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The kesterite compound Cu2ZnSnS4(CZTS) is one of the most interesting materials for absorber layers of thin-film solar cells,not only because it is composed of earth abundant and non-toxic elements,but also owing to the fact that its absorption coefficient is high (on the order of 104 cm-1) and its optimal band gap is 1.5 eV for single-junction solar cells. Plenty of methods are used to deposit the CZTS layer,such as evaporation,sputtering,spray-pyrolysis,sol-gel, pulsed laser deposition and electro-chemical deposition.Among these methods,sputtering is considered as one of the most viable deposition techniques for producing a large-scale panel of thin film solar cells with demonstrable productivity and easy adjustment.In this paper,Cu2ZnSnS4 thin films are prepared by in-situ annealing after being sputtered with a quaternary compound target.This technology can reduce the extrinsic defects in the thin film.It is desirable to control the growth of grain boundary,increase grain size and make the thin film more compact and smooth. The in-situ annealing is a method which can heat a work piece fast to a certain temperature and maintain the temperature for some time after sputtering.As is well known,one of the major reasons for affecting CZTS device performance is the low open circuit voltage (Voc),and it is also a challenge to obtain a high value because there are a lot of defect states at the grain boundaries.The experiment shows that using the method of in-situ annealing after sputtering can obtain large size grains and smooth and compact surface.The obtained thin films are Cu-poor,Zn-rich and Sn-poor,which can restrain the Cu vacancies (VCu) and anti-site defects (CuZn,SnZn,and SnCu).The free carrier concentration (NA) increases with the increase of Zn content,while the open circuit voltage of CZTS solar cells increases with the increase of NA. In order to develop CZTS solar cells based on the thin films,the n-type CdS buffer layer (70 nm) is grown using chemical bath deposition,and intrinsic ZnO (70 nm) and ZnO:Al (250 nm) films are deposited by RF-magnetron sputtering.In the end,Ni-Al metal grids as the top electrode are prepared by thermal evaporation.The final solar cells with an active area of 0.25 cm2 are determined by mechanical scribing.The solar cell based the CZTS film with in-situ annealing has better-performance parameters,its open circuit voltage and short-circuit current density are 575 mV and 8.32 mA/cm2,respectively.The photoelectric conversion efficiency of 1.82% is achieved.In order to enhance the efficiency of device,it is important to minimize Cu/Zn disorder in CZTS film and control the element composition by optimizing high-temperature crystallization process.The relevant research work on reducing defects in the films,increasing the carrier collection and enhancing the Jsc is under way. This method not only avoids the contamination caused by the external annealing but also simplifies the preparation process of the thin film,which greatly saves the preparation time of the solar cell and is beneficial to industrial production.annealing is a method which can heat a work piece fast to a certain temperature and maintain the temperature for some time after sputtering.As is well known,one of the major reasons for affecting CZTS device performance is the low open circuit voltage (Voc),and it is also a challenge to obtain a high value because there are a lot of defect states at the grain boundaries.The experiment shows that using the method of in-situ annealing after sputtering can obtain large size grains and smooth and compact surface.The obtained thin films are Cu-poor,Zn-rich and Sn-poor,which can restrain the Cu vacancies (VCu) and anti-site defects (CuZn,SnZn,and SnCu).The free carrier concentration (NA) increases with the increase of Zn content,while the open circuit voltage of CZTS solar cells increases with the increase of NA. In order to develop CZTS solar cells based on the thin films,the n-type CdS buffer layer (70 nm) is grown using chemical bath deposition,and intrinsic ZnO (70 nm) and ZnO:Al (250 nm) films are deposited by RF-magnetron sputtering.In the end,Ni-Al metal grids as the top electrode are prepared by thermal evaporation.The final solar cells with an active area of 0.25 cm2 are determined by mechanical scribing.The solar cell based the CZTS film with in-situ annealing has better-performance parameters,its open circuit voltage and short-circuit current density are 575 mV and 8.32 mA/cm2,respectively.The photoelectric conversion efficiency of 1.82% is achieved.In order to enhance the efficiency of device,it is important to minimize Cu/Zn disorder in CZTS film and control the element composition by optimizing high-temperature crystallization process.The relevant research work on reducing defects in the films,increasing the carrier collection and enhancing the Jsc is under way. This method not only avoids the contamination caused by the external annealing but also simplifies the preparation process of the thin film,which greatly saves the preparation time of the solar cell and is beneficial to industrial production.
