TWI811582B - 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 highly stable semiconductor nanomaterial.

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

Since quantum dots have narrow luminescence half-width, relatively pure color, and their optoelectronic properties can be controlled by adjusting the size of their cores, quantum dots are still the subject of active research for applications such as display devices. However, when quantum dots are used in display devices, there is a need to increase stability, quantum yield, service life, and other related properties.

Currently, the biggest challenge in 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 size of quantum dots (mainly the thickness of the shell) can increase stability, but this requires additional multiple reaction steps after quantum dot synthesis to form additional shells, or the synthesis reaction time of quantum dots needs to be extended. Both of these often result in higher costs and lower quantum yields.

The present invention provides a quantum dot with a two-layer shell coating the core to provide better protection and improve the stability of the quantum dot, thereby effectively avoiding or reducing the impact of external factors on the quantum dot.

The invention provides a quantum dot including: a core composed of InP, a first shell composed of ZnSe, a second shell and a gradient alloy progressive layer. The first shell covers 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 graduated layer of gradient alloy is formed between the core and the first shell. Gradient alloy progressive layers include alloys composed of In, P, Zn and Se. The contents of In and P gradually decrease along the direction from the core to the first shell. The contents of Zn and Se gradually increase along the direction from the core to the first shell. The particle size of quantum dots is greater than or equal to 11 nanometers. Quantum dots can emit light when excited and have a photoluminescence quantum yield (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 above-mentioned quantum dots is 11 nanometers to 15 nanometers.

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

In an embodiment of the present invention, the above-mentioned 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-mentioned 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 decrease in photoluminescence quantum yield of the above-mentioned quantum dots before baking and after baking is less than or equal to 5%.

In an embodiment of the present invention, the core of the quantum dot is capable of absorbing a light source in a fixed wavelength range and emitting at least one light in a different wavelength range.

Based on the above, the present invention provides quantum dots with two layers of shell coating 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 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 can be applied to display devices with strong light, high temperature, etc. (such as light emitting diode (LED) devices or projector color wheels).

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

Figure 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 made of indium phosphide (InP), a first shell 106 , a second shell 108 and a gradient alloy progressive layer 104 . The first shell 106 covers 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 made of zinc selenide (ZnSe), and the second shell 108 is made of zinc sulfide (ZnS). However, the present invention is not limited thereto. Other materials for the protection core 102 can also be used as the materials of 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 a better protective effect on the core 102 (for example, zinc sulfide), but the lattice mismatch (lattice) between the material with a better protective effect and the core 102 mismatch) is large, and it is not easy to form a good bond between the two materials. Therefore, the first shell 106 is made of a material (for example, zinc selenide) that has a lower protection effect but 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 . It is worth noting that the gradient alloy layer 104 can further reduce the lattice mismatch between the core 102 and the first shell 106 . That is to say, 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 and thereby increase the particle size of the quantum dot 100 by 100s. On the other hand, the gradient alloy progressive layer 104 can also reduce defects and increase quantum yield. Therefore, compared with quantum dots without a gradient alloy progressive layer, embodiments of the present invention can not only effectively increase the thickness of the shell layer 106 and improve the stability of the quantum dots, but also maintain the quantum yield of the quantum dots 100. In one embodiment, the gradient alloy 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 between 11 nanometers and 15 nanometers. 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, etc. In this article, the so-called “particle size” refers to the diameter of the quantum dots. 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 core 102 of the quantum dot 100 is capable of absorbing light from a fixed wavelength range of light sources and emitting light of at least one different wavelength range. 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 light, green light, or blue light) according to 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, quantum dots 100 are capable of emitting light when excited and have a photoluminescence quantum yield greater than or equal to 50%. In alternative embodiments, 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%, such as 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 is free of 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 can be applied to display devices with strong light, high temperature, etc. (such as light emitting diode (LED) devices or projector color wheels).

In order to prove the feasibility of the present invention, experimental examples are listed below 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, processing procedures, etc. may be appropriately changed without exceeding the scope of the present invention. Therefore, the present invention should not be interpreted restrictively based on the experiments described below.

Experimental example 1

Place 0.575 mmol of indium acetate, 0.284 mmol of zinc acetate, 2.29 mmol of palmitic acid and 125 mmol of 1-Octadecene in a vacuum environment at 140 ^o C. Heating for 2 hours, after which the reaction system was switched to _N2 environment and the reaction system was lowered to room temperature.

