Solid state heterojunction device

1. A solid-state p-n heterojunction comprising an organic p-type material in contact with an n-type material wherein said n-type material comprises mesoporous SnO 2 coated with at least two materials and wherein the outermost coating closest to the p-type material is a surface-coating of a surface coating material having a conduction band edge closer to vacuum level and/or a higher band-gap than SnO 2 .

2. A solid-state p-n heterojunction as claimed in claim 1 wherein the heterojunction is sensitised to light by additionally comprising at least one sensitizer.

3. A solid-state p-n heterojunction as claimed in claim 2 wherein said sensitizer is an organic dye, a metal-complexed dye, a quantum-dot photosensitizer or a mixture thereof.

4. A solid state p-n heterojunction as claimed in claim 2 wherein said sensitizer is at least one selected from the group consisting of a ruthenium complex dye, a metal-phthalocyanine complex dye, a metal-porphryin complex dye, a squarine dye, a thiophene based dye, a fluorene based dye, a polymer dye, a quantum dot sensitizer, and mixtures thereof.

5. A solid state p-n heterojunction as claimed in claim 1 wherein said p-type material is an organic hole-transporter.

6. A solid state p-n heterojunction as claimed in claim 5 wherein said organic hole-transporter is at least one optionally oligomerized, polymerized and/or cross-linked compound of formula (tI), (tII), (tIII), (tIV) and/or (tV) below,

wherein:

N, if present, is a nitrogen atom;

n, if applicable, is in the range of 1-20;

A is a mono-, or polycyclic system comprising at least one pair of a conjugated double bond (—C═C—C═C—), the cyclic system optionally comprising one or more heteroatoms, and optionally being substituted, whereby in a compound comprising more than one structures A, each A may be selected independently from another A present in the same structure (tI-tV);

each of A 1 -A 4 , if present, is an A independently selected from the A as defined above;

v in (tII) recites the number of cyclic systems A linked by a single bond to the nitrogen atom and is 1, 2 or 3;

(R)w is an optional residue selected from a hydrocarbon residue comprising from 1 to 30 carbon atoms, optionally substituted and optionally comprising 1 or more heteroatoms, with w being 0, 1 or 2 provided that v+w does not exceed 3, and, if w=2, the respective Rw 1 or Rw 2 being the same or different;

R a represents a residue capable, optionally together with other R a present on the same structure (tI-tV), of decreasing the melting point of an organic compound and is selected from a linear, branched or cyclic alkyl, or a residue comprising one or more oxygen atoms, wherein the alkyl and/or the oxygen comprising residue is optionally halogenated;

x is the number of independently selected residues R a linked to an A and is selected from 0 to a maximum possible number of substituents of a respective A, independently from the number x of other residues R a linked to another A optionally present;

with the proviso that per structure (tI-tV) there is at least one R a being an oxygen containing residue as defined above; and, if several R a are present on the same structure (tI-tV), they are the same or different; and wherein two or more R a may form an oxygen-containing ring;

R p represents an optional residue enabling a polymerisation reaction with compounds comprising structure (tI-tV) used as monomers, and/or a cross-linking reaction between different compounds comprising structures (tI-tV);

z is the number of residues R p linked to an A, and is 0, 1, and/or 2, independently from the number z of other residues R p linked to another A optionally present;

R p may be linked to an N-atom, to an A, and/or to a substituent R p of other structures according (tI-tV), resulting in repeated, cross-linked and/or polymerised moieties of (tI-tV);

(R a/p ) x/z and (R 1-4 a/P ) x/z , if present, represent independently selected residues R a and R p as defined above.

7. A solid state p-n heterojunction as claimed in claim 5 wherein said organic hole-transporter is a compound of formula tXVII below:

wherein R is C1-C6 alkyl or C1-C6 O-alkyl.

8. A solid state p-n heterojunction as claimed in claim 1 wherein said n-type material is porous.

9. A solid-state p-n heterojunction as claimed in claim 1 wherein said n-type material is substantially planar and said heterojunction forms a substantially planar junction.

10. A solid state p-n heterojunction as claimed in claim 1 wherein said surface coating material has a band gap of 4.6 to 8 eV, and/or a conduction band edge of −4.8 eV or less negative relative to vacuum level.

11. A solid state p-n heterojunction as claimed in claim 1 wherein said surface coating material comprises at least one single metal oxide, compound metal oxide, doped metal oxide, carbonate, sulphide, selenide, teluride, nitrides and/or multicompound semiconductor.

