Nanophotonic light trapping in 3-dimensional thin-film silicon architectures

Daniel Lockau; Tobias Sontheimer; Christiane Becker; Eveline Rudigier-Voigt; Frank Schmidt; Bernd Rech

doi:10.1364/OE.21.000A42

Nanophotonic light trapping in 3-dimensional thin-film silicon architectures

Daniel Lockau, Tobias Sontheimer, Christiane Becker, Eveline Rudigier-Voigt, Frank Schmidt, and Bernd Rech

Optics Express
Vol. 21,
Issue S1,
pp. A42-A52
(2013)
•https://doi.org/10.1364/OE.21.000A42

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Daniel Lockau, Tobias Sontheimer, Christiane Becker, Eveline Rudigier-Voigt, Frank Schmidt, and Bernd Rech, "Nanophotonic light trapping in 3-dimensional thin-film silicon architectures," Opt. Express 21, A42-A52 (2013)

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Related Topics
Table of Contents Category
- Photovoltaics
Optics & Photonics Topics
?

The topics in this list come from the OSA Optics and Photonics Topics applied to this article.
Previously assigned OCIS codes
- Solar energy (350.6050)
- Nanophotonics and photonic crystals (350.4238)
- Thin film devices and applications (310.6845)

About this Article
History
- Original Manuscript: August 31, 2012
- Manuscript Accepted: October 9, 2012
- Published: November 26, 2012

Accessible

Open Access

Abstract

Emerging low cost and large area periodic texturing methods promote the fabrication of complex absorber structures for thin film silicon solar cells. We present a comprehensive numerical analysis of a 2μm square periodic polycrystalline silicon absorber architecture designed in our laboratories. Simulations are performed on the basis of a precise finite element reconstruction of the experimentally realized silicon structure. In contrast to many other publications, superstrate light trapping effects are included in our model. Excellent agreement to measured absorptance spectra is obtained. For the inclusion of the absorber into a standard single junction cell layout, we show that light trapping close to the Yablonovitch limit can be realized, but is usually strongly damped by parasitic absorption.

