A method for preparing an ITO electrode loaded with silver nanoparticles and its application

Abstract

This invention discloses a method for preparing an ITO electrode loaded with silver nanoparticles and its application. The disclosed method includes growing silver nanoparticles on the surface of an ITO thin film on a target ITO glass substrate using an electrochemical method to form a silver nanoparticle layer; removing the silver nanoparticles from the side edges of the ITO electrode; and performing cleaning and annealing treatments. The prepared ITO electrode loaded with silver nanoparticles can be used in organic optoelectronic devices. This invention has low equipment requirements, low preparation cost, and short preparation cycle; moreover, it can be used in optoelectronic devices manufactured by solution processing or vapor deposition. In the field of solution-processed optoelectronic devices, electrochemical preparation of silver nanoparticles is more easily integrated with solution processing technology.

Description

Technical Field

[0001] This invention belongs to the field of organic optoelectronic device technology, specifically relating to a method for preparing an ITO electrode substrate loaded with ITO conductive glass silver nanoparticles and its application in the preparation of organic optoelectronic devices, especially organic electroluminescent diodes (blue light devices). Background Technology

[0002] Organic optoelectronic devices encompass technologies such as organic light-emitting diodes (OLEDs), organic solar cells (OSCs), and organic detectors (ODs). Introducing metal nanoparticles into organic optoelectronic devices and utilizing the surface plasmon resonance of these nanoparticles can effectively improve their photoelectric performance.

[0003] Localized surface plasmons (LSPs) of metal nanoparticles refer to charge density oscillations existing in metal nanoparticles or discontinuous metal nanostructures. When the surface of a metal nanoparticle is subjected to an electromagnetic disturbance that causes a non-zero charge density in a certain region, an electrostatic restoring force is generated, causing the charge distribution to oscillate. If the frequency of the electromagnetic disturbance and the plasma oscillation frequency are the same, resonance occurs, known as localized surface plasmon resonance (LSPR). According to Mie theory, when light shines on a metal nanoparticle, the incident light interacts with the surface charge of the metal nanoparticle near the resonance frequency, resulting in strong light absorption and scattering, and simultaneously forming a strong electromagnetic field enhancement near the surface of the metal nanoparticle. On the one hand, this electromagnetic field affects the electron transition dynamics of nearby particles, thereby improving the optoelectronic performance of devices under certain conditions; on the other hand, this collective oscillation of electrons on the surface of the metal nanoparticle also modulates the distribution and transmission of the light field, enhancing the light band resonating with the electron oscillation frequency. Utilizing this modulation and local enhancement effect of the light field, the optoelectronic performance of devices can be effectively improved.

[0004] Commonly used metal nanoparticles include Au, Ag, Cu, Al, and Pt. Common methods for introducing metal nanoparticles into organic optoelectronic devices include high-vacuum vapor deposition and solution coating. Existing high-vacuum vapor deposition methods are costly; solution coating methods require the introduction of a dielectric material. Summary of the Invention

[0005] In view of the defects or deficiencies of the prior art, the present invention provides a method for preparing an ITO electrode loaded with silver nanoparticles.

[0006] Therefore, the method for preparing the silver nanoparticle-loaded ITO electrode provided by the present invention includes:

[0007] Step 1: Silver nanoparticles are grown on the surface of the ITO film on the target ITO glass substrate using an electrochemical method to form a silver nanoparticle layer; the anode in the electrochemical method is an ITO glass substrate, the cathode is the target ITO glass substrate, and the area of ​​the ITO film on the target ITO glass substrate is smaller than the area of ​​the ITO film on the anode; the electrolyte solution is prepared from silver salt, polyethylene glycol and deionized water.

[0008] Step 2: Remove the silver nanoparticles from the side edges of the ITO film with silver nanoparticles grown on the surface obtained in Step 1; in order to avoid the influence of the silver nanoparticles on the functional layer of the optoelectronic device.

[0009] Step 3: Clean the surface of the ITO film loaded with silver nanoparticles after step 2 by ultrasonic cleaning in ethanol and acetone chemical reagents in sequence.

[0010] Step 4: Anneal the target ITO glass substrate after step 3 at 300℃-700℃ to obtain the ITO electrode loaded with silver nanoparticles.

[0011] An alternative approach is to wrap the edge of the target ITO glass substrate with conductive rubber in step 1, and then connect the conductive rubber to the cathode of the electrochemical power source.

[0012] Alternatively, the silver salt may be selected from silver nitrate.

