METAL CHALCOGENIDE NANOPARTICLES FOR PREPARING LIGHT ABSORPTION LAYER OF SOLAR CELLS AND METHOD OF PREPARING THE SAME

Abstract

Disclosed are metal chalcogenide nanoparticles forming a light absorption layer of solar cells including a first phase including copper (Cu)-tin (Sn) chalcogenide and a second phase including zinc (Zn) chalcogenide, and a method of preparing the same.

Claims

1. A method of synthesizing metal chalcogenide nanoparticles forming a light absorption layer of solar cells, the method comprising: preparing a first solution comprising at least one Group VI source selected from the group consisting of compounds comprising sulfur (S) or selenium (Se); preparing a second solution comprising a copper (Cu) salt and a tin (Sn) salt and a third solution comprising a zinc (Zn) salt; mixing, heating and reacting the first solution and the second solution; and mixing, heating and reacting the third solution with a reaction product of the mixing, heating and reacting, wherein the metal chalcogenide nanoparticles have a core-shell structure comprising a core comprising copper (Cu)-tin (Sn) chalcogenide and a shell comprising zinc (Zn) chalcogenide.

2. The method according to claim 1, wherein, when the third solution of the mixing, heating and reacting is mixed, a Group VI source is further added.

3. The method according to claim 1, wherein solvents of the first solution, second solution and third solution are at least one selected the group consisting of water, diethylene glycol, methanol, ethanol, oleylamine, ethylene glycol, triethylene glycol, dimethyl sulfoxide, dimethyl formamide, and NMP (N-methyl-2-pyrrolidone).

4. The method according to claim 1, wherein the copper (Cu) salt, the tin (Sn) salt, and the zinc (Zn) salt are each independently at least one selected from the group consisting of a chloride, a bromide, an iodide, a nitrate, a nitrite, a sulfate, an acetate, a sulfite, an acetylacetonate, and a hydroxide.

5. The method according to claim 1, wherein the Group VI source is at least one selected from the group consisting of Se, Na.sub.2Se, K.sub.2Se, CaSe, (CH.sub.3).sub.2Se, SeO.sub.2, SeCl.sub.4, H.sub.2SeO.sub.3, H.sub.2SeO.sub.4, Na.sub.2S, K.sub.2S, CaS, (CH.sub.3).sub.2S, H.sub.2SO.sub.4, S, Na.sub.2S.sub.2O.sub.3, NH.sub.2SO.sub.3H and hydrates thereof, thiourea, thioacetamide, selenoacetamide, and selenourea.

6. The method according to claim 1, wherein the copper (Cu)-tin (Sn) chalcogenide is Cu.sub.aSnS.sub.b wherein 1.2≦a≦3.2 and 2.5≦b≦4.5, and/or Cu.sub.xSnSe.sub.y wherein 1.2≦x≦3.2 and 2.5≦y≦4.5.

7. The method according to claim 1, wherein the zinc (Zn) chalcogenide is ZnS and/or ZnSe.

8. The method according to claim 1, wherein a composition ratio of the metal in the metal chalcogenide nanoparticles is determined in a range of 0.5≦Cu/(Zn+Sn)≦1.5 and 0.5≦Zn/Sn≦2.0.

9. The method according to claim 8, wherein a composition ratio of the metal in the metal chalcogenide nanoparticles is determined in a range of 0.7≦Cu/(Zn+Sn)≦1.2 and 0.8≦Zn/Sn≦1.4.

10. The method according to claim 1, wherein the core has a diameter of 5 nanometers to 200 nanometers.

11. The method according to claim 1, wherein the shell has a thickness of 1 nanometer to 100 nanometers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing, in which:

[0069] FIG. 1 is an SEM image of Cu.sub.2SnS.sub.3—ZnS nanoparticles formed according to Example 1;

[0070] FIG. 2 is a TEM image of Cu.sub.2SnS.sub.3—ZnS nanoparticles formed according to Example 1;

[0071] FIG. 3 is an XRD graph of Cu.sub.2SnS.sub.3—ZnS nanoparticles formed according to Example 1;

[0072] FIG. 4 is an SEM image of Cu.sub.2SnS.sub.3—ZnS nanoparticles formed according to Example 1;

[0073] FIG. 5 is an XRD graph of Cu.sub.2SnS.sub.3—ZnS nanoparticles formed according to Example 1;

[0074] FIGS. 6A and 6B are an SEM image of a thin film prepared according to Example 17;

