KR20160096864A - Method for the fabrication of Cu(InGa)Se2 thin film solar cell and thereof - Google Patents

Abstract

The present invention relates to technology for growing a CIS thin film crystal by RTP. Cu_(2-x)Se is transformed into CuSe and/or CuSe2 by a first step RTP, thereby promoting crystal growth by the assistance of a liquid state in a second step RTP performed at a higher temperature compared to the first step, and also performing CIS thin film crystal growth having few defects. So, the problem of crystal growth in the RTP process can be solved.

Description

TECHNICAL FIELD [0001] The present invention relates to a CIS-based thin film solar cell using a two-step RTP process and a CIS-based thin film solar cell produced by the above-

The present invention relates to a method of manufacturing a CIS-based thin film solar cell, and more particularly, to a method of manufacturing a CIS-based thin-film solar cell using RTP, in which a crystal growth is promoted with the help of a liquid phase, This invention relates to a method for manufacturing a CIS thin film solar cell using the "liquid assisted grain growth" effect.

An IB-IIIA-VIA group including a part of the IB group (Cu, Ag, Au), IIIA group (B, Al, Ga, In, Ti) and VIA group (O, S, Se, Te, Po) Compound semiconductors are excellent light absorption p-type semiconductors for thin film solar cell structures. In particular, the p-type semiconductor is classified into CIS, CIGS, and CIGSS depending on whether or not In and Ga are used at the same time and whether Se and S are used at the same time. Typically, a thin film solar cell using the p- It is called a battery. In all cases the formula Cu can also be expressed _{- - (z S z Se 1} ) 2 ( _{wherein, 0≤y, z≤1) (In 1} y Gay).

In particular, the CIGS photoabsorption layer has been considered as a candidate material most likely to be a light absorbing layer of a high-efficiency thin film solar cell, and commercialization attempts have been made by many domestic and foreign companies due to the possibility of low-cost large-area deposition. The most important advantages of CIGS compound are its high photo-conversion efficiency, which is 21.7% (ZSW, 2014) for CIGS thin film solar cells (about 0.5 cm ² ) The maximum conversion efficiency of

Various physico-chemical methods have been successfully applied to form the CIS-based light-absorbing layer on the back electrode, but typical methods include co-evaporation and precursor-selenization .

The simultaneous evaporation method is a method in which individual elements Cu, In, Ga, and Se are placed in an effusion cell, evaporated in a high vacuum atmosphere, and deposited on a substrate at a high temperature (550 to 600 ° C.) ) Can be measured and adjusted, respectively, so that it is possible to effectively control the composition distribution of the CIS-based thin film to be produced. However, the simultaneous evaporation method is a batch process when a point source is used in a bell jar, and the simultaneous evaporation method has a disadvantage in that the composition of a thin film produced when using a large- There is a difficulty in.

A typical process utilizing the simultaneous evaporation method is a three-step process, such as a patented technology (US 5436204) of the National Renewable Energy Laboratory (NREL) in the United States. In this method, production of a thin film solar cell with a record efficiency of 20% Is reported to be possible.

The NREL technique can be summarized as shown in FIG. Referring to FIG. 1A, in the first of three stages of NREL, In and Ga react with excess Se at a relatively low temperature (about 400 ° C.) to form (InGa) ₂ Se ₃ . In the second step, only Cu at high temperature (about 600 ° C) is introduced with an excess of Se to react with (InGa) ₂ Se ₃ prepared in the first step to form chalcopyrite CIGS. During the second step, Cu is supplied to (InGa) ₂ Se ₃ , and the excess Cu remaining after forming the Cu (InGa) Se ₂ phase forms a metallic secondary phase, which is present in a liquid state at a relatively low temperature of 520 ° C Fig. 1b Cu-Se phase balance diagram). In addition, the liquid phase has a high diffusion rate and becomes a medium for determining CIGS. Therefore, a sufficiently high substrate temperature is required for crystal grain growth to exist in a liquid phase with sufficient supply of Cu so that a liquid phase can be produced. (InGa) ₂ Se ₃ is after the run out by injecting Cu in excess there is exists with high temperature stability merchant β-Cu _x Se and the liquid phase (Cu, Se), present in the CIGS surface and the crystal close to (grain boundary) It is known that the liquid phase promotes crystal growth of CIGS to produce a high-quality CIGS thin film with few defects. This effect is referred to as so-called "liquid assisted grain growth ". In the third final step, further In and Ga are implanted to convert the by-product, β-Cu _x Se, into CIGS, which finally forms a CIGS thin film with a composition of a little Cu.

