SnO_2薄膜的PECVD法制备及其在CdTe电池中的应用研究
摘要
二氧化锡(SnO_2)是一种宽带隙的金属氧化物。SnO_2 薄膜具有可见光透过性强、紫外吸收系数大、有一定红外反射能力、化学性能稳定以及室温下抗酸碱能力强等优点。已经广泛应用于太阳电池、透明电极材料、气敏材料、光电材料以及电热材料等领域。本文依托863 计划“CdTe 薄膜太阳电池制造技术及中试生产线”,重点研究了SnO2薄膜在太阳电池上的作为透明高阻层(HRT)应用。CdTe 电池作为目前最有广泛应用前景的一种薄膜太阳电池,其材料制备上的研究已经开展的很普遍,为了进一步提高电池效率,已经开始在电池结构上寻求突破,如:在TCO 和CdS 之间加入透明高阻层(HRT)以及在CdTe 和背电极间加入重掺杂的过渡层。这些结构上的改变都极大的提高了CdTe 太阳电池的转换效率。而未掺杂的SnO_2薄膜由于它和广泛采用的前电极SnO2:F 是同一种物质,有着相同的功函数并且和CdS 层有良好的欧姆接触,所以是一种较为理想的HRT 过渡层材料。
本文综合介绍了各种制备SnO_2薄膜的方法及优缺点,比较选择出PECVD法作为制备本征SnO_2薄膜的最佳方案。最终制备出做为HRT 过渡层使用的本征SnO_2薄膜,并进行了薄膜退火研究。用X 射线衍射仪(XRD)、紫外-可见光光谱仪(UV-Vis absorption Spectrometer)以及光电子能谱(XPS)等测试手段对制备出的薄膜进行结构和性能表征。结果表明:在200℃左右沉积出的SnO_2薄膜均为非晶态,但在400℃左右薄膜开始逐渐变为多晶态。不同的SnCl_4/O_2流量比对SnO_2薄膜的透过率影响明显,发现最佳的流量比值,并对其电导率变化的机制进行讨论
最后,我们研究了HRT 在电池中的作用。分析了HRT 与SnO_2:F 界面势垒和HRT 与CdS 界面的点接触特性。并将PECVD 制备得到本征SnO_2薄膜用于CdTe 电池中,在其他各项工艺相同的情况下制备出有HRT 过渡层和无HRT过渡层的两组CdTe 太阳电池,以期进行对比。结果表明,拥有HRT 过渡层
SnO_2 is a kind of wide bandgap materials, it has been widely applied in many fields such as solar cell, electric heating devices, transparent electrodes and gas sensors, due to its excellent properties, i.e. wide bandgap, high transparency in visible region, high stability. This thesis research the production of intrinsic SnO_2 film by PECVD and the application of this film on CdTe thin films solar cells as HRT buffer layer. This means which inserting a HRT buffer layer between the TCO and CdS has been proved that increasing the cells’efficiency more. Intrinsic SnO_2 film has not only the same work function with TCO but also the good ohmic contact with CdS film, so it can be used as a kind of HRT materials.
In this paper, intrinsic SnO_2 films were successfully fabricated by PECVD and annealed in N_2/O_2 gas. The prepared films were characterized by X-ray diffraction, UV-Visibile absorption and XPS. It was found that intrinsic SnO_2 films were amorphous structure at 200℃and turned to the polycrystalline at 400℃. The high SnCl_4 content result in low transparent, on the other hand, it bring high conductance.
Finally, the effect of HRT buffer layer in cells had been studied. As analyzed the result of HRT buffer layer effecting with SnO_2:F and CdS layer, the conclusion had been obtained, which was useful that electron moving through CdS layer to SnO_2:F layer. In the same manufacture process, two group of CdTe cells which one had HRT buffer layer and another had not HRT buffer layer were compared. The result was indicated that the cells which have HRT layer have better properties than other group, so its efficiency increased evidently. As for this experiment, the cells’efficiency with HRT buffer layer increase more 14.4% than the cells without HRT buffer layer.
