將週期微奈米陣列吸收層應用於矽基薄膜太陽能電池有機會大幅改善其光吸收不佳的特性，本論文主要以有限元素法對週期奈米線及奈米洞陣列兩種結構進行光吸收性的模擬計算與探討。在固定厚度下，針對晶格排列方式、晶格常數、柱體填充比以及截面形狀等各項參數進行對照與比較，並以理論最大效率作一量化。計算後將發現不論變化何種參數，奈米洞陣列都將展現較奈米線陣列具有更佳之光吸收改善。
之後以最佳結果之參數，進一步研究若在奈米洞陣列底部預留一厚度對光陷阱效應的影響。模擬將發現底部預留厚度將較完全蝕刻到底的結構具更進一步的光吸收改善。若以總厚度2.33 μm無預留厚度的奈米洞陣列為基準，將發現僅需總厚度1.5 μm、預留厚度600nm便可具有較此基準更高的最大理論效率。選擇此參數之結構並進一步加入抗反射層及金屬背反射層，用以設計一更薄的太陽能電池，計算結果顯示此設計具有較相同厚度之矽薄膜225%的理論最大效率增益，且相當接近等效體積吸收層以幾何光學設計所能達到的Yablonovitch光陷阱極限，並且在相當寬的入射角範圍內(本文僅分析橫向電場模態( TE-mode )入射) 仍維持相當高的光吸收改善。

In this study, the optical absorption characteristics of silicon nanostructure arrays, including nanowire and nanohole structures, which have potential applications in thin-film solar cells, are investigated via a finite element method. The fixed overall thickness is considered, in which the effects of lattice arrangement, lattice constant, filling ratio, and the cross-section shape of pillars are simulated and quantified in terms of ultimate efficiency. No matter which parameter, it is found that silicon nanohole arrays exhibit much better absorption improvement than silicon nanowire arrays do.
Moreover, we also numerically study the light-trapping effect as the preserved thickness existing in the bottom of the optimum parameters. We find better absorption enhancement than with the full-etched arrays. When choosing an overall thickness of 2.33 μm for the full-etched nanohole arrays as the reference, it is observed that the active layer possessing the higher ultimate efficiency only needs an overall thickness of 1.5 μm and a preserved thickness of 600 nm. We select these parameters to design a thinner active layer and add the anti-reflection coating and the back metal reflector to it. The results show it has a 225% higher ultimate efficiency than a Si thin film of equal thickness and is very close to the Yablonovitch light trapping limit for the same volume of active material. The optical enhancement effect can be maintained over a large range of incident angles (only analysis transverse electric modes incidence).

1. M. Yamaguchi and C. Amano, “Efficiency calculations of thin-film GaAs solar cells on Si substrates,” Journal of Applied Physics. Vol. 58, 3601-3606 (1985)
2. K. Barnham, J. Connolly, P. Griffin, G. Haarpaintner, J. Nelson, E. Tsui, A. Zachariou, J. Osborne, C. Button, G. Hill, M. Hopkinson, M. Pate, J. Roberts, and T. Foxon, “Voltage enhancement in quantum well solar cells,” Journal of Applied Physics. Vol. 80, 1201-1206 (1996)
3. R. R. King, D. C. Law, K. M. Edmondson, C. M. Fetzer, G. S. Kinsey, H. Yoon, R. A. Sherif, and N.H. Karam, “40% efficient metamorphic GaInP/GaInAs/Ge multijunction solar cells,” Applied Physics Letters. Vol. 90, 183516 (2007)
4. B. O'Regan and M. Gratzel, “A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films,” Nature. Vol. 353, 737-740 (1991)
5. E. Yablonovitch ,and G.D. Cody, “Intensity enhancement in textured optical sheets for solar cells,” IEEE Transactions on Electron Devices, Vol.ED-29, NO.2, 300-305 (1982)
6. L. Tsakalakos, “Nanostructures for photovoltaics,” Materials Science and Engineering R, Vol.62, 175-189 (2008)