FIG. 2 shows a precursor-selenization process, in which the precursor-selenization process is considered to be the closest to commercialization of CIGS solar cells. In the first step, a Cu-Ga-In alloy or a precursor containing Se is prepared. In the second step, CIGS is produced by inducing high-temperature selenization in a H ₂ Se gas or Se vapor atmosphere. Lt; / RTI >

Although the sputtering process has been widely used as a method for producing the precursor in the precursor-selenification process, it has been widely used in a variety of applications such as electrodeposition, co-evaporation, inkjet printing, nanoparticles, Method is possible.

The CIGSS binary compound of Cu (In, Ga) (Se, S) ₂ may also be prepared by adding H ₂ S gas and / or S vapor as needed during the selenization process.

In order to improve the toxicity and relatively slow selenization rate of H ₂ Se, which is mainly used in the second stage of the precursor-selenization process, the Avancis (currently Saint Gobain, France) in Germany has previously deposited the Se layer on the metal precursor to form CuGaIn / Se , It is known that the process time is drastically reduced by rapid thermal process (RTP) in Se / H ₂ S atmosphere.

The present invention relates to a binary precursor containing Se, and more particularly to a CIS-based thin film solar cell using RTP in the case of Cu _2-x Se (where 0? _X <1) as an upper layer, In the case of Cu _{2 - x} Se located in the upper layer, since the CIS system thin film is formed without the help of the liquid phase during selenization while supplying H ₂ Se gas or Se vapor at about 600 ° C. through RTP as in the conventional method, The liquid phase is generated in the second stage of the three-phase simultaneous evaporation method of NREL to promote the crystal growth of the CIS-based thin film and to produce the same effect as to produce a high-quality CIS-based thin film with few defects.

For example, a Cu precursor having an excessive amount of Cu, such as Cu ₂ Se, can not generate β-Cu _x Se and a liquid phase in RTP as in the phase equilibrium shown in FIG. 1B. Therefore, the crystal growth rate of the finally produced CIS thin film is slow But there are many defects.

Patent Registration No. 10-1388458 Patent Registration No. 10-1181252 US Patent Registration US 5,436,204

A precursor-selenization process using a H ₂ Se gas or a Se vapor and a three-step simultaneous evaporation process of a NREL using Cu-Ga-In precursors generally used can form a high-quality CIGS thin film, . In addition, the RTP process using a double layer precursor containing Se can drastically reduce the process time, but there are disadvantages (speed, crystal defects, etc.) due to lack of crystal growth of the CIS-based thin film produced. It is an object of the present invention to provide a technique capable of solving the problem of crystal growth in the RTP process using the above-mentioned Se-containing bilayer precursor.

Particularly, the object of the present invention is a double layer precursor including Se in both the upper and lower layers. In particular, when the upper layer is RTP using a conventional method such as Cu _{2 - x} Se, And a method of manufacturing a novel CIS-based thin-film solar cell capable of solving the problems of low crystal growth rate and many drawbacks.

The present invention relates to a method for producing a CIS-based thin film solar cell, which comprises the steps of: preparing an upper layer and a lower layer precursors each containing Se on a substrate and a rear electrode, wherein the upper layer is Cu _{2- x} Se Lt; x < 1) (a); A first step RTP (Rapid Thermal Process) step (b) performed in an atmosphere in which Se is supplied such that a part or all of Cu _{2 - x} Se is changed into CuSe or CuSe ₂ by pre-annealing the double layer precursor; And a second stage RTP step (c) performed at a temperature higher than the first step in an atmosphere in which Se is supplied to the CIS-based thin film solar cell using the two-step RTP process.

