A preparation method of cesium lead bromide perovskite quantum dots doped with alkali metal ions at A site

Abstract

The application provides an A-site alkali metal ion doped perovskite CsPbBr3 quantum dot and a preparation method, can avoid the defects of uncontrollable product and complex experimental steps in in-situ doping reaction, has the advantages of simple and controllable process and rapid and convenient reaction. The application uses a rapid, simple and convenient ultrasonic post-processing method to perform A-site doping on lead halide perovskite CsPbBr3 quantum dots. The A-site doped perovskite quantum dots prepared by the application have uniform size, regular morphology, good optical performance and stability.

Description

Technical Field

[0001] This invention belongs to the field of perovskite quantum dot preparation technology, specifically relating to a method for preparing A-site alkali metal ion-doped cesium lead bromide perovskite quantum dots. Background Technology

[0002] Perovskite quantum dots, as an emerging semiconductor material, have broad application potential in optoelectronic devices. CsPbBr3 quantum dots, as a representative material, are attracting increasing attention from researchers due to their excellent photoelectric properties and stability. However, existing research on A-site doped CsPbBr3 quantum dots is limited, and most studies employ in-situ doping methods. These in-situ doping methods are cumbersome and the final synthesized product is uncontrollable.

[0003] Furthermore, the application of perovskite quantum dot materials in optoelectronic devices is limited by their stability and photoelectric properties. In traditional synthesis methods, the stability and luminous efficiency of CsPbBr3 quantum dots still need further improvement. Simultaneously, the surface of perovskite quantum dots is easily affected by oxidation or other environmental factors, leading to a decline in their photoelectric properties. Therefore, further improvements are needed to enhance the stability and luminous efficiency of CsPbBr3 quantum dots. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing A-site alkali metal ion-doped cesium lead bromide perovskite quantum dots.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing A-site alkali metal ion-doped cesium lead bromide perovskite quantum dots, characterized in that it includes:

[0008] Preparation of cesium oleate precursor;

[0009] Synthesize perovskite quantum dots to obtain a colloidal quantum dot solution;

[0010] A solution of an alkali metal salt at the A site was mixed with a quantum dot solution, subjected to ultrasonic reaction, centrifuged, and the precipitate was discarded to obtain A-site alkali metal ion-doped quantum dots. x Cs 1-xPbBr3 quantum dot solution, in which 0 <x<1;

[0011] A x Cs 1-x The PbBr3 quantum dot solution was mixed with an organic solvent, centrifuged, and the precipitate was discarded to obtain purified A. x Cs 1- x PbBr3 quantum dot solution.

[0012] In a preferred embodiment of the preparation method described in this invention, the alkali metal at the A site is one or more of Na, K, and Rb.

[0013] In a preferred embodiment of the preparation method described in this invention, the volume ratio of the alkali metal salt solution at the A site to the quantum dot solution is 10–100 μL: 1 mL.

[0014] In a preferred embodiment of the preparation method described in this invention, the power of the ultrasonic reaction is 5-50W and the reaction time is 2-10s.

[0015] In a preferred embodiment of the preparation method described in this invention, the centrifugation speed is 2000-6000 rpm and the centrifugation time is 3-10 min.

[0016] In a preferred embodiment of the preparation method described in this invention, the organic solvent is one of ethyl acetate and methyl acetate.

[0017] As a preferred embodiment of the preparation method described in this invention, wherein: A x Cs 1-x The volume ratio of PbBr3 quantum dot solution to organic solvent is 1:2 to 3.

[0018] As a preferred embodiment of the preparation method described in this invention, wherein: the step of A x Cs 1-x The PbBr3 quantum dot solution was mixed with an organic solvent and then centrifuged at a speed of 5000–10000 rpm for 3–10 min.

[0019] Another objective of this invention is to overcome the shortcomings of the prior art and provide an A-site alkali metal ion-doped cesium lead bromide perovskite quantum dot.

[0020] Another objective of this invention is to overcome the shortcomings of the prior art and provide an application of A-site alkali metal ion-doped cesium lead bromide perovskite quantum dots.

[0021] Beneficial effects of this invention:

[0022] (1) The A-site doped perovskite quantum dots prepared by the present invention have uniform size, regular morphology, and good optical performance and stability.

