Preparation method of cesium-lead-bromine-chlorine blue light quantum dot colloid and blue light film

Abstract

The invention relates to the technical field of metal halide luminescent materials, and discloses a preparation method of a cesium-lead-bromine-chlorine blue-light quantum dot colloid and a preparation method of a blue-light film. The method comprises the following steps: dissolving cesium bromide and lead bromide in N, N-dimethylformamide, adding oleic acid and oleylamine to form a precursor solution, and injecting the precursor solution into a toluene anti-solvent to prepare CsPbBr3 quantum dot colloid; and then dropwise adding a toluene saturated solution of alkaline earth metal chloride (calcium chloride, strontium chloride, barium chloride or magnesium chloride) for post-treatment to realize ion exchange of Cl <-> and Br <-> and synergistic defect passivation, so that the emission peak is continuously adjustable in the range of 450-500 nm, the half-peak width is less than 30 nm, and the photoluminescence quantum yield is greater than 60%. And further mixing the quantum dot colloid with a polymethyl methacrylate toluene solution and forming a film to obtain a stable blue light quantum dot film which can be used for a backlight source or a display device.

Description

Technical Field

[0001] This invention relates to the field of metal halide luminescent materials technology, and more particularly to perovskite quantum dots and methods for preparing thin films thereof. Background Technology

[0002] All-inorganic perovskite quantum dots (CsPbX3, X=Cl, Br, I) possess advantages such as high photoluminescence quantum yield, tunable emission wavelength, and narrow half-maximum width at half-maximum (HWHM), making them promising candidates for applications in backlight displays and light-emitting diodes (LEDs). Deep blue light-emitting materials (e.g., λ < 460 nm) are crucial for achieving high color gamut displays. However, according to published literature, the external quantum efficiency of deep blue perovskite LEDs (PeLEDs) is generally below 5%, significantly lagging behind green and red devices, primarily due to insufficient luminous efficiency and stability.

[0003] To obtain blue colloidal quantum dots, current technologies mostly employ strategies such as mixed halide perovskites (e.g., CsPb(Br / Cl)3) or strongly confined structures. Mixed halide systems typically require the simultaneous introduction of multiple halogen sources during synthesis, resulting in complex reaction pathways and a tendency for spectral drift due to component inhomogeneity, phase separation, or ion migration. Strongly confined systems often require excess ligands to stabilize the surface, which can hinder carrier injection and affect device performance. Furthermore, many approaches still rely on multi-step reactions or complex ligand combinations, making it difficult to achieve continuous and controllable tuning of the emission wavelength in a single process.

[0004] Therefore, there is an urgent need for a simple, reproducible, and scalable method for preparing blue perovskite quantum dots that can maintain a narrow half-width at half-maximum while achieving continuous tunability of the emission peak in the range of 450 nm to 500 nm, and also take into account high photoluminescence quantum yield and stability. Summary of the Invention

[0005] Problems with existing technologies: Existing blue light perovskite quantum dot systems generally have the following shortcomings: (1) Multiple halogen sources or complex ligand systems need to be introduced simultaneously during the synthesis process, resulting in many process steps and poor reproducibility; (2) Strongly confined systems often require excessive ligands to stabilize the surface, which may hinder carrier injection and reduce device efficiency; (3) Materials are prone to aggregation and increased defects in solid films, affecting luminescence efficiency and stability.

[0006] The purpose of this invention is to overcome the above-mentioned shortcomings of the prior art and provide a cesium lead bromine chlorine blue light quantum dot material and its preparation method. By post-processing chlorine doping, the emission peak can be continuously tunable in the range of 450 nm to 500 nm, and blue light emission with narrow half-width and high photoluminescence quantum yield can be obtained.

[0007] Another objective of this invention is to provide a blue quantum dot film containing the aforementioned blue quantum dot material and a method for preparing the same, so as to improve the stability and processability of the material under solid-state conditions.

[0008] Another object of the present invention is to provide a backlight or display device comprising the blue quantum dot film.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: (i) A cesium lead bromine chloro blue quantum dot material, wherein the material has a single independent emission peak under 365 nm wavelength excitation light, the emission peak wavelength range is 450 nm to 500 nm, and the position of the emission peak can be controlled by the dosage of the post-processed chlorine source; the half width at half maximum of the material is less than 30 nm, and the photoluminescence quantum yield is greater than 60%.

