KR101407161B1 - Manufacturing method of CZTS-based thin film solar cell light absorber - Google Patents

Abstract

The present invention relates to a method of manufacturing a CZTS-based thin film solar cell light absorber. The method of manufacturing a CZTS-based thin film solar cell light absorber according to one embodiment of the present invention includes a step of preparing a CZTS-based precursor; a step of placing a sample tray in a rapid thermal process reactor and performing a rapid thermal process (RTP); a preannealing step for synthesizing nSex or SnSx; and a selenization step after the preannealing step.

Description

[0001] The present invention relates to a CZTS-based thin film solar cell light absorber,

The present invention relates to a method for producing a CZTS (CZTS and CZTSe) thin film used as a solar cell light absorbing layer, and more particularly, to a method for producing a CZTS (CZTS and CZTSe) The present invention relates to a technique capable of manufacturing a CZTS-based solar cell light absorbing layer thin film while minimizing the thickness of the light absorbing layer.

Thin film solar cells using CIGS (CIS, CGS, CIGS, CIGSS, etc.) compound semiconductors can control the energy band gap (1.0 ~ 1.7eV) In addition, cell efficiency is up to 20.4%, and it is currently being studied with great interest not only in Korea but also in the world. However, CIS and CIGS thin film solar cell materials have a disadvantage in that they use less expensive and inexpensive materials such as In and Ga. In order to compensate for the drawbacks of increasing the unit price due to such shortage of materials, compound semiconductors such as Cu ₂ ZnSnSe ₄ (CZTSe) and Cu ₂ ZnSnS ₄ (CZTS) ) Have been actively studied as an alternative to CIGS thin film materials, and they are known to have an energy band gap from 0.8 eV (CZTSe) to 1.5 eV (CZTS).

The present invention relates to a CZTS-based light absorbing layer (collectively referred to as CZTS and CZTSe). In the CZTS system, the components of a precursor react with each other through RTP from a precursor to produce a CZTS-based light absorbing layer thin film. The Sn in the precursor does not participate in the process of preparing the CZTS-based light-absorbing layer thin film, evaporates and is lost, thereby causing a problem of interfacial separation between the Mo and CZTS-based light-absorbing layer . Such interfacial separation deteriorates the efficiency of the CZTS thin film, resulting in a decrease in efficiency of the thin film solar cell using the CZTS light absorption layer.

Patent Registration No. 10-1093663

The object of the present invention is to solve the problem of increasing the loss of Sn from the precursor when the temperature is elevated to a high temperature in the RTP process in order to produce a CZTS-type light absorbing layer thin film, thereby reducing the efficiency of the solar cell.

In order to achieve the above object, the present invention provides a method for producing a CZTS-based light absorbing layer by selenizing or sulphating a CZTS-based precursor through RTP (Rapid Thermal Process), the method comprising: And a cover covering the case. The sample tray is placed in an RTP reactor in which a purge gas flows continuously through an inlet and an outlet and a heat source for RTP (Rapid Thermal Process), and RTP is performed. (Se or S) coating layer in which Sn or S coating layer and Sn on the coating layer are sequentially stacked on the inner surface of the cover, the RTP is a pre-annealing process for synthesizing SnSe _x or SnS _x , And a step of selenization or a step of sulphurization after the annealing process. Provided.

Particularly, it is preferable that the CZTS-based precursor is formed by forming a Mo electrode on a glass substrate, then stacking an Sn layer, a Cu layer and a Zn layer on the glass substrate in order, or an Se layer or an S layer.

Particularly, it is preferable that the pre-annealing process is performed at 230 to 480 ° C, and the selenization or sulfuration process is performed at 500 to 600 ° C.

Particularly, the inner surface of the cover of the sample tray is patterned into a portion having a Sn / (Se or S) coating layer and a portion having no Sn / (Se or S) coating layer and heat generated from the heat source through the portion having no Sn / It is preferable to allow it to pass.

Particularly, the Sn / (Se or S) coating layer is formed on the inner surface of the cover of the sample tray only in the corner portion except for the central portion, or the portion where the Sn / (Se or S) Shaped cross-section.

