KR102596328B1 - Preparation method for CZTS thin film solar cell absorbing layer, CZTS thin film solar cell absorbing layer prepared therefrom - Google Patents

Abstract

The present invention relates to a method of manufacturing a CZTS-based thin-film solar cell light-absorbing layer and a CZTS-based thin-film solar cell light-absorbing layer manufactured therefrom, specifically, i) forming a first electrode layer on a substrate, ii) the first electrode layer. 1 forming a zinc (Zn) precursor layer on the electrode layer, iii) forming a copper (Cu) precursor layer on the zinc (Zn) precursor layer, iv) tin on the copper (Cu) precursor layer ( Sn) forming a precursor layer, and v) forming an alkali metal compound layer, wherein forming the alkali metal compound layer includes the first electrode layer and zinc. A first alkali metal compound layer formed between the (Zn) precursor layers, a second alkali metal compound layer formed between the zinc (Zn) precursor layer and the copper (Cu) precursor layer, the copper (Cu) precursor layer, and tin ( Sn) relates to a method of manufacturing a CZTS-based thin film solar cell light absorption layer, characterized in that at least two of the third alkali metal compound layers are formed between the precursor layers.

Description

Manufacturing method of CZTS thin film solar cell light absorption layer, CZTS thin film solar cell light absorption layer manufactured therefrom {Preparation method for CZTS thin film solar cell absorbing layer, CZTS thin film solar cell absorbing layer prepared therefrom}

The present invention relates to a method for manufacturing a CZTS-based thin film solar cell light absorption layer, and a CZTS-based thin film solar cell light absorption layer manufactured therefrom.

Solar cells, which can produce electricity directly from sunlight, can be said to be the most attracting future energy production method because they can safely produce clean energy. These solar cells have been developed focusing on silicon solar cells using silicon (Si) as the main material and CIS or CIGS thin-film solar cells with a composition of Cu(In,Ga)Se _2. However, they are more advanced than these silicon solar cells and thin-film solar cells. There is growing interest in flexible thin-film solar cells, which are easy to process, have low manufacturing costs, and can be applied in various forms.

Flexible thin-film solar cells are thin and light, so they can be applied to buildings and automobiles, and are easy to transport and install, enabling expanded application in application fields such as building integrated photovoltaics (BIPV) and mobile fields. In addition, manufacturing costs can be lowered by adopting low-cost flexible substrates, which can contribute to the expansion of the renewable energy market by shortening energy pay-back time.

However, in order to realize a low manufacturing cost of a flexible thin film solar cell, the application of low-cost materials in addition to a flexible substrate is necessary.

In this regard, instead of indium (In) and gallium (Ga), which are expensive raw materials used in CIS or CIGS thin film solar cells, zinc (Zn) and tin (Sn), which are elements with abundant reserves and are relatively inexpensive, are used. Copper-zinc-tin-sulfur-selenium (CZTS, CZTSe, CZTSSe)-based (hereinafter referred to as CZTS-based) materials, such as Cu ₂ ZnSnS ₄ (CZTS) or Cu ₂ ZnSnSe ₄ (CZTSe), are attracting attention as materials for the light absorption layer of solar cells. .

However, while solar cells using CZTS-based materials as light absorption layers have the advantage of being manufactured at low cost, their light efficiency is low, and research is being conducted to improve this.

In order to improve the efficiency of solar cells using CZTS-based materials as the light absorption layer, control of the secondary phase within the light absorption layer is necessary. The secondary phase generated within the light absorption layer can become another current pass for the light-generated current inside the device, and as a result, the shunt resistance decreases, which results in a decrease in the filling rate, ultimately leading to a decrease in the shunt resistance. This reduces efficiency. As a method to suppress the generation of such secondary phases, it is known that alkali metal elements can suppress the generation of secondary phases by occupying lattice sites of copper during the CZTS-based light absorption layer formation process.

As a related conventional technology, Korean Patent Publication No. 10-2018-0034248 discloses a flexible CZTS-based thin film solar cell using sodium hydroxide and a method for manufacturing the same, specifically comprising the steps of preparing a substrate; forming a rear electrode on the substrate; and doping the back electrode with a solution containing sodium (Na). Before forming the CZTS precursor thin film through the method, the sodium electrode on which the molybdenum electrode is formed is disclosed. The effect of improving the electrical properties of a CZTS-based thin film, which is the light absorption layer of a solar cell, is disclosed by simply doping a sodium-free substrate using a sodium-containing solution.

However, in order for CZTS-based thin film solar cells to enter the market, further technology development for higher efficiency is needed.

If the alkali metal element is not uniformly distributed throughout the light absorption layer during the formation process of the CZTS-based light absorption layer, the effect of suppressing secondary phase generation may be reduced. Therefore, it is very important for high efficiency to uniformly distribute the alkali metal compound layer during the precursor formation process so that the alkali metal element can be uniformly distributed during the formation process of the CZTS-based light absorption layer.

To solve this problem, the present inventors designed a precursor layer to include an alkali metal compound layer in a multi-layer structure to manufacture a light absorption layer, developed a CZTS-based thin film solar cell with improved photoelectric conversion efficiency, and completed the present invention.

Republic of Korea Patent Publication No. 10-2018-0034248

The purpose of the present invention is to provide a method for manufacturing a CZTS-based thin film solar cell light absorption layer and a CZTS-based thin film solar cell light absorption layer manufactured therefrom.

In order to achieve the above purpose,

In one aspect of the present invention

i) forming a first electrode layer on a substrate, ii) forming a zinc (Zn) precursor layer on the first electrode layer, iii) forming a copper (Cu) precursor layer on the zinc (Zn) precursor layer. forming a precursor layer comprising, iv) forming a tin (Sn) precursor layer on the copper (Cu) precursor layer, and v) forming an alkali metal compound layer. ,

The step of forming the alkali metal compound layer is,

A first alkali metal compound layer formed between the first electrode layer and the zinc (Zn) precursor layer, a second alkali metal compound layer formed between the zinc (Zn) precursor layer and the copper (Cu) precursor layer, and the copper (Cu ) A method for manufacturing a CZTS-based thin film solar cell light absorption layer is provided, characterized in that at least two of the third alkali metal compound layer formed between the precursor layer and the tin (Sn) precursor layer are formed.

At this time, the step of forming the alkali metal compound layer is

The first alkali metal compound layer or the second alkali metal compound layer may be formed, and the third alkali metal compound layer may be formed.

In addition, the step of forming the alkali metal compound layer is

The first alkali metal compound layer and the third alkali metal compound layer may be formed.

In addition, the step of forming the alkali metal compound layer,

A fourth alkali metal compound layer may be further formed on the tin (Sn) precursor layer.

The alkali metal compound layer may include one or more alkali metals selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs).

The alkali metal compound layer may have a thickness of 2 nm to 20 nm.

The substrate may be a flexible substrate.

The manufacturing method may further include manufacturing a light absorption layer by heat-treating the precursor layer in an atmosphere in which at least one of sulfur (S) and selenium (Ce) is supplied.

The manufacturing method may further include performing pretreatment to remove oxygen on the substrate before forming the first electrode layer on the substrate.

The manufacturing method can form at least one light absorption layer selected from the group consisting of copper zinc tin sulfide (CZTS), copper zinc tin selenium (CZTSe), and copper zinc tin sulfur (CZTSSe).

The above manufacturing method can form a light absorption layer with a thickness of 0.3 μm to 3 μm.

