A Preparation Method of High-Quality Ag2Se Colloidal Quantum Dot Ink and Film

Abstract

The invention discloses a method for preparing high-quality Ag2Se colloidal quantum dot (CQDs) ink and film, comprising the following steps: S1, mixing an Ag2Se CQDs solution with a ligand solution, shaking, and then centrifuging to obtain an Ag2Se CQDs substrate at the bottom of a centrifuge tube, wherein the ligand solution is a mixed solution of silver iodide, potassium iodide, and N,N-dimethylformamide; S2, adding n-octane to the Ag2Se CQDs substrate, shaking for 30 seconds, and then washing the substrate; S3, adding n-butylamine, n-hexylamine solution, and ligand solution to the Ag2Se CQDs substrate after washing several times, standing for 2 minutes, and then shaking for 1 minute, adding ethyl acetate, and centrifuging to obtain the Ag2Se CQDs substrate at the bottom of the centrifuge tube; S4, adding a mixed solution of N,N-dimethylformamide, dimethyl sulfoxide, n-butylamine, β-phenylethylamine, and n-hexylamine to the Ag2Se CQDs substrate, shaking, and then centrifuging to obtain the final Ag2Se The present invention realizes the preparation of liquid phase Ag2Se CQDs ink for the first time through the steps of preparing CQDs substrate, the preparation method is simple and effective, and the prepared Ag2Se CQDs film is smooth and uniform with low roughness.

Description

Technical Field

[0001] The present invention relates to a method for preparing high-quality Ag2Se colloidal quantum dot (CQDs) ink and film, and specifically to a process of replacing long-chain ligands with short-chain ligands on the surface of Ag2Se CQDs and preparing a film by spin coating the Ag2Se CQDs ink. Background Art

[0002] Ag2Se colloidal quantum dots (CQDs) are quasi-zero-dimensional nanomaterials with a surface coating of long-chain organic ligands (such as oleylamine, oleic acid, and octadecene) ranging in size from 2 to 20 nm and smaller than their exciton Bohr radius (5.2 nm). When thin films of Ag2Se CQDs are used in detectors, the long-chain ligands on the surface interfere with charge transfer between adjacent quantum dot particles, reducing the rate of charge transfer between quantum dots and resulting in poor device performance. Therefore, when preparing the quantum dot films of Ag2Se CQDs used in devices, short-chain organic ligands are used in place of long-chain ligands. This increases the rate of charge transfer between adjacent quantum dots and improves device performance.

[0003] Currently, in many applications based on Ag2Se CQDs, such as photodetectors, photodiodes, and transistors, the performance indicators of their devices are not as good as other quantum dot materials. One of the main reasons is that in Ag2Se CQDs-based devices, the preparation method of the Ag2Se CQDs thin film layer adopts the traditional solid-phase ligand exchange thin film method. The charge transport rate between adjacent quantum dots in this ligand exchange process is low, which leads to the inability to improve the performance of the device. In addition, when preparing thin films by solid-phase ligand exchange, the method of coating the film first and then exchanging during the exchange process can easily lead to the loss of surface ligands of colloidal quantum dots, introduce new defect states, and cause the performance of the device to deteriorate. Therefore, finding a new method for preparing thin films and preparing thin films with smooth surfaces, good density and uniformity has become a key factor in achieving performance improvements in applications such as photodetectors, solar cells, and transistors. Summary of the Invention

[0004] The present invention aims to provide a method for preparing high-quality Ag2Se CQDs ink and film. The method utilizes a liquid-phase ligand exchange and spin coating method to prepare high-quality Ag2Se CQDs ink and film, which is simple and efficient.

[0005] To achieve the above objectives, the present invention provides the following technical solutions:

[0006] A method for preparing high-quality Ag2Se colloidal quantum dot thin films comprises the following steps:

[0007] S1: The Ag2Se CQDs solution and the ligand solution were mixed, shaken, and then centrifuged to obtain the Ag2Se CQDs substrate at the bottom of the centrifuge tube. The ligand solution was a mixture of silver iodide, potassium iodide, and N,N-dimethylformamide.

