A red light electroluminescent device based on metal nanoclusters and a preparation method thereof

Abstract

The application belongs to the technical field of light-emitting devices, and provides a preparation method of a red light electroluminescent device based on metal nanoclusters, including the following steps: dissolving tetrahydrothiophene gold and 4'-ethynylbenzo 15-crown-5 in a dichloromethane solution; adding triethylamine solution dropwise, volatilizing the solvent and redissolving with a dichloromethane solution to obtain an orange-red solution; sealing the solution, diffusing and crystallizing, and collecting orange-red needle-shaped crystals; dissolving the orange-red needle-shaped crystals and Cu(NCMe)4PF6 in a dichloromethane solution to obtain a transparent red solution; sealing the solution, diffusing and crystallizing, and collecting red needle-shaped crystals; dissolving the red needle-shaped crystals in a dichloromethane solution containing TCTA and OXD-7 to obtain a host-guest mixed solution; preliminarily preparing a host-guest and insulating layer modified cluster red light electroluminescent device: transferring the product into a vacuum cavity, and sequentially depositing an ultrathin LiF, PO-T2T, LiF and Al layer. The red light electroluminescent device of the embodiment has obvious brightness improvement, high external quantum efficiency and good device stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of light-emitting devices, and particularly relates to a red light electroluminescent device based on metal nanoclusters and a preparation method thereof. BACKGROUND

[0002] Metal nanoclusters have high photoluminescence quantum yield (PLQY), low toxicity, simple synthesis and many other advantages. The special inorganic-organic hybrid environment brought by the core-shell structure of the metal nanoclusters makes them have a highly adjustable excitation state composition, which facilitates the coverage of the visible light-near infrared I region (400 nm-900 nm) in the light-emitting waveband.

[0003] However, the special structure of the organic ligand-inorganic metal core results in a glass transition temperature (Tg) of most metal nanoclusters being lower than 200℃, so the spin-coating coating method needs to be preferentially selected in the growth process of the nanometer film. The unique nanometer size of the metal nanoclusters makes them need to be hybridized with the host material to enter the host-guest doped film in the form of a dopant. However, when a high-energy level structure host material is used, the carrier transport balance and the excimer confinement are engineering problems that need to be considered, because they determine the utilization efficiency of the electric exciton, and then affect the key electrical parameters such as the external quantum efficiency, current power and power efficiency of the device.

[0004] Therefore, under the premise of formulating a reasonable host-guest material system, how to reasonably utilize the functional layer to regulate the energy transfer path and limit the carrier recombination area becomes an urgent industrial technical problem that needs to be solved for further improving the electroluminescent device based on metal nanoclusters. SUMMARY

[0005] The purpose of the embodiment of the application is to provide a preparation method of a red light electroluminescent device based on metal nanoclusters, which aims to solve the problems proposed in the background technology.

[0006] The embodiment of the application is implemented in this way. The preparation method of the red light electroluminescent device based on metal nanoclusters comprises the following steps:

[0007] S1, dissolving tetrahydrothiophene gold and 4'-ethynylbenzo 15-crown-5 in dichloromethane solution, and stirring until completely dissolved;

[0008] S2, adding triethylamine solution, low-temperature stirring, volatilizing the solvent and re-dissolving with dichloromethane solution to obtain an orange-red solution;

[0009] S3, low-temperature sealing the orange-red solution, diffusing and crystallizing with n-hexane, and collecting orange-red needle-shaped crystals after standing;

[0010] S4, dissolving orange-red needle-shaped crystals and powder Cu(NCMe)4PF6 in dichloromethane solution, stirring in the dark to obtain a transparent red solution;

[0011] S5, low-temperature sealing of the transparent red solution, diffusion crystallization with ether, and collecting red needle-shaped crystals after standing;

[0012] S6, dissolving red needle-shaped crystals in a dichloromethane solution containing electron acceptor material TCTA and electron donor material OXD-7 to obtain a host-guest mixed solution;

[0013] S7, preliminary preparation of a host-guest and insulating layer modified cluster red electroluminescent device:

[0014] S71, cleaning ITO conductive glass and performing ultraviolet ozone treatment;

[0015] S72, spin-coating PEDOT:PSS solution on ITO glass, then performing annealing treatment to obtain a hole injection layer, and then transferring to a glove box filled with N2 gas;

[0016] S73, spin-coating the host-guest mixed solution on the PEDOT:PSS layer as a light-emitting layer;

[0017] S8, transferring the product obtained in S7 into a vacuum chamber, and sequentially depositing an ultrathin LiF layer, a PO-T2T layer, a LiF layer and an Al layer by thermal evaporation, wherein the ultrathin LiF layer serves as an insulating layer, the PO-T2T layer serves as an electron transport layer and a hole blocking layer, and the LiF and Al layers serve as a top electrode, thereby obtaining the red electroluminescent device based on metal nanoclusters.

