the LiF and Al layers served as a top electrode; thus a BCzPh:PO-T2T exciton complex based TADF-OLED was obtained.

[0043] As shown in Figure 1 , the exciton complex of donor-acceptor mode can be constructed by using the electron acceptor property of BCzPh and the electron donor property of PO-T2T. In addition, as shown in Figure 2 , the BCzPh:PO-T2T film shows a photoluminescence peak position completely different from the original material, indicating the formation of a new energy level, i.e. the formation of an exciton complex. As shown in Figure 3As shown, the overall concentration of the electron donor-acceptor material is changed, and the photoluminescence average lifetime changes significantly, which is due to the surface defect state generated in the low concentration and the concentration quenching in the high concentration. The best concentration represented by the long lifetime is 5.0 mg / ml. As shown, Figure 4 As shown, the variable-temperature photoluminescence lifetime of the exciplex indicates that as the temperature decreases, the photoluminescence lifetime appears a short lifetime component with a sharp decrease, and the average lifetime is significantly enhanced, which indicates the thermal activation delayed fluorescence property of the exciplex. As shown, Figure 5 As shown, the surface morphology of the optimized BCzPh:PO-T2T thin film has high crystallinity and uniform size, and the excellent thin film uniformity further proves the feasibility of the light-emitting diode manufacturing. Further, as shown, Figure 6 As shown, the morphology of the thin film surface is further observed by scanning electron microscope images, which further confirms the flatness of the thin film. As shown, Figure 7 As shown, the electroluminescent device is prepared by using the exciplex of BCzPh:PO-T2T, and the structure in the figure ensures the smooth transport of the two types of carriers in the device. Figure 8 The electroluminescence spectrum of the device is shown, which has high chroma and stability. And as shown, Figure 9 , 10, the EQE, CE, and PE of the electroluminescent device all reach high values in the field.

[0044] The present application proposes a preparation method of a light-emitting device based on an exciplex. In the preparation process, an efficient green-emitting exciplex is prepared by using an electron donor material PO-T2T and an electron acceptor material BCzPh. The complex not only has high solubility in various organic solvents, but also has high steric hindrance, so that the nanometer thin film obtained by solvent method spin coating has high luminescence intensity and luminescence uniformity, and the photoluminescence quantum yield (PLQY) reaches 53%. Further, the complex is used as an emission layer to prepare a pure green TADF-OLED with an electroluminescence (EL) wavelength of 511 nm. The device has a high brightness of 117011 cd m -2 and a high external quantum efficiency (EQE) of 13.36 %.

[0045] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can make equivalent substitutions or changes to the technical solutions and inventive concepts of the present application within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for producing a luminescent device based on an excimer, characterized in that The method comprises the following steps: Step 1: BCzPh and PO-T2T are respectively dissolved in chromatographic grade dichloromethane in an inert gas atmosphere to obtain corresponding solutions; Step 2: The PO-T2T solution and the BCzPh solution are poured into a container and stirred in an inert gas environment at room temperature to obtain a mixed solution of exciplexes; Step 3: A light-emitting device of BCzPh: PO-T2T exciplex is prepared; The ITO conductive glass is cleaned with soap, deionized water, ethanol, chloroform, acetone and isopropanol in sequence, and is subjected to ultraviolet ozone treatment; The PEDOT: PSS solution is spin-coated on the treated ITO conductive glass through a filter head, and then is subjected to annealing treatment; then the ITO conductive glass is transferred into a glove box filled with inert gas, and PVK dissolved in a chlorobenzene solution is spin-coated on the PEDOT: PSS film, and then is subjected to annealing treatment, so as to form a PEDOT: PSS / PVK layer, which is used as a hole injection layer and a hole transport layer; The mixed solution of exciplexes prepared in step 2 is spin-coated on the PEDOT: PSS / PVK layer as a light-emitting layer; Step 4: The product obtained in step 3 is transferred into a vacuum chamber, and TPBi, LiF and Al layers are sequentially deposited by thermal evaporation, wherein the TPBi layer is used as an electron transport layer and a hole blocking layer, and the LiF and Al layers are used as a top electrode; thus a light-emitting device based on exciplexes is obtained.

2. The method of claim 1, wherein the method further comprises the step of: In step 2, the addition ratio of the PO-T2T solution to the BCzPh solution is 1:

1. ​ 3. The method of claim 1, wherein the method further comprises the step of: In step 2, the stirring time in the inert gas environment at room temperature is 5 min, and the stirring speed is 600-1000 r / min. ​ 4. The method of claim 1, wherein the method further comprises the step of: In step 1, the concentration ratio of BCzPh to PO-T2T is 1:1, and the volume ratio is 1:

1. ​ 5. The method of claim 1, wherein the method further comprises the step of: The inert gas in steps 1-3 is nitrogen. ​ 6. The method of claim 1, wherein the method further comprises the step of: In step 3, the spin-coating speed of PEDOT: PSS is 2000 r / min, the spin-coating speed of PVK is 2000 r / min, and the spin-coating speed of the exciplex solution on the PEDOT: PSS / PVK layer is 1500 r / min. ​ 7. The method of claim 1, wherein the method further comprises the step of: In step 3, the annealing treatment of the PEDOT: PSS is specifically annealing at a temperature of 170℃ for 30 min, and the annealing treatment of the PVK is specifically annealing at a temperature of 150℃ for 15 min. ​

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