Method for producing the rear contact layer for CdTe thin-film solar cells

Abstract

The present invention concerns a method for the manufacture of the first layer of a back contact layer for thin-layer solar cells in superstrate configuration. In the prior art, this layer is deposited as a compound, for example as a layer of Sb.sub.2Te.sub.3. In accordance with the invention, however, a tellurium-rich surface layer of the cadmium telluride layer is produced, on which a first material is deposited which is capable of forming an electrically conductive second material with tellurium and of producing the second material by reaction of the first material and tellurium in the surface layer. The second material forms the first layer of the back contact layer.

Claims

1. A method for the manufacture of a back contact layer for CdTe thin-layer solar cells in superstrate configuration, characterized in that a first back contact layer is produced by means of the following steps: producing a tellurium-rich surface layer of the cadmium telluride layer, depositing a layer of an elemental first material consisting solely of antimony on the tellurium-rich surface layer, and producing a first back contact layer via reaction of the first material and tellurium in the surface layer to create Sb.sub.2Te.sub.3.

2. The method as claimed in claim 1, characterized in that the tellurium-rich surface layer is produced by means of a NP etch step or a bromomethanol etching step.

3. The method as claimed in claim 2, characterized in that the formation of a tellurium-rich surface layer is promoted by heating the substrate during the etching step.

4. The method as claimed in claim 1, characterized in that the first material is applied to the tellurium-rich surface layer by sputtering, vapour deposition, electrochemical or wet chemical deposition, or by a CVD method.

5. The method as claimed in claim 1, characterized in that, after depositing the first material onto the tellurium-rich surface layer, the formation of the first back contact layer is promoted by heating the substrate.

6. The method as claimed in claim 5, characterized in that heating of the substrate is carried out at 50 C.-300 C. for 1 min-30 min.

7. A method for the manufacture of a back contact layer for CdTe thin-layer solar cells in superstrate configuration, characterized in that a first back contact layer is produced by means of the following steps: producing a tellurium-rich surface layer of the cadmium telluride layer, depositing a layer of an elemental first material consisting solely of arsenic on the tellurium-rich surface layer, and producing a first back contact layer via reaction of the first material and tellurium in the surface layer to create As.sub.2 Te.sub.3.

8. The method as claimed in claim 7, characterized in that the tellurium-rich surface layer is produced by means of a NP etch step or a bromomethanol etching step.

9. The method as claimed in claim 8, characterized in that the formation of a tellurium-rich surface layer is promoted by heating the substrate during the etching step.

10. The method as claimed in claim 7, characterized in that the first material is applied to the tellurium-rich surface layer by sputtering, vapour deposition, electrochemical or wet chemical deposition, or by a CVD method.

11. The method as claimed in claim 7, characterized in that, after depositing the first material onto the tellurium-rich surface layer, the formation of the first back contact layer is promoted by heating the substrate.

12. The method as claimed in claim 11, characterized in that heating of the substrate is carried out at 50 C.-300 C. for 1 min-30 min.

13. A method for the manufacture of a back contact layer for CdTe thin-layer solar cells in superstrate configuration, characterized in that a first back contact layer is produced by means of the following steps: producing a tellurium-rich surface layer of the cadmium telluride layer, depositing a layer of an elemental first material consisting solely of mercury on the tellurium-rich surface layer, and producing a first back contact layer via reaction of the first material and tellurium in the surface layer to create HgTe.

14. The method as claimed in claim 13, characterized in that the tellurium-rich surface layer is produced by means of a NP etch step or a bromomethanol etching step.

15. The method as claimed in claim 14, characterized in that the formation of a tellurium-rich surface layer is promoted by heating the substrate during the etching step.

16. The method as claimed in claim 13, characterized in that the first material is applied to the tellurium-rich surface layer by sputtering, vapour deposition, electrochemical or wet chemical deposition, or by a CVD method.

17. The method as claimed in claim 13, characterized in that, after depositing the first material onto the tellurium-rich surface layer, the formation of the first back contact layer is promoted by heating the substrate.

18. The method as claimed in claim 17, characterized in that heating of the substrate is carried out at 50 C.-300 C. for 1 min-30 min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 to FIG. 5 diagrammatically show the sequence of the process steps in accordance with the invention for a first embodiment in which a Sb.sub.2Te.sub.3 layer is produced as the first back contact layer.

(2) FIG. 1 shows the prepared solar cells with the substrate (1) onto which the transparent front contact (21) as well as the CdS layer (3) and over it the CdTe layer (4) have already been applied.

(3) FIG. 2 diagrammatically shows the etching process using an NP etch (6).

(4) After the etching process, as can be seen in FIG. 3, a Te-rich layer (41) remains, from which the majority of the Cd has been liberated.

(5) FIG. 4 diagrammatically shows that a layer of Sb has been disposed over the Te-rich layer (41).

(6) As can be seen in diagrammatic form in FIG. 5, the Te-rich layer (41) and the Sb layer (7) react under the action of heat to form a Sb.sub.2Te.sub.3 layer (5).

(7) FIG. 6 diagrammatically shows the sequence of layers of the prepared solar cell after application of the back contact (22) to the Sb.sub.2Te.sub.3 layer (5). The back contact layer (22) can in this case be configured as a sequence of layers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) The process of the invention will now be illustrated by means of two exemplary embodiments, which are in no way limiting in nature.

(9) In accordance with a first embodiment, after applying the front contact layer (21), the CdS layer (3) and the CdTe layer (4) to the glass substrate (1) (FIG. 1), the CdTe surface layer is activated, in accordance with the prior art, using CdCl.sub.2 at 400 C. Next, the NP etching step (FIG. 2) is carried out with a NP etch solution (6): HNO.sub.3 (1%)/H.sub.3PO.sub.4(77%)/H.sub.2O(22%), at a temperature of 20 C. A Te-rich layer (41) is formed with a layer thickness of 150 nm (FIG. 3). The cadmium in this layer is only present in substantially sub-stoichiometric quantities.

(10) Next, a 45 nm thick layer of Sb (7) is sputtered onto the Te-rich layer (41) at a substrate temperature of 150 C. (FIG. 4).

(11) Next, the whole sequence of layers is heated up again for a period of 12 min at 150 C. in a vacuum in order to promote the formation of the Sb.sub.2Te.sub.3 compound (5). The resulting thickness of the Sb.sub.2Te.sub.3 layer is 90 nm (FIG. 5).

(12) Subsequently, the back contact layer (22) is deposited, which back contact layer consists of a sequence of layers formed by a molybdenum layer and a nickel layer with added vanadium. The molybdenum layer (150 nm) is deposited on the Sb.sub.2Te.sub.3 layer by sputtering. Next, another layer of nickel with added vanadium is deposited on the molybdenum layer (sputtering, 150 nm).

(13) Alternatively, in a second exemplary embodiment, subsequent to producing the Te-rich layer (41), a 35 nm thick layer of Zn is sputtered onto the Te-rich layer (41) instead of the Sb layer (7) and a subsequent heat treatment is carried out using the same parameters as described in the first exemplary embodiment to produce a 70 nm thick ZnTe layer instead of the Sb.sub.2Te.sub.3 layer (5). Subsequently, the back contact layer (22) is deposited as described in the first exemplary embodiment.

LIST OF REFERENCE NUMERALS

(14) 1 substrate (glass) 21 front contact (transparent, TCO) 22 back contact (metal) 3 CdS layer 4 CdTe layer 41 Te-rich layer after etching 5 Sb.sub.2Te.sub.3 layer 6 NP etching 7 sputtered Sb layer