[0018] Preferably, in S1, the stirring speed is 800-1000 r / min, and the stirring time is 8-10 min.

[0019] Preferably, in S2, the stirring speed is 600-800 r / min, and the volatilized solvent is subjected to rotary evaporation at a speed of 80-100 r / min and a temperature of 23-28℃.

[0020] Preferably, in S4, the stirring speed is 800-1000 r / min.

[0021] Preferably, in S6, the concentration of red crystals in the host-guest mixed solution is 2.0 mg / mL, the concentration of TCTA is 4.0 mg / mL, and the concentration of OXD-7 is 3.5 mg / mL.

[0022] After the step of dissolving the red needle-shaped crystal in the dichloromethane solution containing the electron acceptor material TCTA and the electron donor material OXD-7, the method further comprises the steps of: performing violent shaking for 1-2 minutes, and ultrasonic treatment for 1-2 minutes.

[0023] Preferably, in S71, the step of cleaning the ITO conductive glass comprises the steps of: sequentially cleaning the ITO conductive glass with soap, deionized water, ethanol, chloroform, acetone and isopropanol.

[0024] Preferably, in S72, the rotation speed of the spin coating of the PEDOT:PSS solution is 3800-4200 r / min, and the rotation time is 28-32 seconds.

[0025] The annealing treatment is performed at a temperature of 165-175 DEG C for 25-35 minutes.

[0026] Preferably, in S73, the rotation speed of the spin coating of the host-guest mixed solution on the PEDOT:PSS layer is 2800-3200 r / min, and the rotation time is 38-32 seconds.

[0027] Preferably, in S8, the evaporation speed of the ultra-thin LiF, PO-T2T and LiF is 0.05-0.2 nm / s, and the thicknesses are 0.5-2 nm, 30-50 nm and 1-2 nm, respectively; the evaporation speed of Al is 1-3 nm / s, and the thickness is 100-120 nm.

[0028] Another object of the embodiment of the present application is to provide a red light electroluminescent device based on metal nanoclusters prepared by the preparation method.

[0029] The preparation method of the red light electroluminescent device based on metal nanoclusters provided by the embodiment of the present application uses the metal nanoclusters Au6Cu2 and the mixed host materials TCTA and OXD-7 to construct a red light electroluminescent device based on metal nanoclusters, the absorption spectrum of the selected metal nanoclusters is highly coincident with the electroluminescent curve of the host materials, and the host-guest energy transfer condition is met; the host-guest mixed solution is used as an emission layer to prepare a red light light-emitting diode with an electroluminescent (EL) peak of 602 nm, and the device has a high brightness of 3253 cd m -2 -2 and a high external quantum efficiency (EQE) of 1.16%. -2 By inserting an ultra-thin electrically inert functional layer LiF between the emission layer (EmL) and the electron transport layer (ETL), the energy transfer direction of the host materials is further specified, the exciton recombination area is limited, the device parameters are further improved, the brightness reaches 3887 cd m -2 , and the external quantum efficiency reaches 1.55%.

[0030] The preparation method provided in this invention is simple to operate, time-consuming, energy-efficient, and has simple process requirements; the prepared red photoluminescent device based on metal nanoclusters has significantly improved brightness, high external quantum efficiency, and good device stability. Attached Figure Description

[0031] Figure 1 The absorption spectrum and photoluminescence spectrum of the Au6Cu2 thin film with metal nanoclusters provided in Embodiment 1 of the present invention are included as an optical photograph of the thin film.

[0032] Figure 2 The transient photoluminescence spectrum (TRPL) and corresponding fitting curve of the Au6Cu2 thin film with metal nanoclusters provided in Example 1 of the present invention;

[0033] Figure 3 The photoluminescence quantum yield (PLQY) of the Au6Cu2 thin film with and without the introduction of the host material provided in Embodiment 1 of the present invention;

[0034] Figure 4 Scanning electron microscope (SEM) images and corresponding elemental analyses of the Au6Cu2 thin film containing metal nanoclusters after the introduction of the host material, provided in Example 1 of this invention;

[0035] Figure 5 The transient absorption spectrum (TA) and corresponding kinetic fitting curve of the Au6Cu2 thin film with metal nanoclusters after the introduction of the host material provided in Embodiment 1 of the present invention;

[0036] Figure 6 This is a schematic diagram of the energy level structure of a red photoluminescent device based on metal nanoclusters provided in Embodiment 1 of the present invention, wherein the energy level structure of the metal nanoclusters Au6Cu2 is derived from literature and Dow diagrams.

