Method for manufacturing CZTS based thin film having dual band gap slope, method for manufacturing CZTS based solar cell having dual band gap slope and CZTS based solar cell thereof

Abstract

A method for manufacturing a CZTS based thin film having a dual band gap slope, comprising the steps of: forming a Cu.sub.2ZnSnS.sub.4 thin film layer; forming a Cu.sub.2ZnSn(S,Se).sub.4 thin film layer; and forming a Cu.sub.2ZnSnS.sub.4 thin film layer. A method for manufacturing a CZTS based solar cell having a dual band gap slope according to another aspect of the present invention comprises the steps of: forming a back contact; and forming a CZTS based thin film layer on the back contact by the method described above.

Claims

1. A CZTS-based solar cell, comprising: a back contact; and a CZTS-based thin film layer formed on the back contact; wherein the CZTS-based thin film layer comprises a first Cu.sub.2ZnSnS.sub.4 thin film layer, a Cu.sub.2ZnSn(S,Se).sub.4 thin film layer, and a second Cu.sub.2ZnSnS.sub.4 thin film layer which are sequentially formed, and a band gap energy of the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer is lower than those of the first Cu.sub.2ZnSnS.sub.4 thin film layer and the second Cu.sub.2ZnSnS.sub.4 thin film layer.

2. The CZTS-based solar cell of claim 1, wherein the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer is thicker than the first Cu.sub.2ZnSnS.sub.4 thin film layer and the second Cu.sub.2ZnSnS.sub.4 thin film layer.

3. A method of manufacturing a CZTS-based thin film having a dual band gap slope, comprising: forming a first Cu.sub.2ZnSnS.sub.4 thin film layer; forming a Cu.sub.2ZnSn(S,Se).sub.4 thin film layer on the first Cu.sub.2ZnSnS.sub.4 thin film layer; and forming a second Cu.sub.2ZnSnS.sub.4 thin film layer on the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer.

4. The method of claim 3, wherein: forming the first Cu.sub.2ZnSnS.sub.4 thin film layer comprises: synthesizing a precursor thin film layer comprising Cu, Zn and Sn; and subjecting the precursor thin film layer to primary sulfurization; forming the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer comprises selenizing the sulfurized thin film layer; and forming the second Cu.sub.2ZnSnS.sub.4 thin film layer comprises subjecting the selenized thin film layer to secondary sulfurization.

5. The method of claim 4, wherein the synthesizing the precursor thin film layer is performed using any one process selected from among co-evaporation, sputtering, electrodeposition, nanoparticle deposition and solution coating.

6. The method of claim 4, wherein the primary sulfurization and the secondary sulfurization are performed by thermal treatment in an H.sub.2S atmosphere or injection of S into a thin film using a vacuum evaporation process.

7. The method of claim 4, wherein the selenizing is performed by thermal treatment in an H.sub.2Se atmosphere or injection of Se into a thin film using a vacuum evaporation process.

8. The method of claim 3, wherein: forming the first Cu.sub.2ZnSnS.sub.4 thin film layer comprises synthesizing a precursor thin film layer comprising Cu, Zn, Sn and S; forming the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer comprises selenizing the precursor thin film layer; and forming the second Cu.sub.2ZnSnS.sub.4 thin film layer comprises sulfurizing the selenized thin film layer.

9. The method of claim 8, wherein the synthesizing the precursor thin film layer is performed using any one process selected from among co-evaporation, sputtering, electrodeposition, nanoparticle deposition and solution coating.

10. The method of claim 8, wherein the selenizing is performed by thermal treatment in an H.sub.2Se atmosphere or injection of Se into a thin film using a vacuum evaporation process.

11. The method of claim 8, wherein the sulfurizing is performed by thermal treatment in an H.sub.2S atmosphere or injection of S into a thin film using a vacuum evaporation process.

12. The method of claim 3, wherein: forming the first Cu.sub.2ZnSnS.sub.4 thin film layer comprises: synthesizing a first precursor thin film layer comprising Cu, Zn and Sn; and subjecting the first precursor thin film layer to primary sulfurization; forming the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer comprises: synthesizing a second precursor thin film layer comprising Cu, Zn and Sn on the sulfurized thin film layer; and selenizing the second precursor thin film layer; and forming the second Cu.sub.2ZnSnS.sub.4 thin film layer comprises: synthesizing a third precursor thin film layer comprising Cu, Zn and Sn on the selenized thin film layer; and subjecting the third precursor thin film layer to secondary sulfurization.

13. The method of claim 12, wherein the synthesizing the first to third precursor thin film layers is performed using any one process selected from among co-evaporation, sputtering, electrodeposition, nanoparticle deposition and solution coating.