Specifically, the CIS based thin film is _{Cu (A 1-y B y} ) (Se 1 - z Sz) 2 ( where the A and B are, each independently, is any one of elements selected from In and Ga, 0 ≤ y? 1, 0? z <1).

In particular, it is preferable that the lower layer of the double layer precursor is made of at least one metal selected from In and Ga and Se.

In particular, it is preferred that the upper layer of the bilayer precursor is Cu ₂ Se.

In particular, it is preferable that the double layer precursor is formed by sputtering.

Particularly, the first-step RTP temperature range is preferably 210 to 332 ° C.

In particular, the first step RTP time is preferably 5 minutes or more.

In particular, the second-step RTP temperature range is preferably 400 to 600 ° C.

In particular, the second step RTP time is preferably 3 minutes or more.

The present invention also provides a CIS-based thin film solar cell manufactured by the above-described method.

The present invention provides a method for manufacturing a CIS-based thin film solar cell through RTP of two stages in total, wherein a molar ratio of Cu, such as Cu ₂ Se, through a first-stage RTP for free annealing, The Cu _{2 - x} Se precursor layer higher than Se is converted into CuSe and / or CuSe ₂ , and the CIS-based thin film is formed by the liquid phase assisted crystal growth in the second step RTP process, which is a higher process than the first- .

That is, in the method for producing CIS-based thin film solar cells through the RTP of the double layer precursor containing Se of the present invention, "liquid assisted grain growth" is possible by simulating the three-step simultaneous evaporation method of NREL Therefore, there is an advantage that a CIS type thin film solar cell having a high crystal growth rate and few defects can be produced.

A precursor-selenization process using a H ₂ Se gas or a Se vapor and a three-step simultaneous evaporation process of a NREL using Cu-Ga-In precursors generally used can form a high-quality CIGS thin film, And the RTP process using a double layer precursor including Se can drastically reduce the entire process time, but there is a disadvantage that the crystal growth of the generated CIGS is insufficient. The present invention is advantageous in that both the shortening of the process time and the crystal growth promoting effect of the RTP process can be obtained.

1A is a process diagram of a three-step simultaneous evaporation method of NREL.
1B is a phase diagram of Cu-Se.
Figure 2 is a precursor-selenization process.
Figure 3 is a flow chart of the method of the present invention.
FIG. 4 shows XRD, GIXRD, SEM and ICP-AES measurement results of glass substrate / Mo / Cu ₂ Se and glass substrate / Mo / In ₂ Se / Cu ₂ Se precursor as a result of Experimental Example 1.
FIGS. 5A and 5B are the results of Experimental Example 2, FIG. 5A is a measurement result of the HT-XRD phase of a Cu ₂ Se precursor, and FIG. 5B is a partial enlarged view of FIG.
6A to 6C are the results of Experimental Example 3, wherein FIG. 6A is a temperature and time profile of four pre-anneals (a) to (d), FIG. 6B is an SEM measurement image, and FIG. 6C is an XRD measurement result.
7A and 7B are the results of Experimental Example 4. FIG. 7A is a graph showing the results of measurement of the phase change according to the temperature of the glass substrate / Mo / In ₂ Se ₃ / Cu ₂ Se using HT-XRD, 7a is an enlarged view of a portion thereof.
Figure 8a, 8b and 9, as a result of Experimental Example 5, Figure 8a is a glass substrate _{/ Mo / In 2 Se 3 /} Cu 2 Se step of the precursor layer RTP (pre-annealing), the presence and stage 2 RTP temperature (500 ℃, 550 ° C), FIG. 8b is a partial enlarged view of FIG. 8a, and FIG. 9 is an SEM measurement image.
10 and 11 are the results of Experimental Example 6, FIG. 10 is the XRD measurement results of the CIS thin film specimen according to the two-stage RTP time (1, 3, and 5 minutes), and FIG.

The present invention relates to a method of forming a CIS-based thin film on a CIS-based thin film solar cell (for example, CIS, CIGS, CIGSS, etc.), and more particularly, A method for manufacturing a CIS-based thin film through RTP (pre-annealing) and a second step of high-temperature RTP (corresponding to RTP for ordinary selenization) in two stages.