[0075] FIG. 7 is an XRD graph of a thin film prepared according to Example 17;

[0076] FIG. 8 is an XRD graph of a thin film prepared according to Comparative Example 3;

[0077] FIG. 9 is an XRD graph of a thin film prepared according to Comparative Example 4;

[0078] FIG. 10 is an IV characteristic graph of a thin film solar cell prepared according to Example 18;

[0079] FIG. 11 is an IV characteristic graph of a thin film solar cell manufactured according to Comparative Example 5;

[0080] FIG. 12 is an IV characteristic graph of a thin film solar cell manufactured according to Comparative Example 6;

[0081] FIG. 13 is a table illustrating SEM-EDX results of Cu.sub.2SnS.sub.3—ZnS nanoparticles demonstrating even particle distribution in particles synthesized according to the present invention;

[0082] FIGS. 14A-14E are an EDS mapping result of Cu.sub.2SnS.sub.3—ZnS nanoparticles demonstrating even metal distribution in particles synthesized according to the present invention; and

[0083] FIGS. 15A-15B are a line-scan result of a Cu.sub.2SnS.sub.3—ZnS nanoparticle composition demonstrating even metal distribution in particles synthesized according to the present invention.

BEST MODE

[0084] Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only for illustration of the present invention and should not be construed as limiting the scope and spirit of the present invention.

Example 1

[0085] Cu.sub.2SnS.sub.3—ZnS Particles

[0086] After adding a DEG solution including 30 mmol of thioacetamide to a DEG solution including 10 mmol of CuCl.sub.2 and a DEG solution including 5 mmol of SnCl.sub.2, temperature was elevated to 175° C. and then the solution was reacted while stirring for three hours. Subsequently, a DEG solution including 7 mmol of ZnCl.sub.2 was slowly added to the reacted solution dropwise at room temperature. Subsequently, the solution was heated to 180° C. or more and then, maintaining the temperature, stirred for three hours. Subsequently, the solution was purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles. A scanning electron microscope (SEM) image, a transmission electron microscope (TEM) image and an XRD graph of the formed particles are illustrated in FIGS. 1 to 3.

Example 2

[0087] Cu.sub.2SnS.sub.3—ZnS Particles

[0088] After adding a DEG solution including 30 mmol of thioacetamide to a DEG solution including 10 mmol of CuSO.sub.4 and a DEG solution including 5 mmol of SnCl.sub.2, temperature was elevated to 175° C. and then the solution was reacted while stirring for three hours. Subsequently, a DEG solution including 7 mmol of ZnCl.sub.2 was slowly added to the reacted solution dropwise at room temperature. Subsequently, the solution was heated to 180° C. or more and then, maintaining the temperature, stirred for three hours. Subsequently, the solution was purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Example 3

[0089] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0090] After adding a DEG solution including 30 mmol of thioacetamide to a DEG solution including 10 mmol of CuSO.sub.4 and a DEG solution including 5 mmol of Sn(OAc).sub.2, temperature was elevated to 175° C. and then the solution was reacted while stirring for three hours. Subsequently, a DEG solution including 7 mmol of ZnCl.sub.2 was slowly added to the reacted solution dropwise at room temperature. Subsequently, the solution was heated to 180° C. or more and then, maintaining the temperature, stirred for three hours. Subsequently, the solution was purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Example 4

[0091] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0092] After adding a DEG solution including 30 mmol of thiourea to a DEG solution including 10 mmol of CuCl.sub.2 and a DEG solution including 5 mmol of SnCl.sub.2, temperature was elevated to 175° C. and then the solution was reacted while stirring for three hours. Subsequently, a DEG solution including 7 mmol of ZnCl.sub.2 was slowly added to the reacted solution dropwise at room temperature. Subsequently, the solution was heated to 180° C. or more and then, maintaining the temperature, stirred for three hours. Subsequently, the solution was purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Example 5

[0093] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0094] After adding a DEG solution including 15 mmol of thioacetamide to a DEG solution including 10 mmol of CuCl.sub.2 and a DEG solution including 5 mmol of SnCl.sub.2, temperature was elevated to 175° C. and then the solution was reacted while stirring for five hours. Subsequently, a DEG solution including 6 mmol of ZnCl.sub.2 and a DEG solution including 6 mmol of thioacetamide were slowly added to the reacted solution dropwise at room temperature. Subsequently, the solution was heated to 180° C. or more and then, maintaining the temperature, stirred for three hours. Subsequently, the solution was purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Example 6

