KR20170036606A - A CZTS based solar cell comprising a double light aborbing layer - Google Patents

Abstract

The present invention relates to a thin film solar cell including a dual light absorbing layer and a method for manufacturing the same, and more particularly, to a thin film solar cell that has a dual-layered light absorbing layer by applying a sulfurization process and a selenization process to a primary light absorbing layer and a secondary light absorbing layer having different bandgaps, and improves photo-conversion efficiency through improvement of a light absorption rate. The thin film solar cell according to the present invention includes two light absorbing layers having different bandgaps, and thus may absorb a wide region corresponding to the sunlight wavelength, thereby achieving high photo-conversion efficiency. In particular, when the light absorbing layer is formed between the rear electrode and the buffer layer in an order of CZTS/CZTSe, electrons formed in the two-layered light absorbing layer may form a smooth band interface between the light absorbing layer and the buffer layer, so that current characteristics may be entirely improved.

Description

[0001] The present invention relates to a CZTS thin film solar cell comprising a double light absorbing layer,

The present invention relates to a thin film solar cell including a dual light absorbing layer and a method of manufacturing the same. More particularly, the present invention relates to a thin film solar cell including a double light absorbing layer, To a thin film solar cell having a photoabsorption layer and a photoelectric conversion efficiency by improving a light absorptivity, and a method of manufacturing the same.

As fossil fuel depletion and environmental concerns grow, research on alternative energy sources is increasing. Among them, solar cell has been studied extensively among alternative energy sources because of advantages such as practicality, environment friendliness, and reflecting structure. Solar cells are largely divided into silicon, compound, organic and tentem solar cells.

The initial solar cell research was centered on silicon solar cells. However, since expensive silicon material costs or silicon is an indirect transition type semiconductor, it is necessary to solve a thick device thickness (several hundreds of micrometers) required to absorb an appropriate amount of solar light, Compound thin film solar cells (CdTe, copper-indium-gallium-sulfur (CIGS)) have been developed. Among them, CIGS solar cell has attracted attention as a next generation solar cell showing almost the same efficiency as monocrystalline silicon solar cell, but CIGS also has a disadvantage that it is expensive compared to demand due to the use of rare elements (indium, gallium).

In order to overcome this problem, Cu ₂ ZnSnSe ₄ (CZTSe), Cu ₂ ZnSnS ₄ (CZTS) or Cu ₂ ZnSn (S, Se) ₄ (CZTSSe) having a similar crystal structure (chalcogenide) (Hereinafter, referred to as "CZTS system") such as Cu-Zn-Sn- (S, Se)

The CZTS solar cell is a direct transition semiconductor compound that can be converted to 1.0 ~ 2.7eV bandgap through additional element doping, enabling flexible bandgap formation. In addition, it has a light absorption coefficient of 10-4 cm or more, which makes it possible to fabricate a high efficiency solar cell with a very thin thickness (1 to 2 μm) as compared with a silicon solar cell. Therefore, the CZTS solar cell is being actively researched as a next-generation eco-friendly low-cost solar cell that can replace expensive silicon solar cells that are currently in commercial use.

In the CZTS thin film solar cell, which is advantageous for realizing a low cost thin film solar cell, the photoelectric conversion efficiency characteristic depends on the light absorption rate of the absorption layer. A high photoelectric conversion efficiency can be realized when the wavelength region of incident sunlight is widely absorbed. Therefore, it is necessary to develop an absorbing layer material having a wide range of solar wavelength band that can absorb both sunlight in a short wavelength and a long wavelength region.

Accordingly, the present inventors have made a CZTS thin film solar cell capable of absorbing a broad wavelength region of the sunlight by including two light absorption layers having different band gaps. As a result, the CZTS / CZTSe sequence formed between the rear electrode and the buffer layer The present inventors have completed the present invention by confirming that the solar cell device including the double light absorbing layer has improved electrical characteristics.

Korean Patent No. 10-1542342

Accordingly, an object of the present invention is to provide a solar cell including a double light absorbing layer and having excellent cell characteristics and photoelectric conversion efficiency.

It is still another object of the present invention to provide a method of manufacturing the solar cell.

In order to achieve the above-mentioned object of the present invention,

The present invention provides a thin film solar cell including a dual light absorbing layer having two different band gap characteristics.

