A one-step method for preparing Cs4PbX6 perovskite nanocrystals embedded with CsPbX3 and its applications

Abstract

The application discloses a one-step method for preparing CsPbX3-embedded Cs4PbX6 perovskite nanocrystals and application thereof. The perovskite nanocrystals are of a core-shell structure, CsPbX3 is a crystal core, Cs4PbX6 is a perovskite shell coated outside the crystal core, and a CsPbX3 / Cs4PbX6 composite perovskite nanocrystal with a core-shell structure is formed. The core-shell structure not only improves the stability of the material, but also enhances the intrinsic emission performance of the material. The preparation method is a one-step slow cooling method, and specifically comprises the following steps: PbX2 and CsX are added into an organic solvent and heated until completely dissolved; the temperature is reduced to room temperature at a speed of 2 DEG C / h, and the crystal is naturally grown at room temperature for one week; and the fluorescent nanocrystals grown at the bottom of the bottle are the perovskite nanocrystals. The preparation method is simple, the obtained product has high stability, excellent light emission performance, narrow emission width and adjustable maximum emission wavelength in the visible light range, and the nanocrystals can be applied to green light LED devices.

Description

Technical Field

[0001] This invention relates to the field of nanocrystalline materials, and more particularly to a one-step method for preparing Cs4PbX6 perovskite nanocrystals embedded with CsPbX3 and their applications. Background Technology

[0002] All-inorganic cesium lead halide perovskite (CsPbX3 (X=Cl,Br,I,Cl / Br,Cl / I)) nanocrystals have become one of the most promising new functional nanomaterials in recent years due to their excellent photophysical properties, such as high photoluminescence quantum yield (PLQY, up to 100% after processing), narrow emission width, and tunable bandgap covering the entire visible light range. CsPbX3 nanocrystals have shown promising application prospects in photovoltaics, lasers, light-emitting diodes, and photodetectors.

[0003] Currently, commonly used preparation methods include hot injection, room temperature saturated recrystallization, high-frequency ultrasonication, microfluidic control, and mechanical polishing. Among these, hot injection is the most common method for preparing high-quality nanocrystals, but it suffers from drawbacks such as complex operation, the need for an inert atmosphere, high cost, and low yield. Furthermore, the prepared perovskites are all mononuclear structures, such as mononuclear cesium lead bromide (CsPbBr3), formamidinium lead bromide (FAPbBr3), and methylammonium lead bromide (MAPbBr3). Due to surface effects and quantum size effects, these mononuclear perovskite quantum dots exhibit poor stability, low strength, low quantum yield, and low luminescence intensity.

[0004] However, the preparation method of core-shell perovskite nanocrystals usually requires two steps: first, to prepare mononuclear perovskite nanocrystals, and second, to place the mononuclear nanocrystals into a solution of a second reactant system to further form composite perovskite nanocrystals with a core-shell structure. Moreover, the preparation environment needs to be carried out in a vacuum or nitrogen atmosphere. Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, the purpose of this invention is to provide a one-step method for preparing Cs4PbX6 perovskite nanocrystals embedded with CsPbX3 and their applications, thereby overcoming the drawbacks of conventional preparation methods, such as complex operation, requirement for inert atmosphere protection, high cost, and low yield. This preparation method is a one-step slow cooling method. Compared to previous methods, this method is simpler, more convenient to operate, can be performed at room temperature, and only requires a single reaction to synthesize this core-shell structured perovskite nanocrystal. The prepared Cs4PbX6 nanocrystals embedded with CsPbX3 exhibit excellent stability, remaining stable in air for more than 6 months, and possess excellent luminescence properties with a narrow emission width, and their maximum emission wavelength is tunable across the entire visible light range.