In particular, the heat source is preferably an IR heater.

In particular, the pre-annealing is preferably performed for 3 to 30 minutes.

The present invention relates to a method for producing a CZTS-based light absorbing layer thin film by CZTS-based precursor through RTP-based selenization or sulphation by supplying SnSe _x as a precursor from Se and Sn coated inside the cover of a sample tray, It is possible to reduce the loss of Sn in the precursor during the selenization or the sulphation of the precursor, thereby making it possible to manufacture a CZTS-type photoabsorption layer having excellent photoelectric efficiency. Also, a reduction in the loss of Sn can reduce the production of bidentate by-products such as ZnSe, which is known to cause a decrease in photoelectric efficiency and a decrease in interfacial adhesion

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram illustrating an example of a preferred multilayer structure of a CZTSe precursor of the present invention.
FIG. 2A is an RTP system of the present invention, and FIG. 2B is an enlarged view of a reactor and a sample tray portion of the RTP system.
2C is a cross-sectional view of the cover in a state in which the Se layer and the Sn layer are stacked in order on the inner side of the sample tray cover.
2D and 2E are views showing an example of a preferable pattern of the Sn / Se coating layer on the inner side of the sample tray cover.
3A is a two-component thermodynamic equilibrium diagram of Sn-Se.
FIG. 3B shows the XRD measurement results of the glass / Mo / Sn / Se sample.
FIG. 3C shows the result of measuring the decomposition of SnSe ₂ with respect to time.
FIG. 3D is an RTP temperature profile used in the experimental example, and FIG. 3E is a view for explaining the phase change of the Sn / Se coating layer coated on the inner side of the sample tray cover in the RTP process.
FIG. 4A is a graph showing the results of Raman spectroscopy when a CZTSe light absorbing layer (SnSe external supply) prepared by the method of the present invention is prepared and a CZTSe light absorbing layer (No SnSe supply) And FIG. 4B is a result of Raman analysis of the Mo surface after interfacial separation of Mo and CZTSe light absorbing layers in each sample of FIG. 4A.
FIG. 5 shows SEM measurement results for each sample of FIG. 4A.

In the present invention, in order to solve the problem that the Sn in the precursor layer is evaporated and lost due to the formation of a multi-layered CZTS-based precursor layer on the Mo back electrode and the selenization or sulfuration of the CTZS-based precursor, Application of a sample tray system, which was used to manufacture a CIGS light absorbing layer of quartz material of Registration No. 10-1111047, was applied to the inner surface of a quartz sample tray cover by sputtering and evaporation, coated Sn layer (light-absorbing layer during manufacture CZTSe) in turn, or, S layer and in SnSe, RTP process, and then (CZTS light absorption during manufacturing) coating, as the Sn layer sequence _x Or SnS _x is supplied to the CZTS-based precursor layer, thereby minimizing the loss of Sn and improving the adhesion between Mo and the CZTS-based light-absorbing layer thin film.

Hereinafter, the CZTSe light absorbing layer thin film will be described with reference to the CZTSe light absorbing layer thin film. CZTS and CZTSe light absorbing layer are replaced with Se instead of S, Sn is lost in the same RTP process, and the loss of Sn can be reduced by the same method. Hereinafter, for convenience of explanation, I will explain.

CZTSe  Precursor

As described above, in the present invention, Cu, Zn, Sn and Se, which are the materials of the CZTSe light absorbing layer, are laminated on the Mo electrode to form a CZTSe precursor, and then Se and Sn are simultaneously implanted into the precursor by RTP (Rapid Thermal Process) And the CZTSe light absorbing layer thin film is completed. For reference, in the case of CZTS, the S layer may be stacked instead of Se.

In particular, as shown in Fig. 1, it is preferable that the Mo thin film layer, the Cu thin film layer, the Zn thin film layer and the Se thin film layer are sequentially stacked on the Mo electrode. Of course, it is also possible that the precursor layers composed of a composite component such as CuSn and CuZn are laminated in multiple layers. However, in this case, since the composition control is difficult and the manufacturing cost is increased, it is preferable that the single- .

