Light-emitting element and light-emitting device

Abstract

The light-emitting layer (EL) has: a plurality of quantum dots (QD) that are positioned between the anode (E1) and the cathode (E2) and contain a first element that is a metal element; and a base material (Mx) comprising two or more types of elements including a second element which is higher than the first element and is not included in the plurality of quantum dots (QD), and including a plurality of quantum dots (QD).

Description

Technical Field

[0001] The present disclosure relates to a light emitting element and a light emitting device. Background Art

[0002] Patent Document 1 discloses a light-emitting element in which spaces between quantum dots are filled with a polymer compound. Prior art literature Patent Literature

[0003] Patent Document 1: WO2012 / 128173 (published on September 27, 2012) Summary of the invention Technical problems to be solved by the present disclosure

[0004] In the prior art, there is a problem that the light emitting efficiency of the light emitting element is low. Technical solutions for solving technical problems

[0005] The light-emitting element of each embodiment of the present invention comprises: an anode and a cathode; and a light-emitting layer, which is located between the anode and the cathode, and the light-emitting layer has: a plurality of quantum dots, which contain a metal element, namely a first element; and a substrate, which is composed of two or more elements and includes the plurality of quantum dots, and the two or more elements include a second element, which is closer to the upper period than the first element and is not included in the plurality of quantum dots. Beneficial Effects

[0006] According to one aspect of the present disclosure, the light emission efficiency of a light emitting element can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a cross-sectional view showing a configuration example of a light emitting element according to one embodiment of the present disclosure. Figure 2 Yes means Figure 1 A schematic diagram of an example of the region between quantum dots is shown. Figure 3 Yes means Figure 1 A schematic diagram of another example of the region between quantum dots is shown. Figure 4 This is a diagram showing a short cycle based on the old IUPAC method. Figure 5 Yes means Figure 1 The circuit diagram of the equivalent circuit of the light emitting element is shown. Figure 6 Yes means Figure 1 The circuit diagram of the equivalent circuit of the light emitting element is shown. Figure 7 Yes means Figure 1Schematic diagram of an example of the energy band structure of the light-emitting layer shown. Figure 8 This is a cross-sectional view for explaining the step of replacing the ligand coordinated to the quantum dot. Fig. 9 This is a schematic diagram showing a quantum dot dispersion. Fig.10 It is a graph showing the JV characteristics of the diode element according to the example of the present disclosure. Fig.11 It is a cross-sectional view showing a configuration example of a light emitting element according to one embodiment of the present disclosure. Fig.12 Yes means Fig.11 Schematic diagram of an example of the energy band structure of the light-emitting layer shown. Fig.13 It is a plan view showing a configuration example of a light emitting device according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0008] [First embodiment] (Cross-sectional structure of light-emitting element) Figure 1 1 is a cross-sectional view showing a configuration example of a light emitting element according to an embodiment of the present disclosure. Figure 1 As shown, the light-emitting element 10 includes an anode E1 and a cathode E2 facing each other and a light-emitting layer EL located between the anode E1 and the cathode E2. The light-emitting layer EL includes a plurality of quantum dots QD and a substrate Mx. The light-emitting element 10 may also include one or both of a charge functional layer F1 located between the anode E1 and the light-emitting layer EL and a charge functional layer F2 located between the cathode E2 and the light-emitting layer EL. The charge functional layer F1 may include any one or more of a hole injection layer HIL, a hole transport layer HTL, and an electron shielding layer. The charge functional layer F2 includes any one or more of an electron injection layer, an electron transport layer ETL, and a hole blocking layer. The current flowing through the light-emitting layer EL includes a current I1 flowing through the quantum dots QD and a current I2 flowing away from the quantum dots QD.

[0009] The quantum dots QD each contain at least a first element, and the first element is a metal element. The quantum dot QD may also have any one of a shellless structure, a core-shell structure, and a multi-shell structure. The first element may be contained in the core of the quantum dot QD, or in the shell. The substrate Mx is composed of two or more elements so as to contain at least a second element. The second element is closer to the upper period than the first element and is not contained in the quantum dot QD. The substrate Mx may also be a mixed crystal of a metal sulfide containing the first element and a metal sulfide containing the second element. The first element may be Zn, and the second element may be Mg. The substrate Mx may also include a continuous film, which is at any position in the thickness direction of the light-emitting layer EL and is in the thickness direction ( Figure 1 The vertical direction) is perpendicular to the surface direction ( Figure 1 In the left and right directions and the depth direction), (except for the cross-sectional area of ​​the quantum dots QD contained) it has a diameter of 1000nm 2 The area above.

[0010] Figure 4 This is a diagram showing a short periodic table based on the old IUPAC method. Figure 4 The "*" in the table represents lanthanide elements and the "**" represents actinide elements. Figure 4 The short period shown is used to determine whether it is an upper period, a lower period or the same period. Figure 4 As shown, the smaller the period number, the higher the period. For example, the first period including H (hydrogen) and He (helium) is the highest period.

[0011] The substrate Mx refers to a component that contains and holds other substances, and can be called a substrate, a base material, or a filling material. The substrate Mx can be solid at room temperature. The substrate Mx can also be a component that contains and holds a plurality of quantum dots QD. The substrate Mx can also be a constituent element of the light-emitting layer EL containing a plurality of quantum dots QD.

[0012] Figure 2 as well as Figure 3 They are respectively Figure 1 Schematic diagram of an example of the region between quantum dots shown. The substrate Mx may also be filled in the light-emitting layer EL. Figure 1 As shown, two quantum dots QD among the plurality of quantum dots QD can be focused on, and the substrate Mx fills the region (space) K between the two quantum dots QD. Figure 2 and Figure 3 As shown, the two quantum dots QD are called the first quantum dot QD1 and the second quantum dot QD2. In the cross-sectional view, region K is a region surrounded by two straight lines (common external tangent lines) connected to the peripheries of the first and second quantum dots QD1 and QD2, and the relative peripheries of the first and second quantum dots QD1 and QD2. Figure 3 As shown, even if the first quantum dot QD1 is close to the second quantum dot QD2, there may be a region K. “Filling between multiple quantum dots” may be as follows Figure 2 (or Figure 3 ) as described in the description above. The substrate Mx may also fill the area (space) outside the multiple quantum dots QD in the light-emitting layer EL. The light-emitting layer EL has a quantum dot group including multiple quantum dots QD, and the substrate Mx may also fill the area (space) outside the quantum dot group. Here, more than three quantum dots QD are collectively referred to as a quantum dot group. The substrate Mx may fill the area (space) outside the multiple quantum dots QD in the light-emitting layer EL.