[0013] Alternatively, the polyethylene glycol may be selected from PEG-400, PEG-800, PEG-2000, PEG-4000, PEG-10000, or PEG-20000.

[0014] An alternative is that the electrolyte solution contains 10-100 mg of silver nitrate, 20-100 mg of polyethylene glycol, and 500-1000 ml of water.

[0015] An alternative approach is to use a voltage of 0.5-3V and a reaction time of 30s-300s for the electrochemical method.

[0016] An alternative arrangement is that the anode and cathode are arranged in parallel, with the anode ITO film facing the cathode ITO film, and the projection of the ITO film onto the anode along the direction toward the anode is located in the central region of the anode.

[0017] An alternative is that the distance between the anode and the cathode is 5cm-10cm.

[0018] Alternatively, the silver nanoparticles may have a particle size of less than 200 nm, preferably 10-50 nm.

[0019] Compared to high-vacuum vapor deposition technology, the preparation method of this invention has lower equipment requirements, lower cost, and shorter preparation cycle. Furthermore, in the field of solution-processed optoelectronic devices, electrochemical methods and solution processing technology are more easily integrated, as both belong to wet manufacturing processes. The process does not require switching between dry and wet manufacturing, nor does it require switching between high vacuum and atmospheric pressure conditions.

[0020] Compared to solution-coated silver nanoparticles, this invention more easily forms uniformly distributed silver nanoparticles on an ITO plane without the need to introduce additional dielectric materials; and it has advantages in preparing nanoparticles with smaller particle sizes (10-50 nm) and non-spherical morphology.

[0021] The silver nanoparticle-loaded ITO electrode prepared by the method of this invention can be applied to organic optoelectronic devices such as light emission and photovoltaics, Raman scattering, biomolecular sensors, and electrochromic devices.

[0022] This invention also provides an organic light-emitting diode (OLED). The provided OLED is fabricated using an ITO electrode loaded with silver nanoparticles, prepared by the method described in claim 1. More specifically, the OLED comprises, from bottom to top, an ITO electrode loaded with silver nanoparticles, a hole injection layer, a hole transport layer, an emissive layer, an electron transport layer, a cathode buffer layer, and a cathode layer; the hole injection layer is located on the silver nanoparticle layer. Further optional embodiments include: the thickness of the hole injection layer being any value from 20 nm to 40 nm; and / or the thickness of the hole transport layer being any value from 25 nm to 60 nm; and / or the thickness of the emissive layer being any value from 20 nm to 45 nm; and / or the thickness of the electron transport layer being any value from 15 nm to 45 nm; and / or the thickness of the cathode buffer layer being any value from 1 nm to 5 nm; and / or the thickness of the cathode layer being selected from any value from 100 nm to 150 nm. Attached Figure Description

[0023] Figure 1 This is a SEM image of the morphology of the silver nanoparticle layer prepared in Example 1 of the present invention;

[0024] Figure 2 This is a visual representation of the uniformity of silver nanoparticles grown on the ITO surface under different anode areas in Example 1(b) and Comparative Example (a) of the present invention;

[0025] Figure 3This is a schematic diagram of the blue organic electroluminescent device structure in Embodiment 2 of the present invention;

[0026] Figure 4 The figures show a comparison of the performance (brightness-current density) curves of the blue organic electroluminescent device before and after the use of silver nanoparticles in the embodiments of the present invention. In the figure, (a) is the brightness-voltage-current density curve and (b) is the current density-brightness curve. Detailed Implementation

[0027] Unless otherwise specified, the scientific and technical terms used in this article are intended for understanding by those skilled in the art.

[0028] The specific embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0029] Example 1:

[0030] In this embodiment, the resistivity of the ITO glass substrate used is ≤10Ω / □, and the transmittance in the visible light band is ≥85%. Electrode etching is completed according to the device design requirements. The area of ​​the target ITO glass substrate is 1.0cm*2.5cm, and the area of ​​the anode ITO glass substrate is 10cm*10cm.

[0031] The anode and cathode were cleaned by ultrasonic cleaning in deionized water, ethanol and acetone for 30 minutes each.

[0032] ITO electrodes are prepared using the method of this invention:

[0033] Step 1: Electrochemically deposit a layer of silver nanoparticles on the target ITO surface;

[0034] In this embodiment, conductive rubber is used to wrap the edge of the cathode ITO and connect it to the power cathode. The area covered by the conductive rubber does not overlap with the effective light-emitting area of ​​the subsequent OLED device. The cathode ITO and the anode ITO are opposite to each other and remain parallel. At the same time, the projection of the cathode on the anode is located in the central region of the anode. The distance between the anode and the cathode in this embodiment is 5 cm.