[0037] Figure 7 The electroluminescence spectra of the red photoluminescent device based on metal nanoclusters provided in Embodiment 1 of the present invention under different bias voltages are shown, with the device having a built-in 500 cd / m² value. -2 Optical photographs taken at that time;

[0038] Figure 8 The brightness-voltage-current density curves (JVL) of the red photoluminescent device based on metal nanoclusters under different LiF thicknesses provided in Embodiment 1 of the present invention.

[0039] Figure 9 The brightness-external quantum efficiency (EQE), current power (CE), and power efficiency (PE) curves of red photoluminescent devices based on metal nanoclusters under different LiF thicknesses provided in Embodiment 1 of the present invention.

[0040] Figure 10 The metal nanocluster-based red electroluminescent device provided in Embodiment 1 of the present application has a luminance decay curve at 50 cd m -2 at a luminance of 50 cd m DETAILED DESCRIPTION

[0041] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0042] The specific implementation of the present application is described in detail below in combination with specific embodiments.

[0043] Embodiment 1, a metal nanocluster-based red electroluminescent device, a preparation method thereof includes the following steps:

[0044] 1) 11.0 mg of tetrahydrothiophene gold Au(tht)Cl and 10.0 mg of 4'-ethynylbenzo-15-crown-5 are dissolved in 20 mL of chromatographically pure dichloromethane solution, and stirred at a speed of 1000 r / min on a magnetic stirrer for 10 min until fully dissolved;

[0045] 2) 20 μL of triethylamine solution is added as a reaction catalyst at a speed of 700 r / min on a magnetic stirrer, and stirred at 0℃ for 2.5 h, the speed of the magnetic stirrer is 700 r / min; then the solvent is volatilized by using a rotary evaporator, the speed of the rotary evaporator is 100 r / min during rotary evaporation, and the temperature is kept at 25℃; and 3 mL of chromatographically pure dichloromethane solution is used to re-dissolve to obtain an orange-red solution;

[0046] 3) The orange-red solution obtained in step 2) is sealed at 5℃, and hexane diffusion crystallization is used, and the orange-red needle-shaped crystals on the inner wall of the container are collected after standing for 96 h;

[0047] 4) 29.5 mg of the orange-red needle-shaped crystals obtained in step) and 5.5 mg of powder Cu(NCMe)4PF6 are dissolved in 1 mL of chromatographically pure dichloromethane solution, and the transparent red solution is obtained after stirring in the dark for 30 min, wherein the speed of the magnetic stirrer is 800 r / min;

[0048] 5) The transparent red solution obtained in step 4) is sealed at 0℃, and ether diffusion crystallization is used, and the red needle-shaped crystals on the inner wall of the container are collected after standing for 72 h, which is metal nanocluster Au6Cu2;

[0049] 6) 2.0 mg of red needle-like crystals obtained in step 5) were dissolved in 1 mL of a dichloromethane solution containing 4.0 mg of the electron acceptor material TCTA and 3.5 mg of the electron donor material OXD-7 and stirred vigorously for 2 min, and a host-guest mixed solution was obtained after 1 min of ultrasonication;

[0050] 7) A host-guest and insulating layer modified cluster red electroluminescent device was prepared as follows:

[0051] 7.1) The ITO conductive glass was cleaned with soap, deionized water, ethanol, chloroform, acetone and isopropanol in sequence, and was subjected to ultraviolet ozone treatment;

[0052] 7.2) The PEDOT:PSS solution (Baytron PVP Al 4083) was spin-coated on the treated ITO glass through a filter head at a rotation speed of 4000 r / min for 30 s, followed by annealing treatment to obtain a hole injection layer; then the substrate was transferred into a glove box filled with N2 gas, wherein the annealing temperature was 170°C and the annealing time was 30 min;

[0053] 7.3) The host-guest mixed solution prepared in step 6) was spin-coated on the PEDOT:PSS layer as a light-emitting layer at a rotation speed of 3000 r / min for 30 s;

[0054] 8) An insulating layer ultra-thin LiF, an electron transport layer PO-T2T, an electron injection layer LiF and a metal electrode Al were evaporated onto the glass substrate by evaporation operation to prepare a red electroluminescent device (diode LED) based on metal nanoclusters, wherein the evaporation speed of the ultra-thin LiF, PO-T2T and LiF was 0.1 nm / s, and the final thicknesses were 1.0 nm, 37.5 nm and 1.2 nm, respectively; the evaporation speed of Al was 1 nm / s, and the final thickness was 100 nm.

