Cadmium telluride solar cell and preparation method thereof

Abstract

The invention relates to a cadmium telluride solar cell and a preparation method thereof, the cadmium telluride solar cell comprises a TCO layer, a buffer layer, a window layer, a light absorption layer, a back electrode layer and a back contact layer, the back contact layer is located between the light absorption layer and the back electrode layer, and the back contact layer is made of boron or carbon doped transition metal nitride. The back contact layer made of boron or carbon doped transition metal nitride is introduced between the light absorption layer and the back electrode layer, and transition gold elements in the back contact layer can be compatible with the cadmium telluride absorption layer, so that the obstruction of a contact barrier to hole transport is reduced, the interface characteristic between the CdTe absorption layer and the back contact layer is optimized, and the light emitting efficiency is improved. According to the present invention, the cadmium telluride absorption layer can form the good ohmic contact with the cadmium telluride absorption layer, such that the effect of the back field buffer layer can be provided so as to reflect the photo-induced electrons on the back surface in the cadmium telluride to the PN junction, such that the recombination of the electrons on the back surface can be substantially reduced, and the carrier collection efficiency of the cell can be improved so as to improve the open-circuit voltage and the conversion efficiency of the cell;

Description

Technical Field

[0001] The present invention relates to the technical field of battery preparation, and in particular to a cadmium telluride solar cell and a preparation method thereof. Background Art

[0002] Cadmium telluride (CdTe), as an outstanding representative of II-VI compound semiconductor materials, has shown great application potential and advantages in the field of thin-film solar cells due to its unique bandgap width (1.45eV) that is highly compatible with the terrestrial solar spectrum, and its visible light absorption coefficient far exceeds that of silicon materials. However, despite the significant progress made in conversion efficiency and material cost of cadmium telluride solar cells, its performance improvement and long-term stability guarantee still face a series of technical bottlenecks.

[0003] In particular, the p-type CdTe layer of cadmium telluride solar cells has an extremely high work function (about 5.7 eV). This characteristic causes a significant Schottky barrier to form at the interface when in direct contact with most metal back electrodes, which seriously hinders the effective transmission of photogenerated carriers and thus limits the overall performance of the cell. Traditional solutions mostly rely on introducing a high work function semiconductor layer as a back contact layer between the CdTe layer and the back electrode to reduce the contact barrier. However, although the widely used copper (Cu) back contact material can partially solve this problem, its rapid diffusion characteristics pose a potential threat to the stability of the CdTe layer, which may cause long-term degradation of battery performance or even failure. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to introduce a back contact layer composed of boron or carbon-doped transition metal nitride between the absorption layer and the back electrode layer, which can reduce the contact barrier, reduce the recombination loss of carriers at the interface, and promote the efficient transmission of holes in a cadmium telluride solar cell and a preparation method.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is a cadmium telluride solar cell, including a TCO layer, a buffer layer, a window layer, a light absorption layer and a back electrode layer, and also includes a back contact layer, wherein the back contact layer is located between the light absorption layer and the back electrode layer, and the back contact layer is made of boron or carbon doped transition metal nitride.

[0006] Preferably, the transition metal nitride is one or more of titanium nitride, zirconium nitride, tantalum nitride, cobalt nitride, tungsten nitride or hafnium nitride.

[0007] A method for preparing a cadmium telluride solar cell comprises the following steps:

[0008] S1. Depositing tin oxide on the provided TCO layer to obtain a buffer layer;

[0009] S2. Depositing cadmium selenide on the buffer layer to obtain a window layer;

[0010] S3. depositing arsenic-doped cadmium telluride on the window layer to obtain a light absorbing layer;

[0011] S4. Obtaining a back contact layer by magnetron sputtering a boron or carbon-doped transition metal nitride on the light absorbing layer;

[0012] S5. Depositing a back electrode layer on the back contact layer to obtain a battery.

[0013] Preferably, in S4, the method of obtaining the back contact layer by magnetron sputtering boron or carbon-doped transition metal nitride on the light absorption layer comprises:

[0014] S401. Select a sputtering source, select one of boron or carbon, and one of transition metals titanium, zirconium, tantalum, cobalt, tungsten or hafnium in the transition metal nitride as a sputtering source;

[0015] S402. Using a mixed gas of argon and nitrogen as a sputtering gas, sputter the selected sputtering source onto the light absorbing layer to obtain a back contact layer.

[0016] Preferably, the sputtering source in S401 is composed of a high-purity Ti target and a TiB2 target, wherein the power of the Ti target is maintained at 450W, and the power of the TiB2 target is maintained at 70W.