In order to minimize the loss of Sn, it is preferable to deposit Sn at the bottom of the precursor, and to deposit Zn and Sn, which form a good alloy with Zn, in Zn and Sn. In the experimental example of the present invention, the thickness of the CZTSe precursor is 400 to 500 nm. When Se is deposited only inside the quartz cover which is supplied to the CZTSe precursor layer in the RTP process, the Se deposition is not sufficient. And Se was deposited thereon. Thereafter, selenization was performed in an Ar atmosphere through RTP (rapid thermal process). On the other hand, as shown in FIG. 1, Se precursor layers in the CZTSe precursors were 1, 3, and 5 탆, respectively, and the influence of the Se precursor layer thickness on the selenization process was examined.

The Sn, Cu, and Zn thin film layers, which are metal layers, can be stacked using a sputtering system, and the Se thin film layers can be stacked using a thermal evaporation system. In the experiments of the present invention, a Mo-coated glass was used to prepare a CZTSe precursor. As the target of the sputtering, Cu, Zn, and Sn having a purity of 4N were used, and all of them were deposited by DC sputtering. The process conditions were Ar 30 sccm, base pressure 3.0 x 10 ^-6 Torr, working pressure 5.0 mTorr, and substrate rotating velocity 8 rpm.

RTP Selenization  Device

FIGS. 2A and 2B are a drawing and a partially enlarged view of a preferred RTP selenization system 100 of the present invention. The RTP-based selenization system 100 used in the present invention is disclosed in Korean Patent No. 10-1111047 Respectively.

That is, a sample tray 10 including a case 11 of a quartz-shaped container shape and a cover 12 of a quartz lid covering the case 11 is used. A CZTSe precursor sample in which respective materials are stacked is placed in a case 11 to cover the cover 12 and Se and Sn are coated on the inner surface 12b of the cover to supply Se and Sn, Are stacked in order. Se can be Sn / Se laminated by thermal sputtering and sputtering Sn onto the heat-deposited surface of Se. For reference, in the production of the CZTS light absorbing layer, S is coated on the inner side surface 12b by thermal evaporation instead of Se, and then Sn is coated thereon by sputtering and stacked with Sn / S.

In the conventional RTP method, a CZTSe precursor sample is placed in a sample tray and covered with a quartz cover to minimize Se loss during the process. However, such a conventional method has difficulty in sufficiently supplying Sn and Se. In the present invention, Se and Sn are sequentially coated on the inner surface 12b of the quartz cover in a double layer and supplied as SnSe _x binary system vapor during the process, thereby preventing loss of Sn in the CZTSe precursor.

2A and 2B, the sample tray 10 of the present invention is contained in a tubular reactor 20 made of a quartz material and has an exothermic heat such as an IR heater for heating the sample tray 10 out of the reactor 20 (31), and it is preferable that the tube-shaped reactor (20) is provided at regular intervals around the outside of the reactor (20). The heat generating means (31) is preferably installed in the heat generating tube (30). The exothermic tube 30 preferably has a donut shape surrounding the reactor 20 at the center. For example, one IR lamp is installed every 45 degrees so that heat is transferred to the sample tray 10 in the reactor 20 through a total of eight IR lamps. An inert gas such as Ar or H ₂ S is continuously fed into the reactor 20 for purge during the RTP reaction and a plurality of thermometers 40 are provided in the reactor 20 to provide various Measure the temperature of the point.

As shown in FIG. 2C, Se layer -> Sn layer is sequentially stacked on the inner side surface 12b of the cover 12 in order, but there must be a portion where there is no Sn / Se coating layer as shown in FIGS. 2d and 2e. This is because the Sn coating layer absorbs all the light of the heating means 31 such as the IR lamp and the light (= heat) can not reach the CZTSe sample in the case 11, There should be no. FIG. 2d shows a shape without a Sn / Se coating layer in the middle part, and FIG. 2e may show a shape in which a Sn / Se coating layer part and a missing part intersect like a checkerboard. The pattern of the Sn / Se coating layer may be coated with Se and Sn sequentially by sputtering and vapor deposition using masks of various patterns, respectively.

