JP7281522B2 - Semiconductor nanomaterials with high stability - Google Patents

Description

The present invention relates to semiconductor nanomaterials, and in particular to semiconductor nanomaterials with high stability.

Semiconductor nanoparticles, also called quantum dots (QDs), are semiconductor materials with nano-sized (generally <100 nm) dimensions and crystal structures and can contain hundreds to thousands of atoms. Since the QDs are very small, they have a large specific surface area and also exhibit quantum confinement effects. Therefore, QDs, based on their size, have unique physico-chemical properties that differ from those of corresponding bulk semiconductor materials.

The photoluminescence of QDs has a narrow full width at half maximum (FWHM) and emits purer colors. Moreover, the photoelectric properties of QDs can be easily controlled by adjusting the size of the core. Therefore, QDs are still under active research, for example for display applications. However, when QDs are used in display devices, there is a need to further improve their stability, photoluminescence quantum yield, lifetime, and other related properties.

Currently, the biggest challenge for QD applications is long-term stability. External factors such as intense light, high temperature, humidity, volatiles, and oxidants can cause irreversible decay of QD photoluminescence intensity. Stability can be enhanced by increasing the size of the QDs, primarily the thickness of the shell, either by adding multiple reaction steps to form an extra outer shell after the original QD synthesis, Alternatively, it is necessary to lengthen the QD synthesis reaction time, both of which increase the cost and often lead to a decrease in the photoluminescence quantum yield.

The present invention provides a quantum dot with a bilayer shell enveloping the core to provide better protection and improve the stability of the quantum dot, thereby effectively blocking the influence of external factors on the quantum dot. Avoid or reduce.

The present invention provides a quantum dot that includes a core composed of InP, a first shell composed of ZnSe, a second shell, and a graded alloy intermediate layer. A first shell envelops the surface of the core. A second shell wraps around the surface of the first shell and has a different material than the first shell. A graded alloy intermediate layer is formed between the core and the first shell. The graded alloy interlayer includes an alloy composed of In, P, Zn and Se. The In and P contents gradually decrease along the direction from the core to the first shell. The Zn and Se contents gradually increase along the direction from the core to the first shell. The particle size of the quantum dots is 11 nm or more. Quantum dots can emit light with a photoluminescence quantum yield of 50% or more when excited.

In one embodiment of the invention, the second shell is composed of ZnS.

In one embodiment of the invention, the particle size of the quantum dots is in the range of 11 nm to 15 nm.

In one embodiment of the invention, the particle size of the quantum dots is greater than or equal to 15 nm.

In one embodiment of the invention, upon excitation, the quantum dots can emit light with a photoluminescence quantum yield in the range of 60% to 90%.

In one embodiment of the present invention, the quantum dots are capable of emitting light with a photoluminescence quantum yield of 90% or greater upon excitation.

In one embodiment of the present invention, the photoluminescence quantum yield of the quantum dots before and after storage at elevated temperature decreases by 5% or less.

In one embodiment of the invention, the core of the quantum dot is capable of absorbing light in certain wavelength bands of the light source and emitting light in at least one different wavelength band.

Based on the above, the present invention provides quantum dots with a bilayer shell enveloping the core such that the diameter (or particle size) of the quantum dots is 11 nm or greater. In this case, the quantum dots of the present invention can have better protection to improve the long-term stability of the quantum dots, thereby protecting the quantum dots from external factors (e.g. strong light, high temperature, moisture, volatilization, etc.). substances, oxidizing agents, etc.) can be effectively avoided or reduced. At the same time, the quantum dots of the present invention can also maintain a photoluminescence quantum yield of 50% or higher. Therefore, the quantum dots of the present invention are suitable for application in display devices (eg, light-emitting diode (LED) devices or color wheels of projectors) involving intense light, high temperatures, and the like.

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

1 is a schematic diagram showing a quantum dot according to one embodiment of the invention; FIG.

1 is a transmission electron microscope (TEM) image of quantum dots from Example 1. FIG.

1 is a TEM image of quantum dots from Comparative Example 1;

As used herein, ranges expressed as "one numerical value to another numerical value" are schematic expressions to avoid listing all numerical values within the range herein. Accordingly, the recitation of a particular numerical range includes any numerical value within that numerical range, as well as any numerical value within that numerical range, as well as any numerical value within that numerical range, as well as any numerical value within that numerical range, as well as any numerical value within that numerical range, as well as any numerical value within that numerical range. Smaller numerical ranges are disclosed as defined by any numerical value. For example, a range of "11 nm to 15 nm particle size" discloses a range of "12 nm to 13 nm particle size", regardless of whether other values are recited herein.

FIG. 1 is a schematic diagram showing a quantum dot according to one embodiment of the invention.