[0023] (2) The method of the present invention can avoid the disadvantages of uncontrollable products and complex experimental steps in in-situ doping reaction, and has the advantages of simple and controllable process and fast and convenient reaction. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0025] Figure 1 This is a schematic diagram of the structure of the perovskite crystal doped with alkali metal cations at the A site in Examples 1 to 4 of the present invention.

[0026] Figure 2 The fluorescence and absorption spectra of NaBr and KBr doped samples are shown in Examples 1 and 2 of this invention.

[0027] Figure 3 The images show the X-ray diffraction spectra of Na and K before and after doping in Examples 1 and 2 of this invention.

[0028] Figure 4 The images show the X-ray photoelectron spectra before and after Na and K doping in Examples 1 and 2 of this invention.

[0029] Figure 5 The images show transmission maps of quantum dots after doping with NaBr and KBr, respectively, with the inset showing the size statistical distribution of the quantum dots.

[0030] Figure 6 The images show the fluorescence and absorption spectra when RbBr is used for doping, with insets showing the band gaps of the samples before and after doping.

[0031] Figure 7 The in-situ fluorescence spectrum is obtained when RbCl is used for doping.

[0032] Figure 8 The X-ray diffraction spectra are shown before and after Rb doping.

[0033] Figure 9 The images show the X-ray photoelectron spectra before and after Rb doping.

[0034] Figure 10 The images show transmission maps of CsPbBr3 and quantum dots doped with RbBr and RbCl, respectively, with the inset showing the size statistical distribution of the quantum dots.

[0035] Figure 11 CsPbBr3, Rb x Cs 1-x PbBr3 and Rb x Cs 1-x The changes in PL intensity of Pb(Cl / Br)3 quantum dot samples after continuous irradiation under 365nm ultraviolet excitation light for 100 min, and the changes in PL intensity of samples before and after doping after being placed at 80℃ for 100 min.

[0036] Figure 12 CsPbBr3, Na x Cs 1-x PbBr3 and K x Cs 1-x The changes in PL intensity of PbBr3 quantum dot samples after continuous irradiation under 365nm UV excitation for 100 min, and the changes in PL intensity of samples before and after doping after being placed at 80℃ for 100 min.

[0037] Figure 13 The image shows the crystal structure of the quantum dots prepared in Comparative Example 1.

[0038] Figure 14 The quantum dots were prepared in Comparative Example 4. Detailed Implementation

[0039] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0040] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0041] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0042] Raw materials used in this invention embodiment: McLean: Cs2CO3, PbBr2; Aladdin: RbCl, RbBr, NaBr, KBr; Sigma-Aldrich: OA, OLA, ODE; Shanghai Lingfeng: n-hexane, ethyl acetate.

[0043] The performance characterization and analysis instruments used in the embodiments of this invention are as follows: absorption and fluorescence spectroscopy: Oceaninsight; transmission spectrum: JEOL JEM-1011; X-ray diffraction spectrum: Bruker D2 PHASER (Germany); X-ray photoelectron spectroscopy: PHI5000VersaProbe; time-resolved spectroscopy: Edinburgh LifeSpec II (UK).

[0044] Example 1

[0045] (1) Preparation of cesium oleate precursor:

[0046] Place 0.203g Cs2CO3, 0.625mL oleic acid OA and 10mL 1-octadecene ODE into a 50mL three-necked flask. First, remove the air from the flask, then raise the reaction solution from room temperature to 120℃, and at the same time, dry the reaction solution under vacuum for one hour.

[0047] Then raise the temperature of the reaction solution to 150°C and introduce nitrogen gas into the bottle until the Cs2CO3 in the bottle is completely dissolved; finally, store the prepared cesium oleate precursor in a glove box and heat it to 150°C before the next use.

[0048] (2) Synthesis of CsPbBr3 quantum dots by hot injection method:

[0049] Place 69 mg PbBr2 (0.188 mmol), 0.5 mL OA, 0.5 mL oleylamine (OLA), and 5 mL ODE into a 50 mL three-necked flask;

[0050] First, purge the air from the bottle, then dry the reaction solution in a vacuum environment at 120°C for one hour. After PbBr2 has completely dissolved, introduce nitrogen gas into the bottle and raise the temperature of the reaction solution to 180°C.

[0051] Then, 0.4 mL of the pre-prepared cesium oleate precursor was rapidly injected into the PbBr2 solution. After 5 seconds of reaction, the reaction was quenched with ice water to obtain the crude solution after the reaction.

