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在本征氢化非晶硅(a-Si:H(i))/晶体硅(c-Si)/a-Si:H(i)异质结构上溅射ITO时, 发现后退火可大幅增加ITO/a-Si:H(i)/c-Si/a-Si:H(i)的少子寿命(从1.7 ms到4 ms). 这一增强效应可能的三个原因是: ITO/a-Si:H(i)界面场效应作用、退火形成的表面反应层影响以及退火对a-Si:H(i)材料本身的优化, 但本文研究结果表明少子寿命增强效应与ITO和表面反应层无关; 对不同沉积温度制备的a-Si:H(i)/c-Si/a-Si:H(i)异质结后退火的研究表明: 较低的沉积温度(175 ℃)后退火增强效应显著, 而较高的沉积温度(200 ℃)后退火增强效应不明显, 可以确定低温长高温后退火是获得高质量钝化效果的一种有效方式; 采用傅里叶红外吸收谱(FTIR)研究不同沉积温度退火前后a-Si:H(i)材料本身的化学键构造, 发现退火后异质结少子寿命大幅提升是由于a-Si:H(i)材料本身的结构优化造成的, 其深层次的本质是通过材料的生长温度和退火温度的优化匹配来控制包括H含量、H键合情况以及Si原子无序性程度等微观因素主导作用的一种竞争性平衡, 对这一平衡点的最佳控制是少子寿命大幅提升的本质原因.The excellent surface passivation scheme for suppression of surface recombination is a basic prerequisite to obtain high efficiency solar cells. Particularly, the HIT (heterojunction with intrinsic thin-layer) solar cell, which possesses an abrupt discontinuity of the crystal network at an interface between the crystalline silicon (c-Si) surface and the hydrogenated amorphous silicon (a-Si:H) thin film, usually causes a large density of defects in the bandgap due to a high density of dangling bonds, so it is very important for high energy conversion efficiency to obtain millisecond (ms) range of minority carrier lifetime (i. e. 2 ms). The a-Si:H, due to its excellent passivation properties obtained at low deposition temperatures and also mature processing, is still the best candidate materials for silicon HIT solar cell. Deposition of a transparent conductive oxide (TCO), such as indium tin oxide (ITO), has to be used to improve the carrier transport, since the lateral conductivity of a-Si:H is very poor. Usually, ITO is deposited by magnetron sputtering, but damage of a-Si:H layers by sputtering-induced ion bombardment inevitably occurs, thus triggering the serious degradation of the minority carrier lifetime, i. e., a loss in wafer passivation. Fortunately, this damage can be often recovered by some post-annealing. In this paper, however, the situation is different, and it is found that the minority carrier lifetime of ITO/a-Si:H/c-Si/a-Si:H heterojunction has been drastically enhanced by post-annealing after sputtering ITO on a- Si:H/c-Si/a-Si:H heterojunction (from 1.7 ms to 4.0 ms), not just recovering. It is very important to investigate how post-annealing enhances the lifetime and its physics nature. Combining the two experimental ways of HF treatment and vacuum annealing, three possible reasons for this enhancement effect (the field effect at the ITO/a-Si:H interface, the surface reaction-layer resulting from annealing in air, and the optimization of a-Si:H material itself) have been studied, suggesting this is irrelevant to the first two. The influence of post-annealing on a-Si:H/c-Si/a-Si:H heterojunction deposited at different temperatures has also been investigated. It is found that the remarkable enhancement effect of post-annealing is for low growth temperature(175 ℃) and not for high growth temperature(200 ℃), with the confirmation of an effective way for high quality passivation using growth at low temperature and then annealed at high temperature. Moreover, the configuration of a-Si:H at different growth temperatures between afore and after annealing has been discussed by an application of Fourier transform infrared (FTIR) spectroscopy. It is shown that the large increase of the lifetime of the heterojunction after annealing results from the improvement of microstructure of a-Si:H itself, which is essentially a competitive balance of the dominant role of some micro-factors, including hydrogen content, hydrogen bonding and network disorder in amorphous silicon film determined by the optimized matching between the growth temperature of a-Si:H materials and the annealing temperature of the heterojunction. An optimum control for this balance point is the essential cause of lifetime enhancement.