Additionally, in another aspect of the present invention,

A zinc (Zn) precursor layer disposed on the substrate on which the first electrode is formed; A copper (Cu) precursor layer disposed on the zinc (Zn) precursor; A tin (Zn) precursor layer disposed on the copper (Cu) precursor; And an alkali metal compound layer,

The alkali metal compound layer is,

A first alkali metal compound layer disposed between the first electrode layer and the zinc (Zn) precursor layer, a second alkali metal compound layer disposed between the zinc (Zn) precursor layer and the copper (Cu) precursor layer, and the copper (Cu ) A precursor structure for manufacturing a CZTS-based thin film solar cell light absorption layer is provided, including at least two of the third alkali metal compound layer disposed between the precursor layer and the tin (Sn) precursor layer.

At this time, the precursor structure may further include a fourth alkali metal compound layer disposed on the tin (Zn) precursor layer.

The thickness of the zinc (Zn) precursor layer is 60 nm to 310 nm, the thickness of the copper (Cu) precursor layer is 40 nm to 220 nm, and the thickness of the tin (Sn) precursor layer is 70 nm to 370 nm. You can.

The precursor structure may have Cu/Zn+Sn, an element ratio of copper (Cu) to zinc (Zn) and tin (Sn), of 0.6 to 1.0.

Zn/Sn, the elemental ratio of zinc (Zn) to tin (Sn), may be 1.0 to 1.6.

Additionally, in another aspect of the present invention,

A CZTS-based thin film manufactured by the above manufacturing method and comprising at least one member selected from the group consisting of copper zinc tin sulfide (CZTS), copper zinc tin selenium (CZTSe), and copper zinc tin sulfur (CZTSSe). A solar cell light absorption layer is provided.

Additionally, in another aspect of the present invention,

A CZTS-based thin film solar cell including the light absorption layer is provided.

At this time, the CZTS-based thin film solar cell may be a flexible thin film solar cell formed on a flexible substrate.

The present invention includes a precursor layer for manufacturing a light absorption layer and an alkali metal compound layer with a multi-layer structure, thereby suppressing the generation of sulfuride (S), selenide (Se), and secondary phases in the light absorption layer formed after the sulfurization and selenization heat treatment process. , By ensuring that the CZTS-based light absorption layer is formed uniformly, the efficiency of the CZTS-based thin film solar cell can be improved.

Additionally, by forming the CZTS-based light absorption layer on a flexible substrate, a CZTS-based flexible thin film solar cell can be formed.

Figure 1 is a process flow chart for manufacturing a light absorption layer of a CZTS-based thin film solar cell according to Example 1 of the present invention.
Figure 2 is a cross-sectional view schematically showing a precursor structure for manufacturing a CZTS-based thin film solar cell in Example 1 of the present invention.
Figure 3 is a process flow chart for manufacturing the light absorption layer of the CZTS-based thin film solar cell of Example 2 of the present invention.
Figure 4 is a cross-sectional view schematically showing a precursor structure for manufacturing a CZTS-based thin film solar cell in Example 2 of the present invention.
Figure 5 is a process flow chart for manufacturing the light absorption layer of the CZTS-based thin film solar cell in Example 3 of the present invention.
Figure 6 is a cross-sectional view schematically showing a precursor structure for manufacturing a CZTS-based thin film solar cell in Example 3 of the present invention.
Figure 7 is a process flow chart for manufacturing the light absorption layer of the CZTS-based thin film solar cell in Example 4 of the present invention.
Figure 8 is a cross-sectional view schematically showing a precursor structure for manufacturing a CZTS-based thin film solar cell in Example 4 of the present invention.
Figure 9 is a process flow chart for manufacturing the light absorption layer of the CZTS-based thin film solar cell in Example 5 of the present invention.
Figure 10 is a cross-sectional view schematically showing a precursor structure for manufacturing a CZTS-based thin film solar cell in Example 5 of the present invention.
Figure 11 is a flow chart of a manufacturing method of a flexible thin film solar cell according to comparative examples and examples of the present invention.
Figure 12 is a side view schematically showing a CZTS-based thin film solar cell according to an embodiment of the present invention.
Figure 13 is a flowchart of the manufacturing method of a thin film solar cell according to Comparative Example 1 of the present invention.
Figure 14 is a cross-sectional view schematically showing a thin film solar cell according to Comparative Example 1 of the present invention.
Figure 15 is a flowchart of the manufacturing method of a thin film solar cell according to Comparative Example 2 of the present invention.
Figure 16 is a cross-sectional view schematically showing a thin film solar cell according to Comparative Example 2 of the present invention.
Figure 17 shows a cross-sectional image of the precursor layer included in the thin film solar cell according to Example 1 of the present invention by transmission electron microscopy (TEM) and elemental composition distribution by energy dispersive spectroscopy (EDS). These are analysis images and graphs.
Figure 18 shows a cross-sectional image of the precursor layer included in the thin film solar cell according to Example 2 of the present invention by transmission electron microscopy (TEM) and elemental composition distribution by energy dispersive spectroscopy (EDS). These are analysis images and graphs.
Figure 19 shows a cross-sectional image of the precursor layer included in the thin film solar cell according to Example 3 of the present invention by transmission electron microscopy (TEM) and elemental composition distribution by energy dispersive spectroscopy (EDS). These are analysis images and graphs.
Figure 20 shows a cross-sectional image of the precursor layer included in the thin film solar cell according to Example 4 of the present invention by transmission electron microscopy (TEM) and elemental composition distribution by energy dispersive spectroscopy (EDS). These are analysis images and graphs.
Figure 21 shows a cross-sectional image of the precursor layer included in the thin film solar cell according to Example 5 of the present invention by transmission electron microscopy (TEM) and elemental composition distribution by energy dispersive spectroscopy (EDS). These are analysis images and graphs.
Figure 22 shows a cross-sectional image of the precursor layer included in the thin film solar cell according to Comparative Example 1 by transmission electron microscopy (TEM) and analysis of elemental composition distribution by energy dispersive spectroscopy (EDS). Images and graphs.
Figure 23 shows a cross-sectional image of the precursor layer included in the thin film solar cell according to Comparative Example 2 by transmission electron microscopy (TEM) and analysis of elemental composition distribution by energy dispersive spectroscopy (EDS). Images and graphs.
Figure 24 is a current-voltage characteristic graph of each of the highest efficiency samples of Comparative Examples to Examples of the present invention.
25 shows 4 samples of the comparative example of the present invention, 4 samples of Example 1, 4 samples of Example 2, 4 samples of Example 3, 4 samples of Example 4, and 4 samples of Example 5. This is a statistical analysis graph of efficiency according to sample.
26 shows 4 samples of the comparative example of the present invention, 4 samples of Example 1, 4 samples of Example 2, 4 samples of Example 3, 4 samples of Example 4, and 4 samples of Example 5. This is a statistical analysis graph of open-circuit voltage according to sample.
27 shows 4 samples of the comparative example of the present invention, 4 samples of Example 1, 4 samples of Example 2, 4 samples of Example 3, 4 samples of Example 4, and 4 samples of Example 5. This is a statistical analysis graph of short-circuit current according to the sample.
28 shows 4 samples of the comparative example of the present invention, 4 samples of Example 1, 4 samples of Example 2, 4 samples of Example 3, 4 samples of Example 4, and 4 samples of Example 5. This is a statistical analysis graph of the filling rate according to the sample.

Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings. However, the embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Additionally, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the relevant technical field. Accordingly, the shapes and sizes of elements in the drawings may be exaggerated for clearer explanation, and elements indicated by the same symbol in the drawings are the same element. In addition, the same symbols are used throughout the drawings for parts that perform similar functions and actions. In addition, throughout the specification, “including” a certain element means that other elements may be further included, rather than excluding other elements, unless specifically stated to the contrary.

