WO2019115575A1

WO2019115575A1 - Composition comprising a semiconductor light emitting nanoparticle

Info

Publication number: WO2019115575A1
Application number: PCT/EP2018/084453
Authority: WO
Inventors: Itai Lieberman; Christian MATUSCHEK
Original assignee: Merck Patent Gmbh
Priority date: 2017-12-15
Filing date: 2018-12-12
Publication date: 2019-06-20
Also published as: TW201930547A

Abstract

The present invention relates to a composition comprising at least a semiconductor light emitting nanoparticle; and an polymer.

Description

COMPOSITION COMPRISING A SEMICONDUCTOR LIGHT EMITTING NANOPARTICLE The present invention relates to a composition comprising at a

semiconductor light emitting nanoparticle and an organic phase. The present invention relates further to a method of manufacturing a layered composite comprising the aforementioned composition, to an optical medium comprising the layered composition, to an optical device comprising said optical medium and to the use of a semiconductor light emitting nanoparticle.

Semiconducting nanocrystals such as quantum dots, quantum rods, tetrapods and the like are of great interest as color converter materials in LEDs and displays due to their narrow fluorescence emission. Using fluorescent quantum dots for applications such as down conversion layers in LCDs, color filters and color converters directly on top of LEDs requires the Semiconducting nanocrystals to be incorporated into a thin layer that would provide protection for the nanocrystals. A polymer film which contain quantum dots are one way to achieve a desired thin layer. Various polymers have been used for this purpose, such as acrylate, siloxanes, silazanes, epoxies, silicones, and so on. In particular, acrylates are abundantly used for backlight film applications. Incorporation of quantum dots into this kind of layers causes a drop in their emission quantum Yield (QY). This is caused by aggregation of the quantum dots in the solid polymer film and due to chemical processes, which affect the organic molecules attached to the surface of the quantum dots (known as ligands) and cause detachment of the ligands from the quantum dots’ surface occurs. Furthermore, when incorporated into display devices, the quantum dots containing polymer thin films are subjected to elevated temperature, humidity conditions and high light influx. These conditions further damage the ligands’ coverage of the quantum dots’ surface. The observable result is deterioration of the quantum dots’ performance in parameters of quantum yield (QY), a shift in the center wavelength (CWL) of the fluorescence curve and changes in the full-width- half-max (FWHM) of the fluorescence spectrum.

Another disadvantage is that many acrylate polymers are photocurable. This means that photo-initiators need to be incorporated into the film prior to its curing, followed by illumination of the polymer. This photo-initiators are known to create large amounts of radicals during the polymerization process, which may also damage the performance of the quantum dots.

In general terms, it is an object of the present invention to at least partly overcome at least one of the disadvantages that are known from the prior art.

Another object of the invention is to provide an optical medium which exhibits a higher quantum yield per a semiconductor light emitting nanoparticle, preferably a quantum dot, than those known in the art.

Another object of the invention is to provide an optical medium which has a stable quantum yield over lifetime. Another object of the invention is to provide an optical medium where its centre wavelength of the fluorescence curve does not shift during use of the optical medium. Another object of the invention is to provide a medium which does not show changes in the

FWHM of the fluorescence spectrum over lifetime of the optical medium. Another object of the invention is to provide an optical medium which can have incorporated quantum dots in a polymer matrix where the polymer matrix is produced by thermal curing.

Another object is to provide improved optical devices are less complex, emit improved color spectra and more intense light at specified wavelengths. Another object is to provide optical devices which consume less electrical energy but have the same optical output like conventional optical devices. It is another object of the invention to provide optical devices which comprise optical media that can have incorporated matrix polymers with a semiconductor light emitting nanoparticle, preferably a quantum dot, where the matrix polymers are produced by thermal curing.

Another object is to provide a composition comprising a semiconductor light emitting nanoparticle, preferably a quantum dot, more preferably a plurality of quantum dots, for application on substrates which can be used to manufacture layers with quantum dots, wherein the quantum dots are more stable with respect to their quantum yield (QY), centre wavelength (CWL) and full width half max of the fluorescence spectrum (FWHM) than those known in the art. Moreover, it is an object of the invention to provide a semiconductor light emitting nanoparticle, preferably a quantum dot, more preferably a plurality of quantum dots, in a composition, wherein the quantum dots are more efficient and/or exhibit higher output than those known in the art. It is another object of the invention to provide a

semiconductor light emitting nanoparticle, preferably a quantum dot, more preferably a plurality of quantum dots which can be incorporated into matrix polymers which are produced by thermal curing.

It is another object to provide a method of manufacturing a layered composite comprising at least one layer comprising a semiconductor light emitting nanoparticle, preferably a quantum dot, more preferably a plurality of quantum dots; which is at least partially coated with a polymer which causes as little as deterioration of efficiency in quantum yield as possible.

It has been found that a quantum dot, preferably a plurality of quantum dots encapsulated in a crosslinked poly(maleic anhydride alkylene copolymer) surprisingly provides a solution of some of the aforementioned objects. It has been further found that said encapsulated quantum dot(s) can also be used in matrix polymers which are produced by thermal curing. Moreover, it has been found that the claimed invention does not require a ligand exchange at the nanocrystals, such as quantum dots, preliminary to encapsulating these quantum dots, in contrary to procedures common in the prior art. Accordingly, the process of the invention involves less chemical steps, i.e. is more efficient. Moreover, the quantum dots having their initial ligands, i.e. as purchased, exhibit a higher performance compared with those quantum dots which had a ligand exchange. A contribution to achieving at least one of the above described objects is made by the subject matter of the category forming claims of the present disclosure. A further contribution is made by the subject matter of the dependent claims of the present disclosure which represent specific embodiments of the present disclosure.