[0017] Preferably, the sputtering source in S401 is composed of a high-purity Ti target and a C target, wherein the power of the Ti target is maintained at 450W, and the power of the C target is maintained at 60W.

[0018] Preferably, the sputtering source in S401 is composed of a high-purity W target and a C target, wherein the power of the W target is maintained at 420W, and the power of the C target is maintained at 60W.

[0019] Preferably, the sputtering source in S401 is composed of a high-purity Ta target and a C target, wherein the power of the Ta target is maintained at 200W, and the power of the C target is maintained at 60W.

[0020] Preferably, the flow ratio of argon to nitrogen in S402 is (1-10):(3-4).

[0021] The specific beneficial effects of the present invention are:

[0022] A back contact layer made of boron or carbon-doped transition metal nitride is introduced between the light absorption layer and the back electrode layer. The transition gold element in the back contact layer is compatible with the cadmium telluride absorption layer, reducing the obstruction of the contact barrier to hole transmission, optimizing the interface characteristics between the CdTe absorption layer and the back contact layer, and forming a good ohmic contact with the cadmium telluride absorption layer. It plays the role of a back field buffer layer, reflecting the photogenerated electrons at the back surface of the cadmium telluride to the PN junction, greatly reducing the recombination of electrons at the back surface, and improving the carrier collection efficiency of the battery, thereby improving the open circuit voltage and conversion efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiment of the present invention and its design scheme, the following briefly introduces the drawings required for this embodiment. The drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 It is a schematic diagram of the cross-sectional structure of a cadmium telluride thin film solar cell in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0026] When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Instead, they are only examples of devices and methods consistent with some aspects of the present application as detailed in the attached claims.

[0027] like Figure 1 The embodiment shown provides a cadmium telluride solar cell, comprising a TCO layer, a buffer layer, a window layer, a light absorbing layer and a back electrode layer, and further comprising a back contact layer, wherein the back contact layer is located between the light absorbing layer and the back electrode layer, and the back contact layer is made of a boron or carbon-doped transition metal nitride, specifically, the TCO layer, the buffer layer, the window layer, the light absorbing layer, the back contact layer and the back electrode layer are sequentially arranged from bottom to top;

[0028] Wherein: the TCO layer (substrate layer) is a commercial FTO transparent conductive film, and the thickness of the FTO transparent conductive film is 350nm;

[0029] The buffer layer is a tin oxide (SnO2) buffer layer with a specific thickness of 50nm;

[0030] The window layer is a cadmium sulfide (CdS) film or a cadmium selenide (CdSe) film with a thickness of 100 nm;

[0031] The light absorption layer is an arsenic-doped cadmium telluride film, wherein the thickness is 3-4 μm;

[0032] The back contact layer is a thin film layer made of boron or carbon doped transition metal nitride with a thickness of 5-30 mm; wherein the transition metal nitride is one or more of titanium nitride, zirconium nitride, tantalum nitride, cobalt nitride, tungsten nitride or hafnium nitride.

[0033] The back electrode layer is a gold back electrode with a thickness of 150nm.

[0034] Boron or carbon-doped transition metal nitrides (such as TiN, ZrN, CoN, TaN, W2N, etc.) are used as back contact layer materials. This type of material not only has a wide band gap, excellent chemical and thermal stability, but more importantly, it can effectively match or even exceed the p-type CdTe layer by adjusting the work function characteristics through doping, thereby significantly reducing the contact barrier, reducing the recombination loss of carriers at the interface, and promoting the efficient transmission of holes.

[0035] Example 1

[0036] This embodiment provides a method for preparing a cadmium telluride solar cell, comprising:

[0037] S1. Depositing tin oxide on the provided TCO layer to obtain a buffer layer;

[0038] Among them, the TCO layer (substrate layer) uses FTO transparent conductive film with a thickness of 350nm. During the production, the substrate is ultrasonically cleaned with deionized water and ethanol in turn to remove surface impurities and oil stains. Then, it is blown dry with high-purity nitrogen (N2) to ensure that the substrate surface is clean and free of residue;

[0039] After processing the substrate layer, a 50nm thick tin oxide (SnO2) buffer layer is deposited on the FTO transparent conductive film by magnetron sputtering to form a buffer layer on the substrate layer, thus completing the preparation of the buffer layer;

[0040] S2. Depositing cadmium selenide on the buffer layer to obtain a window layer;

[0041] The window layer is a cadmium sulfide (CdS) film or a cadmium selenide (CdSe) film. During preparation, a cadmium sulfide (CdS) film or a cadmium selenide (CdSe) film with a thickness of 100 nm is prepared on a SnO2 buffer layer by a close-space sublimation method as the window layer.