[0052] The crude solution was centrifuged at 5000 rpm for 8 min, the supernatant was discarded, the precipitate was dispersed in 5 mL of n-hexane, and then centrifuged again at 9000 rpm for 8 min. The precipitate was discarded, and the supernatant obtained was the colloidal CsPbBr3 quantum dot solution.

[0053] (3) Post-treatment doping of Na ions:

[0054] First, the one containing Na +The salt is dissolved in water to obtain a saturated NaBr aqueous solution (6.1M), 10 μL of the saturated NaBr aqueous solution is mixed with 1 mL of CsPbBr₃ quantum dot solution, and then the mixed solution is reacted for 5 s under tip sonication with a power of 10 W;

[0055] Subsequently, the mixed reaction solution is immediately centrifuged at a rotation speed of 5000 rpm for 5 min to completely separate the aqueous phase and the hexane phase and stop the reaction from proceeding. Finally, the precipitate is discarded, and the obtained supernatant is A-site Na + successfully doped Na x Cs 1-x PbBr₃ (0<x<1) quantum dot solution.

[0056] (4) Purification step of quantum dots after doping:

[0057] Mix Na x Cs 1-x PbBr₃ (0<x<1) quantum dot solution and ethyl acetate at a volume ratio of 1:2, then centrifuge at 8000 rpm for 5 min, finally discard the precipitate, and the obtained supernatant is purified Na x Cs 1-x PbBr₃ (0<x<1) quantum dot solution.

[0058] Example 2

[0059] The difference between this example and Example 1 is that the NaBr aqueous solution (6.1M) in step (3) is replaced with a KBr aqueous solution (5.6M), and the remaining steps are the same as those in Example 1, to obtain purified K x Cs 1-x PbBr₃ (0<x<1) quantum dot solution.

[0060] Example 3

[0061] The difference between this example and Example 1 is that the NaBr aqueous solution (6.1M) in step (3) is replaced with a RbBr aqueous solution (6.1M), and the remaining steps are the same as those in Example 1, to obtain purified Rb x Cs 1-x PbBr₃ (0<x<1) quantum dot solution.

[0062] Example 4

[0063] The difference between this example and Example 1 is that the NaBr aqueous solution (6.1M) in step (3) is replaced with a RbCl aqueous solution (8.3M), and the remaining steps are the same as those in Example 1, to obtain purified Rb x Cs 1-x PbBr₃ (0<x<1) quantum dot solution.

[0064] The properties of the A-site alkali metal cation-doped perovskite crystals obtained in Examples 1-4 were characterized and analyzed, and the results are as follows: Figures 1-10 As shown.

[0065] in, Figure 1 The diagram shows the structure of the perovskite crystals doped with alkali metal cations at the A site in Examples 1-4 of this invention. It can be seen that after doping with alkali metal cations at the A site, the crystal structure of the perovskite is not destroyed but will produce certain distortions.

[0066] Figure 2 The fluorescence and absorption spectra of NaBr and KBr doped samples in Examples 1 and 2 of this invention show that after Na and K doping, the absorption and fluorescence of the samples exhibit a certain blue shift, corresponding to the lattice shrinkage caused by doping.

[0067] Figure 3 The X-ray diffraction spectra before and after Na and K doping in Examples 1 and 2 of this invention show that Na and K doping does not destroy the structure of the original perovskite sample, and two characteristic diffraction peaks corresponding to the (100) and (200) characteristic crystal planes can still be detected. However, after Na and K doping, these two characteristic diffraction peaks shift to larger diffraction angles, corresponding to the lattice shrinkage caused by doping.

[0068] Figure 4 The X-ray photoelectron spectra of Na and K before and after doping in Examples 1 and 2 of this invention show that Na and K were successfully incorporated into CsPbBr3 quantum dots. The presence of the target doping elements Na and K can be detected in the doped samples compared with the original samples.

[0069] Figure 5 The images show the transmission spectra of quantum dots doped with NaBr and KBr, respectively. The inset shows the size statistical distribution of the quantum dots, demonstrating that Na and K doping does not disrupt the cubic structure of the quantum dots. Figures 1-4 Together, they proved that Na and K were successfully incorporated into CsPbBr3 quantum dots.

[0070] Figure 6 The images show the fluorescence and absorption spectra when RbBr is used for doping. The inset shows the band gap of the sample before and after doping. It can be seen that after Rb doping, the absorption and fluorescence of the sample have a certain blue shift, and the band gap of the doped sample increases, which corresponds to the lattice shrinkage caused by doping.