[0006] To address the aforementioned problems, one aspect of the present invention provides a method for preparing Cs4PbX6 perovskite nanocrystals embedded with CsPbX3. The method involves mixing PbX2, CsX, and the ligand raw materials according to a molar ratio of 1–2PbX2–2–5CsX, and an organic ligand raw material according to a volume ratio of 25–30DMF–20–25HX. PbX2, CsX, and the ligand raw material are weighed individually and then added together into a flask. The flask is then placed in a water bath and heated until completely dissolved. After dissolution, the flask is immediately removed, and its temperature is lowered to room temperature at a rate of 2°C / h. Crystals are allowed to grow naturally at room temperature. The fluorescent nanocrystals growing at the bottom of the flask are the perovskite nanocrystals described above. After one week, the crystals grown at the bottom of the flask are filtered and washed to obtain a crude product. The crude product is dried at 30–80°C for 8–12 hours to obtain Cs4PbX6 perovskite nanocrystals embedded with CsPbX3.

[0007] Preferably, X is Br.

[0008] Preferably, the temperature at which the mixture is heated to complete dissolution is 60–120°C.

[0009] Preferably, the solvent used for washing is one or a mixture of several of γ-butyrolactone, n-hexane, and toluene.

[0010] Another aspect of the present invention provides a one-step method for preparing Cs4PbX6 perovskite nanocrystals embedded with CsPbX3 and their application in green LED devices. The prepared nanocrystals are ground into powder, and then the nanocrystal powder is sieved to obtain Cs4PbX6 perovskite nanocrystal powder particles with CsPbX3 embedded in a basically uniform particle size. Subsequently, these powders are encapsulated with blue light chips and adhesives to prepare green LED devices.

[0011] Preferably, the specific steps for further grinding are as follows: the prepared Cs4PbX6 perovskite nanocrystals embedded with CsPbX3 are placed in an agate mortar and ground into Cs4PbX6 perovskite nanocrystal powder embedded with CsPbX3, and the grinding time is 5-10 minutes.

[0012] Preferably, the specific steps of the sieving process are as follows: the milled Cs4PbX6 perovskite nanocrystalline powder embedded with CsPbX3 is subjected to two sieving processes. First, it is sieved through a 400-mesh nylon mesh with a pore size of 0.0385 mm. Then, the nanocrystalline powder after the first sieving is collected. Next, it is sieved through a 500-mesh nylon mesh with a pore size of 0.03 mm. Finally, the nanocrystalline powder after the second sieving is collected.

[0013] Preferably, the blue light chip is mainly an InGaN blue light chip with an emission wavelength of 365nm. The main function of this blue light chip is to serve as an excitation light source to excite Cs4PbX6 perovskite nanocrystal powder embedded with CsPbX3.

[0014] Preferably, the adhesive is mainly an LED silicone encapsulant, which is divided into component A and component B. The main components of component A are 60%-90% epoxy resin and 10%-40% benzyl alcohol, and the main components of component B are 95%-100% triethylenetriamine and 0-5% water. When preparing and encapsulating white LEDs, components A and B need to be used simultaneously, and the ratio of the two components is 1:1.

[0015] Preferably, the specific steps for packaging and preparing a green LED device are as follows: weigh out Cs4PbX6 perovskite nanocrystal powder embedded with CsPbX3 according to the ratio, then add the two components of the adhesive in a 1:1 ratio, then tighten the cap of the sample collection bottle and put it into a mixer to stir evenly for 90 seconds. Then, the evenly mixed components are dripped onto the blue light chip by dispensing. Subsequently, the dispensed sample is dried to obtain the green LED device.

[0016] Preferably, the drying process mainly consists of two steps: first, the freshly packaged sample is placed in an oven at 80°C for preheating for 30 minutes, and then the pretreated sample is placed in an oven at 150°C for baking for 180 minutes.

[0017] This invention provides a novel method for preparing highly luminescent nanocrystals. The method is simple, easy to operate, and produces nanocrystals with good stability, excellent PL emission, and tunable emission wavelength across the entire visible light range.