[0013] The outer edge (upper surface and lower surface) of the light-emitting layer EL may be covered by a substrate Mx. In addition, it may be configured such that the quantum dots QD are located away from the outer edge of the light-emitting layer EL in a portion where the substrate Mx is present. The outer edge of the light-emitting layer EL may be formed not only by the substrate Mx, but also by a portion of the quantum dots QD being exposed from the substrate Mx. The substrate Mx may represent a portion of the light-emitting layer EL where a plurality of quantum dots QD are removed.

[0014] The substrate Mx may contain a plurality of quantum dots QD. The substrate Mx may be formed to fill the space formed between the plurality of quantum dots QD. The plurality of quantum dots QD may be embedded in the substrate Mx at intervals.

[0015] The substrate Mx may include a continuous film having a thickness of 1000 nm along a plane direction perpendicular to the layer thickness direction. 2 The continuous film refers to a film that is not separated on one plane by materials other than the material constituting the continuous film. The continuous film may also be an integrated film-like film that is continuously connected by chemical bonds of the material constituting the substrate Mx.

[0016] The substrate Mx may also be the same material as the shell contained in each of the multiple quantum dots QD. In this case, the average distance between adjacent cores (inter-core distance) may be more than 3nm, or more than 5nm. Alternatively, the average distance between the adjacent cores may be more than 0.5 times the average core diameter. The inter-core distance is the distance after averaging the shortest distance between 20 adjacent cores. The inter-core distance may be kept wider than the distance when the shells are in contact with each other. The average core diameter is obtained by averaging the core diameters of 20 adjacent cores in cross-sectional observation. The core diameter may be set to the diameter of a circle having the same area as the core area in cross-sectional observation.

[0017] The concentration of the substrate Mx in the light-emitting layer EL is, for example, the area ratio occupied by the substrate Mx in the cross section of the light-emitting layer EL. In cross-sectional observation, the concentration may be greater than 10% and less than 90%, or greater than 30% and less than 70%. For example, the concentration may be measured based on the area ratio in image processing in cross-sectional observation. When the quantum dot QD is a core-shell structure, the concentration of the shell may be greater than 1% and less than 50%. The shell and the substrate Mx are made of the same material (same composition), and when the shell and the substrate Mx cannot be distinguished, the concentration of the area in which the shell and the substrate Mx are combined may be the numerical range obtained by adding the numerical range of the concentration of the above-mentioned substrate Mx to the numerical range of the concentration of the above-mentioned shell. The ratio of the core to the shell and the substrate Mx of the quantum dot QD may be adjusted so that the total ratio is appropriately less than 100%. In this way, when the shell and the substrate Mx cannot be distinguished, the shell may also be regarded as part of the substrate Mx.

[0018] The light emitting layer EL may also be composed of a plurality of quantum dots QD and a substrate Mx. When analyzing the light emitting layer EL, the intensity of carbon detected by the chain structure may be lower than the noise.

[0019] The band gap of the constituent material of the substrate Mx is preferably wider than the constituent material (e.g., core material) of the quantum dot QD. As a material constituting the substrate Mx, a semiconductor or an insulator can be used. Examples of constituent materials of the substrate Mx include metal sulfides and / or metal oxides. Metal sulfides may be, for example, zinc sulfide (ZnS), zinc magnesium sulfide (ZnMgS, ZnMgS2), gallium sulfide (GaS, Ga2S), zinc tellurium sulfide (ZnTeS), magnesium sulfide (MgS), zinc gallium sulfide (ZnGa2S4), and magnesium gallium sulfide (MgGa2S4). Metal oxides may also be zinc oxide (ZnO), titanium oxide (TiO2), tin oxide (SnO2), tungsten oxide (WO3), and zirconium oxide (ZrO2). In addition, the chemical formula recorded in brackets after the compound name is a representative example. In addition, as for the composition ratio recorded in the chemical formula, it is ideal as long as the composition of the actual compound is stoichiometric as shown in the chemical formula, but it may not necessarily be stoichiometric.

[0020] The structure of the substrate Mx is observed with a width of about 100 nm in the cross-section observation of the light-emitting layer EL, and it is sufficient to know that it is the above structure, and it is not necessary to observe the above structure in the entire light-emitting layer EL. The substrate Mx may also contain a substance different from the main material (for example, an inorganic compound such as an inorganic semiconductor) as an additive.

[0021] The first element and the second element may be of the same family. Figure 4 The short periodic table shown here determines whether they are in the same group. The group number in the old IUPAC method is consistent with the number of valence electrons of the form. So, in other words, the number of valence electrons of the first element can be the same as the number of valence electrons of the second element.

[0022] Refer again Figure 4 , Group I elements include Group IA elements and Group IB elements. Group IA elements are of the same family, Group IB elements are of the same family, and Group IA elements and Group IB elements are of the same family. In short, Group I elements are of the same family. Similarly, Group II elements are of the same family, Group III elements are of the same family, Group IV elements are of the same family, Group V elements are of the same family, Group VI elements are of the same family, Group VII elements are of the same family, and Group VIII elements are of the same family.

[0023] Alternatively, the group containing the first element and the group containing the second element may also be adjacent. Figure 4 The short periodic table shown in FIG. 1 is used to determine whether two groups are adjacent. In other words, the difference between the number of valence electrons of the first element and the number of valence electrons of the second element may be 1.

[0024] Refer again Figure 4 , Group IA is adjacent to Group IIA, Group IA is adjacent to Group IIB, Group IB is adjacent to Group IIA, and Group IB is adjacent to Group IIB. In short, Group I is adjacent to Group II. Similarly, Group II is adjacent to Group III, Group III is adjacent to Group IV, Group IV is adjacent to Group V, Group V is adjacent to Group VI, Group VI is adjacent to Group VII, and Group VII is adjacent to Group VIII.