In one embodiment of the present invention, the solar cell may have a substrate, a rear electrode, a light absorbing layer, a buffer layer, a window layer, and a front electrode sequentially formed.

In one embodiment of the present invention, the double light absorbing layer may have one light absorbing layer band gap of 0.9 eV to 1.1 eV and another light absorbing layer band gap of 1.4 eV to 1.6 eV.

The present invention also provides a method of manufacturing a semiconductor device, comprising: forming a precursor layer on a back electrode; And forming a precursor layer on the sulfided precursor layer and then subjecting the precursor layer to a selenization treatment.

The present invention also provides a method of manufacturing a semiconductor device, comprising: forming a precursor layer on a rear electrode; And forming a precursor layer on the selenized precursor layer and then sulfiding the precursor layer.

In one embodiment of the present invention, the sulfidation treatment may be performed in a furnace in which the temperature of a portion where a sulfur source is placed and a portion where a device is placed are controlled differently.

In one embodiment of the present invention, the portion where the sulfur source is placed is controlled to a temperature of 250 to 350 ° C, and the portion where the device is placed can be controlled to a temperature of 550 to 600 ° C.

In one embodiment of the present invention, the precursor layer may be formed by sputtering, evaporation, CVD (Chemical Vapor Deposition), MOCVD (Metal Organic Chemical Vapor Deposition), Close-spaced sublimation , CSS, spray pyrolysis, chemical spraying, screen printing, non-vacuum liquid deposition, CBD (chemical bath deposition), VTD (vapor transport deposition) , And an electrodeposition method.

The thin film solar cell according to the present invention includes two light absorbing layers having different band gaps, so that it can absorb a wide wavelength region of the sunlight, thereby realizing high photoelectric conversion efficiency. In particular, when the light absorption layer is formed between the rear electrode and the buffer layer in the order of CZTS / CZTSe, electrons formed in the two light absorption layers can form a smooth band interface between the light absorption layer and the buffer layer.

1 shows the structure of a CZTS thin film solar cell.
FIGS. 2A, 2B, and 2C are schematic views schematically showing a manufacturing procedure of a light absorbing layer according to Comparative Example and Embodiments 1 and 2, respectively.
Fig. 3 shows a manufacturing process of a solar cell element in a comparative example.
Fig. 4 shows a process flow of manufacturing the solar cell element according to the first embodiment.
5 shows a process of manufacturing a solar cell element according to the second embodiment.
Fig. 6 shows a device structure to which each absorption layer according to Comparative Example, Examples 1 and 2 is applied.
FIG. 7 is a graph showing current-voltage characteristics of each solar cell device according to Comparative Example, Examples 1 and 2. FIG.

The present invention relates to a thin film solar cell including a dual light absorbing layer having two different band gap characteristics.

The embodiments of the present invention can be modified in various forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are provided to more fully describe the present invention. It is to be understood that any film (or layer) may be directly present on the other film (or layer) if it is described herein as being "on (or over) And a third other film (or layer) may be interposed therebetween.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings.

1 is a schematic configuration diagram of a thin film solar cell.

Referring to FIG. 1, a thin film solar cell may include a substrate 100, a rear electrode 200, a light absorption layer 300, a buffer layer 400, a window layer 500, and a front electrode 600.

The substrate 100 uses a substrate of hard material or a flexible material. For example, when the substrate 110 is made of a rigid substrate, it may include a glass plate, a quartz plate, a silicon plate, a synthetic resin plate, a metal plate, and the like. Preferably, a transparent insulating material may be used for the substrate. Specifically, soda lime glass, borosilicate glass, and alkali free glass substrate are included.

The rear electrode 200 formed on the substrate 100 may be formed of a metal such as Mo, Cu, Al, Ni, W, C, Ti, (Cu), gold (Au), or an alloy thereof. In this case, the electrode is preferably a molybdenum (Mo) electrode. Molybdenum (Mo) has high electrical conductivity and is capable of ohmic bonding with a CZTS-based light absorption layer, and is excellent in heat resistance characteristics and interfacial adhesion. The back electrode thickness may be from 0.2 탆 to 5 탆 and may be formed by a sputtering process.

