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  • Editor: Christian Seassal
  • Vol. 22, Iss. S3 — May. 5, 2014
  • pp: A992–A1000
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Laterally assembled nanowires for ultrathin broadband solar absorbers

Kyung-Deok Song, Thomas J. Kempa, Hong-Gyu Park, and Sun-Kyung Kim  »View Author Affiliations


Optics Express, Vol. 22, Issue S3, pp. A992-A1000 (2014)
http://dx.doi.org/10.1364/OE.22.00A992


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Abstract

We studied optical resonances in laterally oriented Si nanowire arrays by conducting finite-difference time-domain simulations. Localized Fabry-Perot and whispering-gallery modes are supported within the cross section of each nanowire in the array and result in broadband light absorption. Comparison of a nanowire array with a single nanowire shows that the current density (JSC) is preserved for a range of nanowire morphologies. The JSC of a nanowire array depends on the spacing of its constituent nanowires, which indicates that both diffraction and optical antenna effects contribute to light absorption. Furthermore, a vertically stacked nanowire array exhibits significantly enhanced light absorption because of the emergence of coupled cavity-waveguide modes and the mitigation of a screening effect. With the assumption of unity internal quantum efficiency, the JSC of an 800-nm-thick cross-stacked nanowire array is 14.0 mA/cm2, which yields a ~60% enhancement compared with an equivalent bulk film absorber. These numerical results underpin a rational design strategy for ultrathin solar absorbers based on assembled nanowire cavities.

© 2014 Optical Society of America

1. Introduction

Nanowires (NWs) are well-suited for a variety of optoelectronic applications [1

1. X. Duan, Y. Huang, R. Agarwal, and C. M. Lieber, “Single-nanowire electrically driven lasers,” Nature 421(6920), 241–245 (2003). [CrossRef] [PubMed]

13

13. P. Krogstrup, H. I. Jørgensen, M. Heiss, O. Demichel, J. V. Holm, M. Aagesen, J. Nygard, and A. Fontcuberta i Morral, “Single-nanowire solar cells beyond the Shockley–Queisser limit,” Nat. Photonics 7(4), 306–310 (2013). [CrossRef]

] in part because their morphology [8

8. S.-K. Kim, R. W. Day, J. F. Cahoon, T. J. Kempa, K.-D. Song, H.-G. Park, and C. M. Lieber, “Tuning Light Absorption in Core/Shell Silicon Nanowire Photovoltaic Devices through Morphological Design,” Nano Lett. 12(9), 4971–4976 (2012). [CrossRef] [PubMed]

,14

14. B. Cho, J. Bareno, Y. L. Foo, S. Hong, T. Spila, I. Petrov, and J. E. Greene, “Phosphorus Incorporation during Si(001): P Gas-source Molecular Beam Epitaxy: Effects on Growth Kinetics and Surface Morphology,” J. Appl. Phys. 103(12), 123530 (2008). [CrossRef]

,15

15. M. C. Plante and R. R. Lapierre, “Control of GaAs nanowire morphology and crystal structure,” Nanotechnology 19(49), 495603 (2008). [CrossRef] [PubMed]

] and composition [16

16. T. Kuykendall, P. Ulrich, S. Aloni, and P. Yang, “Complete composition tunability of InGaN Nanowires using a combinatorial approach,” Nat. Mater. 6(12), 951–956 (2007). [CrossRef] [PubMed]

18

18. M. M. Adachi, M. P. Anantram, and K. S. Karim, “Optical Properties of Crystalline-Amorphous Core-Shell Silicon Nanowires,” Nano Lett. 10(10), 4093–4098 (2010). [CrossRef] [PubMed]

] can be finely tuned during synthesis rather than post hoc as in top-down fabrication. In addition, NWs can have diameters less than the wavelength of light, allowing for large scattering to physical cross section [19

19. G. Brönstrup, N. Jahr, C. Leiterer, A. Csáki, W. Fritzsche, and S. Christiansen, “Optical Properties of Individual Silicon Nanowires for Photonic Devices,” ACS Nano 4(12), 7113–7122 (2010). [CrossRef] [PubMed]

,20

20. G. Brönstrup, C. Leiterer, N. Jahr, C. Gutsche, A. Lysov, I. Regolin, W. Prost, F. J. Tegude, W. Fritzsche, and S. Christiansen, “A Precise Optical Determination of Nanoscale Diameters of Semiconductor Nanowires,” Nanotechnology 22(38), 385201 (2011). [CrossRef] [PubMed]

] and localized optical resonances [7

7. T. J. Kempa, J. F. Cahoon, S.-K. Kim, R. W. Day, D. C. Bell, H.-G. Park, and C. M. Lieber, “Coaxial Multishell Nanowires with High-Quality Electronic Interfaces and Tunable Optical Cavities for Ultrathin Photovoltaics,” Proc. Natl. Acad. Sci. U.S.A. 109(5), 1407–1412 (2012). [CrossRef] [PubMed]

,8

8. S.-K. Kim, R. W. Day, J. F. Cahoon, T. J. Kempa, K.-D. Song, H.-G. Park, and C. M. Lieber, “Tuning Light Absorption in Core/Shell Silicon Nanowire Photovoltaic Devices through Morphological Design,” Nano Lett. 12(9), 4971–4976 (2012). [CrossRef] [PubMed]

]. These properties of NWs have been utilized to demonstrate low-threshold lasers [21

21. F. Qian, Y. Li, S. Gradecak, H.-G. Park, Y. Dong, Y. Ding, Z. L. Wang, and C. M. Lieber, “Multi-Quantum-Well Nanowire Heterostructures for Wavelength-Controlled Lasers,” Nat. Mater. 7(9), 701–706 (2008). [CrossRef] [PubMed]