[0071] Figure 7 The in-situ fluorescence spectrum when RbCl is used for doping shows that when Rb is doped with RbCl, there is a halogen exchange between Cl and Br ions, which corresponds to a gradual blue shift of the fluorescence peak.

[0072] Figure 8The X-ray diffraction spectra before and after Rb doping show that Rb doping does not destroy the structure of the original perovskite sample, and two characteristic diffraction peaks corresponding to the (100) and (200) characteristic crystal planes can still be detected. After Rb doping, both characteristic diffraction peaks shift to larger diffraction angles, corresponding to the lattice shrinkage caused by doping. In the RbCl sample, there is also the influence of halogen exchange between Cl ions and Br ions, so the degree of shift of its diffraction peaks is even greater.

[0073] Figure 9 The X-ray photoelectron spectra before and after Rb doping show that Rb was successfully incorporated into the CsPbBr3 quantum dots. The doped sample can detect the presence of the target dopant element Rb compared to the original sample. Furthermore, the successful Rb doping alters the binding energy of Cs in the crystal structure, shifting the Cs binding energy towards a smaller value, while the Pb binding energy remains unchanged.

[0074] Figure 10 The images show transmission maps of CsPbBr3 and quantum dots doped with RbBr and RbCl, respectively. The inset shows the size statistical distribution of the quantum dots, demonstrating that Rb doping does not disrupt the cubic structure of the quantum dots. Figures 6-9 Together, they proved that Rb was successfully incorporated into CsPbBr3 quantum dots.

[0075] Example 5

[0076] This embodiment tests the optical properties and stability of the perovskite quantum dot materials prepared in Examples 1-4, as well as the perovskite quantum dot material without A-site alkali metal ions. The test results are shown in Table 1. The luminescence quantum yield PLQY is calculated using a relative method based on the absorption and fluorescence of the sample measured by a spectrometer; the average fluorescence lifetime τ... avg The fluorescence lifetime was obtained using LifeSpec II detectors in Edinburgh, UK. The decay curve of the sample was obtained by measuring the delay time and intensity of the sample's emission relative to the excitation light. A second-order fit was then performed on the decay curve to obtain the average lifetime of the sample. (Radiative loss fluorescence lifetime τ) r Non-radiative loss fluorescence lifetime τ nr : Calculated using PLQY and τavg.

[0077] PL QY calculation by relative method: Rhodamine B was used as a control sample. The absolute PL QY of Rhodamine B was tested by the Edinburgh Spectrometer and found to be 90%. The relative PL QY of the sample was calculated by the following formula.

[0078]

[0079] In this equation, the subscripts S and R represent the test sample and the control sample, respectively. Φ is the quantum efficiency, I is the overall fluorescence intensity, A is the absorbance at the excitation wavelength, and n is the refractive index of the solvents used for the test sample and the reference sample. The absorption and fluorescence of the samples were measured using Oceaninsight.

[0080] Mean lifetime: The decay curve of the sample was measured using a LifeSpec II instrument in Edinburgh, UK. The t1 and t2 values ​​of the decay curve were obtained by second-order fitting using Origin. The mean lifetime of the sample can then be obtained using the following formula:

[0081]

[0082]

[0083] The radiation loss fluorescence lifetime τ is then calculated using the following formula. r Non-radiative loss fluorescence lifetime τ nr :

[0084]

[0085]

[0086]

[0087] Where k r k nr denoted as radiative transition constant and non-radiative transition constant, respectively.

[0088] Table 1. Performance test results of different quantum dot materials

[0089]

[0090] As shown in Table 1, when RbCl doping is used, the emission wavelength of the sample is blue-shifted due to the halogen exchange effect, and the material band gap increases. However, under the combined effect of Rb doping, the radiation lifetime is reduced, but the overall PL QY is ultimately reduced.

[0091] When RbBr, KBr and NaBr are used as dopants, the influence of halogens is excluded and only A-site cation doping is considered. Rb, K and Na partially replace Cs in the original sample and passivate the surface defects of the nanocrystals to a certain extent, introducing new charge trapping centers. This leads to a decrease in radiative recombination lifetime and average decay lifetime, and an increase in nonradiative recombination lifetime, which ultimately leads to an increase in PL QY.

[0092] Furthermore, photothermal stability tests were conducted under 20mW 365nm ultraviolet light irradiation and 80℃ temperature conditions, showing that its stability in hydrothermal environments increased by two times or more. Figure 11 , 12 As shown.