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Keywords:
- Cu2ZnSnS4 /
- magnetron sputtering /
- in-situ annealing /
- solar cell
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[22] Katagiri H, Jimbo K 2011 IEEE Photovolt. Spec. Conf. 23 003516
[23] Tanaka K, Fukui Y, Moritake N, Uchiki H 2011 Sol.Energy Mater. Sol. Cells 95 838
[24] Chen S Y, Wang L W, Walsh A 2012 Appl. Phys. 101 223901
[25] Fernandes P A, Salom P M P, Cunha A F 2010 Appl. Phys. 43 215403
[26] Sammi K, Misol O, Woo K K 2013 Thin Solid Films. 549 59
[27] Tapas K C, Devendra T 2012 Sol. Energy Mater. Sol. Cells 101 46
[28] Zhang J, Long B, Cheng S Y 2013 Int. J. Photoenergy ID 986076 1
[29] Vipul K, Patel K K, Patel S J 2013 J. Crystal Growth 362 174
[30] Li J, Wang H, Luo M 2016 Sol. Energy Mater. Sol. Cells 149 242
[31] Li J, Kim S Y, Nam D 2017 Sol. Energy Mater. Sol. Cells 159 447
[32] Sun K W, Su Z H, Han Z L, Liu F Y, Lai T Q, Li J, Liu Y X 2014 Acta Phys. Sin. 63 018801 (in Chinese) [孙凯文, 苏正华, 韩自力, 刘芳洋, 赖延清, 李劼, 刘业翔 2014 物理学报 63 018801]
[33] Kong F T, Gunawan O, Kuwahara M 2016 Sol. Energy Mater. Sol. Cells 6 184
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[1] Jiang M L, Yan X Z 2013 Sol. Cells Res. Appl. Prospect.5 107
[2] Liu H, Xue Y M, Qiao Z X, Li W, Zhang C, Yin F H, Feng S J 2015 Acta Phys. Sin. 64 068801 (in Chinese) [刘浩, 薛玉明, 乔在祥, 李微, 张超, 尹富红, 冯少君 2015 物理学报 64 068801]
[3] Yan C, Chen J, Liu F Y 2014 J. Alloy. Compod. 610 486
[4] Wang W, Winkler M T 2014 Energy Mater. 4 7
[5] Kato T, Hiroi H, Sakai N 2012 Proceedings of the 27th European Photovoltaic Solar Energy Conference and Exhibition Frankfurt, Germany 2236
[6] Liu F F, He Q, Zhou Z Q, Sun Y 2014 Acta Phys. Sin.63 067203 (in Chinese) [刘芳芳, 何青, 周志强, 孙云 2014 物理学报 63 067203]
[7] Liu F F, Sun Y, He Q 2014 Acta Phys. Sin. 63 047201 (in Chinese) [刘芳芳, 孙云, 何青 2014 物理学报 63 047201]
[8] Mao Q N, Zhang X Y, Li X G, He J X, Yu P R, Wang D 2014 Acta Phys. Sin. 63 118802 (in Chinese) [毛启楠, 张晓勇, 李学耕, 贺劲鑫, 于平荣, 王东 2014 物理学报 63 118802]
[9] Brammertz G, Buffière M, Oueslati S 2013 Appl. Phys. Lett. 103 163904
[10] Katagiri H, Jimbo K, Maw W S 2009 Thin Solid Films 517 2455
[11] Xie M, Zhuang D, Zhao M, Li B J, Cao M J, Song J 2014 Vacuum 101 146
[12] He J, Sun L, Chen Y, Jiang J C, Yang P X, Chu J H 2014 RSC Adv. 4 43080
[13] Jo Y H, Mohanty B C, Yeon D H 2015 Sol. Energy Mater. Sol. Cells 132 136
[14] Nakamura R, Kunihiko T, Hisao U 2014 Jpn. J. Appl. Phys. 53 02BC10
[15] Lin Y P, Chi Y F, Hsieh T E 2016 J. Alloy. Compod. 654 498
[16] Shi G, Li Y J, Zuo S H, Jiang J C, Hu G J, Chu J H 2011 Infrared Millim. Waves. 30 1001
[17] Jiang F, Ikeda S 2014 Energy Mater. 4 403
[18] Ericson T, Kubart T, Scragg J J 2012 Thin Solid Films 520 7093
[19] Gurel T, Sevik C, Ça G 2011 Phys. Rev. B: Condens. 84 896
[20] Tanaka T, Kawasaki D 2016 Phys. Status Solidi Topics 36 67
[21] Chalapathi U, Jayasree Y, Uthana S, Sundara R V 2015 Vacuum 117 121
[22] Katagiri H, Jimbo K 2011 IEEE Photovolt. Spec. Conf. 23 003516
[23] Tanaka K, Fukui Y, Moritake N, Uchiki H 2011 Sol.Energy Mater. Sol. Cells 95 838
[24] Chen S Y, Wang L W, Walsh A 2012 Appl. Phys. 101 223901
[25] Fernandes P A, Salom P M P, Cunha A F 2010 Appl. Phys. 43 215403
[26] Sammi K, Misol O, Woo K K 2013 Thin Solid Films. 549 59
[27] Tapas K C, Devendra T 2012 Sol. Energy Mater. Sol. Cells 101 46
[28] Zhang J, Long B, Cheng S Y 2013 Int. J. Photoenergy ID 986076 1
[29] Vipul K, Patel K K, Patel S J 2013 J. Crystal Growth 362 174
[30] Li J, Wang H, Luo M 2016 Sol. Energy Mater. Sol. Cells 149 242
[31] Li J, Kim S Y, Nam D 2017 Sol. Energy Mater. Sol. Cells 159 447
[32] Sun K W, Su Z H, Han Z L, Liu F Y, Lai T Q, Li J, Liu Y X 2014 Acta Phys. Sin. 63 018801 (in Chinese) [孙凯文, 苏正华, 韩自力, 刘芳洋, 赖延清, 李劼, 刘业翔 2014 物理学报 63 018801]
[33] Kong F T, Gunawan O, Kuwahara M 2016 Sol. Energy Mater. Sol. Cells 6 184
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