KR102513863B1 - Flexible CZTSSe thin film solar cells and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a flexible CZTSSe thin film solar cell and a manufacturing method thereof and, more specifically, to a flexible CZTSSe thin film solar cell and a flexible CZTSSe thin film solar cell manufacturing method which introduce a metal oxide intermediate layer without directly forming a p-type compound semiconductor layer made of a CZTSSe thin film on a flexible lower electrode substrate to form a protective layer so as to enable interface control and include dopants in controlled amounts and types into a CZTSSe thin film so as to increase crystal quality of the CZTSSe thin film and reduce processing time.

Description

Flexible CZTSSe thin film solar cell and manufacturing method of the flexible CZTSSe thin film solar cell {Flexible CZTSSe thin film solar cells and manufacturing method thereof}

The present invention relates to a flexible CZTSSe thin film solar cell and a manufacturing method thereof, and more specifically, to a protective layer by introducing a metal oxide intermediate layer without directly forming a p-type compound semiconductor layer made of a CZTSSe thin film on a flexible lower electrode substrate. A flexible CZTSSe thin film solar cell capable of controlling the interface by forming and incorporating dopants into the CZTSSe thin film in a controlled amount and type to improve the crystal quality of the CZTSSe thin film and shorten the process time, and a manufacturing method of the flexible CZTSSe thin film solar cell It is about.

CZTSSe thin-film solar cells can adjust the band gap of the absorption layer from 1.0 eV to 2.8 eV through doping of various elements and control of the composition ratio, and the light absorption coefficient is as high as 10 ^-4 cm ^-1 , making rapid development so far. am. In addition, since the price of the element is low and it is composed of abundant materials on earth, it is economically advantageous, so it is suitable for replacing CIGS-based thin-film solar cells, and many studies are being conducted.

However, the conversion efficiency of CZTSSe thin-film solar cells so far is 13.0% when using SLG/Mo substrate and 11.19% when using Mo foil substrate, which is the world record, showing relatively low conversion efficiency compared to other solar cells. . In addition, in the case of using a flexible substrate, the efficiency is lower than that of a glass substrate due to the absence of an alkali element. Therefore, it is difficult to commercially replace Cu(In,Ga)(S,Se) ₂ (CIGS) thin-film solar cells.

On the other hand, since the thin-film solar cell is manufactured with a thin thickness, the consumption of materials is small and the weight is light, so the application range is wide. The flexible CZTSSe thin film solar cell consists of a multi-layered structure, among which an active layer made of a p-type compound semiconductor layer and known as an absorber layer plays a pivotal role in generating carriers through photo-generation. When enough photons are absorbed, a large amount of charge can be generated to improve the conversion efficiency of the solar cell device.

A general method of manufacturing a light absorbing layer of a solar cell based on CZT (CuZnSn), which is a kind of compound semiconductor, is to first deposit a metal precursor composed of Cu, Zn, and Sn, and then use sulfur (S) or selenium (Se) element to to heat treatment. Such a light absorbing layer may be a CZTS (CuZnSnS), CZTSe (CuZnSnSe), or CZTSS (CuZnSnSSe) solar cell light absorbing layer. At this time, in the deposition of the metal precursor composed of Cu, Zn, and Sn, it is common to sequentially deposit unit films of Cu, Zn, and Sn by a sputtering method. However, when deposited in this order, the metal precursor film forms a very rough surface due to the crystallization of Sn, and due to this, the surface roughness is not improved even after heat treatment using sulfur (S) or selenium (Se) element, so the local position of the absorption layer The non-uniformity of the component ratio and the decrease in parallel resistance in the process after the absorption layer limit the improvement of solar cell efficiency.

To overcome this, there is a method of depositing a precursor using CuS, ZnS, or SnS targets, but this reduces the deposition rate, contamination and corrosion of the evaporator due to sulfur (S) or selenium (Se), and relatively There is a problem of showing improvement characteristics of low surface roughness. That is, the absorption layer is manufactured by selectively synthesizing materials of copper, zinc, tin, gallium, indium, sulfur, and selenium, and the quality of the thin film may be different depending on the synthesis process. In particular, due to heat treatment characteristics at high temperatures, thin films may not be densely synthesized, and vacancies may occur or complete phases may not be formed, which may adversely affect the characteristics of the solar cell as a result.

In addition, it is known that one of the main barriers to the improvement of the conversion efficiency of CZTSSe thin film solar cells is the incomplete lower electrode/absorber layer interface. In the case of a CZTSSe thin-film solar cell, the absorber layer reacts with the Mo lower electrode during the sulfurization and selenization processes, which are the processes of synthesizing the CZTSSe absorber layer, and as a result, an unwanted phase is generated at the interface between the Mo lower electrode and the CZTSSe absorber layer. As more ideal layers are formed, pure Mo changes into thicker ideal layers.

The phase formed at the interface between the lower electrode and the absorber layer is Mo(S,Se) ₂ , and this phase reduces the crystallinity of the absorber layer and greatly reduces the electrical characteristics of the device. Furthermore, thickly formed Mo(S,Se) ₂ deteriorates interface characteristics in CZTSSe thin film solar cells, causing high series resistance (R _s ). Thus, by applying a TiN or TiB ₂ intermediate layer, It is also controlled, but in this case, higher R _s was induced, and device characteristics were not improved.

Therefore, it is required to develop and apply a more suitable material to prevent the change of Mo to an abnormal layer, which is a major problem at the interface, and to improve the device characteristics of the CZTSSe thin film solar cell along with the control of the thickness of the secondary phase and the abnormal layer. .

Moreover, in the case of a flexible CZTSSe solar cell compared to a glass substrate, the crystal quality of the absorber layer tends to be relatively low due to the absence of an alkali element naturally added during the process.

Therefore, it is necessary to develop a new technology capable of further improving the conversion efficiency of the flexible CZTSSe thin film solar cell by solving the above-mentioned problems.

Domestic Patent Registration No. 10-1509306

The present inventors have completed the present invention by developing a technology that can improve the electrical characteristics of a solar cell by improving the film quality of the absorber layer of a flexible CZTSSe thin film solar cell as a result of numerous studies.

Therefore, an object of the present invention is to apply a copper aluminum oxide (CuAlO ₂ ) intermediate layer between a flexible lower electrode substrate and a p-type compound semiconductor layer made of a CZTSSe thin film as an absorber layer, which can be generated in the absorber layer and lower electrode of a flexible CZTSSe solar cell. An object of the present invention is to provide a flexible CZTSSe thin film solar cell capable of reducing the series resistance (R _s ) by preventing an abnormal layer and a manufacturing method thereof.

Another object of the present invention is to form a p-type compound semiconductor layer through co-sputtering and pre-heat treatment to form a thin film with no vacancies and high crystallinity, thereby improving the electrical characteristics of a flexible CZTSSe thin film solar cell and It is to provide a manufacturing method.

Another object of the present invention is to improve the electrical characteristics of a solar cell by improving the crystal quality of the p-type compound semiconductor layer by adding a dopant to the p-type compound semiconductor layer in a desired type and amount by controlling the type and content of the dopant It is to provide a flexible CZTSSe thin film solar cell and its manufacturing method.

The object of the present invention is not limited to the above-mentioned object, and even if not explicitly mentioned, the object of the invention that can be recognized by those skilled in the art from the description of the detailed description of the invention to be described later may also be included. .

In order to achieve the object of the present invention described above, the present invention comprises the steps of forming a Cu-Al mixed layer on a flexible lower electrode substrate; oxidizing the Cu-Al mixed layer to form a Cu-Al oxide (CuAlO ₂ ) intermediate layer; forming a dopant layer on the Cu-Al oxide intermediate layer; forming a p-type compound semiconductor layer made of a CZTSSe thin film on the dopant layer; forming an n-type compound semiconductor layer on the p-type compound semiconductor layer; forming a transparent electrode layer on the n-type compound semiconductor layer; and forming an upper electrode on the transparent electrode layer.

