CN111430474B - Thin film, solar cell, and preparation method and device thereof - Google Patents

Thin film, solar cell, and preparation method and device thereof Download PDF

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CN111430474B
CN111430474B CN202010328867.5A CN202010328867A CN111430474B CN 111430474 B CN111430474 B CN 111430474B CN 202010328867 A CN202010328867 A CN 202010328867A CN 111430474 B CN111430474 B CN 111430474B
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CN111430474A (en
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李宗雨
丘立安
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Nanjing Xianfeng Material Technology Co ltd
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Chengdu Pioneer Materials Inc
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F77/00—Constructional details of devices covered by this subclass
    • H10F77/30—Coatings
    • H10F77/306—Coatings for devices having potential barriers
    • H10F77/311—Coatings for devices having potential barriers for photovoltaic cells
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F71/00—Manufacture or treatment of devices covered by this subclass
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F77/00—Constructional details of devices covered by this subclass
    • H10F77/10—Semiconductor bodies
    • H10F77/12—Active materials
    • H10F77/126—Active materials comprising only Group I-III-VI chalcopyrite materials, e.g. CuInSe2, CuGaSe2 or CuInGaSe2 [CIGS]
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F77/00—Constructional details of devices covered by this subclass
    • H10F77/10—Semiconductor bodies
    • H10F77/14—Shape of semiconductor bodies; Shapes, relative sizes or dispositions of semiconductor regions within semiconductor bodies
    • H10F77/146—Superlattices; Multiple quantum well structures
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F77/00—Constructional details of devices covered by this subclass
    • H10F77/10—Semiconductor bodies
    • H10F77/16—Material structures, e.g. crystalline structures, film structures or crystal plane orientations
    • H10F77/169—Thin semiconductor films on metallic or insulating substrates
    • H10F77/1694—Thin semiconductor films on metallic or insulating substrates the films including Group I-III-VI materials, e.g. CIS or CIGS
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/541—CuInSe2 material PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
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Abstract

一种薄膜、太阳能电池及其制备方法和装置，属于太阳能电池领域。薄膜具有至少一个叠层单元，且每个叠层单元具有超晶格结构且包括叠置的下述层：铜铟镓硒层；在铜铟镓硒层之上的N型半导体层，所述N型半导体层的材质包括硫化镉、硒化铟或硫化铟；在硫化镉层之上的透明导电氧化物层。当超晶格薄膜具有两个以上的叠层单元时，相邻两个叠层单元之间以铜铟镓硒层与透明导电氧化物层相对贴合的欧姆接触的方式叠置。该薄膜可以用于形成高光电转换效率的太阳能电池。

Figure 202010328867

A thin film, a solar cell and a preparation method and device thereof belong to the field of solar cells. The thin film has at least one stacked unit, and each stacked unit has a superlattice structure and includes the following layers stacked: a copper indium gallium selenide layer; an N-type semiconductor layer on the copper indium gallium selenide layer, the The material of the N-type semiconductor layer includes cadmium sulfide, indium selenide or indium sulfide; and a transparent conductive oxide layer on the cadmium sulfide layer. When the superlattice thin film has more than two stacked units, the two adjacent stacked units are stacked in a manner of ohmic contact in which the copper indium gallium selenide layer and the transparent conductive oxide layer are relatively bonded. The thin film can be used to form solar cells with high photoelectric conversion efficiency.

Figure 202010328867

Description

Thin film, solar cell, and preparation method and device thereof
Technical Field
The application relates to the field of solar cells, in particular to a thin film, a solar cell, and preparation methods and devices of the thin film and the solar cell.
Background
Copper Indium Gallium Selenide (CIGS) has been studied and developed for nearly two decades as a new generation of thin film solar cell applications. Compared with other materials, the copper indium gallium selenide has the main characteristics of high absorption coefficient for visible light and near infrared rays, and the energy band (band gap) of the material can be adjusted correspondingly according to the proportion among atoms of the quaternary alloy. These advantages make CIGS a thin film solar cell material with a wide potential for applications.
Improving the conversion efficiency of CIGS thin film solar cells has been a central concern of the technology because it directly impacts the cost of application and commercial value of the thin film cells.