Referring to FIG. 1, a quantum dot 100 includes a core 102 composed of indium phosphide (InP), a first shell 106, a second shell 108, and a graded alloy intermediate layer 104. As shown in FIG. A first shell 106 encases the surface of the core 102 . A second shell 108 wraps around the surface of the first shell 106 . In this embodiment, the first shell 106 completely wraps the surface of the core 102 and the second shell 108 completely wraps the surface of the first shell 106 . First shell 106 and second shell 108 may have different materials. For example, the first shell 106 is composed of zinc selenide (ZnSe) and the second shell 108 is composed of zinc sulfide (ZnS). However, the invention is not so limited and other materials for protecting the core 102 can be used as the materials for the first shell 106 and the second shell 108 . To improve the stability of the quantum dots, second shell 108 is selected from materials that provide better protection to core 102 (eg, zinc sulfide). However, a large lattice mismatch exists between the protective material and the core 102, making it more difficult to form a strong bond between the two materials. Therefore, the first shell 106 uses a material that provides less protection to the core 102 but has a smaller lattice mismatch with the core 102 (eg, zinc selenide).

As shown in FIG. 1, a graded alloy intermediate layer 104 may be formed between core 102 and first shell 106 . Note that the graded alloy intermediate layer 104 can further reduce the lattice mismatch between the core 102 and the first shell 106 . In other words, the graded alloy intermediate layer 104 optimizes the lattice arrangement between the core 102 and the first shell 106 to promote the growth of the first shell 106, thereby reducing the grain size 100s of the quantum dots 100 to You can make it bigger. On the other hand, the graded alloy interlayer 104 can also reduce defects and improve quantum yield. Therefore, compared to quantum dots without a graded alloy intermediate layer, embodiments of the present invention effectively increase the thickness of the shell layer 106 to not only improve the stability of the quantum dots, but also A quantum yield of 100 can also be maintained. In one embodiment, graded alloy interlayer 104 includes an alloy composed of In, P, Zn, and Se. The In and P contents gradually decrease along the direction from the core 102 toward the first shell 106 (i.e., outward from the core), while the Zn and Se contents decrease from the core 102 It gradually increases along the direction towards the first shell 106 .

In some embodiments, the particle size 100s of the quantum dots 100 is 11 nm or greater. In an alternative embodiment, the quantum dot 100 particle size 100s is in the range of 11 nm to 15 nm. In other embodiments, the particle size 100s of the quantum dots 100 is 15 nm or greater, such as 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, and the like. As used herein, the so-called "particle size" refers to the diameter of the quantum dots. If the quantum dot is non-spherical or quasi-spherical, the diameter refers to the length of a cross-section perpendicular to the quantum dot's first axis, which is not necessarily the quantum dot's longest axis. For example, if the cross-section is not circular, the diameter is the average of the longest and shortest axes of the cross-section. For spherical structures, the diameter is measured from one side to the other through the center of the sphere.

On the other hand, core 102 of quantum dot 100 can be used to absorb and emit light. In some embodiments, the core 102 of the quantum dot 100 can absorb light in certain wavelength bands of the light source and emit light in at least one different wavelength band. For example, the core 102 absorbs ultraviolet (UV) light with a peak wavelength of less than 400 nm and emits different colors of visible light (eg, red, green, or blue light) depending on the particle size of the core 102. be able to. In another example, core 102 can absorb blue light and emit different colors of visible light (eg, red light or green light) depending on the particle size of core 102 . In some embodiments, quantum dots 100 can emit light when excited and have a photoluminescence quantum yield of 50% or greater. In alternate embodiments, quantum dots 100 can have photoluminescence quantum yields in the range of 60% to 90%. In other embodiments, the quantum dots 100 have a photoluminescence quantum yield of 90% or greater, such as 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%. can have

In the present invention, the quantum dot 100 can emit light with a photoluminescence quantum yield of 50% or more when excited, which is because the core 102 of the quantum dot 100 has good quality and very few defects. Note that it means In other words, the quantum dot 100 of the present invention can improve long-term stability while maintaining high quantum yield. Therefore, the quantum dots 100 of the present invention are suitable for application in display devices (eg, light-emitting diode (LED) devices or color wheels of projectors) that involve intense light, high temperatures, and the like.

In order to improve the reliability of the present invention, some examples are listed below to further illustrate the quantum dots of the present invention. Although the following experiments are described, the materials used and their respective amounts and proportions, as well as handling details and procedures, etc., can be varied as appropriate without exceeding the scope of the invention. Therefore, the present invention should not be construed as limiting based on the embodiments described below.

Experimental example 1

0.575 mmol of indium acetate, 0.284 mmol of zinc acetate, 2.29 mmol of palmitic acid, and 125 mmol of 1-octadecene are heated at 140° C. for 2 hours under vacuum. The reaction is then changed to a _N2 environment and the reaction is cooled to room temperature.