7. H.A. Atwater, and A. Polman, “Plasmonics for improved photovoltaic devices,” Nature Materials, Vol.9, 205-213 (2010)
8. Y.A. Akimov, W.S. Koh, S.Y. Sian, and S. Ren, “Nanoparticle-enhanced thin film solar cells: Metallic or dielectric nanoparticles?” Applied Physics Letters, Vol.96, 073111 (2010)
9. B.M. Kayes and H.A. Atwater, “Comparison of the device physics principles of planar and radial p-n junction nanorod solar cells,” Journal of Applied Physics, Vol.97, 114302 (2005)
10. L. Hu, and G. Chen, ”Analysis of optical absorption in silicon nanowire arrays for photovoltaic applications,” Nano Letters, Vol. 7, 3249-3252 (2007)
11. D. Duché, L. Escoubas, J.J. Simon, P. Torchio,W. Vervisch, and F. Flory, ”Slow Bloch modes for enhancing the absorption of light in thin films for photovoltaic cells,” Applied Physics Letters, Vol. 92, 193310 (2008)
12. D. Zhou and R. Biswas, “Photonic crystal enhanced light-trapping in thin film solar cells,” Journal of Applied Physics. Vol. 103, 093102 (2008)
13. J. Kupec, and B. Witzigmann, ”Dispersion, wave propagation and efficiency analysis of nanowire solar cells,” Optics Express, Vol. 17, No. 12, 10399-10410 (2009)
14. C. Lin, and M.L. Povilnelli, ”Optical absorption enhancement in silicon nanowire arrays with a large lattice constant for photovoltaic applications,” Optics Express, Vol. 17, NO. 22, 19371-19381 (2009)
15. J.S. Li, H.Y. Yu, S.M. Wong, G. Zhang, X. Sun, G.Q. Lo, and D.L. Kwong, ”Si nanopillar array optimization on Si thin films for solar energy harvesting,” Applied Physics Letters, Vol. 95, 033102(2009)
16. J.S. Li, H.Y. Yu, S.M. Wong, X.C. Li, G. Zhang, G.Q. Lo, and D.L. Kwong, “Design guidelines of periodic Si nanowire arrays for solar cell application,” Applied Physics Letters, Vol. 95, 243113(2009)
17. C. Ji, E.A. Guliants, and W.A. Anderson, ” Silicon nanostructures by metal induced growth (MIG) for solar cell emitters,” the 29th IEEE Photovoltaic Specialists Conference, 1314-1316 (2002)
18. Y.Y. Wu, and P.D. Yang, “Direct observation of vapor-liquid-solid nanowire growth,” Journal of the American Chemical Society, Vol.123, 3165-3166 (2001)
19. Y.Q. Chen, X.F. Cui, K. Zhang, D.Y. Pan, S.Y. Zhang, B. Wang, and J.G. Hou, ”Bulk-quantity synthesis and self-catalytic VLS growth of SnO2 nanowires by lower-temperature evaporation,” Chemical Physics Letters, Vol.369, 16-20 (2003)
20. S.Y. Li, P. Lin, C.Y. Lee, and T.Y. Tseng, “Field emission and photofluorescent characteristics of zinc oxide nanowires synthesized by a metal catalyzed vapor-liquid-solid process,” Journal of Applied Physics, Vol. 95, 3711-3716 (2004)
21. X. Zhang, K. Lew, P. Nimmatoori, J.M. Redwing, and E.C. Dickey, ”Diameter-dependent composition of vapor-liquid-solid grown Si1-xGex nanowires,” Nano Letters, Vol. 7, 3241-3245 (2007)
22. V. Gottschalch, G. Wagner, J. Bauer, H. Paetzelt, and M. Shirnow, ”VLS growth of GaN nanowires on various substrates,” Journal of Crystal Growth, Vol. 310, 5123-5128 (2008)
