Manufacturing method of copper-free cadmium telluride thin-film solar cell device

Abstract

The invention relates to a method for manufacturing a copper-free cadmium telluride thin film solar cell device. The method at least comprises the following steps: a) arranging a substrate at least comprising a front electrode; b) depositing a cadmium telluride absorption layer; c) carrying out activating treatment; d) applying an X-halogen on the cadmium telluride absorber layer, wherein X is selected from the group consisting of P, As, Sb and V; e) performing heat treatment after the step d); and f) depositing a back contact layer, characterized in that the heat treatment in step e) is carried out prior to step f) and in an inert atmosphere or vacuum at a temperature in the range of 40 DEG C to 120 DEG C for a duration of 10 minutes to 60 minutes.

Description

Technical Field

[0001] The invention relates to a copper-free cadmium telluride thin-film solar cell device. Background Art

[0002] In cadmium telluride thin-film solar cell devices, copper as a doping element has some disadvantages, such as poor device stability and short charge carrier lifetime. Substitution of copper as a doping element is the subject of many documents, such as US 2021 / 0280735A1.

[0003] US2021 / 0280735 A1 includes a method for ex-situ doping of cadmium telluride with P, As, Sb or Bi, wherein a cadmium telluride film activated with cadmium chloride is contacted with a solution or vapor containing P-halide, As-halide, Sb-halide or Bi-halide to provide a cadmium telluride film doped with P, As, Sb or Bi. Summary of the invention

[0004] The object of the present invention is to provide an alternative method for manufacturing copper-free cadmium telluride thin film solar cell devices to improve photovoltaic efficiency.

[0005] The objects of the invention are solved by a method according to the independent claim. Preferred embodiments are subject matter of the dependent claims.

[0006] According to the present invention, a method for manufacturing a copper-free cadmium telluride thin film solar cell device comprises at least the following steps: a) providing a substrate comprising at least a front electrode, b) depositing a cadmium telluride absorber layer, c) performing activation treatment, d) applying an X-halogen on the cadmium telluride absorber layer, wherein X is selected from the group consisting of P, As, Sb and V, e) performing a heat treatment after step d), and f) depositing a back contact layer, Characterized in that the heat treatment in step e) is carried out before step f) and is carried out in an inert atmosphere or in a vacuum, The temperature range is from 40°C to 120°C and the duration is from 10 minutes to 60 minutes.

[0007] The advantage of this method is that copper-free CdTe thin-film solar cell devices can be fabricated by ex-situ doping.

[0008] According to the present invention, the substrate refers to any substrate on which the cadmium telluride absorber layer is deposited in step b). In other words, the substrate may include a transparent substrate (e.g., glass), a transparent front electrode, and a buffer layer, a window layer, or other layers. In other embodiments, the substrate may include a transparent or opaque back electrode and a buffer layer or other layers. In other words, the substrate may be glass, a polymer, a metal, a ceramic material, or any other material.

[0009] The cadmium telluride absorption layer refers to at least one layer of CdTe, CdSe, Cd 1-x Hg x Te, Cd 1-x Mn x Te、CdSe x Te 1-x A layer or layer stack of the composition, x varies between 0≤x≤0.5. In an embodiment, the layer stack is deposited by, for example, subsequently depositing one or more layers, such as a cadmium selenide layer and a cadmium telluride layer, followed by interdiffusion of the different layers as required, or depositing in an undivided process. In an embodiment, the cadmium telluride absorber layer is deposited as a cadmium telluride-doped absorber layer, doped with any suitable element known in the art. In a further embodiment, the cadmium telluride-doped absorber layer may be deposited by any known method, such as depositing a doping source layer before, after or between depositing the cadmium telluride absorber layer, or by co-deposition of a cadmium telluride absorber layer and at least one doping material. Advantageously, the cadmium telluride absorber layer may be doped with any known element other than copper. In a further embodiment, the cadmium telluride absorber layer is doped with a Group 15 element, preferably P, As, Sb and V. In a further embodiment, the cadmium telluride absorber layer is deposited onto a provided substrate with the above-mentioned layer on top thereof using any technique known in the art, including but not limited to physical vapor deposition, such as sputtering, evaporation or sublimation, electrodeposition or any other technique. In an embodiment, the cadmium telluride absorber layer is deposited to a thickness of 1 μm to 5 μm, preferably 2 μm to 4 μm.

[0010] In an embodiment, the activation treatment in step c) is performed by applying an activator (e.g., cadmium chloride) on the cadmium telluride absorber layer by a wet chemical method or a vacuum evaporation method, followed by annealing in an air atmosphere at a temperature range of 380° C. to 460° C. for a duration of 5 to 30 minutes, and performing a cleaning step. In an embodiment, step c) is performed after step b) and / or step d).