Disclosure of Invention
In view of the above, the present application is particularly proposed to improve the photoelectric conversion efficiency of the thin film solar cell based on copper indium gallium selenide.
The application is realized as follows:
in a first aspect, embodiments of the present application provide a thin film having at least one stacked unit, and each stacked unit has a superlattice structure and includes the following stacked layers: a P-type semiconductor layer; an N-type semiconductor layer; a transparent conductive oxide layer. When the thin film has two or more stacked units, the adjacent two stacked units are stacked in ohmic contact in which the P-type semiconductor layer and the transparent conductive oxide layer are bonded to each other.
In some optional examples, the P-type semiconductor layer is a copper indium gallium selenide layer; and/or the material of the N-type semiconductor layer comprises cadmium sulfide, indium selenide or indium sulfide.
In some alternative examples, the transparent conductive oxide layer is transparent to visible light and near-infrared light; alternatively, the transparent conductive oxide layer is an aluminum-doped zinc oxide layer or ITO.
In some alternative examples, the laminated unit includes a thickness characteristic of any one or more of: the thickness of the copper indium gallium selenide layer is 50 to 100 nanometers; the thickness of the N-type semiconductor layer is 30-50 nanometers; the transparent conductive oxide layer has a thickness of 40 to 80 nanometers.
In some alternative examples, the copper indium gallium selenide layer has the following atomic ratio characteristics: CuIn(1-x)GaxSe2Wherein x is 0.75-0.7; and/or in the copper indium gallium selenide layer, the copper atoms, the indium atoms, the gallium atoms and the selenium atoms are uniformly distributed, and the 3 sigma value meeting the normal distribution is less than 5%.
In a second aspect, embodiments of the present application provide a solar cell, comprising: a substrate; an electrode layer formed over the substrate; such as the films described above, wherein the copper indium gallium selenide layer is stacked in layered contact with the electrode layer.
In some optional examples, the electrode layer is a metal layer. Optionally, the metal layer comprises a molybdenum layer; and/or the substrate comprises plastic, glass or stainless steel, optionally the substrate comprises polyethylene terephthalate.
In a third aspect, embodiments of the present application provide a method for manufacturing a solar cell, in which an electrode layer and a thin film are formed on a substrate by roll-to-roll multi-cavity sputtering or continuous multi-cavity sputtering.
In some optional examples, the method comprises:
the heated substrate sequentially passes through the electrode target sputtering area, the multi-layer superlattice film sputtering area and the anti-reflection target sputtering area so as to correspondingly sputter an electrode layer, a multi-layer superlattice film and an anti-reflection layer on the substrate layer by layer respectively.
In a fourth aspect, embodiments of the present application provide an apparatus for fabricating a solar cell, including:
a pair of rollers having a first roller and a second roller opposed to each other at a distance, for transferring the substrate wound around the first roller to the second roller by synchronous rotation of the first roller and the second roller;
a sputtering chamber disposed between the first roller and the second roller;
the sputtering chamber is provided with a first cavity, a second cavity and a third cavity which are arranged along the direction from the first roller to the second roller, wherein the first cavity is used for sputtering the electrode layer, the second cavity is used for sputtering the multi-layer superlattice film, and the third cavity is used for sputtering the anti-reflection layer.
The solar cell provided in the example of the application utilizes a CIGS thin film cell structure of superlattice, which is beneficial to improving the conversion efficiency of the cell, so that the cost of generating electricity per watt can be reduced. Meanwhile, the cell also retains the unique advantages of light weight, flexibility and the like of the CIGS thin film cell, so that the CIGS thin film cell is more competitive in large-scale commercialization.
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In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive effort.
FIG. 1 is a schematic diagram of a multilayer thin film structure fabricated by the inventors;
FIG. 2 shows an electron scanning electron micrograph of a cross-section of the multilayer thin-film structural assembly of FIG. 1;
fig. 3 is a schematic structural diagram of a solar cell provided in an embodiment of the present application;
fig. 4 is a schematic structural diagram showing the relative positions of the CIGS film layer and the electrode layer and the substrate of the thin film in the solar cell structure shown in fig. 3;
fig. 5 is a schematic structural diagram of an apparatus for manufacturing a solar cell according to an embodiment of the present disclosure.
