Conclusion and Future Work

4.1 Conclusion

In this work, we have studied the property of a-Si:H as function of the silane flow rate,

electrode spacing and dopant concentration. Increasing the electrode spacing promoted

polymerization and can lead to the inclusion of SiH2 chain within the film. The high quality

intrinsic a-Si:H was obtain at which contains 8~9 atomic % of hydrogen predominated

bonded as SiH configuration. The p-layer and n-layer have been doped with appropriate

dopant concentration. Alloying a-Si:H with carbon causes the bandgap to widen, but it also

reduce the conductivity. Usage of the wide bandgap p-layer would increases the open-circuit

voltage and the short-circuit current of the solar cell by increasing incident light and reducing

electron-hole recombination at the p-i interface. In this study, the optimal a-SiC:H window

layer has bandgap 1.94ev and carbon composition 20 %.The annealing would affect solar cell

performance significantly with optimal annealing temperature of 150℃ The n/Ag interface is .

the main improvement of the solar cell when underwent thermal annealing. The structure of

a-Si:H solar cell with area sizes of 2×2cm² and 1×1cm² was also fabricated, respectively. The

cell performance did not degrade on the cell area was enlarge to 2×2cm². The best conversion

efficiency of 8.67% was achieved for area of 2×2cm².

4.2 Future Work

The performances of single junction a-Si:H solar cells decrease during the initial

stage of due to light induced degradation. The solar cell degradation due to illumination is the

manifestation of the Staebler-Wronski effect. After the initial degradation, the performance of

solar cells stabilizes. Therefore, the a-Si:H solar cell structure and the properties of the

individual a-Si:H based layers must be optimized for the light soaked state. In addition, in this

study we considered only single-junction solar cell. This work can be extended for tandem

solar cells, with a-Si:H cell as the bottom cell and the a-SiGe or µc-Si thin film solar cell as

the top cell for very high efficiency.

Reference

[1] German Advisory Council on Global Change, “World in Transition–Towards Sustainable Energy Systems”, Earthscan, London (2003)

[2] M.A. Green, “Third Generation Photovoltaics:Ultra-High Efficiency at Low Cost”, Springer-Verlag, Berlin, (2003)

[3] D.L. Staebler and C.R. Wronski, “Reversible conductivity changes in discharge–

produced amorphous Si”, Appl. Phys. Lett., 31, 292 (1977)

[4] D.E. Carlson, R.R. Arya, M. Bennet, L.F. Chen, K. Jansen, Y.M. Li, J. Newton, K. Rajan, R. Romero, D. Talenti, E. Twesme, F. Willing and L. Yan, “Commercialization of multi -junction amorphous silicon modules”, Proc. 25th IEEE Photovolt. Specialists Conf., 1023 (1996)

[5] S. Guha, “Amorphous silicon alloy solar cells and modules-opportunities and challenges”, Proc. 25th IEEE Photovolt. Specialists Conf., 1017 (1996)

[6] S. Fujikake, K. Tabuchi, A. Takano, T. Wada, S. Saito, H. Sato, T. Yoshida, Y. Ichikawa and H. Sakai, “Film-substrate a-Si solar cells and their novel process technologies”, Proc. 25th IEEE Photovolt. Specialists Conf., 1045 (1996)

[7] G. Hagedorn, “Hidden energy in solar cells and photovoltaic power stations”, Proc. 9th Europ. Photovolt. Solar Energy Conf., 542 (1989)

[8] J. M. Woodcock, H. Schade, H.Maurus, B. Dimmler, J. Springer and A. Ricaud, “A study of the upscaling of thin film solar cell manufacture towards 500 MWp per annum”, Proc. 14th Europ. Photovolt. Solar Energy Conf., 857 (1997)

[9] D.E. Carlson and C.R. Wronski, “Amorphous Si solar cell”, Appl. Phys. Lett., 28, 671 (1976)

[10] H. Sakai and Y. Ichikawa,“Process technology for a-Si/A-Si double stacked tandem solar cells with stabilized 10% efficiency”, J. Non-Cryst. Solids, 137, 1155 (1991)

[11] G. Nakamura, K. Sato and Y. Yukimoto, “High performance tandem type amorphous solar cells”, Proc. 16th IEEE Photovolt. Specialists Conf., 1331 (1982)

[12] J. Yang, A. Banerjee and S. Guha, “Triple-junction amorphous silicon alloy solar cell with 14.6% initial and 13.0% stable conversion efficiencies”, Appl. Phys. Lett., 70, 2975 (1997)

[13] Y. Tawada, H. Okamoto and Y. Hamakawa, “a-SiC:H/a-Si:H heterojunction solar cell having more than 7.1% conversion efficiency”, Appl. Phys. Lett., 39, 237 (1981)

[14] G. Nakamura, K. Sato, Y. Yukimoto, K. Shirahata, T. Murahashi and K. Fujiwara,

“Amorphous SiGe:H for high performance solar cells”, Jap. J. Appl. Phys., 20, 291 (1981)

[15] H.W. Deckman, C.R. Wronski, H. Witzke and E. Yablonovitch,

“

[16] S. Guha, K.L. Narasimhan, S.M. Pietruszko, “On light-induced effect in amorphous hydrogenated silicon”, J. Appl. Phys., 52, 859 (1981)

[17] A. Matsuda, T. Yamaoka, S.Wolff, M. Koyama, Y. Imanishi, H. Kataoka, H. Matsuura and K. Tanaka, “Preparation of highly photosensitive hydrogenated amorphous Si-C alloys from a glow-discharge plasma”, J. Appl. Phys., 60, 4025 (1986)