[0008] S2: Add n-octane to the Ag2Se CQDs substrate and shake for 30 s, then wash the substrate, centrifuge and discard the n-octane solution, and repeat this step several times;

[0009] S3: After washing several times, n-butylamine, n-hexylamine solution and ligand solution were added to the Ag2Se CQDs substrate respectively, and the mixture was allowed to stand for 2 minutes and then shaken for 1 minute. Ethyl acetate was added and centrifuged to obtain the Ag2Se CQDs substrate at the bottom of the centrifuge tube;

[0010] S4: adding a mixed solution of N,N-dimethylformamide, dimethyl sulfoxide, n-butylamine, β-phenylethylamine and n-hexylamine to the Ag2Se CQDs substrate, shaking, and then centrifuging to obtain the final Ag2Se CQDs substrate;

[0011] S5: A mixed solution of N,N-dimethylformamide, dimethyl sulfoxide and n-butylamine was added to the final Ag2Se CQDs substrate, and the Ag2Se CQDs ink was obtained after shaking. The upper layer of the Ag2Se CQDs ink was then centrifuged and spin-coated to prepare an Ag2Se CQDs film.

[0012] Furthermore, in step S1, the Ag2Se CQDs preparation method is: using AgNO3 powder, Se powder, oleylamine and tri-n-octylphosphine to react at a temperature of 140°C for 30 minutes to synthesize an Ag2Se CQDs solution.

[0013] Preferably, in step S4, N,N-dimethylformamide, dimethyl sulfoxide, n-butylamine, β-phenylethylamine and n-hexylamine are sequentially taken in a volume ratio of 130:100:120:10:10 to prepare a mixed solution.

[0014] Preferably, N,N-dimethylformamide, dimethyl sulfoxide and n-butylamine are sequentially taken in a volume ratio of 125:125:20 to prepare a mixed solution.

[0015] The technical effects achieved by the present invention are:

[0016] The present invention realizes the preparation of liquid-phase Ag2Se CQDs ink for the first time. The preparation method is simple, effective and repeatable. The prepared Ag2Se CQDs film is flat and uniform with low roughness. Different from the traditional solid-phase ligand exchange film preparation method, the present invention adopts the liquid-phase ligand exchange method to prepare high-quality Ag2Se CQDs ink through the adjustment of chemical reagent ratio experiment. The ink preparation process is the replacement of Ag2Se CQDs solution and ligand solution in the liquid phase, which solves the problem of easy loss of surface ligands in solid-phase exchange. The flat, smooth, dense and uniform Ag2Se CQDs film is prepared by spin coating the ink. The Ag2Se CQDs film prepared by solid-phase exchange is applied to the unit device of the detector, and the dark current-voltage ( IV ) and tested the device's dark current. Comparative analysis demonstrates the success and feasibility of the thin film preparation presented herein. Furthermore, the thin film prepared by the present invention can cover large substrate areas greater than 1 × 1 cm, enabling the fabrication of large-scale devices such as focal plane arrays of photodetectors, liquid crystal displays, and large-panel solar cells. This allows for industrialized mass production and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a physical picture of the Ag2Se CQDs ink of Example 1;

[0018] Figure 2 TEM image of Ag2Se CQDs after ligand exchange in Example 1;

[0019] Figure 3 This is a photo of the Ag2Se CQDs film of Example 1 (>1×1 cm);

[0020] Figure 4 This is the AFM image of the Ag2Se CQDs film of Example 1.

[0021] Figure 5 This is a curve diagram showing the relationship between the dark current and voltage of the detector unit device of the Ag2Se CQDs film prepared by solid-liquid phase exchange in Example 1. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below through specific embodiments, but it should not be understood that the scope of the present invention is limited to the following examples.

[0023] Example 1

[0024] The preparation steps of the Ag2Se CQDs film of the present invention are as follows:

[0025] Preparation method of Ag2Se CQDs: Ag2Se CQDs solution was synthesized by reacting AgNO3 powder (8 mmol), Se powder (4 mmol), oleylamine (120 mL) and tri-n-octylphosphine (2 mL) at 140 °C for 30 min.