[0010] (II) Preparation method of the above materials: First, a precursor solution is prepared by dissolving cesium bromide and lead bromide in N,N-dimethylformamide, and then oleic acid and oleylamine are added to form a ligand environment; the precursor solution is injected into toluene as an antisolvent to obtain CsPbBr3 quantum dot colloids; subsequently, a saturated solution of alkaline earth metal chloride in toluene is added dropwise for post-treatment to make Cl - With Br - Ion exchange and synergistic defect passivation occur, thereby achieving a blue shift in the spectrum and improving luminescence performance.

[0011] (iii) A blue quantum dot film comprising the above-mentioned cesium lead bromochlorocyanine blue quantum dot colloidal solution or the cesium lead bromochlorocyanine blue quantum dot material prepared by the above method, and a polymer matrix.

[0012] (iv) Preparation method of the blue quantum dot film: After mixing the quantum dot colloidal solution with the polymer matrix solution, the film is formed by means of scraping or spin coating and then dried to obtain the blue quantum dot film.

[0013] (v) A backlight source or display device comprising the above-mentioned blue quantum dot film.

[0014] Using the above method, the emission peak of the initial CsPbBr3 quantum dots can be continuously and controllably blue-shifted from the green light region to the blue light region of 450 nm to 500 nm, and a narrow-band emission with a full width at half maximum (FWHM) of less than 30 nm can be obtained. Fine tuning of the emission peak can be achieved by adjusting the amount of chlorine source solution added. Thanks to the synergistic passivation effect in the post-processing, the photoluminescence quantum yield of the quantum dots can reach over 60%, preferably over 90%, and up to approximately 98.73%.

[0015] Furthermore, combining quantum dot colloids with polymer matrices such as polymethyl methacrylate to form films can improve the stability of quantum dots in a solid-state environment, making them easier to integrate as backlight materials or light-emitting layers in display devices.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention innovatively achieves simultaneous bandgap modulation due to chloride ion exchange and defect passivation due to alkaline earth metal cation doping through post-treatment with the dropwise addition of an alkaline earth metal chloride solution. This method optimizes the emission wavelength and luminescence efficiency of quantum dots in a single step, resulting in highly efficient blue light emission with a narrow full width at half maximum (FWHM).

[0017] Compared to existing technologies that require the pre-introduction of multiple halogen sources or the use of complex ligand combinations in the synthesis system, this invention employs a two-step "synthesis-follow-processing" method. The precursor synthesis and chlorine source post-processing steps are separated. The emission wavelength of the final product can be directly and controllably adjusted by regulating the amount of alkaline earth metal chloride saturated solution added. The process is simple to operate, operates under mild conditions (quantum dot nucleation is carried out at room temperature, and the ultrasonic dispersion temperature of the chlorine source solution is preferably 45°C), requires no high-temperature heat injection or complex atmosphere protection, is easy to scale up, and exhibits good reproducibility.

[0018] This invention utilizes alkaline earth metal chlorides as a post-treatment agent, which provides Cl... - / M 2+ (M = alkaline earth metal) ion pairs played a synergistic role. Cl - M is responsible for spectral shift. 2+ Responsible for defect passivation, the two work together to enhance the intrinsic optical quality of the material while achieving efficient blue light emission. This provides new ideas and methods for the post-processing modification of perovskite quantum dots. Attached Figure Description

[0019] Figure 1 These are comparative images of the photoluminescence (PL) spectra of the quantum dot colloids obtained in Examples 1 to 7 of the present invention. Figure 2 The photoluminescence (PL) spectrum of the blue quantum dot film obtained in Example 6 of the present invention and its physical image under 365 nm ultraviolet light irradiation; Figure 3 These are comparative images of the quantum dot colloids obtained in Examples 1 to 7 of the present invention under sunlight and irradiation by a 365 nm ultraviolet lamp (UV lamp); Figure 4 The graph shows the photoluminescence quantum yield of the quantum dot colloids obtained in Examples 1 to 7 of the present invention (data from Examples 8 to 10 are not shown in the graph). Detailed Implementation

[0020] To better understand the purpose, technical solution, and advantages of the present invention, the above technical solution will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] A method for preparing cesium-lead-bromochlorocyanuric blue quantum dot colloids and blue light thin films, the raw materials of which include: cesium bromide, lead bromide, alkaline earth metal chloride, oleic acid, oleylamine, toluene, and N,N-dimethylformamide. The molar ratio of lead bromide to cesium bromide is 1:1, the amount of anhydrous calcium chloride is 1 mmol, and the volume ratio of precursor solution to antisolvent is 0.005:1-0.01:1.