[0055] Performance test:

[0056] The metal nanoclusters (i.e. the red needle-like crystals obtained in step 5) prepared in Example 1 were converted into a thin film by a spin-coating process, and the film surface had good flatness, and was analyzed to obtain the absorption spectrum and photoluminescence spectrum as shown in Figure 1 It can be seen from Figure 1 that the film shows bright orange-red light emission with a peak at 610 nm under 365 nm ultraviolet excitation, and the characteristic absorption peaks at 310 nm and 400 nm indicate that the metal nanocluster crystals have high purity;

[0057] The metal nanocluster thin film was measured by transient photoluminescence spectroscopy at an excitation wavelength of 375 nm, and the results are shown in Figure 2As shown in Figure 2 As can be seen, the double exponential fitting curve is good, showing that its average lifetime is about 2.3 μs, and the appropriate lifetime indicates that it will not suffer from severe triplet quenching process while ensuring the emission intensity, and is suitable for use as a phosphorescent dopant of electroluminescent device;

[0058] The photoluminescence quantum yield results of the metal nanocluster film with the host material introduced (i.e. the metal nanocluster film is dissolved in dichloromethane solution containing electron acceptor material TCTA and electron donor material OXD-7 in step 6) are as follows Figure 3 As shown in Figure 3 As can be seen, the introduction of the host material improves the photoluminescence quantum yield of the metal nanocluster film, from 10.19% without introduction to 40.56%;

[0059] The metal nanocluster film with the host material introduced is analyzed by scanning electron microscope, and the SEM image and corresponding element analysis are as follows Figure 4 As shown in Figure 4 As can be seen, by observing the metal core elements Au and Cu, it is found that the metal nanoclusters are uniformly distributed on the film, and the introduction of the host material avoids the concentration quenching caused by excessive accumulation;

[0060] The metal nanocluster film with the host material introduced is tested by transient absorption spectrum, and the results are as follows Figure 5 As shown in Figure 5 As can be seen, the host material makes it produce more triplet excited states through fewer singlet excited states, and the dexter energy transfer process occurs;

[0061] The red light electroluminescent device based on metal nanoclusters prepared in Example 1 is analyzed, and the device energy level structure is as follows Figure 6 As shown in

[0062] The electroluminescence spectra of the red light electroluminescent device based on metal nanoclusters under different bias voltages are as follows Figure 7 As shown in Figure 7 As can be seen, the electroluminescence peak of the device is stably kept at 600 to 602 nm from low voltage to maximum brightness voltage;

[0063] The thickness of the ultra-thin LiF insulating layer is adjusted, and the brightness-voltage-current density curves of the red light electroluminescent device based on metal nanoclusters under different thicknesses of LiF are as follows Figure 8 As shown in Figure 9 As can be seen, the brightness-external quantum efficiency, current power and power density curves are as followsFigure 8 , Figure 9 It can be seen that when the LiF thickness is around 1 nm, the maximum brightness of the device remains basically unchanged, but the current density decreases significantly. This is due to the electrical inertia of LiF. When the LiF thickness gradually increases to around 2 nm, the maximum brightness of the device decreases significantly, and the current density decreases further. This is attributed to the low carrier injection caused by the excessively thick insulating layer.

[0064] Red photoluminescent devices based on metal nanoclusters at 50 cd / m -2 The brightness attenuation curve results under the given brightness are as follows: Figure 10 As shown, according to Figure 10 It can be seen that the brightness decay of the device after introducing LiF is significantly slower and the device stability is improved. This is due to the lower current density causing it to suffer less Joule heating effect.