[0026] S1, 10 mL of 50 mg / mL Ag2Se CQDs solution was mixed with 10 mL of ligand solution, shaken for 2 min, and then centrifuged to obtain the Ag2Se CQDs substrate at the bottom of the centrifuge tube. The ligand solution was prepared by mixing silver iodide (1 mmol), potassium iodide (0.5 mmol), and N,N-dimethylformamide (10 mL).

[0027] S2, add 10 mL of n-octane to the Ag2Se CQDs substrate and shake for 30 s to wash it, then centrifuge and discard the n-octane solution, repeat this step 3 times;

[0028] S3, after washing three times, 10 μL of n-butylamine and 10 μL of n-hexylamine solution and 10 mL of ligand solution were added to the Ag2Se CQDs substrate, and the mixture was allowed to stand for 2 min and then shaken for 1 min. 10 mL of ethyl acetate was added and centrifuged to obtain the Ag2Se CQDs substrate at the bottom of the centrifuge tube;

[0029] S4, a mixed solution of 130 μL N,N-dimethylformamide, 100 μL dimethyl sulfoxide, 120 μL n-butylamine, 10 μL β-phenylethylamine, and 10 μL n-hexylamine was added to the Ag2Se CQDs substrate, and the mixture was shaken for 3 min to fully dissolve the Ag2Se CQDs substrate to obtain the Ag2Se CQDs solution, which was then centrifuged to obtain the final Ag2Se CQDs substrate;

[0030] S5. A mixed solution of 125 μL N,N-dimethylformamide, 125 μL dimethyl sulfoxide, and 20 μL n-butylamine was added to the final Ag2Se CQDs substrate and shaken for 3 min to obtain Ag2Se CQDs ink. After centrifugation, the upper layer of Ag2Se CQDs ink was spin-coated to prepare an Ag2Se CQDs film.

[0031] The Ag2Se CQDs film prepared in Example 1 of the present invention has the following test results:

[0032] Figure 1 This is a real picture of the Ag2Se CQDs ink in Example 1. It can be seen that the Ag2Se CQDs ink after shaking is viscous and adheres to the wall of the centrifuge tube.

[0033] Figure 2This is a TEM image of the Ag2Se CQDs after ligand exchange in Example 1, which shows that the Ag2Se CQDs are evenly distributed and the adjacent quantum dots of the Ag2Se CQDs wrapped by the short-chain ligands are very close to each other.

[0034] Figure 3 This is a photo of the Ag2Se CQDs film with a size of >1×1 cm in Example 1, indicating that the spin-coated Ag2Se CQDs ink can be used to prepare a film with a size of >1×1 cm, and the film surface is flat, smooth, dense and uniform, and the film substrate is an ITO substrate.

[0035] Figure 4 The AFM image of the Ag2Se CQDs film in Example 1 shows that the film has good density, a smooth surface, and a root mean square roughness ( RMS )Low, RMS =2.4 nm.

[0036] Comparative Example 1

[0037] Preparation of solid-phase Ag2Se CQDs film: A layer of Ag2Se CQDs solution was spin-coated on MoO3 to obtain an unexchanged Ag2Se CQDs film. A methanol solution of 1,2-ethanedithiol with a concentration of 10 mg / mL was dropped on the Ag2Se CQDs film and allowed to stand for 30 s. The film was then rinsed three times with methanol to obtain a solid-phase exchanged Ag2Se CQDs film. This step was repeated 12 times to obtain a solid-phase Ag2Se CQDs film layer of a certain thickness.

[0038] In order to test the performance of different Ag2Se CQDs films prepared in Example 1 and Comparative Example 1, the present invention respectively installed solid-phase and liquid-phase Ag2Se CQDs films on photovoltaic Ag2Se CQDs photodetectors for testing.