[18] A. Matsuda and K. Tanaka, “Guiding principle for preparing highly photosensitive Si-based amorphous alloys”, J. Non-Cryst. Solids, 97, 1367 (1987)

[19] J. Meier, S. Dubail, R. Platz, P. Torres, U. Kroll, J.A. Anna Selvan, N. Pellaton Vaucher, Ch. Hof, D. Fischer, H. Keppner, R. Flückiger, A. Shah, V. Shklover and K.D. Ufert,

“Towards high-efficiency thin-film silicon solar cells with the “ micromorph ” concept”, Sol. En. Mat. and Sol. Cells, 49, 35 (1997)

[20] J. Meier, U. Kroll, S. Dubail, S. Golay, S. Fay and J. Dubail, “Efficiency enhancement of amorphous silicon p-i-n solar cells by LP-CVD ZnO”, Proceedings of the 28^th IEEE Photovoltaic Specialist Conference, 746 (2000)

[21] A.V. Shah, M. Vanecek, J. Meier, F. Meillaud, J.Guillet, K. Fischer, C.Droz, X. Niquille, S. Tay, E. Vallat-Sauvain, V. Terrazzoni-Saudrix and J. Bailat, “Absorption loss at nanorough silver back reflector of thin-film silicon solar cells”, J. Non-Cryst. Solids, 388, 639 (2004)

[22] J. Perrin, O. Leroy and M.C. Bordage, “Cross-Sections, Rate Constants and Transport Coefficients in Silane Plasma Chemistry”, Contrib. Plasma Phys., 36, 3 (1996)

[23] A. Matsuda, K. Nomoto, Y. Takeuchi, A. Suzuki, A. Yuuki and J. Perrin, “Temperature dependence of the sticking and loss probabilities of silyl radicals on hydrogenated amorphous silicon”, Surf. Sci., 227, 50 (1990)

[24] R.A. Street, “Hydrogenated Amorphous Silicon”, Cambridge University Press, Cambridge (1991)

[25] H. Seidel, L. Csepregi, A. Heuberger, H. Baumgartel, “Anisotropic etching of crystalline silicon in alkaline solutions“, J. Electrochem. Soc., 137, 3612 (1990)

[26] R.E.I. Schropp, M. Zeman, “Amorphous and Microcrystalline Silicon Solar Cells”, Kluwer Academic publishers, Boston, p.47(1998)

[27] M.H. Brodksy, M. Cardona and J.J. Cuomo, “Infrared and Raman spectra of the silicon-hydrogen bonds in amorphous silicon prepared by glow discharge and sputtering”, Phys. Rev., B16, 3556 (1977)

[28] H. Shanks, C.J. Fang, L. Ley, M. Cardona, F.J. Demond, and S. Kalbitzer, “Infared spectrum and structure of hydrogenated amorphous silicon”, Phys. Status Solidi, B110, 43 (1980)

[29] J. Knights and R.A. Lujan, “ Microstructure of plasma-deposited a-Si:H films”, Appl.

Phys .Lett., 35, 244 (1979)

[30] R.A. Street, J.C. Knights, and D.K. Biegelsen, “Luminescence studies of plasma- deposited hydrogenated silicon”, Phys. Rev., B19, 3027 (1978)

[31] W.E. Spear and P. Le Comber, “Substitutional doping of amorphous silicon”, Solid State Electron., 8, 653 (1965)

[32] R.A. Street, “Doping and the Fermi Energy in Amorphous Silicon”, Phys. Rev. Lett., 49,1187 (1982)

[33] T. Hanma, H. Okamoto, Y. Hamakawa and T. Mastsubara, “Hydrogen content dependence of the optical energy gap in a-Si:H ”, J. Non-Cryst. Solids, 59, 333 (1983)

[34] D.A. Anderson and W.E. Spear, “Photoconductivity and recombination in doped amorphous silicon”, Phil. Mag., 35, 1 (1977)

[35] Y. Catherine, G. Turban, and B. Grolleau, “Reaction mechanisms in plasma deposition of SixC1-x:H films ”, Thin Solid Films, 76, 23 (1981)

[36] M. Kondo, K. Hayashi, H. Nishio, S. Kurata, A. Lshikawa, A. Takenaka, K. Nishimura, A.Nakajima, H. Yamagishi and K.Y. Taeada, “ Development of high efficient large area a-Si solar modules ”, Proceedings of the 13^th European Photovoltaic Solar Energy Conference, Nice, 311 (1995)

[37] Y. Tawada, M. Kondo, H. Okamoto, and Y. Hamakawa, “a-SiC:H/a-Si:H heterojunction solar cell having more than 7.5% conversion efficiency”, Proc. 15^th IEE Photovoltaic Specialists Conf., 245 (1981)

[38] G.A. Swartz, “Reverse bias and heat treatment to improve performance of a-Si solar cells”, Appl. Phys. Lett., 44, 697 (1984)

[39] Tulay Serin and Necmi Serin, “The effect of annealing on the resistance of a p/i/n structure“, Semicond. Sci. Technol., 9, 2097 (1994)

[40] Y. Arai, M. Ishii, H. Shinohara, and Shumpei Yamazaki, “ A single p-i-n junction amorphous-silicon solar cell with conversion efficiency of 12.65%”, Electron Device Letters, 12, 460 (1991)

[41] F. Meillaud, A. Shah, J. Bailat, E. Vallat-Sauvain, T. Roschek, B. Rech, D. Domine, T. Soderdtrom, M. Python and C. Ballif, “Microcrystalline Silicon Solar Cells: Theory and Diagnostic Tools ”, Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference, 2, 1572 (2006)