In a preferred embodiment, the forming of the Cu-Al mixed layer is performed so that the atomic ratio of Cu to Al is 40:60 to 60:40 using a co-vacuum evaporation method.

In a preferred embodiment, the Cu-Al mixed layer is formed to a thickness of 5 nm to 25 nm.

In a preferred embodiment, the step of forming the Cu—Al oxide intermediate layer is performed by heat treatment for 1 hour to 2 hours at a temperature condition of 300° C. to 500° C. in an oxygen atmosphere.

In a preferred embodiment, the elemental composition ratio of the Cu-Al oxide (CuAlO ₂ ) forming the Cu-Al oxide intermediate layer is Al ₂ O ₃ : Cu ₂ O = 1 : 1 at%.

In a preferred embodiment, the step of forming the dopant layer is formed to a thickness of 5 nm to 20 nm using a vacuum evaporation method.

In a preferred embodiment, the dopant layer is made of one selected from the group consisting of sodium fluoride (NaF), potassium fluoride (KF), rubidium fluoride (RbF) and cesium fluoride (CsF).

In a preferred embodiment, in the forming of the p-type compound semiconductor layer, Zn and Cu or Sn and Cu are deposited on the dopant layer by co-sputtering to form a first metal mixed layer in which Cu-Zn or Cu-Sn is mixed. forming; depositing Sn and Cu or Zn and Cu on the first metal mixture layer by co-sputtering to form a second metal mixture layer in which Cu-Sn or Cu-Zn are mixed; The first metal mixed layer forms a first alloy layer composed of a Cu-Zn alloy or a Cu-Sn alloy, and the second metal mixed layer forms a second alloy layer composed of a Cu-Sn alloy or a Cu-Zn alloy. forming first and second alloy layers by performing a primary heat treatment on the first and second metal mixture layers; and forming a CZTSSe thin film including subjecting the first and second alloy layers to secondary heat treatment together with S and Se powder.

In the step of forming the first metal mixed layer or the second metal mixed layer, DC power of 60 to 80 W is applied to Zn and DC power of 20 to 40 W is applied to Cu, and 900 to 1100 seconds at a process pressure of 7 to 9 mTorr. It is performed by simultaneously depositing during the process, or by applying DC power of 60 to 80 W for Sn and DC power of 35 to 55 W for Cu, and simultaneously depositing for 1400-1600 seconds at a process pressure of 7-9 mTorr.

In a preferred embodiment, in the first and second alloy layer forming steps, the first and second metal mixed layers are subjected to primary heat treatment for 80 to 100 minutes in an atmospheric pressure atmosphere of Ar or N ₂ and a temperature condition of 200 to 400 ° C. and natural cooling for 150 to 210 minutes.

In a preferred embodiment, the CZTSSe thin film forming step is to form the first and second alloy layers together with S and Se powder in an Ar atmosphere, 450 to 550 Torr pressure, and 500 to 600 ° C. temperature conditions for 5 to 10 minutes. During the secondary heat treatment step; and naturally cooling to room temperature.

In a preferred embodiment, the secondary heat treatment is performed by putting the first and second alloy layers and S and Se powders in a graphite box, and the S and Se powders are included in a weight ratio of 1:90 to 1:120 .

In a preferred embodiment, the Cu-Zn alloy includes Cu ₆ Zn ₈ , and the Cu-Sn alloy includes Cu ₃ Sn and Cu ₆ Sn ₅ .

In a preferred embodiment, the CZTSSe thin film has secondary phases including SnS(e) ₂ , ZnS(e), Cu ₂ S(e), and Cu ₂ SnS(e) ₃ suppressed and Cu ₂ ZnSn(S,Se) consists of ₄

In a preferred embodiment, the flexible lower electrode substrate is a thin metal plate or a thin conductive polymer plate.

In addition, a flexible lower electrode substrate; a Cu-Al oxide intermediate layer formed on the lower electrode substrate; a p-type compound semiconductor layer formed on the Cu-Al oxide intermediate layer by any one of the manufacturing methods described above; an n-type compound semiconductor layer formed on the p-type compound semiconductor layer; a transparent electrode layer formed on the n-type compound semiconductor layer; It provides a flexible CZTSSe thin film solar cell comprising a; and an upper electrode layer formed on the transparent electrode layer.

In a preferred embodiment, the flexible lower electrode substrate is a thin metal plate or a thin conductive polymer plate.

In a preferred embodiment, the p-type compound semiconductor layer contains a dopant element in a controlled content and type.

In a preferred embodiment, the dopant element is at least one selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb) and cesium (Cs).

In a preferred embodiment, the n-type compound semiconductor layer is ZnSnO, Zn(O,S), CdS, SnO ₂ , It includes at least one selected from the group consisting of In ₂ S ₃ and In ₂ O ₃ .

In a preferred embodiment, the transparent electrode layer includes at least one selected from the group consisting of ZnO, AlZnO, GaZnO, MgZnO, InSnO, MgAlZnO and MgGaZnO.

In a preferred embodiment, the upper electrode layer includes at least one selected from the group consisting of Mo, Pt, Ni, Au, Ag, and Al.

According to the present invention described above, an intermediate layer of copper aluminum oxide (CuAlO ₂ ) is applied between a flexible lower electrode substrate and a p-type compound semiconductor layer made of a CZTSSe thin film, which is an absorber layer. By preventing the layer in advance, the series resistance (R _s ) can be reduced.

In addition, according to the present invention, by forming a p-type compound semiconductor layer through co-sputtering and pre-heat treatment, it is possible to form a thin film having no vacancies and high crystallinity, thereby improving the electrical characteristics of the solar cell.

In addition, according to the present invention, the electrical characteristics of the solar cell can be improved by controlling the type and content of the dopant and adding the dopant to the p-type compound semiconductor layer in a desired type and amount to improve the crystal quality of the p-type compound semiconductor layer.

Therefore, the present invention can ultimately improve the conversion efficiency of the flexible CZTSSe solar cell.

These technical effects of the present invention are not limited to the above-mentioned scope, and even if not explicitly mentioned, the effects of the invention that can be recognized by those skilled in the art from the description of specific contents for the practice of the invention described later included of course

1 is a schematic flowchart showing a manufacturing method of a flexible CZTSSe thin film solar cell according to an embodiment of the present invention.
Figure 2a is a schematic diagram showing a p-type compound semiconductor layer manufacturing process of a flexible CZTSSe thin film solar cell according to another embodiment of the present invention, Figure 2b is a flow chart showing each step for manufacturing a p-type compound semiconductor layer.
FIG. 3 is a schematic diagram of a flexible CZTSSe thin film solar cell manufactured by the method shown in FIG. 1 including a p-type compound semiconductor layer manufactured by the method shown in FIG. 2B according to another embodiment of the present invention.
Figure 4a is a scanning electron microscope cross-sectional photograph of a thin film after depositing a metal precursor by common sputtering and after depositing it by single sputtering, and Figure 4b is a scanning electron microscope cross-sectional photograph of a thin film after metal precursor deposition and pre-heat treatment, and Figure 4c is a scanning electron microscope cross-sectional photograph of the light absorption layer thin film completed after heat treatment of the pre-heated thin film together with powder mixed with S and Se at a high temperature.
5 is a graph showing the optical characteristics results according to the deposition thickness of the Cu-Al oxide intermediate layer.
Figure 6 is a TEM comparison image of a flexible CZTSSe thin film solar cell, (a) is a Cu-Al oxide intermediate layer and dopant layer are not formed during the manufacturing process, (b) only a dopant layer is formed, (c) is a Cu -All of the Al oxide intermediate layer and the dopant layer are formed.
7 shows XRD and SEM surface image comparison results of a thin film solar cell with and without a Cu-Al oxide intermediate layer formed during the manufacturing process of a flexible CZTSSe thin film solar cell.
8 shows XRD and SEM surfaces of a flexible CZTSSe thin film solar cell in which only a dopant layer is formed, a Cu-Al oxide intermediate layer and a dopant layer are formed, and a Cu-Al oxide intermediate layer and a dopant layer are not formed during the manufacturing process, respectively. This is the image comparison result.
9 is a graph of EDS depth profile comparison results of a thin film solar cell with a Cu-Al oxide intermediate layer formed and a thin film solar cell without a Cu-Al oxide intermediate layer formed during the manufacturing process of a flexible CZTSSe thin film solar cell.
10 is a comparison result of electrical characteristics of flexible CZTSSe thin film solar cells in which only a dopant layer is formed, a Cu-Al oxide intermediate layer and a dopant layer are formed, and a Cu-Al oxide intermediate layer and a dopant layer are not formed during the manufacturing process, respectively. it's a graph
11 is a result graph showing electrical characteristics of a solar cell device to which an absorber layer synthesized through a general process and preliminary heat treatment is applied.
12a to 12d are graphs showing electrical characteristics of solar cell devices to which CZTSSe thin films fabricated through common sputtering and single sputtering are applied.

Terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, terms such as "comprise" or "having" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the description of the invention, but one or more other It should be understood that it does not preclude the possibility of addition or existence of features, numbers, steps, operations, components, parts, or combinations thereof.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present invention, they should not be interpreted in an ideal or excessively formal meaning. don't

In interpreting the components, even if there is no separate explicit description, it is interpreted as including the error range. In particular, when the terms "about", "substantially", etc. of degree are used, they may be construed as being used in a sense at or close to that number when manufacturing and material tolerances inherent in the stated meaning are given. .

In the case of a description of a temporal relationship, for example, 'after', 'after', 'after', 'before', etc., when the temporal precedence is described, 'immediately' or 'directly' It also includes non-continuous cases unless used.

Hereinafter, the technical configuration of the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments.

However, the present invention is not limited to the embodiments described herein and like reference numerals denote like elements in different forms.

The technical feature of the present invention is that it is possible to control the interface by forming a protective layer by introducing a metal oxide intermediate layer without directly forming a p-type compound semiconductor layer made of a CZTSSe thin film on a flexible lower electrode substrate, and to control the dopant content and types can be included in the CZTSSe thin film, and in forming the CZTSSe thin film, rather than sequentially stacking each metal, after forming a metal mixed layer in which Zn and Cu or Sn and Cu are sequentially deposited by co-sputtering, respectively, A two-component compound useful for forming a CZTSSe thin film is formed through a process of forming an alloy layer through pre-heat treatment, that is, primary heat treatment, and then secondary heat treatment together with sulfur and selenium, SnS(e) ₂ , ZnS(e), A flexible CZTSSe thin film solar cell capable of improving the crystal quality of the CZTSSe thin film and shortening the process time by suppressing the formation of secondary phases such as Cu ₂ S(e) and Cu ₂ SnS(e) ₃ and a manufacturing method thereof.

Accordingly, the method for manufacturing a flexible CZTSSe thin film solar cell of the present invention includes forming a Cu-Al mixed layer on a flexible lower electrode substrate; oxidizing the Cu-Al mixed layer to form a Cu-Al oxide (CuAlO ₂ ) intermediate layer; forming a dopant layer on the Cu-Al oxide intermediate layer; forming a p-type compound semiconductor layer made of a CZTSSe thin film on the dopant layer; forming an n-type compound semiconductor layer on the p-type compound semiconductor layer; forming an n-type semiconductor transparent electrode layer on the n-type compound semiconductor layer; and forming an upper electrode on the transparent electrode layer. Here, all known substrates may be used as the flexible lower electrode substrate as long as they are conductive and flexible. As an embodiment, a thin metal plate or a conductive polymer plate may be used. In particular, a stainless steel sheet or Mo foil may be used as a thin metal sheet.

First, the step of forming the Cu-Al mixed layer may be performed so that the atomic ratio of Cu to Al is 40:60 to 60:40 on the flexible lower electrode substrate by using a co-vacuum evaporation method. Since the Cu-Al mixed layer is oxidized to form a Cu-Al oxide intermediate layer, in order to form an intermediate layer having characteristics that can serve as a protective layer without forming an abnormal layer on the lower electrode without acting as a secondary phase or self-defect, It needs to be formed by uniformly mixing copper and aluminum. If the co-vacuum evaporation method is used, it can be formed by uniformly mixing copper and aluminum in a desired ratio. In particular, if the ratio of Cu: Al included in the Cu-Al mixed layer is 60: 40 or more, it serves properly as a protective layer, but the series resistance can be greatly increased due to excessive generation of Cu ₂ O phase during oxidation, and the Cu: Al If the ratio is less than 40:60, excessive formation of the Al ₂ O ₃ phase may occur during oxidation. When the Al ₂ O ₃ layer is excessively formed, the thin film may be peeled off by reacting with the solution in the step of forming the n-type compound semiconductor layer on the p-type light absorption layer.

The Cu-Al mixed layer may be formed to a thickness of 5 nm to 25 nm. If the thickness is less than 5 nm, the CZTSSe thin film formed on the dopant layer may not be properly formed or may grow in the form of an island. In this case, Mo as the lower electrode substrate When foil is used, it can be changed into a Mo(S,Se) ₂ or more layer, so it can not function as a protective layer at all, and a secondary phase can also be formed in the p-type compound semiconductor layer (ie, the absorption layer). On the other hand, in the case of 25 nm or more, the thickness is too thick, and the movement of charges is not smooth, resulting in an increase in DC resistance.

Next, the step of forming the Cu-Al oxide intermediate layer may be performed by heat-treating the Cu-Al mixed layer using a furnace in an oxygen atmosphere. It may be performed by heat-treating the Cu-Al mixed layer. That is, when a temperature of less than 300 ° C is applied, the oxide is not properly formed and exists in a metallic state, which may affect the formation of the absorption layer. When the temperature is higher than 500 ° C, the flexible lower electrode substrate is Mo may cause oxidation. At this time, the elemental composition ratio of Cu-Al oxide (CuAlO ₂ ) forming the Cu-Al oxide intermediate layer may be Al ₂ O ₃ : Cu ₂ O = 2:3 to 3:2 at%, particularly 1:1 at may be %. This is because, when the composition ratio is greatly out of the set range, the formation of the secondary phase of the absorption layer may be affected due to the omission of Al and Cu.

In addition, the step of forming the dopant layer may be formed to a thickness of 5 nm to 20 nm using a vacuum evaporation method, and the dopant layer may serve as a role of helping the growth of the CZTSSe crystal when synthesizing the CZTSSe absorption layer. That is, in the case of the present invention, since a flexible metal substrate or a conductive polymer substrate is used instead of a glass substrate containing an alkali-based dopant, a separate dopant layer is formed because no dopant is included. Experimentally, it was confirmed that if the thickness of the dopant layer is less than the set range, it does not have a beneficial effect on CZTSSe crystal growth, and if it is exceeded, the quality of the absorber layer is deteriorated by causing abnormal crystal enlargement of the CZTSSe absorber layer.

At least one selected from the group consisting of sodium fluoride (NaF), potassium fluoride (KF), rubidium fluoride (RbF) and cesium fluoride (CsF) may be used as the dopant forming the dopant layer. As in the embodiment, only one type of NaF may be used, but a plurality of types of dopants may be used depending on the characteristics of the absorption layer to be obtained. As described above, in the present invention, by providing a separate step of forming the dopant layer, unlike when using a glass substrate, the type and content of various elements included in the glass substrate are not controlled and used randomly, so that the CZTSSe crystal can grow optimally. It is possible to provide a dopant of a controlled type and amount.