In the present invention, the CIS-based thin film is used in a comprehensive meaning including all the thin films of the following chemical formula 1, namely, CIS, CIGS, CIGSS, CZTS and the like.

[Chemical Formula 1]

_{Cu (A 1-y B y} ) (Se 1 - z S z) 2

Here, A and B are each independently any element selected from In and Ga, and 0? Y? 1 and 0? Z <1.

A sputter deposition process is most preferable in order to make a precursor of a double layer precursor including Se in a large area, for example, (InGa) ₂ Se ₃ / Cu _{2 -x} Se (where 0 ≦ x <1) However, the Cu _{2 - x} Se precursor is generated when sputtering is performed. In the production of a precursor including Cu and Se by sputtering, a precursor which is disadvantageous to crystal growth of CIGS such as Cu ₂ Se is formed is that the precursor containing Cu and Se is prepared by sputtering, This is because the molar ratio of Cu is formed of Cu _{2 - x} Se more than Se, like Cu ₂ Se.

As described in the above-mentioned background art, when a CIS-based thin film solar cell is manufactured using RTP in the case of Cu _{2 - x} Se as an upper layer as a double layer precursor containing Se, Cu _{2 - x} In case of RTP under the Se atmosphere (for example, H ₂ Se gas, Se vapor, etc.) at about 400 to 600 ° C as in the conventional method, since the CIS system thin film is formed without the help of the liquid phase, Late, defects often occur in crystals.

FIG. 3 is a schematic diagram of the method of the present invention. In the present invention, RTP is divided into two stages. The RTP of the first stage is a pre-annealing section, for example, 210 ~ Cu ₂ eseo 332 ℃) _- a _x Se (for example, Cu ₂ Se) for CuSe and / or CuSe and then to transition to the _second, RTP for the second phase is approximately 400 ~ 600 ℃, in particular, Based thin film is formed with the help of a liquid phase (L3, see the equilibrium diagram of FIG. 1B) at a temperature of 500 ° C or higher, thereby forming a CIS-based thin film solar cell having a high crystal growth rate and few defects.

That is, for the present invention to solve the problems of the prior art, Cu _{2 - x} Se to CuSe and / or the first step of shifting in the Se is high molar composition of the as CuSe ₂ RTP process, the pre-annealed (pre-annealing ) &Lt; / RTI &gt; Of course, even if only a part of Cu _{2 - x} Se is not changed into CuSe and / or CuSe ₂ and only a part of the Cu _{2 - x} Se is changed, it can exhibit the liquid assisted grain growth effect of the present invention.

The CuSe and / or CuSe ₂ -substituted components through the first step RTP are reacted with the first step RTP at a high temperature (about 400 to 600 ° C) higher than the first step RTP, Since the "liquid phase" (L3, see the equilibrium diagram of FIG. 1B) is formed, the same effect as the liquid phase assisted crystal growth effect of the NREL three-phase simultaneous evaporation method can be obtained. That is, not only the CIS-based thin film crystal growth rate is accelerated, but crystal defects are lower than in the prior art.

[Reaction Scheme 1]

CuSe ₂ ↔ γ-CuSe + L3 (T ~ 332 ° C)

_{γ-CuSe ↔ β-Cu 2} - x Se + L3 (T ~ 380 ℃)

Hereinafter, the present invention will be described in more detail with reference to experimental examples. In the following experiments, CIS thin films were tested, but this is only an example, and the present invention is not limited to Cu_{2 - x}Se structure can be similarly applied.

Experimental Example  1: glass substrate / Mo / Cu ₂ Se  And glass substrate / Mo / In ₂ Se / Cu ₂ Se  Precursor physical property measurement

In this experiment, XRD, GIXRD, SEM and ICP-AES were measured to confirm the structure and crystal shape of glass substrate / Mo / Cu ₂ Se and glass substrate / Mo / In ₂ Se / Cu ₂ Se precursor. 4.

In the following figures, it is noted that Cu _{2 - x} Se is conveniently represented by Cu ₂ Se. Cu ₂ which is formed by the sputtering _was expressed for convenience by mixing Cu ₂ Se and since most of the _x Se to form a Cu ₂ Se.