[0018] Compared with the prior art, the present invention has the following significant advantages and beneficial effects:

[0019] 1. The perovskite nanocrystal material provided in this invention is prepared by a one-step slow cooling method. Compared with the usual two-step method of first preparing a single core and then preparing a composite core-shell perovskite, this preparation method only requires one reaction to obtain the product. The preparation process has low environmental requirements and does not require the use of a glove box or other nitrogen or vacuum environment. It can be operated at room temperature. Therefore, the whole operation process is simple, which greatly reduces the cost of raw materials and instruments.

[0020] 2. The core-shell perovskite nanocrystals provided by this invention have uniformly distributed nanocrystal particles and a distinct crystal lattice structure. Compared with core-shell perovskite nanocrystals prepared by a two-step method (reference document: CN 107474823 A), they have a narrower half-width at half-maximum (HWHM) and higher stability, and can be stored in air for more than 6 months.

[0021] 3. The core-shell structured perovskite nanocrystal material prepared in this invention can be used to manufacture green LED devices without adding any phosphors, and this invention provides a reliable application basis for optoelectronic devices such as liquid crystal display backlights and transmission polarization controllers. Attached Figure Description

[0022] Figure 1 This is a physical image of the nanocrystalline material of Example 1 of the present invention;

[0023] Figure 2 The photoluminescence spectrum of the nanocrystalline material of Example 1 of the present invention under ultraviolet light excitation at a wavelength of 365 nm is shown.

[0024] Figure 3 This is a TEM transmission electron microscope image of the nanocrystalline material of Example 1 of the present invention;

[0025] Figure 4 This is a physical image of the green LED device prepared based on Cs4PbX6 perovskite nanocrystal powder embedded with CsPbX3 in Embodiment 3 of the present invention.

[0026] Figure 5 The electroluminescence spectrum and color coordinate diagram of the green LED device prepared based on Cs4PbX6 perovskite nanocrystal powder embedded with CsPbX3 in Embodiment 3 of the present invention; Detailed Implementation

[0027] To better understand the above technical solutions, the following detailed description, in conjunction with the accompanying drawings and specific embodiments, will illustrate the technical solutions in detail. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any way. It should be noted that all other embodiments obtained by those skilled in the art without departing from the concept of the present invention and without creative effort are within the protection scope of the present invention.

[0028] This invention provides a Cs4PbX6 perovskite nanocrystal embedded with CsPbX3, comprising: PbX2 with a purity ≥99%, CsX2 with a purity ≥99% (X is one of Cl, Br, and I), providing Pb and halogen elements for the formation of nanocrystals; dimethylformamide (DMF) and hydrogen halide (HX) with a purity ≥99%, which mainly serve as organic ligands to facilitate better nanocrystal formation; γ-butyrolactone, n-hexane, and toluene with a purity ≥99%, which mainly serve to wash other substances on the crystal surface and ensure the purity of the crystal; wherein the required raw materials are mixed in a molar ratio of 1-2PbX2-2-5CsX; and the organic ligand raw materials are mixed in a volume ratio of 25-30DMF-20-25HX. The perovskite nanocrystals are core-shell composite materials, with a CsPbX3 core and a Cs4PbX6 shell. This core-shell structure effectively passivates the crystal surface of the perovskite nanocrystal composite, reduces surface defect luminescence, and enhances the intrinsic emission performance of the material.

[0029] This invention provides a Cs4PbX6 perovskite nanocrystal embedded with CsPbX3 prepared using a slow-cold-heat method. According to the above-mentioned proportions, PbX2, CsX, and ligand raw materials are weighed one by one, and then added together into a flask. The flask is then placed in a water bath and heated until completely dissolved. After dissolution, it is immediately removed, and the temperature is lowered to room temperature at a rate of 2℃ / h. Crystals are allowed to grow naturally at room temperature; the fluorescent nanocrystals growing at the bottom of the flask are the perovskite nanocrystals. After one week, the crystals grown at the bottom of the flask are filtered and washed to obtain a crude product. The crude product is dried at 30–80℃ for 8–12 hours to obtain Cs4PbX perovskite nanocrystals embedded with CsPbX3.