23. O. Gunawan, and S. Guha, ”Characteristics of vapor-liquid-solid grown silicon nanowire solar cells,” Solar Energy Materials and Solar Cells, Vol.93, 1388-1393 (2009)
24. B.Z. Tain, X.L. Zheng, T.J. Kempa, Y. Fang, N.F. Yu, G.H. Yu, J.L. Huang, and C.M. Lieber, “Coaxial silicon nanowires as solar cells and nanoelectronic power sources,” Nature, Vol.449, 885-889 (2007)
25. L. Tsakalakos, J. Balch, J. Fronheiser, B.A. Korevaar, O. Sulima, and J.Rand, “Silicon nanowire solar cells,” Applied Physics Letters, Vol. 91, 233117 (2007)
26. J.A. Czaban, D.A. Thompson, and R.R. LaPierre, “GaAs core-shell nanowires for photovoltaic applications,” Nano Letters, Vol.9, 148-154 (2009)
27. Z.Y. Fan, H. Razavi, J.W. Do, A. Moriwaki, O. Ergen, Y.L. Chueh, P.W. Leu, J.C. Ho, T. Takahashi, L.A. Reichertz, S. Neale, K. Yu, M. Wu, J.W. Ager, and A. Javey, “Three-dimensional nanopillar-array photovoltaics on low-cost and flexible substrates,” Nature Materials, Vol.8, 648-653 (2009)
28. E.C. Garnett, and P.D. Yang, “Silicon nanowire radial p-n junction solar cells,” Jornal of American Chemical Society, Vol.130, 9224-9225 (2008)
29. J. Zhu, Z.F. Yu, G.F. Burkhard, C.M. Hsu, S.T. Connor, Y.Q. Xu, Q. Wang, M. McGehee, S.H. Fan, and Y. Cui, “Optical absorption enhancement in amorphous silicon nanowire and nanocone arrays,” Nano Letters, Vol.9, 279-282 (2008)
30. E. Garnett, and P.D. Yang, “Light trapping in silicon nanowire solar cells,” Nano Letters, Vol.10, 1082-1087 (2010)
31. A. Birner, R.B. Wehrspohn, U.M. Gösele, and K. Busch, “Silicon-Based Photonic Crystals,” Advanced Materials, Vol.13, No.6, 377-388 (2001)
32. S. Richter, R. Hillebrand, C. Jamois, M. Zacharias, U. Gösele, S.L. Schweizer, and R.B. Wehrspohn, “Periodically arranged point defects in two-dimensional photonic crystals,” Physical Review B, Vol.70, 193302 (2004)
33. F. Marty, L. Rousseau, B. Saadany, B. Mercier, O. Français, Y. Mita, and T. Bourouina, “Advanced etching of silicon based on deep reactive ion etching for silicon high aspect ratio microstructures and three-dimensional micro- and nanostructures,” Microelectronics Journal, Vol.36, 673-677 (2005)
34. S. Koynov, M.S. Brandt, and M. Stutzmann, “Black nonreflecting silicon surfaces for solar cells,” Applied Physics Letters, Vol.88, 203107 (2006)
35. M.H. Klühr, A. Sauermann, C.A. Elsner, K.H. Thein, and S.K. Dertinger, “Partially Oxidized Macroporous Silicon: A Three-Dimensional Photonic Matrix for Microarray Applications,” Advanced Materials, Vol.18, 3135-3139 (2006)
36. R.B. Wehrspohn, S.L. Schweizer, and V. Sandoghdar, “Linear and non-linear optical experiments based on macroporous silicon photonic crystals,” Physica Status Solidi A, Vol.204, 3708-3726 (2007)
37. M.J. Huang, C.R. Yang, Y.C. Chiou, and R.T. Lee, ”Fabrication of nanoporous antireflection surfaces on silicon,” Solar Energy Materials and Solar Cells, Vol.92, 1352-1357 (2008)
38. F. Wang, H.Y. Yu, J.S. Li, X.W. Sun, X. Wang, and H.Y. Zheng, “Optical absorption enhancement in nanopore textured-silicon thim film for photovoltaic application,” Optics Letters, Vol.35, No.1, 40-42 (2010)