In one aspect of the present invention,

i) forming a first electrode layer on a substrate, ii) forming a zinc (Zn) precursor layer on the first electrode layer, iii) forming a copper (Cu) precursor layer on the zinc (Zn) precursor layer. forming a precursor layer comprising, iv) forming a tin (Sn) precursor layer on the copper (Cu) precursor layer, and v) forming an alkali metal compound layer. ,

The step of forming the alkali metal compound layer is,

A first alkali metal compound layer formed between the first electrode layer and the zinc (Zn) precursor layer, a second alkali metal compound layer formed between the zinc (Zn) precursor layer and the copper (Cu) precursor layer, and the copper (Cu ) A method for manufacturing a CZTS-based thin film solar cell light absorption layer is provided, characterized in that at least two of the third alkali metal compound layer formed between the precursor layer and the tin (Sn) precursor layer are formed.

Hereinafter, the manufacturing method of the CZTS-based thin film solar cell light absorption layer provided in one aspect of the present invention will be described in detail with reference to the drawings.

FIG. 11 is a flowchart of a manufacturing method of a CZTS-based thin film solar cell, and FIG. 12 is a schematic diagram schematically showing a CZTS-based thin film solar cell manufactured by the method of FIG. 11.

Referring to FIG. 11, after forming a first electrode 200 on the substrate 100 and forming a precursor layer 300 on the first electrode 200, a light absorption layer ( 400), as shown in FIG. 12, a substrate 100, a first electrode 200 disposed on the substrate 100, a light absorption layer 400 disposed on the first electrode 200, A CZTS-based thin film solar cell including a second electrode 700 disposed on the light absorption layer 400 can be formed.

A method of manufacturing a CZTS-based thin film solar cell light absorption layer provided in one aspect of the present invention includes forming the precursor layer 300, wherein the precursor layer 300 is formed by forming a first layer on a substrate. forming an electrode layer, ii) forming a zinc (Zn) precursor layer on the first electrode layer, iii) forming a copper (Cu) precursor layer on the zinc (Zn) precursor layer, iv) It includes forming a tin (Sn) precursor layer on a copper (Cu) precursor layer, and v) forming an alkali metal compound layer.

1 to 10 are cross-sectional views schematically showing a process flow chart for manufacturing a light-absorbing layer according to an embodiment of the present invention or a precursor structure for manufacturing the light-absorbing layer.

The step of forming the precursor includes i) forming the first electrode layer 200 on the substrate 100.

At this time, the substrate 100 may be a flexible substrate. For example, it may be made of one or more types selected from the group consisting of molybdenum foil (Mo foil), titanium foil (Ti foil), and stainless steel (SUS).

The substrate 100 may be a substrate that has been pretreated using at least one of an ammonium fluoride (NH ₄ F) solution and a hydrofluoric acid (HF) solution.

The pretreatment process for the substrate may be a pretreatment process using a solution in which an ammonium fluoride (NH ₄ F) solution and a hydrofluoric acid (HF) solution are mixed at a certain ratio.

The method of pretreating the substrate may be a pretreatment process using a solution in which an ammonium fluoride (NH ₄ F) solution and a hydrofluoric acid (HF) solution are mixed at a certain ratio.

At this time, the ammonium fluoride (NH ₄ F) solution is a solution in which ammonium fluoride (NH ₄ F) is mixed with deionized water (DIW) at a ratio of 20% to 50% by weight. You can.

Additionally, the hydrofluoric acid (HF) solution may be a solution in which hydrofluoric acid (HF) is mixed with deionized water (DIW) at a ratio of 1% to 10% by weight.

The pretreatment solution may be a solution in which the ammonium fluoride (NH4F) solution and the hydrofluoric acid (HF) solution are mixed at a ratio of 4:1 to 8:1.

This is to remove oxygen from the surface of the substrate through the pretreatment solution and prevent excessive etching. If the mixing ratio is less than 4:1, a problem may occur in which oxygen from the substrate 100 is not removed, If it exceeds 8:1, the surface of the substrate 100 may be excessively etched, which may cause a problem in which the resistance characteristics of the thin film solar cell deteriorate.

Additionally, the temperature of the pretreatment solution may be 20°C to 30°C, and the pretreatment time may be 10 to 40 seconds.

This is to remove oxygen from the substrate surface through the pretreatment solution and prevent excessive etching. If the pretreatment process temperature and time are below the above range, oxygen from the substrate 100 may not be removed, and the temperature and time may not be removed. If this range is exceeded, the surface of the substrate 100 may be excessively etched, which may cause a problem in which the resistance characteristics of the thin film solar cell deteriorate.

The first electrode 200 may be made of at least one of molybdenum (Mo), titanium (Ti), or an alloy thereof, and is preferably made of molybdenum (Mo). Molybdenum (Mo) has high electrical conductivity, allows ohmic contact with a CZTS-based light absorption layer, and has excellent heat resistance and interfacial adhesion. The thickness of the first electrode 200 may be 0.2 μm to 5 μm, and may be formed through a sputtering process.

Forming the precursor 300 includes ii) forming a zinc (Zn) precursor layer 310 on the first electrode layer 200, and iii) forming copper on the zinc (Zn) precursor layer 310. It includes forming a (Cu) precursor layer 320, iv) forming a tin (Sn) precursor layer 330 on the copper (Cu) precursor layer 320.

The precursor layer 300 is characterized in that a zinc (Zn) precursor layer 310, a copper (Cu) precursor layer 320, and a tin (Sn) precursor layer are sequentially formed on the first electrode 200. do.

At this time, the zinc (Zn) precursor layer 310 is preferably a zinc (Zn) metal layer, and may be formed with a thickness in the range of 60 nm to 310 nm.

If the thickness of the zinc (Zn) precursor layer is 60 nm or less or 310 nm or more, crystal growth of the light absorption layer 400 formed from the precursor layer 300 may not be formed well, and the light absorption layer 400 may not be formed well. If the thickness becomes too thin or too thick, a problem may occur in which efficiency characteristics are not displayed.

The copper (Cu) precursor layer 320 is preferably a copper (Cu) metal layer, and may be formed with a thickness in the range of 40 nm to 220 nm.

If the thickness of the copper (Cu) precursor layer is 40 nm or less or 220 nm or more, crystal growth of the light absorption layer 400 formed from the precursor layer 300 may not be formed well, and the light absorption layer ( If the thickness of 400) becomes too thin or too thick, a problem may occur in which efficiency characteristics do not appear.

The tin (Sn) precursor layer 330 is preferably a tin (Sn) metal layer, and may be formed with a thickness in the range of 70 nm to 370 nm.

If the thickness of the tin (Sn) metal layer is 70 nm or less or 370 nm or more, crystal growth of the light absorption layer 400 formed from the precursor layer 300 may not be formed well, and the light absorption layer 400 may not be formed well. If the thickness becomes too thin or too thick, a problem may occur in which efficiency characteristics are not displayed.

In addition, the precursor layer 300 has an element ratio of copper (Cu) to zinc (Zn) and tin (Sn), Cu/Zn+Sn, of 0.6 to 1.0, and the source of zinc (Zn) to tin (Sn) is 0.6 to 1.0. The thicknesses of the zinc (Zn) precursor layer 310, the copper (Cu) precursor layer 320, and the tin (Sn) precursor layer may be adjusted so that the consumption Zn/Sn is 1.0 to 1.6.

The zinc (Zn) precursor layer 310, copper (Cu) precursor layer 320, and tin (Sn) precursor layer of the precursor layer 300 are formed using sputtering and co-evaporation methods. ) can be formed by any one of the following methods.

