TW202219246A - Semiconductor nanomaterial with high stability - Google Patents

Abstract

Quantum dot is a semiconductor nanomaterial. The quantum dot includes a core constituted of InP, a first shell constituted of ZnSe, a second shell constituted of ZnS, and a gradient alloy intermediate layer. The core is wrapped by the first shell. The first shell is wrapped by the second shell, and the first and second shells have different materials. The gradient alloy intermediate layer is between the core and the first shell. The gradient layer includes an alloy constituted of In, P, Zn and Se. A content of the In and P gradually decreases from the core to the first shell. A content of the Zn and Se gradually increases from the core to the first shell. A particle size of the quantum dot is equal to or more than 11 nm. The quantum dot is capable of emitting light upon excitation with a photoluminescence quantum yield equal to or more than 50%.

Description

Highly stable semiconductor nanomaterials

The present invention relates to a semiconductor nanomaterial, and in particular to a high stability semiconductor nanomaterial.

Semiconductor nanoparticles, also known as quantum dots (QDs), are semiconductor materials with nanometer size (usually less than 100 nanometers) and crystalline structure, and can include hundreds to thousands of atoms. Since quantum dots are very small, they have a large specific surface area and have quantum confinement effects. Thus, based on their size, quantum dots have unique physicochemical properties that differ from the intrinsic properties of their corresponding bulk semiconductor materials.

Quantum dots are still the subject of active research for applications such as display devices due to their narrow luminescence half-widths, pure colors, and optoelectronic properties that can be controlled by adjusting the size of their cores. However, when quantum dots are used in display devices, there is also a need to increase stability, quantum yield, lifetime, and other related properties.

Currently, the biggest challenge for quantum dot applications is long-term stability. External factors such as strong light, high temperature, moisture, volatile substances and oxidants can cause irreversible attenuation of the luminous intensity of quantum dots. Increasing the quantum dot size (mainly the thickness of the shell) can increase the stability, but this requires additional multi-step reaction steps to form additional shells after the quantum dot synthesis, or a prolonged reaction time for the quantum dot synthesis. Both of these tend to lead to higher costs and lower quantum yields.

The invention provides a quantum dot with two layers of shells covering the core, so as to provide better protection and improve the stability of the quantum dot, thereby effectively avoiding or reducing the influence of external factors on the quantum dot.

The invention provides a quantum dot comprising: a core composed of InP, a first shell composed of ZnSe, a second shell and a gradient alloy progressive layer. The first shell coats the surface of the core. The second shell covers the surface of the first shell and has a different material from the first shell. A graded alloy progressive layer is formed between the core and the first shell. The graded alloy progressive layer includes an alloy composed of In, P, Zn and Se. The content of In and P gradually decreases along the direction from the core to the first shell. The contents of Zn and Se increase gradually along the direction from the core to the first shell. The particle size of the quantum dots is greater than or equal to 11 nanometers. Quantum dots are capable of emitting light when excited and have a photoluminescence quantum yield greater than or equal to 50%.

In an embodiment of the present invention, the above-mentioned second shell is composed of ZnS.

In an embodiment of the present invention, the particle size of the quantum dots is 11 nm to 15 nm.

In an embodiment of the present invention, the particle size of the quantum dots is greater than or equal to 15 nanometers.

In an embodiment of the present invention, the above quantum dots can emit light when excited, and have a photoluminescence quantum yield of 60% to 90%.

In an embodiment of the present invention, the above quantum dots can emit light when excited, and have a photoluminescence quantum yield greater than or equal to 90%.

In an embodiment of the present invention, the reduction range of the photoluminescence quantum yield of the quantum dots before and after baking is less than or equal to 5%.

In an embodiment of the present invention, the cores of the quantum dots can absorb light sources in a fixed wavelength range and emit at least one light in different wavelength ranges.

Based on the above, the present invention provides quantum dots with two outer shells covering the core, so that the quantum dots have a diameter (or particle size) equal to or greater than 11 nm. In this case, the quantum dots of the present invention can have better protection, so as to improve the long-term stability of the quantum dots, thereby effectively avoiding or reducing external factors (such as strong light, high temperature, moisture, volatile substances and oxidants) etc.) on quantum dots. At the same time, the quantum dots of the present invention can also maintain a photoluminescence quantum yield greater than or equal to 50%. Therefore, the quantum dots of the present invention may be suitable for display devices (eg, light emitting diode (LED) devices or projector color wheels) with strong light, high temperature, and the like.

In this specification, a range represented by "one numerical value to another numerical value" is a general expression that avoids enumerating all the numerical values in the range in the specification. Therefore, reciting a specific numerical range is equivalent to disclosing any numerical value within that numerical range and a smaller numerical range bounded by any numerical value within the numerical range, as if the arbitrary numerical value and the numerical value were expressly written in the specification. The smaller value range is the same. For example, describing the range of "the particle size is 11 nm to 15 nm" is equivalent to disclosing the range of "the particle size is 12 nm to 13 nm", regardless of whether other numerical values are listed in the specification.

