A method for preparing pure red light perovskite quantum dots with excellent thermal conductivity

Abstract

The present invention provides a method for preparing pure red light perovskite quantum dots with excellent thermal conductivity, comprising the following steps: S10: providing a monovalent cation precursor containing cesium; S20: providing a mixed precursor, the mixed precursor including a precursor containing iodine element, a precursor containing bromine element, a precursor containing a lead source, phosphonyl azide, an organic acid and an organic amine; S30: adding the monovalent cation precursor containing cesium to the mixed precursor for reaction, the reaction being carried out by a hot injection method under nitrogen or an inert gas, and the reaction temperature being 150°C - 200°C, to obtain the pure red light perovskite quantum dots with excellent thermal conductivity. The present invention improves the electrical and thermal conductivity of perovskite quantum dots by introducing hypophosphite ligands to replace part of the acid and amine long-chain ligands.

Description

Technical Field

[0001] The present invention belongs to the technical field of perovskite quantum dot preparation, and particularly relates to a method for preparing pure red light perovskite quantum dots with excellent thermal conductivity. Background Art

[0002] In recent years, metal halide perovskite quantum dots, as a new type of luminescent material, have the advantages of high color purity, high fluorescence quantum yield, adjustable emission wavelength, and narrow spectral half-width, and have broad application prospects in the fields of light-emitting diodes, solar cells, photodetectors, etc. Especially in the field of new generation high-definition displays, they are one of the most potential luminescent materials at present.

[0003] To meet the requirements of electro-luminescence for high color purity, low power consumption, and low cost, perovskite light-emitting diodes (PeLEDs) have become strong candidates for the next generation of display fields. Although great progress has been made in the performance of PeLEDs, with an external quantum efficiency (EQE) of over 20%, there are still problems in the perovskite light-emitting layer, such as low saturation brightness, serious EQE roll-off, and poor working stability. The practical application of high-performance pure red light PeLEDs (emission wavelength of 620 nm - 650 nm) for electro-luminescence remains a key challenge.

[0004] Chinese Patent No. CN 117425363 A discloses a high-brightness pure red light-emitting diode, which includes an ITO conductive glass, a hole injection layer, a hole transport layer, a perovskite quantum dot light-emitting layer, an electron transport layer, and an electrode layer arranged in sequence. Although this technology can achieve a luminous brightness of over 20000 cd m -2 However, the high resistance of the perovskite quantum dot light-emitting layer still causes insufficient Joule heat dissipation, and the accumulation of Joule heat easily causes degradation and decomposition of the quantum dot luminescent material, so it needs to be improved. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing pure red light perovskite quantum dots with excellent thermal conductivity. The present invention introduces hypophosphite ligands in the form of reaction products to replace part of the acid and amine long-chain ligands to improve the electrical and thermal conductivity of perovskite quantum dots.

[0006] A method for preparing pure red light perovskite quantum dots with excellent thermal conductivity includes the following steps:

[0007] S10: Provide a monovalent cation precursor containing cesium;

[0008] S20: Provide a mixed precursor, which includes a precursor containing iodine element, a precursor containing bromine element, a precursor containing lead source, phosphazide, organic acid, and organic amine;

[0009] S30: Add the cesium-containing monovalent cation precursor to the mixed precursor for reaction. The reaction is carried out by thermal injection under nitrogen or inert gas, and the reaction temperature is 150°C - 200°C to obtain the pure red light perovskite quantum dots with excellent thermal conductivity.

[0010] By adopting the above technical solution: As Figure 1 shown, in the reaction, phosphoryl azide contains an azide group, which can react with the carboxylic acid group in the organic acid under heating conditions to generate acyl azide and hypophosphite. The generated acyl azide further eliminates nitrogen under heating to generate isocyanate, and then the isocyanate reacts with the organic amine in the mixed precursor to generate urea derivatives.