The light absorbing layer 300 formed on the rear electrode 200 absorbs light to form electron-hole pairs, and transmits electrons and holes to the other electrodes to flow current. The light absorption layer may be a light absorbing layer of CZTS (Copper, Zinc, Tin, Sulfur or Selenide) series.

In one embodiment of the present invention, the light absorbing layer 300 may be a double light absorbing layer having two different band gap characteristics.

One of the double absorption layers may have a band gap of 0.9 eV to 1.1 eV and the other band of the absorption layer may be 1.4 eV to 1.6 eV.

6, the solar cell of the present invention has a structure in which the light absorption layer has two bandgaps different from each other as shown in FIG. 6 (Example 1: Cu ₂ ZnSnS ₄ / Cu ₂ ZnSnSe _{4, and} Example 2: Cu ₂ ZnSnSe ₄ / Cu ₂ ZnSnS ₄ ).

The buffer layer 400 formed on the light absorption layer may be at least one selected from the group consisting of CdS, ZnS, Zn (O, S), CdZnS and ZnSe, It plays a role of solving the high band gap.

The window layer 500 formed on the buffer layer 400 may be at least one selected from the group consisting of ZnO: Al, ZnO: AZO, ZnO: B (BZO), and ZnO: Ga (GZO) And functions as a transparent electrode on the front surface, so that the light transmittance can be high and the electric conductivity can be good.

The front electrode 600 formed on the window layer 500 functions to collect current from the surface of the solar cell. In the following embodiments, aluminum is used. However, if the front electrode used in the related art is limited specifically, It does not.

The present invention also provides a method of manufacturing a semiconductor device, comprising: forming a precursor layer on a back electrode; And a step of forming a precursor layer on the sulfided precursor layer and then performing a cellarizing treatment.

The present invention also provides a method of manufacturing a semiconductor device, comprising: forming a precursor layer on a rear electrode; And forming a precursor layer on the selenized precursor layer, followed by sulfiding the thin film solar cell.

The precursor layer may include one or more selected from the group consisting of a Cu layer, Zn layer, Sn layer, CuS layer, ZnS layer, SnS layer, CuSe layer, ZnSe layer, SnSe layer, CuSSe layer, ZnSSe layer, The above layers may be formed in a laminated structure.

The precursor layer may be formed by sputtering, evaporation, chemical vapor deposition (MOCVD), close-spaced sublimation (CSS), sputtering A chemical vapor deposition method, a chemical vapor deposition method, a chemical vapor deposition method, a screen printing method, a non-vacuum liquid phase film forming method, a CBD method (chemical bath deposition), a VTD method (vapor transport deposition), and an electrodeposition (Deposited) by any one of the following methods.

The sulfiding or selenization process may be performed in an inert gas atmosphere in a closed chamber. When a sealed chamber is used, penetration of selenium or sulfur element can be effectively carried out. The inert gas may be argon (Ar), but the inert gas is not limited thereto.

The sulfidation treatment may be performed in a furnace in which the temperature of a portion where a sulfur source is placed and a portion where a device is placed are controlled differently. For example, the sulphidation process is performed in a 2-zone furnace, where a sulfur source is located in a first zone of the furnace and a precursor layer is formed in a second zone of the furnace having a temperature higher than the first zone The device may be located. At this time, the portion where the sulfur source is placed is controlled to a temperature of 250 to 350 ° C, and the portion where the element is placed can be controlled to a temperature of 550 to 600 ° C. The sulfur source may be in the form of a powder, and argon (Ar) gas may be supplied to the two heat treatment zones through a quartz tube, and the sulfidation process may be performed for 10 to 60 minutes.

The thickness of the CZTS light absorbing layer formed through this process may be 0.5 nm to 3.0 탆.

In one embodiment of the present invention, the thin film solar cell manufacturing method may further include forming a rear electrode on the substrate before the step of forming the light absorbing layer on the rear electrode, Forming a buffer layer on the light absorbing layer after forming the buffer layer; Forming a window layer on the buffer layer; And forming a second electrode on the window layer.

The buffer layer may be formed by a vacuum process, a thermal deposition process, or a chemical solution deposition (Chemical Bath Deposition) method, but the method of forming the buffer layer is not limited thereto.