FIG. 1 is a schematic diagram of a quantum dot according to an embodiment of the present invention.

Referring to FIG. 1 , the quantum dot 100 includes a core 102 composed of indium phosphide (InP), a first shell 106 , a second shell 108 , and a gradient alloy progressive layer 104 . The first shell 106 coats the surface of the core 102 . The second shell 108 covers the surface of the first shell 106 . In this embodiment, the first shell 106 completely covers the surface of the core 102 , and the second shell 108 completely covers the surface of the first shell 106 . The first shell 106 and the second shell 108 may be of 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 present invention is not limited to this, and other materials for protecting the core 102 can also be used as materials for the first shell 106 and the second shell 108 . In order to improve the stability of the quantum dots, the second shell 108 will use a material with better protection effect on the core 102 (eg, zinc sulfide), but the lattice mismatch between the material with better protection effect and the core 102 (lattice mismatch) is larger, and it is not easy to form a good bond between the two materials. Therefore, the first shell 106 is selected from a material (eg, zinc selenide) that has a lower protection effect but has a lower lattice mismatch with the core 102 .

As shown in FIG. 1 , a graded alloy progressive layer 104 may be formed between the core 102 and the first shell 106 . Notably, the graded alloy progressive layer 104 can further reduce the lattice mismatch between the core 102 and the first shell 106 . That is, the gradient alloy progressive layer 104 can optimize the lattice arrangement between the core 102 and the first shell 106 to promote the growth of the first shell 106 , thereby increasing the particle size 100s of the quantum dots 100 . On the other hand, the graded alloy progressive layer 104 can also reduce defects and improve quantum yield. Therefore, compared with the quantum dots without the gradient alloy progressive layer, the embodiment of the present invention can not only effectively increase the thickness of the shell layer 106 , improve the stability of the quantum dots, but also maintain the quantum yield of the quantum dots 100 . In one embodiment, the graded alloy progressive layer 104 includes an alloy composed of In, P, Zn, and Se. The contents of In and P gradually decrease along the direction from the core 102 to the first shell 106 (ie, the direction outward from the core), while the contents of Zn and Se gradually increase along the direction from the core 102 to the first shell 106 .

In some embodiments, the particle size 100s of the quantum dots 100 is greater than or equal to 11 nanometers. In an alternative embodiment, the particle size 100s of the quantum dots 100 is 11 nm to 15 nm. In other embodiments, the particle size 100s of the quantum dots 100 is greater than or equal to 15 nanometers, such as 16 nanometers, 17 nanometers, 18 nanometers, 19 nanometers, 20 nanometers, and the like. Herein, the so-called "particle size" refers to the diameter of the quantum dot. When the quantum dot is not spherical or quasi-spherical, the diameter refers to the length of the cross section perpendicular to the first axis of the quantum dot, and the first axis is not necessarily the longest axis of the quantum dot. For example, where the cross-section is not circular, the diameter is the average of the major and minor axes of the cross-section. For spherical structures, the diameter is measured from side to side through the center of the sphere.

On the other hand, the core 102 of the quantum dot 100 can be used to absorb and emit light. In some embodiments, the cores 102 of the quantum dots 100 are capable of absorbing light from a fixed wavelength range of light sources and emitting at least one different wavelength range of light. For example, the core 102 can absorb ultraviolet (UV) light with a peak wavelength less than 400 nm and emit visible light of different colors (eg, red, green, or blue) depending on the particle size of the core 102 . For another example, the core 102 can absorb blue light and emit visible light of different colors (eg, red light or green light) according to the particle size of the core 102 . In some embodiments, the quantum dots 100 are capable of emitting light when excited with a photoluminescence quantum yield greater than or equal to 50%. In alternative embodiments, the quantum dots 100 may have a photoluminescence quantum yield of 60% to 90%. In other embodiments, the quantum dots 100 may have a photoluminescence quantum yield greater than or equal to 90%, eg, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% % photoluminescence quantum yield.

It is worth noting that the quantum dot 100 of the present invention can emit light when excited, and it has a photoluminescence quantum yield equal to or greater than 50%, which means that the core 102 of the quantum dot 100 has good crystal quality and defects rare. In other words, the quantum dots 100 of the present invention can improve long-term stability and maintain high quantum yield. Therefore, the quantum dots 100 of the present invention may be suitable for display devices (eg, light emitting diode (LED) devices or projector color wheels) with strong light, high temperature, and the like.

In order to prove the practicability of the present invention, the following experimental examples are given to further illustrate the quantum dots of the present invention. Although the following experiments are described, the materials used, their amounts and ratios, processing details, and processing flow, etc. may be appropriately changed without departing from the scope of the present invention. Therefore, the present invention should not be construed restrictively based on the experiments described below.