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References

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Year
|
Author
|
Publication

O. Kluth, C. Zahren, H. Stiebig, B. Rech, and H. Schade, “Surface morphologies of rough transparent conductive oxide films applied in silicon thin-film solar cells,” in “Proceedings of the 19th EU PVSEC,” 1587–1590 (2004).
V. T. Daudrix, J. Guillet, F. Freitas, A. Shah, C. Ballif, P. Winkler, M. Ferreloc, S. Benagli, X. Niquille, D. Fischer, and R. Morf, “Characterisation of rough reflecting substrates incorporated into thin-film silicon solar cells,” Prog. Photovoltaics 14, 485–498 (2006).
[Crossref]
M. Python, E. Vallat-Sauvain, J. Bailat, D. Domin, L. Fesquet, A. Shah, and C. Ballif, “Relation between substrate surface morphology and microcrystalline silicon solar cell performance,” J. Non-Cryst. Solids 354, 2258–2262 (2008).
[Crossref]
Z. Yu, A. Raman, and S. Fan, “Fundamental limit of light trapping in grating structures,” Opt. Express 18, A366–A380 (2010).
[Crossref] [PubMed]
Z. Yu and S. Fan, “Angular constraint on light-trapping absorption enhancement in solar cells,” Appl. Phys. Lett. 98, 011106 (2011).
[Crossref]
E. Yablonovitch, “Statistical ray optics,” J. Opt. Soc. Am. 72, 899–907 (1982).
[Crossref]
M. Agrawal and P. Peumans, “The physical limits of light trapping in thin-films and photonic structures that operate at the limit,” in “Proceedings of the 34th IEEE Photovoltaic Specialists Conference 2009” (IEEE, 2009), 002204–002207.
[Crossref]
X. Sheng, S. Johnson, J. Michel, and L. Kimerling, “Optimization-based design of surface textures for thin-film si solar cells,” Opt. Express 19, A841–A850 (2011).
[Crossref] [PubMed]
J. Zhu, Z. Yu, S. Fan, and Y. Cui, “Nanostructured photon management for high performance solar cells,” Mater. Sci. Eng. R 70, 330–340 (2010).
[Crossref]
C. Battaglia, C.-M. Hsu, K. Söderstöm, J. Escarré, F.-J. Haug, M. Charrière, M. Boccard, M. Despeisse, D. T. L. Alexander, M. Cantoni, Y. Cui, and C. Ballif, “Light trapping in solar cells: Can periodic beat random?” ACS Nano 6, 2790–2797 (2012).
[Crossref] [PubMed]
U. Paetzold, E. Moulin, D. Michaelis, W. Bottler, C. Wachter, V. Hagemann, M. Meier, R. Carius, and U. Rau, “Plasmonic reflection grating back contacts for microcrystalline silicon solar cells,” Appl. Phys. Lett. 99, 181105–181105 (2011).
[Crossref]
T. Sontheimer, C. Becker, U. Bloeck, S. Gall, and B. Rech, “Crystallization kinetics in electron-beam evaporated amorphous silicon on ZnO:Al-coated glass for thin film solar cells,” Appl. Phys. Lett. 95, 101902–101902 (2009).
[Crossref]
T. Sontheimer, E. Rudigier-Voigt, M. Bockmeyer, C. Klimm, P. Schubert-Bischoff, C. Becker, and B. Rech, “Large-area fabrication of equidistant free-standing Si crystals on nanoimprinted glass,” Phys. Status Solidi (RRL) 5, 376–378 (2011).
[Crossref]
T. Sontheimer, E. Rudigier-Voigt, M. Bockmeyer, D. Lockau, C. Klimm, C. Becker, and B. Rech, “Light harvesting architectures for electron beam evaporated solid phase crystallized si thin film solar cells: Statistical and periodic approaches,” J. Non-Cryst. Solids 358, 2303–2307 (2012).
[Crossref]
S. Burger, L. Zschiedrich, J. Pomplun, and F. Schmidt, “JCMsuite: An adaptive FEM solver for precise simulations in nano-optics,” in “Proceedings of Integrated Photonics and Nanophotonics Research and Applications” (OSA, 2008), ITuE4.
E. Palik and G. Ghosh, Handbook of Optical Constants of Solids (Academic Press, 1998).
F. Ruske, M. Roczen, K. Lee, M. Wimmer, S. Gall, J. Hüpkes, D. Hrunski, and B. Rech, “Improved electrical transport in Al-doped zinc oxide by thermal treatment,” J. Appl. Phys. 107, 013708 (2010).
[Crossref]
F. Haug, T. Soderstrom, O. Cubero, V. Terrazzoni-Daudrix, and C. Ballif, “Plasmonic absorption in textured silver back reflectors of thin film solar cells,” J. Appl. Phys. 104, 064509 (2008).
[Crossref]
C. Haase and H. Stiebig, “Thin-film silicon solar cells with efficient periodic light trapping texture,” Appl. Phys. Lett. 91, 061116 (2007).
[Crossref]
E. Moulin, U. Paetzold, J. Kirchhoff, A. Bauer, and R. Carius, “Study of detached back reflector designs for thin-film silicon solar cells,” Phys. Status Solidi (RRL) 6, 65–67 (2012).
[Crossref]
C. Becker, D. Lockau, T. Sontheimer, P. Schubert-Bischoff, E. Rudigier-Voigt, M. Bockmeyer, F. Schmidt, and B. Rech, “Large-area 2D periodic crystalline silicon nanodome arrays on nanoimprinted glass exhibiting photonic band structure effects,” Nanotechnology 23, 135302 (2012).
[Crossref] [PubMed]
M. Berginski, B. Rech, J. Hüpkes, H. Stiebig, and M. Wuttig, “Design of ZnO:Al films with optimized surface texture for silicon thin-film solar cells,” in Proc. SPIE 6197, 61970Y (2006).
[Crossref]
A. Čampa, J. Krč, and Marco Topič, “Analysis and optimisation of microcrystalline silicon solar cells with periodic sinusoidal textured interfaces by two-dimensional optical simulations,” J. Appl. Phys. 105, 083107 (2009).
[Crossref]
O. Isabella, S. Solntsev, D. Caratelli, and M. Zeman, “3-D optical modeling of thin-film silicon solar cells on diffraction gratings,” Prog. Photovolt.: Res. Appl., DOI: (2012).
[Crossref]
M. Berginski, J. Hüpkes, A. Gordijn, W. Reetz, T. Watjen, B. Rech, and M. Wuttig, “Experimental studies and limitations of the light trapping and optical losses in microcrystalline silicon solar cells,” Sol. Energy Mater. Sol. Cells 92, 1037–1042 (2008).
[Crossref]

2012 (4)