[0022] Example 1 (Control Group) The steps for preparing cesium lead bromide (CsPbBr3) quantum dot colloids (control group, without chlorine source post-treatment) are as follows: S1, 1 mmol lead bromide, 1 mmol cesium bromide, and 2.5 mL N,N-dimethylformamide were stirred thoroughly until the solution was clear. 250 µL oleylamine and 250 µL oleic acid were slowly added dropwise, and the mixture was stirred for 10 min at a stirring rate of 700 rpm to obtain precursor solution 1.

[0023] S2, 1 mmol anhydrous calcium chloride, 5 mL toluene, 250 µL oleylamine and 250 µL oleic acid, sonicated at 45 °C for 30 min to obtain calcium chloride toluene saturated solution 2.

[0024] S3, at room temperature (20-25℃), 25 µL of precursor solution 1 was injected into 5 mL of toluene and stirred vigorously at a stirring rate of 1200 rpm for 5 min to obtain cesium lead bromide perovskite quantum dot colloids with a luminescent center of ~510 nm, a full width at half maximum (FWHM) of ~26.5 nm, and a photoluminescence quantum yield of 77.43%.

[0025] Comparative Example 1 Based on the steps in Example 2, in step S4, the calcium chloride toluene saturated solution was replaced with an equal volume of pure toluene (1 µL) added dropwise to the cesium lead bromine quantum dot colloid. The resulting colloid showed essentially no change in emission peak under 365 nm excitation, remaining near approximately 510 nm, without a significant blue shift, indicating that the blue shift originated from the chlorine source post-treatment.

[0026] To investigate the effect of the amount of chlorine source solution added on the luminescence performance of quantum dots, experiments with different addition gradients were set up: In Examples 2 to 7, the amount of calcium chloride toluene saturated solution added in step S4 was 1 µL, 2.5 µL, 5 µL, 7.5 µL, 10 µL and 25 µL, respectively.

[0027] Example 2 The steps for preparing cesium lead bromine chloride (CsPb(Br / Cl)3) blue quantum dot colloids are as follows: S1, 1 mmol lead bromide, 1 mmol cesium bromide, and 2.5 mL N,N-dimethylformamide were stirred thoroughly until the solution was clear. 250 µL oleylamine and 250 µL oleic acid were slowly added dropwise, and the mixture was stirred for 10 min at a stirring rate of 700 rpm to obtain precursor solution 1.

[0028] S2, 1 mmol anhydrous calcium chloride, 5 mL toluene, 250 µL oleylamine and 250 µL oleic acid, sonicated at 45 °C for 30 min to obtain calcium chloride toluene saturated solution 2.

[0029] S3. At room temperature (20-25℃), 25 µL of precursor solution 1 was injected into 5 mL of toluene and stirred vigorously at a stirring rate of 1200 rpm for 5 min to obtain cesium lead bromide perovskite quantum dot colloid.

[0030] S4. Add 1 µL of the calcium chloride toluene saturated solution prepared in step S2 to the cesium lead bromide perovskite quantum dot colloid to obtain the cesium lead bromide chloride perovskite quantum dot colloid with a luminescence center of ~489 nm, a half-width of ~23.3 nm, and a luminescence efficiency of 98.73%.

[0031] Example 3 The preparation steps in this embodiment are basically the same as those in Embodiment 2, except that: In step S4, 2.5 µL of a calcium chloride toluene saturated solution was added to the cesium lead bromide perovskite quantum dot colloid to obtain the cesium lead bromide chloride perovskite quantum dot colloid. With the above adjustments, compared with Example 2, the luminescence center is ~486 nm, the half-width is ~23.4 nm, and the luminous efficiency is 96.38%.

