Photovoltaic device comprising a metal halide perovskite and a passivating agent

1. A photovoltaic device comprising a semiconductor, which semiconductor comprises:

(a) a metal halide perovskite; and

(b) a passivating agent which is an organic compound;

wherein:

molecules of the passivating agent are chemically bonded to anions or cations in the metal halide perovskite; and

the passivating agent is an organic compound having a molecular weight of less than 1000 g mol −1 .

2. A photovoltaic device according to claim 1 , wherein the chemical bonds between molecules of the passivating agent and anions or cations in the metal halide perovskite are selected from halogen bonds and chalcogen-metal bonds.

3. A photovoltaic device according to claim 1 , wherein cations or anions in the metal halide perovskite to which molecules of the passivating agent are bonded are under-coordinated.

4. A photovoltaic device according to claim 1 , wherein at least some of the anions or cations in the metal halide perovskite to which molecules of the passivating agent are bonded are at the surface of the metal halide perovskite.

5. A photovoltaic device according to claim 1 , wherein molecules of the passivating agent form a self-assembled layer on a surface of the metal halide perovskite.

6. A photovoltaic device according to claim 1 , wherein at least some of the anions or cations in the metal halide perovskite to which molecules of the passivating agent are bonded are at defect sites in bulk of the crystal structure of the metal halide perovskite.

7. A photovoltaic device according to claim 1 , wherein molecules of the passivating agent are bonded to under-coordinated cations or under-coordinated anions in the bulk of the crystal structure of the metal halide perovskite.

8. A photovoltaic device according to claim 6 , wherein at least some of the anions or cations in the metal halide perovskite to which molecules of the passivating agent are bonded are at grain boundaries in bulk of the crystal structure of the metal halide perovskite.

9. A photovoltaic device according to claim 1 , wherein the passivating agent is iodopentafluorobenzene.

10. A photovoltaic device according to claim 1 , and further comprising:

a further passivating agent which is a further organic compound;

wherein molecules of the further passivating agent are disposed at grain boundaries within the metal halide perovskite and are not chemically bonded to anions or cations in the metal halide perovskite.

11. A photovoltaic device according to claim 10 , wherein the molecules of the further passivating agent block interaction between anions and cations in the metal halide perovskite at the grain boundaries.

12. A photovoltaic device according to claim 1 wherein the metal halide perovskite is a perovskite of the formula (I):

[A][B][X] 3   (I)

wherein:

[A] is at least one organic cation;

[B] is at least one metal cation, wherein [B] comprises at least one of Ca 2+ , Sr 2+ , Cd 2+ , Cu 2+ , Ni 2+ , Mn 2+ , Fe 2+ , Co 2+ , Pd 2+ , Ge 2+ , Sn 2+ , Pb 2+ , Yb 2+ and Eu 2+ ; and

[X] is at least one halide anion.

13. A photovoltaic device according to claim 1 , wherein the photovoltaic device comprises a layer of said semiconductor.

14. A photovoltaic device according to claim 13 , wherein the layer of the semiconductor is without open porosity.