At this time, the buffer layer may be made of CdS, ZnS, Zn (O, S), CdZnS, Inx (OH, S) y, ZnSe and Zn1-xMgxO, but the buffer layer is not limited thereto.

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

If the thickness of the buffer layer is less than 10 nm or more than 200 nm, the light transmittance is decreased, and electrons are difficult to be transmitted to the upper electrode due to the increase of the depletion layer width.

The window layer may be formed by a sputtering method, a vacuum method, a thermal deposition method, or a chemical solution deposition method, but the method of forming the window layer is not limited thereto.

At this time, the window layer may be made of ZnO: Al, ZnO: AZO, ZnO: B (BZO) and ZnO: Ga (GZO), but the window layer is not limited thereto and may have a high light transmittance Excellent materials can be appropriately selected and used.

Meanwhile, the thickness of the window layer may be 100 to 1000 nm.

If the thickness of the window layer is less than 100 nm or more than 1000 nm, a decrease in light transmittance and a decrease in the current-voltage characteristic may cause a problem that the light efficiency of the device is reduced.

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

< Comparative Example >

CZTS system  Photovoltaic device manufacturing

The soda lime glass substrate (SLG) was washed with acetone and methanol at 300 ° C for 10 minutes each with ultrasonic waves, and then washed with distilled water. Then, a molybdenum (Mo) rear electrode layer having a thickness of 0.5 μm was formed on the substrate by a sputtering process .

Thereafter, the absorption layer precursor was deposited to a thickness of about 0.7 μm in the order of Zn, Sn, and Cu. After the formation of Cu ₂ ZnSnSe ₄ by applying a selenization process at 540 ° C. through a rapid thermal process (RTP), a CdS buffer layer having a thickness of about 50 nm is formed, and then about 50 nm thick ZnO and aluminum After forming a window layer in which doped ZnO was formed to a thickness of about 0.3 탆, an aluminum front electrode having a thickness of about 0.5 탆 was formed.

The device manufacturing process sequence is illustrated in FIG. 2A.

< Example  1>

Two The light absorbing layer  Included CZTS system  Solar cell manufacturing

In the device according to Example 1, only the absorption layer process was performed differently in the element process of the comparative example.

The precursors (Zn, Sn, Cu) were deposited to a thickness of about 0.3 탆 on the back electrode in the same manner and then subjected to a sulfurization process in the furnace. In the furnace, the temperature of the portion where the sulfur source is placed and the portion where the device is placed is controlled differently in the sulfurization process. Sulfurization process was applied for 10 minutes by controlling the temperature of the part where the sulfur source was placed at about 300 ° C and the part where the device was placed at about 570 ° C. Through this process, a Cu ₂ ZnSnS ₄ light absorbing layer was first formed on the back electrode. After the precursors (Zn, Sn, Cu) were deposited to a thickness of about 0.4 탆, a rapid thermal annealing process as in the comparative example was applied and a selenization process was performed at 540 캜 for 10 minutes to form a Cu ₂ ZnSnSe ₄ light absorption layer . The device was fabricated through the same process as the comparative example in the two light absorbing layers thus formed.

The device manufacturing process sequence is illustrated in Figure 2B.

< Example  2>

Two The light absorbing layer  Included CZTS system  Solar cell manufacturing

In the device according to Example 2, only the absorption layer process was carried out differently in the device process of the comparative example.

The precursor was deposited to a thickness of about 0.4 탆 on the back electrode in the same manner and then subjected to a rapid thermal annealing process as in the comparative example to apply a selenization process at 540 캜 for 10 minutes to form a Cu ₂ ZnSnSe ₄ light absorbing layer on the rear positive First. Thereafter, the precursor was deposited to a thickness of about 0.3 占 퐉, and then the sulfiding process was carried out in the furnace. In the furnace, the temperature of the portion where the sulfur source is placed and the portion where the device is placed is controlled differently in the sulfurization process. The sulfur source was controlled at about 300 ° C and the device was placed at about 570 ° C for 10 minutes. Through this process, a Cu ₂ ZnSnS ₄ light absorbing layer was formed. The device was fabricated through the same process as the comparative example in the two light absorbing layers thus formed.

The device manufacturing process sequence is illustrated in Figure 2C.