In addition, the precursor layer 300 has at least two alkali metal compound layers 340 formed between the zinc (Zn) precursor layer 310, the copper (Cu) precursor layer 320, and the tin (Sn) precursor layer. It is characterized by

The method for manufacturing a CZTS-based thin film solar cell light absorption layer provided in one aspect of the present invention includes forming an alkali metal compound layer on a precursor layer, thereby forming a CZTS-based light absorption layer. It has the effect of suppressing the creation of secondary images and forming a uniform light absorption layer.

In addition, in the present invention, by forming the alkali metal compound layer as a multi-layer, the light efficiency improvement effect is significantly superior compared to the case where the alkali metal compound layer is formed as a single layer.

For this purpose, the thickness of the alkali metal compound layer may be 2 nm to 20 nm. If the thickness of the alkali metal compound layer is less than 2 nm, the effect of the alkali metal may be insignificant, and if it exceeds 20 nm, the thickness of the precursor layer 300 is formed after the sulfurization or selenization or sulfurization-selenization process. A problem may occur in which the light absorption layer 400 is peeled off from the substrate 100.

In addition, in the step of forming the alkali metal compound layer, a first alkali metal compound layer is formed between the first electrode layer and the zinc (Zn) precursor layer, and a first alkali metal compound layer is formed between the zinc (Zn) precursor layer and the copper (Cu) precursor layer. At least two of the second alkali metal compound layer and the third alkali metal compound layer formed between the copper (Cu) precursor layer and the tin (Sn) precursor layer may be formed.

The alkali metal compound layer may form the first alkali metal compound layer and the second alkali metal compound layer, as shown in FIG. 1, and preferably forms the first alkali metal compound layer or the second alkali metal compound layer. , it is possible to form the third alkali metal compound layer. That is, as shown in FIG. 3, the first alkali metal compound layer and the third alkali metal compound layer can be formed, and as shown in FIG. 5, the second alkali metal compound layer and the third alkali metal compound layer can be formed. there is. In addition, more preferably, as shown in FIG. 7, the first alkali metal compound layer, the second alkali metal compound layer, and the third alkali metal compound layer may be formed, and as shown in FIG. 9, the structure of FIG. 7 A fourth alkali metal compound layer may be further formed on the tin (Sn) precursor layer.

At this time, the first to fourth alkali metal compound layers may be any one selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), or cesium (Cs) and fluorine (F). The same alkali metal may be included in each layer, but the layer is not limited thereto, and different alkali metals may be included.

Additionally, the first to fourth alkali metal compound layers may be formed by any one of sputtering and co-evaporation.

Accordingly, in the conventional case, when doping an alkali metal into the metal of the precursor layer through a solution process, there is an advantage that problems such as etching of a part of the precursor layer do not occur.

The method for manufacturing a CZTS-based thin film solar cell light absorption layer provided in one aspect of the present invention is to manufacture the light absorption layer 400 by heat treating the precursor layer in an atmosphere in which at least one of sulfur (S) and selenium (Ce) is supplied. Additional steps may be included.

The light absorption layer 400 is characterized in that it is one or more types of light absorption layers selected from the group consisting of copper zinc tin sulfide (CZTS), copper zinc tin selenium (CZTSe), and copper zinc tin sulfur selenide (CZTSSe). .

The light absorption layer 400 absorbs light to form electron-hole pairs, and transfers electrons and holes to different electrodes to allow current to flow.

The light absorption layer 400 may be formed by forming a precursor layer and simultaneously subjecting it to a sulfurization, selenization, or sulfurization-selenization process.

The laminated precursor layer may subsequently be subjected to sulfurization treatment or selenization treatment or sulfurization-selenization treatment, and the sulfurization treatment or selenization treatment or sulfurization-selenization treatment process may be performed to effectively penetrate selenium or sulfur elements. It can be performed under an inert gas atmosphere in a closed chamber.

At this time, the inert gas may be argon (Ar), but the inert gas is not limited thereto.

At this time, the light absorption layer 400 may be formed to have a thickness of 0.3 ㎛ to 3.0 ㎛.

In another aspect of the present invention

A zinc (Zn) precursor layer disposed on the substrate on which the first electrode is formed; A copper (Cu) precursor layer disposed on the zinc (Zn) precursor; It includes a tin (Zn) precursor layer disposed on the copper (Cu) precursor,

disposed at least two of between the first electrode layer and the zinc (Zn) precursor layer, between the zinc (Zn) precursor layer and the copper (Cu) precursor layer, and between the copper (Cu) precursor layer and the tin (An) precursor layer. A precursor structure for manufacturing a CZTS-based thin film solar cell light absorption layer including an alkali metal compound layer may be provided.

The precursor structure is a precursor structure for manufacturing the CZTS-based thin film solar cell light absorption layer of the present invention, and may be a structure manufactured through the step of manufacturing a precursor in the method of manufacturing the CZTS-based thin film solar cell light absorption layer.

The precursor structure is a structure in which a zinc (Zn) precursor layer 310, a copper (Cu) precursor layer 320, and a tin (Sn) precursor layer are sequentially formed on the first electrode 200, preferably. , may include a zinc (Zn) precursor layer with a thickness of 60 nm to 310 nm, a copper (Cu) precursor layer with a thickness of 40 nm to 220 nm, and a tin (Sn) precursor layer with a thickness of 70 nm to 370 nm, and is more preferred. Specifically, the element ratio of copper (Cu) to zinc (Zn) and tin (Sn), Cu/Zn+Sn, is 0.6 to 1.0, and the element ratio of zinc (Zn) to tin (Sn), Zn/Sn, is 1.0. The thicknesses of the zinc (Zn) precursor layer 310, copper (Cu) precursor layer 320, and tin (Sn) precursor layer may be adjusted to range from 1.6 to 1.6.

In addition, the precursor structure includes a first alkali metal compound layer disposed between the first electrode layer and the zinc (Zn) precursor layer, and a second alkali metal compound layer disposed between the zinc (Zn) precursor layer and the copper (Cu) precursor layer. It includes at least two of a compound layer and a third alkali metal compound layer disposed between the copper (Cu) precursor layer and the tin (Sn) precursor layer.

The precursor structure provided in one aspect of the present invention includes a multi-layered alkali metal compound layer as described above, so that during the heat treatment process for forming the CZTS-based light absorption layer, secondary phase generation can be suppressed and a uniform light absorption layer can be formed. Therefore, it is possible to form a CZTS-based thin film solar cell with improved luminous efficiency.

As shown in FIG. 1, the multi-layered alkali metal compound layer may form the first alkali metal compound layer and the second alkali metal compound layer, and as shown in FIG. 3, the first alkali metal compound layer and the third alkali metal compound layer. A compound layer can be formed, and as shown in FIG. 5, the second alkali metal compound layer and the third alkali metal compound layer can be formed. In addition, more preferably, as shown in FIG. 7, the first alkali metal compound layer, the second alkali metal compound layer, and the third alkali metal compound layer may be formed, and as shown in FIG. 9, the structure of FIG. 7 A fourth alkali metal compound layer may be further formed on the tin (Sn) precursor layer.

At this time, each of the first to fourth alkali metal compound layers may have a thickness of 2 nm to 20 nm.

At this time, the first to fourth alkali metal compound layers may be any one selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), or cesium (Cs) and fluorine (F). The same alkali metal may be included in each layer, but the layer is not limited thereto, and different alkali metals may be included.

In another aspect of the present invention

It is manufactured by the method of manufacturing the light absorption layer, and includes at least one selected from the group consisting of copper zinc tin sulfide (CZTS), copper zinc tin selenium (CZTSe), and copper zinc tin sulfur (CZTSSe), A CZTS-based thin film solar cell light absorption layer is provided.

In addition, in another aspect of the present invention, a CZTS-based thin film solar cell including the light absorption layer is provided.