After that, 0.39mmol of tris(trimethylsilyl)phosphine and 0.39mmol of trioctylphosphine are added at room temperature, then the temperature is raised to 270°C and this temperature is maintained for 2 minutes to form a reaction solution.

Then, after the temperature of the reaction solution is lowered to 150° C., selenium (2.4 mmol) dissolved in 4.05 mmol of trioctylphosphine and zinc stearate (25.27 mmol) dissolved in 88 mmol of 1-octadecene are added. . The reaction temperature is then raised to 320° C. and maintained for 30 minutes.

At a temperature of 320° C., add selenium (2.4 mmol) dissolved in 4.05 mmol trioctylphosphine and zinc stearate (25.27 mmol) dissolved in 88 mmol 1-octadecene and maintain for 30 minutes.

Then, at a temperature of 320° C., sulfur (16 mmol) dissolved in 16.2 mmol of trioctylphosphine is added and maintained for 10 minutes.

At a temperature of 320° C., zinc stearate (6.32 mmol) dissolved in 22 mmol of 1-octadecene is added and maintained for 10 minutes.

At a temperature of 320° C., sulfur (16 mmol) dissolved in 16.166 mmol of trioctylphosphine is added and maintained for 10 minutes.

At a temperature of 320° C., zinc stearate (5.55 mmol) dissolved in 19.33 mmol of 1-octadecene is added and maintained for 10 minutes.

At a temperature of 320° C., sulfur (96 mmol) dissolved in 96.96 mmol of trioctylphosphine is added and maintained for 10 minutes.

At a temperature of 320° C., zinc stearate (33.32 mmol) dissolved in 116 mmol of 1-octadecene is added and maintained for 30 minutes.

After cooling the reaction to 200° C., 20.75 mmol of 1-dodecanethiol is added and maintained for 25 minutes.

After stopping the reaction by cooling, ethanol is added to the reaction solution to precipitate the product, and the solid is recovered by centrifugation and re-dissolved in toluene.

Comparative example 1

0.575 mmol of indium acetate, 0.359 mmol of zinc acetate, 1.725 mmol of palmitic acid, and 30 mmol of 1-octadecene are heated at 120° C. for 2 hours under vacuum. The reaction system is then changed to a _N2 environment and the temperature is maintained at 280°C.

After that, 0.43 mmol of tris(trimethylsilyl)phosphine and 0.43 mmol of trioctylphosphine are added at 280° C. and the temperature is maintained for 2 minutes to form a reaction solution.

Then, after lowering the temperature of the reaction solution to 180° C., selenium (0.115 mmol) dissolved in 4.05 mmol of trioctylphosphine, zinc acetate (5.175 mmol) dissolved in 30 mmol of 1-octadecene, and 10 .35 mmol of oleic acid are added. The reaction temperature is then raised to 280°C.

Then, at a temperature of 280° C., sulfur (0.029 mmol) dissolved in 0.029 mmol of trioctylphosphine is added, after which the temperature is raised to 300° C. and maintained for 30 minutes.

At a temperature of 300° C., sulfur (0.115 mmol) dissolved in 0.115 mmol of trioctylphosphine is added and maintained for 30 minutes.

At a temperature of 300° C., sulfur (0.23 mmol) dissolved in 0.23 mmol of trioctylphosphine is added and maintained for 30 minutes.

At a temperature of 300° C., sulfur (2.30 mmol) dissolved in 2.30 mmol of trioctylphosphine is added and maintained for 30 minutes.

After the reaction was stopped by cooling, ethanol was added to the reaction solution to precipitate the product, and the solid was recovered by centrifugation and re-dissolved in toluene.

Particle size comparison

2 and 3 are TEM images of the quantum dots of Experimental Example 1 and Comparative Example 1, respectively. As shown in FIGS. 2 and 3, the InP quantum dots of Experimental Example 1 have a particle size of about 11 nm, and the InP quantum dots of Comparative Example 1 have a particle size of about 6 nm. This clearly shows that the particle size of the InP quantum dots of Experimental Example 1 is larger than that of the InP quantum dots of Comparative Example 1. In addition, as shown in FIG. 2, the InP quantum dots of Experimental Example 1 are not spherical, but polygonal with edges and corners.

high temperature storage

The solutions containing 1% by weight of InP quantum dots of Experimental Example 1 and Comparative Example 1 are each dissolved in n-hexane and stored at 60° C. for 4 hours. Next, the quantum yields (QY) of Experimental Example 1 and Comparative Example 1 before and after storage at high temperature are compared. As shown in Table 1 below, the quantum yield of Experimental Example 1 before storage at high temperature was 83%, and the quantum yield after storage at high temperature decreased to 79%. The quantum yield is reduced by 4%. In one embodiment, the reduction in photoluminescence quantum yield of the quantum dots of the present invention before and after storage at elevated temperatures is no more than 5%. In an alternative embodiment, the reduction in photoluminescence quantum yield of the quantum dots of the present invention before and after storage at elevated temperatures may be between 0% and 6%. On the other hand, before and after storage at high temperature, the quantum yield of Comparative Example 1 decreased from 81% to 58%, and the decrease in quantum yield was larger at 23%. This result indicates that compared to the thin shell layer of the InP quantum dots of Comparative Example 1, the InP quantum dots of Experimental Example 1 have a thicker shell, which can provide better protection. This indicates that the stability can be improved.