[0035] In this embodiment, the specific amount of silver nitrate (purity ≥99.9%) used in the electrolyte solution is 30 mg; the specific amount of deionized water used is 1000 ml; and the dispersant used is 15 g of PEG-20000.

[0036] The electrochemical reaction voltage in this embodiment is 2.5V, and the duration is 70s;

[0037] Step 2, ITO side edge silver nanoparticle treatment;

[0038] Silver nanoparticles on the side edge of the cathode ITO film were physically scraped off using a blade at a 30°-60° angle.

[0039] Step 3: Cleaning of the ITO surface loaded with silver nanoparticles;

[0040] The silver nanoparticle-loaded ITO glass substrate after step 2 was ultrasonically cleaned in ethanol for 10 minutes, and then the ITO electrode was ultrasonically cleaned in acetone for 10 minutes.

[0041] Step 4: Heat annealing treatment of silver nanoparticles;

[0042] The ITO glass substrate obtained in step 3 was annealed at a temperature of 400+10℃ for 15 minutes to obtain the ITO electrode loaded with silver nanoparticles in this embodiment.

[0043] Figure 1 The SEM morphology of the silver nanoparticles on the surface of the ITO electrode prepared in this embodiment is given, which shows that uniform silver nanoparticles have been formed on the surface of the ITO electrode. The results show that the size of the silver nanoparticles is 20-50 nm. A visual image of the prepared ITO electrode surface is shown below. Figure 2 As shown in (b).

[0044] Comparative example:

[0045] The difference between this comparative example and Example 1 is that both the anode and cathode are conductive ITO with an area of ​​2.5cm*2.5cm.

[0046] A visual representation of the uniformity of silver nanoparticles grown on the cathode / target ITO surface is shown below. Figure 2 As shown in (a), the surface color varies in depth, indicating poor uniformity of the grown silver nanoparticles. However, when a large-area ITO anode (10cm*10cm, i.e., the area used in Example 1) is used, the uniformity of the silver nanoparticles grown on the cathode / target ITO surface is significantly improved, as shown in [example image]. Figure 2 As shown in (b).

[0047] Example 2:

[0048] This embodiment uses the ITO electrode loaded with silver nanoparticles prepared in Example 1 to fabricate the structure as follows. Figure 3 The organic electroluminescent blue light device shown has the following structure from bottom to top: ITO electrode (glass substrate, anode ITO layer, metal silver nanoparticle layer), hole injection layer, hole transport layer, light emission layer, electron transport layer, cathode buffer layer, and cathode layer prepared in Example 1.

[0049] The molecular structure of the OLED functional material used in this embodiment is as follows:

[0050]

[0051] The method for fabricating the organic electroluminescent blue light device in this embodiment is as follows:

[0052] The ITO electrode prepared in Example 1 was moved into a vacuum vapor deposition apparatus, and MoO3 was vacuum evaporated under high vacuum to form a hole injection layer with a thickness of 20 nm.

[0053] A hole transport layer with a thickness of 60 nm is formed by high-vacuum evaporation of NPB material on the hole injection layer;

[0054] A 35 nm thick light-emitting layer is formed by high-vacuum evaporation of the light-emitting layer material (light-emitting host material CBP, light-emitting guest material compound BCzVBi, with the doping amount of the guest material being 6.5% of the total mass of the host material) on the hole transport layer.

[0055] A 28nm electron transport layer is formed by high-vacuum evaporation of the compound TPBi on the light-emitting layer;

[0056] A cathode buffer layer with a thickness of 1.5 nm was formed by vacuum evaporation of LiF on the electron transport layer;

[0057] Metallic Al was vacuum-deposited onto the cathode buffer layer with a thickness of 100 nm.

[0058] In the above process, the vacuum environment is ≤5*10 -4 The deposition rates of the hole injection layer, hole transport layer, light emission layer, and electron transport layer are 1 A / s, the deposition rate of the cathode buffer layer is 0.2 A / s, and the deposition rate of the cathode Al layer is 5 A / s.

[0059] Table 1 and Figure 4 The study showed the effect of the presence or absence of silver nanoparticles on the performance parameters of OLED blue light devices (the detection methods for each parameter shown in Table 1 can be found in: GB / T 20871.61-2013. Organic Light Emitting Diode Displays - Part 61: Test Methods for Optical and Photoelectric Parameters). Figure 4 The test methods for the two curves shown can be found in GB / T 20871.61-2013, "Organic Light Emitting Diode Displays - Part 61: Test Methods for Optical and Photoelectric Parameters". It can be seen that silver nanoparticles can effectively improve the luminous performance of OLED blue light devices, with the maximum current efficiency increasing by 28% and the turn-on voltage decreasing by 0.1V. Moreover, while improving the luminous efficiency, it does not significantly affect the emission color coordinates of the device.