14. The method of claim 12, wherein the primary sulfurization and the secondary sulfurization are performed by thermal treatment in an H.sub.2S atmosphere or injection of S into a thin film using a vacuum evaporation process.

15. The method of claim 12, wherein the selenizing is performed by thermal treatment in an H.sub.2Se atmosphere or injection of Se into a thin film using a vacuum evaporation process.

16. A method of manufacturing a CZTS-based solar cell having a dual band gap slope, comprising: forming a back contact; and forming a CZTS-based thin film layer, which comprise the steps of: forming a first Cu.sub.2ZnSnS.sub.4 thin film layer on the back contact; forming a Cu.sub.2ZnSn(S,Se).sub.4 thin film layer on the first Cu.sub.2ZnSnS.sub.4 thin film layer; and forming a second Cu.sub.2ZnSnS.sub.4 thin film layer on the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer.

17. The method of claim 16, wherein: forming the first Cu.sub.2ZnSnS.sub.4 thin film layer comprises: synthesizing a precursor thin film layer comprising Cu, Zn and Sn; and subjecting the precursor thin film layer to primary sulfurization; forming the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer comprises selenizing the sulfurized thin film layer; and forming the second Cu.sub.2ZnSnS.sub.4 thin film layer comprises subjecting the selenized thin film layer to secondary sulfurization.

18. The method of claim 17, wherein the synthesizing the precursor thin film layer is performed using any one process selected from among co-evaporation, sputtering, electrodeposition, nanoparticle deposition and solution coating.

19. The method of claim 17, wherein the primary sulfurization and the secondary sulfurization are performed by thermal treatment in an H.sub.2S atmosphere or injection of S into a thin film using a vacuum evaporation process.

20. The method of claim 17, wherein the selenizing is performed by thermal treatment in an H.sub.2Se atmosphere or injection of Se into a thin film using a vacuum evaporation process.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a flowchart illustrating a process of manufacturing a CZTS-based thin film according to the present invention;

(2) FIG. 2 is a schematic view illustrating the structure of a CZTS-based thin film layer formed according to the present invention;

(3) FIG. 3 is a flowchart illustrating a process of manufacturing a CZTS-based thin film according to a first embodiment of the present invention;

(4) FIG. 4 is a flowchart illustrating a process of manufacturing a CZTS-based thin film according to a second embodiment of the present invention;

(5) FIG. 5 is a flowchart illustrating a process of manufacturing a CZTS-based thin film according to a third embodiment of the present invention;

(6) FIG. 6 is a graph illustrating changes in band gap depending on changes in the Ga proportion in the CIGS thin film; and

(7) FIG. 7 is a schematic view illustrating the case where a double band gap slope is formed in the CIGS thin film.

DESCRIPTION OF THE REFERENCE NUMERALS IN THE DRAWINGS

(8) 100: substrate 200: back contact

(9) 300: CZTS-based thin film layer

MODE FOR INVENTION

(10) Hereinafter, a detailed description will be given of embodiments of the present invention with reference to the appended drawings.

(11) FIG. 1 is a flowchart illustrating a process of manufacturing a CZTS-based thin film according to the present invention, and FIG. 2 is a schematic view illustrating the structure of a CZTS-based thin film layer according to the present invention.

(12) In order to form a CZTS-based thin film having a double band gap slope according to the present invention, as illustrated in FIG. 1, a Cu.sub.2ZnSnS.sub.4 thin film layer, a Cu.sub.2ZnSn(S,Se).sub.4 thin film layer and a Cu.sub.2ZnSnS.sub.4 thin film layer are sequentially formed.

(13) As illustrated in FIG. 2, a CZTS-based thin film layer 300 is provided on a Mo back contact 200 on a glass substrate 100, the CZTS-based thin film layer comprising a Cu.sub.2ZnSnS.sub.4 thin film layer, a Cu.sub.2ZnSn(S,Se).sub.4 thin film layer and a Cu.sub.2ZnSnS.sub.4 thin film layer which are sequentially formed.

(14) The band gap of Cu.sub.2ZnSnS.sub.4 is known to fall in the range of 1.32˜1.85 eV, the band gap of Cu.sub.2ZnSnSe.sub.4 approximates to 1.02 eV lower than that, and the band gap of Cu.sub.2ZnSn(S,Se).sub.4 is positioned therebetween.

(15) Therefore, the CZTS-based thin film layer 300 having the above layer configuration according to the present invention has a high band gap at the front side and the back contact 200 side and has a low band gap therein, and thus the CZTS-based thin film layer 300 having a dual band gap slope formed therein toward the front side and the back contact side may be formed.