Experimental Example  2: Glass substrate / Mo / Cu ₂ Se Temperature Phase behavior  Measure

X-ray diffraction (X-ray reflection) was performed at room temperature from room temperature to 600 ° C while supplying Se vapor using HT-XRD to confirm the phase change of the glass substrate / Mo / Cu ₂ Se precursor according to the temperature. data were collected. The collected data was analyzed using "X'pert High Score Plus program &quot;.

FIG. 5A is a result of measurement of the HT-XRD phase of a Cu ₂ Se precursor, and FIG. 5B is a partial enlarged view of FIG. 5A. The glass substrate / Mo / Cu ₂ Se precursor deposited by sputtering was found to be changed into CuSe at about 210 ° C. and CuSe ₂ at 260 ° C. as the temperature was raised.

CuSe ₂ while discharging the Se at 330 ℃ and variations as CuSe, finally at 380 ℃ high temperature stability merchant Cu _{2 -} is separated into the top fabric (peritectically) to _x Se. According to the thermodynamic equilibrium, a peritectic reaction as shown in the above-mentioned reaction formula 1 is expected, which is the same as the experimental result.

Cu ₂ formed by sputtering through the present experiment _- if the heat treatment the _x Se precursor at a suitable temperature and a Se atmosphere, CuSe and / or capable of modification to CuSe ₂ and the CuSe and / or CuSe ₂ conventional high-temperature RTP process, such as the In the form of Cu + L or Cu _{2 - x} Se + L.

That is, RTP is divided into two steps as in the method of the present invention, and Cu ₂ Se is transformed into CuSe and / or CuSe ₂ by pre-annealing at a predetermined temperature in the first step RTP step, And then proceed to the second step RTP step.

The pre-annealing can be pre-annealed from 210 ° C at which Cu ₂ Se begins to transform into CuSe ₂ up to 332 ° C where Cu ₂ Se of Scheme 1 is converted into a double phase of γ-CuSe + L 3.

Experimental Example  3: Step 1 RTP ( Free annealing ) Time experiment

As described above, the first stage RTP pre-annealing temperature is 210 to 332 ° C. However, for the convenience of experiment, the pre-annealing temperature is set to 300 ° C. in the above temperature range.

First, in order to find an appropriate pre-annealing time at 300 ° C, experiments were performed on glass substrate / Mo / Cu ₂ Se precursor with four temperature profiles as shown in FIG. 6a. The SEM measurement results of the glass substrate / Mo / Cu ₂ Se thin film pre-annealed according to the time profile of FIG. 6A are shown in FIG. 6B. As shown in FIG. 6 (b), at a pre-annealing temperature of 300 ° C, Cu ₂ Se → CuSe was converted from 5 minutes or more, but 10 minutes was better than 5 minutes. The experiment was further carried out.

On the other hand, when the temperature is lowered by ramping to 550 deg. C, which is a typical RTP temperature, after the pre-annealing at 300 DEG C for 10 minutes as in the profile (d), the crystal structure of CuSe is well formed there was. Thus, when Cu ₂ Se is formed through pre-annealing with CuSe, CuSe can be formed in the second step RTP by forming a liquid phase assisted crystal growth CIS system thin film with the help of liquid phase as in the above-mentioned reaction formula 1.

As a result of XRD measurement, FIG. 6 (c) shows that Cu _{2 - x} Se is more changed to CuSe from the temperature profile (a) to (d).

Experimental Example  4 : In ₂ Se ₃ / Cu ₂ Se Phase change according to temperature change

In this experiment, the phase change process according to the temperature of Mo / In ₂ Se ₃ / Cu ₂ Se was measured using HT-XRD, as shown in FIGS. 7A and 7B (a partially enlarged view of FIG. 7A). Particularly, it was confirmed that the upper layer of Cu ₂ Se among the bilayer precursor layers containing Se was changed into CuSe at about 200 ° C, and CIS started to be formed at about 300 ° C.