PREFERRED EMBODIMENTS

1. A composition comprising at least these components:

a) a semiconductor light emitting nanoparticle, preferably a quantum dot, more preferably a plurality of quantum dots;

b) a maleic anhydride alkene copolymer;

c) a multifunctional amine; and

d) an acrylic polymer;

e) an organic phase;

wherein the maleic anhydride alkene copolymer has at least a first repeating unit and a second repeating unit.

2. The composition of embodiment 1 wherein the first repeating unit and the second repeating unit differ from each other. 3. The composition of any one of embodiments 1 or 2, wherein the second repeating unit is based on a linear C10 - C30 1 -olefin. 4. The composition of any one of the preceding embodiments, wherein the multifunctional amine is Bis(hexamethylene)triamine. 5. The composition of any one of the preceding embodiments, wherein the acrylic polymer is selected from poly (methyl methacrylate) and poly (dicyclopentanyl acrylate).

6. The composition of any one of the preceding embodiments, wherein the semiconductor light emitting nanoparticle, preferably the quantum dot, more preferably said plurality of quantum dots; is at least partially coated with component b.

7. A method of manufacturing a layered composite, comprising at least these steps:

(I) providing a substrate;

(II) applying a composition according to any one of embodiments 1 to 6 on the substrate (I) in order to form a layer on the substrate. 8. A method of manufacturing a layered composite, comprising at least the steps of

(A) manufacturing a mixture phase by at least these steps:

i) providing a liquid phase comprising at least a semiconductor light emitting nanoparticle, preferably a quantum dot, more preferably a plurality of quantum dots

ii) adding a liquid phase comprising a maleic anhydride alkene copolymer; iii) adding a multifunctional amine;

iv) adding an acrylic polymer;

(B) applying the mixture to a substrate in order to form a layer; and

(C) drying the mixture on the substrate; wherein the layer comprises at least the semiconductor light emitting nanoparticle, preferably the quantum dot, more preferably the plurality of quantum dots

wherein each quantum dot has a shell comprising component b.

9. The method of embodiment 8, wherein the layer is a polymer film.

10. A layered composite obtainable by the process of any one of embodiments 7 to 9.

11. A layered composite comprising,

at least an acrylic polymer; and

a substrate;

wherein the acrylic polymer comprises semiconductor light emitting nanoparticle, preferably a quantum dot, more preferably a plurality of quantum dots;

wherein the quantum dot, preferably the plurality of quantum dots, is at least partially coated by a maleic anhydride alkene copolymer;

12. The layered composite of any one of embodiments 10 or 11 , wherein the first repeating unit and the second repeating unit of the maleic anhydride alkene copolymer differ from each other.

13. The layered composite of any one of embodiments 10 to 12, wherein the second repeating unit of the maleic anhydride alkene copolymer is based on a linear C10 to C30 1 -olefin. 14. The layered composite of any one of embodiments 10 to 13, wherein the acrylic polymer is selected from the group consisting of poly (methyl methacrylate) and poly (dicyclopentanyl acrylate. 15. An optical medium comprising a layered composite according to any one of embodiment 10 to 13, or obtainable by a process according to any one of embodiments 7 to 8.

16. An optical device comprising the optical medium of embodiment 15.

17. A use of quantum dot, preferably a plurality of quantum dots, coated with a maleic anhydride alkene copolymer for improving the quantum yield of the quantum dots.

18. A use of a maleic anhydride alkene copolymer to improve the quantum yield of quantum dots. 19. The use of any one of embodiments 17 or 18, wherein the maleic anhydride alkene copolymer is at least partially crosslinked.

DETAILED DESCRIPTION OF THE INVENTION

A first aspect of the invention is a composition comprising at least these components:

a) a quantum dot, preferably a plurality of quantum dots;

b) a maleic anhydride alkene copolymer;

c) a multifunctional amine;

d) an acrylic polymer; and

e) an organic phase;

The composition can be of any kind known to a skilled person. The composition is a suspension, so it comprises liquid and solid constituents. An example of a liquid constituent is the organic phase. Quantum dots are an example of solid constituents. Each one of the further constituents of the composition can be of solid or liquid state at room temperature (20°C).

Each one of the further constituents solid at room temperature can be present as a solid in the composition, or at least partially dissolve or form a gel through the liquid constituents of the composition.

The quantum dots as constituents of the composition can be any kind of quantum dots known to and considered potentially useful by the skilled person. Quantum dots in the context of the present invention are

semiconducting particles, yet more preferred semiconducting nanoparticle. The quantum dots can emit light. Yet more preferred, a quantum dot is a semiconducting light emitting particle, or a a semiconducting light emitting nanoparticle. The quantum dot can emit tunable, sharp and colored light.