39. S.E. Han, and G. Chen, ”Optical absorption enhancement in silicon nanohole arrays for solar photovoltaics,” Nano Letters, Vol. 10 , 1012-1015 (2010)
40. S.B. Mallick, M. Agrawal, and P. Peumans, “Optimal light trapping in ultra-thin photonic crystal crystalline silicon solar cells,” Optics Express, Vol. 18, No. 6, 5691-5706 (2010)
41. M.A. Green, “Third Generation Photovoltaics: Advanced Solar Energy Conversion,” Springer-Verlag, Berlin (2003)
42. Z.Y. Fan, D.J. Ruebusch, A.A. Rathore, R. Kapadia, O. Ergen, P. W. Leu, and A. Javey, “Challenges and prospects of nanopillar-based solar cells,” Nano Research, Vol.2, No.11,829-843 (2009)
43. M.A. Green, K. Emery, Y. Hisikawa, and W. Warta, “Solar Cell Efficiency Tables (Version 35),” Progress in Photovoltaics: Research and Applications. Vol. 18, 144-150 (2010)
44. ASTM, “Reference Solar Spectral Irradiance: Air Mass 1.5 Spectra,” http://rredc.nrel.gov/solar/spectra/am1.5/
45. D.F. Edwards, ”Silicon (Si),” in Handbook of optical constants of solids, E.D. Palik, ed. (Academic, Orlando, FL, 1985)
46. W. Shockley, and H.J. Queisser, “Detailed balance limit of efficiency of p-n junction solar cells,” Journal of Applied Physics, Vol.32, 510-519 (1961)
47. J. Jin, “The finite element method in electromagnetics,” 2nd ed., John Wiley & Sons, Inc., New York (2002)
48. J.P. Berenger, ”A perfectly matched layer for the absorption of electromagnetic waves,” Journal of Computational Physics, Vol.114, No.2, 185-200 (1994)
49. Z.S. Sacks, D.M. Kingsland, R. Lee, and J.F. Lee, “A perfectly matched anisotropic absorber for use as an absorbing boundary condition,” IEEE Transactions on Antennas and Propagation, Vol. AP-43, 1460-1463 (1995)
50. J.M. Lin and W.C. Chew, ”Combining PML and ABC for finite element analysis of scattering problems,” Microwave and Optical Technology Letters, Vol.12, 192-197 (1996)
51. J.P. Berenger, “Three-dimensional perfectly matched layer for the absorption of electromagnetic waves,” Journal of Computational Physics, Vol.127, NO.2, 363-379 (1996)
52. S.G. Tikhodeev, A.L. Yablonskii, E.A. Muljarov, N.A. Gippius, and T. Ishihara, “Quasiguided modes and optical properties of photonic crystal slabs,” Physical Review B, Vol.66, 045102 (2002)
53. E. Yablonovitch, “Statistical Ray Optics,” Journal of the Optical Socienty of America, Vol.72, 899-907 (1982)
54. E. Yablonovitch, and G.D. Cody, “Intensity enhancement in textured optical sheets for solar cells,” IEEE Transactions on Electron Devices, Vol.29, 300-305 (1982)
55. J. Gee, “Optically enhanced absorption in thin silicon layers using photonic crystals,” in Twenty-Ninth IEEE Photovoltaic Specialists Conference, 150-153 (2002)
56. H.R. Philipp, “Silicon Nitride (Si3N4),” in Handbook of optical constants of solids, E.D. Palik, ed. (Academic, Orlando, FL, 1985)
57. D.W. Lynch and W.R. Hunter, “Silver (Ag),” in Handbook of optical constants of solids, E.D. Palik, ed. (Academic, Orlando, FL, 1985)
58. H.W. Deckman, C.B. Roxlo,and E. Yablonovitch, “Maximum statistical increase of optical absorption in textured semiconductor films,” Optics Letters, Vol.8, No.9, 491-493 (1983)