The performances of thin film solar cells are considerably limited by the low light absorption. Plasmonic nanostructures have been introduced in the thin film solar cells as a possible solution around this issue in recent years. Here, we propose a solar cell design, in which an ultrathin Si film covered by a periodic array of Ag strips is placed on a metallic nanograting substrate. The simulation results demonstrate that the designed structure gives rise to 170% light absorption enhancement over the full solar spectrum with respect to the bared Si thin film. The excited multiple resonant modes, including optical waveguide modes within the Si layer, localized surface plasmon resonance (LSPR) of Ag stripes, and surface plasmon polaritons (SPP) arising from the bottom grating, and the coupling effect between LSPR and SPP modes through an optimization of the array periods are considered to contribute to the significant absorption enhancement. This plasmonic solar cell design paves a promising way to increase light absorption for thin film solar cell applications. 1. Introduction The low conversion efficiencies and high production costs have been the major difficulties facing photovoltaic technology. For solar cells based on bulk crystalline silicon, around 40% of a solar cell module’s price comes from the silicon (Si) materials and its processing costs. To reduce the costs, thin film solar cells with an active layer thickness of about 1 to 2？μm are desired. Thin film solar cells with the thickness of material film smaller than the carrier diffusion length can also reduce carrier recombination and improve carrier collection efficiency in bulk recombination-dominated semiconductors. In addition, a significant reduction of the active materials enables some scare semiconductor materials such as Te and In to be used in a large scale. However, the performance of all thin film solar cells is limited by the poor light absorption due to the reduced absorber thickness. For example, the indirect band gap semiconductor Si material has poor absorption to near-band gap light, where the absorption length is larger than 300？μm. Therefore, light trapping schemes are essential for the design of ultrathin solar cells with improved absorption. In the past years, many light trapping techniques have been investigated for solar cell applications. A typical example is the use of micron-size pyramidal surface textures [1]. However, such textures are not suitable for thin film solar cells due to large texturing size with respect to the film thickness. Recently, the concept of
References
[1]
M. A. Green, “Lambertian light trapping in textured solar cells and light-emitting diodes: analytical solutions,” Progress in Photovoltaics, vol. 10, no. 4, pp. 235–241, 2002.
[2]
H. A. Atwater and A. Polman, “Plasmonics for improved photovoltaic devices,” Nature Materials, vol. 9, no. 3, pp. 205–213, 2010.
[3]
K. R. Catchpole and A. Polman, “Plasmonic solar cells,” Optics Express, vol. 16, no. 26, pp. 21793–21800, 2008.
[4]
P. Spinelli, V. Ferry, J. van de Groep et al., “Plasmonic light trapping in thin-film Si solar cells,” Journal of Optics, vol. 14, no. 2, Article ID 024002, 11 pages, 2012.
[5]
D. M. Schaadt, B. Feng, and E. T. Yu, “Enhanced semiconductor optical absorption via surface plasmon excitation in metal nanoparticles,” Applied Physics Letters, vol. 86, no. 6, Article ID 063106, 3 pages, 2005.
[6]
D. Qu, F. Liu, Y. Huang, W. Xie, and Q. Xu, “Mechanism of optical absorption enhancement in thin film organic solar cells with plasmonic metal nanoparticles,” Optics Express, vol. 19, no. 24, pp. 24795–24803, 2011.
[7]
C. H？gglund, M. Z？ch, G. Petersson, and B. Kasemo, “Electromagnetic coupling of light into a silicon solar cell by nanodisk plasmons,” Applied Physics Letters, vol. 92, no. 5, Article ID 053110, 3 pages, 2008.
[8]
S. Pillai, K. R. Catchpole, T. Trupke, and M. A. Green, “Surface plasmon enhanced silicon solar cells,” Journal of Applied Physics, vol. 101, no. 9, Article ID 093105, 8 pages, 2007.
[9]
K. R. Catchpole and A. Polman, “Design principles for particle plasmon enhanced solar cells,” Applied Physics Letters, vol. 93, no. 19, Article ID 191113, 3 pages, 2008.
[10]
R. A. Pala, J. White, E. Barnard, J. Liu, and M. L. Brongersma, “Design of plasmonic thin-film solar cells with broadband absorption enhancements,” Advanced Materials, vol. 21, no. 34, pp. 3504–3509, 2009.
[11]
W. Wang, S. Wu, K. Reinhardt, Y. Lu, and S. Chen, “Broadband light absorption enhancement in thin-film silicon solar cells,” Nano Letters, vol. 10, no. 6, pp. 2012–2018, 2010.