[0025] (Equivalent circuit of light emitting element) Figure 5 and Figure 6 They are respectively Figure 1 The circuit diagram of the equivalent circuit of the light emitting element shown in FIG. Figure 5 As shown, the light emitting element 10 is connected to a power supply voltage V and includes a light emitting diode element D1 and a non-light emitting diode element D2. Resistor r1 represents the resistance of the light emitting diode element D1, and resistor r2 represents the resistance of the non-light emitting diode element D2. Resistor R is connected in parallel with diode elements D1 and D2, and represents the resistance of the path through which the leakage current flows. Resistor r is connected in series with diode elements D1 and D2, and represents wiring resistance, etc.

[0026] The current I1 flowing through the quantum dot QD corresponds to the current I1 flowing through the light-emitting diode element D1, and contributes to the light emission of the light-emitting element 10. The current I2 flowing away from the quantum dot QD corresponds to the current I2 flowing through the non-light-emitting diode element D2, and does not contribute to the light emission of the light-emitting element 10. The ratio of the current I1 injected into the quantum dot QD in the current I (= I1 + I2) flowing through the light-emitting layer EL is I1 / (I1 + I2), which is called "current injection efficiency".

[0027] A common light emitting element is designed so that the resistance R has a high resistance value of tens of MΩ or more. Therefore, the leakage current flowing through the resistance R is usually small enough to be ignored, and the path flowing through the resistance R can also be ignored. The resistance r is about hundreds of Ω or less.

[0028] When a voltage higher than the so-called "rising voltage" is applied to the diode elements D1 and D2, they are turned on and currents I1 and I2 flow. When the light emitting element 10 is driven by a threshold voltage and emits light, both the diode elements D1 and D2 are turned on. The transient characteristics of the diode elements D1 and D2 near the rising voltage have little effect on the electrical characteristics and light emitting characteristics of the light emitting element 10 in the state where both the diode elements D1 and D2 are turned on. The rising voltages V1 and V2 of the diode elements D1 and D2 are opposite in polarity to the power supply voltage.

[0029] Therefore, it is possible to Figure 5 The equivalent circuit shown is replaced by Figure 6 The equivalent circuit is shown. Figure 6 Applying Kirchhoff's current law yields the following equations (1) and (2). The electrical characteristics of the diode elements D1 and D2 can be described by Shockley's diode equation shown in the following equation (3), and depend on the saturation current. [Mathematical formula 1] [Mathematical formula 2] [Mathematical formula 3] Here, I D : The current flowing through the diode element; I0: saturation current; q: charge element quantity; V D : applied voltage; n: diode coefficient; k: Boltzmann (Stefan-Boltzmann) constant; T: Temperature. When equation (3) is applied to diode element D1, the current I D = current I1, when equation (3) is applied to diode element D2, current I D =current I2.

[0030] The saturation current depends on the intrinsic carrier density as shown in the following equation (4). The intrinsic carrier density depends on the band gap as shown in the following equation (5). [Formula 4] [Mathematical formula 5] Here, S: joint area. n i : Intrinsic carrier density. x p +x n : Depletion layer width. τ r : Recombined life span; N C : effective state density of the donor; N V : effective state density of the receptor; Eg: Band gap.

[0031] The physical properties of the material are determined by the effective state density NC 、N V and the band gap Eg, and is reflected in the saturation current I0. As shown in the following equation (6), the saturation current simply depends on the band gap.

[0032] [Mathematical formula 6] I0∝exp(-E g / 2kT)……(6) Generally, the energy gap Eg in a mixed crystal ABC in which a compound AC composed of elements A and C is mixed with a compound BC composed of elements B and C is ABC Ratio X relative to compound AC A , as shown in the following formula (7), it represents a nonlinear relationship that is convex downward. α, β, and γ are parameters determined by elements A, B, and C. The "element B" recorded in this paragraph does not mean B (boron), and it can be understood that "element C" does not mean C (carbon). The "element A", "element B", and "element C" recorded in this paragraph are just pseudonyms for the three elements.

[0033] [Formula 7] E gABC =αx A +βx A 2 +γ……(7) This nonlinear relationship is the change in the valence electron density distribution caused by the difference in electronegativity or ionic radius of each element forming the mixed crystal. Therefore, a linear approximation can be made for mixed crystals containing elements with electronegativity close to each other and ionic radius close to each other. For example, the electronegativity and ionic radius of Mg (magnesium) and Zn (zinc) are close, with the electronegativity of Mg being about 1.31 and the electronegativity of Zn being about 1.65. It is known from experiments that most of the effective state density n in II-VI compounds containing ZnS and MgS is i For 10 19 cm -3 Therefore, a mixed crystal MgZnS of MgS (magnesium sulfide) and ZnS (zinc sulfide) can be linearly approximated as shown in the following formula (8).

[0034] [Mathematical formula 8] E gMgZnS =E gZnS +(E gMgS -E gZnS )x Mg ……(8) Here, Eg MgZnS : Energy gap of mixed crystal MgZnS. Eg ZnS : Energy gap of ZnS. Eg MgS: Energy gap of MgS. x Mg : The ratio of MgS in the mixed crystal MgZnS.

[0035] (Band structure of the light-emitting layer) Figure 7 Yes means Figure 1 Schematic diagram of an example of the energy band structure of the light-emitting layer shown. Figure 7 Rectangles represent the HOMO (highest occupied molecular orbital), LUMO (lowest unoccupied molecular orbital) and the band gaps between the hole transport layer HTL, the substrate Mx, the quantum dots QD and the electron transport layer ETL. Figure 7 As shown, the band gap of the substrate Mx is greater than the band gap of the quantum dot QD. Typically, there is a tendency that the more upper periodic elements there are, the weaker the core shielding of the electrons on the nucleus, and the stronger the binding with the surrounding elements. As a result, the material containing the elements of the upper periodicity has a tendency to have a deep VBM (valence band) and a shallow CBM (conduction band) compared with the material containing the elements of the lower periodicity, and thus, there is a tendency for the band gap to be large. In the present disclosure, VBM or CBM is deep, which means that the difference between the energy level of LUMO (lowest empty orbital) or HOMO (highest occupied orbital) and vacuum is large. In addition, VBM or CBM shallow means that the difference between the energy level of LUMO or HOMO and vacuum is small.