Next, the step of forming a p-type compound semiconductor layer made of a CZTSSe thin film on the dopant layer is a mixture of Cu-Zn or Cu-Sn by depositing Zn and Cu or Sn and Cu on the dopant layer by co-sputtering. 1 forming a metal mixed layer; depositing Sn and Cu or Zn and Cu on the first metal mixture layer by co-sputtering to form a second metal mixture layer in which Cu-Sn or Cu-Zn are mixed; The first metal mixed layer forms a first alloy layer composed of a Cu-Zn alloy or a Cu-Sn alloy, and the second metal mixed layer forms a second alloy layer composed of a Cu-Sn alloy or a Cu-Zn alloy. forming first and second alloy layers by performing a primary heat treatment on the first and second metal mixture layers; and forming a CZTSSe thin film including subjecting the first and second alloy layers to secondary heat treatment together with S and Se powder.

In the step of forming the first metal mixed layer or the second metal mixed layer, DC power of 60 to 80 W is applied to Zn and DC power of 20 to 40 W is applied to Cu, and a process pressure of 7 to 9 mTorr is applied for 800 to 1200 seconds. It is carried out by simultaneous deposition, Sn is applied with DC power of 60 to 80 W, and Cu is applied with DC power of 35 to 55 W, and simultaneously deposited for 1400 to 1600 seconds under a process pressure condition of 7-9 mTorr. Here, the sputtering process conditions are different for each metal element, and these sputtering conditions are particularly good for Cu ₆ Zn ₈ among binary compounds of copper-zinc alloy formed through the first heat treatment step after co-sputtering copper and zinc or copper and tin. It is experimentally determined through a number of repeated experiments as process conditions for forming, and in particular, Cu ₃ Sn and Cu ₆ Sn ₅ among the two-component compounds of the copper-tin alloy. In addition, in the case of Zn, since the deposition rate is low on the flexible substrate, it can be deposited for 100 to 200 seconds longer than that on the glass substrate.

The first and second alloy layer forming steps include first heat-treating the first and second metal mixed layers in an Ar or N ₂ atmospheric pressure atmosphere and a temperature condition of 200-400 ° C for 80-100 minutes and 150 to 210 minutes In one embodiment, the first heat treatment may be performed at a temperature of 250° C. to 350° C. for 1 hour to 2 hours in an Ar atmosphere at atmospheric pressure. As described above, the primary heat treatment conditions were experimentally determined through a number of repeated experiments to determine the optimal conditions for forming the desired two-component compound in the copper-zinc alloy and the copper-tin alloy. Prior to synthesizing the CZTSSe absorber layer, Cu -Zn, Zn-Sn, Cu-Sn alloys can be formed in advance to lower the energy required for the reaction during CZTSSe reaction.

The CZTSSe thin film forming step is a step of secondary heat treatment for 5 minutes to 10 minutes in an Ar atmosphere, a pressure of 450 to 550 Torr, and a temperature of 500 to 600 ° C. for the first and second alloy layers together with S and Se powder; and naturally cooling to room temperature. The secondary heat treatment is performed by putting the first and second alloy layers and the S and Se powders in a graphite box. In particular, the S and Se powders have a ratio of 1:90 to 1:120. It can be included in a weight ratio of

That is, the process of forming the CZTSSe absorption layer thin film by reacting the first and second alloy layers with S and Se in the present invention is as follows.

4/3Cu ₃ Sn + Se ₂ (g) → 2Cu ₂ Se + 4/3Sn (1)

2/3Cu ₆ Sn ₅ + Se ₂ (g) → 2Cu ₂ Se + 10/3Sn

Cu ₅ Zn ₈ + Se → 2Cu ₂ Se + 2ZnSe

4Cu + S ₂ (g) → 2Cu ₂ S

2Sn + S ₂ (g) → 2Se

SnS + Se → SnSe ₂ + SnSe

2SnSe + Se ₂ (g) → 2SnSe ₂

2Cu ₂ S(e) + 2SnS(e) ₂ + S(e) ₂ → 2Cu ₂ SnS(e) ₃ (2)

Cu ₂ SnS(e) ₃ +ZnS(e) → Cu ₂ ZnSn(S,Se) ₄ (3)

Cu ₂ S + SnSe ₂ + ZnSe → Cu ₂ ZnSn(S,Se) ₄

As can be seen from the above synthesis chemical formula, since the CZTSSe thin film is finally synthesized through Reaction Formula (3), Cu ₂ SnS(e) ₃ , Cu ₂ S, SnSe ₂ , and ZnSe compounds are well formed in order to obtain a high-quality CZTSSe thin film. In order for Cu ₂ SnS(e) ₃ , Cu ₂ S, SnSe ₂ , and ZnSe compounds to form well, Cu ₅ Zn _8, Cu ₃ Sn, Cu ₆ Sn ₅ and It can be seen that the content ratio of added sulfur and selenium is important, as well as the formation of the same two-component compound.

Therefore, in the above-described step of forming the p-type compound semiconductor layer of the present invention, the joint sputtering condition, the first heat treatment condition, and the second heat treatment condition are closely related to each other, and all of these conditions must be precisely controlled to SnS ( _e ) Inorganic thin film including a high-quality CZTSSe thin film composed of Cu ₂ ZnSn(S,Se) ₄ with secondary phase containing 2 , ZnS(e), Cu ₂ S(e), and Cu ₂ SnS(e) ₃ suppressed A p-type compound semiconductor layer for a solar cell can be obtained.

In addition, the thickness of the CZTSSe thin film formed in the step of forming the p-type compound semiconductor layer may be 1 um to 2 um. If the thickness is less than 1 um, a problem in that the crystal does not grow properly may occur in the process of forming the CZTSSe absorption layer. This is because, when the thickness exceeds 2 μm, the length at which light reaches the absorption layer increases and the generation and separation of charge hole pairs may not be performed well.

Next, the step of forming the n-type compound semiconductor layer may be performed using a chemical bath deposition (CBD) method using a specially manufactured device in which a beaker is doubly bonded. Here, the n-type compound semiconductor layer may include at least one selected from ZnSnO, Zn(O,S), CdS, SnO ₂ , In ₂ S ₃ and In ₂ O ₃ .

As an embodiment, the n-type compound semiconductor layer was stirred for 1 minute by mixing 0.0031 M CdSO ₄ , 19 M ammonia, and 0.2 M thiourea. The process may be performed at a temperature, a deposition time of 10 minutes to 20 minutes, and a flow rate of 0.5 L/m to 2.0 L/m.

The n-type compound semiconductor layer may be formed with a thickness of 25 nm to 60 nm. If it is less than 25 nm, the reaction is not performed properly, so a thin film is not formed or it is too thin to play a buffer role. As the light reaching the is reduced, the J _sc of the solar cell may decrease due to the decrease in transmittance.

Next, forming the transparent electrode layer may be performed using an n-type semiconductor material including at least one selected from ZnO, Al-ZnO, GaZnO, MgZnO, InSnO, MgAlZnO, and MgGaZnO. As an embodiment, an i-ZnO layer having a thickness of 25 nm to 75 nm is formed by applying AC power of 40 W to 60 W using sputtering equipment, and AC power of 60 W to 80 W and AC power of 350 ° C to 350 ° C are formed on the i-ZnO layer. A temperature of 450° C. may be applied to form an AZO layer of 400 nm to 700 nm. At this time, the process pressure may be 1 mTorr to 7 mTorr. In the step of forming the transparent electrode layer, the thickness and process conditions are experimentally determined, and if they are out of the set range, they may not play a buffer role properly and may not increase the series resistance to facilitate the flow of charges. This may lead to a decrease in the charging rate and conversion efficiency of the solar cell.

