Method for manufacturing a copper-free CdTe based thin film solar cell device

Abstract

A method for manufacturing a copper-free CdTe based thin film solar cell device, comprising the following steps: a) providing a substrate at least comprising a front electrode, b) depositing a CdTe based absorber layer, c) performing an activation treatment, d) applying a X-halogen to the CdTe based absorber layer, wherein X is selected out of a group consisting of P, As, Sb and V; e) performing a thermal treatment after step d) and f) depositing a back contact, characterized in that, the thermal treatment in step e) is performed before step f) and at temperatures in the range of 40 C. to 120 C. in inert atmosphere or vacuum for a duration in the range of 10 minutes to 60 minutes.

Claims

1. A method for manufacturing a copper-free CdTe based thin film solar cell device at least comprising the following steps Providing a substrate at least comprising a front electrode, Depositing a CdTe based absorber layer, Performing an activation treatment, Applying a X-halogen to the CdTe based absorber layer, wherein X is selected out of a group consisting of P, As, Sb and V; Performing a thermal treatment after step d), Depositing a back contact, characterized in that, the thermal treatment in step e) is performed before step f) and at temperatures in the range of 40 C. to 120 C. in inert atmosphere or vacuum for a duration in the range of 10 to 60 minutes.

2. The method according to claim 1, characterized in that the method further comprises a step g) of performing a dopant activation treatment under presence of at least one of the following materials: PCl.sub.3, Cd.sub.3P.sub.2, AsCl.sub.3, As.sub.2Se.sub.3 Cd.sub.3As.sub.2, SbCl.sub.3, Cd.sub.3Sb.sub.2, Sb.sub.2Se.sub.3 VCl.sub.3 or VCl.sub.4 at 400 C.

3. The method according to claim 1 or 2, characterized in that the method further comprises a step h) of depositing a layer comprising at least one element X, wherein X is selected out of the group consisting of P, As, Sb and V before step f).

4. The method according to any of the previous claims, characterized in that after step h) an annealing treatment is performed in step i).

5. The method according to claim 4, characterized in that the annealing treatment in step i) is performed at temperatures in the range of 200 C. to 300 C. for a duration in the range of 20 minutes to 60 minutes in inert atmosphere or vacuum.

6. The method according to any of the previous claims, characterized in that the back contact is deposited as a back contact layer stack at least comprising a first back contact layer and a second back contact layer.

7. The method according to claim 6, characterized in that ZnTe is deposited as the first back contact layer.

8. The method according to claim 6 or 7, characterized in that a metal layer is deposited as the second back contact layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The accompanying drawings are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles. Other embodiments of the invention and many of the intended advantages will be readily appreciated, as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numbers designate corresponding similar parts.

[0057] FIG. 1 shows an exemplary process flow of a method according to the invention.

DETAILED DESCRIPTION

[0058] A process flow of an exemplary embodiment of a method for manufacturing a copper-free CdTe based thin film solar cell device according to the invention is shown in FIG. 1. First in step S1, a substrate at least comprising a front electrode is provided (step a)), wherein the substrate is a glass substrate with a front electrode made of tin oxide on top. In other embodiments, the substrate may comprise further layers like buffer layers, window layers or any else. In the following step S2, a CdTe based absorber layer is deposited by closed space sublimation (step b)). The CdTe based absorber layer is thereby deposited as a single layer of CdTe with a thickness of 3.5 m. In other embodiments, the CdTe based absorber layer may be deposited as a layer stack of alternating, individual layers of CdSe and CdTe with a total thickness of the layer stack of 3.5 m. In other embodiments, it is also possible to deposit a doped CdTe based absorber layer, wherein doping may be achieved by methods known from state of the art, for instance by co-deposition of a CdTe based absorber layer and at least one doping material or any other known method. Following in step S3, an activation treatment is performed (step c)) by applying an activation agent onto the CdTe based absorber layer by a wet chemical method followed by annealing in air atmosphere at a temperature in the range of 380 C. to 470 C. for a duration in the range of 7 minutes to 35 minutes and a cleaning step. In the next step S4, a X-halogen is applied to the CdTe based absorber layer, wherein X is selected out of the group consisting of P, As, Sb and V (step d)). In the example, AsCl.sub.3 is applied as the X-halogen in liquid form as a solution by a wet chemical method under inert conditions known from state of the art. Following in step S5, a thermal treatment after step d) is performed (step e)) at a temperature of 80 C. in N2 atmosphere for a duration in the range of 30 minutes. Next in step S6, a dopant activation treatment under presence of at least one of the following materials is performed (step g)): PCl.sub.3, Cd.sub.3P.sub.2, AsCl.sub.3, Cd.sub.3As.sub.2, SbCl.sub.3, Cd.sub.3Sb.sub.2, VCl.sub.3 or VCl.sub.4. In the example, the dopant activation treatment is performed under presence of Cd.sub.3As.sub.2 at 400 C. in vacuum. Step S6 is especially useful if wet chemical doping is performed in step d), as in the present example, or if CdSe was deposited during deposition of the CdTe based absorber layer in step b). In other embodiments, step g), i.e. step S6, may be saved. Afterwards in step S7, a layer comprising at least one element X, wherein X is selected out of the group consisting of P, As, Sb and V is deposited before step f) (step h)). In the example, an As.sub.2Se.sub.3 layer is deposited by sputtering with a thickness of 30 nm at a temperature of 250 C. Next in step S8, a back contact is deposited (step f)), wherein the back contact may be deposited as a layer stack. The back contact layer stack may comprise a first back contact layer, for instance an As doped ZnTe layer. However, in the present example, a ZnTe layer is not needed since the As.sub.2Se.sub.3 layer is deposited. In the other way, if no As.sub.2Se.sub.3 layer is deposited, a X-doped ZnTe layer would be advantageous or even necessary. The back contact layer stack may comprise an intermediate back contact layer, deposited directly after the first back contact layer or, in the present example, after depositing the As.sub.2Se.sub.3 layer. In the present example, the intermediate back contact layer is deposited by sputtering Mo at room temperature in the presence of nitrogen to form a 30 nm MoN.sub.x layer. In the present example, the back contact layer stack is finished by depositing a second back contact layer by sputtering a Mo layer with a thickness of 250 nm. Afterwards in step S9, an annealing treatment is performed (step i)) at a temperature of 200 C. in air for 30 minutes.