[0011] In an embodiment, step d) is carried out before or after the activation treatment in step c). In a preferred embodiment, step d) is carried out after step c). Advantageously, the applied X-halogen is not thereby heated above the boiling point, which it would reach during the activation treatment in step c).

[0012] In step d), X-halogen is used in liquid or gaseous form. Examples of X-halogen include, but are not limited to, PCl3, AsCl3, SbCl3, VF5, VCl4, VCl3, wherein X is selected from the group consisting of P, As, Sb and V. Liquid X-halogen refers to X-halogen, X-halogen solution, X-halogen suspension or gel-like X-halogen in liquid phase.

[0013] X-halogens that exist in liquid form include PCl3, AsCl3, VF5, VCl4, etc., which exist in liquid form at room temperature.

[0014] X-halogen solution refers to X-halogen dissolved in a solvent. Therefore, the solvent is suitable for dissolving the X-halogen. For example, a suitable solvent for VF5 is water, while a suitable solvent for AsCl3 and PCl3 is ether.

[0015] The gelled X-halogen refers to an X-halogen or an X-halogen solution in liquid phase, each of which contains an additional gelling agent, and has a viscosity ranging from 1 mPa s to 250 mPa s, preferably from 2 mPa s to 50 mPa s. For example, such a gelling agent may be polyethylene glycol (PEG) or other gelling agents known to those skilled in the art.

[0016] X-halogen suspension refers to X-halogen solution, X-halogen in liquid form or gel-like X-halogen containing dispersed solid particles. Such solid particles can provide more doping elements and are suitable for forming a layer rich in cadmium and / or selenium near the back contact layer. In other words, the solid particles may contain at least cadmium and / or selenium and doping elements, such as Group 15 elements, preferably P, As, Sb and V. In an embodiment, the solid particles can be, for example, a doping activator such as Cd2As3 or As2Se3. In an embodiment, the particle size range of the dispersed solid particles is 1 μm to 100 μm. In a further embodiment, the X-halogen suspension includes 10 mg to 10 g of solid particles.

[0017] In a further embodiment, the X-halogen solution, X-halogen suspension or gel-like X-halogen comprises X-halogen in a concentration range of 0.1 mmol / l to 50 mmol / l.

[0018] In some embodiments, in step d), alternatively or additionally, an X-hydride is applied on the cadmium telluride absorber layer, wherein X is selected from the group consisting of P, As, Sb and V. Examples of X-hydrides include, but are not limited to, PH3, AsH3, SbH3, BiH3, VH5. Advantageously, the X-hydride exists in a gas phase at room temperature, i.e., in a temperature range of 18°C ​​to 40°C.

[0019] According to the present invention, an inert atmosphere refers to an atmosphere with an oxygen content of less than 50 ppm and no humidity or a reducing atmosphere, such as an Ar, N2 or H2 atmosphere. A vacuum refers to a pressure range of 10 -4 Pa to 10 4 Between Pa.

[0020] In an embodiment, the back contact layer in step f) is deposited at an elevated temperature of 200° C. to 300° C. In a further embodiment, the back contact layer is deposited in vacuum. In some embodiments, the back contact layer is deposited as a single back contact layer or a back contact layer stack. In a further embodiment, the metal layer is deposited as a back contact layer in step f).

[0021] In an embodiment, the X-halogen is applied by known methods such as wet chemical impregnation, gas impregnation, dip coating, roller coating, and the like.

[0022] In further embodiments, the method may further include known technical steps for fabricating substrate-free cadmium telluride thin film solar cell devices, such as a phosphorus nitride etching step (phosphorus nitride etching) for forming a tellurium-rich surface portion on the cadmium telluride absorber layer.

[0023] In an embodiment, the method further comprises step g), i.e., performing a dopant activation treatment at a temperature of 400° C. in the presence of at least one of the following materials: PCl 3 , Cd 3 P 2 , AsCl 3 , As 2 Se 3 , Cd 3 As 2 , SbCl 3 , Sb 2 Se 3 , Cd 3 Sb 2 , VCl 3 or VCl 4 . Advantageously, an excess of doping elements (such as As or V) can be used to dope the cadmium telluride absorber layer to achieve a higher doping level.

[0024] In further embodiments, step g) is performed after step e) and before step f). In some embodiments, step g) is performed in an inert atmosphere.

[0025] "In the presence of..." means that the atmosphere in which the doping activation treatment is performed contains at least one of the above substances. In a further embodiment, the atmosphere contains up to 10% of at least one of the above substances.