According to the present invention, the term“semiconducting” means a material that has electrical conductivity to a degree between that of a conductor (such as copper) and that of an insulator (such as glass) at room temperature. Preferably, a semiconducting material has an electrical conductivity increases with the temperature. The term“nanoparticle” means particles which have a size in between 0.1 nm and 999 nm, preferably 0.5 nm to 150 nm, more preferably 1 nm to 50 nm. The term“size” in the present context means the average diameter of the longest axis of the particles referred to. The average diameter of a certain particle is calculated based on the measurement of 100 such individual particles in a TEM image created by a Tecnai G2 Spirit Twin T-12 Transmission Electron Microscope (TEM) using the arithmetic mean.

The term“light emitting” refers to the property of a material or object to emit light of a wavelength from 250 nm to 800 nm upon an external activation such as an incident beam of light of a specific wavelength or a specific wavelength range. Thus term“semiconducting light emitting nanoparticle” in the present context refers to a light emitting material which size is in between 0.1 nm and 999 nm, preferably 1 nm to 150 nm, more preferably 3 nm to 50 nm, having electrical conductivity to a degree between that of a conductor (such as copper) and that of an insulator (such as glass) at room temperature, preferably, a semiconductor is a material whose electrical conductivity increases with the temperature, and the size is in between 0.1 nm and 999 nm, preferably 0,5 nm to 150 nm, more preferably 1 nm to 50 nm. According to the present invention, said quantum dot comprises a core and at least one shell layer. The shell layer is made from at least one shell material. The shell material covers the core at least in part, preferably in full. In the present invention, particularly preferred core materials are selected from the group consisting of CdS, CdSe, CdTe, ZnS, ZnSe, ZnSeS, ZnTe, ZnO, GaAs, GaP, GaSb, HgS, HgSe, HgSe, HgTe, InAs, InP, InPS,

InPZnS, InPZn, InPZnSe, InCdP, InPCdS, InPCdSe, InGaP, InGaPZn,

InSb, AIAs, AIP, AlSb, Cu2S, Cu2Se, CulnS2, CulnSe2, Cu2(ZnSn)S4, Cu2(lnGa)S4, Ti02 alloys and a combination of any of two or more thereof.

In a preferred embodiment of the present invention, the core comprises at least one element of the group 13 of the periodic table, and at least one element of the group 15 of the periodic table. By preference, In is selected from the elements of the group 13, and P is selected from the elements of the group 15. Yet more preferred, the core of the quantum dot can be represented by the following formula (I), or formula (G). lni_-xGaxZn_zP (I) wherein 0£x£1 , 0£z£1. Preferred examples of a core according to formula I are InP, ln_xZn_zP, and lni_-xGa_xP. A person skilled in the art can easily understand that there is a counter ion in or around the core and thus, the chemical formula (I) is electrically neutral. ln i_-x-2/3zGaxZnzP ( ) wherein 0£x£1 , 0£z£1. Preferred examples of a core according to formula G are InP, lni-2/3zZn_zP, or lni_-xGa_xP.

In case of Ihi-_2/3zZh_zR, x is 0, and 0<z£1 , the Zn atom can be located directly onto the surface of the core or alloyed with InP. The ratio between Zn and In can be in the range between 0.05 and 5, preferably between 0.07 and 1 .

According to the present invention, a type of shape of the core of the semiconducting light emitting nanoparticle, and shape of the

semiconducting light emitting nanoparticle to be synthesized are not particularly limited. For examples, spherical shaped, elongated shaped, star shaped, polyhedron shaped, pyramidal shaped, tetrapod shaped, tetrahedron shaped, platelet shaped, cone shaped, and irregular shaped core and - or a semiconducting light emitting nanoparticle can be

synthesized. in some embodiments of the present invention, the average diameter of the core is in the range from 1.5 nm to 3.5 nm.

The shell layer of the quantum dot of the present invention may comprise or consist of a first element of group 12 of the periodic table and a second element of group 16 of the periodic table. Preferably, the first element is Zn. Preferably, the second element is selected from the group consisting of S, Se, and Te. Preferably, the shell layer is represented by following formula (II),

ZnS_xSe_yTe_z, (II) with 0£x<1 , 0£y<1 , 0£z<1 , and x+y+z=1. In a preferred embodiment, the shell layer is selected from the group consisting of ZnSe, ZnS_xSe_y,

ZnSe_yTe_z and ZnS_xTe_z. In another preferred embodiment of the present invention, said shell layer is an alloyed shell layer or a graded shell layer. Preferably, said graded shell layer is selected from the group consisting of ZnS_xSe_y, ZnSe_yTe_z, and ZnS_xTe_z, yet more preferably ZnS_xSe_y. The ratio of y/x is preferably larger than 0.5, more preferably larger than 1 and even more preferably larger than 2. The ratio of y/z is preferably larger than 1 and more preferably larger than 2, and even more preferably larger than 4. In another preferred embodiment of the present invention, the quantum dot further comprises a second shell layer which covers at least partially, preferably completely said first shell layer. The second shell layer may comprise or consist of a third element of group 12 of the periodic table and a fourth element of group 16 of the periodic table. Preferably, the third element is Zn. Preferably, the fourth element is S, Se, or Te. Yet more preferred, the fourth element and the second element are not the same.

