The present disclosure relates to the field of solar cells, and in particular, to a cadmium telluride solar cell and a preparation method thereof.
Compared with monocrystalline silicon solar cells, cadmium telluride solar cells have the advantages of convenient fabrication, low costs, and light weight. Cadmium telluride (CdTe) thin-film solar cells, or referred to as CdTe cells for short, are a type of thin-film solar cells based on a heterojunction of p-type CdTe and n-type cadmium sulfide (CdS). Generally, a standard CdTe thin-film solar cell includes five layers: a back electrode, a back contact layer, a CdTe absorbing layer, a CdTe window layer, and a transparent conductive oxide (TCO) layer. The production costs of the CdTe thin-film solar cells are much lower than those of solar cell technologies using crystalline silicon and other materials. In addition, the CdTe thin-film solar cells are very compatible with the solar spectrum, and can absorb 95% or more of sunlight. On the basis of extensive and in-depth application research, CdTe cells have developed from laboratory research to large-scale industrial production. Conventional cadmium telluride processes adopt CdS/CdTe, which has the following disadvantages. First, the use of CdS reduces the absorption of short-wavelength light, reducing the performance of the cell. Second, the CdS used is toxic, which is harmful to the environment and working personnel, and conventionally, chemical bath deposition (CBD) is mostly used for preparing CdS, which produces a lot of waste liquid, and is difficult to control. Third, because a good ohmic contact needs to be formed between the CdTe layer and the back contact layer to achieve high efficiency of solar cells, the interface between the CdTe layer and the back contact layer of the CdTe cell is usually processed by copper diffusion. However, copper will diffuse into the CdS layer through the CdTe layer and form deep-level defects, destroying the p-n junction of CdS/CdTe, resulting in greatly reduced stability of solar cells and continuous degradation of cell performance.
In view of the foregoing disadvantages in the related process, an object of the present disclosure is to provide a cadmium telluride solar cell and a preparation method thereof to resolve the problems of low conversion efficiency, low short-circuit current density of a cell, and poor initial performance and long-term stability of a cell in a cell structure of cadmium sulfide/cadmium telluride used in the related art.
In order to accomplish the foregoing object and other related objects, the present disclosure provides a method for preparing a cadmium telluride solar cell, including at least the following steps:
Optionally, a method for forming the light absorbing layer in the step 2) includes:
Further, a method for forming the laminated structure of cadmium selenide and cadmium telluride in the step 2-1) includes: first forming a cadmium selenide layer on the surface of the window layer away from the substrate layer by CSS; and then forming a cadmium telluride layer on a surface of the cadmium selenide layer by CSS, to form the laminated structure of cadmium selenide and cadmium telluride.
Further, the cadmium selenide layer has a thickness of 100-1700 nm, and the cadmium telluride layer has a thickness of 1300-3900 nm.
Optionally, a method for forming the laminated structure of cadmium selenide and cadmium telluride in the step 2-1) includes: first forming a cadmium selenide layer on the surface of the window layer away from the substrate layer by CSS; then forming a cadmium telluride layer on a surface of the cadmium selenide layer by CSS, to form a laminated substructure of cadmium selenide and cadmium telluride; and repeating the operations of forming a laminated substructure of cadmium selenide and cadmium telluride at least once on the laminated substructure of cadmium selenide and cadmium telluride, to form the laminated structure of cadmium selenide and cadmium telluride.
Further, the cadmium selenide layer has a thickness of 25-450 nm, the cadmium telluride layer has a thickness of 400-1000 nm, and the laminated structure of cadmium selenide and cadmium telluride includes three to six laminated substructures of cadmium selenide and cadmium telluride.
Optionally, in the step 2-2), the activation annealing is carried out at a temperature of 350-600° C. for 5-40 min.
Optionally, between the step 2) and the step 3), the method further includes performing copper diffusion on the structure obtained in the step 2) to diffuse copper ions into the surface of the light absorbing layer away from the window layer.
Further, the copper diffusion includes: immersing the structure obtained in the step 2) into a 0.02-0.15 mmol copper chloride solution for 15-180 s, rinsing, and drying.
Optionally, the window layer is formed in the step 1) by magnetron sputtering, the back electrode layer is formed in the step 3) by magnetron sputtering, and the back electrode layer is made of one or more selected from the group consisting of molybdenum, aluminum, and chromium.
Optionally, in the step 1), magnesium is doped in an amount of 0-8 mol % in the magnesium-doped zinc oxide; and in the step 2), selenium is doped in an amount of 3-20 mol % in the light absorbing layer.
The present disclosure further provides a cadmium telluride solar cell, including at least:
Optionally, copper ions are diffused into the surface of the light absorbing layer away from the window layer.