本文综合介绍了各种制备SnO_2薄膜的方法及优缺点,比较选择出PECVD法作为制备本征SnO_2薄膜的最佳方案。最终制备出做为HRT 过渡层使用的本征SnO_2薄膜,并进行了薄膜退火研究。用X 射线衍射仪(XRD)、紫外-可见光光谱仪(UV-Vis absorption Spectrometer)以及光电子能谱(XPS)等测试手段对制备出的薄膜进行结构和性能表征。结果表明:在200℃左右沉积出的SnO_2薄膜均为非晶态,但在400℃左右薄膜开始逐渐变为多晶态。不同的SnCl_4/O_2流量比对SnO_2薄膜的透过率影响明显,发现最佳的流量比值,并对其电导率变化的机制进行讨论
最后,我们研究了HRT 在电池中的作用。分析了HRT 与SnO_2:F 界面势垒和HRT 与CdS 界面的点接触特性。并将PECVD 制备得到本征SnO_2薄膜用于CdTe 电池中,在其他各项工艺相同的情况下制备出有HRT 过渡层和无HRT过渡层的两组CdTe 太阳电池,以期进行对比。结果表明,拥有HRT 过渡层
SnO_2 is a kind of wide bandgap materials, it has been widely applied in many fields such as solar cell, electric heating devices, transparent electrodes and gas sensors, due to its excellent properties, i.e. wide bandgap, high transparency in visible region, high stability. This thesis research the production of intrinsic SnO_2 film by PECVD and the application of this film on CdTe thin films solar cells as HRT buffer layer. This means which inserting a HRT buffer layer between the TCO and CdS has been proved that increasing the cells’efficiency more. Intrinsic SnO_2 film has not only the same work function with TCO but also the good ohmic contact with CdS film, so it can be used as a kind of HRT materials.
In this paper, intrinsic SnO_2 films were successfully fabricated by PECVD and annealed in N_2/O_2 gas. The prepared films were characterized by X-ray diffraction, UV-Visibile absorption and XPS. It was found that intrinsic SnO_2 films were amorphous structure at 200℃and turned to the polycrystalline at 400℃. The high SnCl_4 content result in low transparent, on the other hand, it bring high conductance.
Finally, the effect of HRT buffer layer in cells had been studied. As analyzed the result of HRT buffer layer effecting with SnO_2:F and CdS layer, the conclusion had been obtained, which was useful that electron moving through CdS layer to SnO_2:F layer. In the same manufacture process, two group of CdTe cells which one had HRT buffer layer and another had not HRT buffer layer were compared. The result was indicated that the cells which have HRT layer have better properties than other group, so its efficiency increased evidently. As for this experiment, the cells’efficiency with HRT buffer layer increase more 14.4% than the cells without HRT buffer layer.