In a further preferred embodiment of the present invention, the second shell layer is represented by following formula (IG),

ZnS_xSe_yTe_z, - (IG) wherein the formula (I ), 0£x<1 , 0£y<1 , 0£z<1 , and x+y+z=1 , preferably, the shell layer is ZnSe, ZnS_xSe_y, ZnSe_yTe_z, or ZnS_xTe_z with the proviso that the shell layer and the 2nd shell layer is not the same. In some embodiments of the present invention, said second shell layer can be an alloyed shell layer or a graded shell layer, preferably said graded shell layer is ZnS_xSe_y, ZnSe_yTe_z, or ZnS_xTe_z, more preferably it is ZnS_xSe_y.

In some embodiments of the present invention, the quantum dot can further comprise one or more additional shell layers onto the second shell layer and thus have a multishell.

According to the present invention, the term“multisheN” stands for the stacked shell layers consisting of three or more shell layers.

For example, a third and fourth, or optionally fifth shell layer can be selected from one of these sequences: CdSe/CdS, CdSeS/CdZnS,

CdSeS/CdS/ZnS, ZnSe/CdS, CdSe/ZnS, InP/ZnS, InP/ZnSe,

InP/ZnSe/ZnS, InZnP /ZnS, InZnP /ZnSe, InZnP /ZnSe/ZnS, InGaP/ZnS, InGaP/ZnSe, InGaP/ZnSe/ZnS, InZnPS / ZnS, InZnPS ZnSe, InZnPS

/ZnSe/ZnS, ZnSe/CdS, ZnSe/ZnS or combination of any of these, can be used. Preferably, InP/ZnS, InP/ZnSe, lnP/ZnSe_xSi_-x, lnP/ZnSe_xSi_-x/ZnS, InP/ZnSe/ZnS, InZnP /ZnS, lnP/ZnSe_xTei_-x/ZnS, lnP/ZnSe_xTei_-x, InZnP /ZnSe, InZnP /ZnSe/ZnS, InGaP/ZnS, InGaP/ZnSe, InGaP/ZnSe/ZnS.

In some embodiments of the present invention, the surface of the quantum dot can be over coated with one or more kinds of surface ligands. Without wishing to be bound by theory it is believed that such surface ligands may lead to disperse the nanosized fluorescent material in a solvent more easily. Examples of suited surface ligands in common use include phosphines and phosphine oxides such as Trioctylphosphine oxide (TOPO),

Thoctylphosphine (TOP), and Thbutylphosphine (TBP); phosphonic acids such as Dodecylphosphonic acid (DDPA), Tridecylphosphonic acid (TDPA), amines such as Oleylamine, Dedecyl amine (DDA), Tetradecyl amine

(TDA), Hexadecyl amine (HDA), and Octadecyl amine (ODA), Oleylamine (OLA), 1 -Octadecene (ODE), thiols such as hexadecane thiol and hexane thiol; mercapto carboxylic acids such as mercapto propionic acid and mercaptoundecanoicacid; carboxylic acids such as oleic acid, stearic acid, myristic acid; acetic acid and a combination of any of these. Furthermore, the ligands can include Zn-oleate, Zn-acetate, Zn-myristate, Zn-Stearate, Zn-laurate and other Zn-carboxylates. Moreover, polyethylenimine (PEI) can be used by preference The maleic anhydride alkene polymer of the composition of the present invention can be of any kind which is known to and considered useful by a skilled person in order to work the invention. More specifically, the maleic anhydride alkene copolymer has at least a first repeating unit and a second repeating unit, which are different. Repeating units are formed by the polymerization of one or more monomers. The first repeating unit is formed from a maleic anhydride in the maleic anhydride alkene polymer. The maleic anhydride alkene copolymer forms an outer polymer shell which covers the quantum dot, core and shell at least in part, preferably in full. The second repeating unit can be formed from a linear or branched olefin, yet more preferred from a linear or branched 1 -olefin.

According to the present invention, the term“1 -olefin” means an alpha olefin.

Preferably said alpha olefin is represented by following chemical formula CH2=CH₂-(CH₂)n-CH3 wherein n is an integer 7 to 27.

5 The second repeating unit is formed from a linear 1 -olefin in a further

preferred embodiment. Yet more preferred, the linear 1 -olefin has a substituted or un-substituted C1 to C30 radical, preferably a C4 to C26 radical, for example a C10 to C20 radical, yet more preferred a C15 to C20 radical. A C4 radical denotes a carbon chain of 4 carbon, the resulting 10 olefin has a carbon chain of 6. A C20 radical denotes a chain of 20 carbon, the resulting olefin has a carbon chain of 22. Accordingly, a 1 -olefin with a C4 linear radical is a 1 -olefin with a radical of 4 carbon atoms in a chain. An unsubstituted example for this is 1 -Hexene. In analogy, a 1 -olefin with a linear and unsubstituted C16 radical is 1 -Octadecen. Preferred examples of 15 1 -olefins are 1-decene, 1 -dodecene, 1 -tetradecene, 1 -hexadecene, 1- octadecene and 1 -eicosen.

In a preferred embodiment of the present invention, said second repeating unit is represented by following chemical formula (Ilia) or chemical formula 20 (lllb),

^

30

wherein n is an integer 7 to 27, m is an integer 1 or more,

When two or more different monomers are polymerized, as in the present invention, two or more repeating units can be found in the resulting polymer. The two or more different repeating units can be arranged to sequences in the resulting polymer in various ways. For example, they can be distributed in the polymer chains statistically, alternating, forming segments of identical repeating units (block copolymers) and so on.