Optionally, the back electrode layer has a thickness of 220-250 nm, the window layer has a thickness of 40-70 nm, the light absorbing layer has a thickness of 2.0-4.0 μm, the substrate layer is made of fluorine-doped tin oxide, conductive glass, titanium oxide, or aluminum-doped zinc oxide, and the back electrode layer is made of one or more selected from the group consisting of molybdenum, aluminum, and chromium.
As described above, the present disclosure provides a method for preparing a cadmium telluride solar cell. In this method, a light absorbing layer is a composite structure of cadmium selenide, selenium-doped cadmium telluride, and cadmium telluride. The composite structure effectively reduces the energy band of cadmium telluride, so that the absorption of light with wavelengths of 700-900 nm by the cell is greatly increased, which allows the solar cell to absorb long-wavelength and short-wavelength light to the maximum, increases the short-circuit current density of the cell, and improves the efficiency of the cell. In addition, a window layer of the solar cell is made of magnesium-doped zinc oxide, and the layer, as a buffer layer in the solar cell, can buffer the contact between a cadmium selenide layer and a substrate layer, to reduce the recombination of charge carriers between interfaces, thereby further increasing the current density. Finally, the composite layer of cadmium selenide, selenium-doped cadmium telluride, and cadmium telluride that has a selenium-doped gradient can effectively prevent the diffusion of copper ions to the window layer of magnesium-doped zinc oxide, and reduce the formation of deep-level defects, thereby improving the initial performance and long-term stability of the solar cell. Moreover, this method has a simple operation and a simple process that is easy to control.
The implementation mode of the present disclosure will be described below through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present disclosure according to contents disclosed by the specification. The present disclosure can also be implemented or applied through other different specific implementation modes. Various modifications or changes can also be made to all details in the specification based on different points of view and applications without departing from the spirit of the present disclosure. Refer to
Referring to
As shown in the step S1 in
For example, the substrate layer 1 is made of fluorine-doped tin oxide, conductive glass, titanium oxide, or aluminum-doped zinc oxide, and the substrate layer can be used as a front electrode of the solar cell to conduct electrons and block holes; and a film can be plated on the substrate layer 1 as a substrate to conduct electrons and block holes.
For example, the window layer 2 may be formed by magnetron sputtering, or may be formed by screen printing or radio frequency sputtering; and the window layer 2 has a thickness of 40-70 nm. Preferably, the window layer 2 is made of magnesium-doped zinc oxide with magnesium doped in an amount of 0-8 mol %.
As shown in the step S2 in
In this embodiment, the light absorbing layer 3 is a composite structure of cadmium selenide, selenium-doped cadmium telluride, and cadmium telluride. The composite structure effectively occurs energy offset with the valance band of cadmium telluride, so that the absorption of light with wavelengths of 700-900 nm by the cell is greatly increased, which allows the solar cell to absorb long-wavelength and short-wavelength light to the maximum, increases the short-circuit current density of the cell, and improves the efficiency of the cell. In addition, the window layer 2 of the solar cell is made of magnesium-doped zinc oxide, and the layer, as a buffer layer in the solar cell, can buffer the contact between the cadmium selenide layer and the substrate layer 1, to reduce the recombination of charge carriers between interfaces, thereby further increasing the current density.
For example, selenium is doped in an amount of 3-20 mol % in the light absorbing layer 3.
For example, a method for forming the light absorbing layer 3 includes:
Preferably, in the step 2-1), the laminated structure 30 of cadmium selenide and cadmium telluride may be formed at once or in multiple repetitions. Specifically, a method of forming at once is described as follows.
Refer to
A method of forming in multiple repetitions is described as follows.
Refer to
For example, in the step 2-2), the activation annealing is carried out at a temperature of 350-600° C. for 5-40 min.
In this embodiment, a composite layer of cadmium selenide, selenium-doped cadmium telluride, and cadmium telluride that has a certain selenium-doped gradient with excellent performance is formed through the deposition of the laminated structure 30 of cadmium selenide and cadmium telluride with activation annealing. This method can achieve the homogenization and controllability of the selenium-doped cadmium telluride layer, thereby further increasing the photocurrent and improving the short-circuit current density of the solar cell.
For example, referring to
Generally, cadmium telluride solar cells are processed with copper diffusion to improve the efficiency of the cells. Cadmium sulfide is usually used as a window layer in the related art. During the diffusion, copper ions diffuse into the cadmium sulfide layer due to their characteristics to replace cadmium vacancies, thereby forming deep-level defects and destroying the p-n junction of cadmium sulfide and cadmium telluride, resulting in poor performance of the cell. In this embodiment, the selenium-doped cadmium telluride layer is used. Because selenium is much more soluble in cadmium telluride than sulfur, a composite layer of cadmium selenide, selenium-doped cadmium telluride, and cadmium telluride that has a certain selenium-doped gradient with excellent performance is formed through the deposition of the laminated structure of cadmium selenide and cadmium telluride with activation annealing, which can effectively prevent the diffusion of copper ions to the window layer of magnesium-doped zinc oxide, and reduce the formation of deep-level defects, thereby improving the initial performance and long-term stability of the solar cell.