[0042] S3. depositing arsenic-doped cadmium telluride on the window layer to obtain a light absorbing layer;

[0043] Among them, the light absorption layer adopts an arsenic-doped cadmium telluride film with a thickness of 3-4μm. During the preparation, the near-space sublimation method is used to deposit the arsenic-doped cadmium telluride film with a thickness of 3-4μm on the CdS or CdSe film. The source materials used in the space sublimation method are cadmium telluride (CdTe) and cadmium arsenide (Cd2As3) powders with a purity of 99.999%, the source temperature is 650℃, and the substrate temperature is 550℃.

[0044] S4. After the light absorption layer is completed, when the light absorption layer is p-type CdTe:As, evaporate a layer of cadmium chloride (CdCl2) film on the p-type CdTe:As film, then place it in a tube furnace and heat treat it at 400℃ for 15 minutes. Rinse the CdTe:As film that has been heat treated with CdCl2 with deionized water and blow dry with nitrogen. Use a specific ratio of phosphorus nitric acid etching solution (nitric acid: phosphoric acid: water = 1:70:29) to etch the heat-treated film for 35 seconds to remove surface defects and impurities and improve battery performance. After etching, rinse with deionized water and blow dry with nitrogen; then sputter the back contact layer.

[0045] S5. Obtain a back contact layer on the light absorption layer by magnetron sputtering boron or carbon doped transition metal nitride; the material used for the back contact layer is boron or carbon doped transition metal nitride, and during the production, magnetron sputtering is used to deposit a boron (B) doped titanium nitride (TiN) film on the etched CdTe:As film. During the deposition process, high-purity (99.99%) Ti target and TiB2 (99.99%) target were selected as sputtering sources to introduce B element for doping, the power of the Ti target was maintained at 450W, and the power of the TiB2 target was maintained at 70W. A mixed gas of argon (Ar) and nitrogen (N2) was used as the sputtering gas, wherein argon was mainly used to generate sputtering plasma, and nitrogen reacted with the sputtered titanium atoms to generate TiN, and the flow ratio of argon to nitrogen was adjusted to 5:1;

[0046] S6. A back electrode layer is deposited on the back contact layer to obtain a battery. The back electrode layer is a gold (Au) back electrode. During the production, a vacuum thermal evaporation method is used to prepare a gold (Au) back electrode with a thickness of 150 nm on the back contact layer.

[0047] S7. After all coatings are completed, the obtained samples are subjected to vacuum annealing treatment at 200°C for 30 minutes to promote As and B element doping; after the samples are cooled, the entire battery preparation process is completed.

[0048] Example 2

[0049] In another embodiment, S5 can also be a method of obtaining a back contact layer by magnetron sputtering boron or carbon-doped transition metal nitride on the light absorption layer, by depositing a carbon (C)-doped titanium nitride (TiN) film on the etched CdTe:As film by magnetron sputtering. During the deposition process, high-purity Ti target and C target were selected as sputtering sources to introduce C element for doping. The power of the Ti target was maintained at 450W, and the power of the C target was maintained at 60W. A mixed gas of argon (Ar) and nitrogen (N2) was used as the sputtering gas, wherein argon was mainly used to generate sputtering plasma, and nitrogen reacted with the sputtered titanium atoms to generate TiN, and the flow ratio of argon to nitrogen was adjusted to 7:1. The same preparation conditions were used to obtain a CdTe solar cell device with C-doped TiN as the back contact layer.

[0050] Example 3

[0051] In another embodiment, S5 can also be a method of obtaining a back contact layer by magnetron sputtering boron or carbon-doped transition metal nitride on the absorption layer, wherein magnetron sputtering is used to deposit a carbon (C)-doped tungsten nitride (W2N) film on the etched CdTe:As film, and during the deposition process, high-purity W target and C target are selected as sputtering sources to introduce the C element for doping; the power of the W target is maintained at 420W, and the power of the C target is maintained at 60W, and a mixed gas of argon (Ar) and nitrogen (N2) is used as the sputtering gas, wherein argon is mainly used to generate sputtering plasma, and nitrogen reacts with the sputtered tungsten atoms to generate W2N, and the flow ratio of argon to nitrogen is adjusted to 10:1; the same preparation conditions are used to obtain a CdTe solar cell device with C-doped W2N as the back contact layer.