Then, 0.39 mmol of Tris(trimethylsilyl)phosphine and 0.39 mmol of Trioctylphosphine were added at room temperature, then 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 ^° C, and selenium (2.4 mmol) dissolved in 4.05 mmol trioctylphosphine and zinc stearate (Zinc) dissolved in 88 mmol 1-octadecene were added. stearate, 25.27 mmol), then heated to 320 ^o C and maintained for 30 minutes.

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

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

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

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

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

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

At a temperature of 320 ^o C, add zinc stearate (33.32 mmol) dissolved in 116 mmol of 1-octadecene and maintain for 30 minutes

After cooling the above reaction solution to 200 ^° C, 20.75 mmol of 1-Dodecanethiol was added and maintained for 25 minutes.

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

Comparative example 1

Place 0.575 mmol of indium acetate, 0.359 mmol of zinc acetate, 1.725 mmol of palmitic acid and 30 mmol of 1-Octadecene in a vacuum environment at 120 ^o C. Heating for 2 hours, after which the reaction system was switched to _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 reaction solution was lowered to 180 ^° C, and selenium (0.115 mmol) dissolved in 4.05 mmol trioctylphosphine and zinc acetate (Zinc acetate, dissolved in 30 mmol 1-octadecene) were added. 5.175 mmol) and 10.35 mmol of oleic acid, and the reaction temperature was increased to 280 ^o C.

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

Sulfur (0.115 mmol) dissolved in trioctylphosphine (0.115 mmol) was added at a temperature of 300 ^° C and maintained for 30 minutes.

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

Sulfur (2.30 mmol) dissolved in 2.30 mmol of trioctylphosphine was added at a temperature of 300 ^° C and maintained for 30 minutes.

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

Particle size comparison

Figures 2 and 3 are TEM images of the quantum dots of Experimental Example 1 and Comparative Example 1 respectively. It can be seen from Figures 2 and 3 that the particle size of the InP quantum dots in Experimental Example 1 is approximately 11 nanometers, while the particle size of the InP quantum dots in Comparative Example 1 is approximately 6 nanometers. Obviously, the particle size of the InP quantum dots of Experimental Example 1 is larger than the particle size 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 InP quantum dots (1 wt%) of Experimental Example 1 and Comparative Example 1 were respectively dissolved in n-hexane and then baked at 60 ^° C for 4 hours. Next, compare the quantum yield (QY) before and after baking in Experimental Example 1 and Comparative Example 1. As shown in Table 1 below, the quantum yield before baking in Experimental Example 1 was 83%, and the quantum yield after baking dropped to 79%, that is, the decrease was approximately 4%. In one embodiment, the decrease in photoluminescence quantum yield of the quantum dots of the present invention before and after baking is less than or equal to 5%. In alternative embodiments, the decrease in photoluminescence quantum yield of the quantum dots of the present invention before and after baking can be between 0% and 6%. On the other hand, the quantum yield before and after baking in Comparative Example 1 dropped from 81% to 58%, that is, the drop rate was as high as 23%. This result shows that compared with the thinner shell 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 and thereby improve stability.

Table 1 Experimental example 1 (mean ± two standard deviations) Comparative example 1 (mean ± two standard deviations) 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 quantum dots of the present invention are formed by mixing a precursor containing In, a precursor containing P, a precursor containing Zn, and a precursor containing Se, and heating them at a high temperature (about 270 ^° C to 320 ^° C). C) to react to form quantum dots with gradient alloys. Compared with the formation method of first forming an InP core and then forming a shell 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 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 quantum dot formation method of the present invention is carried out at high temperature, so it can effectively shorten the reaction time and reduce damage to the InP core, 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 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 can be applied to display devices with strong light, high temperature, etc. (such as light emitting diode (LED) devices or projector color wheels).

100:Quantum dots 100s: particle size 102:Nucleus 104: Gradient alloy progressive layer 106:First shell 108:Second shell

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

100:Quantum dots

100s: particle size

102:Nucleus

104: Gradient alloy progressive layer

106:First shell

108:Second shell

Claims (8)

A quantum dot consisting of: Core, composed of InP; The first shell is composed of ZnSe and covers the surface of the core; a second shell covering the surface of the first shell and having a different material than the first shell; and A gradient alloy progressive layer is formed between the core and the first shell. The gradient alloy progressive layer includes an alloy composed of In, P, Zn and Se, wherein the contents of In and P are along the The contents of Zn and Se gradually decrease along the direction from the core to the first shell, and the contents of the Zn and Se gradually increase 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 particle size of the quantum dot is 11 nanometers to 15 nanometers. 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 according to 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 decrease in photoluminescence quantum yield of the quantum dot before baking 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 in a fixed wavelength range and emitting at least one light in a different wavelength range.