In a preferred embodiment of the present invention, the maleic anhydride alkene polymer has two repeating unit, one originating from maleic anhydride, and the second repeating unit from a linear 1 -olefin. Yet more preferred, the maleic anhydride alkene polymer of the invention has two repeating units wherein the repeating units are alternating in the polymer chains of the polymer.

The maleic anhydride polymer of the composition in the present invention has in a preferred embodiment has a number-average polymer weight ( M_n ) in the range from 10,000 to 500,000 g/mol, preferably from 15,000 to

200,000 g/mol, for example in the range from 20,000 to 150,000 g/mol or from 20,000 to 100,000 g/mol, yet more preferred in the range from 30,000 to 50,000 g/mol. Molecular weights are usually indicated on the commercial sample.

The multifunctional amine of the composition of the invention can be anyone which is known to and considered useful by a skilled person in order to work the invention. Examples of multifunctional amines are methylene diamine, ethylene diamine, hexamethylene diamine, yet more preferred, bis(hexamethylene)triamine. The acrylic polymer of the composition of the invention can be any kind of acrylic polymer which is known to and considered useful by a skilled person in order to work the invention. Preferred examples of acrylic polymers are poly(methyl methacrylate) (PMMA) and poly(dicyclopentanylacrylate).

The acrylic polymer of the composition in the present invention has in a preferred embodiment has a number-average polymer weight ( M_n ) in the range from 50,000 to 200,000 g/mol, for example from 70,000 to 170,000 g/mol, and yet more preferred, in the range from 100,000 to 150,000 g/mol. Molecular weights are usually indicated on the commercial sample.

The organic phase of the composition of the invention can be any organic phase which is known to and considered useful by a skilled person in order to work the invention. Suited organic phases can be aprotic or polar, or both, aprotic and polar. Examples of constituents to a preferred organic phase are toluene, hexane, heptane and, yet more preferred chloroform, or a combination of two or more thereof. In a preferred embodiment, the organic phase is formed by a single constituent, selected from those mentioned above.

In a further preferred embodiment of the invention, the quantum dot is at least partially coated with component b. Preferably, the quantum dot is coated with component b. in the range of 10 to 100 %, preferably 20 to 100 %, or 50 to 90 %, yet more preferred in the range from 60 to100%, for example from 70 to 99 %, or from 80 to 98 %, all the % being based on the amount of surface of the quantum dot on which component b.

superimposes the quantum dot. Yet further preferred, the quantum dot is fully coated with component b. A second aspect of the invention is a method of manufacturing a layered composite, comprising at least these steps:

(I) providing a substrate; (II) applying a composition as described in any one of the embodiments above on the substrate (I) in order to form a layer on the substrate.

A layered composite in the present context refers to an object, which comprises at least a substrate and at least one layer. The layered composite can have more than one layer, e.g. 2, 3, 4, 5, 6 ,7 ,8 ,9 or 10 layers. These layers can be all positioned on one side of the substrate. With some substrates, one or more of the layer can be on a surface of the substrate which is averted from the surface onto which the layer of the invention is formed. Moreover, the layered composite can have two or more layers formed from one or more, equal or different compositions, as mentioned above.

Providing a substrate can be performed by any means which is known to and considered potentially useful by a skilled person to work the present invention. Preferred ways of providing includes mounting on a substrate holder, placing on a rotating dish, e.g. in a spincoater.

A suitable substrate can be of any kind known to and considered potentially useful by the skilled person to work the present invention. Preferred examples of a substrate are a piece of glass and a layered structure.

Applying a composition as described above, that is a composition comprising quantum dots, maleic anhydride alkene copolymer,

multifunctional amine, acrylic polymer and organic phase, each of the constituents chosen as described above, can be performed by any means which is known to and considered potentially useful by a skilled person to work the present invention. Preferred ways of applying include spin-coating and dip-coating.

After having applied the composition to the substrate, wherein a layer is formed, this layer can be subjected to a treatment with heat in order to stabilize it, as an auxiliary measure. Any means of heat treatment can be employed which are known to and considered potentially useful by a skilled person to work the present invention. Amongst them, heat treatment in a stream of hot gas and or heating the layer in an oven are preferred. The heat treatment may affect evaporation of solvent as well as polymerization and/or cross-linking reactions of one or more constituents of the

composition. By such heat treatment, a stable layer comprising

aforementioned quantum dots is obtained on the substrate. A third aspect of the invention is a method of manufacturing a layered composite, comprising the steps of

(A) manufacturing a mixture by at least these steps:

i) providing a liquid phase comprising a quantum dot, preferably a plurality of quantum dots;

iv) adding an acrylic polymer;

(B) applying the mixture to a substrate in order to form a layer; wherein the formed layer can be a polymer film; and

(C) drying the mixture on the substrate;

wherein the layer comprises the quantum dots;

wherein each quantum dots have a shell comprising the maleic anhydride alkene copolymer.