[0011] Particularly, acyl azide and subsequent reaction products (isocyanate and urea derivatives), as by-products of this reaction, are easily removed in subsequent purification treatments. During the reaction process, phosphoryl azide consumes part of the organic acid in the mixed precursor, and the hypophosphite generated by the reaction competes with the organic acid long-chain ligand as a ligand for the perovskite quantum dots. Therefore, the reaction of phosphoryl azide consuming organic acid is beneficial for the hypophosphite ligand to replace more organic acid long-chain ligands to coordinate with lead on the surface of the perovskite quantum dots, making this kind of quantum dots have better electrical and thermal conductivity.

[0012] Particularly, the phosphorus-oxygen double bond contained in hypophosphite enables this ligand to form a stronger coordination effect with lead atoms on the surface of the quantum dots and stabilize the lattice of the quantum dots. In addition, during the crystallization process of the quantum dots, there is a competitive relationship between the ammonium group in the organic amine and cesium ions for surface capping, and the isocyanate generated by the side reaction will continue to react to consume the organic amine in the mixed precursor, enabling more cesium ions to cap on the surface of the quantum dots, thereby increasing the size of the obtained quantum dots, which is further beneficial for the carrier transport in the quantum dot light-emitting layer of the light-emitting diode.

[0013] Furthermore, the cesium-containing monovalent cation precursor includes one of cesium oleate, cesium carbonate, cesium acetate, cesium oxalate, and cesium stearate.

[0014] Furthermore, the iodine element-containing precursor includes zinc iodide (ZnI 2 ), strontium iodide (SrI 2 ), zirconium iodide (ZrI 4 ), and cobalt iodide (CoI 2 ) or a mixture of one or more of them in different proportions.

[0015] Furthermore, the bromine element-containing precursor includes zinc bromide (ZnBr 2 ), strontium bromide (SrBr2 ), zirconium bromide (ZrBr 4 ), cobalt bromide (CoBr 2 ), or a mixture of one or more of them in different proportions.

[0016] Furthermore, the precursor containing a lead source includes one or more of lead acetate, lead iodide, lead oleate, and lead stearate.

[0017] Furthermore, the organic acid in the mixed precursor is at least one of oleic acid, octanoic acid, stearic acid, and palmitic acid;

[0018] The organic amine is at least one of oleylamine, octylamine, and dodecylamine.

[0019] Furthermore, in the system of this application, a solvent may also be contained, including but not limited to octadecene (ODE), mesitylene, etc.

[0020] Furthermore, the phosphonyl azide precursor includes but is not limited to R 2 N 3 OP, RN 3 O 2 P, R 2 N 3 O 2 P, N 3 O 3 P, RN 3 O 3 P, R 2 N 3 O 3 P, or several of them;

[0021] Wherein, each R is independently a substituted or unsubstituted C1 to C20 aliphatic hydrocarbon, a substituted or unsubstituted C6 to C20 aromatic hydrocarbon, or a combination thereof.

[0022] Furthermore, the phosphonyl azide precursor includes but is not limited to one of diphenylphosphoryl azide, phenylphosphoryl azide, methyl phenylphosphate azide, phenyl phosphate azide, and diphenyl phosphate azide.

[0023] Furthermore, the phosphonyl azide reacts with the carboxylic acid group in the organic acid under heating conditions to generate acyl azide and hypophosphite;

[0024] The reaction of the phosphonyl azide consuming the organic acid is beneficial to the substitution of the hypophosphite ligand for the organic acid ligand, and then coordination with the lead on the surface of the perovskite quantum dots.

[0025] Furthermore, the hypophosphite ligand includes but is not limited to R 2 POOH, RPO(OH) 2 、R2 O 3 P, H 3 PO 4 , RO 2 P(OH) 2 , R 2 O 2 one or more of POOH;

[0026] wherein each R is independently a substituted or unsubstituted C1-C20 aliphatic hydrocarbon, a substituted or unsubstituted C6-C20 aromatic hydrocarbon, or a combination thereof; for example, the hypophosphite ligand is one of diphenylphosphoric acid, phenylphosphoric acid, methyl methylphosphonate, phenyl phosphate, or diphenyl phosphate.