At this time, the CZTS-based thin film solar cell may be a flexible thin film solar cell.

Referring to Figure 12, the CZTS-based thin film solar cell is

Substrate 100;

a first electrode 200 disposed on the substrate 100;

A light absorption layer 400 manufactured using the above manufacturing method is disposed on the substrate 100;

A buffer layer 500 disposed on the light absorption layer 400;

a window layer 600 disposed on the buffer layer 500; and

It includes a second electrode 700 disposed on the window layer 600.

Hereinafter, a CZTS-based thin film solar cell according to another aspect of the present invention will be described in detail for each configuration.

The substrate 100 may be made of a flexible material. For example, at least one of molybdenum foil (Mo foil), titanium foil (Ti foil), or stainless steel (SUS) may be used.

The substrate 100 may be a substrate that has been pretreated using at least one of an ammonium fluoride (NH ₄ F) solution and a hydrofluoric acid (HF) solution to remove oxygen from the surface.

The first electrode 200 may be at least one of molybdenum (Mo), titanium (Ti), or an alloy thereof, and is made of molybdenum (Mo), which is capable of ohmic bonding with a CZTS-based light absorption layer and has excellent heat resistance and interfacial adhesion. It may be desirable to use

The light absorption layer 400 is a layer containing at least one member selected from the group consisting of copper zinc tin sulfide (CZTS), copper zinc tin selenium (CZTSe), and copper zinc tin sulfur selenide (CZTSSe), A zinc (Zn) precursor layer 310, a copper (Cu) precursor layer 320, and a tin (Sn) precursor layer sequentially formed on the first electrode 200 and the zinc (Zn) precursor layer 310, It is formed by heat treating two or more alkali metal compound layers disposed between the copper (Cu) precursor layer 320 and the tin (Sn) precursor layer in an atmosphere in which at least one of sulfur (S) and selenium (Ce) is supplied, Alkali metal elements may be uniformly distributed within the light absorption layer 400.

The buffer layer 500 disposed on the light absorption layer 400 is a layer to alleviate the high band gap between the window layer 500 and the light absorption layer 400, and is composed of CdS, ZnS, Zn(O,S), and CdZnS. and ZnSe, but is not limited thereto.

The buffer layer 400 may be formed by a vacuum process, thermal deposition process, chemical bath deposition, etc., but is not limited thereto.

The thickness of the buffer layer 400 may be 10 to 200 nm.

If the thickness of the buffer layer 400 is less than 10 nm or more than 200 nm, light transmittance decreases, and there may be a problem in which electrons are difficult to transfer to the upper electrode due to an increase in the width of the depletion layer.

The window layer 600 disposed on the buffer layer 500 is a layer that functions as a transparent electrode on the front of the solar cell, and is composed of ZnO:Al, ZnO:AZO, ZnO:B (BZO), and ZnO:Ga (GZO). It may be one or more types selected from the group consisting of, but is not limited to, materials having high light transmittance and excellent electrical conductivity may be appropriately selected and used.

The window layer 600 may be formed by a method such as sputtering or thermal deposition, but is not limited thereto.

The thickness of the window layer 600 may be 100 to 1000 nm. If the thickness of the window layer 600 is less than 100 nm or more than 1000 nm, a problem may occur in which the light efficiency of the device is reduced due to a decrease in light transmittance and a decrease in current-voltage characteristics.

The second electrode 700 disposed on the window layer 600 functions to collect current from the surface of the solar cell. In the examples below, aluminum is used, but the type of electrode used in the industry must be specifically selected. It is not limiting.

Hereinafter, the present invention will be described in more detail through examples. These examples are for illustrating the present invention in more detail, and the scope of the present invention is not limited to these examples.

<Example 1> CZTS-based thin film solar cell (1)

Step 1: Wash the molybdenum foil (Mo foil) substrate with acetone and methanol for 10 minutes each at 300°C ultrasonically, then wash with distilled water, and immerse the washed molybdenum foil (Mo foil) substrate in the pretreatment solution prepared by the following method. Pretreatment was performed at 30 degrees for 20 seconds. Afterwards, a first electrode with a thickness of 0.5 μm was formed on the substrate to which the above pretreatment was applied by applying a sputtering process.

(Preparation of substrate pretreatment solution)

An ammonium fluoride solution was prepared by mixing 33.5% by weight of ammonium fluoride (NH ₄ F) and 66.5% by weight of deionized water (DIW). Afterwards, 7% by weight of Hydrofluoric Acid (HF) and 93% by weight of deionized water (DIW) were mixed to create a hydrofluoric acid solution. A substrate pretreatment solution was prepared by mixing the ammonium fluoride solution and hydrofluoric acid in a ratio of 6:1.

Step 2: A precursor layer was formed by depositing a first NaF layer of 5 nm, zinc of 217 nm, a second NaF layer of 5 nm, copper of 164 nm, and tin of 274 nm on the first electrode in that order.

Step 3: A Cu ₂ ZnSn(S,Se) ₄ light absorption layer was formed by applying a sulfide-selenide process to the precursor layer at 480°C through a rapid thermal process (RTP).

Step 4: After forming a CdS buffer layer with a thickness of about 50 nm on the light absorption layer, ZnO with a thickness of about 50 nm and aluminum-doped ZnO with a thickness of about 0.3 μm are formed as a window layer, and then a second aluminum layer with a thickness of about 0.5 μm is formed. By forming electrodes, a CZTS-based thin film solar cell was completed.

A total of four samples were produced using the above method, and each cell was made according to Examples 1-1 to 1-4.

<Example 2>

A CZTS-based thin film solar cell was manufactured in the same manner as in Example 1, except that step 2 of Example 1 was changed as follows.

Step 2: A precursor layer was formed by depositing 5 nm of the first NaF layer, 217 nm of zinc, 164 nm of copper, 5 nm of the third NaF layer, and 274 nm of tin on the first electrode in this order.

<Example 3>

A CZTS-based thin film solar cell was manufactured in the same manner as in Example 1, except that step 2 of Example 1 was changed as follows.

Step 2: A precursor layer was formed by depositing 217 nm of zinc, 5 nm of the second NaF layer, 164 nm of copper, 5 nm of the third NaF layer, and 274 nm of tin on the first electrode in this order.

<Example 4>

A CZTS-based thin film solar cell was manufactured in the same manner as in Example 1, except that step 2 of Example 1 was changed as follows.

Step 2: A precursor layer was formed by depositing 4 nm of the first NaF layer, 217 nm of zinc, 3 nm of the second NaF layer, 164 nm of copper, 3 nm of the third NaF layer, and 274 nm of tin on the first electrode in this order. .

<Example 5>

A CZTS-based thin film solar cell was manufactured in the same manner as in Example 1, except that step 2 of Example 1 was changed as follows.

Step 2: On the first electrode, in the following order: first NaF layer 3 nm, zinc 217 nm, second NaF layer 3 nm, copper 164 nm, third NaF layer 2 nm, tin 274 nm, fourth NaF layer 2 nm. A precursor layer was formed by vapor deposition.

<Comparative example 1>

A CZTS-based thin film solar cell was manufactured in the same manner as in Example 1, except that step 2 of Example 1 was changed as follows.

Step 2: A precursor layer was formed by depositing 217 nm of zinc, 164 nm of copper, and 274 nm of tin in that order on the first electrode.

<Comparative example 2>

A CZTS-based thin film solar cell was manufactured in the same manner as in Example 1, except that step 2 of Example 1 was changed as follows.

Step 2: A precursor layer was formed by depositing a first NaF layer of 10 nm, zinc 217 nm, copper 164 nm, and tin 274 nm in that order on the first electrode.