As shown in the step S3 in
For example, the back electrode layer 4 may be formed by, but not limited to, magnetron sputtering, and the back electrode layer 4 is made of one or more selected from the group consisting of molybdenum, aluminum, and chromium.
By using the method for preparing a cadmium telluride solar cell in this embodiment, the highest recorded cell parameters can be obtained by optimizing each parameter, respectively a conversion efficiency of 17.02%, an open-circuit voltage of 823 mV, a short-circuit current density of 27.86 mA/cm2, and a fill factor of 74.2%.
The present disclosure further provides a cadmium telluride solar cell structure. The structure may be prepared by the preparation method in Embodiment 1, or may be prepared by other methods. This is not limited herein.
Still referring to
The light absorbing layer 3 is a composite structure of cadmium selenide, selenium-doped cadmium telluride, and cadmium telluride. The composite structure effectively reduces the energy band of cadmium telluride, so that the absorption of light with wavelengths of 700-900 nm by the cell is greatly increased, which allows the solar cell to absorb long-wavelength and short-wavelength light to the maximum, increases the short-circuit current density of the cell, and improves the efficiency of the cell. In addition, the window layer 2 of the solar cell is made of magnesium-doped zinc oxide, and the layer, as a buffer layer in the solar cell, can buffer the contact between the cadmium selenide layer and the substrate layer 1, to reduce the recombination of charge carriers between interfaces, thereby further increasing the current density.
For example, copper ions 5 are diffused into the surface of the light absorbing layer 3 away from the window layer 2.
Generally, cadmium telluride solar cells are processed with copper diffusion to improve the efficiency of the cells. Cadmium sulfide is usually used as a window layer in the related art. During the diffusion, copper ions diffuse into the cadmium sulfide layer due to their characteristics to replace cadmium vacancies, thereby forming deep-level defects and destroying the p-n junction of cadmium sulfide and cadmium telluride, resulting in poor performance of the cell. In this embodiment, the light absorbing layer is a composite structure of cadmium selenide, selenium-doped cadmium telluride, and cadmium telluride, which can effectively prevent the diffusion of copper ions to the window layer of magnesium-doped zinc oxide, and reduce the formation of deep-level defects, thereby improving the initial performance and long-term stability of the solar cell.
For example, the back electrode layer 4 has a thickness of 220-250 nm, the window layer 2 has a thickness of 40-70 nm, the light absorbing layer 3 has a thickness of 2.0-4.0 μm, the substrate layer 1 is made of fluorine-doped tin oxide, conductive glass, titanium oxide, or aluminum-doped zinc oxide, and the back electrode layer 4 is made of one or more selected from the group consisting of molybdenum, aluminum, and chromium.
As described above, the present disclosure provides a method for preparing a cadmium telluride solar cell. In this method, a light absorbing layer is a composite structure of cadmium selenide, selenium-doped cadmium telluride, and cadmium telluride. The composite structure effectively reduces the energy band of cadmium telluride, so that the absorption of light with wavelengths of 700-900 nm by the cell is greatly increased, which allows the solar cell to absorb long-wavelength and short-wavelength light to the maximum, increases the short-circuit current density of the cell, and improves the efficiency of the cell. In addition, a window layer of the solar cell is made of magnesium-doped zinc oxide, and the layer, as a buffer layer in the solar cell, can buffer the contact between a cadmium selenide layer and a substrate layer, to reduce the recombination of charge carriers between interfaces, thereby further increasing the current density. Finally, the composite layer of cadmium selenide, selenium-doped cadmium telluride, and cadmium telluride that has a selenium-doped gradient can effectively prevent the diffusion of copper ions to the window layer of magnesium-doped zinc oxide, and reduce the formation of deep-level defects, thereby improving the initial performance and long-term stability of the solar cell. Moreover, this method has a simple operation and a simple process that is easy to control. Therefore, the present disclosure effectively overcomes various disadvantages in the related art, and has a high value in industrial use.
The foregoing embodiments merely exemplify the principles and effects of the present disclosure, but are not intended to limit the present disclosure. Any person skilled in the art may make modifications or changes on the foregoing embodiments without departing from the spirit and scope of the present disclosure. Therefore, all equivalent modifications or changes made by a person of ordinary skill in the art without departing from the spirit and technical idea of the present disclosure shall be covered by the claims of the present disclosure.
Number | Date | Country | Kind |
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201910865180.2 | Sep 2019 | CN | national |
Filing Document | Filing Date | Country | Kind |
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PCT/CN2020/115092 | 9/14/2020 | WO |