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Hydrogenated microcrystalline silicon germanium (c-Si1-xGex:H) thin films have been developed as alternative bottom sub-cell absorbers for multi-junction thin film silicon solar cells due to their narrower band-gaps and higher absorption coefficients than conventional hydrogenated microcrystalline silicon (c-Si:H) thin films. However, since the structure complexity was increased a lot by Ge incorporation, the influences of c-Si1-xGex:H film properties on Ge composition have not been understood yet. In this work, c-Si1-xGex:H thin films with various Ge content and similar crystalline volume fraction are fabricated by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD). The evolutions of c-Si1-xGex:H material properties by Ge incorporation are characterized by X-ray fluorescence spectrometry, Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, absorption coefficient spectrum, and conductivity measurement. The results show that the properties of c-Si1-xGex:H thin films are strongly determined by Ge content. With the increase of Ge content, the absorption coefficient, (111) grain size, microstructure factor, and dark conductivity of c-Si1-xGex:H thin films increase, while the H content, (220) grain size, and photosensitivity of c-Si1-xGex:H thin film decrease. Then, c-Si1-xGex:H is used as the intrinsic layer in the single junction solar cells. The performances of c-Si1-xGex:H solar cells with different Ge content and two types of transparent conductive oxide (SnO2 and ZnO) substrates are systematically studied. The results indicate that although c-Si1-xGex:H thin films become more defective and less compact with Ge incorporation, c-Si1-xGex:H solar cells exhibit a significant improvement in near-infrared response, especially under the circumstances of thin cell thickness and inefficient light trapping structure. Meanwhile, by using ZnO substrates, initial efficiencies of 7.15% (Jsc=22.6 mA/cm2, Voc=0.494 V, FF=64.0%) and 7.01% (Jsc=23.3 mA/cm2, Voc=0.482 V, FF=62.4%) are achieved by c-Si0.9Ge0.1:H solar cell and c-Si0.73Ge0.27:H solar cell, respectively. Furthermore, the c-Si0.73Ge0.27:H solar cell is used as the bottom sub-cell of the double-junction solar cell, and a Jsc.bottom of 12.30 mA/cm2 can be obtained with the bottom sub-cell thickness as thin as 800 nm, which is even higher than that of c-Si:H bottom sub-cell with 1700 nm thickness. Finally, an initial efficiency of 10.28% is achieved in an a-Si:H/c-Si0.73Ge0.27:H double junction cell structure. It is demonstrated that by using the c-Si1-xGex:H solar cell as the bottom sub-cell in multi-junction thin film silicon solar cells, a higher tandem cell performance can be achieved with a thin thickness, which has a great potential for cost-effective photovoltaics.
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Keywords:
- hydrogenated microcrystalline silicon germanium /
- near-infrared response /
- thin film silicon solar cell /