Experimental example 1

0.575 mmol of indium acetate, 0.284 mmol of zinc acetate (Zinc acetate), 2.29 mmol of palmitic acid (Palmitic acid) and 125 mmol of 1-octadecene (1-Octadecene) in a vacuum environment at 140 ^o C After heating for 2 hours, the reaction system was transferred to a _N2 environment and the reaction system was brought to room temperature.

Next, 0.39 mmol of tris(trimethylsilyl)phosphine and 0.39 mmol of trioctylphosphine were added at room temperature, and the temperature was raised to 270 ^° C and maintained at this temperature for 2 minutes. A reaction solution is formed.

Then, the temperature of the above reaction solution was lowered to 150 ^o C and then selenium (Selenium, 2.4 mmol) dissolved in 4.05 mmol trioctylphosphine and zinc stearate (Zinc stearate (Zinc) dissolved in 88 mmol of 1-octadecene were added. stearate, 25.27 mmol), then warmed to 320 ^o C and held for 30 minutes.

Additional selenium (2.4 mmol) in 4.05 mmol of trioctylphosphine and 88 mmol of zinc stearate (25.27 mmol) in 1-octadecene were added at 320 ^o C and maintained 30 minutes.

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

Zinc stearate (6.32 mmol) dissolved in 22 mmol of 1-octadecene was added at 320 ^° C and maintained for 10 minutes.

Sulfur (16 mmol) dissolved in 16.166 mmol of trioctylphosphine was added at 320 ^° C and maintained for 10 min.

Zinc stearate (5.55 mmol) dissolved in 19.33 mmol of 1-octadecene was added at 320 ^° C and maintained for 10 minutes.

Sulfur (96 mmol) dissolved in 96.96 mmol of trioctylphosphine was added at 320 ^° C and maintained for 10 min.

Add zinc stearate (33.32 mmol) dissolved in 116 mmol of 1-octadecene at 320 ^o C and hold for 30 min

The above reaction solution was cooled to 200 ^o C, 20.75 mmol of 1-dodecanethiol (1-Dodecanethiol) was added and maintained for 25 minutes.

After cooling down to stop the reaction, ethanol was added to the reaction solution to precipitate the product, and the precipitate was collected by centrifugation and then dissolved in toluene.

Comparative example 1

0.575 mmol of indium acetate, 0.359 mmol of zinc acetate (Zinc acetate), 1.725 mmol of palmitic acid (Palmitic acid) and 30 mmol of 1-octadecene (1-Octadecene) in a vacuum environment at 120 ^o C After heating for 2 hours, the reaction system was transferred to a _N2 environment and the temperature was maintained at 280 ^° C.

Next, 0.43 mmol of tris(trimethylsilyl)phosphine and 0.43 mmol of trioctylphosphine were added at 280 ^° C and maintained at this temperature for 2 minutes to form a reaction solution.

Then, the temperature of the above-mentioned reaction solution was lowered to 180 ^o C and then selenium (Selenium, 0.115 mmol) dissolved in 4.05 mmol trioctylphosphine and zinc acetate (Zinc acetate, 0.115 mmol) dissolved in 30 mmol 1-octadecene were added. 5.175 mmol) and 10.35 mmol of oleic acid, and raise the reaction temperature to 280 ^o C.

Next, at a temperature of 280 ^° C, sulfur dissolved in 0.029 mmol of trioctylphosphine (Sulfur, 0.029 mmol) was added and the temperature was increased to 300 ^° C and maintained for 30 minutes.

Sulfur in 0.115 mmol of trioctylphosphine (Sulfur, 0.115 mmol) was added at 300 ^° C and maintained for 30 min.

Sulfur dissolved in 0.23 mmol of trioctylphosphine (Sulfur, 0.23 mmol) was added at a temperature of 300 ^° C and maintained for 30 min.

Sulfur in 2.30 mmol of trioctylphosphine (Sulfur, 2.30 mmol) was added at 300 ^° C and maintained for 30 min.