C. Battaglia, C.-M. Hsu, K. Söderstöm, J. Escarré, F.-J. Haug, M. Charrière, M. Boccard, M. Despeisse, D. T. L. Alexander, M. Cantoni, Y. Cui, and C. Ballif, “Light trapping in solar cells: Can periodic beat random?” ACS Nano 6, 2790–2797 (2012).
[Crossref] [PubMed]

T. Sontheimer, E. Rudigier-Voigt, M. Bockmeyer, D. Lockau, C. Klimm, C. Becker, and B. Rech, “Light harvesting architectures for electron beam evaporated solid phase crystallized si thin film solar cells: Statistical and periodic approaches,” J. Non-Cryst. Solids 358, 2303–2307 (2012).
[Crossref]

E. Moulin, U. Paetzold, J. Kirchhoff, A. Bauer, and R. Carius, “Study of detached back reflector designs for thin-film silicon solar cells,” Phys. Status Solidi (RRL) 6, 65–67 (2012).
[Crossref]

C. Becker, D. Lockau, T. Sontheimer, P. Schubert-Bischoff, E. Rudigier-Voigt, M. Bockmeyer, F. Schmidt, and B. Rech, “Large-area 2D periodic crystalline silicon nanodome arrays on nanoimprinted glass exhibiting photonic band structure effects,” Nanotechnology 23, 135302 (2012).
[Crossref] [PubMed]

2011 (4)

T. Sontheimer, E. Rudigier-Voigt, M. Bockmeyer, C. Klimm, P. Schubert-Bischoff, C. Becker, and B. Rech, “Large-area fabrication of equidistant free-standing Si crystals on nanoimprinted glass,” Phys. Status Solidi (RRL) 5, 376–378 (2011).
[Crossref]

U. Paetzold, E. Moulin, D. Michaelis, W. Bottler, C. Wachter, V. Hagemann, M. Meier, R. Carius, and U. Rau, “Plasmonic reflection grating back contacts for microcrystalline silicon solar cells,” Appl. Phys. Lett. 99, 181105–181105 (2011).
[Crossref]

X. Sheng, S. Johnson, J. Michel, and L. Kimerling, “Optimization-based design of surface textures for thin-film si solar cells,” Opt. Express 19, A841–A850 (2011).
[Crossref] [PubMed]

Z. Yu and S. Fan, “Angular constraint on light-trapping absorption enhancement in solar cells,” Appl. Phys. Lett. 98, 011106 (2011).
[Crossref]

2010 (3)

J. Zhu, Z. Yu, S. Fan, and Y. Cui, “Nanostructured photon management for high performance solar cells,” Mater. Sci. Eng. R 70, 330–340 (2010).
[Crossref]

Z. Yu, A. Raman, and S. Fan, “Fundamental limit of light trapping in grating structures,” Opt. Express 18, A366–A380 (2010).
[Crossref] [PubMed]

F. Ruske, M. Roczen, K. Lee, M. Wimmer, S. Gall, J. Hüpkes, D. Hrunski, and B. Rech, “Improved electrical transport in Al-doped zinc oxide by thermal treatment,” J. Appl. Phys. 107, 013708 (2010).
[Crossref]

2009 (2)

T. Sontheimer, C. Becker, U. Bloeck, S. Gall, and B. Rech, “Crystallization kinetics in electron-beam evaporated amorphous silicon on ZnO:Al-coated glass for thin film solar cells,” Appl. Phys. Lett. 95, 101902–101902 (2009).
[Crossref]

A. Čampa, J. Krč, and Marco Topič, “Analysis and optimisation of microcrystalline silicon solar cells with periodic sinusoidal textured interfaces by two-dimensional optical simulations,” J. Appl. Phys. 105, 083107 (2009).
[Crossref]

2008 (3)

M. Berginski, J. Hüpkes, A. Gordijn, W. Reetz, T. Watjen, B. Rech, and M. Wuttig, “Experimental studies and limitations of the light trapping and optical losses in microcrystalline silicon solar cells,” Sol. Energy Mater. Sol. Cells 92, 1037–1042 (2008).
[Crossref]

M. Python, E. Vallat-Sauvain, J. Bailat, D. Domin, L. Fesquet, A. Shah, and C. Ballif, “Relation between substrate surface morphology and microcrystalline silicon solar cell performance,” J. Non-Cryst. Solids 354, 2258–2262 (2008).
[Crossref]