Icon: 100-a multilayer thin film structure assembly; 101-a substrate; 102-a back electrode; 103-an absorbing layer; 104-a buffer layer; 105-intrinsic zinc oxide; 106-aluminum doped zinc oxide; 107-an anti-reflective layer; 108-an upper electrode; 109-a transparent conductive layer; 200-solar cell; 201-a substrate; 202-an electrode layer; 203-a film; 301-copper indium gallium selenide layer; 302-a cadmium sulfide layer; 303-aluminum doped zinc oxide; 600-a device; 601-a first roller; 602-a second roller; 603-a sputtering chamber; 604-a first chamber; 605-a second chamber; 606-a third chamber; 607-target material; 608-substrate PET.
Detailed Description
In the present application, all the embodiments, implementations, and features of the present application may be combined with each other without contradiction or conflict. In the present application, conventional equipment, devices, components, etc. are either commercially available or self-made in accordance with the present disclosure. In this application, some conventional operations and devices, apparatuses, components are omitted or only briefly described in order to highlight the importance of the present application.
Referring to fig. 1 and 2, In a study, the inventors fabricated a CIGS thin film solar cell, which is a multi-layered thin film structure assembly 100 having a main structure of a substrate 101 (stainless steel sheet, glass, polymer (e.g., PET), other metal sheet, etc.), a back electrode 102 (typically molybdenum or titanium), an absorber layer 103(p-CIGS), a buffer layer 104 (typically n-CdS, or In) and a buffer layer 104 (typically n-CdS2Se3/In2S3)A transparent conductive layer 109 (typically a bilayer of intrinsic zinc oxide 105 and aluminum doped zinc oxide 106, or ITO), an upper electrode 108 (typically Ni/Al), an optional anti-reflective layer 107 (typically MgF)2). By passingThe material of the substrate 101 is selected in combination with the fabrication process, so that a light and flexible battery can be obtained.
Essentially, such a CIGS solar cell is a large area p-n junction. Under the action of external sunlight, sunlight is absorbed in the p-type semiconductor CIGS thin film, and a large number of Holes (Holes) are generated; while the n-type semiconductor material CdS (or In)2Se3/In2S3) Electrons are generated. Photovoltaics are created by the accumulation of "holes" and "free electrons" (Carriers) within the film by these electrical Carriers (Carriers). If an external circuit, load, etc. forms a closed circuit, a current is formed.
The inventors have discovered that in the multi-layered thin film structure assembly 100, the structure and properties of each film will affect the performance of the battery. For example, small area glass substrates (less than 0.5cm in size) can be obtained by screening the atomic ratio in the CIGS layer and optimizing the selenization process technology2) The photoelectric conversion efficiency can reach 22.9%, and on a flexible high Polymer (PET) substrate, the photoelectric conversion efficiency can reach 20.4%. However, as the area of the cell substrate increases (e.g., beyond 1cm square), the resulting cell conversion efficiency decreases immediately (e.g., down to 10%).
In other words, the conversion efficiency varies greatly for different substrate dimensions on the basis of the same structure. And, the light-to-electricity conversion efficiency is inversely proportional to the p-n junction area. I.e., the p-n junction area increases above the threshold (e.g., 1cm square as described above), the device's photo-electric conversion efficiency continues to decrease significantly as its area further increases. For example, in some examples of the present application, the light-to-electricity conversion efficiency may be at least 22% or more, depending on how many layers of the superlattice cell combination are present, on a 250 cm square substrate. Further, the more the superlattice combinations of CIGS layers are, the more sufficient the light energy can be absorbed, and the photoelectric conversion efficiency can be increased to 30% or more.
Therefore, one of the main disadvantages of the aforementioned multilayer thin-film structure assembly 100 is the low photoelectric conversion efficiency, especially for large sizeAnd (3) components. In the related research of the CIGS battery piece with large size known by the inventor, the photoelectric conversion efficiency is low, and the small-area substrate (0.5-1 cm) is not reached2) The conversion efficiency obtained above (over 20%).