[0027] Furthermore, the prepared perovskite quantum dots have an emission wavelength of 630 nm - 650 nm, and the emission wavelength is affected by factors such as the reaction temperature, the ratio of organic acid to organic amine, the ratio of the precursor containing bromine element to the precursor containing iodine element, and the addition amount of phosphazide. Those skilled in the art can obtain perovskite quantum dots with the desired emission wavelength through a limited number of experiments based on the concept of the present invention. Therefore, any modifications, supplements, or substitutions in a similar manner within the scope of the principles of the present invention shall be included within the protection scope of the present invention.

[0028] It can be predicted that the perovskite quantum dots obtained by the preparation method of the present application have a structural formula of CsPbBr x I 3-x .

[0029] The beneficial effects of the present invention are mainly reflected in: the present invention provides a preparation method of pure red light perovskite quantum dots with excellent thermal conductivity, and its emission wavelength is 630 nm - 650 nm. Phosphazide is selected as the reaction precursor, which consumes the organic acid and organic amine in the precursor during the reaction. The reaction product hypophosphite ligand more replaces some of the organic acid long-chain ligands of the quantum dots, directly improving the electrical and thermal conductivity of the perovskite quantum dots. At the same time, the hypophosphite contains P=O, which can form a stronger coordination effect with the lead atoms on the surface of the quantum dots, stabilizing the lattice of the quantum dots. The light-emitting diodes prepared with this kind of perovskite quantum dots can obtain higher brightness and EQE, the spectrum is more stable under high current density, and at the same current density and working time, the temperature on the surface of the light-emitting diode is lower, and the optoelectronic performance is significantly improved. This provides an effective and feasible solution to solve the problem of poor performance of light-emitting diodes caused by insufficient Joule heat dissipation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the reaction of diphenylphosphoryl azide with carboxylic acid groups and the reaction of acyl azide molecular intermediates with ammonium groups used in Example 1 of the present invention;

[0031] Figure 2 Comparison diagram of the electrical conductivity of the quantum dots with excellent thermal conductivity prepared in Example 1 of the present invention and the quantum dots prepared in Comparative Example 1;

[0032] Figure 3 Imaging diagram of the surface temperature of the light-emitting diodes prepared with the quantum dots of Example 1 of the present invention and the quantum dots of Comparative Example 1 operating at the same current density for the same time;

[0033] Figure 4 Graph of the change of the spectrum of the light-emitting diode prepared with the quantum dots of Example 1 over time;

[0034] Figure 5 Graph of the change of the spectrum of the light-emitting diode prepared with the quantum dots of Comparative Example 1 over time;

[0035] Figure 6 Imaging diagram of the surface temperature of the light-emitting diode with the quantum dots of Comparative Example 2 at the same current density and operating time as in Example 1;

[0036] Figure 7 External quantum efficiency - luminance curve graph of the light-emitting diode prepared with the perovskite quantum dots of Example 1;

[0037] Figure 8 Current density - luminance curve graph of the light-emitting diode prepared with the perovskite quantum dots of Example 1;

[0038] Figure 9 Size comparison diagram of the quantum dots prepared in Example 1 of the present invention and the quantum dots prepared in Comparative Example 1. Detailed implementation manners

[0039] To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific implementation manners described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] A preparation method of pure red light perovskite quantum dots with excellent thermal conductivity includes the following steps:

[0041] S10: Provide a monovalent cation precursor containing cesium;

[0042] S20: Provide a mixed precursor, which includes a precursor containing iodine element, a precursor containing bromine element, a precursor containing lead source, phosphoryl azide, organic acid and organic amine;

[0043] S30: Add the cesium-containing monovalent cation precursor to the mixed precursor for reaction. The reaction is carried out by thermal injection under nitrogen or inert gas, and the reaction temperature is 150°C - 200°C to obtain the pure red light perovskite quantum dots with excellent thermal conductivity.