[0036] like Figure 7 As shown, regarding the current I1 that contributes to light emission, electrons are injected from the CBM of the electron transport layer ETL into the CBM of the quantum dot QD, and holes are injected from the VBM of the hole transport layer HTL into the VBM of the quantum dot QD. Then, the electrons and holes are recombined through the quantum dot QD to excite the quantum dot QD. The excited quantum dot QD emits light.

[0037] On the other hand, Figure 7 As shown by the dotted arrow in the middle, regarding the current I2 that does not contribute to luminescence, electrons are injected from the CBM of the electron transport layer ETL into the CBM of the substrate Mx. Compared with the CBM of the quantum dot QD, the CBM of the substrate Mx is shallow. Therefore, it is difficult to inject electrons into the substrate Mx. In addition, compared with the luminescent diode element D1, the rise voltage of the non-luminescent diode element D2 is large. In addition, the difference in the band gap between the substrate Mx and the quantum dot QD affects the current injection efficiency. The larger the band gap of the substrate Mx, the higher the current injection efficiency.

[0038] (Material combination 1) When the quantum dot QD contains a II-VI compound, the second element in the substrate Mx may include any one or more of a group I element that is closer to the upper period than the group II element contained in the quantum dot QD, a group II element that is closer to the upper period than the group II element contained in the quantum dot QD, and a group III element that is closer to the upper period than the group II element contained in the quantum dot QD. Group II-VI compounds refer to all compounds composed of group II elements and group VI elements in a composition ratio of approximately 1:1. Group II-VI compounds include ZnS, ZnO, and ZnSe. For example, when the quantum dot QD contains Zn (zinc), the second element may include any one or more of H (hydrogen), Li (lithium), Be (beryllium), B (boron), Na (sodium), Mg (magnesium), Al (aluminum), K (potassium), Ca (calcium) and Sc (scandium).

[0039] In the case where the shell of the quantum dot QD comprises ZnO or ZnS, it is preferred that the substrate Mx comprises Li x Be y Mg z Zn (1-x-y-z) O or Li x Be y Mg z Zn (1-x-y-z) S. In any combination, 0≤x, 0≤y, 0≤z and 0<x+y+z≤1. Furthermore, considering Examples 1 and 2 described later, 0.1≤x+y+z<1 is more preferable.

[0040] In the case where the shell of the quantum dot QD comprises ZnO or ZnS, it is also preferred that the substrate Mx comprises Al x Zn (1-x) O or Al x Zn (1-x) In the case where the shell of the quantum dot QD comprises ZnSe, it is preferred that the substrate Mx comprises Al x Zn (1-x) Se. In both examples, 0<x≤1 is more preferred. Further, 0.1≤x<1 is more preferred.

[0041] (Material combination 2) When the quantum dot QD includes a III-V compound, the second element in the substrate Mx may also include any one or more of a group II element that is closer to the upper period than the group III element included in the quantum dot QD, a group III element that is closer to the upper period than the group III element included in the quantum dot QD, and a group IV element that is closer to the upper period than the group III element included in the quantum dot QD. The III-V compound refers to a compound composed entirely of group III elements and group V elements in a composition ratio of approximately 1:1. The III-V compound includes AlN, GaN, and InN.

[0042] In the example where the shell of the quantum dot QD comprises A1N, it is preferred that the substrate Mx comprises B x C y A1 (1-x-y) N. In the case where the shell of the quantum dot QD comprises GaN, it is preferred that the substrate Mx comprises B x C y Ga (1-x-y) N. In both examples, 0≤x, 0≤y and 0<x+y≤1. Furthermore, more preferably, 0.1≤x+y<1. "B" described in this paragraph means B (boron), and "C" means C (carbon).

[0043] (Material combination 3) When the quantum dot QD contains a group I-III-VI2 compound, the second element in the substrate Mx may include any one or more of a group I element that is closer to the upper period than the group I element contained in the quantum dot QD, a group II element that is closer to the upper period than the group I element or the group III element contained in the quantum dot QD, a group III element that is closer to the upper period than the group III element contained in the quantum dot QD, and a group VI element that is closer to the upper period than the group VI element contained in the quantum dot QD. Group I-III-VI2 compounds refer to all compounds composed of group I elements, group III elements and group VI elements in a composition ratio of about 1:1:2. Group I-III-VI2 compounds include CuAlS2, CuAlSe2, CuGaS2, AgAlS2, AgAlSe2 and AgGaSe2.

[0044] In the case where the shell of the quantum dot QD comprises CuAlS2, it is preferred that the substrate Mx comprises CuB x Al (1-x) O 2y S (2-2y) In the case where the shell of the quantum dot QD comprises CuAlSe2, it is preferred that the substrate Mx comprises CuB x Al (1-x) O 2y S (2-2y) ,CuB x Al (1-x) O 2y Se (2-2y) ,CuB x Ga (1-x) O 2y S (2-2y) , AgB x Al (1-x) O 2y S (2-2y) , and AgB x Al (1-x) O 2y Se (2-2y)In the case where the shell of the quantum dot QD comprises CuGaS2, it is preferred that the substrate Mx comprises CuB x Al (1-x) O 2y S (2-2y) ,CuB x Al (1-x) O 2y Se (2-2y) , AgB x Al (1-x) O 2y S (2-2y) and AgB x Al (1-x) O 2y Se (2-2y) In the case where the shell of the quantum dot QD comprises AgAlS2, it is preferred that the substrate Mx comprises CuB x Al (1-x) O 2y S (2-2y) In the case where the shell of the quantum dot QD comprises AgAlSe2, it is preferred that the substrate Mx comprises CuB x Al (1-x) O 2y S (2-2y) ,CuB x Al (1-x) O 2y Se (2-2y) CuB x Ga (1-x) O 2y S (2-2y) In the case where the shell of the quantum dot QD comprises AgGaSe2, it is preferred that the substrate Mx comprises CuB x Al (1-x) O 2y S (2-2y) ,CuB x Al (1-x) O 2y Se (2-2y) ,CuB x Ga (1-x) O 2y S (2-2y) , AgB x Al (1-x) O 2y S (2-2y) , AgB x Al (1-x) O 2y Se (2-2y) and AgB x Ga (1-x) O 2y S (2-2y)In any combination, 0≤x≤1, 0≤y≤1 and 0<x+y≤2. Moreover, 0.1≤x+y<2 is more preferred. “B” described in this paragraph means B (boron).