[0093] in, Figure 11 (a~c) show the changes in PL intensity of the samples before and after doping under continuous irradiation with 365nm ultraviolet light for 100min, representing CsPbBr3 and Rb, respectively. x Cs 1-x PbBr3 and Rb x Cs 1-x Pb(Cl / Br)3 quantum dots; (d~f) represent the PL intensity changes of the samples before and after doping after being placed at 80℃ for 100 min, respectively, for CsPbBr3 and Rb. x Cs 1-x PbBr3 and Rb x Cs 1- x Pb(Cl / Br)3 quantum dots.

[0094] Figure 12 (a~c) show the changes in PL intensity of the samples before and after doping under continuous irradiation with 365nm ultraviolet light for 100min, respectively for CsPbBr3 and Na. x Cs 1-x PbBr3 and K x Cs 1-x PbBr3 quantum dots; (d~f) represent the PL intensity changes of the samples before and after doping after being placed at 80℃ for 100 min, respectively, for CsPbBr3 and Na. x Cs 1-x PbBr3 and K x Cs 1-x PbBr3 quantum dots.

[0095] Comparative Example 1

[0096] The difference between this comparative example and Example 1 is that the NaBr aqueous solution (6.1M) in step (3) is replaced with an unsaturated NaBr aqueous solution (<6.1M). All other steps are the same as in Example 1. The crystal structure of the obtained quantum dots is as follows: Figure 13 As shown, its crystal structure has been damaged to some extent.

[0097] Comparative Example 2

[0098] The difference between this comparative example and Example 1 is that the volume ratio of the alkali metal salt solution at site A to the quantum dot solution in step (3) is replaced with 1:1. The remaining steps are the same as in Example 1, but because the amount of aqueous solution is too large, the quantum dot solution will be directly destroyed. Therefore, when processing 1 mL of quantum dots, the range of saturated aqueous solution should be controlled between 10 and 100 μL.

[0099] Comparative Example 3

[0100] The difference between this comparative example and Example 1 is that the volume ratio of quantum dot solution to ethyl acetate in step (4) is replaced with 1:1. The remaining steps are the same as in Example 1, but the photoluminescence quantum efficiency of the sample is affected because the ethyl acetate has a poor effect on reducing the washing effect of ligands.

[0101] Comparative Example 4

[0102] The difference between this comparative example and Example 1 is that the volume ratio of quantum dot solution to ethyl acetate in step (4) is replaced with 1:4. All other steps are the same as in Example 1, and the resulting quantum dots are as shown in the figure. Figure 14 As shown, a higher concentration of ethyl acetate leads to the aggregation of quantum dots in the ligand, which significantly affects the various properties of the quantum dots.

[0103] Comparative Example 5

[0104] The difference between this comparative example and Example 1 is that the doped alkali metal ions are replaced with Li. + However, due to its small ionic radius, the doping effect is poor, which has a certain impact on the optical properties of quantum dots.

[0105] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing A-site alkali metal ion-doped cesium lead bromide perovskite quantum dots, characterized in that: include, Preparation of cesium oleate precursor; Synthesize perovskite quantum dots to obtain a colloidal quantum dot solution; A saturated aqueous solution of an alkali metal salt at the A site was mixed with a quantum dot solution, subjected to ultrasonic reaction, centrifuged, and the precipitate was discarded to obtain A-site alkali metal ion-doped A-site alkali metal salt. x Cs 1-x PbBr3 quantum dot solution, in which 0 <x<1; A x Cs 1-x The PbBr3 quantum dot solution was mixed with an organic solvent, centrifuged, and the precipitate was discarded to obtain purified A. x Cs 1-x PbBr3 quantum dot solution; The alkali metal salt at the A site is selected from sodium bromide, potassium bromide, or rubidium bromide; The volume ratio of the aqueous solution of the saturated A-site alkali metal salt to the quantum dot solution is 10~100 μL: 1 mL; The power of the ultrasonic response is 5~50W, and the response time is 2~10s; The centrifugation speed is 2000~6000 rpm, and the centrifugation time is 3~10 min; The organic solvent is one of ethyl acetate and methyl acetate; The A x Cs 1-x The volume ratio of PbBr3 quantum dot solution to organic solvent is 1:2~3; The A x Cs 1-x The PbBr3 quantum dot solution was mixed with an organic solvent and then centrifuged at a speed of 5000-10000 rpm for 3-10 min.

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