The inventors believe that the above problems exist with CIGS solar cells because: in the structure of the p-n junction of the CIGS based on the small-area substrate, the factors such as the proportion of film components, the uniformity of each atomic proportion, crystal defects in the film and the like are easier to control, and the microstructure of the CIGS is more perfect, so that the accumulation concentration of carriers is relatively higher, and the CIGS has higher photoelectric conversion efficiency in the macro. However, in the case of a large-area substrate, factors such as film composition control, uniformity of each atomic ratio, and crystal defects are not easily controlled, so that a high-quality thin film structure having a p-n junction cannot be obtained. And, therefore, a low-quality thin film structure results in a decrease in carrier concentration.
Therefore, the inventor believes that to improve the photoelectric conversion efficiency of CIGS solar cells fabricated on large-area substrates, the fundamental point of the effort must be to increase the hole and electron carrier concentrations within the thin film, so that the current of the circuit is greatly increased and the photoelectric conversion efficiency is improved under the same photovoltaic voltage.
Based on the above knowledge, the inventors tried to select the following approaches to improve the photoelectric conversion efficiency of CIGS thin film cells:
1. the atomic ratio of Cu, In, Ga and In the CIGS film layer is optimized, so that the energy band Eg of the CIGS is between 1.17eV and 1.20eV (the CIGS absorption layer of the energy band can maximally absorb visible light and near infrared light).
For example, by adjusting the ratio of Ga/(Ga + In) of the CIGS film cross section, the obtained cell has higher conversion efficiency, and the energy band Eg is controlled between 1.04eV and 1.68eV, so that the CIGS film can absorb visible light energy In a wider wavelength range.
In addition, during the optimized manufacturing process of the CIGS thin film, especially when the CIGS thin film is formed on a large-area cell slice, the atomic ratio of the four elements of the CIGS is uniformly distributed on the whole substrate, and particularly, the uniform distribution of the selenium atoms is particularly important in the selenizing process. And experiments show that the more uniform the distribution of chemical components, the higher the overall conversion efficiency is. For example, the concentration distribution of selenium (Se) in the substrate satisfies that the concentration variance 1 σ thereof is less than 2%, and the overall photoelectric conversion efficiency can be improved by 2%.
2. Doping elements such as Na (sodium), K (potassium) and Sb (antimony) in the CIGS thin film can promote the concentration of carriers in the thin film, thereby being beneficial to improving the photoelectric conversion efficiency of the cell.
3. Reducing defects and impurities inside the CIGS thin film, such as grain boundary area, may improve the photoelectric conversion efficiency of the cell. In addition, the more defects the CIGS crystal has, the lower the concentration of hole carriers, thereby reducing the photo-electric conversion efficiency to CIGS. Further, the larger the crystal grain of CIGS, the lower the defect concentration of the thin film, and the more advantageous the photoelectric conversion efficiency.
The crystal size of the CIGS thin film can be increased by improving the temperature of the substrate during the process, which is generally heated to above 680 ℃ in practice and using longer film deposition times, thereby limiting the yield (T-put) of the CIGS thin film cell. However, for flexible CIGS thin film solar cells with high molecular polymers (e.g., PET, polyethylene terephthalate) as the substrate, the substrate cannot be heated to 680 ℃ (structural damage occurs). Therefore, the flexible thin film battery using plastic as a substrate has a lower photoelectric conversion efficiency than a battery using glass or stainless steel as a substrate.
Although the photoelectric conversion efficiency of CIGS-based solar cells can be increased by the above means, it is still significantly lower than that of crystalline silicon-based solar cells.
In view of the above, the inventors have developed a new method for improving the photoelectric conversion efficiency of a CIGS-based solar cell through research. In general, in the present examples, improvements from battery-based structures are selected to improve the conversion efficiency of their batteries. As described above, in the present application, the above-described new method achieves improvement of photoelectric conversion efficiency mainly by increasing the carrier concentration in the P — N junction. And the means for increasing the carrier concentration mainly proposes a CIGS-based superlattice thin film structure.
Thus, in the examples of the present application, it is possible to improve the optical-to-electrical conversion efficiency of the device (e.g., at least up to 22% or more) by adjusting the number of layers of the superlattice cell combination on a 250 cm square substrate. Further, the more the superlattice combinations of CIGS layers are, the more easily the optical energy is sufficiently absorbed, and the photoelectric conversion efficiency can be made to be 30% or more.
