One-step synthesis of large-sized monodisperse PbS semiconductor quantum dots

Abstract

A one-step method for the synthesis of large, monodisperse PbS semiconductor quantum dots (CQDs) relates to the field of quantum dot synthesis. By combining a sulfur precursor prepared from sulfur (S) with a lead precursor prepared from lead oxide (PbO), and by manipulating process parameters, PbS CQDs of varying sizes (diameters: 7.53-9.89 nm) were obtained. This method enables the controlled preparation of PbS CQDs with exciton peak positions (1.7-2.0 μm) in the short-wave infrared range. Compared to classical quantum dot synthesis methods such as hot injection, multiple hot injection, and cation exchange, this method offers advantages: low raw material toxicity, a simple preparation process, excellent process reproducibility, controllable synthesis of large-sized PbS CQDs through process parameter manipulation, relatively uniform grain size distribution, and good batch-to-batch consistency. The PbS CQDs prepared by this method are suitable for applications in short-wave infrared photodetectors, solar cells, and other fields.

Description

Technical Field

[0001] The present invention relates to the field of preparation of semiconductor quantum dots, and in particular to a one-step preparation method of large-sized monodisperse PbS quantum dots. Background Art

[0002] PbS CQDs have potential applications in the field of infrared optoelectronics due to their highly tunable band gap, multi-exciton generation effect, and low-cost solution preparation process. Large-sized PbS CQDs with a band gap of less than 0.73eV and a corresponding wavelength greater than 1.7μm are more susceptible to water and oxygen corrosion and more difficult to prepare than their smaller counterparts due to the increased number of (100) crystal planes. The short-wave infrared band is between 1-3μm (1.24-0.41eV) and has been at the forefront of research due to its many potential applications in night vision, optical communications, biomedical imaging, and other fields. Large-sized PbSCQDs materials with exciton peaks in the short-wave infrared range are more suitable for applications in fields such as artificial intelligence and autonomous driving, which require low-cost short-wave infrared optoelectronic materials, compared to indium gallium arsenide (InGaAs) and mercury cadmium telluride (HgCdTe), which have complex preparation processes and high costs. In order to obtain PbS CQDs short-wave infrared optoelectronic devices with good performance, it is necessary to explore and optimize the preparation process parameters of PbS CQDs to achieve large-size, monodisperse, high-quality PbS CQDs with controllable size.

[0003] Currently, the synthesis methods for PbS CQDs include classic hot injection, multiple hot injection, and cation exchange. The classic hot injection method uses a lead oxide (PbO) and hexamethyldisilathione ((TMS)2S) system. By rapidly injecting (TMS)2S diluted in octadecene (ODE) into a lead oleate precursor, PbS CQDs of varying sizes with exciton absorption peaks ranging from 800-1800nm are obtained. However, the sulfur source in this synthesis method is highly toxic and expensive, making it unsuitable for large-scale production. The multiple hot injection method uses a (PbO) and hexamethyldisilathione ((TMS)2S) system, injecting (TMS)2S into the Pb precursor 1-9 times, achieving better size control. However, this method has many steps and requires high control of injection speed, etc. The cation exchange method uses pre-synthesized zinc sulfide (ZnS) nanorods as a sulfur precursor and injects them into a lead precursor made from PbCl2, which effectively achieves the synthesis of PbS CQDs of different sizes with exciton absorption peaks in the range of 1118-1903nm; however, this method is relatively complicated and requires the successful preparation of zinc sulfide (ZnS) nanorods in advance. Summary of the Invention

[0004] The purpose of the present invention is to propose a method for synthesizing large-sized PbS CQDs with controllable sizes by changing the synthesis time, with cheap and relatively safe raw materials and a simple synthesis method.

[0005] A one-step synthesis method for large-sized monodisperse PbS semiconductor quantum dots, characterized by using a combination of a sulfur precursor prepared using sulfur as a raw material and a lead precursor prepared using lead oxide as a raw material;

[0006] The following steps are involved:

[0007] S1, Preparation of sulfur precursor:

[0008] In an environment where both H2O and O2 contents were less than 0.01 ppm, sulfur powder was added to oleylamine to prepare a 0.167 mmol / ml sulfur precursor solution. Ultrasonic dissolution was performed under a sealed environment, and the solution became transparent amber.

[0009] S2, preparation of lead precursor:

[0010] PbO, oleic acid, and octadecene were magnetically stirred, vacuumed, degassed, heated to 110°C, purged with argon, and allowed to reach 110°C. The mixture was then vacuumed, purged with argon, and heated to 120°C until stable. A 0.189 mmol / ml lead precursor solution was prepared, wherein the volume ratio of oleic acid to octadecene was 0.1875:1.