引文
1 Roy G.Gordon, Criteria for Choosing Transparent Conducting Oxides, MRS Bulletn Augst,2000 p28-36
2 Brian G.Lews and David C.Paine, Applications and Processing of Transparent Conducting Oxides, MRS Bulletn Augst,2000 p38-43
3 Timothy J.Cotts, David L.Young, and Xiaonan Li, Characterization of Transparent Conducting Oxides, MRS Bulletn, Augst 2000 p58-65
4 G.Mavrodiev, M.Gajdardziska, N.Novkovski, Thin Solid Films 113(1984)93
5 Maissel L.I, Handbook of Thin Film Technology, MeGraw-Hill, New York, 1970, Chap 18
6 Radak P.Shan, Sathiadm K, Laser-induced damage to spary pyrolysis deposited transparent conducting films, J.Appl.Phys, 1986(59),902-904
7 T.Minami, H.Sato, H.Nanto, Doping effect of SnO2 on gas sensing characteristics of sputtered ZnO thin film Chemical sensor. Sensor and Actuators B:Chemical.1995.24.781
8 W.G.Adams and R.E.Day, In Proceedings of the Royal Society, pages A25,113,1877
9 A.L.Fahrenbruch and H.Bube, Fundamentals of Solar Cells, Academic Press, London,1983
10 D.M.Chapin, C.S.Fuller, and G.L.Person, Journal of Applied Physics,1954 11 D.A.Cusano, Solid-St Electron, 1963, 6,217
12 E.I.Adirovich, Y.M.Yuabov, and G.R.Yagudaev.Fiz.Tekh.Poluprovodnikov, 1969, 1(3), 81-85
13 D.Bonnet and H.Rabenhorst, Conf.Rec.9thIEEC PVSC, Silver Spring, 1972,129-927
14 T.L.Chu, S.S.Chu, and K.Murthy et al, Conf.Rec.16thIEEC PVSC, San Diego, 1982, 922-927
15 X.Wu, R.G.Dhere, D.S.Albin et al, NCPV program review meeting Lakewood, Colorado 14-17 October 2001, 47-48
16 R.C.Powell, R.Sasala, and G.Rich et al, Conf.Rec.25thIEEC PVSC, 1996,785-788
17 王长贵,世界光伏发电技术现状与发展趋势, 新能源, 2000,1,44
18 Alessandro Romeo, thesis of doctor, Diss.ETH.Nr. 14436 Growth and Characterization of high Efficiency CdTe/CdS Solar Cell
19 Levi.D.H, Fulegel.B.D, Ahrenkiel.R.K, Dynamics of photoexcited carrier relaxation and recombination in CdTe/CdS thin films, IEEE 25th PVSC, Washington, DC,1966, 913～916
20 Adi.R, Mostavan.A, Rusmaeni.N,et al, Fabrication and characterization of CdS
and ZnS thin films made by CSS and CSVT, Technical Digest of the International PVSEC-9, Miyazak Japan, 1996, 137～439
21 W.Song, D.Mao, and V.Kaydanov,et al, NCPV Photobolatic Program Review, Proceedings of the 15th Conference, Denver,CO, 1998, AIP Conference Proceedings 194～199
22 R.G.Gordon, R.Broomhall-Dillard, X.Liu, D.Pang, and J.Barton, Transparent Conductors and Barrier Layers for Thin Film Solar Cells, December 2001, NERL/SR-520-31379
23 X.Li, R.Ribelin, Y.Mahathongdy, D.Albin, R.Dhere,et al, The Effect of High-Resistance SnO2 on CdS/CdTe Device Performance, NERL/CP-520-25607
24 R.W.Birkmire, J.E.Philips, W.N.Shafarman, S.S.Hegedus, and B.E.Mccandless, Optimization of Processing and Modeling Issues for Thin Film Solar Cell Devices, February 2000, NERL/SR-520-27929
25 甑汉光,等离子体加工技术,北京,清华大学出版社, 1990
26 刘彭义陈俊芳, 用PECVD 制备SnO2薄膜的结构、成分和气敏特性, 传感器世界,1997,8,24～28
27 雷永泉万师石永康编。新能源材料. 天津大学出版社. (2000)
28 [美]胡晨明,R.M.怀特,李采华译,太阳电池,北京大学出版社(1990)
29 R.W.Birkmire, Solar Energy Materials and Solar Cells, 2001,65(1), 17～28
30 X.Wu, J.C.Keane, R.G.Dhere et al, 16.5% efficient CdS/CdTe Polycrystalline Thin Films Solar Cell, 17th European Photovoltaic Solar Energy Conference, 2001, Munich,Germany
