Mixed organic-inorganic perovskite formulations
A formulation for use in the preferential formation of thin films of a perovskite material AMX 3 with a certain required crystalline structure, wherein said formulation comprises two or more compounds which between them comprise one or more first organic cations A; one or more metalcations M; one or more second cations A′; one or more first anions X and one or more second anions X′.
1. A formulation for use in the formation of a light absorbing perovskite material having a general formula (I) of:
AMX 3 (I)
wherein A is one or more monovalent cations, M is one or more divalent metal cations, and X is one or more halide anions, the formulation comprising two or more compounds which between them comprise:
the one or more monovalent cations A;
the one or more divalent metal cations M;
the one or more halide anions X;
one or more further monovalent cations A′; and
one or more further halide anions X′;
wherein the one or more further monovalent cations A′ and the one or more further halide anions X′ are selected to form one or more A′X′-containing compounds which are able to be fully separated from the AMX 3 material at a temperature of less than 200° C.
2. A formulation according to claim 1 , wherein the perovskite material is black in colour.
3. A formulation according to claim 1 , wherein the perovskite material has a band gap below 3.0 eV.
4. A formulation according to claim 1 , wherein the formulation comprises an excess of the one or more further monovalent cations A′ and the one or more further halide anions X′.
5. A formulation according to claim 4 , wherein the ratio of the one or more further monovalent cations A′ and the one or more further halide anions X′ to the one or more monovalent cations A and the one or more halide anions X is from 1.6:1 to 2.1:1.
6. A formulation according to claim 1 , wherein A is one or two monovalent cations, M is a divalent metal cation, and X is one or more halide anions, and the formulation comprises two or more compounds which between them comprise:
the one or two monovalent cations A;
the divalent metal cation M;
the one or more halide anions X;
a further monovalent cation A′; and
a further halide anion X′.
7. A formulation according to claim 1 , wherein A comprises a first monovalent cation and the formulation comprises:
a first precursor compound comprising the first monovalent cation A and a halide anion X;
a second precursor compound comprising a further monovalent cation A′ and a halide anion X; and
a third precursor compound comprising a metal cation M and a further halide anion X′.
8. A formulation according to claim 1 , wherein A comprises a first monovalent cation Ai, and a second monovalent cation A 2 , and the formulation comprises:
a first precursor compound comprising the first monovalent cation A 1 and a halide anion X;
a second precursor compound comprising a further monovalent cation A′ and a halide anion X;
a third precursor compound comprising the second monovalent cation A 2 and a halide anion X; and
a fourth precursor compound comprising a metal cation M, and a further halide anion X′.
9. A formulation according to claim 1 , wherein at least one of the one or more monovalent cations A, and the one or more further monovalent cations A′, are selected from ammonium (NH 4 + ), methyl ammonium (CH 3 NH 3 + ), formamidinium (HC(NH 2 ) 2 + ), methylformamidinium (H 3 CC(NH) 2 ) 2 + ), guanidinium (C(NH) 2 ) 3 + ), tetramethylammonium ((CH 3 ) 4 N + ), dimethylammonium ((CH 3 ) 2 NH 2 + ) and trimethylammonium ((CH 3 ) 3 NH + ), Cs + Rb + , Cu + , Pd + , Pt + , Ag + , Au + , Rh + , and Ru + .
10. A formulation according to claim 1 , wherein A comprises any of:
methyl ammonium (CH 3 NH 3 + ) and formamidinium (HC(NH 2 ) 2 + );
formamidinium (HC(NH 2 ) 2 + ) and Cs + ; and
formamidinium (HC(NH 2 ) 2 + ).
11. A formulation according to claim 10 , wherein A′ comprises one or more of ammonium (NH 4 + ) and methyl ammonium (CH 3 NH 3 + ).
12. A formulation according to claim 1 , wherein M comprises one or more of Pb 2+ , Sn 2+ , and Bi 2+ .
13. A formulation according to claim 1 , wherein X comprises one or more halide anions selected from fluoride, chloride, bromide, and iodide.
14. A formulation according to claim 1 , wherein X′ comprises one or more halide anions selected from fluoride, chloride, bromide, and iodide.
15. A precursor solution for use to make a perovskite material of the general formula AMX 3 , said precursor solution comprising a suitable solvent system and two or more compounds which between them comprise one or more first cations A; one or more metal cations, M; one or more second cations A′; one or more first anions X and one or more second anions X′; and further wherein the ratio of ions is selected such that A:M:X is 1:1:3, and the amount of and choice of the one or more second cations A′ and second anions X′ is selected to form one or more A′X′-containing compounds which are able to be fully separated from the AMX 3 material at a temperature of less than 200° C.
16. A precursor solution according to claim 15 , and comprising a solvent system comprising one or more solvents selected from dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N-cyclohexyl-2-pyrrolidone (CHP), and dimethylacetamide (DMAc).