- plasma-enhanced chemical vapor deposition
[1] Shah A, Torres P, Tscharner R, Wyrsch N, Keppner H 1999 Science 285 692
[2] Kang D W, Chowdhury A, Sichanugrist P, Abe Y, Konishi H, Tsuda Y, Shinagawa T, Tokioka H, Fuchigami H, Konagai M 2015 Curr. Appl. Phys. 15 1022
[3] Schttauf J W, Niesen B, Lfgren L, Bonnet-Eymard M, Stuckelberger M, Hnni S, Boccard M, Bugnon G, Despeisse M, Haug F J, Meillaud F, Ballif C 2015 Sol. Energy Mater. Sol. Cells 133 163
[4] Kim S, Chung J W, Lee H, Park J, Heo Y, Lee H M 2013 Sol. Energy Mater. Sol. Cells 119 26
[5] Yan B, Yue G, Sivec L, Yang J, Guha S, Jiang C 2011 Appl. Phys. Lett. 99 113512
[6] Sai H, Matsui T, Koida T, Matsubara K, Kondo M, Sugiyama S, Katayama H, Takeuchi Y, Yoshida I 2015 Appl. Phys. Lett. 106 213902
[7] Ganguly G, Ikeda T, Nishimiya T, Saitoh K, Kondo M 1996 Appl. Phys. Lett. 69 4224
[8] Ni J, Liu Q, Zhang J J, Ma J, Wang H, Zhang X D, Zhao Y 2014 Sol. Energy Mater. Sol. Cells 126 6
[9] Zhang L P, Zhang J J, Zhang X, Shang Z R, Hu Z X, Zhang Y P, Geng X H, Zhao Y 2008 Acta Phys. Sin. 57 7338 (in Chinese) [张丽平, 张建军, 张鑫, 尚泽仁, 胡增鑫, 张亚萍, 耿新华, 赵颖 2008 物理学报 57 7338]
[10] Boshta M, Alavi B, Braunstein R, Brner K, Dalal V L 2005 Sol. Energy Mater. Sol. Cells 87 387
[11] Cao Y, Zhang J J, Li T W, Huang Z H, Ma J, Ni J, Geng X H, Zhao Y 2013 Acta Phy. Sin. 62 036102 (in Chinese) [曹宇, 张建军, 李天微, 黄振华, 马峻, 倪牮, 耿新华, 赵颖 2013 物理学报 62 036102]
[12] Cao Y, Zhang J J, Li T W, Huang Z H, Ma J, Yang X, Ni J, Geng X H, Zhao Y 2013 J. Semicond. 34 034008
[13] Cao Y, Zhou J, Wang Y J, Ni J, Zhang J J 2015 J. Alloys Compd. 632 456
[14] Matsui T, Chang C W, Takada T, Isomura M, Fujiwara H, Kondo M 2008 Appl. Phys. Express 1 031501
[15] Cao Y, Zhang J J, Li C, Li T W, Huang Z H, Ni J, Hu Z Y, Geng X H, Zhao Y 2013 Sol. Energy Mater. Sol. Cells 114 161
[16] Zhang J J, Shimizu K, Zhao Y, Geng X H, Hanna J 2006 Phys. Status Solidi A 203 760
[17] Kim S, Park C, Lee J C, Chob J S, Kim Y 2013 Curr. Appl. Phys. 13 457
[18] Tang Z, Wang W, Wang D, Liu D, Liu Q, He D 2010 J. Alloys Compd. 504 403
[19] Krause M, Stiebig H, Carius R, Zastrow U, Bay H, Wagner H 2002 J. Non-Cryst. Solids 299-302 158
[20] Cao Y, Zhang J J, Yan G G, Ni J, Li T W, Huang Z H, Zhao Y 2014 Acta Phys. Sin. 63 076801 (in Chinese) [曹宇, 张建军, 严干贵, 倪牮, 李天微, 黄振华, 赵颖 2014 物理学报 63 076801]
[21] Podraza N J, Wronski C R, Collins R W 2006 J. Non-Cryst. Solids 352 1263
[22] Isomura M, Nakahata K, Shima M, Taira S, Wakisaka K, Tanaka M, Kiyama S 2002 Sol. Energy Mater. Sol. Cells 74 519
[23] Vallat-Sauvain E, Kroll U, Meier J, Shah A, Pohl J 2000 J. Appl. Phys. 87 3137
[24] Kim S, Park C, Lee J C, Cho J S, Kim Y 2013 Thin Solid Films 534 214
[25] Moutinho H R, Jiang C S, Perkins J, Xu Y, Nelson B P, Jones K M, Romero M J, Al-Jassim M M 2003 Thin Solid Films 430 135
[26] Kamiya T, Nakahata K, Tan Y T, Durrani Z A K, Shimizu I 2001 J. Appl. Phys. 89 6265
[27] Guo L, Lin R 2000 Thin Solid Films 376 249
[28] Das R, Jana T, Ray S 2005 Sol. Energy Mater. Sol. Cells 86 207