[0045] (Material combination 4) When the quantum dot QD contains a II-IV-V2 group compound, the second element in the substrate Mx may include a group I element that is closer to the upper period than the group II element contained in the quantum dot QD, a group II element that is closer to the upper period than the group II element contained in the quantum dot QD, a group III element that is closer to the upper period than the group II element or the group IV element contained in the quantum dot QD, a group IV element that is closer to the upper period than the group IV element contained in the quantum dot QD, and any one or more of a group V element that is closer to the upper period than the group V element contained in the quantum dot QD. The II-IV-V2 group compound refers to all compounds composed of group II elements, group IV elements, and group V elements in a composition ratio of about 1:1:2. The II-IV-V2 group compound contains ZnSiP2 and CdSiP2.

[0046] In the case where the shell of the quantum dot QD comprises ZnSiP2, the substrate Mx preferably comprises ZnC x Si (1-x) N 2y P (2-2y) In the case where the shell of the quantum dot QD contains CdSiP2, it is preferred that the substrate Mx contains ZnC x Si (1-x) N 2y P (2-2y) or CdC x Si (1-x) N 2y P (2-2y) In any combination, 0≤x≤1, 0≤y≤1 and 0<x+y≤2. Moreover, 0.1≤x+y<2 is more preferred.

[0047] (Material combination 5) When the quantum dot QD includes a group IV compound, the second element in the substrate Mx may include a group IV element that is closer to the upper period than the group IV element included in the quantum dot QD. Group IV compounds refer to all compounds composed of multiple group IV elements. Group IV compounds include SiC, GeC and SnC. In the example where the shell of the quantum dot QD includes GeC, it is preferred that the substrate Mx includes SiC. The "C" recorded in this paragraph refers to C (carbon).

[0048] (halogen) The substrate Mx may also contain halide ions, which halide ions have at least one of fluoride ions, chloride ions, bromide ions, and iodide ions. The substrate Mx may contain more than 1 atomic % of halogen atoms. Preferably, the concentration of halide ions near each quantum dot QD is higher than the concentration of halide ions on its surrounding side. For example, the range within 1 nm from the outermost surface of a quantum dot QD around a certain quantum dot QD can be set as the vicinity of the quantum dot. For example, the average value of the concentration of halogen atoms within 1 nm from the outermost surface of each quantum dot QD can be higher than the average value of the concentration of halogen atoms at other positions by more than 10%, more than 50%, or more than 100%.

[0049] The substrate Mx can contain halide ions by forming the light-emitting layer EL using a quantum dot dispersion containing a halogen element and quantum dots QD.

[0050] Figure 8 2 is a cross-sectional view of a process for explaining a process of replacing a ligand coordinated in a quantum dot. Figure 8 As shown on the left side of , in the replacement process, first, a first solution 20 in which halide ions 16H are dissolved and a second solution 22 in which quantum dots QD coordinated by carbon chains CC as organic ligands are dispersed are injected into a container 18. The first solution 20 contains a first solvent S in which halide ions 16H are soluble, and the second solution 22 contains a second solvent 26 in which carbon chains CC are soluble. For example, the polarity of the second solvent 26 is different from that of the first solvent S, and the specific gravity is lighter than that of the first solvent S. In order to more clearly distinguish the boundary between the first solution 20 and the second solution 22, a separation liquid 28 having a specific gravity and polarity between the first solvent S and the second solvent 26 may also be injected into the container 18.

[0051] The first solvent S disperses the quantum dots QD coordinated by the halide ions 16H well together with the precursor of the substrate Mx. In addition, the first solvent S may be a polar solvent having a greater polarity than the second solvent 26. The second solvent 26 is preferably a non-polar solvent that is not mixed with the first solvent S.

[0052] The carbon chain CC can generally be a carbon chain used as a ligand of the quantum dot QD. The second solvent 26 is a solvent in which the carbon chain CC is soluble, so the quantum dot QD coordinated by the carbon chain CC is easily dispersed in the second solution 22. In addition, an excess of halide ions 16H exceeding the amount of halide ions 16H that can be coordinated to the quantum dot QD is dissolved in the first solution 20. The concentration of halide ions in the first solvent S is preferably 0.01 mol / l or more, more preferably 0.1 mol / l or more.

[0053] Next, the container 18 containing the first solution 20 and the second solution 22 is vibrated at high speed by a stirrer to stir the first solution 20 and the second solution 22. In order to improve the stirring efficiency, a stirrer may be placed in the container 18. In other words, the process of stirring the first solution 20 and the second solution 22 is a process of treating the quantum dots QD with the halide ions 16H, in particular, a process of generating the quantum dots QD coordinated with the halide ions 16H.

[0054] Here, as described above, the first solution 20 contains an excess of halide ions 16H. Generally, when the solution in which the quantum dots QD are dispersed contains two or more ligands, the ligands coordinated by the quantum dots QD are in equilibrium between the ligands in the solution. Therefore, when the first solution 20 and the second solution 22 are stirred, at least a portion of the ligands coordinated by the quantum dots QD are replaced by halide ions 16H from the carbon chain CC.

[0055] For example, the solution in the container 18 is stirred for at least 1 minute. In addition, the stirring of the solution in the container 18 can also be performed at a frequency of 10 times per minute for 1 hour while the temperature of the solution in the container 18 is set to 25°C. If this condition is met, it can be said that the possibility that the ligand coordinated with the quantum dot QD in the container 18 is replaced by the halide ion 16H is sufficiently high. Furthermore, in order to prevent water or oxygen in the atmosphere from mixing with the solution in the container 18, it is more preferable to stir the solution in the container 18 under an atmosphere of nitrogen or argon.

[0056] Therefore, by the above stirring, Figure 8 As shown on the right side of the figure, a third solution 30 in which the halide ion 16H coordinated quantum dots QD are dispersed in the first solvent S and a fourth solution 32 in which the carbon chain CC is dissolved in the second solvent 26 is obtained in the container 18. Thus, the halide ion 16H coordinated quantum dots QD are obtained in the third solution 30. In addition, the above stirring can also be completed at the stage of irradiating the liquid in the container 18 with ultraviolet rays, etc., and confirming that the luminescent liquid layer moves from the upper side of the container 18 to the lower side.

