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EP-4515602-B1 - 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

EP4515602B1EP 4515602 B1EP4515602 B1EP 4515602B1EP-4515602-B1

Inventors

  • PENG, Shou
  • MA, Liyun
  • FU, Ganhua
  • YIN, XINJIAN
  • ARNDT, ROBERT
  • Swoboda, Marko

Dates

Publication Date
20260506
Application Date
20220608

Claims (12)

  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 2 , VSe 2 VTe 2 , VSe 2 , V, VO 2 , NH 4 VO 2 , VCl 2 , VCl 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 claim 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 claims 9 or 11, characterized in that the second doping element is a group 11 or group 15 element.

Description

The invention concerns a method for manufacturing a CdTe based thin film solar cell with a graded refractive index profile within the CdTe-based absorber layer and a CdTe based thin film solar cell with a graded refractive index profile. In the state of the art, CdTe based thin film solar cell devices are produced in superstrate configuration with the following process sequence: on a usually transparent substrate, like a glas substrate a first electrode layer is deposited as a front contact. On this, a CdTe based absorber layer is deposited. The CdTe based absorber layer is then activated with an activating agent, e.g. CdCl2, and a temperature treatment step. Finally, a second electrode layer, e.g. metal layer or a metal compound layer, is applied as a back contact to collect the charge carriers. CdTe based thin film solar cell devices in substrate configuration are known from state of the art as well. It is also well known to include additional layers before depositing the CdTe based absorber layer and before depositing the back contact, like buffer layers. Differences between the refractive index of the glass substrate comprising the front electrode and the CdTe based absorber layer lead to degraded coupling of light into the CdTe based absorber layer and therefore limit the photovoltaic efficiency of the thin film solar cell device. In particular, in cases without a CdS layer formed between the front electrode and the CdTe absorber layer, the difference between the front glass having a refractive index of 1.5 to 1.7 and the CdTe layer having a refractive index of 2.95 is very high, resulting in a significant amount of incident light reflected at the interface to the CdTe layer. In some devices, a CdSeTe absorber layer having a high amount of Se at this interface is formed, e.g. in US 2014/0360565 A1. However, even pure CdSe has a refractive index of 2.54 resulting in still a large difference of refractive indices. Furthermore, doping, in particular p-doping, or increasing p-doping level of the CdTe based absorber layer is important to achieve high efficiency solar cells. P-doping with copper is well known, but is associated with draw backs, like lack of long-term stability. WO 2017 / 081477 A1 discloses a method for preparation of a Cu-doped CdTe based thin film solar cell, wherein a continuous organic layer is applied between an absorber layer and a back contact. The copper may be incorporated into the CdTe absorber layer by providing Cu onto the CdTe absorber layer by thermal evaporation or by treating the surface of the organic layer with Cu. EP 2 337 088 A2 discloses a method for p-doping cadmium telluride (CdTe), wherein CdTe is provided with an interfacial region and subjecting at least a portion of the interfacial region to a thermal treatment. The thermal treatment is performed in the presence of a first material comprising a p-type dopant like Bi, P, As, Sb, Au, Ag or Cu and a second material comprising a halogen like cadmium chloride, hydrochloric acid or chlorine gas. However, some of the used doping elements create sub-bandgap defects reducing efficiency of the solar device. It is therefore an aim of the invention to provide a method for manufacturing a CdTe based thin film solar cell device with improved efficiency and a respective CdTe based thin film solar cell device. The object is solved by a method for manufacturing a CdTe based thin film solar cell device with a graded refractive index profile within the CdTe-based absorber layer and by a CdTe based thin film solar cell device with a graded refractive index profile according to the independent claims. Preferred embodiments are given in the dependent claims. According to the invention a method for manufacturing a CdTe based thin film solar cell device with a graded refractive index profile within the CdTe-based absorber layer, comprises at least the following steps: a) providing a transparent substrate comprising a front electrode, b) forming a doped CdTe based absorber layer on the substrate and c) performing an activation treatment after step b). According to the invention, 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 a first doping element. It is formed 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. Advantageously, this method enables manufacturing of a CdTe based thin film solar cell device with a gradient of the first doping element within the CdTe based absorber layer with a high concentration of the first doping element at a first interface of the CdTe based absorber layer directed towards the substrate. The gradient may have any known non-linea