[0044] In the present invention, the cesium-containing monovalent cation precursor includes one of cesium oleate, cesium carbonate, cesium acetate, cesium oxalate, and cesium stearate. Taking cesium oleate (Cs(OA)) as an example, the preparation method can be various, including but not limited to the following disclosed methods:

[0045] Weigh 100 mg of cesium carbonate (Cs 2 CO 3 ) and add it to a 25 mL three-necked flask. Then add 0.4 mL of oleic acid (OA) to dissolve cesium carbonate (Cs 2 CO 3 ) and add 5 mL of octadecene (ODE) as a solvent. Evacuate the three-necked flask and stir for a period of time, then fill the three-necked flask with nitrogen or inert gas and heat with stirring.

[0046] In the present invention, the obtained product can be purified. The method for purifying quantum dots can be the following steps, but is not limited to this purification method: Transfer the pure red light perovskite quantum dot stock solution prepared in S30 to a centrifuge tube and centrifuge at low speed; Take the upper clear liquid after low-speed centrifugation, add a certain volume of anti-solvent to precipitate the quantum dots and centrifuge at high speed; Disperse the quantum dot precipitate after high-speed centrifugation in octane or toluene, and filter and collect it with a 0.22 μm organic filter head to obtain a pure red light perovskite quantum dot solution. Under certain conditions, the above steps can be repeated, and continue to add anti-solvent to the perovskite quantum dot solution and centrifuge at high speed. In the above, the dividing line between low-speed centrifugation and high-speed centrifugation is 4000 revolutions per minute, that is, the rotation speed less than 4000 revolutions per minute is low-speed centrifugation. The rotation speed higher than 4000 revolutions per minute is high-speed centrifugation.

[0047] Example 1:

[0048] Preparation of pure red light perovskite quantum dots: Weigh 88 mg of Pb I 2 , 319 mg of Zn I 2 , 167 mg of ZnBr 2Add it into a 25 mL three-necked flask, and then add 0.3 mL of diphenylphosphoryl azide (DPPA), 2 mL of oleic acid (OA), 2.4 mL of oleylamine (OAm) and 5 mL of 1-octadecene (ODE) to obtain a mixed precursor; evacuate the three-necked flask for 20 min to remove excess water, oxygen and other components in the device, and then heat it to 170 °C in a nitrogen atmosphere, while maintaining magnetic stirring during this process; quickly inject 0.4 mL of the prepared cesium oleate precursor into the above-mentioned mixed precursor with a syringe for mixing. After reacting for 5 seconds, quickly cool it to room temperature with an ice-water bath to obtain a pure red-light perovskite quantum dot stock solution. After subsequent purification treatment, perovskite quantum dots for testing and fabricating light-emitting diodes are obtained.

[0049] The perovskite quantum dots of this example react at high temperature, have good crystallization quality and high fluorescence quantum yield. As Figure 1 shown, phosphoryl azide (diphenylphosphoryl azide) reacts with the carboxylic acid group in the organic acid (oleic acid) to consume the organic acid (oleic acid) in the mixed precursor and generate a hypophosphite ligand to replace the long-chain ligand of the organic acid (oleic acid). At the same time, the P=O contained in the hypophosphite has a stronger coordination effect with Pb on the surface of the quantum dots. Such quantum dots have more excellent electrical and thermal conductivity than quantum dots with organic acid / organic amine long-chain ligands. Figure 1 is the reaction schematic diagram of diphenylphosphoryl azide and carboxylic acid group; and the reaction schematic diagram of acyl azide molecular intermediate and ammonium group.

[0050] In addition, diphenylphosphoryl azide and oleic acid in this example do not react completely. Only part of the oleic acid participates in the reaction, and there is still a lot of oleic acid in the system. And the reactions that consume oleic acid and oleylamine can adjust the acid-base balance, making the whole system within an acceptable acid-base range.

[0051] As Figure 2 is the comparison chart of the electrical conductivity of the quantum dots of this example and those of Comparative Example 1. Figure 3 is the device surface temperature imaging chart of the light-emitting diodes fabricated from the quantum dots of this example and Comparative Example 1 working at the same current density for the same time. As can be seen from Figures 1-3 it: The quantum dots of this application have better electrical conductivity and excellent thermal conductivity, which is beneficial to the fabrication of stable light-emitting diodes.