[0095] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0096] After adding a DEG solution including 20 mmol of thioacetamide to a DEG solution including 10 mmol of CuCl.sub.2 and a DEG solution including 5 mmol of SnCl.sub.2, temperature was elevated to 175° C. and then the solution was reacted while stirring for three hours. Subsequently, a DEG solution including 6 mmol of ZnCl.sub.2 and a DEG solution including 12 mmol of thioacetamide were slowly added to the reacted solution dropwise at room temperature. Subsequently, the solution was heated to 180° C. or more and then, maintaining the temperature, stirred for three hours. Subsequently, the solution was purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Example 7

[0097] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0098] After adding a DEG solution including 20 mmol of thioacetamide to a DEG solution including 10 mmol of CuCl.sub.2 and a DEG solution including 5 mmol of SnCl.sub.2, temperature was elevated to 175° C. and then the solution was reacted while stirring for six hours. Subsequently, a DEG solution including 6 mmol of ZnCl.sub.2 and a DEG solution including 12 mmol of thioacetamide were slowly added to the reacted solution dropwise at room temperature. Subsequently, the solution was heated to 180° C. or more and then, maintaining the temperature, stirred for three hours. Subsequently, the solution was purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles. A scanning electron microscope (SEM) image and an XRD graph of the formed particles are illustrated in FIGS. 4 and 5.

Example 8

[0099] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0100] After adding an EG solution including 30 mmol of thioacetamide to an EG solution including 10 mmol of CuCl.sub.2 and an EG solution including 5 mmol of SnCl.sub.2, temperature was elevated to 175° C. and then the solution was reacted while stirring for three hours. Subsequently, an EG solution including 6 mmol of ZnCl.sub.2 was slowly added to the reacted solution dropwise at room temperature. Subsequently, the solution was heated to 180° C. or more and then, maintaining the temperature, stirred for three hours. Subsequently, the solution was purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Example 9

[0101] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0102] After adding a DEG solution including 30 mmol of thioacetamide to a DEG solution including 10 mmol of CuCl.sub.2, a DEG solution including 5 mmol of SnCl.sub.2 and a DEG solution including 1 mmol of PVP, temperature was elevated to 175 r and then the solution was reacted while stirring for three hours. Subsequently, an DEG solution including 7 mmol of ZnCl.sub.2 was slowly added to the reacted solution dropwise at room temperature. Subsequently, the solution was heated to 180° C. or more and then, maintaining the temperature, stirred for three hours. Subsequently, the solution was purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Example 10

[0103] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0104] After adding an H.sub.2O solution including 30 mmol of thioacetamide to an H.sub.2O solution including 10 mmol of CuCl.sub.2 and an H.sub.2O solution including 5 mmol of SnCl.sub.2, temperature was elevated to 100° C. and then reacted while stirring for three hours. Subsequently, an H.sub.2O solution including 6 mmol of ZnCl.sub.2 was slowly added to the reacted solution dropwise at room temperature and then temperature was elevated to 100° C. Maintaining the temperature, the solution was stirred for three hours and then purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Example 11

[0105] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0106] After adding an H.sub.2O solution including 30 mmol of thioacetamide to an H.sub.2O solution including 10 mmol of CuCl.sub.2, an H.sub.2O solution including 5 mmol of SnCl.sub.2 and an H.sub.2O solution including 10 mmol of sodium citrate, temperature was elevated to 100° C. and then reacted while stirring for six hours. Subsequently, an H.sub.2O solution including 6 mmol of ZnCl.sub.2 and an H.sub.2O solution including 12 mmol of thioacetamide were slowly added to the reacted solution dropwise at room temperature and then temperature was elevated to 100° C. Maintaining the temperature, the solution was stirred for three hours and then purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Example 12

[0107] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0108] After adding an H.sub.2O solution including 30 mmol of thioacetamide to an H.sub.2O solution including 10 mmol of Cu(NO.sub.3).sub.2, an H.sub.2O solution including 5 mmol of SnCl.sub.2 and an H.sub.2O solution including 10 mmol of sodium mesoxalate, temperature was elevated to 100° C. and then reacted while stirring for six hours. Subsequently, an H.sub.2O solution including 6 mmol of Zn(OAc).sub.2 and an H.sub.2O solution including 12 mmol of thioacetamide were slowly added to the reacted solution dropwise at room temperature and then temperature was elevated to 100° C. Maintaining the temperature, the solution was stirred for five hours and then purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Example 13