The film in the example has at least one laminated unit. Each stacked cell includes a more specific substructure. In general, the stacked unit has a superlattice structure and includes a P-type semiconductor layer, an N-type semiconductor layer, and a transparent conductive oxide layer.
When the film has a plurality of laminated units, the respective laminated units are arranged in a stacked manner. And the two adjacent laminated units are laminated in an ohmic contact mode that the P-type semiconductor layer and the transparent conductive oxide layer are oppositely attached. The ohmic contact refers to a contact between the transparent conductive oxide layer and the copper indium gallium selenide layer (between two films) and a contact between the transparent conductive oxide layer and the N-type semiconductor film, and an I-V curve of the ohmic contact obeys ohm's law. The contact between the CIGS and the thin film of N-type semiconductor material is to form a p-N junction.
In an alternative example, the material of the layers may be defined by:
the P-type semiconductor layer is selected to be a Copper Indium Gallium Selenide (CIGS) layer.
The N-type semiconductor layer is selected from cadmium sulfide (CdS) or cadmium-free chalcogenide (such as indium selenide/In)2Se3Or indium sulfide/In2S3). An N-type semiconductor material is a material that has "residual" free electrons inside it.
The Transparent Conductive Oxide layer (TCO) is made of a material selected from materials that are Transparent to visible light and near-infrared light (e.g., have a transmittance of at least 85%), such as aluminum-doped zinc Oxide (in which a ZnO compound is doped with Al at a concentration of up to1 at%), which has a transmittance of more than 85% for visible light and near-infrared light, and which is less expensive than ITO. Thus, in some examples, ITO may also be used for the aluminum-doped zinc oxide layer.
Corresponding to this, the structure of the stacked unit can be denoted as CIGS/CdS/TCO. When a plurality of stacked units, e.g., three, are present in the film, the structure can be expressed as follows:
CIGS/CdS/TCO/CIGS/CdS/TCO/CIGS/CdS/TCO。
a stacked cell can be used to fabricate single junction CIGS thin film solar cells. In the case of a plurality of ultra-thin (or superlattice) stacked units, the thin film is a multijunction thin film battery consisting of a plurality of extremely thin coating films. The laminated unit of the superlattice structure comprises two different components, and in a thin film formed by a plurality of laminated units, the two components alternately grow in a thin layer of a few nanometers to a dozen nanometers and keep strict periodicity.
In an alternative example, the copper indium gallium selenide layer has a thickness of 50 nanometers to 100 nanometers.
In other examples, the thicknesses of the copper indium gallium selenide layers are 52 nanometers, 56 nanometers, 67 nanometers, 74 nanometers, 88 nanometers and 96 nanometers. The cadmium sulfide layer has a thickness of 30 nanometers to50 nanometers. In other examples, the cadmium sulfide layer has a thickness of 33 nanometers, 36 nanometers, 39 nanometers, 42 nanometers, 47 nanometers, 49 nanometers. The aluminum-doped zinc oxide has a thickness of 40 to 80 nanometers.
In other examples, the aluminum-doped zinc oxide has a thickness of 42 nanometers, 46 nanometers, 49 nanometers, 55 nanometers, 59 nanometers, 73 nanometers, 74 nanometers, 78 nanometers.
Adjusting the composition of the film, particularly the CIGS film, as described above will allow for sufficient absorption of visible and near infrared photons to increase the carrier concentration within the film, macroscopically increasing the photoelectric conversion efficiency in the solar cell. Thus, in the examples of the present application, the cigs layer has the following atomic ratio characteristics: CuIn1-xGaxSe2Wherein x is 0.75-0.7, such as 0.71. 0.72, 0.73, 0.74. And, further, the distribution of the main atoms in the layer can also be controlled, for example, the copper indium gallium selenide layer has a uniform distribution of copper atoms, indium atoms, gallium atoms and selenium atoms, and the 3 σ value satisfying the normal distribution is less than 5%, such as 4.6%, 4.3%, 4.0%, 3.7%, 3.5%, 2.7%, 2.3%, 1.8%.