2 Brian G.Lews and David C.Paine, Applications and Processing of Transparent Conducting Oxides, MRS Bulletn Augst,2000 p38-43
3 Timothy J.Cotts, David L.Young, and Xiaonan Li, Characterization of Transparent Conducting Oxides, MRS Bulletn, Augst 2000 p58-65
4 G.Mavrodiev, M.Gajdardziska, N.Novkovski, Thin Solid Films 113(1984)93
5 Maissel L.I, Handbook of Thin Film Technology, MeGraw-Hill, New York, 1970, Chap 18
6 Radak P.Shan, Sathiadm K, Laser-induced damage to spary pyrolysis deposited transparent conducting films, J.Appl.Phys, 1986(59),902-904
7 T.Minami, H.Sato, H.Nanto, Doping effect of SnO2 on gas sensing characteristics of sputtered ZnO thin film Chemical sensor. Sensor and Actuators B:Chemical.1995.24.781
8 W.G.Adams and R.E.Day, In Proceedings of the Royal Society, pages A25,113,1877
9 A.L.Fahrenbruch and H.Bube, Fundamentals of Solar Cells, Academic Press, London,1983
10 D.M.Chapin, C.S.Fuller, and G.L.Person, Journal of Applied Physics,1954 11 D.A.Cusano, Solid-St Electron, 1963, 6,217
12 E.I.Adirovich, Y.M.Yuabov, and G.R.Yagudaev.Fiz.Tekh.Poluprovodnikov, 1969, 1(3), 81-85
13 D.Bonnet and H.Rabenhorst, Conf.Rec.9thIEEC PVSC, Silver Spring, 1972,129-927
14 T.L.Chu, S.S.Chu, and K.Murthy et al, Conf.Rec.16thIEEC PVSC, San Diego, 1982, 922-927
15 X.Wu, R.G.Dhere, D.S.Albin et al, NCPV program review meeting Lakewood, Colorado 14-17 October 2001, 47-48
16 R.C.Powell, R.Sasala, and G.Rich et al, Conf.Rec.25thIEEC PVSC, 1996,785-788
17 王长贵,世界光伏发电技术现状与发展趋势, 新能源, 2000,1,44
18 Alessandro Romeo, thesis of doctor, Diss.ETH.Nr. 14436 Growth and Characterization of high Efficiency CdTe/CdS Solar Cell
19 Levi.D.H, Fulegel.B.D, Ahrenkiel.R.K, Dynamics of photoexcited carrier relaxation and recombination in CdTe/CdS thin films, IEEE 25th PVSC, Washington, DC,1966, 913～916
20 Adi.R, Mostavan.A, Rusmaeni.N,et al, Fabrication and characterization of CdS
and ZnS thin films made by CSS and CSVT, Technical Digest of the International PVSEC-9, Miyazak Japan, 1996, 137～439
21 W.Song, D.Mao, and V.Kaydanov,et al, NCPV Photobolatic Program Review, Proceedings of the 15th Conference, Denver,CO, 1998, AIP Conference Proceedings 194～199
22 R.G.Gordon, R.Broomhall-Dillard, X.Liu, D.Pang, and J.Barton, Transparent Conductors and Barrier Layers for Thin Film Solar Cells, December 2001, NERL/SR-520-31379
23 X.Li, R.Ribelin, Y.Mahathongdy, D.Albin, R.Dhere,et al, The Effect of High-Resistance SnO2 on CdS/CdTe Device Performance, NERL/CP-520-25607
24 R.W.Birkmire, J.E.Philips, W.N.Shafarman, S.S.Hegedus, and B.E.Mccandless, Optimization of Processing and Modeling Issues for Thin Film Solar Cell Devices, February 2000, NERL/SR-520-27929
25 甑汉光,等离子体加工技术,北京,清华大学出版社, 1990
26 刘彭义陈俊芳, 用PECVD 制备SnO2薄膜的结构、成分和气敏特性, 传感器世界,1997,8,24～28
27 雷永泉万师石永康编。新能源材料. 天津大学出版社. (2000)
28 [美]胡晨明,R.M.怀特,李采华译,太阳电池,北京大学出版社(1990)
29 R.W.Birkmire, Solar Energy Materials and Solar Cells, 2001,65(1), 17～28
30 X.Wu, J.C.Keane, R.G.Dhere et al, 16.5% efficient CdS/CdTe Polycrystalline Thin Films Solar Cell, 17th European Photovoltaic Solar Energy Conference, 2001, Munich,Germany
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