Terms and definitions which are identical to those described before share the same meaning and may have the same, or at least similar preferred embodiments. However, there is no need that the terms described in this aspect are implemented exactly the same way, as suggested before. In line with the aforementioned, reference to the above is made for definition, preferred embodiments and range regarding quantum dots, maleic anhydride alkylene copolymer, multifunctional amine and acrylic polymer.

In step ii) a liquid phase comprising a maleic anhydride polymer is added to the liquid phase of step i). The liquid phase can comprise any kind of liquid or organic phase which is known to the skilled person and considered useful to have quantum dots distributed therein. Reference is made to the findings described in the first aspect to the present invention regarding suited solvents and preferred embodiments. A preferred organic phase for this is chloroform.

In step iii) a multifunctional amine is added to the combined liquid phases of step i) and ii) the multifunctional amine can be added in pure or diluted form. Preferably, the multifunctional amine is added pure. Further preferred, the multifunctional amine is added dropwise. Room temperature, or a temperature between 0° and 30 °C, yet more preferred 10° to 30°C or 20 to 30 °C are preferred conditions when adding the multifunctional amine.

Reference is made to the findings related to the multifunctional amine, as described in the 1^st aspect to the present invention, in particular regarding a preferred choice of multifunctional amine and further preferred

embodiments.

In step iv) an acrylic polymer is added to the combined items from step i), ii) and iii) by agitating the constituents of step i) - iv), the mixture of step (A) is obtained. Agitation can be performed individually in each of the

aforementioned steps i) through iv). In a preferred embodiment, the liquid phase is provided under agitation and agitation is maintained throughout each of the further steps ii), iii) and iv) Moreover, intervals of agitation can be implemented between each of steps i) through iv). This allows the liquid phase form step i., or the combination of the liquid phase from step a. with one or more further constituents to sit and/or homogenize prior to adding another constituent. Manufacturing of the mixture in step (A) can be operated under inert conditions, at room temperature as well as elevated temperature, and/or at standard pressure, elevated or reduced pressure, all this referred to the conditions in the mixing vessel. Preferably, step (A) is operated under inert conditions at a temperature in the range from 0 to 100 °C and ambient pressure, which is 1 bar (1013 hPa), based on the absolute scale (0 kPa = absolute vacuum). Agitation can be achieved by rotating the mixing vessel or by inserting a rotating mixer into a static mixing vessel. A preferred mode of operation includes the use of a flask as static mixing vessel and a stirrer.

Step (B) refers to the same procedure as with step (II) of the second aspect to the invention. Preferred embodiments thereto are also preferred embodiments herein.

Step (C) refers to a procedure as described as optional heat treatment in the second aspect to the invention. Preferred embodiments thereto are also preferred embodiments herein. A fourth aspect of the invention is a layered composite obtainable by a process as described in the third aspect to the invention, or by any one of the embodiments thereto. As already mentioned, a preferred layered composite comprises a substrate and at least a layer wherein the at least one layer is a polymer film.

In a preferred embodiment, the thickness of the layer is in the random of 50 to 2000 nm, for example from 100 to 1500 nm, or from 250 to 1250 nm. The thickness of the layer is most preferred in the range from 500 to 1200nm. The thickness of the layer is determined in a direction perpendicular to a plan created by the surface of the substrate which is adjacent to the layer, and the multiple layers respectively. The thickness of the layer can be determined by cutting a sample piece and analyzing the layers along the cut perpendicular through the substrate using Scanning Electron

Microscopy (SEM). Two or more layers can be part of the layered composite by further preference. A fifth aspect of the invention is a layered composite comprising,

a) an acrylic polymer; and

b) a substrate;

wherein the acrylic polymer comprises a quantum dot, preferably a plurality of quantum dots;

wherein the quantum dot is at least partially coated by a maleic anhydride alkene copolymer;

wherein the maleic anhydride alkene copolymer has at least a first repeating unit and a second repeating unit. Preferred embodiments of the components of the fifth aspect of the invention, in particular of the acrylic polymer, the substrate, the quantum dots, their coating and the maleic anhydride alkene copolymer are the same as described above, and in particular as those described with respect to the first and the fourth aspect of the invention. The acrylic polymer in a) is preferably obtained from a composition according to the first aspect of the invention or one of its embodiments, and/or by one of the methods according to the second and third aspect of the invention, and the embodiments thereto.

In a preferred embodiment of the invention, the first repeating unit and the second repeating unit of the maleic anhydride alkene copolymer differ from each other, as described above. In a further preferred embodiment the maleic anhydride alkene copolymer is cross-linked due to a reaction of the maleic anhydride functionality with amine groups of one or more

multifunctional amines. In a further preferred embodiment, the layered composite has a maleic anhydride alkene copolymer, which has a first and at least a second repeating unit, wherein the first repeating unit is obtained from polymerizing maleic anhydride, and wherein the second repeating unit of the maleic anhydride alkene copolymer is based on a linear 1 -olefin. Preferred examples and further embodiments in this regard are the same as with the maleic anhydride alkene polymer described in the first aspect of the invention. In a further preferred embodiment, the acrylic polymer of the layered composite is selected from poly (methyl methacrylate) (PMMA) and poly(dicyclopentanyl acrylate).