[0109] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0110] After adding an H.sub.2O solution including 30 mmol of Na.sub.2S to an H.sub.2O solution including 10 mmol of CuCl.sub.2 and an H.sub.2O solution including 5 mmol of SnCl.sub.2, the resulting solution was reacted while stirring for three hours at room temperature. Subsequently, an H.sub.2O solution including 6 mmol of ZnCl.sub.2 was slowly added to the reacted solution dropwise and then the resulting solution was stirred for three hours at room temperature. The resulting solution was purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Example 14

[0111] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0112] After adding an H.sub.2O solution including 30 mmol of Na.sub.2S to an H.sub.2O solution including 10 mmol of CuSO.sub.4, an H.sub.2O solution including 5 mmol of SnCl.sub.2 and an H.sub.2O solution including 15 mmol of sodium citrate, the resulting solution was reacted while stirring for three hours at room temperature. Subsequently, an H.sub.2O solution including 6 mmol of ZnCl.sub.2 was slowly added to the reacted solution dropwise and then the resulting solution was stirred for three hours at room temperature. The resulting solution was purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Example 15

[0113] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0114] After adding an H.sub.2O solution including 30 mmol of Na.sub.2S to an H.sub.2O solution including 10 mmol of CuSO.sub.4 and an H.sub.2O solution including 5 mmol of SnCl.sub.2, the resulting solution was reacted while stirring for three hours at room temperature. Subsequently, an H.sub.2O solution including 6 mmol of ZnCl.sub.2 was slowly added to the reacted solution dropwise and then the resulting solution was stirred for three hours at room temperature. The resulting solution was purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Example 16

[0115] Synthesis of Cu.sub.2SnS.sub.3—ZnS Particles

[0116] After adding an H.sub.2O solution including 30 mmol of Na.sub.2S to an H.sub.2O solution including 10 mmol of Cu(NO.sub.3).sub.2 and an H.sub.2O solution including 5 mmol of SnCl.sub.2, the solution was reacted while stirring for three hours at room temperature. Subsequently, an H.sub.2O solution including 6 mmol of ZnCl.sub.2 was slowly added to the reacted solution dropwise and then the resulting solution was stirred for three hours at room temperature. The resulting solution was purified through centrifugation, resulting in Cu.sub.2SnS.sub.3—ZnS nanoparticles.

Comparative Example 1

[0117] After dissolving cupric acetylacetonate (Cu(acac).sub.2), zinc acetate (Zn(OAc).sub.2) and Sn(acac).sub.2Br.sub.2 in an oleylamine solution, temperature was elevated up to 225° C. An oleylamine solution, in which S elements were dissolved, was further added thereto dropwise. Formed particles were purified through centrifugation, resulting in CZTS nanoparticles.

Comparative Example 2

[0118] After dissolving CuCl.sub.2.2H.sub.2O, SnCl.sub.2 and thioacetamide in a diethylene glycol solution, the resulting solution was heated to 175° C. for 2.5 hours. Synthesized particles were purified through centrifugation, resulting in Cu.sub.2SnS.sub.3 particles. In addition, after separately dissolving ZnCl.sub.2, thioacetamide and PVP in a diethylene Glycol solution, the resulting solution was heated to 175° C. for 2.5 hours. Synthesized particles were purified through centrifugation, resulting in ZnS particles.

Example 17

[0119] Preparation of Thin Film

[0120] The Cu.sub.2SnS.sub.3—ZnS prepared according to Example 8 was dispersed in a mixture of alcohol-based solvents to prepare an ink. Subsequently, the ink was coated onto a glass substrate coated with molybdenum (Mo) to form a coating film and then the coating film was dried. Subsequently, the coating film was heated with a glass substrate deposited with Se to provide a Se atmosphere and then subjected to rapid thermal annealing (RTA) at 575° C., resulting in a CZTSSe-based thin film. An SEM image and XRD graph of the obtained thin film are illustrated in FIGS. 6A, 6B and 7, respectively.

Comparative Example 3

[0121] Preparation of Thin Film

[0122] The CZTS nanoparticles prepared according to Comparative Example 1 were dispersed in toluene as a solvent to prepare an ink, and the ink was coated onto a soda lime glass substrate coated with Mo to form a coating film. Subsequently, the coating film was dried and then subjected to heat treatment at 450° C. in a Se atmosphere, resulting in a CZTSSe-based thin film. An XRD graph of the obtained thin film is illustrated in FIG. 8.