Next, the step of forming the upper electrode layer may include at least one selected from the group consisting of Mo, Pt, Au, Al, Ag, and Ni, and may have a thickness of 0.6 μm to 1.5 μm. If the thickness of the upper electrode layer is out of the set range, the resistance of the upper electrode may increase so that the charge does not move smoothly, or a shadow area may occur, which may increase the reflectance of light or block the incidence of light.

Next, the flexible CZTSSe thin film solar cell of the present invention includes a flexible lower electrode substrate; a Cu-Al oxide intermediate layer formed on the lower electrode substrate; a p-type compound semiconductor layer formed on the Cu-Al oxide intermediate layer by any one of the above-described manufacturing methods; an n-type compound semiconductor layer formed on the p-type compound semiconductor layer; a transparent electrode layer formed on the n-type compound semiconductor layer; and an upper electrode layer formed on the transparent electrode layer. As an embodiment, it may have a structure as shown in FIG. 3 .

Here, the flexible lower electrode substrate 10 may be a metal thin plate or a conductive polymer thin plate as described above, but a molybdenum foil was used in the following embodiment.

In particular, the Cu-Al oxide intermediate layer 20 can prevent Mo from changing into a Mo(S,Se) ₂ or more layer when the flexible lower electrode substrate constituting the flexible CZTSSe thin film solar cell of the present invention is a molybdenum foil, and is a p-type Generation of a secondary phase in the compound semiconductor layer 30 can be prevented.

Moreover, as described above in the manufacturing method, after the dopant layer formed on the Cu-Al oxide intermediate layer has a positive effect on crystal growth to help form the p-type compound semiconductor layer, the dopant layer disappears but the p-type compound semiconductor layer ( 30) may include a dopant element in a controlled amount and type, and the dopant element may be at least one selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). there is.

The n-type compound semiconductor layer 40 may include at least one selected from the group consisting of ZnSnO, Zn(O,S), CdS, SnO ₂ , In ₂ S ₃ and In ₂ O ₃ , and may include a transparent electrode layer. (50) may include at least one selected from the group consisting of ZnO, Al-ZnO, GaZnO, MgZnO, InSnO, MgAlZnO and MgGaZnO, and the upper electrode layer 60 is Mo, Pt, Au, Al, Ag and It may include at least one selected from Ni. The upper electrode layer 60 may be a metal electrode, and may be formed on all or part of the upper portion of the transparent electrode layer 50 through thermal evaporation, electron beam deposition, sputtering, or the like.

Example

A flexible CZTSSe thin film solar cell made of a high quality CZTSSe thin film having the schematic diagram shown in FIG. 3 was manufactured according to the flowchart shown in FIG. 1 as follows.

1. Preparing a flexible lower electrode substrate (S100)

After preparing a flexible molybdenum foil as a flexible lower electrode substrate, immerse the molybdenum foil substrate in each beaker containing isopropyl alcohol and deionized water, and then use an ultrasonic cleaner for 1 minute for each solution to proceed with washing, and then dried using high-pressure nitrogen gas.

2. Forming a Cu-Al Mixed Layer (S200)

In order to form a Cu-Al mixed layer on the cleaned substrate, copper and aluminum sources were put into the equipment and deposited simultaneously so that the atomic ratio was 1:1 through simultaneous vacuum evaporation, and it was formed to a thickness of 10 nm.

3. Forming a Cu-Al Oxide Interlayer (S300)

In order to oxidize the Cu-Al mixed layer, it was placed in a furnace and heat-treated for 1 hour and 30 minutes while maintaining 400°C in an oxygen atmosphere to form a Cu-Al oxide intermediate layer.

4. Forming a dopant layer (S400)

On the Cu—Al oxide intermediate layer, sodium fluoride (NaF) was formed to a thickness of 10 nm using a vacuum evaporation method in order to form a dopant for enhancing crystal growth of the p-type compound semiconductor layer.

5. Forming a p-type compound semiconductor layer (S500)

The p-type compound semiconductor layer 30 was manufactured as follows, as shown in FIGS. 2A and 2B.

(1) A flexible lower electrode substrate having a dopant layer obtained through S100 to S400 was prepared (S510)

(2) Deposition of the first metal mixed layer (S520)

On the dopant layer, Zn and Cu were simultaneously deposited for 1000 seconds under conditions of 70 W and 30 W DC power and 8 mTorr process pressure, respectively, using joint sputtering to form a first metal mixed layer in which Cu-Zn metals were mixed. .

(3) Deposition of the second metal mixed layer (S530)

Thereafter, Sn and Cu were simultaneously deposited for 1500 seconds under conditions of DC power supply of 70 W and 45 W and process pressure of 8 mTorr, respectively, to form a second metal mixed layer in which Cu-Sn metal was mixed.

(4) Forming a first alloy layer and a second alloy layer (S540)

Forming a two-component compound of a desired composition while forming a first alloy layer composed of a Cu-Zn alloy and a second alloy layer composed of a Cu-Sn alloy, respectively, after depositing a first metal mixture layer and a second metal mixture layer as a metal mixture precursor As a pre-heat treatment, the first heat treatment was performed as follows. The first heat treatment was performed at a temperature of 300° C. for 90 minutes in a furnace in an atmospheric pressure atmosphere of Ar or N ₂ . Thereafter, natural cooling was performed for 3 hours.

(5) p-type compound semiconductor layer formation step (S550)

The substrate on which the first and second alloy layers were subjected to the first heat treatment was placed in a graphite box containing a mixture of S and Se powders in a weight ratio of 1:100 and heat treated. In the heat treatment process, the initial pressure in the furnace was set to 475 Torr in an Ar atmosphere and heated at 530° C. for 7 minutes and 30 seconds. After heating, it was naturally cooled to room temperature.

6. N-type compound semiconductor layer formation step (S600)

A CdS (cadmium sulfide) buffer layer was formed as an n-type compound semiconductor layer using a chemical solution growth method. At this time, 0.0031 M of CdSO ₄ , 19 M of ammonia, and 0.2 M of thiourea were mixed and stirred for 1 minute. After that, each sample was put into the device, a solution temperature of 60 ° C, a deposition time of 14 minutes and 30 seconds, and 1.0 L The process was performed at a flow rate of /m to form a CdS layer of 30 nm.

7. Transparent electrode layer formation step (S700)

In order to form a ZnO (AZO) layer doped with i-ZnO and Al, an n-type semiconductor transparent electrode layer was formed using an RF sputtering method at room temperature and 450 degrees. The i-ZnO thickness of the transparent electrode layer was 50 nm, and the thickness of the AZO transparent electrode was formed to 400 nm.

8. Upper electrode layer formation step (S800)

In order to form the upper electrode layer, an aluminum (Al) sputtering target was mounted and an electrode pattern was formed to a thickness of 1.0 μm on the transparent electrode layer through DC sputtering. Through the above process, a flexible CZTSSe thin film solar cell 1 (10 nm or NaF/CAO) having a structure of Mo foil/CuAlO ₂ /CZTSSe/CdS/i-ZnO/AZO/Al was completed.

Example 2

In the step of forming the Cu-Al mixed layer (S200), Mo foil/CuAlO ₂ /CZTSSe/CdS/i-ZnO/AZO/Al was prepared in the same manner as in Example 1, except that the thickness of the mixed layer was 20 nm. Structure of flexible CZTSSe thin film solar cell 2 (20 nm) was completed.

Comparative Example 1

Comparative example inorganic thin film solar cell 1 was manufactured in the same manner as in Example 1, except that a thin film obtained by performing a general single sputtering method was used without performing S520 to S540 in Example 1.