[0026] In an embodiment, the method further comprises a step h): depositing a layer comprising at least one element X, wherein X is selected from the group consisting of P, As, Sb and V. Step h) is performed before step f) and after step d). In an embodiment, step h) may be performed before step e).

[0027] Advantageously, in a subsequent process step, a p-type layer is formed at the interface of the cadmium telluride absorber layer and the back contact layer. + layer to reduce the Schottky barrier.

[0028] In an embodiment, the layer comprising at least one element X deposited in step h) may be a layer comprising X as a compound or a doping element.

[0029] In an embodiment, a layer comprising at least one element X, wherein X is P, As or Sb, is deposited in step h). Such a layer comprising P, As or Sb may be, for example, but not limited to, As2Se3, As2Te3, Sb2Te3 or zinc telluride doped with N, P, As, Sb. Advantageously, the layer serves as a source layer and provides additional doping elements for doping the cadmium telluride absorber layer in subsequent process steps. In some embodiments, the layer may also serve as a sacrificial layer for providing a tellurium-rich intermediate layer for the back contact layer in subsequent process steps.

[0030] In a further embodiment, in step h), the layer is deposited to a thickness between 10 nm and 100 nm.

[0031] In an embodiment, the layer in step h) may be deposited by known methods, such as but not limited to sputtering. In a further embodiment, the layer in step h) is deposited in an inert atmosphere or in a vacuum. In an embodiment, the layer in step h) is deposited at a temperature ranging from 100°C to 250°C.

[0032] In an embodiment, after step h), an annealing treatment is performed in step i). Advantageously, this can provide more doping elements for doping the cadmium telluride absorber layer, in which the doping elements are distributed, and in some embodiments, form a tellurium-rich intermediate layer toward the back contact layer.

[0033] In an embodiment, step i) is performed after step f). In this case, a back contact layer annealing treatment is also performed in step i).

[0034] In an embodiment, the annealing treatment in step i) is performed in an inert atmosphere or in a vacuum at a temperature ranging from 200° C. to 300° C. for a duration ranging from 20 minutes to 60 minutes.

[0035] In an embodiment, the back contact layer is deposited as a back contact layer stack and includes at least a first back contact layer and a second back contact layer.

[0036] In an embodiment, the first back contact layer is deposited at a temperature ranging from 200° C. to 300° C. in an inert atmosphere or in a vacuum.

[0037] In a further embodiment, the first back contact layer is deposited to a thickness between 5 nm and 100 nm.

[0038] In an embodiment, zinc telluride is deposited as a first back contact layer.

[0039] In further embodiments, the zinc telluride may be deposited as a doped zinc telluride layer, for example doped with P, As, Sb, and or N. In some embodiments, the doped zinc telluride layer contains up to 5 wt-% of at least one doping element.

[0040] In an embodiment, the metal layer is deposited as a second back contact layer.

[0041] In a further embodiment, the second back contact layer may be deposited in an inert atmosphere or vacuum at a temperature ranging from 100° C. to 300° C. Advantageously, no annealing is required after depositing the back contact layer in step f), thereby saving process steps.

[0042] In a further embodiment, a highly conductive metal is deposited as a metal layer, the sheet resistance of the highly conductive metal being less than 1 ohm / square. Examples of such metal layers include, but are not limited to, molybdenum or aluminum.

[0043] In a further embodiment, the second back contact layer is deposited to a thickness ranging from 10 nm to 100 nm.

[0044] In an embodiment, the second back contact layer is deposited immediately after the first back contact layer. In a further embodiment, the intermediate back contact layer is deposited after the first back contact layer and before the second back contact layer. In an embodiment, the intermediate back contact layer is a metal nitride layer, such as molybdenum nitride or aluminum nitride, but not limited thereto. In a further embodiment, the metal nitride intermediate back contact layer comprises the same metal as the metal layer deposited as the second back contact layer. In a further embodiment, the intermediate back contact layer is deposited to a thickness between 10 nm and 50 nm. In an embodiment, the intermediate back contact layer is deposited in an inert atmosphere or vacuum at a temperature range of 10° C. to 100° C.

[0045] To implement the present invention, it is advantageous to combine the embodiments with the features of the above claims. However, the embodiments of the present invention described in the above description are only illustrative, and the present invention is not limited thereto. Any modifications, variations and equivalent arrangements and combinations of the embodiments should be deemed to be included within the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The purpose of the accompanying drawings is to further understand the embodiments of the present invention, and the accompanying drawings are incorporated into and constitute a part of this specification. The accompanying drawings illustrate embodiments of the present invention and together with the description explain the principles of the present invention. Other embodiments of the present invention and many expected advantages will be readily understood as they can be better understood by reference to the following detailed description. The elements in the drawings are not necessarily drawn to scale. The same reference numerals represent corresponding similar parts.