Comparative Example 4

[0123] Preparation of Thin Film

[0124] The Cu.sub.2SnS.sub.3 nanoparticles and ZnS nanoparticles prepared according to Comparative Example 2 were dispersed in a mixture of alcohol-based solvents to prepare an ink. Subsequently, the ink was coated onto a glass substrate coated with molybdenum (Mo) to form a coating film and then the coating film was dried. Subsequently, the coating film was heated with a glass substrate deposited with Se to provide an Se atmosphere and then subjected to rapid thermal annealing (RTA) at 575° C., resulting in a CZTS Se-based thin film. An XRD graph of the obtained thin film is illustrated in FIG. 9.

Example 18

[0125] Preparation of Thin Film Solar Cell

[0126] The CZTSSe-based thin film prepared according to Example 17 was etched using a potassium cyanide (KCN) solution, a CdS layer having a thickness of 50 nm was formed thereon by chemical bath deposition (CBD), and a ZnO layer having a thickness of 100 nm and an Al-doped ZnO layer having a thickness of 500 nm were sequentially stacked thereon by sputtering, thereby completing preparation of a thin film. Subsequently, an Al electrode was formed at the thin film, thereby completing manufacture of a thin film solar cell. A graph showing current-voltage (I-V) characteristics of the thin film solar cell is illustrated in FIG. 10.

Comparative Example 5

[0127] Preparation of Thin Film Solar Cell

[0128] A CdS layer was formed on the CZTSSe-based thin film prepared according to Comparative Example 3 by chemical bath deposition (CBD) and then a ZnO layer and an ITO layer were sequentially stacked thereon by sputtering, thereby completing preparation of a thin film solar cell. A graph showing current-voltage (I-V) characteristics of the thin film solar cell is illustrated in FIG. 10.

Comparative Example 6

[0129] Preparation of Thin Film Solar Cell

[0130] A CdS layer was mounted on the CZTS Se-based thin film prepared according to Comparative Example 4 by chemical bath deposition (CBD) and then a ZnO layer and an ITO layer were sequentially stacked thereon by sputtering, thereby completing preparation of a thin film solar cell. A graph showing current-voltage (I-V) characteristics of the thin film solar cell is illustrated in FIG. 12.

Experimental Example 1

[0131] Photoelectric efficiencies of the thin film solar cells of Example 18 and Comparative Examples 5 and 6 were measured and measurement results are shown in Table 2 below and FIGS. 10 to 12.

TABLE-US-00001 TABLE 1 Photoelectric J.sub.sc (mA/cm.sup.2) V.sub.oc (V) FF efficiency (%) Example 18 18.7 0.240 0.299 1.34 Comparative 10.5 0.188 0.372 0.73 Example 5 Comparative 9.1 0.171 0.371 0.58 Example 6

[0132] In Table 1, J.sub.sc, which is a variable determining the efficiency of each solar cell, represents current density, V.sub.oc denotes an open circuit voltage measured at zero output current, the photoelectric efficiency means a rate of cell output according to irradiance of light incident upon a solar cell plate, and fill factor (FF) represents a value obtained by dividing the product of current density and voltage values at maximum power by the product of Voc and J.sub.sc.

[0133] As seen in Table 1 above, when the metal chalcogenide nanoparticles prepared according to the present invention were used in light absorption layer formation, the light absorption layer showed superior photoelectric efficiency due to high current density and voltage, when compared with metal chalcogenide nanoparticles prepared according to a prior method.

[0134] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

INDUSTRIAL APPLICABILITY

[0135] As described above, metal chalcogenide nanoparticles according to the present invention include a first phase including copper (Cu)-tin (Sn) chalcogenide and a second phase including zinc (Zn) chalcogenide in one particle. Therefore, when a thin film is prepared using the metal chalcogenide nanoparticles, generation of a second phase may be suppressed, and the thin film may have an entirely uniform composition since one particle includes all of the metals. In addition, since nanoparticles include S or Se, the nanoparticles are stable against oxidation and the amount of a Group VI element in a final thin layer may be increased. Furthermore, the volumes of particles are extended in a selenization process due to addition of a Group VI element and thereby a light absorption layer having higher density may be grown.

[0136] In addition, since the metal chalcogenide nanoparticles according to the present invention are prepared through a solution process, process costs may be dramatically reduced, when compared with conventional processes. Furthermore, a harmful reducing agent such as hydrazine is not used and, as such, risk due to use of the reducing harmful agent may be removed.