Process for large-scale production of cdte/cds thin film solar cells

• US 20040248340A1
• Filed: 04/05/2004
• Published: 12/09/2004
• Est. Priority Date: 10/05/2001
• Status: Active Grant

• Current Assignee: Arendi S.A.R.L. (Arendi Holding LTD.)
• Original Assignee: Solar Systems & Equipments S.r.l
• Inventors: Romeo, Nicola, Bosio, Alessio, Romeo, Alessandro
• Granted Patent: US 7,211,462 B2
• Time in Patent Office: Days
• US Class Current: 438/102
• CPC Class Codes: C23C 14/0629 of zinc, cadmium or mercury
• CPC Class Codes: C23C 14/086 of zinc, germanium, cadmium, indium, tin, thallium or bismuth
• CPC Class Codes: C23C 14/5806 Thermal treatment
• CPC Class Codes: H01L 31/022425 for solar cells
• CPC Class Codes: H01L 31/073 comprising only AIIBVI compound semiconductors, e.g. CdS/CdTe solar cells
• CPC Class Codes: H01L 31/1828 the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe
• CPC Class Codes: H01L 31/1884 Manufacture of transparent electrodes, e.g. TCO, ITO
• CPC Class Codes: Y02E 10/543 Solar cells from Group II-VI materials
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

A process for large-scale production of CdTe/CdS thin film solar cells, films of the cells being deposited, in sequences on a transparent substrate, the sequence comprising the steps of: depositing a film of a transparent conductive oxide (TCO) on the substrate; depositing a film of CdS on the TCO film; depositing a film of CdTe on the CdS film; treating the CdTe film with CdCl₂; depositing a back-contact film on the treated CdTe film. Treatment of the CdTe film with CdCl₂ comprises the steps of: forming a layer of CdCl₂ on the CdTe film by evaporation, while maintaining the substrate at room temperature; annealing the CdCl₂ layer in a vacuum chamber at a temperature generally within a range of 380° C. and 420° C. and a pressure generally within a range of 300 mbar and 1000 mbar in an inert gas atmosphere; removing the inert gas from the chamber so as to produce a vacuum condition, while the substrate is kept at a temperature generally within a range of 350° C. and 420° C. whereby any residual CdCl₂ is evaporated from the CdTe film surface.

Claims

1. A process for large-scale production of CdTe/CdS thin film solar cells, films of the cells being deposited, in sequence, on a transparent substrate, the sequence comprising the steps of:

depositing a film of a transparent conductive oxide (TCO) on the substrate;

depositing a film of CdS on the TCO film;

depositing a film of CdTe on the CdS film;

treating the CdTe film with CdCl₂; and

depositing a back-contact film on the treated CdTe film;

wherein the treatment of the CdTe film with CdCl₂ comprises the steps of

forming a layer of CdCl₂ on the CdTe film by evaporation, while maintaining the substrate at room temperature;

annealing the CdCl₂ layer in a vacuum chamber at a temperature generally within a range of 380°

C. and 420°

C. and a pressure generally within a range of 300 mbar and 1000 mbar in an inert gas atmosphere; and

removing the inert gas from the chamber so as to produce a vacuum condition, while the substrate is kept at a temperature generally within a range of 350°

C. and 420°

C. whereby any residual CdCl₂ is evaporated from the CdTe film surface.

2. The process set forth in claim 1, wherein the CdCl₂ layer is between about 100 nm and about 200 nm thick.

3. The process set forth in claim 1, wherein annealing of the CdCl₂ layer is carried out for about 15-20 minutes.

4. The process set forth in claim 1, wherein the inert gas is Ar.

5. The process set forth in claim 1, wherein the back-contact film is formed of a Sb₂Te₃ layer covered by a layer of Mo.

6. The process set forth in claim 5, wherein the Sb₂Te₃ layer is formed by sputtering at a temperature between about 250°

C. and about 300°

C.

7. The process set forth in claim 1, wherein the back-contact film is formed of a As₂Te₃ layer covered with a layer of Mo.

8. The process set forth in claim 7, wherein the As₂Te₃ layer is formed by sputtering at a temperature between about 200°

C. and about 250°

C.

9. The process set forth in claim 1, wherein the transparent conductive oxide is In₂O₃ doped with fluorine.

10. The process set forth in claim 9, wherein the TCO layer is formed by sputtering in an inert gas atmosphere comprising a mixture of hydrogen and a gaseous fluoroalkyle compound.

11. The process set forth in claim 10, wherein a mixture of Ar and hydrogen is used which comprises between about 1% and about 3% hydrogen bv volume, and wherein the fluoroalkyle compound is CHF₃.

12. The process set forth in claim 1, wherein, as a source material for formation of the CdS and the CdTe films by close-spaced sublimation, a CdS or, respectively, CdTe material generally in the form of a compact block is used.

13. The process set forth in claim 12, wherein the compact block CdS (or CdTe) material is formed by covering pieces of CdS (or CdTe) material with boron oxide, heating the covered material to a temperature generally greater than its melting point in an inert gas atmosphere and at a pressure generally greater than 50 atm, and then cooling the material to room temperature, whereby the material is solidified in a generally compact block-like form.

19. The process set forth in claim 1, wherein the transparent substrate is soda-lime glass.

14. A process for large-scale production of CdTe/CdS thin film solar cells, films of the cells being deposited, in sequence, on a transparent substrate, the sequence comprising the steps of:

depositing a film of a transparent conductive oxide (TCO) on the substrate;

depositing a film of CdS on the TCO film;

depositing a film of CdTe on the CdS film;

treating the CdTe film with CdCl₂; and

depositing a back-contact film on the treated CdTe film;

wherein the transparent conductive oxide is In₂O₃ doped with fluorine.

15. The process set forth in claim 14, wherein the TCO layer is formed by sputtering in an inert gas atmosphere comprising a mixture of hydrogen and a gaseous fluoroalkyle compound.

16. The process set forth in claim 15, wherein a mixture of Ar and hydrogen is used which comprises between about 1% and about 3% hydrogen by volume and wherein the fluoroalkyle compound is CHF₃.

20. A CdTe/CdS thin film solar cell product of the process set forth in claim 14.

17. A process for large-scale production of CdTe/CdS thin film solar cells, films of the cells being deposited, in sequence, on a transparent substrate, the sequence comprising the steps of:

depositing a film of a transparent conductive oxide (TCO) on the substrate;

depositing a film of CdS on the TCO film;

depositing a film of CdTe on the CdS film;

treating the CdTe film with CdCl₂; and

depositing a back-contact film on the treated CdTe film;

wherein as a source material for the formation of the CdS and the CdTe films by close-spaced sublimation, a CdS or, respectively, CdTe material generally in the form of a compact block is used.

18. The process set forth in claim 17, wherein the compact block of CdS (or CdTe) material is formed by covering pieces of CdS (or CdTe) material with boron oxide, heating the covered material to a temperature generally greater than its melting point in an inert gas atmosphere and at a pressure generally greater than about 50 atm. and then cooling the material to room temperature, whereby the material is solidified in a generally compact block-like form.