The reason put Sn coating layer over Se coating layer in the present invention, since the evaporation temperature of the Se is lower than Sn Se When immediately evaporated in a RTP process, SnSe _x by giving prevent the Sn coating layer on the Se coating layer because it does not create an SnSe _x reason So as to be synthesized to be a steric compound.

RTP  fair

In the present invention, the temperature is controlled in two steps in the RTP process for selenization. A preannealing process for forming SnSe _x by reacting the Sn / Se layer coated on the inner surface 12b of the cover 12; and a pre-annealing process in which SnSe _x is evaporated at a temperature higher than the pre- And a selenization process to form a CZTSe light absorbing layer. For reference, in the case of the CZTS light absorbing layer, SnS _x is produced in the pre-annealing process, and sulfuration is performed instead of selenization.

FIG. 3A shows the results of the high temperature XRD measurement of the selenization process of the Sn-Se binary phase balance degree and the temperature of the layers stacked in the order of Sn and Se on the Mo electrode of FIG. 3B. The melting points of Se and Sn are about 220 and 230 ℃, respectively. In the above phase diagrams, it can be seen that SnSe and SnSe ₂ appear as the binary compound of Sn-Se. Further, a region in which the liquid phase and the solid compound coexist appears, and L ₁ + γ-SnSe, L ₁ + δ-SnSe, L ₂ + SnSe and L ₂ + SnSe ₂ exist. 1078K It can be confirmed that the miscibility of the liquid phase exists at a high temperature.

As shown in the XRD results of FIG. 3B, recent research results on the mechanism of selenization of metallic Sn have been reported. The selenization mechanism was analyzed by using high temperature XRD by depositing Sn and Se on each layer of Mo coated glass. The initial Se layer is present in an amorphous state and only Sn peaks are present. After that, Se crystallizes in the range of 110-220 ° C and begins to melt at 220 ° C. Sn is present in a single phase up to 230 캜, and then begins to melt and react with Se. The SnSe formed at 230 ℃, Se is constantly generated SnSe ₂ at about 280 ℃ as oversupply. The SnSe ₂ thus produced is decomposed again into SnSe and Se at about 500 ° C. In this process, loss of Sn occurs.

Referring to the ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy) of FIG. 3C, the Sn loss due to decomposition of SnSe ₂ into SnSe and Se at a high temperature of 480 ° C. is shown. It can be seen that, at high temperature, SnSe ₂ is decomposed into SnSe and Se, as well as Se, as well as Sn. In particular, since after 30 minutes SnS _e2 is excessively decomposed to SnSe pre-annealing time is less than 30 minutes preferably, in view of the Sn and the time for the SnSe ₂ is formed by Se the reaction pre-annealing is haejueoya is more than 3 minutes .

In the present invention, when the temperature of the pre-annealing section is set to 230 ° C or more at which Sn and Se are both melted, Sn may react to form a binary compound of SnSex, and the maximum temperature of the pre- ₂ is decomposed into SnSe and Se, it is preferably 480 DEG C lower than the selenization temperature. This is also preferable in the CZTS light absorbing layer in the above temperature range on the same principle. This nopeunde point of Sn than the melting point of S melting, in order to form a SnS _x and the lower limit is preferably 230 ℃ because they must be the melting point or higher of Sn, the upper limit value also in view of that the SnS ₂ is decomposed into SnS and S 480 Lt; 0 > C.

On the other hand, the selenization temperature of RTP is preferably 500 to 600 ° C as is commonly known. Selenization does not occur well at temperatures below 500 ° C, and glass substrate melts at temperatures above 600 ° C. In particular, the sulfuration temperature is more preferably 550 to 600 ° C.