Comparative Example 2

Except for not performing S200 to S400 in Example 1, a comparative inorganic thin film solar cell 2 (None) was manufactured in the same manner as in Example 1.

Comparative Example 3

Except for not performing S200 and S300 in Example 1, a comparative inorganic thin film solar cell 3 (NaF or W/O) was prepared in the same manner as in Example 1.

Experimental Example 1

As in the example, a thin film obtained by depositing a metal precursor for forming a p-type compound semiconductor layer by joint sputtering (up to S530) and a thin film obtained by depositing a single sputtering were observed by FE-SEM, and a cross-sectional photograph thereof is shown in FIG. 4a.

As shown in FIG. 4A , it can be seen that the thin film deposited by joint sputtering is relatively more densely deposited. When deposited by single sputtering, since Cu, Zn, and Sn are respectively deposited, thin films are deposited in layers such as Cu/Zn/Sn. On the other hand, when depositing by co-sputtering, since Cu and Sn or Cu and Zn are simultaneously deposited, a thin film may be deposited in a form in which Cu-Sn or Cu-Zn are mixed in advance. When a thin film is deposited in a mixed form, such as the first metal mixed layer and the second metal mixed layer of Example 1, the energy required to form Cu-Sn and Cu-Sn-based alloys or compounds or to form the CZTSSe light absorbing layer is reduced. , it seems that a denser thin film can be obtained than the deposited thin film by forming a stack like Cu/Zn/Sn.

Experimental Example 2

As in Example 1, the metal precursor for forming the p-type compound semiconductor layer was deposited by joint sputtering and then the thin film obtained by the first heat treatment (up to S540) and the thin film obtained by single sputtering and then the first heat treatment FE-SEM , and the cross-sectional photograph is shown in FIG. 4b.

The reason why the first heat treatment is performed after depositing the metal precursor is to make the Cu, Zn, and Sn precursors deposited through sputtering into two-component compounds such as Cu ₆ Sn ₅ , CuSn, and Cu ₆ Zn ₈ through a heat treatment process. As shown in FIG. 4B, looking at the FE-SEM cross-sectional image after the first heat treatment, it can be seen that the thin film is relatively more dense and uniformly formed in the thin film deposited by cavity sputtering. When the precursor is deposited by joint sputtering, since compounds in the form of Cu-Sn and Cu-Zn can be formed even before the first heat treatment, two-component compounds such as Cu ₆ Sn ₅ , CuSn, and Cu ₆ Zn ₈ are formed during the first heat treatment. compounds can be easily formed. On the other hand, in the case of depositing by single sputtering, since Cu-Sn and Cu-Zn compounds cannot be formed by forming a layer with a structure such as Cu/Zn/Sn before the first heat treatment, even after the first heat treatment, relatively Cu It is difficult to form two-component compounds such as ₆ Sn ₅ , CuSn, and Cu ₆ Zn ₈ . Therefore, when joint sputtering is performed, a high-quality thin film can be obtained by accelerating the formation of a two-component compound through the first heat treatment.

Experimental Example 3

As in Example 1, a metal precursor for forming a p-type compound semiconductor layer was deposited by joint sputtering, followed by first heat treatment, and then second heat treatment with a powder mixture of S and Se, and then a thin film (up to S550) and single sputtering. The thin film obtained by the first heat treatment and the second heat treatment after depositing was observed with FE-SEM, and the resulting photograph is shown in FIG. 4c.

As shown in FIG. 4C, in the case of the thin film prepared by depositing the precursor by co-sputtering as in Example 1, the size of the upper crystal grains was relatively larger, and the particles and vacancies with small crystal grains were reduced. When depositing precursors by single sputtering, precursors such as Cu, Zn, and Sn are deposited in an unmixed state before the first heat treatment. On the other hand, when depositing the precursor by co-sputtering, the Zn, Sn, and Cu precursors form a layer in which Cu-Zn and Cu-Sn are mixed. Therefore, during the first heat treatment at 200-400 ° C, the formation of two-component compounds such as Cu-Zn and Cu-Sn is well achieved compared to thin films deposited by single sputtering. As a result, it can be seen that when heat treatment is performed at 500 to 600 ° C with the addition of S and Se, not only dense shapes and large crystal grains can be formed, but also the formation of vacancies can be prevented.

Experimental Example 4

The optical properties of the Cu-Al oxide interlayer obtained in Examples 1 and 2 were measured through UV-vis, and the results are shown in FIG. 5 .

Referring to FIG. 5, when the Cu—Al oxide intermediate layer is 10 nm thick as in Example 1, the transmittance in the visible ray region is about 95%, and when the thickness is 20 nm as in Example 2, the transmittance in the visible ray region is about 90%. showed In addition, it can be seen that the band gap energy of the Cu-Al oxide intermediate layer having a thickness of 10 nm is 3.75 eV and 3.89 eV when the thickness is 20 nm.

Experimental Example 5

Flexible CZTSSe thin film solar cell 1 (10 nm) obtained in Example 1, comparative inorganic thin film solar cell 2 (None) obtained in Comparative Example 2, and comparative inorganic thin film solar cell 3 (NaF) obtained in Comparative Example 3 were observed by TEM. And the resulting picture is shown in Figure 6.

From FIG. 6, (a) shows a cross section of Comparative Inorganic Thin Film Solar Cell 2 (None) in which neither the Cu—Al oxide intermediate layer nor the dopant layer is formed, and Comparative Inorganic Thin Film Solar Cell 3 (NaF) in which only the dopant layer is formed. ) and (c) showing the cross section of flexible CZTSSe thin film solar cell 1 (10 nm) in which both the Cu-Al oxide intermediate layer and the dopant layer are formed, the flexible CZTSSe thin film solar cell of the present invention 1 (10 nm) is about 700, where the thickness of the Mo (S, Se) ₂ or more layer formed between the Mo lower electrode substrate and the CZTSSe light absorption layer is reduced by more than half from about 1.7 μm compared to (a) and (b) It can be confirmed that it is formed in the order of nm. Therefore, it was determined that the Cu-Al oxide intermediate layer sufficiently suppressed the formation of Mo(S,Se) ₂ or more layers in the flexible CZTSSe thin film solar cell (10 nm).

Experimental Example 6

XRD analysis and SEM observation were performed on the flexible CZTSSe thin film solar cells 1 (10 nm) and 2 (20 nm) obtained in Examples 1 and 2 and the comparative inorganic thin film solar cell 3 (W / O) obtained in Comparative Example 3, and The results are shown in FIG. 7 .

Referring to FIG. 7, flexible CZTSSe thin film solar cells 1 and 2 (10 nm and 20 nm), it was confirmed that the MoSe ₂ diffraction peak was reduced to an invisible level. In particular, when 10 nm was applied, the MoS ₂ diffraction peak was also greatly reduced, and it could be determined that the degree of formation was significantly reduced. The surface SEM image also clearly differed depending on whether or not the Cu-Al oxide interlayer was included. When the copper aluminum oxide interlayer of 10 nm was included, the growth of surface crystals appeared more clearly, and when the interlayer of 20 nm was included, the crystal shape was slightly reduced.

Experimental Example 7

XRD for flexible CZTSSe thin film solar cell 1 (10 nm) obtained in Example 1, comparative inorganic thin film solar cell 2 (None) obtained in Comparative Example 2, and comparative inorganic thin film solar cell 3 (NaF) obtained in Comparative Example 3 Analysis and SEM observation were performed and the results are shown in FIG. 8 .