[0057] Next, a quantum dot dispersion in which the above-mentioned halide ion 16H-coordinated quantum dots QD are dispersed is synthesized. Fig. 9 , the quantum dot dispersion of this embodiment is described in detail. Fig. 9 3 is a schematic diagram showing a quantum dot dispersion. For example, after the above stirring, only the third solution 30 is extracted from the container 18 by a pipette or the like and injected into the Fig. 9 In the container 34 shown.

[0058] Here, a solution in which the precursor J of the substrate Mx is dispersed in the first solvent S in advance may be injected into the container 18. Figure 8As shown, the quantum dot dispersion L in which the halide ion 16H coordinated quantum dots QD and the precursor J are dispersed in the first solvent S is synthesized.

[0059] Alternatively, the substrate Mx may contain halide ions by containing a halogen element in the precursor J of the substrate Mx. For example, when the substrate Mx contains Mg, MgCl2 (magnesium dichloride) may be used as a material containing Mg for the precursor J. When the substrate Mx contains Li, LiCl (lithium chloride) may be used as a material containing Li for the precursor J. Example 1

[0060] The light emitting element 10 of Example 1 of the present disclosure was produced.

[0061] First, the quantum dot QD includes ZnS, the substrate Mx includes crystalline MgZnS, and the ratio of currents I1 and I2 flowing through the diode elements D1 and D2 is I1:I2 = 10:1. When I1:I2 = 10:1, the current injection efficiency into the light-emitting diode element D1 is about 91%.

[0062] When the current ratio is 10:1, the saturation current ratio is also 10:1. Experiments have confirmed that the band gap between ZnS and MgS is Eg ZnS ≈3.6eV, Eg MgS ≈4.4eV. The energy gap of the mixed crystal MgZnS required to achieve a current ratio of 10:1 is calculated using equations (4) and (5) as Eg MgZnS ≈3.7 eV. The ratio of MgS in the mixed crystal MgZnS is calculated using formula (8): Mg ≈0.1. Under atmospheric pressure, ZnS adopts the wurtzite structure, MgS adopts the rock salt structure, and the mixed crystal MgZnS maintains the wurtzite structure, with the proportion of MgS ranging from 0% to about 20%. Mg When ≈0.1, the change in the crystal structure of the substrate Mx can be ignored.

[0063] Furthermore, the diode coefficients of the diode elements D1 and D2 are both set to n=3, and the parameters in equations (1) and (2) are calculated: r≈200Ω, r1≈69Ω, r2≈142Ω, V1≈5V, V2≈5.2V.

[0064] Then, according to the above calculation results, the light-emitting element 10 of Example 1 was manufactured. Specifically, the anode E1 and the charge functional layer F1 were manufactured on the substrate using the existing technology, and a colloidal dispersion solution in which quantum dots QD were dispersed was coated or printed on the charge functional layer F1 to form a quantum dot layer. Then, a precursor solution of mixed crystal MgZnS was coated on the quantum dot layer to inorganicize the quantum dot layer. Thus, the light-emitting layer EL was formed. In addition, the charge functional layer F2 and the cathode E2 were manufactured on the light-emitting layer EL using the existing technology.

[0065] Regarding the precursor solution, as a precursor of MgZnS, ZnTNT (zinc t-nonane sulfate) and MgTNT (magnesium t-nonane sulfate) are mixed in tertiary thiol. Here, the volume ratio of ZnTNT and MgTNT is 1 / 9 or more (ZnTNT / MgTNT≥1 / 9). The reason why the proportion of Mg in the precursor is greater than the proportion of Mg in the substrate Mx is that Mg is more active than Zn and is easily consumed by side reactions other than the main reaction. As a result of Mg being consumed by side reactions, Mg is difficult to be incorporated into the substrate Mx. In addition, when weighing a material containing Mg and a material containing Zn, since the density (=mass / volume) of Mg is smaller than that of Zn, it is preferred to set the weight of the Mg material to more than 20 times the weight of the Zn material.

[0066] Furthermore, a light-emitting element of a comparative example in which the substrate Mx contained ZnS was produced.

[0067] Fig.10 is a graph showing the JV characteristics of the diode element of Example 1. Fig.10 In FIG. 1 , the solid line represents the relationship between the current density and the voltage (JV characteristic) of the light-emitting diode element D1 , and the dotted line represents the JV characteristic of the non-light-emitting diode element D2 .

[0068] from Fig.10 It can be seen that by adding 10% Mg to ZnS, Mg 0.1 Zn 0.9 When S is used for the base material Mx, the current near the rising voltage is significantly suppressed compared to the case where only ZnS is used for the base material Mx. Example 2

[0069] The light emitting element 10 of Example 2 of the present disclosure was designed.

[0070] The quantum dot QD comprises ZnS, the substrate Mx comprises crystalline LiZnS, and the ratio of the currents I1 and I2 flowing through the diode elements D1 and D2 is I1:I2=10:1. The result calculated in the same way as in Example 1 shows that the energy gap of the mixed crystal LiZnS required to achieve a current ratio of 10:1 is Eg LiZnS ≈3.7eV. In addition, the ratio of LiS in the mixed crystal LiZnS is xLiS ≈0.1.

[0071] The light emitting element 10 of Example 2 can be produced by using a mixture of LiTNT (lithium t-nonane sulfate) and ZnTNT mixed in tertiary mercaptan as a precursor of LiZnS. Example 3

[0072] The light emitting element 10 of Example 3 of the present disclosure was designed.

[0073] The quantum dot QD comprises ZnS, the substrate Mx comprises mixed crystal LiMgZnS, and the ratio of the currents I1 and I2 flowing through the diode elements D1 and D2 is I1:I2=10:1. The result calculated in the same way as in Example 1 shows that the energy gap of the mixed crystal LiMgZnS required to achieve a current ratio of 10:1 is Eg LiMgZnS ≈3.7eV. In addition, the ratio of LiS to MgS in the mixed crystal LiMgZnS is x LiS +x Mgs ≈0.1.