In the experiment of the present invention, RTP was performed with the temperature profile of FIG. Sn and Se of the quartz cover were pre-annealed at 300 ° C for 5 minutes to form a SnSe _X binary compound, and selenized at 550 ° C for 10 minutes to produce a CZTSe light absorbing layer well.

As shown in FIG. 3E, the SnSe _X type binary compound is produced at the initial deposition of Se and Sn at 300 ° C. The resulting binary phase SnSe _X is fed to the CZTSe precursor sample in vapor form. Some others it is possible to form the _X SnSe After the reaction was finished, the cover inner surface (12b).

Experimental Example  1: Raman analysis result

4A is a Raman measurement result when a CZTSe optical absorber layer (SnSe external supply) manufactured by the method of the present invention and a CZTSe optical absorber layer (No supply) using only Se of a precursor layer as a Se source are used in the prior art. The intensity of the CZTSe light absorption layer peak was high, indicating that the CZTSe phase was better formed.

4B is a result of Raman analysis of the Mo surface after separating the Mo and CZTSe interfaces from the CZTSe light absorbing layer thin film sample of FIG. 4A. CZTSe (No supply in FIG. 4B) prepared by using a Se precursor layer as a source of Se without additional supply of SnSe produced a large amount of a second phase (ZnSe) at the interface of Mo / CZTSe as in the conventional method. When ZnSe is formed at the Mo / CZTSe interface, it increases the series resistance and decreases the efficiency of the cell. Therefore, the Mo / CZTSe interfacial adhesion can be lowered and the CZTS thin film may be peeled at the post-process . On the other hand, in the case of the method of the present invention, by supplying SnSe more, the amount of Sn becomes sufficient, thereby reducing the generation of secondary phases such as ZnSe and enhancing the interfacial adhesion.

Experimental Example  2 : SEM  Measurement result

Fig. 5 shows the result of SEM measurement according to the thickness of the Se layer of the CZTSe precursor layer prepared by supplying the "No supply" and the SnSex of the present invention from the outside. In the CZTSe thin film optical absorption layer produced by the method of the present invention It was confirmed that the peeling between Mo and the CZTSe thin film layer was small and adhesion was good.

As a result, the formation of the secondary phase was reduced, and the adhesion between Mo and CZTSe was improved by the sufficient supply of Sn, and it was confirmed that the CZTSe grain was well formed.

Claims (7)

A method for producing a CZTS-based light absorbing layer by selenizing or sulfurizing a CZTS-based precursor through RTP (Rapid Thermal Process)
The CZTS precursor is prepared and placed in a sample tray including a case of quartz and a cover covering the case, and a purge gas flows continuously through the inlet and the outlet and is supplied to a RTP reactor equipped with a heat source for RTP (Rapid Thermal Process) Placing the sample tray and performing RTP,
(Sn or S) coating layer in which Se or S coating layer and Sn on the coating layer are laminated in order on the inner surface of the cover,
Wherein the RTP comprises two steps of a pre-annealing step for synthesizing SnSe _x or SnS _x and a selenization or sulphation step after the pre-annealing step.
The CZTS-based precursor according to claim 1, wherein the CZTS-based precursor is formed by forming a Mo electrode on a glass substrate, and then depositing a Se layer or an S layer on the Sn layer, the Cu layer, A method for manufacturing a battery light absorbing layer.
The method of claim 1, wherein the RTP is performed at a temperature of 230 to 480 ° C, and the selenization or sulphation process is performed at a temperature of 500 to 600 ° C.
The method of claim 1, wherein the inner surface of the cover of the sample tray is patterned into a portion having a Sn / (Se or S) coating layer and a portion having no Sn / (Se or S) coating layer, Wherein the CZTS-based solar cell comprises a plurality of solar cells.
The method according to claim 4, wherein a Sn / (Se or S) coating layer is formed on the inner surface of the cover of the sample tray in a strip shape except for the central portion, Wherein the first and second portions are formed so as to cross each other in a checkerboard shape.
The method of claim 1, wherein the heat source is an IR heater.
The method of claim 1, wherein the pre-annealing process is performed for 3 to 30 minutes.

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