(16) Furthermore, it is preferable that the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer typically known to have excellent photoelectric conversion efficiency be thicker than the Cu.sub.2ZnSnSe.sub.4 thin film layer.

(17) According to the present invention, the CZTS-based solar cell has to further include a front reflective layer or a front contact in addition to the structure of FIG. 2, but such a typical configuration may be applied without particular limitation and a detailed description thereof is omitted.

(18) Specific examples for sequentially forming the Cu.sub.2ZnSnS.sub.4 thin film layer, the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer and the Cu.sub.2ZnSnS.sub.4 thin film layer are described below.

EXAMPLE 1

(19) FIG. 3 is a flowchart illustrating a process of manufacturing a CZTS-based thin film according to a first embodiment of the present invention.

(20) In accordance with the first embodiment, a CZTS-based thin film comprising a Cu.sub.2ZnSnS.sub.4 thin film layer, a Cu.sub.2ZnSn(S,Se).sub.4 thin film layer and a Cu.sub.2ZnSnS.sub.4 thin film layer which are sequentially formed is provided, by forming a precursor thin film comprising Cu, Zn and Sn, and sequentially subjecting the precursor thin film to primary sulfurization, selenization and secondary sulfurization.

(21) Specifically, the precursor thin film comprising Cu, Zn and Sn is first formed.

(22) Although formation of the precursor thin film is typically carried out using a co-evaporation process, any process such as sputtering, electrodeposition, nanoparticle deposition and solution coating may be applied.

(23) Because the precursor thin film of the present embodiment is formed into the CZTS-based thin film through sulfurization and selenization, it has to be formed to a thickness of 0.5˜2 μm.

(24) The Cu—Zn—Sn precursor thin film thus formed is subjected to primary sulfurization, thus forming Cu.sub.2ZnSnS.sub.4. Examples of the sulfurization process may include thermal treatment in an H.sub.2S atmosphere, and thermal treatment after injection of S into a precursor thin film using a vacuum evaporation process.

(25) Such thermal treatment is performed under conditions of a substrate temperature of 400˜530° C. and a pressure of 1 mtorr˜300 torr for 1˜20 min.

(26) The thin film subjected to primary sulfurization is selenized to give Cu.sub.2ZnSn(S,Se).sub.4. Examples of the selenization process may include thermal treatment in an H.sub.2Se atmosphere, and thermal treatment after injection of Se into a precursor thin film using a vacuum evaporation process.

(27) Such thermal treatment is performed under conditions of a substrate temperature of 400˜530° C. and a pressure of 1 mtorr˜300 torr for 1˜20 min.

(28) Finally, the selenized thin film is subjected to secondary sulfurization, thus forming Cu.sub.2ZnSnS.sub.4. Examples of the sulfurization process may include thermal treatment in an H.sub.2S atmosphere, and thermal treatment after injection of S into a precursor thin film using a vacuum evaporation process.

(29) Thermal treatment is implemented under conditions of a substrate temperature of 400˜530° C. and a pressure of 1 mtorr˜300 torr for 1˜20 min.

EXAMPLE 2

(30) FIG. 4 is a flowchart illustrating a process of manufacturing a CZTS-based thin film according to a second embodiment of the present invention.

(31) In accordance with the second embodiment, a CZTS-based thin film comprising a Cu.sub.2ZnSnS.sub.4 thin film layer, a Cu.sub.2ZnSn(S,Se).sub.4 thin film layer and a Cu.sub.2ZnSnS.sub.4 thin film layer which are sequentially formed is provided, by forming a precursor thin film comprising Cu, Zn, Sn and S and sequentially subjecting the precursor thin film to selenization and sulfurization.

(32) Specifically, the precursor thin film comprising Cu, Zn, Sn and S is first formed. This embodiment is different in terms of containing S at the step of forming the precursor thin film from the first embodiment.

(33) The precursor thin film is typically formed using a co-evaporation process, but any process such as sputtering, electrodeposition, nanoparticle deposition and solution coating may be applied.

(34) Because the precursor thin film of the present embodiment is formed into the CZTS-based thin film through selenization and sulfurization, it has to be formed to a thickness of 0.5˜2 μm.

(35) The Cu—Zn—Sn—S precursor thin film thus formed is selenized, thus forming Cu.sub.2ZnSnS.sub.4 and Cu.sub.2ZnSn(S,Se).sub.4.