Referring to FIG. 8, when only NaF dopant was added as in Comparative Inorganic Thin Film Solar Cell 3 (NaF), Mo(S,Se) ₂ peaks were found, but the crystal size of the absorber layer was increased, and the flexible CZTSSe thin film solar cell As shown in Fig. 1, when both the NaF dopant and the Cu-Al oxide intermediate layer were included, a decrease in Mo(S,Se) ₂ and an increase in crystal size were confirmed simultaneously. These results mean that the crystalline quality of the absorption layer was also increased at the same time as the Mo(S,Se) ₂ or more layer was removed through the simultaneous application of the intermediate layer and the dopant.

Experimental Example 8

For the flexible CZTSSe thin film solar cell 1 (10 nm) obtained in Example 1 and the comparative inorganic thin film solar cell 3 (NaF) obtained in Comparative Example 3, the elemental distribution of the CZTSSe thin film, which is the absorption layer, was confirmed by line scanning using a transmission electron microscope. And the results are shown in Figure 9.

9, Comparative Example inorganic thin-film solar cell 3 that does not include a Cu-Al oxide intermediate layer not only has Mo(S,Se) ₂ or more layers formed thickly, but also Cu, Zn, Sn, S, Se forming a CZTSSe thin film. It can be seen that the distribution of elements is also uneven.

On the other hand, in the flexible CZTSSe thin film solar cell 1 including the Cu-Al oxide intermediate layer, the thickness of the Mo(S,Se) ₂ or more layer was reduced, and the distribution of Cu, Zn, Sn, S, and Se elements constituting the CZTSSe thin film was evenly distributed. can confirm that it is. Through this, it was determined that the existence of the Cu—Al oxide intermediate layer between the flexible lower electrode substrate and the absorption layer reduces not only the Mo(S,Se) ₂ or more layer, but also the secondary phase formed in the absorption layer.

Experimental Example 9

Flexible CZTSSe thin film solar cell 1 (NaF / CAO) obtained in Example 1, Comparative inorganic thin film solar cell 2 (None) obtained in Comparative Example 2, and Comparative inorganic thin film solar cell 3 (NaF) obtained in Comparative Example 3 The electrical properties were analyzed and the results are shown in FIG. 10.

Referring to FIG. 10, the current-voltage characteristic factors of Comparative Inorganic Thin Film Solar Cell 2 (None) containing neither the NaF dopant nor the Cu-Al oxide intermediate layer are V _oc 467 mV, J _sc 33.70 mA/cm ² , FF 50.82%, η 8.00%, R _s 18.37 Ω, R _sh 711.34 Ω.

The current-voltage characteristic factors of the comparative inorganic thin-film solar cell 3 (NaF) containing only NaF dopant were V _oc 474 mV, J _sc 33.24 mA/cm ² , FF 53.94%, η 8.50%, R _s 13.40 Ω, R _sh It can be confirmed that it is 949.68 Ω.

The current-voltage characteristics of flexible CZTSSe thin-film solar cell 1 (NaF/CAO) containing both NaF dopant and Cu-Al oxide interlayer were V _oc 454 mV, J _sc 32.91 mA/cm ² , FF 60.29%, η 9.01% , R _s 9.50 Ω, R _sh 884.65 Ω.

As a result, compared to Comparative Example Inorganic Thin Film Solar Cell 2 (None), Comparative Example Inorganic Thin Film Solar Cell 3 (NaF) containing only dopants also had a flexible CZTSSe thin film solar cell 1 (NaF) containing both a NaF dopant and a Cu-Al oxide intermediate layer. /CAO), it was confirmed that the series resistance of the solar cell was sequentially greatly reduced and the filling factor was greatly improved.

Experimental Example 10

The electrical characteristics of the flexible CZTSSe thin-film solar cell 1 device obtained in Example 1 were tested as follows, and the results are shown in FIG. 11 . The electrical characteristics of the device were measured using a solar simulator, which was conducted by irradiating a solar cell with artificial light with an intensity similar to that of sunlight and measuring the conversion ratio of electrical output to incident light (100 mW/cm ² ). More specifically, the measurement is performed by contacting the back electrode portion connected to the light absorbing layer, which is a p-type semiconductor, to +, and the front electrode portion connected to the transparent electrode, which is an n-type semiconductor, to -. In addition, the temperature was maintained at room temperature (25 ° C.) in order to maximally exclude the influence of the temperature of the device. When measured using the device, V _oc , J _sc , FF and photoelectric conversion efficiency of the solar cell can be confirmed.

As shown in FIG. 11, it can be confirmed that all of the V _oc (Open Circuit Voltage), J _sc (Short Circuit Current Density), and FF (Fill Factor) values, which are characteristics of the inorganic thin film solar cell device obtained in the example, increased there was.

In FIG. 11 , it can be confirmed that the difference between the measurement result obtained by manufacturing the solar cell by performing the first heat treatment and the measurement result without performing the first heat treatment is very large. In the case of general cases where the first heat treatment is not performed, the second heat treatment is performed immediately at 500 to 600 ° C. by adding powder mixed with S and Se to the metal precursor deposited using joint sputtering. First, looking at the improvement of V _oc in FIG. 11, a maximum of 20 mV V _oc was improved. As mentioned in many previously published papers and literature, V _oc is a factor that is very greatly affected by the light absorption layer of a solar cell, and secondary phase and vacancies, defects, crystals in the light absorption layer If there is a lot of small growth of , the result of decreasing will appear. In the case of rising Jsc, the separation of charges becomes smooth and increases as they move to the anode of the solar cell without recombination. Recombination tends to be inversely proportional to grain size. FF is an element that is greatly affected by loss and resistance due to recombination, and FF was improved by a decrease in series resistance (series R) and an increase in shunt resistance (Shunt R). Therefore, it was confirmed that the increase in V _oc , J _sc , short-circuit resistance, and decrease in series resistance were caused by the improvement in film quality of the light absorbing layer through pre-heat treatment. Finally, it was confirmed that the photoelectric conversion efficiency increased due to the increase of V _oc , J _sc , and FF when the pre-heat treatment was performed.

Experimental Example 11

The electrical characteristics of the flexible CZTSSe thin film solar cell 1 device (joint sputtering) obtained in Example 1 and the comparative inorganic thin film solar cell 1 device (single sputtering) obtained in Comparative Example 1 were tested as follows, and the results are shown in FIGS. 12d. The measurement was performed using a solar simulator in the same manner and conditions as in Experimental Example 10 above.

As shown in FIGS. 12A to 12D , V _oc (Open Circuit Voltage), J _sc (Short Circuit Current Density), and FF (Fill Factor) values all increased in the inorganic thin film solar cell device manufactured by joint sputtering Able to know.

V _oc (Open Circuit Voltage) is the maximum voltage that can be obtained from the solar cell, and is the value when the current is zero. In CZTSSe thin-film solar cells, the V _oc value is changed by the formation of secondary phases such as SnS(e) ₂ , ZnS(e), Cu ₂ S(e), and Cu ₂ SnS(e) ₃ . The smaller the secondary phase formation, the higher the V _oc value. When joint sputtering and primary heat treatment were applied as in Example 1, a two-component compound could be formed well, and a high-quality CZTSSe thin film could be synthesized. This can be said to suppress the formation of the secondary phase during the synthesis of the CZTSSe thin film.

J _sc (Short Circuit Current Density) is the density of the current flowing through the solar cell when the voltage across the solar cell is 0. The value of J _sc varies depending on the presence or absence of recombination of carriers generated by solar energy. As the recombination of generated carriers decreases, the value of J _sc increases. It was confirmed that the CZTSSe thin film of Example 1 subjected to cavity sputtering had relatively large crystals. This can be said to reduce the grain boundary. A grain boundary is a place where carriers generated by sunlight recombine, and when recombination occurs, smooth movement of charges is impossible. This causes a decrease in solar cell conversion efficiency. Therefore, as in Example 1, when depositing by co-sputtering, dense and large crystal grains are formed to reduce grain boundaries, thereby reducing recombination of carriers and improving solar cell conversion efficiency.