[0074] According to Examples 1 to 3, it is inferred that the band gap of the substrate Mx is greater than the band gap of the quantum dot QD, and the difference between them is preferably greater than 0.1 eV. Here, the band gap of the quantum dot QD can be the band gap of the core of the quantum dot QD, or the band gap of the shell of the quantum dot QD. In addition, when the quantum dot QD contains a compound AC composed of element A and element C, and the substrate Mx contains a mixed crystal ABC in which a compound BC composed of element B and element C is mixed in the compound AC, it is inferred that the proportion of compound BC in the mixed crystal ABC is preferably greater than 0.1. The "element A", "element B" and "element C" recorded in this paragraph are just pseudonyms for the three elements.

[0075] (Variation Example) The materials used for the quantum dots QD and the substrate Mx may also be determined only in such a way that the band gap of the substrate Mx is greater than the band gap of the quantum dots QD. This modification includes: a configuration in which the quantum dots QD do not include the first element, a configuration in which the substrate Mx does not include the second element, and a configuration in which the substrate Mx is composed of only one element. The light-emitting layer EL of this modification is located between the anode E1 and the cathode E2, and includes a plurality of quantum dots QD, and a substrate Mx having a band gap greater than the band gap of the plurality of quantum dots QD and including the plurality of quantum dots QD.

[0076] [Second Embodiment] In the following, other embodiments of the present disclosure will be described. In addition, for the sake of convenience, components having the same functions as those described in the above embodiments are denoted by the same reference numerals, and their description will not be repeated.

[0077] Fig.111 is a cross-sectional view showing a configuration example of a light emitting element according to an embodiment of the present disclosure. Fig.11 As shown, the substrate Mx of this embodiment includes a first portion P1 located on the anode E1 side and a second portion P2 located on the cathode E2 side. The substrate Mx may include a third portion P3 between the first portion P1 and the second portion P2.

[0078] Fig.12 Yes means Fig.11 Schematic diagram of an example of the energy band structure of the light-emitting layer shown. Fig.12 The HOMO and LUMO of the hole transport layer HTL, the substrate Mx, the quantum dots QD, and the electron transport layer ETL and the band gap therebetween are represented by rectangles. Fig.12 As shown, the band gap of the first portion P1 of the substrate Mx is smaller than the band gap of the second portion P2 of the substrate Mx.

[0079] Preferably, the size of the band gap in the substrate Mx increases stepwise or continuously from the anode E1 side toward the cathode E2 side. Preferably, the band gap of the third portion P3 of the substrate Mx is larger than the band gap of the first portion P1 of the substrate Mx, and smaller than the band gap of the second portion P2 of the substrate Mx.

[0080] [Third Embodiment] Other embodiments of the present disclosure are described below.

[0081] Fig.13 1 is a top view showing a configuration example of a light emitting device according to an embodiment of the present disclosure. Fig.13 As shown, the light emitting device 100 includes a display unit 15 including a plurality of sub-pixels X and a driving circuit 25 for driving the display unit 15. For example, the sub-pixel X includes the light emitting element 10 and the pixel circuit 5 described in the first embodiment or the second embodiment. The light emitting device 100 may be a display device or a lighting device.

[0082] The present disclosure is not limited to the above-mentioned embodiments, and various changes can be made within the scope of the claims. The embodiments obtained by appropriately combining the technical solutions disclosed in different embodiments are also included in the technical scope of the present disclosure. Moreover, by combining the technical means disclosed in each embodiment, new technical features can be formed. Description of Reference Numerals

[0083] 10: Light-emitting components 100: Light-emitting devices E1: Anode E2: Cathode EL: Light Emitting Layer Mx: Base material QD: Quantum Dot

Claims

1. A light emitting element, characterized in that: It has: an anode and a cathode; and a light-emitting layer located between the anode and the cathode, The light-emitting layer has: a plurality of quantum dots comprising a metal element, namely a first element; and A substrate is composed of two or more elements and includes the plurality of quantum dots. The two or more elements include a second element that is located in a higher period than the first element and is not included in the plurality of quantum dots.

2. The light emitting element according to claim 1, characterized in that The substrate fills spaces between the plurality of quantum dots.

3. The light emitting element according to claim 1 or 2, characterized in that: The light-emitting layer has a quantum dot group, and the quantum dot group includes the plurality of quantum dots. The substrate fills the area outside the quantum dot group.

4. The light emitting element according to any one of claims 1 to 3, characterized in that The first element and the second element are of the same group.

5. The light emitting element according to any one of claims 1 to 3, characterized in that: The group containing the first element and the group containing the second element are adjacent.

6. The light emitting element according to any one of claims 1 to 3, characterized in that: The number of valence electrons of the first element is the same as the number of valence electrons of the second element.

7. The light emitting element according to any one of claims 1 to 3, characterized in that: The difference between the number of valence electrons of the first element and the number of valence electrons of the second element is 1.

8. The light emitting element according to any one of claims 1 to 7, characterized in that: The substrate includes a continuous film of a mixed crystal composed of the two or more elements.

9. The light emitting element according to any one of claims 1 to 8, characterized in that: The substrate contains a continuous film of an inorganic compound.

10. The light emitting element according to any one of claims 1 to 9, characterized in that: The band gap of the substrate is larger than the band gaps of the plurality of quantum dots.

11. The light emitting element according to any one of claims 1 to 10, characterized in that: The plurality of quantum dots contain II-VI group compounds, The second element includes any one or more of a Group I element that is closer to the upper period than the Group II element contained in the multiple quantum dots, a Group II element that is closer to the upper period than the Group II element contained in the multiple quantum dots, and a Group III element that is closer to the upper period than the Group II element contained in the multiple quantum dots.

12. The light emitting element according to claim 11, characterized in that The shells of the plurality of quantum dots contain ZnO or ZnS, The substrate includes Li x Be y Mg z Zn (1-x-y-z) O or Li x Be y Mg z Zn (1-x-y-z) S, 0≤x, 0≤y, 0≤z, and 0<x+y+z≤1.