[0052] Example 4

[0053] In another embodiment, S5 can also be a method of obtaining a back contact layer by magnetron sputtering boron or carbon-doped transition metal nitride on the absorption layer, by depositing a carbon (C)-doped tantalum nitride (TaN) film on the etched CdTe:As film by magnetron sputtering. During the deposition process, high-purity Ta target and C target were selected as sputtering sources to introduce C element for doping. The power of the Ta target was maintained at 200W, and the power of the C target was maintained at 60W. A mixed gas of argon (Ar) and nitrogen (N2) was used as the sputtering gas, wherein argon was mainly used to generate sputtering plasma, and nitrogen reacted with the sputtered tantalum atoms to generate TaN, and the flow ratio of argon to nitrogen was adjusted to 10:3. A CdTe solar cell device with C-doped TaN as the back contact layer was obtained under the same preparation conditions.

[0054] Comparative Example 1

[0055] In the comparative embodiment, step S3 adopts a space sublimation method, using cadmium telluride (CdTe) with a purity of up to 99.999% as a source material to deposit and form a CdTe thin film layer. In step S5, the method of forming a back contact layer by co-evaporation deposition of ZnTn:Cu on the absorption layer is also effective. In addition, another method is to co-evaporate and deposit a ZnTn:Cu film on an etched CdTe film, thereby realizing Cu as a back contact layer. Using the conditions prepared by these methods, a CdTe solar cell device with Cu as a back contact layer can be obtained.

[0056] The following table shows the performance parameter data of the cadmium telluride thin film solar cells prepared in Examples 1 to 4 and Comparative 1;

[0057]

[0058] It can be seen from the above test data that the cadmium telluride thin film solar cells manufactured by the methods adopted in Examples 1 to 4 of the present invention have relatively large improvements in open circuit voltage, short circuit current, fill factor and photoelectric conversion efficiency compared with the cadmium telluride thin film solar cells manufactured by the method adopted in Comparative Example 1, thereby improving the carrier collection efficiency of the battery, thereby improving the open circuit voltage and conversion efficiency of the battery.

[0059] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A cadmium telluride solar cell, comprising a TCO layer, a buffer layer, a window layer, a light absorption layer and a back electrode layer, characterized in that: The invention also includes a back contact layer, wherein the back contact layer is located between the light absorbing layer and the back electrode layer, and the back contact layer is made of boron or carbon doped transition metal nitride.

2. The cadmium telluride solar cell according to claim 1, characterized in that: The transition metal nitride is one or more of titanium nitride, zirconium nitride, tantalum nitride, cobalt nitride, tungsten nitride or hafnium nitride.

3. A method for preparing a cadmium telluride solar cell, characterized in that: The following steps are involved: S1. Depositing tin oxide on the provided TCO layer to obtain a buffer layer; S2. Depositing cadmium selenide on the buffer layer to obtain a window layer; S3. depositing arsenic-doped cadmium telluride on the window layer to obtain a light absorbing layer; S4. Obtaining a back contact layer by magnetron sputtering a boron or carbon-doped transition metal nitride on the light absorbing layer; S5. Depositing a back electrode layer on the back contact layer to obtain a battery.

4. The method for preparing a cadmium telluride solar cell according to claim 3, characterized in that: In S4, the method of obtaining the back contact layer by magnetron sputtering boron or carbon doped transition metal nitride on the light absorption layer comprises: S401. Select a sputtering source, select one of boron or carbon, and one of transition metals titanium, zirconium, tantalum, cobalt, tungsten or hafnium in the transition metal nitride as a sputtering source; S402. Using a mixed gas of argon and nitrogen as a sputtering gas, sputter the selected sputtering source onto the light absorbing layer to obtain a back contact layer.

5. The method for preparing a cadmium telluride solar cell according to claim 4, characterized in that: The sputtering source in S401 is composed of high-purity Ti target and TiB2 target, wherein the power of the Ti target is maintained at 450W and the power of the TiB2 target is maintained at 70W.

6. The method for preparing a cadmium telluride solar cell according to claim 4, characterized in that: The sputtering source in S401 is composed of high-purity Ti target and C target, wherein the power of the Ti target is maintained at 450W, and the power of the C target is maintained at 60W.

7. The method for preparing a cadmium telluride solar cell according to claim 4, characterized in that: The sputtering source in S401 is composed of high-purity W target and C target, wherein the power of the W target is maintained at 420W and the power of the C target is maintained at 60W.

8. The method for preparing a cadmium telluride solar cell according to claim 4, characterized in that: The sputtering source in S401 is composed of high-purity Ta target and C target, wherein the power of the Ta target is maintained at 200W, and the power of the C target is maintained at 60W.

9. The method for preparing a cadmium telluride solar cell according to claim 4, characterized in that: The flow ratio of argon to nitrogen in S402 is (1-10):(3-4).

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