Cu2ZnSnS4 Nanoparticles

• US 20140273337A1
• Filed: 03/14/2014
• Published: 09/18/2014
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: Nanoco Technologies Limited (Nanoco Group Plc)
• Original Assignee: Nanoco Technologies Limited (Nanoco Group Plc)
• Inventors: Masala, Ombretta, Harris, James, Pickett, Nigel, Gresty, Nathalie
• Granted Patent: US 9,206,054 B2
• Time in Patent Office: Days
• US Class Current: 438/95
• CPC Class Codes: C01G 19/006 Compounds containing, besides tin, two or more other elements, with the exception of oxygen or hydrogen
• CPC Class Codes: C01P 2002/72 by d-values or two theta-values, e.g. as X-ray diagram
• CPC Class Codes: C01P 2002/84 by UV- or VIS- data
• CPC Class Codes: C01P 2002/88 by thermal analysis data, e.g. TGA, DTA, DSC
• CPC Class Codes: H01L 31/0326 comprising AIBIICIVDVI kesterite compounds, e.g. Cu2ZnSnSe4, Cu2ZnSnS4
• CPC Class Codes: H01L 31/035218 the quantum structure being quantum dots
• CPC Class Codes: H01L 31/1828 the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe
• CPC Class Codes: Y02E 10/543 Solar cells from Group II-VI materials

Abstract

Materials and methods for preparing Cu₂ZnSnS₄ (CZTS) layers for use in thin film photovoltaic (PV) cells are disclosed herein. The CZTS materials are nanoparticles prepared by a colloidal synthesis in the presence of a labile organothiol. The organothiol serves as both a sulphur source and as a capping ligand for the nanoparticles.

Claims

1. A process for making Cu₂ZnSnS₄ nanoparticles, comprising reacting a copper precursor, a zinc precursor and a tin precursor in the presence of an organothiol ligand.

2. A process as recited in claim 1, wherein the copper precursor is an acetate, chloride, bromide, iodide or acetylacetonate.

3. A process as recited in claim 1, wherein the copper precursor is copper (I) acetate.

4. A process as recited in claim 1, wherein the zinc precursor is an acetate, chloride, bromide, iodide or acetylacetonate.

5. A process as recited in claim 1, wherein the zinc precursor is zinc (II) acetate.

6. A process as recited in claim 1, wherein the tin precursor is a tin (IV) chloride solution, fuming tin (IV) chloride, tine(IV) acetate, tin(IV) bis(acetylacetonate) dichloride, triphenyl(triphenylmethyl) tin, or tin (IV) chloride pentahydrate.

7. A process as recited in claim 1 where the tin precursor is tin (IV) chloride as a solution in dichloromethane.

8. A process as recited in claim 1, wherein the organothiol ligand is an alkanethiol, alkenethiol or aromatic thiol.

9. A process as recited in claim 1, wherein the organothiol ligand has a boiling point in the range 190-300°

C.

10. A process as recited in claim 1, wherein the organothiol ligand is 1-dodecanethiol.

11. A process as recited in claim 1, wherein the process comprises:

a. providing the copper precursor, the zinc precursor, the tin precursor and the organothiol ligand in a first solvent at a first temperature to form a mixture;

b. heating the mixture to a second temperature to distil the first solvent; and

c. heating the mixture to a third temperature for a time interval to form the Cu₂ZnSnS₄ nanoparticles;

12. A process as recited in claim 11, wherein the first solvent is dichloromethane.

13. A process as recited in claim 11, wherein the third temperature is greater than 180°

C.

14. A process as recited in claim 11, wherein the third temperature is 240°

C.

15. A process as recited in claim 11, wherein the time interval is 60 minutes.

16. A process for making a Cu₂ZnSnS₄ absorber layer comprising:

a. depositing an ink on a substrate to form a film, wherein the ink comprises Cu₂ZnSnS₄ nanoparticles comprising an organothiol ligand; and

b. annealing the film at a first temperature not greater than 350°

C., under an inert atmosphere.

17. The process of claim 16, further comprising:

a. annealing at a second temperature, for a second time interval, under an inert atmosphere; and

b. optionally annealing at a third temperature, for a third time interval, under a sulphur-rich or selenium-rich atmosphere.

18. A nanoparticle comprising a semiconductor material comprising Cu, Zn, Sn, S and a labile organothiol ligand bound to the surface of the semiconductor material.

19. A nanoparticle according to claim 18, having the formula Cu₂ZnSnS₄.

20. A nanoparticle according to claim 18, wherein at least 50% of the organothiol ligand becomes unbound from the surface when the nanoparticle is heated to 350°

C.

21. A nanoparticle according to claim 18, wherein the labile organothiol ligand is dodecanethiol.