Fabrication process for A/M/X materials

A process for producing a crystalline A/M/X material, which crystalline A/M/X material comprises a compound of formula:

• [A]a[M]b[X]c
• wherein:
• [A] comprises one or more A cations, wherein each A cation is selected from (H2N—C(H)═NH2)+, an alkali metal cation, C1-10 alkylammonium, C2-10 alkenylammonium, C1-10 alkyliminium, C3-10 cycloalkylammonium and C3-10 cycloalkyliminium optionally substituted with one or more substituents selected from amine, C1-6 alkylamine, imine, C1-6 alkylimine, C1-6 alkyl, C2-6 alkenyl, C3-6 cycloalkyl and C6-12 aryl;
• [M] comprises one or more M cations which are metal or metalloid cations, wherein each M cation is selected from Pd4+, W4+, Re4+, Os4+, Ir4+, Pt4+, Sn4+, Pb4+, Ge4+, Te4+, Ca2+, Sr2+, Cd2+, Cu2+, Ni2+, Mn2+, Fe2+, Co2+, Pd2+, Ge2+, Sn2+, Pb2+, Yb2+, Eu2+, Li+, Na+, K+, Rb+, Cs+, Cu+, Ag+, Au+, Hg+, Bi3+, Sb3+, Cr3+, Fe3+, Co3+, Ga3+, As3+, Ru3+, Rh3+, In3+, Ir3+ and Au3+;
• [X] comprises one or more X anions, wherein each X anion is selected from F−, Cl−, Br− and I−;
• a is a number from 1 to 6;
• b is a number from 1 to 6;
• and
• c is a number from 1 to 18,
• the process comprising:
• a) contacting an aqueous solution comprising an A precursor and an aqueous solvent with an organic solution comprising an M precursor and an organic solvent, wherein the organic solution comprises a hydrohalic acid;
• and
• b) allowing a precipitate to form when the said aqueous and organic solutions are contacted,
• wherein the process further comprises producing an optoelectronic device comprising the crystalline A/M/X material, and wherein the optoelectronic device is a light-emitting device.