METHOD FOR MANUFACTURING CDTE BASED THIN FILM SOLAR CELL WITH GRADED REFRACTIVE INDEX PROFILE WITHIN THE CDTE-BASED ABSORBER LAYER AND CDTE BASED THIN FILM SOLAR CELL WITH GRADED REFRACTIVE INDEX PROFILE

Abstract

A method for manufacturing a CdTe based thin film solar cell device with a graded refractive index profile within the CdTe-based absorber layer. The method comprises the following steps: a) providing a transparent substrate comprising a front electrode, b) forming a doped CdTe based absorber layer on the substrate, c) performing an activation treatment after step b). The doped CdTe based absorber layer in step b) is formed as a doped CdTe based absorber layer stack comprising a first and a second layer. The first layer is formed as a first doping element containing layer comprising vanadium as the first doping element by depositing a first doping element-rich layer and subsequently depositing a CdSe layer or a CdSeTe layer, or by depositing a CdSe layer or a CdSeTe layer each doped with the first doping element. The second layer is formed by depositing a CdTe layer. A CdTe based thin film solar cell device with a graded refractive index profile.

Claims

1. Method for manufacturing a CdTe based thin film solar cell device with a graded refractive index profile within the CdTe-based absorber layer, at least comprising the following steps: a) Providing a transparent substrate comprising a front electrode, b) Forming a doped CdTe based absorber layer on the substrate, c) Performing an activation treatment after step b), characterized in that the doped CdTe based absorber layer in step b) is formed as a doped CdTe based absorber layer stack comprising a first and a second layer, wherein the first layer is formed as a first doping element containing layer comprising vanadium as the first doping element by depositing a first doping element-rich layer and subsequently depositing a CdSe layer or a CdSeTe layer; or by depositing a CdSe layer or a CdSeTe layer each doped with the first doping element; and the second layer is formed by depositing a CdTe layer.

2. Method according to claim 1, characterized in that the first doping element-rich layer is at least one out of the group comprising VTe.sub.2, VSe.sub.2 VTe.sub.2, VSe.sub.2, V, VO.sub.2, NH.sub.4VO.sub.2, VCl.sub.2, VCl.sub.4.

3. Method according to claim 1 or 2, characterized in that the substrate provided in step a) further comprises an oxygen containing layer.

4. Method according to claim 3, characterized in that the oxygen containing layer is an oxidic buffer layer.

5. Method according to any of the claims 1 to 4, characterized in that the second layer of the CdTe based absorber layer stack is doped with a second doping element.

6. Method according to any of the claims 1 to 5, characterized in that the method further comprises a step d) forming a back contact after step c).

7. Method according to claim 6, characterized in that the back contact is formed by forming a back contact layer stack, comprising a first back contact layer and a second back contact layer, wherein the first back contact layer is a Te-rich layer and the second back contact layer is a metal layer or a high resistance layer.

8. Method according to any of the claims 1 to 7, characterized in that the activation treatment is performed under inert atmosphere or vacuum.

9. CdTe based thin film solar cell device with a graded refractive index profile at least comprising a transparent substrate comprising a front electrode, a back contact, and a doped CdTe based absorber layer comprising vanadium as a first doping element and arranged between the front electrode and the back contact, wherein the doped CdTe absorber layer comprises a graded refractive index along a thickness of the CdTe based absorber layer with a lowest refractive index at a first interface of the CdTe based absorber layer oriented towards the substrate and a highest refractive index at a second interface of the CdTe based absorber layer oriented towards the back contact.

10. CdTe based thin film solar cell device according to claim 9, characterized in that the doped CdTe based absorber layer comprises a gradient of the first doping element along the thickness of the CdTe based absorber layer with a highest concentration of the first doping element at the first interface of the CdTe based absorber layer.

11. CdTe based thin film solar cell device according to claim 9 or 10, characterized in that the doped CdTe based absorber layer comprises a second doping element having a gradient along the thickness of the CdTe based absorber layer with a highest concentration of the second doping element at the second interface of the CdTe based absorber layer.

12. CdTe based thin film solar cell device according to any of the claim 9 or 11, characterized in that the second doping element is a group 11 or group 15 element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] FIG. 1A shows a specific embodiment of the inventive method for manufacturing a CdTe based thin film solar cell device with a graded refractive index profile within the CdTe-based absorber layer.

[0069] FIG. 1B shows another specific embodiment of the inventive method for manufacturing a CdTe based thin film solar cell device with a graded refractive index profile within the CdTe-based absorber layer.

[0070] FIG. 2 shows an embodiment of an inventive CdTe based thin film solar cell device with a graded refractive index profile.