After cooling down to stop the reaction, ethanol was added to the reaction solution to precipitate the product, and the precipitate was collected by centrifugation and then 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. It can be seen from FIG. 2 and FIG. 3 that the particle size of the InP quantum dots of Experimental Example 1 is about 11 nm, while the particle size of the InP quantum dots of Comparative Example 1 is about 6 nm. Obviously, the particle diameter 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 were not spherical but polygonal with corners.

high temperature storage

The InP quantum dots (1 wt %) of Experimental Example 1 and Comparative Example 1 were dissolved in n-hexane, respectively, and then baked at a temperature of 60 ^° C for 4 hours. Next, the quantum yields (QY) of Experimental Example 1 and Comparative Example 1 before and after baking were compared. As shown in Table 1 below, the quantum yield of Experimental Example 1 before baking was 83%, and the quantum yield after baking was reduced to 79%, that is, the reduction range was about 4%. In one embodiment, the reduction range of the photoluminescence quantum yield of the quantum dots of the present invention before and after baking is less than or equal to 5%. In an alternative embodiment, the reduction in photoluminescence quantum yield of the quantum dots of the present invention before and after baking may be between 0% and 6%. In contrast, the quantum yield of Comparative Example 1 before and after baking decreased from 81% to 58%, that is, the decrease was as high as 23%. This result shows that, compared with the thinner shell layer of the InP quantum dot of Comparative Example 1, the InP quantum dot of Experimental Example 1 has a thicker shell layer, which can provide better protection and improve stability.

Table 1 Experimental example 1 (mean ± double standard deviation) Comparative Example 1 (mean ± double standard deviation) before baking QY = 83 ± 2.3% QY = 81 ± 3.1% after baking QY = 79 ± 4.2% QY = 58 ± 5.3% degree of declining 4% twenty three%

In addition, the method for forming the quantum dots of the present invention is to mix the In-containing precursor, the P-containing precursor, the Zn-containing precursor, and the Se-containing precursor together, and heat it at a high temperature (about 270 ^° C to 320 ^° C). C) to carry out the reaction to form quantum dots with gradient alloys. Compared with the formation method of forming the InP core first and then forming the shell layer covering the InP core (that is, this method does not form a gradient alloy), the quantum dots of the present invention can have a gradient alloy between the InP core and the ZnSe shell Progressive layers to optimize the lattice arrangement between the InP core and the ZnSe shell. That is to say, the gradient alloy progressive layer of the present invention can not only effectively increase the thickness of the shell layer, but also maintain the quantum yield of the quantum dots. In addition, the method for forming the quantum dots of the present invention is carried out at high temperature, therefore, the reaction time can be effectively shortened and the damage to the InP core can be reduced, thereby improving the quality of the InP core and maintaining a high quantum yield.

To sum up, the present invention provides quantum dots with two shells covering the core, so that the quantum dots have a diameter (or particle size) equal to or greater than 11 nm. In this case, the quantum dots of the present invention can have better protection, so as to improve the long-term stability of the quantum dots, thereby effectively avoiding or reducing external factors (such as strong light, high temperature, moisture, volatile substances and oxidants) etc.) on quantum dots. At the same time, the quantum dots of the present invention can also maintain a photoluminescence quantum yield greater than or equal to 50%. Therefore, the quantum dots of the present invention may be suitable for display devices (eg, light emitting diode (LED) devices or projector color wheels) with strong light, high temperature, and the like.

100: Quantum Dots 100s: particle size 102: Nuclear 104: Gradient alloy progressive layer 106: First Shell 108: Second Shell

FIG. 1 is a schematic diagram of a quantum dot according to an embodiment of the present invention. FIG. 2 is a transmission electron microscope (TEM) image of the quantum dot of Experimental Example 1. FIG. FIG. 3 is a TEM image of the quantum dots of Comparative Example 1. FIG.

100: Quantum Dots

100s: particle size

102: Nuclear

104: Gradient alloy progressive layer

106: First Shell

108: Second Shell

Claims (8)

A quantum dot comprising: The core is composed of InP; a first shell, consisting of ZnSe, and covering the surface of the core; a second shell covering the surface of the first shell and having a different material from the first shell; and A graded alloy progressive layer is formed between the core and the first shell, the graded alloy progressive layer includes an alloy composed of In, P, Zn and Se, wherein the contents of In and P are along the same The content of Zn and Se gradually increases along the direction from the core to the first shell, and the content of the Zn and Se gradually increases along the direction from the core to the first shell, The particle size of the quantum dots is greater than or equal to 11 nanometers, and the quantum dots can emit light when excited, and have a photoluminescence quantum yield greater than or equal to 50%. The quantum dot of claim 1, wherein the second shell is composed of ZnS. The quantum dot according to claim 1, wherein the quantum dot has a particle size of 11 nm to 15 nm. The quantum dot according to claim 1, wherein the particle size of the quantum dot is greater than or equal to 15 nanometers. The quantum dot of claim 1, wherein the quantum dot is capable of emitting light when excited and has a photoluminescence quantum yield of 60% to 90%. The quantum dot of claim 1, wherein the quantum dot is capable of emitting light when excited and has a photoluminescence quantum yield greater than or equal to 90%. The quantum dot according to claim 1, wherein the reduction range of the quantum yield of photoluminescence of the quantum dot before and after baking is less than or equal to 5%. The quantum dot of claim 1, wherein the core of the quantum dot is capable of absorbing a light source of a fixed wavelength range and emitting light of at least one different wavelength range.

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