[0039] The photovoltaic Ag2Se CQDs photodetector consists of, from bottom to top, a substrate (quartz substrate size of 25 mm × 25 mm × 1 mm), an Au anode layer (thickness 29 nm), a MoO3 layer (thickness 20 nm), an Ag2Se CQDs layer (thickness 100 nm), a ZnO layer (thickness 152 nm), and an ITO cathode layer (thickness 160 nm).

[0040] The preparation steps of photovoltaic Ag2Se CQDs photodetector are as follows:

[0041] S1, cleaning the substrate: the substrate material is a quartz substrate;

[0042] S2, preparing the Au anode layer: sputtering the Au anode layer on the cleaned substrate;

[0043] S3, preparing MoO3 layer: thermally evaporating MoO3 layer on Au anode layer;

[0044] S4, preparation of Ag2Se CQDs layer: spin coating Ag2Se CQDs on the MoO3 layer;

[0045] S5, preparing a ZnO layer: sputtering a ZnO layer on the ZnO NCs layer;

[0046] S6, preparing an ITO cathode layer: sputtering ITO (indium tin oxides) on the ZnO layer as a cathode layer.

[0047] The results are as follows Figure 5 As shown, Figure 5 The relationship curve between the dark current and voltage of the detector unit device of Ag2Se CQDs film prepared by solid-liquid phase exchange. The lower the dark current value, the better the performance of the unit device. Figure 5 It can be seen that the dark current of the unit device of the Ag2Se CQDs film prepared by solid phase exchange is very large and does not show rectification characteristics. However, the dark current of the unit device of the Ag2Se CQDs film prepared by liquid phase exchange is 4 orders of magnitude lower than that of the solid phase exchange at negative bias, and shows better rectification characteristics, indicating that the detection performance of the unit device of the liquid phase exchange film is better. This shows that the successful preparation of the film of the present invention has great potential for application in the field of detectors, and also has certain guiding significance for the development of devices in other optoelectronic fields.

Claims

1. A method for preparing high-quality Ag2Se colloidal quantum dot thin films, characterized in that: The following steps are involved: S1: The Ag2Se CQDs solution and the ligand solution were mixed, shaken, and then centrifuged to obtain the Ag2Se CQDs substrate at the bottom of the centrifuge tube. The ligand solution was a mixture of silver iodide, potassium iodide, and N,N-dimethylformamide. S2: Add n-octane to the Ag2Se CQDs substrate and shake for 30 s, then wash the substrate, centrifuge and discard the n-octane solution, and repeat this step several times; S3: After washing several times, n-butylamine, n-hexylamine solution and ligand solution were added to the Ag2Se CQDs substrate respectively, and the mixture was allowed to stand for 2 minutes and then shaken for 1 minute. Ethyl acetate was added and centrifuged to obtain the Ag2Se CQDs substrate at the bottom of the centrifuge tube; S4: adding a mixed solution of N,N-dimethylformamide, dimethyl sulfoxide, n-butylamine, β-phenylethylamine and n-hexylamine to the Ag2Se CQDs substrate, shaking, and then centrifuging to obtain the final Ag2Se CQDs substrate; S5: A mixed solution of N,N-dimethylformamide, dimethyl sulfoxide and n-butylamine was added to the final Ag2Se CQDs substrate, and the Ag2Se CQDs ink was obtained after shaking. The upper layer of the Ag2Se CQDs ink was then centrifuged and spin-coated to prepare an Ag2SeCQDs film.

2. The method according to claim 1, characterized in that In step S1, the Ag2Se CQDs solution is prepared by reacting AgNO3 powder, Se powder, oleylamine and tri-n-octylphosphine at a temperature of 140°C for 30 minutes to synthesize the Ag2Se CQDs solution.

3. The method according to claim 1, characterized in that In step S4, N,N-dimethylformamide, dimethyl sulfoxide, n-butylamine, β-phenylethylamine and n-hexylamine are sequentially taken in a volume ratio of 130:100:120:10:10 to prepare a mixed solution.

4. The method according to claim 1, wherein In step S5, N,N-dimethylformamide, dimethyl sulfoxide and n-butylamine are sequentially taken in a volume ratio of 125:125:20 to prepare a mixed solution.

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