(36) Because S is contained in the precursor thin film, it is possible to form the structure in which Cu.sub.2ZnSnS.sub.4 and Cu.sub.2ZnSn(S,Se).sub.4 are sequentially positioned through selenization, without performing sulfurization. Examples of the selenization process may include thermal treatment in an H.sub.2Se atmosphere, and thermal treatment after injection of Se into a precursor thin film using a vacuum evaporation process.

(37) Such thermal treatment is performed under conditions of a substrate temperature of 400˜530° C. and a pressure of 1 mtorr˜300 torr for 1˜20 min.

(38) Finally, the selenized thin film is subjected to secondary sulfurization, thus forming Cu.sub.2ZnSnS.sub.4. Examples of the sulfurization process may include thermal treatment in an H.sub.2S atmosphere, and thermal treatment after injection of S into a precursor thin film using a vacuum evaporation process.

(39) Thermal treatment is implemented under conditions of a substrate temperature of 400˜530° C. and a pressure of 1 mtorr˜300 torr for 1˜20 min.

EXAMPLE 3

(40) FIG. 5 is a flowchart illustrating a process of manufacturing a CZTS-based thin film according to a third embodiment of the present invention.

(41) In accordance with the third embodiment, a CZTS-based thin film comprising a Cu.sub.2ZnSnS.sub.4 thin film layer, a Cu.sub.2ZnSn(S,Se).sub.4 thin film layer and a Cu.sub.2ZnSnS.sub.4 thin film layer which are sequentially formed is provided, by forming three precursor thin films comprising Cu, Zn and Sn, and sequentially subjecting respective precursor thin films to primary sulfurization, selenization and secondary sulfurization.

(42) Specifically, a first precursor thin film comprising Cu, Zn and Sn is formed above all.

(43) The first precursor thin film is typically formed using a co-evaporation process, but any process such as sputtering, electrodeposition, nanoparticle deposition and solution coating may be applied.

(44) Because the first precursor thin film of the present embodiment is formed into the Cu.sub.2ZnSnS.sub.4 thin film layer through sulfurization, it is formed to be thin to the extent of 0.1˜0.5 μm.

(45) The first precursor thin film thus formed is subjected to primary sulfurization, thus forming the Cu.sub.2ZnSnS.sub.4 thin film layer. Examples of the sulfurization process may include thermal treatment in an H.sub.2S atmosphere, and thermal treatment after injection of S into a precursor thin film using a vacuum evaporation process. Such thermal treatment is performed under conditions of a substrate temperature of 400˜530° C. and a pressure of 1 mtorr˜300 torr for 1˜20 min.

(46) Provided on the Cu.sub.2ZnSnS.sub.4 thin film layer is a second precursor thin film comprising Cu, Zn and Sn. The second precursor thin film is formed in the same manner as in the first precursor thin film, and a description thereof is omitted. However, because the second precursor thin film is formed into the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer through selenization, its thickness is set to 0.5˜1 μm.

(47) The second precursor thin film is selenized to give the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer. Examples of the selenization process may include thermal treatment in an H.sub.2Se atmosphere, and thermal treatment after injection of Se into a precursor thin film using a vacuum evaporation process. Such thermal treatment is performed under conditions of a substrate temperature of 400˜530° C. and a pressure of 1 mtorr˜300 torr for 1˜20 min.

(48) Provided on the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer is a third precursor thin film comprising Cu, Zn and Sn. The formation process and the thickness of the third precursor thin film are the same as in the first precursor thin film, and a description thereof is omitted.

(49) The third precursor thin film thus formed is subjected to secondary sulfurization, thus forming the Cu.sub.2ZnSnS.sub.4 thin film layer. Examples of the sulfurization process may include thermal treatment in an H.sub.2S atmosphere, and thermal treatment after injection of S into a precursor thin film using a vacuum evaporation process. Furthermore, thermal treatment is conducted under conditions of a substrate temperature of 400˜530° C. and a pressure of 1 mtorr˜300 torr for 1˜20 min.

(50) The third embodiment is performed in such a manner that three precursor thin films are formed and each precursor thin film is subjected to sulfurization or selenization, and is thus different from the other embodiments. Although the third embodiment has more complicated processes compared to the other embodiments, it makes it easy to adjust the thickness of the Cu.sub.2ZnSnS.sub.4 thin film layer and the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer, thus facilitating the formation of the structure wherein the Cu.sub.2ZnSn(S,Se).sub.4 thin film layer is thicker than the Cu.sub.2ZnSnS.sub.4 thin film layer.

(51) 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. Therefore, the scope of the present invention should be understood not by specific embodiments but by claims, and all technical ideas equivalent thereto will be understood to be incorporated into the scope of the present invention.