FF (Fill Factor) is a factor that determines the maximum output of a solar cell and is expressed as follows.

F F =

The FF value increases as the loss due to recombination and resistance of light-generated carriers decreases. Therefore, when pre-heating and co-sputtering were applied, the formation of secondary phases was suppressed, a large-grained CZTSSe absorber layer was formed, and the formation of vacancies in the absorber layer was suppressed, thereby improving the FF value.

These experimental results show that when co-sputtering and primary heat treatment are performed as in the present invention when manufacturing a p-type compound semiconductor layer, the values of V _oc (Open Circuit Voltage), J _sc (Short Circuit Current Density), and FF (Fill Factor) increase, It shows that the photoelectric conversion efficiency is improved.

From the above experimental results, when the Cu-Al oxide intermediate layer is formed between the flexible lower electrode substrate and the absorption layer in the CZTSSe thin film solar cell including the flexible lower electrode substrate as in the present invention, the thickness of the Mo (S, Se) ₂ or more layer reduction can be seen. In addition, the distribution of the elements constituting the CZTSSe thin film, which is the absorption layer, is made more even, and finally, the R _s value of the CZTSSe thin film solar cell is significantly lowered, and the FF value is improved to achieve improved electrical characteristics of the solar cell, and ultimately, the flexible CZTSSe solar cell It can be seen that there is an effect of improving the conversion efficiency.

In addition, it can be seen that the addition of the dopant through the dopant layer improves the crystal quality of the flexible CZTSSe solar cell and CZTSSe thin-film solar cell and increases the fill factor (FF), thereby improving the conversion efficiency of the solar cell.

Therefore, the present invention improves the electrical characteristics of a solar cell by simultaneously applying a dopant and a Cu-Al oxide intermediate layer to a flexible CZTSSe solar cell, as well as manufacturing a p-type compound semiconductor layer by co-sputtering and primary heat treatment. It can be seen that it greatly contributed to the improvement of conversion efficiency.

Moreover, as described above, in the flexible CZTSSe thin film solar cell manufacturing method of the present invention, the Cu-Al oxide intermediate layer is manufactured through a co-vacuum evaporation method, which not only simplifies the manufacturing process, but also uses relatively inexpensive materials, It can be said that it is a novel and advanced interface and absorption layer quality control method that contributes to the improvement of device characteristics of flexible CZTSSe thin film solar cells even with thickness.

Although the present invention has been shown and described with preferred embodiments as described above, it is not limited to the above embodiments, and to those skilled in the art within the scope of not departing from the spirit of the present invention Various changes and modifications will be possible.

10: flexible lower electrode substrate 20: Cu-Al oxide intermediate layer
30: p-type compound semiconductor layer 40: n-type compound semiconductor layer
50: transparent electrode layer 60: upper electrode layer

Claims (22)

Forming a Cu-Al mixed layer on a flexible lower electrode substrate; oxidizing the Cu-Al mixed layer to form a Cu-Al oxide (CuAlO ₂ ) intermediate layer; forming a dopant layer on the Cu-Al oxide intermediate layer; forming a p-type compound semiconductor layer made of a CZTSSe thin film on the dopant layer; forming an n-type compound semiconductor layer on the p-type compound semiconductor layer; forming a transparent electrode layer on the n-type compound semiconductor layer; and forming an upper electrode on the transparent electrode layer.
Forming the p-type compound semiconductor layer
depositing Zn and Cu or Sn and Cu on the dopant layer by co-sputtering to form a first metal mixed layer in which Cu-Zn or Cu-Sn is mixed;
depositing Sn and Cu or Zn and Cu on the first metal mixture layer by co-sputtering to form a second metal mixture layer in which Cu-Sn or Cu-Zn are mixed;
The first metal mixed layer forms a first alloy layer composed of a Cu-Zn alloy or a Cu-Sn alloy, and the second metal mixed layer forms a second alloy layer composed of a Cu-Sn alloy or a Cu-Zn alloy. forming first and second alloy layers by performing a primary heat treatment on the first and second metal mixed layers; and
A flexible CZTSSe thin film solar cell manufacturing method, characterized in that it is formed by including;
According to claim 1,
The forming of the Cu-Al mixed layer is performed using a co-vacuum evaporation method so that the atomic ratio of Cu to Al is 40: 60 to 60: 40.
According to claim 2,
The Cu-Al mixed layer is a flexible CZTSSe thin film solar cell manufacturing method, characterized in that formed to a thickness of 5 nm to 25 nm.
According to claim 1,
The step of forming the Cu-Al oxide intermediate layer is a flexible CZTSSe thin film solar cell manufacturing method, characterized in that carried out by heat treatment for 1 hour to 2 hours at a temperature condition of 300 ℃ to 500 ℃ in an oxygen atmosphere.
According to claim 4,
A flexible CZTSSe thin film solar cell manufacturing method, characterized in that the elemental composition ratio of Cu-Al oxide (CuAlO ₂ ) forming the Cu-Al oxide intermediate layer is Al ₂ O ₃ : Cu ₂ O = 1: 1 at%.
According to claim 1,
The step of forming the dopant layer is a flexible CZTSSe thin film solar cell manufacturing method, characterized in that formed to 5 nm to 20 nm using a vacuum evaporation method.
According to claim 6,
The dopant layer is made of one selected from the group consisting of sodium fluoride (NaF), potassium fluoride (KF), rubidium fluoride (RbF) and cesium fluoride (CsF) Manufacturing a flexible CZTSSe thin film solar cell, characterized in that method.
delete According to claim 1,
Forming the first metal mixed layer or the second metal mixed layer
Zn is applied with a DC power of 60 to 80 W and Cu is applied with a DC power of 20 to 40 W, and simultaneously deposited for 900 to 1100 seconds under a process pressure condition of 7-9 mTorr, or
Flexible CZTSSe thin film solar cell characterized by applying DC power of 60 to 80 W for Sn and DC power of 35 to 55 W for Cu, and simultaneously depositing for 1400-1600 seconds under process pressure conditions of 7-9 mTorr manufacturing method.
According to claim 1,
The first and second alloy layer forming steps include first heat-treating the first and second metal mixed layers in an Ar or N ₂ atmospheric pressure atmosphere and a temperature condition of 200-400 ° C for 80-100 minutes and 150 minutes to Flexible CZTSSe thin film solar cell manufacturing method, characterized in that carried out including the step of natural cooling for 210 minutes.
According to claim 1,
In the CZTSSe thin film forming step, the first and second alloy layers are subjected to secondary heat treatment for 5 minutes to 10 minutes in an Ar atmosphere, a pressure of 450 to 550 Torr, and a temperature of 500 to 600 ° C together with S and Se powder. ; and naturally cooling to room temperature.
According to claim 11,
The secondary heat treatment is performed by putting the first and second alloy layers and S and Se powders in a graphite box, wherein the S and Se powders are included in a weight ratio of 1:90 to 1:120 Flexible CZTSSe Method for manufacturing thin-film solar cells.
According to claim 1,
The Cu-Zn alloy includes Cu ₆ Zn ₈ , and the Cu-Sn alloy includes Cu ₃ Sn and Cu ₆ Sn ₅ .
According to claim 1,
The CZTSSe thin film is characterized in that the secondary phase including SnS(e) ₂ , ZnS(e), Cu ₂ S(e), Cu ₂ SnS(e) ₃ is suppressed and composed of Cu ₂ ZnSn(S,Se) ₄ Flexible CZTSSe thin film solar cell manufacturing method.
The method according to any one of claims 1 to 7 and 9 to 14,
The flexible CZTSSe thin film solar cell manufacturing method, characterized in that the flexible lower electrode substrate is a metal thin plate or a conductive polymer thin plate. delete delete delete delete delete delete delete

Images