Based on the thin films described above, referring to fig. 3 and 4, the present application also provides a solar cell 200 including a substrate 201, an electrode layer 202, and a thin film 203. The layers were organized in the following manner: the electrode layer 202 is located between the substrate 201 and the membrane 203. The film 203 includes a plurality of stacked units, each including a copper indium gallium selenide layer 301, a cadmium sulfide layer 302, and aluminum-doped zinc oxide 303, which are sequentially stacked.
The film 203 is arranged in such a way that the copper indium gallium selenide layer of the film is stacked in laminated contact with the electrode layer. Wherein the electrode layer may optionally be a metal layer, such as a molybdenum layer, and the electrode layer is thus a molybdenum electrode. When the molybdenum electrode is doped with trace (such as 0.1 to 0.5 at%) of sodium element, the molybdenum electrode can produce better effect. The substrate may be selected from plastic, glass or stainless steel. Optionally, the substrate comprises polyethylene terephthalate.
Since the film thickness of the CIGS film layer can be limited to several tens of nanometers in the thin film structure having the superlattice property in the above-described solar cell, crystal grains thereof are easily formed in a short time. For example, a plastic (Teflon) substrate can form CIGS crystal grains having a size of about several tens of nanometers at 340 ℃. Therefore, the scheme of the application also has the following characteristics: very low substrate temperatures can be used when sputtering p-type CIGS thin films, and can typically be below 340 degrees celsius. In contrast, the sputtering substrate temperatures currently in commercial use are all above 600 degrees celsius. The process involved in the solution of the present application is therefore a low temperature sputtering, allowing various substrates, such as plastic substrates, to be used for the fabrication of superlattice CIGS thin film solar cells, and such cells have the advantage of being ultra light in weight, flexible and suitable for various application surfaces.
In experiments, when the film thickness of the CIGS film layer reaches the average size of the grain size, the film layer may exhibit a Structure resembling columnar crystals, otherwise known as a "Bamboo" Structure. In such a microstructure, the grain boundary area of the CIGS film layer is reduced, and the reduction in the grain boundary area often means that the defect density in the thin film layer is greatly reduced, so that the holes generated by the excited p-type semiconductor (CIGS) can be prevented from being trapped by the defects, and thus the concentration of the holes is increased.
When multiple layers of CIGS are stacked and the thickness of each CIGS film layer reaches the average grain size, the concentration of carrier holes is much higher than that of single-junction CIGS in the film with superlattice characteristics, so that the photoelectric conversion efficiency is greatly improved. In addition, Quantum effects (Quantum effects) occur when the thickness of the CIGS film layer is below the Mean Free Path of collisions (i.e., λ, typically 50nm or less) within the film by "Holes" generated by photon excitation. Based on this, carrier holes are more easily separated from electrons and are also less easily trapped by defects, thus leading to more surviving holes produced by photon excitation.
The photovoltaic voltage generated by a solar cell with the above superlattice structure and based on a CIGS thin film can be according to VtotalCalculated as N × 0.65 (Volt). Where N is the number of repeating CIGS/CdS/TCO (CdS can also be called Buffer Layer) structures. Since the p-n junctions of the superlattice are actually series independent power sources, each producing 0.65V of photovoltaic, the total voltage output is the series combination of these photovoltaic power sources.
In some examples, the above-described thin film design with superlattice structure is adopted, so that the temperature of the required substrate of the solar cell can be obviously reduced (e.g. from 680 ℃ to 340 ℃, or even lower, e.g. 320 ℃ or 300 ℃), and therefore, the solar cell is suitable for various substrates, and can achieve a more ideal grain structure and improve the conversion efficiency eta.
In connection with the foregoing, the inventors have innovatively proposed, in the present application, a solar cell structure based on a superlattice structure and a CIGS material (superlattice CIGS thin film solar cell) in general. Which has a large-sized structure for easy commercial use and an ideal photoelectric conversion efficiency. Also, the above excellent performance of the solar cell structure benefits from: the p-n junction film thickness in its Structure is similar to the CIGS grain size (e.g., both between 50nm and 100nm in size), resulting in film grains shaped like a "Bamboo Structure" (Bamboo Structure) and corresponding "quantum effects". Based on the synergistic effect of the film grain structure and the quantum effect, the photoelectric conversion efficiency of the CIGS thin film battery with the superlattice under large size is greatly improved.