12. A solid state p-n heterojunction as claimed in claim 1 wherein said SnO 2 is additionally coated with at least one intermediate coating between the “core” SnO 2 material and the surface coating of the surface coating material, wherein the intermediate coating comprises a material with a higher band-gap and/or a conduction band closer to the vacuum level than SnO 2 and/or a material with a band gap similar to that of SnO 2 .

13. A solid state p-n heterojunction as claimed in claim 1 wherein said SnO 2 is additionally coated with at least one intermediate coating between the “core” SnO 2 material and the surface coating of the surface coating material, wherein the intermediate coating comprises a material with a lower band-gap and/or a conduction band further from the vacuum level than SnO 2 and/or a material with a band gap similar to that of SnO 2 .

14. A solid state p-n heterojunction as claimed in claim 1 having at least one intermediate coating of a material with a band gap similar to that of SnO 2 .

15. A solid state p-n heterojunction as claimed in claim 1 having at least one intermediate coating of a material selected from the group consisting of a single metal oxide, compound metal oxide, doped metal oxide, carbonate, sulphide, selenide, teluride, nitrides, multicompound semiconductor, and combinations thereof.

16. A solid state p-n heterojunction as claimed in claim 1 wherein said SnO 2 is essentially pure SnO 2 , or is doped throughout with at least one dopant material of greater valency than Sn (>4, n-type doping), and/or is doped with at least one dopant material of lower valency than Sn (<4, p-type doping).

17. A solid state p-n heterojunction as claimed in claim 16 wherein said SnO 2 is doped with at least one element selected from the group consisting of F, Sb, N, Ge, Si, C, and combinations thereof.

18. An optoelectronic device comprising at least one solid state p-n heterojunction as claimed in claim 1 .

19. An optoelectronic device as claimed in claim 18 wherein said device is a solar cell or photo-detector.

20. A method of using mesoporous SnO 2 having at least two surface coatings in which the outermost coating is a material having a conduction band closer to vacuum level and/or a higher band gap than SnO 2 as an n-type material in a solid state p-n heterojunction, wherein said heterojunction is an organic solid state p-n heterojunction as claimed in claim 1 .

21. A method for the manufacture of a solid-state p-n heterojunction as claimed in claim 1 , said method comprising:

i) forming a layer of an n-type semiconductor material comprising mesoporous SnO 2 having least two surface coatings in which the outermost coating is a material having a conduction band closer to vacuum level and/or a higher band gap than SnO 2 ,

ii) optionally coating said n-type material with a light sensitizing material, and

iii) contacting said n-type material with a solid state p-type semiconductor material.

22. A method as claimed in claim 21 wherein said layer of an n-type semiconductor material comprising mesoporous SnO 2 having least two surface coatings in which the outermost coating is a material having a conduction band closer to vacuum level and/or a higher band gap than SnO 2 is formed by sintering of a layer of fine SnO 2 particles followed by surface coating of the sintered layer with said surface coating material.

23. A method as claimed in claim 21 wherein said porous layer of an n-type semiconductor material comprising mesoporous SnO 2 having least two surface coatings in which the outermost coating is a material having a conduction band closer to vacuum level and/or a higher band gap than SnO 2 is formed by surface coating fine SnO 2 particles with said surface coating materials, followed by sintering of a layer of the coated SnO 2 particles.

24. A method as claimed in claim 21 wherein said layer is a compact n-type semiconductor material comprising SnO 2 coated with said surface coating materials.

25. A solid-state p-n heterojunction formed or formable by the method of claim 21 .

26. An optoelectronic device comprising at least one solid-state p-n heterojunction formed or formable by the method of claim 21 .

27. The solid-state p-n heterojunction as claimed in claim 2 wherein the sensitizer is at the junction of the p-type and n-type materials.

28. The solid-state p-n heterojunction as claimed in claim 5 wherein the organic hole transporter is substantially amorphous.

29. The solid-state p-n heterojunction as claimed in claim 8 wherein said n-type material has a surface area of 1-400 m 2 g −1 .

30. The solid-state p-n heterojunction as claimed in claim 8 wherein said n-type material is in the form of an electrically continuous layer.

31. The solid-state p-n heterojunction as claimed in claim 30 wherein said electrically continuous layer has a thickness 0.5 to 20 μm.

32. The solid-state p-n heterojunction as claimed in claim 11 wherein said surface coating material is MgO.

33. The solid-state p-n heterojunction as claimed in claim 14 wherein the band gap of the intermediate coating of the material is 3±1.5 eV.

34. The optoelectronic device as claimed in claim 26 wherein the optoelectronic device is photovoltaic cell or light sensing device.