DETAILED DESCRIPTION

[0071] 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.

[0072] In an embodiment according to FIG. 1A, the method for manufacturing a CdTe based thin film solar cell device with a graded refractive index profile within the CdTe-based absorber layer at least comprises a step S1 of providing a transparent substrate. The transparent substrate comprises a transparent base substrate, for instance a glass substrate, a front electrode, for instance an n-type transparent conductive oxide like fluorine-doped tin-oxide, and an oxidic buffer layer, for instance magnesium doped zinc oxide (MZO). In the following step S2, a doped CdTe based absorber layer is formed as a CdTe based absorber layer stack comprising a first and a second layer. The first layer of the CdTe based absorber layer stack is formed as a first doping element containing layer wherein the first doping element is vanadium. In embodiments, the first doping element containing layer is formed in step S2.1 by depositing a CdSe layer or a CdSeTe layer each doped with vanadium for instance by depositing from a vanadium doped CdSe or CdSeTe source or by co-deposition of vanadium and CdSe or CdSeTe. The first doping element containing layer is formed with a thickness of 300 nm. Further on, in step S2.2, the second layer of the CdTe based absorber layer stack is formed by depositing a CdTe layer with a thickness of 3.2 m in vacuum of 1 Pa or under inert atmosphere. In embodiments, the second layer of the CdTe based absorber layer stack may be deposited as a doped layer, for instance a p-doped CdTe layer doped for instance with As. Methods for depositing a doped CdTe layer are well known to experts and state of the art. After forming the CdTe based absorber layer stack in step S3, an activation treatment is performed, comprising a step of applying an activation agent like CdCl.sub.2 and a step of a thermal treatment at 400 C. to 450 C. in vacuum of 10 Pa with a H2 partial pressure of 510 Pa for 15 minutes. Finally, in step S4, a back contact is formed as a back contact layer stack comprising a first back contact layer and a second back contact layer. The first back contact layer is formed by depositing a highly p-doped ZnTe with a thickness of 30 nm. The second back contact layer is deposited as metal layer, for instance Mo with a thickness of 300 nm.

[0073] The embodiment according to FIG. 1B comprises the steps S1, S3 and S4 carried out as described for FIG. 1A. In step S2 a doped CdTe based absorber layer is formed as a CdTe based absorber layer stack comprising a first and a second layer. The first layer of the CdTe based absorber layer stack is formed as a first doping element containing layer wherein the first doping element is vanadium. According to FIG. 1B in this embodiment, the first doping element containing layer is formed by depositing a first doping element-rich layer in step S2.10, for instance a VSe.sub.2 layer with a thickness of 50 nm in vacuum of 1 Pa, and subsequently depositing a CdSe layer or a CdSeTe layer with a thickness of 250 nm in step S2.11 in vacuum as well.

[0074] FIG. 2 shows schematically an embodiment of a CdTe based thin film solar cell device 1 not true to scale with a graded refractive index profile manufactured according to a method from FIG. 1A or FIG. 1B. The CdTe based thin film solar cell device 1 in the upper part of FIG. 2 comprises at least a transparent substrate 10 comprising a glass substrate, a front electrode of fluorine-doped tin-oxide and an oxidic buffer layer of magnesium doped zinc oxide (MZO); a doped CdTe based absorber layer 11, and a back contact 12, comprising a first back contact layer of ZnTe and a second back contact layer of Mo. The doped CdTe absorber layer 11 comprises a graded refractive index n along a thickness x of the CdTe based absorber layer 11 with a lowest refractive index n of 2.0 to 2.5 at a first interface of the CdTe based absorber layer 11 oriented towards the substrate and a highest refractive index n of 2.5 to 3 at a second interface of the CdTe based absorber layer 11 oriented towards the back contact shown schematically in the middle part of FIG. 2. The CdTe based absorber layer 11 further comprises a gradient of the first doping element, i.e. vanadium, along the thickness x of the CdTe based absorber layer 11 with a highest concentration of vanadium c vup to 1 wt.-% at the first interface of the CdTe based absorber layer 11 shown in the lower part of FIG. 2. Furthermore, the doped CdTe based absorber layer 11 comprises a gradient of a second doping element, here arsenic, along the thickness x of the CdTe based absorber layer 11 with a highest concentration of arsenic c Asup to 1 wt.-% at the second interface of the CdTe based absorber layer 11 shown in the lower part of FIG. 2 as well. The CdTe based absorber layer 11 comprises up to 1 wt.-% vanadium and up to 0.5 wt.-% arsenic.