Examples of solar cells based in part on superlattice thin films of CIGS are given below, and the theoretical photoelectric conversion efficiencies that they can achieve are calculated.
Example 1
CIGS/CdS/ITO superlattice, the photoelectric conversion efficiency is calculated in theory as follows.
Superlattice thin film structures were designed as CIGS100nm/CdS50nm/ITO50nm …. With a total film thickness of 1.0 μm, the above structure has 5 layers of such a repeating structure (the area size is within 250.00 square centimeters). Assuming that the CIGS photoelectric conversion efficiency of each layer is about 10%, the transmittance of ITO to visible light and near infrared is 90%.
The total photoelectric conversion efficiency can be calculated as follows.
η＝0.1+0.9*0.1+0.9*0.9*0.1+0.9*0.9*0.9*0.1+0.9*0.9*0.9*0.9*0.1
＝40.9％。
The total photovoltaic voltage of its output should be Vtotal＝0.65*5＝3.25V。
Even though the CIGS photoelectric conversion efficiency of each layer is 5%, the transmittance of ITO to visible light and near infrared light is 90%. The total photoelectric conversion efficiency was calculated as follows.
η＝0.05+0.9*0.05+0.9*0.9*0.05+0.9*0.9*0.9*0.05
+0.9*0.9*0.9*0.9*0.05＝20.5％。
The total photovoltaic voltage of its output should be Vtotal＝0.65*5＝3.25V。
In contrast, the photovoltaic efficiency of a device (CIGS800nm/CdS50-70nm/ITO150nm) having the same structure described above (meaning that the materials from which the layers are made and the order in which the layers are arranged are the same) but constructed in a non-superlattice form (except that the layers differ in thickness from those in the superlattice and therefore in total thickness) is no greater than 15%.
It should be noted that the above calculation assumes that visible light and near-infrared light are not absorbed by the material and converted into thermal energy, and therefore the above calculation is ideal.
Example 2
CIGS/CdS/ITO superlattice, the photoelectric conversion efficiency is calculated in theory as follows.
Theoretical estimation of conversion efficiency of a superlattice structure of CIGS50nm/CdS50nm/ITO50nm … …:
when the thickness of the CIGS film layer reaches 50nm or less than 50nm, the thickness is close to the mean collision free path lambda of carriers, such as holes, in the CIGS film layer. At this time, the thin film may exhibit a "quantum effect" whose photoelectric conversion efficiency is closer to its theoretical calculation value.
Under the effect of quantum effects, the electron carrier holes or electrons in CIGS semiconductors easily pass through the entire film without "chance" of contacting or running defects such as "lattice holes" (vacaices), dislocations (dislocations), Grain Boundaries (Grain Boundaries), etc., within bamboo-like grains, so that the concentration of the electron carrier is maintained at a relatively high level. As the concentration of the electro-carriers in the film increases, the conversion efficiency increases accordingly.
In order to make it easier for those skilled in the art to implement the above solution, the present application also provides a method for manufacturing the above solar cell and a corresponding apparatus.
In general, the method of the solar cell can be obtained by selectively manufacturing electrode layers and thin films On a substrate through Roll-to-Roll multi-cavity sputtering or continuous (On-line) multi-cavity sputtering. For example, the substrate heated to the design temperature is sequentially passed through the electrode target sputtering region, a superlattice multilayer thin film sputtering region and the antireflection target sputtering region to respectively sputter an electrode layer, a superlattice multilayer thin film and an antireflection layer on the substrate layer by layer.
Correspondingly, referring to fig. 5, an apparatus 600 for fabricating a solar cell includes a pair of rollers and a sputtering chamber 603. The target fixing structure, the negative pressure maintaining structure, the power supply mechanism and the like in the device can be selectively arranged according to requirements. It is noted that the device can be used for flexible solar cells, and correspondingly, the substrate used is also flexible and can thus be rolled and bent.
The counter roller has a first roller 601 and a second roller 602 which are opposed to each other at a distance. The counter roller serves to provide a drive to move the substrate PET608, and the substrate PET608 wound around the first roller 601 is transferred to the second roller 602 by the synchronous rotation of the first roller 601 and the second roller 602. The sputtering chamber 603 is arranged between the first roller 601 and the second roller 602 for depositing a corresponding target 607 by sputtering onto a substrate PET608 in the above-mentioned desired position as it passes through the respective sputtering zone.