[0030] The heating temperature is 60–120°C; the solvent used for washing is one or a mixture of several of γ-butyrolactone, n-hexane, and toluene.

[0031] This invention provides a one-step method for preparing Cs4PbX6 perovskite nanocrystals embedded with CsPbX3 and their application in green LED devices. The prepared nanocrystals are ground into powder, and then the nanocrystal powder is sieved to obtain Cs4PbX6 perovskite nanocrystal powder particles with CsPbX3 embedded in a basically uniform particle size. Subsequently, these powders are encapsulated with blue light chips and adhesives to prepare green LED devices.

[0032] The specific steps for further grinding are as follows: Place the prepared Cs4PbX6 perovskite nanocrystals embedded with CsPbX3 into an agate mortar and grind them into Cs4PbX6 perovskite nanocrystal powder embedded with CsPbX3 for 5-10 minutes.

[0033] The specific steps of the sieving process are as follows: The ground Cs4PbX6 perovskite nanocrystalline powder embedded with CsPbX3 is subjected to two sieving processes. First, it is sieved through a 400-mesh nylon screen with a pore size of 0.0385 mm. Then, the nanocrystalline powder after the first sieving is collected. Next, it is sieved through a 500-mesh nylon screen with a pore size of 0.03 mm. Finally, the nanocrystalline powder after the second sieving is collected.

[0034] The blue light chip is mainly an InGaN blue light chip with an emission wavelength of 365nm. The main function of this blue light chip is to serve as an excitation light source to excite Cs4PbX6 perovskite nanocrystal powder embedded with CsPbX3.

[0035] The adhesive is mainly an LED silicone encapsulant, which is divided into component A and component B. Component A mainly consists of 60%-90% epoxy resin and 10%-40% benzyl alcohol, while component B mainly consists of 95%-100% triethylenetriamine and 0-5% water. When preparing and encapsulating white LEDs, components A and B need to be used simultaneously, and the ratio of the two components is 1:1.

[0036] The specific steps for packaging and preparing green LED devices are as follows: Weigh out Cs4PbX6 perovskite nanocrystal powder embedded with CsPbX3 according to the ratio, then add the two components of the adhesive in a 1:1 ratio, tighten the cap of the sample collection bottle and put it into a mixer to stir evenly for 90 seconds, then apply the evenly mixed components to the blue light chip by dispensing, and finally dry the dispensed sample to obtain the green LED device.

[0037] The drying process mainly consists of two steps. First, the freshly packaged sample is placed in an oven at 80°C for preheating for 30 minutes. Then, the pretreated sample is placed in an oven at 150°C for baking for 180 minutes.

[0038] The present invention also specifically discloses the following embodiments.

[0039] Example 1

[0040] Preparation of Cs4PbBr6 perovskite nanocrystals embedded with CsPbBr3.

[0041] Weigh 2 mmol PbBr2, 10 mmol CsBr, dimethylformamide and HBr (50 mL, volume ratio 6:5) and add them to the flask.

[0042] Place the flask in a water bath and heat at 60°C with stirring until dissolved.

[0043] After dissolving, remove the flask from the water bath and place it at room temperature to cool naturally to room temperature.

[0044] After about 7 days, crystals can be observed at the bottom of the flask. The crystals are then filtered and washed with γ-butyrolactone and toluene.

[0045] The crystals were transferred to a vacuum drying oven and dried at 60°C for 12 hours to obtain pure Cs4PbBr6 perovskite nanocrystals embedded with CsPbBr3. Figure 1 As shown.

[0046] The fluorescence emission spectra of the Cs4PbBr6 perovskite nanocrystal powder embedded with CsPbBr3 obtained above were measured using fluorescence spectroscopy. The obtained fluorescence emission spectra are as follows: Figure 2 As shown, from Figure 2 As can be seen, under 365nm excitation, its emission wavelength is at 518nm, which is consistent with previous research results.