[0032] Example 4 The preparation steps in this embodiment are basically the same as those in Embodiment 2, except that: In step S4, 5 µL of a calcium chloride toluene saturated solution was added to the cesium lead bromide perovskite quantum dot colloid to obtain the cesium lead bromide perovskite quantum dot colloid. With the above adjustments, compared with Example 2, the luminescence center was ~483 nm, the half-width was ~19.9 nm, and the luminous efficiency was 95.28%.

[0033] Example 5 The preparation steps in this embodiment are basically the same as those in Embodiment 2, except that: In step S4, 7.5 µL of calcium chloride toluene saturated solution in cesium lead bromide perovskite quantum dot colloid was added to obtain cesium lead bromide perovskite quantum dot colloid. With the above adjustments, compared with Example 2, the luminescence center is ~474 nm, the half-width is ~22.9 nm, and the luminous efficiency is 94.28%.

[0034] Example 6 The preparation steps in this embodiment are basically the same as those in Embodiment 2, except that: In step S4, 10 µL of a calcium chloride toluene saturated solution was added to the cesium lead bromide perovskite quantum dot colloid to obtain a cesium lead bromide chloride perovskite quantum dot colloid. The above adjustments, compared to Example 2, resulted in a luminescence center of ~458 nm, a full width at half maximum (FWHM) of ~27 nm, and a luminous efficiency of 68.71%. Further, 5 mL of a 20% solids content PMMA toluene solution was mixed evenly with the above cesium lead bromide chloride quantum dot colloid, then spin-coated onto an ITO glass slide and dried to obtain a blue quantum dot film.

[0035] Example 7 The preparation steps in this embodiment are basically the same as those in Embodiment 2, except that: In step S4, 25 µL of a calcium chloride toluene saturated solution was added to the cesium lead bromide perovskite quantum dot colloid to obtain the cesium lead bromide chloride perovskite quantum dot colloid. With the above adjustments, compared with Example 2, the luminescence center was ~453 nm, the half-width was ~18.45 nm, and the luminous efficiency was 63.74%.

[0036] Example 2-1 (Strontium Chloride Source) The preparation steps in this embodiment are basically the same as those in Embodiment 2, except that: In step S2, 1 mmol of anhydrous calcium chloride was replaced with 1 mmol of strontium chloride (SrCl2); in step S4, 1 µL of calcium chloride toluene saturated solution was replaced with 1 µL of strontium chloride toluene saturated solution. With the remaining raw material amounts and operating conditions unchanged, the prepared quantum dot colloid, under 365 nm excitation, showed a blue shift of the luminescence center to ~488 nm, a full width at half maximum (FWHM) of approximately 25.8 nm, and an increase in photoluminescence quantum yield to 80.12%. Compared to Example 1, the use of SrCl2 further improved the luminescence efficiency and caused a wavelength shift, proving that SrCl2... 2+ When B-site doping occurs, the difference between the ionic radius and the coordination environment results in specific regulation of the band gap and defect passivation effect of the quantum dot.

[0037] Example 2-2 (Barium Chloride Source) The preparation steps in this embodiment are basically the same as those in Embodiment 2, except that: In step S2, 1 mmol of anhydrous calcium chloride was replaced with 1 mmol of barium chloride (BaCl2); in step S4, 1 µL of calcium chloride toluene saturated solution was replaced with 5 µL of barium chloride toluene saturated solution. With the remaining raw material amounts and operating conditions unchanged, the prepared quantum dot colloid, under 365 nm excitation, showed an emission center at ~483 nm, a full width at half maximum (FWHM) of approximately 27.1 nm, and a photoluminescence quantum yield of 83.47%. The results indicate that BaCl2... 2+ The introduction of Ba can also achieve chloride ion exchange and B-site doping, but due to Ba 2+ With a larger ionic radius, the perturbation of the perovskite lattice is more significant. While achieving spectral modulation, the wavelength range corresponding to its optimal luminescence performance is slightly different from that of calcium and strontium, demonstrating the diverse tunability of alkaline earth metal cation selection on the final luminescence properties.