13. The light emitting element according to claim 12, characterized in that: 0.1≤x+y+z<1.

14. The light emitting element according to claim 11, characterized in that The shells of the plurality of quantum dots contain ZnO or ZnS, and the substrate contains Al x Zn (1-x) O or Al x Zn (1-x) S, or The shells of the plurality of quantum dots contain ZnSe, and the substrate contains Al x Zn (1-x) Se, 0<x≤1.

15. The light emitting element according to claim 14, characterized in that: 0.1≤x＜1。 16. The light emitting element according to any one of claims 1 to 10, characterized in that: The plurality of quantum dots contain group III-V compounds, The second element includes any one or more of a Group II element that is in a higher period than the Group III element contained in the multiple quantum dots, a Group III element that is in a higher period than the Group III element contained in the multiple quantum dots, and a Group IV element that is in a higher period than the Group III element contained in the multiple quantum dots.

17. The light emitting element according to claim 16, characterized in that The shells of the plurality of quantum dots contain AlN, and the substrate contains B x C y Al (1-x-y) N, or The shells of the plurality of quantum dots contain GaN, and the substrate contains B x C y Al (1-x-y) N or B x C y Ga (1-x-y) N, Among them, 0≤x, 0≤y, and 0<x+y≤1.

18. The light emitting element according to claim 17, characterized in that 0.1≤x+y<1.

19. The light emitting element according to any one of claims 1 to 10, characterized in that: The plurality of quantum dots contain I-III-VI2 group compounds, The second element includes any one or more of a Group I element that is at a higher period than the Group I element contained in the multiple quantum dots, a Group II element that is at a higher period than the Group I element or the Group III element contained in the multiple quantum dots, a Group III element that is at a higher period than the Group III element contained in the multiple quantum dots, and a Group VI element that is at a higher period than the Group VI element contained in the multiple quantum dots.

20. The light emitting element according to claim 19, characterized in that The shells of the plurality of quantum dots contain CuAlS2, and the substrate comprises CuB x Al (1-x) O 2y S (2-2y) , The shells of the plurality of quantum dots contain CuAlSe2, and the substrate comprises CuB x Al (1-x) O 2y S (2-2y) ,CuB x Al (1-x) O 2y Se (2-2y) ,CuB x Ga (1-x) O 2y S (2-2y) , AgB x Al (1-x) O 2y S (2-2y) , and AgB x Al (1-x) O 2y Se (2-2y) Any one of The shells of the plurality of quantum dots contain CuGaS2, and the substrate contains CuB x Al (1-x) O 2y S (2-2y) ,CuB x Al (1-x) O 2y Se (2-2y) , AgB x Al (1-x) O 2y S (2-2y) and AgB x Al (1-x) O 2y Se (2-2y) Any one of The shells of the plurality of quantum dots comprise AgAlS2, and the substrate comprises CuB x Al( 1-x) O 2y S (2-2y) , The shells of the plurality of quantum dots include AgAlSe2, and the substrate includes CuB x Al (1-x) O 2y S (2-2y) ,CuB x Al (1-x) O 2y Se (2-2y) CuB x Ga (1-x) O 2y S (2-2y) Any of, or The shells of the plurality of quantum dots comprise AgGaSe2, and the substrate comprises CuB x Al (1-x) O 2y S (2-2y) ,CuB x Al (1-x) O 2y Se (2-2y) ,CuB x Ga (1-x) O 2y S (2-2y) , AgB x Al (1-x) O 2y S (2-2y) , AgB x Al (1-x) O 2y Se (2-2y) and AgB x Ga (1-x) O 2y S (2-2y) Any one of , 0≤x≤1, 0≤y≤1, and 0<x+y≤2.

21. The light emitting element according to claim 20, characterized in that 0.1≤x+y<2.

22. The light emitting element according to any one of claims 1 to 10, characterized in that: The plurality of quantum dots contain II-IV-V2 group compounds, The second element includes any one or more of a Group I element that is closer in period to the Group II element contained in the multiple quantum dots, a Group II element that is closer in period to the Group II element contained in the multiple quantum dots, a Group III element that is closer in period to the Group II element or the Group IV element contained in the multiple quantum dots, a Group IV element that is closer in period to the Group IV element contained in the multiple quantum dots, and a Group V element that is closer in period to the Group V element contained in the multiple quantum dots.

23. The light emitting element according to claim 22, characterized in that The shells of the plurality of quantum dots contain ZnSiP2, and the substrate contains ZnC x Si (1-x) N 2y P (2-2y) ,or, The shells of the plurality of quantum dots contain CdSiP2, and the substrate contains ZnC x Si (1-x) N 2y P (2-2y) or CdC x Si (1-x) N 2y P (2-2y) , 0≤x≤1, 0≤y≤1 and 0<x+y≤2.

24. The light emitting element according to claim 23, characterized in that: 0.1≤x+y<2.

25. The light emitting element according to any one of claims 1 to 10, characterized in that The plurality of quantum dots contain GeC, The substrate contains SiC.

26. A light emitting element, characterized in that: It has: an anode and a cathode; and a light-emitting layer located between the anode and the cathode, The light-emitting layer has: a plurality of quantum dots; and A substrate comprises the plurality of quantum dots and has a larger band gap than the plurality of quantum dots.

27. The light emitting element according to any one of claims 1 to 26, characterized in that: The band gap of the substrate is greater than the band gap of the plurality of quantum dots by more than 0.1 eV.

28. The light emitting element according to any one of claims 1 to 27, characterized in that A first portion of the substrate located on the anode side has a smaller band gap than a second portion of the substrate located on the cathode side.

29. The light emitting element according to any one of claims 1 to 28, characterized in that The substrate further contains halogen atoms.

30. The light emitting element according to claim 29, characterized in that The substrate contains 1 atomic % or more of halogen atoms.

31. The light emitting element according to claim 29 or 30, characterized in that: The average value of the concentration of halogen atoms within 1 nm from the outermost surface of the plurality of quantum dots is higher than the average value of the concentration of halogen atoms at other positions by more than 10%.

32. The light emitting element according to any one of claims 1 to 31, characterized in that The substrate includes a continuous film having a thickness of 1000 nm in a plane direction perpendicular to the thickness direction at any position of the light-emitting layer in the thickness direction. 2 The area above.

33. A light emitting device, characterized in that: The light-emitting device comprises the light-emitting element according to any one of claims 1 to 32.

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