< Experimental Example  1>

Of solar cell element Light conversion  Evaluation of efficiency

The light conversion efficiencies of the solar cells including the thin films according to Examples 1 and 2 and the thin films according to the comparative examples were compared.

As a result, as shown in Table 1 and Fig. 7, the photoelectric conversion efficiency of the device manufactured by the comparative example was 3.08%. On the contrary, in the case of Example 1, the open-circuit voltage, the short-circuit current, and the filling factor characteristics were improved to 5.37% as compared with the comparative example.

The Cu ₂ ZnSnS ₄ layer increases the bandgap of the light absorbing layer as a whole and the open voltage is improved. The electrons formed in the two light absorption layers move to the upper electrode through the smooth band interface of the Cu ₂ ZnSnSe ₄ layer and the CdS buffer layer The current characteristics are improved and the efficiency is improved as a whole.

On the other hand, in the case of Example 2, the open-circuit voltage was improved much as compared with the comparative example, but the short-circuit current characteristic was decreased. In Example 2, as compared to Example 1, the sulfidation process is applied to the last step of the absorption layer. Therefore, the sulfur in the absorbent layer of Example 2 is more distributed than in Example 1 as a whole. Since sulfur increases the bandgap of the absorber layer, the open-circuit voltage can be improved due to the increased absorption bandgap. However, the Cu ₂ ZnSnS ₄ layer applied to the upper part of the absorption layer of Example 2 becomes unstable in the band interface characteristic with the CdS buffer layer. This instability lowers the characteristic of electrons moving to the front electrode, and therefore, the short-circuit current characteristic is lowered in the second embodiment.

As a result of the above-mentioned results, it is possible to effectively improve the photoelectric conversion efficiency in the case of stacking Cu ₂ ZnSnS ₄ / Cu ₂ ZnSnSe _{4 on} the rear electrode in the order of double light absorption layer structure as in Embodiment 1 of the present invention Respectively.

Electrical characteristics of solar cell devices according to Examples 1, 2 and Comparative Example Sample Absorption layer structure Open-circuit voltage
(V) Short-circuit current
(mA / cm ² ) Filling rate
(%) efficiency
(%) Comparative Example Substrate / Mo / CZTSe 0.321 24.04 39.88 3.08 Example 1 Substrate / Mo / CZTS / CZTSe 0.367 35.47 41.29 5.37 Example 2 Substrate / Mo / CZTSe / CZTS 0.536 12.49 51.48 3.45

The present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

100: substrate
200: rear electrode
300: light absorbing layer
400: buffer layer
500: window layer
600: front electrode

Claims (8)

A thin film solar cell comprising a dual light absorbing layer having two different band gap characteristics. The method according to claim 1,
A thin film solar cell comprising a substrate, a rear electrode, a light absorbing layer, a buffer layer, a window layer, and a front electrode sequentially formed. The method according to claim 1,
Wherein the double light absorbing layer has one light absorbing layer band gap of 0.9 eV to 1.1 eV and another light absorbing layer band gap of 1.4 eV to 1.6 eV. Forming a precursor layer on the rear electrode, and then sulfiding the precursor layer; And
Forming a precursor layer on the sulfided precursor layer, and subjecting the precursor layer to a selenization treatment. Forming a precursor layer on the rear electrode, and then selenizing the precursor layer; And
Forming a precursor layer on the selenized precursor layer, and then sulfiding the precursor layer. The method according to claim 4 or 5,
Wherein the sulfiding treatment is performed in a furnace in which a temperature of a portion where a sulfur source is placed and a temperature of a portion where a device is placed is controlled differently. 6. The method of claim 6,
Wherein a portion where the sulfur source is placed is controlled to a temperature of 250 to 350 ° C, and a portion where the element is placed is controlled to a temperature of 550 to 600 ° C. The method according to claim 4 or 5,
The precursor layer may be formed by sputtering, evaporation, chemical vapor deposition (MOCVD), close-spaced sublimation (CSS), spray pyrolysis Spray drying, spray pyrolysis, chemical spraying, screen printing, non-vacuum liquid deposition, CBD (Chemical Bath Deposition), VTD (vapor transport deposition), and electrodeposition Wherein the thin film solar cell is formed by any one method.

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