Electroluminescent device

1. A method for the preparation of a thin layer of semiconducting perovskite nanoparticles embedded in a matrix or blend of a material that has a wider band gap than the semiconducting perovskite nanoparticles, the method comprising blending a solution comprising semiconducting perovskite material or a precursor therefor and a material that has a wider band gap than the semiconducting perovskite material or a precursor therefor followed by removal of the solvent from the mixture thus formed, to give said semiconducting perovskite nanoparticles embedded in a matrix or blend of the material that has a wider band gap than the semiconducting perovskite nanoparticles;

wherein the semiconducting perovskite comprises perovskite with an AMX 3 structure, where A is a monovalent cation, M is a divalent cation and X is a halide anion; and;

wherein the ratio by weight of semiconducting perovskite nanoparticles:the material that has a wider band gap than the semiconducting perovskite nanoparticles in which the semiconducting perovskite nanoparticles are embedded is from 0.01:1 to 2:1.

2. The method according to claim 1 , wherein the material that has a wider band gap than the semiconducting perovskite nanoparticles has a band gap of greater than 1.5 eV.

3. The method according to claim 1 , wherein the material that has a wider band gap than the semiconducting perovskite nanoparticles is selected from the group consisting of an insulating material and a semiconducting material.

4. The method according to claim 3 , wherein the insulating material is selected from an insulating polymer, an insulating organic molecule and an insulating inorganic material; including wherein the insulating polymer or insulating organic molecule is a polar polymer or a polar organic molecule;

wherein the insulating material is a polyimide, including a polyamic acid of benzophenone tetracarboxylic dianhydride 4,4-oxydianiline m-phenylenediamine polymer (PIP) having the following formula:

polystyrene; poly (9-vinylcarbazole), of the form:

the organic compound 4,4-bis(N-carbazolyl)-1,1-biphenyl, of the form:

or alumina.

5. The method according to claim 1 , wherein the thickness of the thin layer of semiconducting perovskite nanoparticles embedded in the matrix or blend of the material that has a wider band gap than the semiconducting perovskite nanoparticles is ≤500 nm.

6. The method according to claim 1 wherein:

the divalent cation M is:

a divalent metal cation, including tin (Sn 2+ ) or lead (Pb 2+ ); and/or

the monovalent cation A is:

a primary, secondary or tertiary ammonium cation [HNR 1 R 2 R 3 ] + , wherein each of R 1 , R 2 and R 3 may be the same or different and is selected from hydrogen, an unsubstituted or substituted C 1 -C 20 alkyl group and an unsubstituted or substituted C 5 -C 18 aryl group; and/or

of the form [R 1 R 2 N—CH═NR 3 R 4 ] + :

wherein each of R 1 , R 2 , R 3 and R 4 may be the same or different and is selected from hydrogen, an unsubstituted or substituted C 1 -C 20 alkyl group and an unsubstituted or substituted C 5 -C 18 aryl group; and/or

of the form (R 1 R 2 N)(R 3 R 4 N)C═NR 3 R 6 :

wherein each of R 1 R 2 , R 3 , R 4 , R 5 and R 6 may be the same or different and is selected from hydrogen, an unsubstituted or substituted C 1 -C 20 alkyl group and an unsubstituted or substituted C 5 -C 18 aryl group; and/or

an alkali metal cation, including caesium (Cs + ) or rubidium (Rb + ); and/or

X is:

a halide anion selected from chloride, bromide, iodide, and fluoride and, in the AMX 3 structure each halide may be the same or different.

7. The method according to claim 1 ,

wherein the perovskite material has an A 1-j B i MX 3 structure, wherein:

A and B are each a monovalent cation as claimed in claim 6 , where A and B are different;

M is a divalent metal cation as claimed in claim 6 ;

X is a halide anion as claimed in claim 6 ; and

i is between 0 and 1; or

wherein the perovskite material has an AMX 3-k Y k structure, wherein:

A is a monovalent cation as claimed in claim 6 ;

M is a divalent metal cation as claimed in claim 6 ;

X and Y are each a halide anion as claimed in claim 6 , where X and Y are different; and

k is between 0 and 3; or

wherein the perovskite material has an AM 1-j N j X 3 structure, wherein:

A is a monovalent cation as claimed in claim 6 ;

M and N are each a divalent metal cation as claimed in claim 6 ;

X is a halide anion as claimed in claim 6 ; and

j is between 0 and 1; or

wherein the perovskite material has an A 1-i B i M 1-j N j X 3-k Y k structure, wherein:

A and B are each a monovalent cation as claimed in claim 6 , where A and B are different;

M and N are each a divalent metal cation as claimed in claim 6 ;

X and Y are each a halide anion as claimed in claim 6 , where X and Y are different; and

where i is between 0 and 1, j is between 0 and 1, and k is between 0 and 3.

8. A thin layer of semiconducting perovskite nanoparticles embedded in a matrix or blend of a material that has a wider band gap than the semiconducting perovskite nanoparticles prepared according to the method as recited in claim 1 .

9. A solid state device including a thin layer of semiconducting perovskite nanoparticles embedded in a matrix or blend of a material that has a wider band gap than the semiconducting perovskite nanoparticles made according to the method of claim 1 .

10. The solid state device according to claim 9 , wherein the solid state device is a light emitting diode or a solar cell.