[0011] S3, Synthesis of PbS CQDs:

[0012] The sulfur precursor obtained in step S1 was quickly injected into the lead precursor in step 2 to obtain a PbS CQDs solution. The solution changed from light yellow to dark brown. After reacting for 90-360 minutes, about 1 / 3 of the reaction system volume of n-hexane refrigerant was added and the solution was cooled to room temperature in a water bath.

[0013] S4, purification of PbS CQDs:

[0014] The mixture obtained in step S3 was washed with a mixture of n-butanol and anhydrous methanol in a molar ratio of 2:1. After centrifugation, the supernatant was removed to obtain a black precipitate, which was the PbS CQDs black powder.

[0015] Compared to existing preparation technologies, the synthesis method of this invention utilizes low-toxic raw materials, offers a simple and efficient preparation process with excellent reproducibility. Through the manipulation of process parameters, it is possible to achieve the controlled synthesis of monodisperse quantum dots of varying sizes, larger than 5 nm. The exciton peak position of 1700-2000 nm can be controlled within the short-wave infrared range. The large, monodisperse PbS quantum dots prepared by this invention are suitable for applications in short-wave infrared photodetectors, solar cells, and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the X-ray diffraction pattern (XRD) of PbS CQDs in Example 1.

[0017] Figure 2 This is the normalized absorption spectrum of PbS CQDs in Example 1.

[0018] Figure 3 High-resolution transmission electron microscopy (HRTEM) images and interplanar spacing measurement results of PbS CQDs in Example 1.

[0019] Figure 4 This is the normalized absorption spectrum of PbS CQDs in Example 2-4.

[0020] Figure 5 This is a high-resolution transmission electron microscopy (HRTEM) image of PbS CQDs in Example 4.

[0021] Figure 6 This is the absorption spectrum of the PbS CQDs synthesized as expected in Comparative Example 1. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to the embodiments.

[0023] Example 1: Synthesis of large-sized monodisperse PbS CQDs, the specific steps are as follows:

[0024] S1, Preparation of sulfur precursor:

[0025] In a glove box, under an environment where the H2O and O2 contents were both lower than 0.01 ppm, 0.04 g of sulfur powder (S) was added to 7.5 ml of oleylamine (OLA). After sealing the solution with a lid, the glove box was taken out and dissolved using ultrasound for 60 min to obtain 2.25 ml of a transparent amber sulfur precursor solution.

[0026] S2, preparation of lead precursor:

[0027] 2.0 g of PbO, 7.5 ml of oleic acid (OA) and 40 ml of octadecene (ODE) were placed in a three-necked flask and magnetically stirred at a speed of 700 r / min; vacuum degassing was carried out for 10 minutes; the flask was heated to 110°C under argon; when the temperature reached 110°C, vacuum was applied for 5 minutes; and the flask was heated to 120°C under argon to stabilize the temperature.

[0028] S3, Synthesis of PbS CQDs:

[0029] The temperature was stabilized at 120°C, and 2.25 ml of S precursor was quickly injected into the lead precursor solution in the three-necked flask using a syringe. The solution changed from light yellow to dark brown. After reacting for 90 minutes, 20 ml of n-hexane refrigerant was added and the solution was cooled to room temperature in a water bath.

[0030] S4, Purification of PbS CQDs:

[0031] The mixture in S3 was placed in centrifuge tubes, and a solution of n-butanol and anhydrous methanol with a molar ratio of 2:1 was used as the cleaning liquid. The centrifuge speed was set to 4000 r / min and the time was set to 3 min. After centrifugal precipitation, the supernatant was removed to obtain a black precipitate, which was the PbS CQDs black powder.

[0032] According to the color of the supernatant, the PbS CQDs were treated by repeating step S4 2-3 times to obtain a relatively clean black powder of PbS CQDs without excessive organic residue.

[0033] Add n-hexane to the PbS CQDs black powder to dissolve and filter to obtain a PbS CQDs solution, which is then placed in a 5 ml reagent bottle and stored in a glove box.

[0034] The PbS CQD solution obtained in this example was tested by spin coating. Specifically, EDT was used for ligand exchange and acetonitrile was used as a cleaning agent. The spin coating parameters were set as follows: first stage: 750 rpm, 30 seconds; second stage: 1500 rpm, 30 seconds.

[0035] After coating, the PbS CQDs film was subjected to phase, structure, crystallinity, morphology, and optical tests.

[0036] like Figure 1 The figure shows the X-ray diffraction pattern (XRD) of PbS CQDs. Its crystal structure belongs to cubic salt rock structure. Narrow and sharp diffraction peaks appear in the figure, corresponding to the (111), (200), (220), (311), (222), (400), and (420) crystal planes.