A sixth aspect of the invention is an optical medium comprising a layered composite as described above or as obtainable by aforementioned processes. The optical medium can be an optical sheet, for example, a color filter, a color conversion film, remote phosphor tape, or another film or filter. A seventh aspect of the invention is an optical device comprising said optical medium. In some embodiments of the present invention, the optical device can be selected from the group consisting of liquid crystal display device (LCD), Organic Light Emitting Diode (OLED), backlight unit for an optical display, Light Emitting Diode device (LED), Micro Electro

Mechanical Systems (here in after“MEMS”), electro wetting display, an electrophoretic display, a lighting device and a solar cell.

An eighth of the invention is a use of quantum dots coated with a maleic anhydride alkene copolymer for improving the quantum yield of the quantum dots. A ninth aspect of the invention is a use of maleic anhydride alkene copolymer to improve the quantum yield of quantum dots.

In a preferred embodiment of the aforementioned eighth and ninth aspect, the maleic anhydride alkene copolymer is at least partially crosslinked. Yet more preferred, the maleic anhydride alkene copolymer is crosslinked by using a multifunctional amine, preferably selected from those mentioned above when describing the first aspect to the present invention. FIGURES

Figure 1 shows a graph of experimental normalized quantum yield (nQY) over time.

Figure 2 shows a polymer coated quantum dot.

Figure 1 shows experimental data obtained from measurements of the quantum yield (QY) of the examples described below. Shown is the normalized quantum yield (nQY) (arbitrary units) is traced as a function of time (days). The nQY is calculated by dividing the y-value at time x (y_x) of each measurement through the initial y-value at time=0 (yo). x usually had values between 0 and 68, depending on the example. As consequence, the nQY represents a relative decrease in quantum yield with time. A higher nQY stands for a better performance. All examples exhibit a decrease in nQY with time. The decrease of nQY with time is much less pronounced for Example 1 compared with the other examples. Most of the other examples show a decrease of nQY within the first 10 days of 0,4 or more, whereas the nQY of Example 1 decreases of about 0.1 in the same time. Further, Example 1 shows a nQY at time >= 50 days of around 0.67, whereas Comparative Example 5 shows a nQY at time >= 50 days of around 0.5, and all other examples of <= 0,4. Accordingly, Example 1 has a much better overall performance than the comparative examples. Figure 2 shows a quantum dot 1 with ligands 2. The quantum dot 1 can comprise a core (striped area) and a shell (surrounding line). This quantum dot 1 is covered by a polymer 4. Polymer 4 is also referred to as“outer polymer shell”. Polymer molecules of polymer 4 can be connected by linker 5. 3 stands for interactions and/or bonds between polymer 4 and the quantum dot 1.

TEST METHODS

Quantum Yield

Measurements of Quantum Yield (QY), Center Wavelength (CWL, also referred to as: peak wavelength) and Full width half max (FWHM, also referred to as: peak band) are performed on a Hamamatsu Quantaurus QY Absolute PL quantum yield spectrometer C11347-11 (in the following referred to as“Hamamatsu Quantaurus”). Samples are prepared by depositing a solution on a cleaned 3 cm x 3 cm glass substrate and spincoating the solution for 30 seconds at 1000 rpm. The resulting layer is dried under argon at 120 °C for 8 minutes. The glass substrate is cut into pieces of 1 cm x 1 cm. The excitation wavelength is set to 450 nm.

Photoluminescence curves obtained from measurements on the samples are integrated in the range from 500 nm to 800 nm.

Laver thickness The samples are scratched on the backside and then cut into two pieces.

The broken edge is investigated by Scanning Electron Microscopy (SEM).

EXAMPLES

The invention is set out in more detail below with examples and drawings, the examples and drawings not implying any restriction of the invention. Furthermore, the schematic representations are not to scale.

Example 1

5mL of a quantum dot solution (50mg/mL in Chloroform), are mixed with 5mL of a solution of poly(maleic anhydride-alt-octadecene) (purchased from Sigma-Aldrich, Saint Louis, USA, product number 419117, M_n = 30,000 to 50,000 g/mol, acid number 301 -315 mg KOH/g) (175mg/mL in Chloroform) and stirred at room temperature (20°C) under argon overnight. Then, 5mL solution of crosslinker (Bis(hexamethylene)triamine) (8,5mg/mL in

Chloroform) are added dropwise under argon and stirred additionally under argon at room temperature for 1 h. Then 3 mL of poly (dicyclopentanyl acrylate) are added to the solution and the solvent (Chloroform) is removed by rotavap. The solution is deposited on a cleaned 3x3cm glass substrate and spincoated for 30sec at 1000rpm. The layer is dried under argon at 120°C for 8 min. The glass substrate is cut into 1x1 cm pieces and measured by Hamamatsu Quantaurus. Chloroform is always analytical grade.

The measurement with the samples from Example 1 are compared with a comparative sample, where a commercial dispersant (BYK-163, available from BYK-Chemie GmbH, Wesel, Germany) is used instead of a cross- linked poly(maleic anhydride-alt-octadecene).

Observations: The layer of example 1 shows much higher quantum yield, in particular after longer periods of testing, than a layer of a comparative example, where no cross-linked poly(maleic anhydride-alt-octadecene) is employed. Comparative example 1

3ml_ of quantum dot solution (50mg/mL in Chloroform) are mixed with 9ml_ BYK-163 solution (9,3mg/mL in Chloroform) and stirred under argon at room temperature overnight. Then 0,81 ml_ of poly (dicyclopentanyl acrylate), available from Hitachi Chemical co., Ltd., Japan, are added to the solution and the solvent (Chloroform) is removed by rotavap. The solution is deposited on a cleaned 3x3cm glass substrate and spincoated for 30sec at 1000rpm. The layer is dried under argon at 120°C for 8 min. The glass substrate is cut into 1x1 cm pieces and measured by Hamamatsu

Quantaurus.

