JP-2026076252-A - Quantum dots

Abstract

[Problem] The objective is to provide quantum dots that can enhance EQE. [Solution] The quantum dot of the present invention is a quantum dot having a core-shell structure, wherein an intermediate layer is included between the core and the shell, the core contains Zn and Se, the intermediate layer contains ZnSeS, and the shell contains ZnS and has a substantially constant thickness. In the present invention, it is preferable that the thickness of the shell is 0.5 nm or more and 3 nm or less. [Selection Diagram] Figure 4

Inventors

• ▲高▼▲崎▼ 幹大
• 高三潴 由香
• 松澤 宏則

Assignees

• ＴＯＰＰＡＮホールディングス株式会社

Dates

Publication Date

20260511

Application Date

20260122

Priority Date

20210226

Claims (13)

1. A quantum dot with a core-shell structure, An intermediate layer is included between the core and the shell. The aforementioned core includes Zn and Se, The aforementioned intermediate layer includes ZnSeS, The aforementioned shell contains ZnS and has a substantially constant thickness. A quantum dot characterized by the following features.
2. The quantum dot according to claim 1, characterized in that the thickness of the shell is 0.5 nm or more and 3 nm or less.
3. The quantum dot according to claim 2, characterized in that the thickness of the shell is 2 nm or more and 3 nm or less.
4. The quantum dot according to claim 1 or 3, characterized in that the particle shape of the quantum dot is substantially rectangular.
5. A quantum dot according to claim 1 or 3, characterized by containing a halogen.
6. The quantum dot according to claim 5, characterized in that the halogen is chlorine or bromine.
7. A quantum dot according to claim 1 or 3, characterized by containing Cu.
8. The quantum dot according to claim 7, characterized in that the remaining amount of Cu is 100 ppm or less.
9. A quantum dot according to claim 1 or 3, characterized in that its external quantum efficiency is 7% or higher.
10. A quantum dot according to claim 1 or 3, characterized in that the fluorescence quantum yield is 70% or higher.
11. A quantum dot according to claim 1 or 3, characterized in that its fluorescence wavelength is 410 nm or more and 470 nm or less.
12. The quantum dot according to claim 11, characterized in that the fluorescence wavelength is 430 nm or more and 470 nm or less.
13. The quantum dot according to claim 1 or claim 3, characterized in that its fluorescence half-width is 20 nm or less.

Description

This invention relates to a cadmium-free core-shell quantum dot. Quantum dots are also called fluorescent nanoparticles because they emit fluorescence and are nanoscale in size; semiconductor nanoparticles because their composition is derived from semiconductor materials; or nanocrystals because their structure has a specific crystalline structure. Quantum dot performance can be expressed using metrics such as fluorescence quantum yield (QY) and external quantum efficiency (EQE). In applications of quantum dot displays, when photoluminescence (PL) is used as the light emission principle, a method is employed in which a blue LED is used as the excitation light for the backlight, and the quantum dots are used to convert it into green or red light. On the other hand, when electroluminescence (EL) is used as the light emission principle, or when all three primary colors are emitted by quantum dots using other methods, blue fluorescent quantum dots are required. A representative example of blue quantum dots is cadmium selenide (CdSe) quantum dots, which utilize cadmium (Cd). However, Cd is internationally regulated, posing a significant obstacle to the practical application of materials using CdSe quantum dots. On the other hand, the development of quantum dots that do not use cadmium (Cd) is also being considered. For example, development of chalcopyrite-based quantum dots such as CuInS₂ and AgInS₂ , and indium phosphide (InP)-based quantum dots is progressing (see, for example, Patent Document 1). However, the quantum dots currently under development generally have a wide fluorescence half-width and are not suitable as blue fluorescence quantum dots. Furthermore, Non-Patent Document 1 below describes in detail a direct synthesis method of ZnSe using diphenylphosphine selenide, which is considered to be relatively reactive with organozinc compounds; however, this method is not suitable for producing blue fluorescent quantum dots. Furthermore, Non-Patent Document 2 (listed below) also reports a method for synthesizing ZnSe in an aqueous system. Although the reaction proceeds at low temperatures, the fluorescence half-width is somewhat broad (over 30 nm), and the fluorescence wavelength is less than 430 nm. Therefore, it is unsuitable for use as a replacement for conventional blue LEDs to achieve a wider color gamut. Furthermore, Non-Patent Document 3 reports a method for synthesizing ZnSe-based quantum dots by forming a precursor such as copper selenide (CuSe) and then performing cation exchange of copper with zinc (Zn). However, because the precursor copper selenide particles are large (15 nm) and the reaction conditions for cation exchange between copper and zinc are not optimal, it is found that copper remains in the ZnSe-based quantum dots after cation exchange. From the results of our investigation, it has been found that ZnSe-based quantum dots with residual copper cannot emit light. Alternatively, even if light is emitted, if copper remains, the emission is due to defects, resulting in emission with a full width at half maximum of 30 nm or more in the emission spectrum. The particle size of the precursor copper selenide also affects this copper residue; if the particles are large, copper is more likely to remain even after cation exchange, and even if ZnSe can be confirmed by XRD, emission often does not occur due to the presence of even a small amount of residual copper. Therefore, Non-Patent Document 3 can be cited as an example where copper remains because the particle size control of the precursor and the cation exchange method have not been optimized. For this reason, blue fluorescence has not been reported. While there are many reported cases using the cation exchange method, there are no reports of strong luminescence for the reasons mentioned above. International Publication No. 2007/060889 Pamphlet Organic Electronics 15 (2014) 126-131Materials Science and Engineering C 64 (2016) 167-172J. Am. Chem. Soc. (2015) 137 29 9315-9323 Figures 1A and 1B are schematic diagrams of quantum dots in embodiments of the present invention.This is a schematic diagram of an LED device using quantum dots according to an embodiment of the present invention.This is a longitudinal cross-sectional view of a display device using an LED device according to an embodiment of the present invention.This is a flowchart illustrating the manufacturing process of quantum dots in an embodiment of the present invention.This is the fluorescence (Photolemia: PL) spectrum of Example 1.This is the absorption spectrum of Example 1.This is the X-ray diffraction (XRD) spectrum of Example 1.This table shows the measurement results for each quantum dot in Examples 1 to 7.Figure 9A is a photograph of the TEM-EDX analysis results in Comparative Example 1, and Figure 9B is a photograph of the TEM-EDX analysis results in Example 1.Figure 10A is a schematic partial view of Figure 9A, and Figure 10B is a schematic partial view of Figure 9B. The