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 metal cations M; one or more second cations A′; one or more first anions X and one or more second anions X′.
1. A method of producing a photovoltaic device comprising a photoactive material, which photoactive material comprises a perovskite of general formula (I):
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 method comprising:
forming a precursor solution by dissolving in a solvent system 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.;
disposing/depositing a layer of the precursor solution; and
removing at a temperature of less than 200° C. the solvent system and the more volatile A′X′ compounds to produce a solid layer of the perovskite material.
2. A method according to claim 1 , wherein the layer of the precursor solution is disposed on a first region, the first region comprising any of:
an n-type region comprising at least one n-type layer; and
a p-type region comprising at least one p-type layer.
3. A method according to claim 2 , and further comprising:
disposing a second region above the solid layer of the perovskite material.
4. A method according to claim 3 , wherein the first region comprises one of an n-type region comprising at least one n-type layer and a p-type region comprising at least one p-type layer, and the second region comprises the other of the n-type region comprising at least one n-type layer and the p-type region comprising at least one p-type layer.
5. A method according to claim 3 , wherein the first region comprises an n-type region comprising at least one n-type layer, and the second region comprises an electrode and/or metal layer.
6. A method according to claim 5 , wherein the electrode and/or metal layer of the second region is in direct contact with the solid layer of the perovskite material.
7. A method according to claim 1 , wherein the step of removing the solvent system comprises heating the layer of the precursor solution to a temperature of between 60° C. and 200° C.
8. A method according to claim 1 , wherein the solvent system has a boiling point below 220° C.
9. A method according to claim 1 , wherein the solvent system has a boiling point below 190° C.
10. A method according to claim 1 , wherein the precursor solution is subjected to a curing process for the formation of the perovskite material.
11. A method according to claim 1 , further comprising the full or substantially full removal of the reaction product formed between one or more further cations A′ and one or more second anions X′, under temperature and pressure conditions which maintain the required crystalline structure of the perovskite material.