[0037] like Figure 2 As shown, it is the normalized absorption spectrum of PbS CQDs film, and the position of the first exciton peak is 1684nm.

[0038] like Figure 3As shown in the figure, the high-resolution transmission electron microscopy (HRTEM) image and interplanar spacing measurement results of PbS CQDs show that the quantum dots have good monodispersity; the lattice fringes of the quantum dots have clear boundaries, indicating that they have no obvious lattice defects; the interplanar spacing measurement results at positions 1, 2 and 3 are 0.348nm, 0.217nm and 0.302nm, respectively, which belong to the (111), (220) and (200) crystal planes of the PbS cubic salt rock structure.

[0039] It can be seen that the controllable synthesis of PbS CQDs (size: 7.53 nm) in this embodiment has a first exciton peak position of 1684 nm, which has application value in the fields of short-wave infrared photodetectors and the like.

[0040] Example 2: The difference from Example 1 is that the synthesis reaction time is different. In step S2, the reaction time is 210 min.

[0041] Example 3: The difference from Example 1 is that the only difference is the synthesis reaction time. In step S2, the reaction time is 270 min.

[0042] Example 4: The difference from Example 1 is that the only difference is the synthesis reaction time. In step S2, the reaction is carried out for 360 min.

[0043] like Figure 4 As shown, this is the normalized absorption spectrum of PbS CQDs in Example 2-4. It can be seen that as the synthesis time increases, the position of the first exciton peak red-shifts from 1848 nm in Example 2 to 1924 nm in Example 4.

[0044] like Figure 5 As shown, this is a high-resolution transmission electron microscopy (HRTEM) image of the PbS CQDs of Example 4. It can be seen that the prepared PbS CQDs have good monodispersity and the lattice fringe boundaries of the quantum dots are clear.

[0045] The size distribution deviation, i.e., the monodispersity, in Examples 1-4 is shown in Table 1.

[0046] Table 1

[0047]

[0048]

[0049] The calculation formula for size distribution deviation is intended to refer to polystyrene microspheres, and the formula is as follows:

[0050]

[0051]

[0052] Among them, d i represents the particle size of the microspheres,

[0053] n i Indicates particle size d i The number of microspheres at

[0054] E(D) represents the average particle size of CQDs particles analyzed by HRTEM images;

[0055] Coefficient of variation C v That is, the size distribution deviation.

[0056] The present invention can achieve controllable synthesis of monodisperse quantum dots PbS CQDs of different large sizes by fixing the precursor ratio of Pb and S and the synthesis temperature while changing the synthesis time, and the exciton peak position can be controlled in the short-wave infrared range.

[0057] Comparative Example 1: Using the S precursor and Pb precursor solution of Example 1, the S precursor was injected into the Pb precursor solution three times using a syringe pump, the reaction time was 60 min, and the other reaction conditions were the same as in Example 1. The absorption spectrum of the obtained PbS CQDs material is as follows: Figure 6 As shown in the figure, it can be seen that the material does not have the exciton absorption peak of PbS CQDs in the band of 600-2000nm, and does not show any light absorption characteristics in the infrared short-wave band.

Claims

1. A one-step synthesis method for large-sized monodisperse PbS semiconductor quantum dots, characterized in that: A sulfur precursor prepared from sulfur as a raw material and a lead precursor prepared from lead oxide as a raw material are combined; The following steps are involved: S1, Preparation of sulfur precursor: In an environment where both H2O and O2 contents were less than 0.01 ppm, sulfur powder was added to oleylamine to prepare a 0.167 mmol / ml sulfur precursor solution. Ultrasonic dissolution was performed under a sealed environment, and the solution became transparent amber. S2, preparation of lead precursor: PbO, oleic acid, and octadecene were magnetically stirred, vacuumed, degassed, heated to 110°C, purged with argon, and allowed to stabilize at 110°C. The mixture was then vacuumed, purged with argon, and heated to 120°C. A 0.189 mmol / ml lead precursor solution was prepared, wherein the volume ratio of oleic acid to octadecene was 0.1875:

1. S3, Synthesis of PbS CQDs: The sulfur precursor obtained in step S1 was quickly injected into the lead precursor in step 2 to obtain a PbS CQDs solution. The solution changed from light yellow to dark brown. After reacting for 90-360 min, 1 / 3 of the reaction system volume of n-hexane refrigerant was added and the solution was cooled to room temperature in a water bath. S4, Purification of PbS CQDs: The mixture obtained in step S3 was washed with a mixture of n-butanol and anhydrous methanol in a volume ratio of 2:

1. After centrifugation, the supernatant was removed to obtain a black precipitate, which was the PbS CQDs black powder.

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