To achieve a layered structure of the solar cell, each film layer is fabricated by sputtering a target 607 through a corresponding component in a sputtering chamber. The sputtering chamber 603 has a first chamber 604, a second chamber 605, and a third chamber 606 disposed in the direction from the first roller 601 to the second roller 602. The first chamber 604 is used for sputtering an electrode layer, the second chamber 605 is used for sputtering a multi-layer film, and the third chamber 606 is used for sputtering an anti-reflection layer.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (15)

1. A thin film having at least one stacked unit, each of the stacked units having a superlattice structure and comprising stacked layers of:
the P-type semiconductor layer is a copper indium gallium selenide layer;
the N-type semiconductor layer is made of cadmium sulfide, indium selenide or indium sulfide;
a transparent conductive oxide layer;
when the film is provided with more than two laminated units, the two adjacent laminated units are laminated in an ohmic contact mode that the P-type semiconductor layer is relatively attached to the transparent conductive oxide layer;
the superlattice structure is bi-layered and is composed of the P-type semiconductor layer and the N-type semiconductor layer, which are stacked.
2. The film of claim 1, wherein the transparent conductive oxide layer is transparent to visible light and near infrared light.
3. The film of claim 1 wherein the transparent conductive oxide layer is an aluminum-doped zinc oxide layer.
4. The film of claim 1, wherein the laminate unit comprises a thickness characteristic of any one or more of:
the thickness of the copper indium gallium selenide layer is 50 to 100 nanometers;
the thickness of the N-type semiconductor layer is 30-50 nanometers;
the transparent conductive oxide layer has a thickness of 40 to 80 nanometers.
5. The film of claim 1 or 4, wherein the CIGS layer has the following atomic ratio characteristics: CuIn1-xGaxSe2Wherein x is 0.75-0.7.
6. The film of claim 1 or 4, wherein the CIGS layer has a uniform distribution of Cu atoms, in atoms, Ga atoms, and Se atoms, and a 3 σ value satisfying a normal distribution of less than 5%.
7. A solar cell, comprising:
a substrate;
an electrode layer formed over the substrate;
the film according to any one of claims 1 to 6, wherein the CIGS layer of the film is stacked in stacked contact with the electrode layer.
8. The solar cell of claim 7, wherein the electrode layer is a metal layer;
and/or the substrate comprises plastic, glass, or stainless steel.
9. The solar cell of claim 8, wherein the metal layer comprises a molybdenum layer.
10. The solar cell of claim 8, wherein the substrate comprises polyethylene terephthalate.
11. A method of manufacturing a solar cell according to claim 7 or 8 or 9 or 10, characterized in that the electrode layer and the thin film according to any of claims 1 to 6 are manufactured on the substrate by continuous multi-chamber sputtering.
12. The method of claim 11, wherein the continuous multi-chamber sputtering comprises roll-to-roll multi-chamber sputtering.
13. The method of claim 11, wherein the method comprises:
and enabling the heated substrate to sequentially pass through an electrode target sputtering area, a superlattice multilayer film sputtering area and an anti-reflection target sputtering area so as to correspondingly sputter an electrode layer, a multilayer superlattice film and an anti-reflection layer on the substrate layer by layer respectively, wherein the multilayer superlattice film is the film.
14. The method of claim 13, wherein the temperature of the substrate is less than 340 degrees celsius.
15. An apparatus for fabricating the solar cell of claim 7, 8, 9 or 10, comprising:
a pair of rollers having a first roller and a second roller opposed to each other at a distance, for transferring the substrate wound around the first roller to the second roller by synchronous rotation of the first roller and the second roller;
a sputtering chamber disposed between the first roller and the second roller;
the sputtering chamber is provided with a first cavity, a second cavity and a third cavity which are arranged along the direction from the first roller to the second roller, wherein the first cavity is used for sputtering the electrode layer, the second cavity is used for sputtering the multi-layer superlattice film, and the third cavity is used for sputtering the anti-reflection layer;
wherein the multilayer superlattice thin film is as claimed in any one of claims 1 to 6.
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