Photovoltaic device comprising a metal halide perovskite and a passivating agent

1. A semiconductor, wherein the 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.

2. The semiconductor according to claim 1 , wherein chemical bonds between the molecules of the passivating agent and the anions or cations in the metal halide perovskite are selected from the group consisting of: halogen bonds; chalcogen-metal bonds; nitrogen-metal bonds; and phosphorus-metal bonds.

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

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

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

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

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

8. The semiconductor according to claim 7 , wherein at least some of the anions or cations in the metal halide perovskite to which the molecules of the passivating agent are bonded are at grain boundaries in bulk of the crystal structure of the metal halide perovskite.

9. The semiconductor according to claim 1 , wherein the passivating agent is a compound selected from:

(a) a halogen bond donor compound;

(b) an organic compound comprising at least one thiol or sulfide group; and

(c) an organic compound comprising at least one heteroatom selected from N and P.

10. The semiconductor according to claim 9 , wherein the passivating agent is the halogen bond donor compound of formula X-EWG, wherein

X is a halogen selected from I, Br, Cl and F; and

EWG is an electron withdrawing group.

11. The semiconductor according to claim 9 , wherein the passivating agent is iodopentafluorobenzene.

12. The semiconductor according to claim 9 , wherein the passivating agent is thiophene, 3-hexylthiophene or tetrahydrothiophene.

13. The semiconductor according to claim 1 , wherein the passivating agent is:

a halogen bond donor compound, and molecules of the halogen bond donor compound are bonded to halide anions in the metal halide perovskite by halogen bonding; or

the passivating agent is an organic compound comprising at least one thiol or sulfide group, and molecules of the organic compound are bonded to metal cations in the metal halide perovskite by sulfur-metal bonds.

14. The semiconductor according to claim 9 , wherein the passivating agent is the organic compound comprising the at least one heteroatom selected from N and P, wherein the organic compound comprising the at least one heteroatom selected from N and P is selected from a substituted or unsubstituted amine, a substituted or unsubstituted imine, substituted or unsubstituted pyridine, substituted or unsubstituted pyrrolidine, substituted or unsubstituted pyrrole and a substituted or unsubstituted phosphine.

15. The semiconductor according to claim 14 , wherein the passivating agent is a compound selected from pyrrolidine, piperidine, morpholine, 2H-pyrrole, 2-pyrroline, 3-pyrroline, pyrrole and pyridine.

16. The semiconductor according to claim 15 , wherein the passivating agent is pyridine.

17. The semiconductor according to claim 1 , which the semiconductor further comprises:

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.

18. The semiconductor according to claim 17 , wherein the further passivating agent comprises non-polar organic molecules.

19. The semiconductor according to claim 18 , wherein the further passivating agent comprises a polycyclic aromatic hydrocarbon.

20. The semiconductor according to claim 18 , wherein the further passivating agent comprises any of naphthalene, anthracene, phenanthrene, pyrene, and fluoranthene.

21. The semiconductor 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+ , Sn 2+ , Yb 2+ and Eu 2+ ; and

[X] is at least one halide anion.

22. The semiconductor according to claim 1 , wherein the semiconductor comprises a continuous layer comprising crystalline domains.

23. The semiconductor according to claim 22 , wherein the crystalline domains have domain sizes of from 100 nm to 1000 nm.

24. A semiconductor device comprising the semiconductor as defined in claim 1 .

25. The semiconductor device according to claim 24 , wherein the semiconductor device is an optoelectronic device.

26. The semiconductor device according to claim 25 , wherein the optoelectronic device is a light emitting device.

27. A process for producing a semiconductor, wherein the 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

wherein the process comprises treating the metal halide perovskite with the passivating agent, wherein the passivating agent is an organic compound suitable for chemically bonding to the anions or cations in the metal halide perovskite.

28. The process according to claim 27 , wherein the treating the metal halide perovskite with the passivating agent comprises:

disposing on a surface of the metal halide perovskite at least one composition comprising the passivating agent; or

adding the passivating agent to a solution of the metal halide perovskite before formation of a metal halide perovskite solid.