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Keywords:
- amorphous silicon /
- passivation /
- annealing /
- minority carrier lifetime
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[22] Aaesha A, Kazi I, Ammar N 2013 Sol. Energy 98 236
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[1] Martn I, Vetter M, Orpella A, Puigdollers J, Cuevas A, Alcubilla R 2001 App. Phy. Lett. 79 2199
[2] Garn M, Rau U, Brendle W, Martn I, Alcubilla R 2005 J. Appl. Phys. 98 093711
[3] Chowdhury Z R, Kherani N P 2014 Appl. Phys, Lett. 105 263902
[4] Frank F, Martin B, Christian R, Martin H, Glunz S W 2014 Sol. Energy Mater. Sol. Cells 120 270
[5] Vernhes R, Zabeida O, Klemberg-Sapieha J E, Martinu L 2006 J. Appl. Phys. 100 063308
[6] Qiu H B, Li H Q, Liu B W, Zhang X, Shen Z N 2014 Chin. Phys. B 23 027301
[7] Zhu X H, Chen G H, Yin S Y, Rong Y D, Zhang W L, Hu Y H 2005 Chin. Phys. Soc. 14 0834
[8] Sangho K, Vinh A D, Chonghoon S, Jaehyun C, Youngseok L, Nagarajan B, Shihyun A, Youngkuk K, Junsin Y 2012 Thin Solid Films 521 45
[9] Hoex B, Schmidt J J, Pohl P, Van de Sanden M C M, Kessels W M M 2008 J. Appl. Phys. 104 044903
[10] Bordihn S, Mertens V, Engelhart P, Kersten F, Mandoc M M, Muller J W, Kessel W M M 2012 ECS J. Sol-Gel Sci. Technol. 1 320
[11] Tfflinger J A, Laades A, Korte L, Leendertz C, Montaez L M, Sturzebecher U, Sperlich H P, Rech B 2015 Sol. Energy Mater. Sol. Cells 135 49
[12] Dingemans G, Terlinden N M, Pierreux D, Profijt H B, Sanden M C M, Kessels W M M 2011 Electrochem. Solid-State Lett. 14 H1
[13] Lei Q S, Wu Z M, Geng X H, Zhao Y, Sun J, Xi J P 2006 Chin. Phys. Soc. 15 3033-06
[14] Geissbuhler J, Wolf S D, Demaurex B, Seif J P, Alexander D T L, Barraud L, Ballif C 2013 App. Phy. Lett. 102 231604
[15] Keiichiro M, Masato S, Taiki H, Daisuke F, Motohide K, Naoki Y, Tsutomu Y, Yoshinari I, Takahiro M, Naoteru M, Tsutomu Y, Tsuyoshi T, Mikio T, Eiji M, Shingo O 2014 IEEE J. Photovolt. 4 1433
[16] Xue Y, Gao C J, Gu J H, Feng Y Y, Yang S E, Lu J X, Huang Q, Feng Z Q 2013 Acta Phys. Sin. 62 197301(in Chinese) [薛源, 郜超军, 谷锦华, 冯亚阳, 杨仕娥, 卢景霄, 黄强, 冯志强 2013 62 197301]
[17] Zhao Z Y, Zhang X D, Wang F Y, Jiang Y J, Du J, Gao H B, Zhao Y, Liu C C 2014 Acta Phys. Sin. 63 136802(in Chinese) [赵振越, 张晓丹, 王奉友, 姜元建, 杜建, 高海波, 赵颖, 刘彩池 2014 63 136802]
[18] Zhu X H, Chen G H, Zhang W L, Ding Y, Ma Z J, Hu Y H, He B, Rong Y D 2005 Chin. Phys. Soc. 14 2348
[19] Stefaan D W, Antoine D, Zachary C H, Christophe B 2012 Green 2 7
[20] Takeshi K, Takeshi Y 2004 Solar Energy Mater. Solar Cells. 81 119
[21] Stefaan D W, Michio K 2007 App. Phy. Lett. 90 042111
[22] Aaesha A, Kazi I, Ammar N 2013 Sol. Energy 98 236
[23] Miroslav M, Michal N, Jaroslav K, Marina F, Cosimo G, Giovanni M, Luca V, Salvatore L 2014 Mat. Sci. Eng. B 189 1
[24] Bndicte D, Stefaan D W, Antoine D, Zachary C H, Christophe B 2012 App. Phy. Lett. 101 171604
[25] Oh W K, HussainS Q, Lee Y J, Lee Y, Ahn S, Yi J 2012 Mater. Res. Bull. 47 3032
[26] Shirakata S, Sakemi T, Awai K, Yamamoto T 2006 Superlattices Microstruct. 39 218
[27] Kakeno T, Sakai K, Komaki H, Yoshino K, Sakemi H, Awai K, Yamamoto T, Ikari T 2005 Mater. Sci. Eng. B 118 70
[28] Thomas M, Stefan S, Maximilian S, Wolfgang R F 2008 App. Phy. Lett. 92 033504
[29] Riither R, Livingstone J 1994 Thin Solid Films 251 30
[30] Zhang D, Tavakoliyaraki A, Wu Y, Swaaij R. A. C. M. M. van, Zeman M 2011 Energy Procedia 8 207
[31] Yablonovitch E, Allara D L, Chang C C, Gmitter T, Bright T B 1986 Phys. Rev. Lett. 57 249
[32] Jonathon M, Daniel M, Andres C 2009 App. Phy. Lett. 94 162102
[33] Stefaan D W, Sara O, Christophe B 2008 App. Phy. Lett. 93 032101
[34] Schulze T F, Beushausen H N, Leendertz C, Dobrich A, Rech B, Korte L 2010 App. Phy. Lett. 96 252102
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