In particular, referring to Figure 7a, the back electrode of Mo peak intensity started to decrease from about 300 ℃, were stabilized at about 400 ℃, it was confirmed to have been finally MoSe ₂ layer is generated. The MoSe ₂ layer is formed after the completion of the CIS-based thin film according to the reaction engineering analysis, and thus the formation of the MoSe ₂ layer means that the CIS thin film formation is completed.

Experimental Example  5: Free annealing  The second stage of 500 ° C and 550 ° C depending on the presence or absence RTP  Experiment according to temperature

The glass substrate / Mo / In ₂ Se ₃ / Cu ₂ Se precursor layer was subjected to two-step RTP (for 5 minutes) at 500 ° C. and 550 ° C. for 10 minutes at 300 ° C. with or without first-step RTP (pre-annealing) XRD analysis was performed to confirm the difference in CIS thin films formed. The result was as shown in Figs. 8A and 8B (a partially enlarged view of Fig. 8A).

Referring to FIG. 8A, it was found that the reaction was not completed in the second annealing step. In the second annealing step, CIS formation was completed and MoSe _{2 was} also generated.

8B, it was found that the FWHM value (2? = 0.17909) of the peak of the CIS 112 was relatively smaller than the FWHM (2? = 0.20467) of the sample without the pre-annealing in the case of the pre- It was confirmed that annealing helped grain growth.

Fig. 9 is an SEM image of the four specimens (a to d). Fig. 9 shows SEM images of the specimens (a) to (d) (CIS), and the MoSe ₂ layer formed after the completion of the CIS was formed. This is because the specimen without the pre-annealing for 5 minutes and the MoSe ₂ layer without the RTP at 500 ° C. (a , b), meaning that the crystal growth of CIS is much faster by free annealing. Also, as shown in the SEM measurement image of FIG. 9, the CIS thin film produced by the method of the present invention can be confirmed to reduce the surface roughness.

Experimental Example  6: Stage 2 RTP  CIS crystal growth experiment over time

After the pre-annealing (300 ° C., 10 minutes) as the first step RTP, the second step RTP time was set to 1, 3, 5 minutes, respectively, and XRD and SEM measurement results were as shown in Figs. 10 and 11, respectively. As shown in FIG. 10, MoSe ₂ was confirmed after at least 3 minutes, and CIS formation was completed 3 minutes later, indicating that MoSe _{2 was} also formed. However, the results indicate that the time for completion of the formation of the appropriate CIS thin film crystal varies depending on the composition and content of the precursor layer, the RTP temperature, and the like.

Claims (10)

A method of manufacturing a CIS-based thin film solar cell,
(A) forming an upper layer and a lower layer of a bilayer precursor including Se on the substrate and the rear electrode, wherein the upper layer of the bilayer precursor is Cu _{2- x} Se (where 0? X <1);
A first step RTP (Rapid Thermal Process) step (b) performed in an atmosphere in which Se is supplied such that a part or all of Cu _{2 - x} Se is changed into CuSe or CuSe ₂ by pre-annealing the double layer precursor; And
And a second stage RTP step (c) carried out at a temperature higher than the first-step RTP in an atmosphere in which Se is supplied to the CIS-based thin film solar cell using the two-step RTP process.
The method of claim 1, wherein the CIS-based thin film has the following composition.
_{Cu (A 1-y B y} ) (Se 1 - z Sz) 2
Each of A and B is independently any one selected from In and Ga, and 0? Y? 1 and 0? Z <1.
The method of claim 1, wherein the lower layer of the bilayer precursor is made of at least one metal selected from In and Ga and Se.
The method of claim 1, wherein the upper layer of the bilayer precursor is Cu ₂ Se.
The method of claim 1, wherein the double layer precursor is formed by sputtering.
The method of claim 1, wherein the first RTP temperature range is 210 to 332 ° C.
The method of claim 1, wherein the first step RTP time is 5 minutes or more.
The method of claim 1, wherein the second RTP temperature range is 400 to 600 ° C.
The method of claim 1, wherein the RTP time of the second step is at least 3 minutes.
9. A CIS-based thin film solar cell produced by the method of any one of claims 1 to 9.

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