[0065] In summary, this invention utilizes the metal cluster Au6Cu2 and the host materials TCTA and OXD-7 to fabricate a red organic light-emitting diode (OLED) based on metal nanoclusters. The introduction of the host materials enhances the luminescence of the metal nanoclusters through the Dexter energy transfer process. The flexible use of an electrically inert LiF insulating layer between the EML and ETL further regulates the energy transfer path and restricts the exciton recombination region. Using this host-guest system as the emitter layer, a red organic light-emitting diode with an electroluminescence (EL) wavelength of 602 nm was fabricated. This device exhibits a wavelength of 3887 cd / m². -2 The device exhibits high brightness and a high external quantum yield of 1.55%. Furthermore, the introduction of LiF significantly reduces the current density, resulting in a marked improvement in device stability. The brightness decay time is approximately three times that of the device without LiF.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a red electroluminescent device based on metal nanoclusters, characterized in that, The method comprises the following steps: S1, dissolving tetrahydrothiophene gold and 4'-ethynylbenzo 15-crown-5 in dichloromethane solution, stirring until completely dissolved; S2, dropwise adding triethylamine solution, low-temperature stirring, volatilizing the solvent and redissolving in dichloromethane solution to obtain an orange-red solution; S3, low-temperature sealing the orange-red solution, diffusing crystallization with n-hexane, and collecting orange-red needle-shaped crystals after standing; S4, dissolving the orange-red needle-shaped crystals and powder Cu(NCMe)4PF6 in dichloromethane solution, stirring in the dark to obtain a transparent red solution; S5, low-temperature sealing the transparent red solution, diffusing crystallization with diethyl ether, and collecting red needle-shaped crystals after standing; S6, dissolving the red needle-shaped crystals in dichloromethane solution containing electron acceptor material TCTA and electron donor material OXD-7 to obtain a host-guest mixed solution; S7, initially preparing a host-guest and insulating layer modified cluster red light electroluminescent device: S71, cleaning ITO conductive glass and performing ultraviolet ozone treatment; S72, spin-coating PEDOT:PSS solution on the ITO glass, then performing annealing treatment to obtain a hole injection layer, and then transferring into a glove box filled with N2 gas; S73, spin-coating the host-guest mixed solution on the PEDOT:PSS layer as a light-emitting layer; S8, transferring the product obtained in S7 into a vacuum cavity, and sequentially depositing ultrathin LiF, PO-T2T, LiF and Al layers by thermal evaporation, wherein the ultrathin LiF is used as an insulating layer, the PO-T2T 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, thereby obtaining the metal nanocluster-based red light electroluminescent device.

2. The method for fabricating a red photoluminescent device based on metal nanoclusters according to claim 1, characterized in that, In S1, the stirring speed is 800-1000 r / min, and the stirring time is 8-10 min.

3. The method for fabricating a red photoluminescent device based on metal nanoclusters according to claim 1, characterized in that, In S2, the stirring speed is 600-800 r / min, and the solvent is volatilized by a rotary evaporator at a speed of 80-100 r / min and a temperature of 23-28℃.

4. The method for fabricating a red photoluminescent device based on metal nanoclusters according to claim 1, characterized in that, In S4, the stirring speed is 800-1000 r / min.

5. The method for fabricating a red photoluminescent device based on metal nanoclusters according to claim 1, characterized in that, In S6, the concentration of the red crystals in the host-guest mixed solution is 2.0 mg / mL, the concentration of TCTA is 4.0 mg / mL, and the concentration of OXD-7 is 3.5 mg / mL. After the step of dissolving the red needle-shaped crystals in dichloromethane solution containing electron acceptor material TCTA and electron donor material OXD-7, the method further comprises the steps of performing vigorous shaking for 1-2 min and ultrasonic treatment for 1-2 min.

6. The method for fabricating a red photoluminescent device based on metal nanoclusters according to claim 1, characterized in that, In S71, the cleaning of the ITO conductive glass comprises the following steps: sequentially cleaning the ITO conductive glass with soap, deionized water, ethanol, chloroform, acetone and isopropanol.

7. The method for fabricating a red photoluminescent device based on metal nanoclusters according to claim 1, characterized in that, In S72, the spin-coating speed of the PEDOT:PSS solution is 3800-4200 r / min, and the spin-coating time is 28-32 s. The annealing temperature is 165-175℃, and the annealing time is 25-35 min.

8. The method for fabricating a red photoluminescent device based on metal nanoclusters according to claim 1, characterized in that, In S73, the rotation speed of the host-guest mixed solution on the PEDOT:PSS layer is 2800-3200 r / min, and the rotation time is 38-32 s.

9. The method for fabricating a red photoluminescent device based on metal nanoclusters according to claim 1, characterized in that, In S8, the evaporation speed of the ultra-thin LiF, PO-T2T and LiF is 0.05-0.2 nm / s, and the thickness is 0.5 nm-2 nm, 30-50 nm and 1-2 nm respectively; the evaporation speed of Al is 1-3 nm / s, and the thickness is 100-120 nm.

10. A red light electroluminescent device based on metal nanoclusters prepared by the preparation method of any one of claims 1-9.

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