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[1] Shah A, Torres P, Tscharner R, Wyrsch N, Keppner H 1999 Science 285 692
[2] Kang D W, Chowdhury A, Sichanugrist P, Abe Y, Konishi H, Tsuda Y, Shinagawa T, Tokioka H, Fuchigami H, Konagai M 2015 Curr. Appl. Phys. 15 1022
[3] Schttauf J W, Niesen B, Lfgren L, Bonnet-Eymard M, Stuckelberger M, Hnni S, Boccard M, Bugnon G, Despeisse M, Haug F J, Meillaud F, Ballif C 2015 Sol. Energy Mater. Sol. Cells 133 163
[4] Kim S, Chung J W, Lee H, Park J, Heo Y, Lee H M 2013 Sol. Energy Mater. Sol. Cells 119 26
[5] Yan B, Yue G, Sivec L, Yang J, Guha S, Jiang C 2011 Appl. Phys. Lett. 99 113512
[6] Sai H, Matsui T, Koida T, Matsubara K, Kondo M, Sugiyama S, Katayama H, Takeuchi Y, Yoshida I 2015 Appl. Phys. Lett. 106 213902
[7] Ganguly G, Ikeda T, Nishimiya T, Saitoh K, Kondo M 1996 Appl. Phys. Lett. 69 4224
[8] Ni J, Liu Q, Zhang J J, Ma J, Wang H, Zhang X D, Zhao Y 2014 Sol. Energy Mater. Sol. Cells 126 6
[9] Zhang L P, Zhang J J, Zhang X, Shang Z R, Hu Z X, Zhang Y P, Geng X H, Zhao Y 2008 Acta Phys. Sin. 57 7338 (in Chinese) [张丽平, 张建军, 张鑫, 尚泽仁, 胡增鑫, 张亚萍, 耿新华, 赵颖 2008 物理学报 57 7338]
[10] Boshta M, Alavi B, Braunstein R, Brner K, Dalal V L 2005 Sol. Energy Mater. Sol. Cells 87 387
[11] Cao Y, Zhang J J, Li T W, Huang Z H, Ma J, Ni J, Geng X H, Zhao Y 2013 Acta Phy. Sin. 62 036102 (in Chinese) [曹宇, 张建军, 李天微, 黄振华, 马峻, 倪牮, 耿新华, 赵颖 2013 物理学报 62 036102]
[12] Cao Y, Zhang J J, Li T W, Huang Z H, Ma J, Yang X, Ni J, Geng X H, Zhao Y 2013 J. Semicond. 34 034008
[13] Cao Y, Zhou J, Wang Y J, Ni J, Zhang J J 2015 J. Alloys Compd. 632 456
[14] Matsui T, Chang C W, Takada T, Isomura M, Fujiwara H, Kondo M 2008 Appl. Phys. Express 1 031501
[15] Cao Y, Zhang J J, Li C, Li T W, Huang Z H, Ni J, Hu Z Y, Geng X H, Zhao Y 2013 Sol. Energy Mater. Sol. Cells 114 161
[16] Zhang J J, Shimizu K, Zhao Y, Geng X H, Hanna J 2006 Phys. Status Solidi A 203 760
[17] Kim S, Park C, Lee J C, Chob J S, Kim Y 2013 Curr. Appl. Phys. 13 457
[18] Tang Z, Wang W, Wang D, Liu D, Liu Q, He D 2010 J. Alloys Compd. 504 403
[19] Krause M, Stiebig H, Carius R, Zastrow U, Bay H, Wagner H 2002 J. Non-Cryst. Solids 299-302 158
[20] Cao Y, Zhang J J, Yan G G, Ni J, Li T W, Huang Z H, Zhao Y 2014 Acta Phys. Sin. 63 076801 (in Chinese) [曹宇, 张建军, 严干贵, 倪牮, 李天微, 黄振华, 赵颖 2014 物理学报 63 076801]
[21] Podraza N J, Wronski C R, Collins R W 2006 J. Non-Cryst. Solids 352 1263
[22] Isomura M, Nakahata K, Shima M, Taira S, Wakisaka K, Tanaka M, Kiyama S 2002 Sol. Energy Mater. Sol. Cells 74 519
[23] Vallat-Sauvain E, Kroll U, Meier J, Shah A, Pohl J 2000 J. Appl. Phys. 87 3137
[24] Kim S, Park C, Lee J C, Cho J S, Kim Y 2013 Thin Solid Films 534 214
[25] Moutinho H R, Jiang C S, Perkins J, Xu Y, Nelson B P, Jones K M, Romero M J, Al-Jassim M M 2003 Thin Solid Films 430 135
[26] Kamiya T, Nakahata K, Tan Y T, Durrani Z A K, Shimizu I 2001 J. Appl. Phys. 89 6265
[27] Guo L, Lin R 2000 Thin Solid Films 376 249
[28] Das R, Jana T, Ray S 2005 Sol. Energy Mater. Sol. Cells 86 207
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