[0060] Table 1

[0061]

[0062] In Table 1, a: the drive current is 20 mA / cm². 2 b: Maximum value; c: Brightness reaches 1.0 cd / m² 2 .

[0063] The reference device in Table 1 is an OLED blue light device with no silver nanoparticles grown on the surface of the ITO electrode. Except for the absence of silver nanoparticles, its preparation technology, preparation method, and device structure parameters are the same as those of the device preparation process described in Example 2.

[0064] The foregoing provides a detailed description of the silver nanoparticle preparation technology, post-processing technology, organic compounds, and device performance used in the embodiments of this invention. Specific embodiments of OLED blue light devices have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only intended to aid in understanding the method and core ideas of this invention; furthermore, those skilled in the art will recognize that modifications may be made to the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as limiting the embodiments described in this application.

Claims

1. A method for preparing a silver nanoparticle-loaded ITO electrode, characterized by, The method comprises: Step 1, growing silver nanoparticles on the ITO film surface of the target ITO glass substrate by electrochemical method to form a silver nanoparticle layer; the anode in the electrochemical method is the ITO glass substrate, and the cathode is the target ITO glass substrate, and the ITO film area of the target ITO glass substrate is smaller than that of the anode; the electrolyte solution is prepared from silver salt, polyethylene glycol and deionized water; the voltage of the electrochemical method is 0.5-3V, the reaction time is 30s-300s, the anode and the cathode are arranged in parallel, and the projection of the ITO film along the direction towards the anode on the anode is located in the central region of the anode; Step 2, removing the silver nanoparticles on the side edge of the ITO film with silver nanoparticles grown on the surface obtained in step 1; to avoid the influence of the silver nanoparticles on the side edge of the electrode on the functional layer of the optoelectronic device; Step 3, cleaning the ITO film surface loaded with the silver nanoparticle layer after the treatment in step 2, and sequentially ultrasonic cleaning in ethanol and acetone chemical reagents; Step 4, annealing the target ITO glass substrate after the treatment in step 3 under the condition of 300-700℃ to obtain the silver nanoparticle-loaded ITO electrode; the polyethylene glycol is selected from PEG-400, PEG-800, PEG-2000, PEG-4000, PEG-10000 or PEG-20000; the electrolyte solution contains 10-100mg silver nitrate, 20-100mg polyethylene glycol and 500-1000ml water; the distance between the anode and the cathode is 5-10cm.

2. The method for preparing the ITO electrode loaded with silver nanoparticles according to claim 1, characterized in that, In step 1, the target ITO glass substrate is wrapped with conductive rubber after the edge of the target ITO glass substrate is wrapped with conductive rubber, and the conductive rubber is connected to the cathode of the electrochemical power supply.

3. The method for preparing the ITO electrode loaded with silver nanoparticles according to claim 1, characterized in that, The silver salt is selected from silver nitrate.

4. The method for preparing the ITO electrode loaded with silver nanoparticles according to claim 1, characterized in that, The particle size of the silver nanoparticles is less than 200nm.

5. An organic optoelectronic device, characterized in that The organic optoelectronic device is prepared by using the silver nanoparticle-loaded ITO electrode prepared by the method of claim 1.

6. An organic light-emitting diode, characterized in that, The organic light emitting diode is prepared by using the silver nanoparticle-loaded ITO electrode prepared by the method of claim 1.

7. The organic light emitting diode according to claim 6, wherein, The organic light emitting diode comprises, from bottom to top, a silver nanoparticle-loaded ITO electrode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, a cathode buffer layer and a cathode layer; the hole injection layer is located on the silver nanoparticle layer.

8. The organic light emitting diode according to claim 7, wherein, The thickness of the hole injection layer is in the range of any one value in 20-40nm; and / or the thickness of the hole transport layer is in the range of any one value in 25-60nm; and / or the thickness of the light emitting layer is in the range of any one value in 20-45nm; and / or the thickness of the electron transport layer is in the range of any one value in 15-45nm; and / or the thickness of the cathode buffer layer is in the range of any one value in 1-5nm; and / or the thickness of the cathode layer is selected from any one value in 100-150nm.

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