[0052] Figure 4 is the chart of the change of the spectrum of the light-emitting diode prepared in this example with time. Therefore, adding phosphoryl azide to the precursor can obtain pure red-light perovskite quantum dots with excellent thermal conductivity and stable spectrum.

[0053] Comparative Example 1: (oleic acid / oleylamine)

[0054] CsPb(Br / I) 3 Preparation of quantum dots:

[0055] Weigh 88 mg of Pb I 2 , 319 mg of Zn I 2 , 167 mg of ZnBr 2 Add them to a 25 mL three-necked flask, and then add 2 mL of oleic acid (OA), 2.4 mL of oleylamine (OAm) and 5 mL of octadecene (ODE) to obtain a mixed precursor; evacuate the three-necked flask for 20 min to remove excess water, oxygen and other components in the device, and then heat it to 170 °C in a nitrogen atmosphere, and keep stirring magnetically during this process; quickly inject 0.4 mL of the prepared cesium oleate precursor into the above-mentioned mixed precursor for mixing. After reacting for 5 seconds, quickly cool it to room temperature with an ice-water bath to obtain CsPb(Br / I) 3 Quantum dot stock solution. After subsequent purification treatment, perovskite quantum dots for testing and fabricating light-emitting diodes are obtained.

[0056] Figure 4 and Figure 5 are the graphs of the spectra of the light-emitting diodes prepared in Example 1 and Comparative Example 1 respectively as a function of time. At a current density of 100 mA / cm -2 , the electroluminescence spectrum of Example 1 is stable, while the spectrum of Comparative Example 1 shows an obvious red shift of the emission peak position and spectral broadening, and the spectral stability is poor.

[0057] Comparative Example 2: (Diphenyl phosphate + oleic acid / oleylamine)

[0058] This comparative example uses the same preparation method as Example 1, except that diphenyl azide phosphate is replaced by diphenyl phosphate. In the preparation process of this example, there is no reaction consuming oleic acid and oleylamine. Therefore, the substitution rate of the synthesized CsPb(Br / I) 3 quantum dots for long-chain ligands is relatively low, resulting in inferior thermal conductivity of the quantum dots compared to Example 1. And the brightness and external quantum efficiency of the fabricated light-emitting diodes are both low.

[0059] Figure 6 is the temperature imaging diagram of the surface of the light-emitting diode in this example under the same current density and working time as in Example 1.

[0060] Comparative Example 3:

[0061] This Comparative Example 3 uses the same preparation method as Example 1, except that:

[0062] Diphenyl azide phosphate is replaced by diphenyl phosphate, and oleic acid is not added.

[0063] This comparative example obtains CsPb(Br / I) 3After the perovskite quantum dot stock solution, the quantum dots lost their optical activity during subsequent purification treatment, and the solution in the centrifuge tube turned yellow, and perovskite quantum dots were not successfully prepared.

[0064] The reason is that the reaction system only contains pure diphenyl phosphate and oleylamine, and their acidity coefficients pKa are 1.12±0.50 and 10.67±0.10 respectively. The pKa values differ too much, resulting in an imbalance in the acidity and alkalinity of the reaction system, exceeding the self-regulation range of the system and unable to achieve acid-base balance. Therefore, ligand detachment is likely to occur during subsequent cleaning, resulting in the loss of optical activity.

[0065] The light-emitting diodes mentioned in the above Example 1 and Comparative Examples 1-2 were all prepared in the following application example mode.