[0047] The microstructure of Cs4PbBr6 perovskite nanocrystal powder embedded with CsPbBr3 was observed using transmission electron microscopy (TEM), and its TEM spectrum is shown in the figure below. Figure 3 As shown in the figure, it can be seen that CsPbBr3 nanocrystals are embedded in Cs4PbBr6 perovskite nanocrystals, which proves the core-shell structure mentioned above.

[0048] Example 2

[0049] Cs4PbBr6 perovskite nanocrystals embedded with CsPbBr3 are encapsulated into green LED devices.

[0050] The nanocrystals prepared in Example 1 were ground into powder with a small diameter in a mortar and then sieved.

[0051] Weigh the Cs4PbBr6 perovskite nanocrystal powder embedded with CsPbBr3 and the glue according to the formula, and put them into a mixer and stir for 90 seconds to obtain a mixed material.

[0052] The mixed component material is applied to the blue light chip by dispensing, and the mixed component material needs to be evenly coated on the blue light chip.

[0053] The coated chip is placed in an oven for baking, and finally a white LED device is prepared by Cs4PbBr6 perovskite nanocrystal powder embedded with CsPbBr3 is obtained.

[0054] The photoelectric performance parameters, including color coordinates and luminous efficacy, of a green LED device fabricated from Cs4PbBr6 perovskite nanocrystals embedded with CsPbBr3 were measured using an integrating sphere spectrometer. The electroluminescence spectrum and color coordinate diagram of the obtained green LED device are shown below. Figure 3 As shown, under a current drive of 30mA, the color coordinates of the green LED device are (0.0991, 0.7768), and the color rendering index is 90Ra.

[0055] Compared with the prior art, the preparation method of this invention is simpler, and the prepared nanocrystals have a narrower half-width at half-maximum (WHM), as shown in the table below:

[0056] This invention Comparison documents Launch Peak 518nm 506nm Half height and width 20nm 21.1nm

Claims

1. A one-step method for preparing Cs4PbX6 perovskite nanocrystals embedded with CsPbX3, characterized in that, include: PbX2 with a purity ≥99% and CsX with a purity ≥99%, where X is one of Cl, Br, or I, provide Pb and halogen elements for the formation of nanocrystals; dimethylformamide (DMF) and hydrogen halides (HX) with a purity ≥99% mainly serve as organic ligands to facilitate better nanocrystal formation; γ-butyrolactone, n-hexane, and toluene with a purity ≥99% are mainly used to wash away other substances on the crystal surface to ensure crystal purity; the required raw materials are prepared in a molar ratio of 1-2PbX2-2-5CsX; the organic ligand raw materials are prepared in a volume ratio of 25-30DMF-20-25HX. The perovskite nanocrystals described are core-shell composite materials, with a core of CsPbX3 and a shell of Cs4PbX6. According to the above proportions, PbX2, CsX, and the ligand raw materials are weighed one by one, and then added together into a flask. The flask is then placed in a water bath and heated until completely dissolved. After dissolution, it is immediately removed, and the temperature is lowered to room temperature at a rate of 2℃ / h. The crystals are allowed to grow naturally at room temperature for one week. The fluorescent nanocrystals growing at the bottom of the flask are the perovskite nanocrystals described. After one week, the crystals grown at the bottom of the flask are filtered and washed to obtain a crude product. The crude product is dried at 30–80℃ for 8–12 hours to obtain Cs4PbX6 perovskite nanocrystals embedded with CsPbX3.

2. The method for preparing Cs4PbX6 perovskite nanocrystals embedded with CsPbX3 in a one-step process according to claim 1, characterized in that, The heating temperature is 60–120°C.

3. The method for preparing Cs4PbX6 perovskite nanocrystals embedded with CsPbX3 in a one-step process according to claim 1, characterized in that, The solvent used in the washing process is one or a mixture of several of γ-butyrolactone, n-hexane, and toluene.

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