Comparative example 2

2mL of quantum dot solution (50mg/mL in Chloroform) are mixed with 0,5mL of poly (dicyclopentanyl acrylate) and the solvent (Chloroform) is removed by rotavap. The solution is deposited on a cleaned 3x3cm glass substrate and spincoated for 30sec at 1000rpm. The layer is dried under Argon at 120°C for 8 min. The layer is not really uniform and looked very inhomogeneous. The glass substrate is cut into 1x1 cm pieces and measured by Hamamatsu Quantaurus.

Comparative example 3-5

5mL of quantum dot solution (50mg/mL in Chloroform) are mixed dropwise with 5mL Chloroform BYK-163 solution with the following concentration of BYK-163 in the chloroform:

and stirred under argon at room temperature overnight. Then poly(maleic anhydride-alt-octadecene) (175mg/mL in Chloroform) are added dropwise to the solutions:

In Comparative example 3 and 5 the amount of PMAO is reduced by further adding chloroform.

These solutions are then stirred under argon at room temperature over the weekend. Then a solution of crosslinker (Bis(hexamethylene)triamine) (19mg/mL in Chloroform) is added dropwise

In Comparative example 3 and 5 the amount of crosslinker is reduced by further adding chloroform. and stirred additionally under argon at room temperature overnight. Then 2,5 ml_ of poly (dicyclopentanyl acrylate, purchased from Hitachi, are added to the solution and the solvent (Chloroform) is removed by rotavap. The solution is deposited on a cleaned 3x3cm glass substrate and spincoated for 30sec at 1000rpm. The layer is dried under argon at 120°C for 8 min. The glass substrate is cut into 1x1 cm pieces and measured by Hamamatsu Quantaurus. Measurements are recorded up to 68 days. The table shows selected values after 6, 20±1 , and 62±1 days.

^*61 days

*^*19 days

*^**63days

Claims

1. A composition comprising at least:

a) a semiconductor light emitting nanoparticle, preferably a quantum dot; b) a maleic anhydride alkene copolymer;

c) a multifunctional amine;

d) an acrylic polymer; and

e) an organic phase;

2. The composition of claim 1 wherein the first repeating unit and the second repeating unit differ from each other.

3. The composition of any one of claims 1 or 2, wherein the second repeating unit is based on a linear C10 - C30 1 -olefin.

4. The composition of any one of the preceding claims, wherein the multifunctional amine is bis(hexamethylene)triamine.

5. The composition of any one of the preceding claims, wherein the acrylic polymer is selected from poly (methyl methacrylate) and poly

(dicyclopentanyl acrylate).

6. The composition of any one of the preceding claims, wherein the semiconductor light emitting nanoparticle, preferably a quantum dot, is at least partially coated with component b.

(I) providing a substrate; (II) applying a composition according to any one of claims 1 to 6 on the substrate (I) in order to form a layer on the substrate.

8. A method of manufacturing a layered composite, comprising the steps of (A) manufacturing a mixture phase by at least these steps:

i) providing a liquid phase comprising at least a semiconductor light emitting nanoparticle, preferably a quantum dot;

iv) adding an acrylic polymer;

(B) applying the mixture to a substrate in order to form a layer; and

(C) drying the mixture on the substrate;

wherein the layer comprises the nanoparticle;

wherein each nanoparticle has a shell comprising the maleic anhydride alkene copolymer.

9. The method of any one of claims 8, wherein the layer is a polymer film.

10. A layered composite obtainable by the process of any one of claims 8 to 9.

11. A layered composite comprising,

at least an acrylic polymer; and

a substrate;

wherein the acrylic polymer comprises a semiconductor light emitting nanoparticle, preferably a quantum dot;

wherein the semiconductor light emitting nanoparticle, preferably a quantum dot, is at least partially coated by a maleic anhydride alkene copolymer;

12. The layered composite of any one of claims 10 or 11 , wherein the first repeating unit and the second repeating unit of the maleic anhydride alkene copolymer differ from each other.

13. The layered composite of any one of claims 10 to 12, wherein the second repeating unit of the maleic anhydride alkene copolymer is based on a linear C10 to C30 1 -olefin.

14. The layered composite of any one of claims 10 to 13, wherein the acrylic polymer is selected from the group consisting of poly (methyl methacrylate) and poly (dicyclopentanyl acrylate).

15. An optical medium comprising a layered composite according to any one of claims 10 to 14, or obtainable by a process according to claim 8.

16. An optical device comprising the optical medium of claim 15.

17. A use of a semiconductor light emitting nanoparticle, preferably a quantum dot, coated with a maleic anhydride alkene copolymer for improving the quantum yield of the nanoparticle.

18. A use of a maleic anhydride alkene copolymer coating to improve the quantum yield of the nanoparticle.

19. The use of any one of claims 17 or 18, wherein the maleic anhydride alkene copolymer is at least partially crosslinked.