[0047] Figure 1An exemplary process flow of the method according to the present invention is shown. DETAILED DESCRIPTION

[0048] Figure 1The process flow of an exemplary embodiment of a method for manufacturing a copper-free cadmium telluride thin-film solar cell device according to the present invention is shown. First, in step S1, a substrate including at least a front electrode is provided (step a)), wherein the substrate is a glass substrate having a front electrode made of tin oxide on top. In other embodiments, the substrate may further include a buffer layer, a window layer or other layers. In the following step S2, a cadmium telluride absorption layer is deposited by a closed space sublimation method (step b)). As a result, the cadmium telluride absorption layer is deposited into a single layer of cadmium telluride with a thickness of 3.5 μm. In other embodiments, the cadmium telluride absorption layer may be deposited as a layer stack of alternating individual layers of cadmium selenide and cadmium telluride, and the total thickness of the layer stack is 3.5 μm. In other embodiments, a doped cadmium telluride absorption layer may also be deposited, wherein the doping may be achieved by methods known in the art, such as by co-deposition of a cadmium telluride absorption layer and at least one doping material or any other known method. After step S3, an activation treatment (step c)) is performed by applying an activator to the cadmium telluride absorption layer by a wet chemical method, followed by an annealing treatment in an air atmosphere, the annealing temperature ranges from 380°C to 470°C, the annealing time ranges from 7 minutes to 35 minutes, and then cleaning. In the next step S4, an X-halogen is applied to the cadmium telluride absorption layer, wherein X is selected from the group consisting of P, As, Sb and V (step d)). In this example, AsCl3 is applied as a X-halogen in liquid form as a solution by a wet chemical method under inert conditions known in the prior art. In step S5, a heat treatment (step e)) is performed in a nitrogen atmosphere after step d) at a temperature of 80°C for a duration of 30 minutes. Next, in step S6, a dopant activation treatment (step g)) is performed in the presence of at least one of the following materials: PCl3, Cd3P2, AsCl3, Cd3As2, SbCl3, Cd3Sb2, VCl3 or VCl4. In the present example, a dopant activation treatment is performed under vacuum conditions at 400° C. in the presence of Cd3As2. Step S6 is particularly useful if a wet chemical doping treatment is performed in step d) (as in the present example), or if cadmium selenide is deposited when depositing the cadmium telluride absorption layer in step b). In other embodiments, step g), i.e., step S6, may be omitted. Then, in step S7, a layer comprising at least one element X is deposited before step f) (step h)), wherein X is selected from the group consisting of P, As, Sb, and V. In the present example, a As2Se3 layer having a thickness of 30 nm is deposited by sputtering at a temperature of 250° C. Next, in step S8, a back contact layer is deposited (step f)), wherein the back contact layer may be deposited as a layer stack. The back contact layer stack may include a first back contact layer, such as an arsenic-doped zinc telluride layer. However, in the present example, since the As2Se3 layer is deposited, a zinc telluride layer is not required. If, on the other hand, no As2Se3 layer is deposited, an X-doped zinc telluride layer is advantageous or even necessary.The back contact layer stack may include an intermediate back contact layer, deposited directly after the first back contact layer, or in this example, after the As2Se3 layer. In this example, the intermediate back contact layer is formed by sputtering Mo at room temperature in the presence of nitrogen to form MoN with a thickness of 30 nm. x In this example, the second back contact layer is deposited by sputtering a Mo layer with a thickness of 250 nm, thereby completing the back contact layer stack. Then in step S9, an annealing treatment (step i)) is performed in air at a temperature of 200° C. for 30 minutes.

Claims

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

2. The method according to claim 1, characterized in that: The method further comprises step g), i.e., performing a dopant activation treatment at a temperature of 400° C. in the presence of at least one of the following materials: PCl3, Cd3P2, AsCl3, As2Se3Cd3As2, SbCl3, Cd3Sb2, Sb2Se3 VCl3 or VCl4.

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 from the group consisting of P, As, Sb and V, before step f).

4. A method according to any one of the preceding claims, characterised in that After step h), an annealing treatment is carried out in step i).

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

6. A method according to any preceding claim, characterised in that The back contact layer is deposited as a back contact layer stack, which includes at least a first back contact layer and a second back contact layer.

7. The method according to claim 6, characterized in that Zinc telluride 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.

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