F. Haug, T. Soderstrom, O. Cubero, V. Terrazzoni-Daudrix, and C. Ballif, “Plasmonic absorption in textured silver back reflectors of thin film solar cells,” J. Appl. Phys. 104, 064509 (2008).
[Crossref]

2007 (1)

C. Haase and H. Stiebig, “Thin-film silicon solar cells with efficient periodic light trapping texture,” Appl. Phys. Lett. 91, 061116 (2007).
[Crossref]

2006 (2)

M. Berginski, B. Rech, J. Hüpkes, H. Stiebig, and M. Wuttig, “Design of ZnO:Al films with optimized surface texture for silicon thin-film solar cells,” in Proc. SPIE 6197, 61970Y (2006).
[Crossref]

V. T. Daudrix, J. Guillet, F. Freitas, A. Shah, C. Ballif, P. Winkler, M. Ferreloc, S. Benagli, X. Niquille, D. Fischer, and R. Morf, “Characterisation of rough reflecting substrates incorporated into thin-film silicon solar cells,” Prog. Photovoltaics 14, 485–498 (2006).
[Crossref]

1982 (1)

E. Yablonovitch, “Statistical ray optics,” J. Opt. Soc. Am. 72, 899–907 (1982).
[Crossref]

Agrawal, M.

M. Agrawal and P. Peumans, “The physical limits of light trapping in thin-films and photonic structures that operate at the limit,” in “Proceedings of the 34th IEEE Photovoltaic Specialists Conference 2009” (IEEE, 2009), 002204–002207.
[Crossref]

Alexander, D. T. L.

Bailat, J.

Ballif, C.

Battaglia, C.

Bauer, A.

Becker, C.

Benagli, S.

Berginski, M.

Bloeck, U.

Boccard, M.

Bockmeyer, M.

Bottler, W.

Burger, S.

S. Burger, L. Zschiedrich, J. Pomplun, and F. Schmidt, “JCMsuite: An adaptive FEM solver for precise simulations in nano-optics,” in “Proceedings of Integrated Photonics and Nanophotonics Research and Applications” (OSA, 2008), ITuE4.

Campa, A.

Cantoni, M.

Caratelli, D.

O. Isabella, S. Solntsev, D. Caratelli, and M. Zeman, “3-D optical modeling of thin-film silicon solar cells on diffraction gratings,” Prog. Photovolt.: Res. Appl., DOI: (2012).
[Crossref]

Carius, R.

Charrière, M.

Cubero, O.

Cui, Y.

J. Zhu, Z. Yu, S. Fan, and Y. Cui, “Nanostructured photon management for high performance solar cells,” Mater. Sci. Eng. R 70, 330–340 (2010).
[Crossref]

Daudrix, V. T.

Despeisse, M.

Domin, D.

Escarré, J.

Fan, S.

Z. Yu and S. Fan, “Angular constraint on light-trapping absorption enhancement in solar cells,” Appl. Phys. Lett. 98, 011106 (2011).
[Crossref]

Z. Yu, A. Raman, and S. Fan, “Fundamental limit of light trapping in grating structures,” Opt. Express 18, A366–A380 (2010).
[Crossref] [PubMed]

J. Zhu, Z. Yu, S. Fan, and Y. Cui, “Nanostructured photon management for high performance solar cells,” Mater. Sci. Eng. R 70, 330–340 (2010).
[Crossref]

Ferreloc, M.

Fesquet, L.

Fischer, D.

Freitas, F.

Gall, S.

Ghosh, G.

E. Palik and G. Ghosh, Handbook of Optical Constants of Solids (Academic Press, 1998).

Gordijn, A.

Guillet, J.

Haase, C.

C. Haase and H. Stiebig, “Thin-film silicon solar cells with efficient periodic light trapping texture,” Appl. Phys. Lett. 91, 061116 (2007).
[Crossref]

Hagemann, V.

Haug, F.

Haug, F.-J.

Hrunski, D.

Hsu, C.-M.

Hüpkes, J.

Isabella, O.

O. Isabella, S. Solntsev, D. Caratelli, and M. Zeman, “3-D optical modeling of thin-film silicon solar cells on diffraction gratings,” Prog. Photovolt.: Res. Appl., DOI: (2012).
[Crossref]

Johnson, S.

X. Sheng, S. Johnson, J. Michel, and L. Kimerling, “Optimization-based design of surface textures for thin-film si solar cells,” Opt. Express 19, A841–A850 (2011).
[Crossref] [PubMed]

Kimerling, L.