The precursor structures of Examples 1 to 5 and Comparative Examples 1 and 2 are shown in Table 1 below.

Precursor layer structure Example 1 Mo foil / Mo electrode / 1st NaF 5 nm / Zn 217 nm / 2nd NaF 5 nm / Cu 164 nm / Sn 274 nm Example 2 Mo foil / Mo electrode / 1st NaF 5 nm / Zn 217 nm / Cu 164 nm / 3rd NaF 5 nm / Sn 274 nm Example 3 Mo foil / Mo electrode / Zn 217 nm / 2nd NaF 5 nm / Cu 164 nm / 3rd NaF 5 nm / Sn 274 nm Example 4 Mo foil / Mo electrode / 1st NaF 4 nm / Zn 217 nm / 2nd NaF 3 nm / Cu 164 nm / 3rd NaF 3 nm / Sn 274 nm Example 5 Mo foil / Mo electrode / 1st NaF 3 nm / Zn 217 nm / 2nd NaF 3 nm / Cu 164 nm / 3rd NaF 2 nm / Sn 274 nm / 4th NaF 2nm Comparison example 1 Mo foil / Mo electrode / Zn 217 nm / Cu 164 nm / Sn 274 nm Comparison example 2 Mo foil / Mo electrode / 1st NaF 10 nm / Zn 217 nm / Cu 164 nm / Sn 274 nm

Figure 17 shows a cross-sectional image of the precursor layer included in the thin film solar cell according to Example 1 of the present invention by transmission electron microscopy (TEM) and elemental composition distribution by energy dispersive spectroscopy (EDS). These are analysis images and graphs.

Referring to FIG. 17, it can be seen that in Example 1, mutual diffusion of Cu and Zn was suppressed by the second NaF 5 nm applied between Zn and Cu, thereby suppressing the creation of an alloy phase such as Cu ₅ Zn ₈ .

Figure 18 shows a cross-sectional image of the precursor layer included in the thin film solar cell according to Example 2 of the present invention by transmission electron microscopy (TEM) and elemental composition distribution by energy dispersive spectroscopy (EDS). These are analysis images and graphs.

Referring to FIG. 18, in Example 2, an alloy phase such as Cu ₅ Zn ₈ is created by mutual diffusion between Zn and Cu, and Cu 6 Sn 5 and Cu ₆ Sn ₅ are formed by the third NaF 5 nm applied between Cu and Sn. It can be confirmed that the formation of the same alloy phase was suppressed.

Figure 19 shows a cross-sectional image of the precursor layer included in the thin film solar cell according to Example 3 of the present invention by transmission electron microscopy (TEM) and elemental composition distribution by energy dispersive spectroscopy (EDS). These are analysis images and graphs.

Referring to FIG. 19, in Example 3, mutual diffusion of Cu and Zn was suppressed by the second NaF 5 nm applied between Zn and Cu, thereby suppressing the creation of alloy phases such as Cu _{5 Zn 8, and the formation of alloy phases such as Cu 5} Zn ₈ was suppressed. It can be confirmed that the formation of alloy phases such as Cu ₆ Sn ₅ was suppressed by the third NaF 5 nm applied.

Figure 20 shows a cross-sectional image of the precursor layer included in the thin film solar cell according to Example 4 of the present invention by transmission electron microscopy (TEM) and elemental composition distribution by energy dispersive spectroscopy (EDS). These are analysis images and graphs.

Referring to FIG. 20, in Example 4, mutual diffusion of Cu and Zn was suppressed by the second NaF 3 nm applied between Zn and Cu, thereby suppressing the generation of alloy phases such as Cu _{5 Zn 8, and the formation of alloy phases such as Cu 5} Zn ₈ was suppressed. It can be confirmed that the formation of alloy phases such as Cu ₆ Sn ₅ was suppressed by the third NaF 3 nm applied.

Figure 21 shows a cross-sectional image by transmission electron microscopy (TEM) and elemental composition distribution by energy dispersive spectroscopy (EDS) of the precursor layer included in the thin film solar cell according to Example 5 of the present invention. These are analysis images and graphs.

Referring to Figure 21, for Example 5, a second NaF of 3 nm was applied between Zn and Cu, but an alloy phase such as Cu 5 Zn 8 was created due to mutual diffusion between Zn and Cu, and an alloy phase such as Cu ₅ Zn ₈ was created between Cu and Sn. Although the third NaF 2 nm was applied, it can be confirmed that an alloy phase such as Cu ₆ Sn ₅ was created due to mutual diffusion of Cu and Sn.

Therefore, as in the results of Examples 4 and 5, the second NaF layer was equally 3 nm thick between Zn and Cu, but diffusion of Cu and Zn was suppressed in Example 4, and in Example 5, Cu It can be seen that and Zn were mutually diffused. Therefore, in order to reproducibly suppress the mutual diffusion of Cu and Zn, the thickness of the NaF layer is preferably 4 nm or more.

However, in Example 5, the mutual diffusion of Cu and Zn means that the mutual diffusion of Cu and Zn was not completely suppressed and a very small alloy phase was created, which suppresses the creation of the alloy phase compared to Comparative Examples 1 and 2. The effect is great.

Figure 22 shows a cross-sectional image of the precursor layer included in the thin film solar cell according to Comparative Example 1 by transmission electron microscopy (TEM) and analysis of elemental composition distribution by energy dispersive spectroscopy (EDS). Images and graphs.

Referring to Figure 22, with respect to Comparative Example 1, an alloy phase such as Cu ₅ Zn ₈ was created by mutual diffusion between Zn and Cu, and an alloy phase such as Cu ₆ Sn ₅ was created by mutual diffusion between Cu and Sn. You can check it.

Figure 23 shows a cross-sectional image of the precursor layer included in the thin film solar cell according to Comparative Example 2 by transmission electron microscopy (TEM) and analysis of elemental composition distribution by energy dispersive spectroscopy (EDS). Images and graphs.

Referring to FIG. 23, in Comparative Example 2, an alloy phase such as Cu ₅ Zn ₈ was created by mutual diffusion between Zn and Cu, and an alloy phase such as Cu ₆ Sn ₅ was created by mutual diffusion between Cu and Sn. You can check it.

The solar cell characteristics of the four cells prepared in each of Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated and shown in Tables 2 to 8 and Figures 24 to 21 below.

efficiency
(%) open voltage
V _OC (V) short circuit current
J _SC (mA/ ^cm2 ) Filling rate
FF(%) Example 1-1 7.27 0.44 30.84 54.07 Example 1-2 6.34 0.42 29.52 51.10 Example 1-3 7.05 0.42 31.13 53.55 Example 1-4 6.35 0.42 30.66 49.72 average 6.75 0.42 30.54 52.11

efficiency
(%) open voltage
V _OC (V) short circuit current
J _SC (mA/ ^cm2 ) Filling rate
FF(%) Example 2-1 7.58 0.44 31.09 55.25 Example 2-2 8.08 0.45 31.64 57.17 Example 2-3 7.98 0.45 31.52 56.49 Example 2-4 7.18 0.43 29.98 55.57 average 7.70 0.44 31.06 56.12

efficiency
(%) open voltage
V _OC (V) short circuit current
J _SC (mA/ ^cm2 ) Filling rate
FF(%) Example 3-1 7.35 0.43 31.14 54.38 Example 3-2 6.91 0.44 29.13 53.83 Example 3-3 7.85 0.45 30.31 57.18 Example 3-4 7.63 0.44 30.90 55.86 average 7.44 0.44 30.37 55.31