[0038] Example 2-3 (Magnesium Chloride Source) The preparation steps in this embodiment are the same as those in Embodiment 2, except that: In step S2, 1 mmol of anhydrous calcium chloride was replaced with 1 mmol of magnesium chloride (MgCl2); in step S4, 1 µL of calcium chloride toluene saturated solution was replaced with 2.5 µL of magnesium chloride toluene saturated solution. With the remaining raw material amounts and operating conditions unchanged, the prepared quantum dot colloid, under 365 nm excitation, had a luminescence center at ~496 nm, a full width at half maximum (FWHM) of approximately 27.5 nm, and a photoluminescence quantum yield of 65.8%. The results indicate that Mg... 2+ As alkaline earth metal cations with smaller ionic radii, their doping behavior perturbs the perovskite lattice through mechanisms similar to those of Ca. 2+ 、Sr 2+ The differences are slight. Although both can introduce Cl... - Achieving spectral fine-tuning, but due to Mg 2 + With Pb 2+ The ionic radii of lead and strontium differ significantly, resulting in relatively limited B-site doping efficiency and weaker defect passivation compared to calcium and strontium. Consequently, the improvement in luminous efficiency is relatively small. This embodiment further confirms that the selection of alkaline earth metal cations has a significant impact on the doping effect and final optical performance. The optimal effect of the technical solution of this invention is achieved on alkaline earth metals such as calcium and strontium, which have radii more compatible with lead ions.

Claims

1. A cesium lead bromochloroblue quantum dot material, characterized in that, The material is synthesized by reacting a quantum dot precursor with an antisolvent, and then its luminescence is regulated by post-treatment with a chlorine source. The material has a single independent emission peak under 365 nm excitation light, and the wavelength range of the emission peak is 450 nm to 500 nm. The position of the emission peak is regulated by the dosage of the chlorine source. The full width at half maximum (FWHM) of the material is less than 30 nm, and the photoluminescence quantum yield is greater than 60%.

2. A method for preparing the cesium lead bromochloroblue quantum dot material according to claim 1, characterized in that, Includes the following steps: S1. Prepare quantum dot precursor solution by dissolving cesium bromide and lead bromide in N,N-dimethylformamide and stirring until clear. Then add oleic acid and oleylamine and continue stirring to obtain precursor solution 1. S2 Preparation of chlorine source solution: Alkaline earth metal chloride is dispersed in toluene and oleic acid and oleylamine are added. After ultrasonic treatment at 35℃~50℃, the supernatant is taken to obtain chlorine source solution 2. S3 forms CsPbBr3 quantum dot colloids by adding 1 drop of the precursor solution to a vigorously stirred toluene antisolvent at room temperature (20℃~25℃). S4. Chlorine source solution 2 is added dropwise to the quantum dot colloid for post-treatment, so that Cl... - With Br - Ion exchange and synergistic defect passivation occur to obtain a cesium lead bromochloroblue photonic quantum dot colloidal solution.

3. The preparation method according to claim 2, characterized in that, The molar ratio of cesium bromide to lead bromide is 1:

1.

4. The preparation method according to claim 2, characterized in that, The volume ratio of the precursor solution 1 to the toluene antisolvent is 0.005:1 to 0.01:

1.

5. The preparation method according to claim 2, characterized in that, The amount of chlorine source solution 2 added is 5 µL to 30 µL.

6. The preparation method according to claim 2, characterized in that, The alkaline earth metal chloride is any one of calcium chloride, strontium chloride, barium chloride, or magnesium chloride.

7. A blue quantum dot thin film, characterized in that, It comprises the cesium lead bromochloroblue quantum dot material of claim 1 or the cesium lead bromochloroblue quantum dot colloidal solution prepared by the method of claim 2, and a polymer matrix.

8. The blue quantum dot thin film according to claim 7, characterized in that, The polymer matrix is ​​polymethyl methacrylate, and the solid content of the polymethyl methacrylate toluene solution is 10%~30%.

9. A method for preparing the blue quantum dot thin film according to claim 7, characterized in that, include: S1. Mix the quantum dot colloidal solution with a polymethyl methacrylate toluene solution; S2 The mixed solution is coated by scraping or spin coating and then dried to obtain a blue quantum dot film.

10. A backlight or display device, characterized in that, It includes the blue quantum dot film according to claim 7 or 8, or the blue quantum dot film prepared by the method according to claim 9.

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