X. Sheng, S. Johnson, J. Michel, and L. Kimerling, “Optimization-based design of surface textures for thin-film si solar cells,” Opt. Express 19, A841–A850 (2011).
[Crossref] [PubMed]

Kirchhoff, J.

Klimm, C.

Kluth, O.

O. Kluth, C. Zahren, H. Stiebig, B. Rech, and H. Schade, “Surface morphologies of rough transparent conductive oxide films applied in silicon thin-film solar cells,” in “Proceedings of the 19th EU PVSEC,” 1587–1590 (2004).

Krc, J.

Lee, K.

Lockau, D.

Meier, M.

Michaelis, D.

Michel, J.

X. Sheng, S. Johnson, J. Michel, and L. Kimerling, “Optimization-based design of surface textures for thin-film si solar cells,” Opt. Express 19, A841–A850 (2011).
[Crossref] [PubMed]

Morf, R.

Moulin, E.

Niquille, X.

Paetzold, U.

Palik, E.

E. Palik and G. Ghosh, Handbook of Optical Constants of Solids (Academic Press, 1998).

Peumans, P.

Pomplun, J.

Python, M.

Raman, A.

Z. Yu, A. Raman, and S. Fan, “Fundamental limit of light trapping in grating structures,” Opt. Express 18, A366–A380 (2010).
[Crossref] [PubMed]

Rau, U.

Rech, B.

Reetz, W.

Roczen, M.

Rudigier-Voigt, E.

Ruske, F.

Schade, H.

Schmidt, F.

Schubert-Bischoff, P.

Shah, A.

Sheng, X.

X. Sheng, S. Johnson, J. Michel, and L. Kimerling, “Optimization-based design of surface textures for thin-film si solar cells,” Opt. Express 19, A841–A850 (2011).
[Crossref] [PubMed]

Söderstöm, K.

Soderstrom, T.

Solntsev, S.

O. Isabella, S. Solntsev, D. Caratelli, and M. Zeman, “3-D optical modeling of thin-film silicon solar cells on diffraction gratings,” Prog. Photovolt.: Res. Appl., DOI: (2012).
[Crossref]

Sontheimer, T.

Stiebig, H.

C. Haase and H. Stiebig, “Thin-film silicon solar cells with efficient periodic light trapping texture,” Appl. Phys. Lett. 91, 061116 (2007).
[Crossref]

Terrazzoni-Daudrix, V.

Topic, Marco

Vallat-Sauvain, E.

Wachter, C.

Watjen, T.

Wimmer, M.

Winkler, P.

Wuttig, M.

Yablonovitch, E.

E. Yablonovitch, “Statistical ray optics,” J. Opt. Soc. Am. 72, 899–907 (1982).
[Crossref]

Yu, Z.

Z. Yu and S. Fan, “Angular constraint on light-trapping absorption enhancement in solar cells,” Appl. Phys. Lett. 98, 011106 (2011).
[Crossref]

Z. Yu, A. Raman, and S. Fan, “Fundamental limit of light trapping in grating structures,” Opt. Express 18, A366–A380 (2010).
[Crossref] [PubMed]

J. Zhu, Z. Yu, S. Fan, and Y. Cui, “Nanostructured photon management for high performance solar cells,” Mater. Sci. Eng. R 70, 330–340 (2010).
[Crossref]

Zahren, C.

Zeman, M.

O. Isabella, S. Solntsev, D. Caratelli, and M. Zeman, “3-D optical modeling of thin-film silicon solar cells on diffraction gratings,” Prog. Photovolt.: Res. Appl., DOI: (2012).
[Crossref]

Zhu, J.

J. Zhu, Z. Yu, S. Fan, and Y. Cui, “Nanostructured photon management for high performance solar cells,” Mater. Sci. Eng. R 70, 330–340 (2010).
[Crossref]

Zschiedrich, L.