efficiency
(%) open voltage
V _OC (V) short circuit current
J _SC (mA/ ^cm2 ) Filling rate
FF(%) Example 4-1 8.40 0.45 31.38 59.92 Example 4-2 8.65 0.45 32.68 58.76 Example 4-3 8.75 0.45 32.43 60.06 Example 4-4 8.56 0.45 31.62 60.45 average 8.59 0.45 32.03 59.80

efficiency
(%) open voltage
V _OC (V) short circuit current
J _SC (mA/ ^cm2 ) Filling rate
FF(%) Example 5-1 8.48 0.44 31.58 61.12 Example 5-2 8.63 0.45 30.81 62.56 Example 5-3 8.62 0.45 31.34 51.58 Example 5-4 8.52 0.44 32.12 59.93 average 8.56 0.44 31.46 61.30

efficiency
(%) open voltage
V _OC (V) short circuit current
J _SC (mA/ ^cm2 ) Filling rate
FF(%) Comparative example 1-1 5.96 0.46 31.68 41.32 Comparative example 1-2 6.18 0.46 30.91 43.59 Comparative Example 1-3 5.01 0.42 29.99 39.51 Comparative Example 1-4 5.89 0.45 30.15 43.33 average 5.76 0.45 30.68 41.94

efficiency
(%) open voltage
V _OC (V) short circuit current
J _SC (mA/ ^cm2 ) Filling rate
FF(%) Comparative example 2-1 5.72 0.45 30.40 42.07 Comparative example 2-2 6.74 0.47 31.09 45.97 Comparative example 2-3 5.19 0.43 29.83 40.60 Comparative example 2-4 6.46 0.47 31.31 43.57 average 6.03 0.45 30.73 53.05

Figure 24 shows the highest efficiency among the four samples of Examples 1 to 4, Comparative Examples 1 and 2, Examples 1-1, 2-2, 3-3, and 4. This is a graph comparing the current-voltage characteristics for the samples -3, Example 5-2, Comparative Example 1-2, and Comparative Example 2-2.

Figure 25 is a statistical analysis graph comparing the efficiency characteristics of the flexible thin film solar cell for each of the four cells prepared in Examples 1 to 4 and the four cells prepared in Comparative Examples 1 and 2.

Figure 26 is a statistical analysis graph comparing the open-circuit voltage characteristics of the flexible thin film solar cell for each of the four cells prepared in Examples 1 to 4 and the four cells prepared in Comparative Examples 1 and 2.

Figure 27 is a statistical analysis graph comparing the short-circuit current characteristics of the flexible thin film solar cell for each of the four cells prepared in Examples 1 to 4 and the four cells prepared in Comparative Examples 1 and 2.

Figure 28 is a statistical analysis graph comparing the filling rate characteristics of the flexible thin film solar cell for each of the four cells prepared in Examples 1 to 4 and the four cells prepared in Comparative Examples 1 and 2.

Referring to Tables 2 to 7 and Figures 24 to 28, it can be seen that the efficiency and filling rate characteristics of the precursor structures of Examples 1 to 5 were improved compared to Comparative Examples 1 and 2. These results mean that the resistance characteristics of the device were improved in the precursor structures according to Examples 1 to 5, resulting in the formation of a light absorption layer with an improved filling factor, thereby improving the efficiency characteristics of the flexible thin film solar cell.

In addition, in Examples 1 to 5, it can be seen that the efficiency characteristics were improved in the order of Example 5 > Example 4 > Example 2 > Example 3 > Example 1.

Through this, efficiency is improved when including a multi-layer alkali metal compound layer, especially when forming a third alkali metal compound layer between the copper (Cu) precursor layer and the tin (Sn) precursor layer (Examples 2 to 5). It can be seen that the effect is excellent.

In addition, when forming a first alkali metal compound layer between the first electrode layer and the zinc (Zn) precursor layer together with the third alkali metal compound layer (Examples 2, 4, and 5), the efficiency improvement effect is more excellent, When forming a second alkali metal compound layer (Examples 4 and 5) between the first alkali metal compound layer and the second alkali metal compound layer and the zinc (Zn) precursor layer and the copper (Cu) precursor layer, It can be seen that an excellent efficiency improvement effect appears.

The effect of the multilayer alkali metal layer structure when forming the light absorption layer from the precursor structure according to the examples and comparative examples can be explained as follows. The reaction during the light absorption layer formation process of the metal precursor formed of Cu, Zn, and Sn can be expressed as follows.

(1) 6Cu (solid) + 5Sn (solid) → Cu ₆ Sn ₅ (solid) → Cu ₆ Sn ₅ (liquid) (at 400℃)

(2) Cu ₆ Sn ₅ (liquid) (at 400℃) → 2Cu ₃ Sn (solid) + 3Sn (liquid)

(3) 4Cu ₃ Sn (solid) + 3S ₂ (Se ₂ ) (gas) → 6Cu ₂ S (Cu ₂ Se) (solid) + 4Sn (liquid)

(4) 5Cu (solid) + 8Zn (solid) → Cu ₅ Zn ₈ (solid)

(5) 4Cu ₅ Zn ₈ (solid) + 21S ₂ (Se ₂ ) (gas) → 10Cu ₂ S (Cu ₂ Se) (solid) + 32ZnS (ZnSe) (solid)

(6) 2Cu ₂ S (Cu ₂ Se) (solid) + ZnS (ZnSe) (solid) + 2Sn (liquid) + 2S ₂ (Se ₂ ) (gas) → Cu ₂ ZnSnS ₄ (Cu ₂ ZnSnSe ₄ ) (solid ) + Cu ₂ SnS ₃ (Cu ₂ SnSe ₃ ) (solid)

At this time, an alloy phase such as Cu ₆ Sn ₅ in formula (1) and Cu ₅ Zn ₈ in formula (5) is formed in the precursor state by inter-diffusion of Cu, Sn, and Zn in the precursor phase. can be created. This alloy phase can form secondary phases such as +ZnS (ZnSe) (solid) in formula (5) and Cu ₂ SnS ₃ (Cu ₂ SnSe ₃ ) (solid) in formula (6) in the light absorption layer formation process. there is.

In Example 1, as shown in Figure 2, the first NaF layer suppresses diffusion of Zn into the first electrode, and the second NaF layer suppresses mutual diffusion of Zn and Cu to produce an alloy phase such as Cu ₅ Zn ₈ . It can be suppressed.

In Example 2, as shown in FIG. 4, the first NaF layer suppresses diffusion of Zn into the first electrode, and the second NaF layer suppresses mutual diffusion of Cu and Sn to produce an alloy phase such as Cu ₆ Sn ₅ It can be suppressed.

In Example 3, as shown in Figure 6, the first NaF layer can suppress the mutual diffusion of Zn and Cu, thereby suppressing the creation of an alloy phase such as Cu ₅ Zn ₈ , and the second NaF layer can suppress the mutual diffusion of Cu and Sn. By suppressing this, the formation of alloy phases such as Cu ₆ Sn ₅ can be suppressed.

In Example 4, as shown in Figure 8, the first NaF layer suppresses diffusion of Zn into the first electrode, and the second NaF layer suppresses mutual diffusion of Zn and Cu to produce an alloy phase such as Cu ₅ Zn ₈ . The third NaF layer can suppress the mutual diffusion of Cu and Sn, thereby suppressing the creation of an alloy phase such as Cu ₆ Sn ₅ .

In Example 5, as shown in FIG. 10, the thickness of the first NaF layer is 3 nm. At this time, the thickness of the first NaF layer is thin, so the effect of suppressing the diffusion of Zn into the first electrode may be somewhat reduced. In addition, the thickness of the second NaF layer is 3 nm, and at this time, the thickness of the second NaF layer is thin, so the effect of suppressing the creation of alloy phases such as Cu ₅ Zn ₈ by suppressing mutual diffusion of Zn and Cu may be somewhat reduced. .