[0066] Application Example: (Preparation of Light-Emitting Diode)

[0067] Ultrasonic clean the ITO glass substrate with acetone-water-ethanol for 15 minutes respectively, and then treat the substrate surface with plasma. Spin-coat the PEDOT:PSS / PFI solution at 4000 revolutions per minute for 50 seconds and anneal at 160 °C for 15 minutes; spin-coat the PTAA chlorobenzene solution at 2000 revolutions per minute for 50 seconds and anneal at 170 °C for 20 minutes; spin-coat the perovskite quantum dot octane solution prepared in Example 1 and Comparative Examples 1-2 at 4000 revolutions per minute for 50 seconds in sequence. Vacuum thermal evaporation is used to prepare the TPBi electron transport layer with an evaporation rate of 0.5 / s and a thickness of 82 nm; vacuum thermal evaporation is used to prepare the LiF electron injection layer with an evaporation rate of 0.1 / s and a thickness of 1 nm; vacuum thermal evaporation is used to prepare the Al negative electrode with an evaporation rate of 1 / s and a thickness of 100 nm.

[0068] Figure 7 It is the external quantum efficiency-luminance curve graph of the light-emitting diode prepared with the perovskite quantum dots prepared in Example 1;

[0069] Figure 8 It is the current density-luminance graph of the light-emitting diode prepared with the perovskite quantum dots prepared in Example 1, with an external quantum efficiency of more than 24% and a luminance of more than 23000 cd m -1 above.

[0070] The perovskite quantum dots used in this example have excellent thermal conductivity, thus improving the optical performance of the prepared light-emitting diodes.

[0071] The above-described embodiments have described the preparation scheme of the present invention in detail. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the present invention. Any modifications, supplements or substitutions in a similar manner within the principle scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing pure red light perovskite quantum dots with excellent thermal conductivity, characterized in that: The steps include: S10: providing a monovalent cation precursor containing cesium; S20: providing a mixed precursor, wherein the mixed precursor comprises a precursor containing an iodine element, a precursor containing a bromine element, a precursor containing a lead source, phosphoryl azide, an organic acid and an organic amine; S30: adding the monovalent cation precursor containing cesium to the mixed precursor for reaction, wherein the reaction is carried out by hot injection under nitrogen or inert gas, and the reaction temperature is 150° C.-200° C., to obtain the pure red light perovskite quantum dots with excellent thermal conductivity; The phosphoryl azide precursor is one of diphenylphosphonic acid azide, phenylphosphonic acid azide, methylphosphonic acid azide, phenylphosphonic acid azide and diphenylphosphonic acid azide; The phosphoryl azide reacts with the carboxylic acid group in the organic acid under heating conditions to generate acyl azide and hypophosphite; The reaction of the phosphoryl azide consuming the organic acid is conducive to the hypophosphite ligand replacing the organic acid ligand, and then coordinating with the lead on the surface of the perovskite quantum dot; The hypophosphite ligand is one of diphenylphosphonic acid, phenylphosphonic acid, methyl methylphosphonate, phenyl phosphate and diphenyl phosphate.

2. The method for preparing pure red light perovskite quantum dots with excellent thermal conductivity according to claim 1, characterized in that: The monovalent cation precursor containing cesium includes one of cesium oleate, cesium carbonate, cesium acetate, cesium oxalate and cesium stearate.

3. The method for preparing pure red light perovskite quantum dots with excellent thermal conductivity according to claim 1, characterized in that: The precursor containing iodine element includes one or more of zinc iodide (ZnI2), strontium iodide (SrI2), zirconium iodide (ZrI4) and cobalt iodide CoI2.

4. The method for preparing pure red light perovskite quantum dots with excellent thermal conductivity according to claim 1, characterized in that: The precursor containing bromine element includes one or more of zinc bromide (ZnBr2), strontium bromide (SrBr2), zirconium bromide (ZrBr4), and cobalt bromide CoBr2.

5. The method for preparing pure red light perovskite quantum dots with excellent thermal conductivity according to claim 1, characterized in that: The precursor containing a lead source includes one or more of lead acetate, lead iodide, lead oleate, and lead stearate.

6. The method for preparing pure red light perovskite quantum dots with excellent thermal conductivity according to claim 1, characterized in that: The organic acid is at least one of oleic acid, caprylic acid, stearic acid and palmitic acid; The organic amine is at least one of oleylamine, octylamine and dodecylamine.

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