ACS Nano (1)

Appl. Phys. Lett. (4)

Z. Yu and S. Fan, “Angular constraint on light-trapping absorption enhancement in solar cells,” Appl. Phys. Lett. 98, 011106 (2011).
[Crossref]

C. Haase and H. Stiebig, “Thin-film silicon solar cells with efficient periodic light trapping texture,” Appl. Phys. Lett. 91, 061116 (2007).
[Crossref]

J. Appl. Phys. (3)

J. Non-Cryst. Solids (2)

J. Opt. Soc. Am. (1)

E. Yablonovitch, “Statistical ray optics,” J. Opt. Soc. Am. 72, 899–907 (1982).
[Crossref]

Mater. Sci. Eng. R (1)

J. Zhu, Z. Yu, S. Fan, and Y. Cui, “Nanostructured photon management for high performance solar cells,” Mater. Sci. Eng. R 70, 330–340 (2010).
[Crossref]

Nanotechnology (1)

Opt. Express (2)

X. Sheng, S. Johnson, J. Michel, and L. Kimerling, “Optimization-based design of surface textures for thin-film si solar cells,” Opt. Express 19, A841–A850 (2011).
[Crossref] [PubMed]

Z. Yu, A. Raman, and S. Fan, “Fundamental limit of light trapping in grating structures,” Opt. Express 18, A366–A380 (2010).
[Crossref] [PubMed]

Phys. Status Solidi (RRL) (2)

Proc. SPIE (1)

Prog. Photovoltaics (1)

Sol. Energy Mater. Sol. Cells (1)

Other (5)

O. Isabella, S. Solntsev, D. Caratelli, and M. Zeman, “3-D optical modeling of thin-film silicon solar cells on diffraction gratings,” Prog. Photovolt.: Res. Appl., DOI: (2012).
[Crossref]

E. Palik and G. Ghosh, Handbook of Optical Constants of Solids (Academic Press, 1998).

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Fig. 1

(a) SEM image of the 2.4μm thick silicon layer after e-beam evaporation on a periodic substrate (large). The inset depicts a similar sample after the etching of amorphous regions. (b) Cross-sectional SEM images of the silicon layer before and after the etching process. Cone opening angle: θ ≈ 20°. Distance between the inner and outer groove surfaces: d ≈ 0.34μm. (c) Cross-section and perspective view of the computational model of the unit cell. Letters “a” and “c” denote amorphous and crystalline regions of the unetched absorber, “s” marks the textured solgel substrate and “e” an extruded intermediate layer. (d) Real part of the refractive index and absorption coefficients of silicon, ZnO:Al and ZrO₂. ZrO₂is assumed to be non-absorptive. (e) Diagram of the simulated solar cell, which is illuminated through its deposition substrate.

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Fig. 2

Comparison of experimental absorptance (red full line without markers) and simulated absorptance, including the approximated superstrate light trapping contribution. The region of highest difference between experiment and simulation is shaded in gray and related to defect absorption. The superstrate light trapping contribution is included for additional reference.

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Fig. 3

Transmittance through the glass superstrate and a textured ZnO:Al layer into a silicon half space. The 2μm periodic solgel texture shown in Fig. 1(c) was applied to the interface, with a vertically extruded 300 nm thick ZnO:Al layer. Box plots depict mean (crosses), median, first / third quartile and whiskers show extreme values. Left subplot: complete scaling of the geometry, including TCO layer thickness; the inset depicts the wavelength resolved transmittance at 2μm domain period. Right subplot: height scaling of the 2μm periodic texture at constant TCO layer thickness.

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Fig. 4

(a) Electrical vertical device layout and the simplified optical layout used for simulation. (b) Simulated generation rate in silicon and losses in other absorbing media for a conformal back reflector layout, depicted as configuration “B” in Fig. 5(a). The generation rate and front TCO a well as transmittance losses of the reflector-less, but otherwise identical layout are included as broken red lines. A white line depicts the superstrate light trapping contribution to silicon absorptance. (c) Absorptance difference of the silicon absorptance from (b) to the reflector-less case and the case of a crystalline absorber without etching grooves.

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Fig. 5

(a) Center cross sections of the different reflector designs. (b) Average absorptance of lossy materials for the three layouts shown in (a), in the wavelength region between 600 nm and 1100 nm. Percentage numbers denote silicon absorptance. Slim bars depict symmetrically split low and high wavelength contributions of silicon absorptance. (c) Difference of absorptance proportions between the back reflector layouts “B” and “C” with individually non-absorptive TCO layers to the corresponding reference results in diagram (b).

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Fig. 6

Average light path enhancement factors for wavelengths between 1000 nm and 1100 nm for the reflector designs “B”, “C” and varying domain periods. Simulations of design “B” are with absorbing TCO. Simulations of design “C” are with non-absorbing back TCO and non-absorbing back as well as front TCO.

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Equations (1)

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LPEF (λ) = \frac{- ln (1 - A_{silicon} (λ) / I (λ))}{α_{silicon} (λ) d},