In addition, the thickness of the third NaF layer is 2 nm, and at this time, the thickness of the first NaF layer is thin, so the effect of suppressing the creation of an alloy phase such as Cu ₆ Sn ₅ by suppressing mutual diffusion of Cu and Sn is somewhat reduced. It can be.

Therefore, in Example 5, the first NaF layer to the third NaF layer did not completely suppress the generation of the alloy phase, and although a very small alloy phase could be formed, the effect of suppressing the generation of the alloy phase was significantly greater than that of Comparative Examples 1 and 2. It can be improved.

The fourth NaF layer can suppress Sn loss due to Sn (liquid) generation in Reaction Formulas (3) and (4). In addition, the fourth NaF layer facilitates chemisorption of S _or Se on _the surface of the precursor during the sulfurization-selenization process of the _precursor to form liquid Na ₂ S By promoting diffusion into the precursor layer, crystal growth in the light absorption layer can be improved.

In this way, by introducing a multi-layer alkali metal layer into the precursor layer, resistance characteristics in the device can be improved by suppressing the production of secondary phases through suppressing the production of an alloy phase in the precursor before forming the light absorption layer. Improvements in resistance characteristics directly affect the improvement in filling rate, as shown in Figure 28, making it possible to improve efficiency.

The present invention is not limited by the above-described embodiments and attached drawings, but is intended to be limited by the attached claims. Accordingly, various forms of substitution, modification, and change may be made by those skilled in the art without departing from the technical spirit of the present invention as set forth in the claims, and this also falls within the scope of the present invention. something to do.

100: substrate
200: first electrode
310: Zinc (Zn) precursor layer
320: Copper (Cu) precursor layer
330: Tin (Sn) precursor layer
340: Alkali metal compound layer
341: First alkali metal compound layer
342: Second alkali metal compound layer
343: Second alkali metal compound layer
344: Fourth alkali metal compound layer
400: Light absorption layer
500: buffer layer
500: Window layer
700: second electrode

Claims (20)

i) forming a first electrode layer on a substrate, ii) forming a zinc (Zn) precursor layer on the first electrode layer, iii) forming a copper (Cu) precursor layer on the zinc (Zn) precursor layer. forming a precursor layer comprising, iv) forming a tin (Sn) precursor layer on the copper (Cu) precursor layer, and v) forming an alkali metal compound layer. ,
The step of forming the alkali metal compound layer is,
A first alkali metal compound layer formed between the first electrode layer and the zinc (Zn) precursor layer, a second alkali metal compound layer formed between the zinc (Zn) precursor layer and the copper (Cu) precursor layer, and the copper (Cu ) Forming at least two of the third alkali metal compound layers formed between the precursor layer and the tin (Sn) precursor layer,
Before forming the first electrode layer on the substrate, the substrate is pretreated with a mixture of an ammonium fluoride (NH ₄ F) solution and a hydrofluoric acid (HF) solution to remove oxygen on the surface of the substrate. removes,
A method of manufacturing a CZTS-based thin film solar cell light absorption layer, characterized in that the thickness of the first to third alkali metal compound layers is 2 nm to 20 nm.
According to claim 1,
The step of forming the alkali metal compound layer is
A method of manufacturing a CZTS-based thin film solar cell light absorption layer, characterized in that forming the first alkali metal compound layer or the second alkali metal compound layer, and forming the third alkali metal compound layer.
According to claim 1,
The step of forming the alkali metal compound layer is
A method of manufacturing a CZTS-based thin film solar cell light absorption layer, characterized in that forming the first alkali metal compound layer and the third alkali metal compound layer.
According to claim 3,
The step of forming the alkali metal compound layer is
A method of manufacturing a CZTS-based thin film solar cell light absorption layer, characterized by forming the second alkali metal compound layer.
According to claim 4,
The step of forming the alkali metal compound layer is,
A method of manufacturing a CZTS-based thin film solar cell light absorption layer, characterized in that further forming a fourth alkali metal compound layer on the tin (Sn) precursor layer.
According to claim 1,
The alkali metal compound layer is a CZTS-based thin film characterized in that it contains one or more alkali metals selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). Manufacturing method of solar cell light absorption layer.
delete According to claim 1,
A method of manufacturing a CZTS-based thin film solar cell light absorption layer, wherein the substrate is a flexible substrate.
According to claim 1,
The manufacturing method is
manufacturing a light absorption layer by heat-treating the precursor layer in an atmosphere supplied with at least one of sulfur (S) and selenium (Ce).
delete According to claim 1,
The manufacturing method is
A CZTS-based thin film solar cell, characterized in that it forms at least one type of light absorption layer selected from the group consisting of copper zinc tin sulfide (CZTS), copper zinc tin selenium (CZTSe), and copper zinc tin sulfur (CZTSSe). Method for manufacturing a light absorption layer.
According to claim 1,
The manufacturing method is
A method of manufacturing a CZTS-based thin film solar cell light absorption layer, characterized by forming a light absorption layer with a thickness of 0.3 μm to 3 μm.
A zinc (Zn) precursor layer disposed on the substrate on which the first electrode is formed; A copper (Cu) precursor layer disposed on the zinc (Zn) precursor; A tin (Zn) precursor layer disposed on the copper (Cu) precursor; And an alkali metal compound layer,
The alkali metal compound layer is,
A first alkali metal compound layer disposed between the first electrode layer and the zinc (Zn) precursor layer, a second alkali metal compound layer disposed between the zinc (Zn) precursor layer and the copper (Cu) precursor layer, and the copper (Cu ) It includes at least two of the third alkali metal compound layer disposed between the precursor layer and the tin (Sn) precursor layer,
The substrate is pretreated using a mixed solution of ammonium fluoride (NH ₄ F) solution and hydrofluoric acid (HF) solution,
A precursor structure for manufacturing a CZTS-based thin film solar cell light absorption layer, wherein the first to third alkali metal compound layers have a thickness of 2 nm to 20 nm.
According to claim 13,
The precursor structure is
A precursor structure for manufacturing a CZTS-based thin film solar cell light absorption layer, further comprising a fourth alkali metal compound layer disposed on the tin (Zn) precursor layer.
According to claim 13,
The thickness of the zinc (Zn) precursor layer is 60 nm to 310 nm,
The thickness of the copper (Cu) precursor layer is 40 nm to 220 nm,
A precursor structure for manufacturing a CZTS-based thin film solar cell light absorption layer, wherein the tin (Sn) precursor layer has a thickness of 70 nm to 370 nm.
According to claim 13,
The precursor structure is
A precursor structure for manufacturing a CZTS-based thin film solar cell light absorption layer, characterized in that Cu/Zn+Sn, the element ratio of copper (Cu) to zinc (Zn) and tin (Sn), is 0.6 to 1.0.
According to claim 13,
A precursor structure for manufacturing a CZTS-based thin film solar cell light absorption layer, characterized in that Zn/Sn, the elemental ratio of zinc (Zn) to tin (Sn), is 1.0 to 1.6.
CZTS, which is manufactured by the manufacturing method of claim 1 and includes at least one member selected from the group consisting of copper zinc tin sulfide (CZTS), copper zinc tin selenium (CZTSe), and copper zinc tin sulfur (CZTSSe). Light absorption layer of thin film solar cell.
A CZTS-based thin-film solar cell including the CZTS-based thin-film solar cell light absorption layer of claim 18.
According to claim 19,
The CZTS-based thin-film solar cell is a CZTS-based thin-film solar cell, characterized in that it is a flexible thin-film solar cell formed on a flexible substrate.