[12]
V. E. Ferry, L. A. Sweatlock, D. Pacifici, and H. A. Atwater, “Plasmonic nanostructure design for efficient light coupling into solar cells,” Nano Letters, vol. 8, no. 12, pp. 4391–4397, 2008.
[13]
R. Biswas and D. Zhou, “Simulation and modelling of photonic and plasmonic crystal back reflectors for efficient light trapping,” Physica Status Solidi A, vol. 207, no. 3, pp. 667–670, 2010.
[14]
R. B. Dunbar, T. Pfadler, and L. Schmidt-Mende, “Highly absorbing solar cells—a survey of plasmonic nanostructures,” Optics Express, vol. 20, no. 2, pp. A177–A189, 2012.
[15]
W. Wang, S. Wu, R. J. Knize, K. Reinhardt, Y. Lu, and S. Chen, “Enhanced photon absorption and carrier generation in nanowire solar cells,” Optics Express, vol. 20, no. 4, pp. 3733–3743, 2012.
[16]
C. Rockstuhl, S. Fahr, and F. Lederer, “Absorption enhancement in solar cells by localized plasmon polaritons,” Journal of Applied Physics, vol. 104, no. 12, Article ID 123102, 7 pages, 2008.
[17]
Y. A. Akimov, W. S. Koh, and K. Ostrikov, “Enhancement of optical absorption in thin-film solar cells through the excitation of higher-order nanoparticle plasmon modes,” Optics Express, vol. 17, no. 12, pp. 10195–10205, 2009.
[18]
H. Shen, P. Bienstman, and B. Maes, “Plasmonic absorption enhancement in organic solar cells with thin active layers,” Journal of Applied Physics, vol. 106, no. 7, Article ID 073109, 5 pages, 2009.
[19]
W. Bai, Q. Gan, G. Song, L. Chen, Z. Kafafi, and F. Bartoli, “Broadband short-range surface plasmon structures for absorption enhancement in organic photovoltaics,” Optics Express, vol. 18, no. 4, pp. A620–A630, 2010.
[20]
E. Battal, T. A. Yogurt, L. E. Aygun, and A. K. Okyay, “Triangular metallic gratings for large absorption enhancement in thin film Si solar cells,” Optics Express, vol. 20, no. 9, pp. 9548–9464, 2009.
[21]
L. J. Guo, “Nanoimprint lithography: methods and material requirements,” Advanced Materials, vol. 19, no. 4, pp. 495–513, 2007.
[22]
J. Y. Chen and K. W. Sun, “Enhancement of the light conversion efficiency of silicon solar cells by using nanoimprint anti-reflection layer,” Solar Energy Materials and Solar Cells, vol. 94, no. 3, pp. 629–633, 2010.
[23]
P. B. Johnson and R. W. Christy, “Optical constants of the noble metals,” Physical Review B, vol. 6, no. 12, pp. 4370–4379, 1972.
[24]
E. D. Palik, Handbook of Optical Constants of Solids, Academic Press, 1985.
[25]
A. W. Snyder and J. D. Love, Optical Waveguide Theory, Springer, 1983.
[26]
V. E. Ferry, J. N. Munday, and H. A. Atwater, “Design considerations for plasmonic photovoltaics,” Advanced Materials, vol. 22, no. 43, pp. 4794–4808, 2010.
[27]
H. Raether, Surface Plasmons on Smooth and Rough Surfaces and on Gratings, Springer, Berlin, Germany, 1988.
[28]
N. Papanikolaou, “Optical properties of metallic nanoparticle arrays on a thin metallic film,” Physical Review B, vol. 75, no. 23, Article ID 235426, 7 pages, 2007.
[29]
J. N. He, G. W. Cai, P. Ding, C. Z. Fan, and E. J. Liang, “Surface plasmons coupling for local field enhancement in nanoring arrays on a metallic film,” Physics Express, vol. 2, no. 10, 2012.
[30]
P. Ding, E. J. Liang, G. W. Cai, W. Q. Hu, C. Z. Fan, and Q. Z. Xue, “Dual-band perfect absorption and field enhancement by interaction between localized and propagating surface plasmons in optical metamaterials,” Journal of Optics, vol. 13, no. 7, Article ID 075005, 7 pages, 2011.
[31]
Y. A. Akimov and W. S. Koh, “Design of plasmonic nanoparticles for efficient subwavelength light trapping in thin-film solar cells,” Plasmonics, vol. 6, no. 1, pp. 155–161, 2011.
