Process of forming a photoactive layer of a perovskite photoactive device

1. A process of forming a thin film photoactive layer of a perovskite photoactive device comprising:

applying at least one coating to a substrate, the coating comprising at least one perovskite precursor solution and a crystallisation retardant for perovskite crystallisation comprising at least one polymer additive; and

crystallizing a perovskite photoactive layer on the substrate, the perovskite photoactive layer comprising a continuous and substantially uniform thin film perovskite layer,

wherein the polymer additive comprises from 0.01 to 5 wt % of reaction constituent; and

wherein the at least one perovskite precursor solution comprises at least one reaction constituent for forming at least one perovskite compound having the formula AMX 3 dissolved in a coating solvent selected from at least one polar aprotic solvent, the polymer additive being soluble in said coating solvent, and in which A comprises an ammonium group or other nitrogen containing organic cation, M is selected from Pb, Sn, Ge, Ca, Sr, Cd, Cu, Ni, Mn, Co, Zn, Fe, Mg, Ba, Si, Ti, Bi, or In, and X is selected from at least one of F, Cl, Br or I,

and wherein the polymer additive retards the crystallisation rate of the perovskite precursor solution during perovskite crystallisation.

2. A process according to claim 1 , wherein the coating solvent is at least one of Dimethylformamide (DMF), Dimethyl sulfoxide (DMSO), γ-butyrolactone, acetone, acetyl acetone, ethyl acetoacetate N-Methyl-2-pyrrolidone (NMP), Dimethylacetamide (DMAC), Tetrahydrofuran (THF) or combinations thereof.

3. A process according to claim 1 , wherein the polymer is selected from the group consisting of poly vinyl alcohol, poly vinyl acetate (PVAc), Acrylonitrile butadiene styrene (ABS), poly amides, poly acrylics, poly imide, poly acrylonitrile, poly butyl methacrylate, poly butadiene, poly carboxy methyl cellulose, poly ethers, poly ethylene acrylates, poly glycols, poly isocyanates, poly methacrylates, poly vinyl butyral, poly vinyl fluoride, poly vinyl methyl ethers, poly amines, polyethylene oxide, polyethylene glycol, Poly(2-ethyl-2-oxazoline) and combinations thereof.

4. A process according to claim 1 , wherein the applied coating comprises a mixture of the perovskite precursor solution and the polymer additive.

5. A process according to claim 1 , wherein the perovskite precursor solution comprises a mixture of at least one MX 2 , at least one of AX and at least one polymer additive dissolved in the coating solvent, in which A comprises an ammonium group or other nitrogen containing organic cation, M is selected from Pb, Sn, Ge, Ca, Sr, Cd, Cu, Ni, Mn, Co, Zn, Fe, Mg, Ba, Si, Ti, Bi, or In, and X is selected from at least one of F, Cl, Br or I.

6. A process according to claim 5 , wherein AX is selected from the group consisting of CH 3 NH 3 X and HC(NH 2 ) 2 X, and wherein X is selected from at least one of F, Cl, Br or I.

7. A process according to claim 5 , wherein M comprises Pb.

8. A process according to claim 1 , wherein the step of applying at least one coating comprises:

coating at least one layer of a first perovskite precursor solution comprising at least one MX 2 and polymer additive dissolved in the coating solvent, thereby forming a perovskite precursor coating;

wherein M is selected from at least one of Pb, Sn, Ge, Ca, Sr, Cd, Cu, Ni, Mn, Co, Zn, Fe, Mg, Ba, Si, Ti, Bi, or In; and X is selected from at least one of F, Cl, Br or I.

9. A process according to claim 8 , further comprising:

coating at least one layer of a second perovskite precursor solution comprising at least one of AX dissolved in a further coating solvent onto the perovskite precursor coating,

wherein X is selected from at least one of F, Cl, Br or I; and A comprises an ammonium group or other nitrogen containing organic cation.

10. A process according to claim 9 , wherein the step of applying at least one coating comprises:

applying a layer of the first perovskite precursor solution onto the substrate; and

coating at least one layer of the second perovskite precursor solution onto the first perovskite precursor solution layer.

11. A process according to claim 9 , wherein the coating of the second perovskite precursor solution is applied by dipping the first perovskite precursor solution coated substrate into a solution of the second perovskite precursor solution.

12. A process according to claim 9 , wherein MX 2 and AX are soluble in the coating solvent, AX is soluble in the further coating solvent, and MX 2 has a low to zero solubility in the further coating solvent, and wherein the further coating solvent is at least one of including isopropanol, n-butanol, isobutanol, ethanol, methanol, acetic acid, ethylene glycol, propylene glycol, glycerol, allyl alcohol, propagyl alcohol, inositol or combinations thereof.

13. A process according to claim 1 , wherein the step of applying at least one coating comprises:

coating at least one layer of a first perovskite precursor solution comprising at least one MX 2 and polymer additive dissolved in the coating solvent; and

coating at least one layer of a second perovskite precursor solution at least one of AX dissolved in a further coating solvent,

wherein M is selected from at least one of Pb, Sn, Ge, Ca, Sr, Cd, Cu, Ni, Mn, Co, Zn, Fe, Mg, Ba, Si, Ti, Bi, or In; X is selected from at least one of F, Cl, Br or I; and A comprises an ammonium group or other nitrogen containing organic cation.

14. A process according to claim 1 , wherein the perovskite compound comprises an organo-metal halide perovskite, and wherein the perovskite compound comprises at least one of CH 3 NH 3 MX 3 or HC(NH 2 ) 2 MX 3 , in which, M is selected from Pb, Sn, Ge, Ti, Bi, or In; and X is selected from at least one of F, Cl, Br or I.

15. A process according to claim 14 , wherein the perovskite compound comprises an organo-lead halide perovskite.

16. A process according to claim 15 , wherein the organo-lead halide perovskite is at least one of CH 3 NH 3 PbX 3 or HC(NH 2 ) 2 PbX 3 , in which X is selected from at least one of F, Cl, Br or I.

17. A process according to claim 1 , wherein the polymer additive comprises from 0.05 to 5 wt % of reaction constituent for forming at least one perovskite compound.

18. A process according to claim 1 , wherein the perovskite precursor solution comprises from 5 to 75 wt % reaction constituent for forming at least one perovskite compound.

19. A process according to claim 1 , wherein the substrate includes one or more layers or coatings selected from at least one of:

at least one coating of a transparent conductive oxide (TCO);

at least one hole transporting layer comprising an organic or inorganic semiconductor; or

at least one electron transporting layer comprising an organic or inorganic conductor.

20. A process according to claim 1 , wherein the applied coating is coated on the substrate to produce a dry layer thickness from 100 nm to 600 nm.

21. A process according to claim 1 , further including the step of: removing the polymer additive from the applied coating.

22. A process according to claim 1 , wherein the substrate is a flexible substrate.

23. A process according to claim 1 , wherein the formed perovskite photoactive layer is located between at least one hole transporting layer comprising an organic or inorganic semiconductor, and at least one electron transporting layer, comprising an organic or inorganic conductor, the perovskite layer consisting essentially of a crystalline perovskite.