Additionally, in the present invention, the method of forming quantum dots includes mixing together In-containing precursors, P-containing precursors, Zn-containing precursors, and Se-containing precursors, followed by high temperature (about 270 to 320° C.) to form quantum dots with graded alloys. Compared to the method of first forming an InP core and then forming a shell layer surrounding the InP core (i.e., this method does not form a graded alloy), the quantum dots of the present invention have a can have a graded alloy intermediate layer between the InP core and the ZnSe shell to optimize the lattice alignment of . In other words, the graded alloy intermediate layer of the present invention can not only effectively increase the thickness of the shell layer, but also maintain the quantum yield of quantum dots. In addition, the method of forming quantum dots of the present invention is performed at high temperature, which can effectively shorten the reaction time and reduce damage to the InP core, thereby improving the quality of the InP core. , a high quantum yield can be maintained.

In summary, the present invention provides quantum dots with a bilayer shell enveloping the core such that the quantum dot has a diameter (or particle size) of 11 nm or greater. In this case, the quantum dots of the present invention can have better protection to improve the long-term stability of the quantum dots, thereby protecting the quantum dots from external factors (e.g. strong light, high temperature, moisture, volatilization, etc.). substances, oxidizing agents, etc.) can be effectively avoided or reduced. At the same time, the quantum dots of the present invention can also maintain a photoluminescence quantum yield of 50% or more. Therefore, the quantum dots of the present invention are suitable for application in display devices (eg, light-emitting diode (LED) devices or color wheels of projectors) involving intense light, high temperatures, and the like.

Although the present invention has been described with reference to the above embodiments, it will be apparent to those skilled in the art that changes can be made to the described embodiments without departing from the spirit of the invention. Accordingly, the scope of the invention is defined by the appended claims rather than by the above detailed description.

In the present disclosure, semiconductor nanomaterials with high stability are provided. Semiconductor nanomaterials include quantum dots in which a bilayer shell surrounds a core. In this case, the quantum dots have a diameter (or particle size) of 11 nm or greater in order to provide better protection and improve long-term stability of the quantum dots, whereby external factors to the quantum dots (e.g. effectively avoid or reduce the effects of strong light, high temperature, humidity, volatile substances, oxidants, etc.). As a result, the quantum dots of the present invention are suitable for application in display devices (eg, light-emitting diode (LED) devices or color wheels of projectors) involving intense light, high temperatures, and the like.

100: Quantum dot 100s: Grain size 102: Core 104: Gradient alloy intermediate layer 106: First shell 108: Second shell

Claims (8)

a core made of InP;
a first shell made of ZnSe and enveloping the surface of the core;
a second shell encasing the surface of the first shell and having a different material than the first shell;
A graded alloy intermediate layer formed between the core and the first shell and comprising an alloy composed of In, P, Zn, and Se, wherein the In and P contents vary from the core to the a graded alloy intermediate layer, wherein the Zn and Se content gradually decreases along the direction toward the first shell and the content of said Zn and Se gradually increases along said direction from said core to said first shell; including
The quantum dots have a particle size of 11 nm or more, and the quantum dots can emit light with a photoluminescence quantum yield of 50% or more when excited.
quantum dots. 2. The quantum dot of claim 1, wherein said second shell is composed of ZnS. 3. The quantum dot according to claim 1, wherein said particle size of said quantum dot is in the range of 11 nm to 15 nm. 3. The quantum dot according to claim 1 , wherein said particle size of said quantum dot is 15 nm or more. 5. The quantum dot of any one of claims 1-4, wherein the quantum dot is capable of emitting light with a photoluminescence quantum yield in the range of 60% to 90% upon excitation. 5. The quantum dot of any one of claims 1-4 , wherein the quantum dot is capable of emitting light with a photoluminescence quantum yield of 90% or greater upon excitation. 7. The quantum dot of any one of claims 1-6, wherein the photoluminescence quantum yield of the quantum dot decreases by 5% or less before and after storage at 60<0>C. 8. Any one of claims 1 to 7, wherein the core of the quantum dot is capable of absorbing light in a certain wavelength band of a light source and emitting light in at least one different wavelength band. quantum dot.

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