,22

22. R. F. Oulton, V. J. Sorger, T. Zentgraf, R.-M. Ma, C. Gladden, L. Dai, G. Bartal, and X. Zhang, “Plasmon Lasers at Deep Subwavelength Scale,” Nature 461(7264), 629–632 (2009). [CrossRef] [PubMed]

], low-loss waveguides [23

23. M. Khorasaninejad and S. S. Saini, “Silicon nanowire optical waveguide (SNOW),” Opt. Express 18(22), 23442–23457 (2010). [CrossRef] [PubMed]

], and high-efficiency light-emitting diodes [24

24. F. Qian, S. Gradecak, Y. Li, C. Y. Wen, and C. M. Lieber, “Core/Multishell Nanowire Heterostructures as Multicolor, High-Efficiency Light-Emitting Diodes,” Nano Lett. 5(11), 2287–2291 (2005). [CrossRef] [PubMed]

]. Recently, laterally [4

4. P. Fan, K. C. Y. Huang, L. Cao, and M. L. Brongersma, “Redesigning Photodetector Electrodes as an Optical Antenna,” Nano Lett. 13(2), 392–396 (2013). [CrossRef] [PubMed]

8

8. S.-K. Kim, R. W. Day, J. F. Cahoon, T. J. Kempa, K.-D. Song, H.-G. Park, and C. M. Lieber, “Tuning Light Absorption in Core/Shell Silicon Nanowire Photovoltaic Devices through Morphological Design,” Nano Lett. 12(9), 4971–4976 (2012). [CrossRef] [PubMed]

,25

25. S.-K. Kim, K.-D. Song, T. J. Kempa, R. W. Day, C. M. Lieber, and H.-G. Park, “Design of Nanowire Optical Cavities as Efficient Photon Absorbers,” ACS Nano140313143802002 (2014), doi:. [CrossRef]

] and vertically oriented [10

10. S. W. Boettcher, J. M. Spurgeon, M. C. Putnam, E. L. Warren, D. B. Turner-Evans, M. D. Kelzenberg, J. R. Maiolo, H. A. Atwater, and N. S. Lewis, “Energy-Conversion Properties of Vapor-Liquid-Solid-Grown Silicon Wire-Array Photocathodes,” Science 327(5962), 185–187 (2010). [CrossRef] [PubMed]

13

13. P. Krogstrup, H. I. Jørgensen, M. Heiss, O. Demichel, J. V. Holm, M. Aagesen, J. Nygard, and A. Fontcuberta i Morral, “Single-nanowire solar cells beyond the Shockley–Queisser limit,” Nat. Photonics 7(4), 306–310 (2013). [CrossRef]

] NWs have been employed as efficient light absorbers that serve as a platform for ultrathin photovoltaics.

NW photovoltaics present unconventional light absorption characteristics because of their subwavelength cavity features. For example, the optical antenna effect explains how incident light can interact with a NW beyond the NW’s physical cross section [26

26. G. Chen, J. Wu, Q. Lu, H. R. Gutierrez, Q. Xiong, M. E. Pellen, J. S. Petko, D. H. Werner, and P. C. Eklund, “Optical Antenna Effect in Semiconducting Nanowires,” Nano Lett. 8(5), 1341–1346 (2008). [CrossRef] [PubMed]

,27

27. L. Cao, P. Fan, A. P. Vasudev, J. S. White, Z. Yu, W. Cai, J. A. Schuller, S. Fan, and M. L. Brongersma, “Semiconductor Nanowire Optical Antenna Solar Absorbers,” Nano Lett. 10(2), 439–445 (2010). [CrossRef] [PubMed]

]. Morphology-dependent optical resonances in a NW cavity also lead to efficient light absorption over a broad range of wavelengths [8

8. S.-K. Kim, R. W. Day, J. F. Cahoon, T. J. Kempa, K.-D. Song, H.-G. Park, and C. M. Lieber, “Tuning Light Absorption in Core/Shell Silicon Nanowire Photovoltaic Devices through Morphological Design,” Nano Lett. 12(9), 4971–4976 (2012). [CrossRef] [PubMed]

,27

27. L. Cao, P. Fan, A. P. Vasudev, J. S. White, Z. Yu, W. Cai, J. A. Schuller, S. Fan, and M. L. Brongersma, “Semiconductor Nanowire Optical Antenna Solar Absorbers,” Nano Lett. 10(2), 439–445 (2010). [CrossRef] [PubMed]

]. Together, these features emphasize the need for further design and synthesis of NW cavities, which could improve absorption efficiencies and short-circuit current densities (JSC’s) and surpass conventional limits. Photovoltaic studies regarding laterally oriented NWs have focused only on single-NW devices [5

5. J. Tang, Z. Huo, S. Brittman, H. Gao, and P. Yang, “Solution-Processed Core-Shell Nanowires for Efficient Photovoltaic Cells,” Nat. Nanotechnol. 6(9), 568–572 (2011). [CrossRef] [PubMed]

8

8. S.-K. Kim, R. W. Day, J. F. Cahoon, T. J. Kempa, K.-D. Song, H.-G. Park, and C. M. Lieber, “Tuning Light Absorption in Core/Shell Silicon Nanowire Photovoltaic Devices through Morphological Design,” Nano Lett. 12(9), 4971–4976 (2012). [CrossRef] [PubMed]

], whereas vertically oriented NW photovoltaics have been studied with respect to both single [13

13. P. Krogstrup, H. I. Jørgensen, M. Heiss, O. Demichel, J. V. Holm, M. Aagesen, J. Nygard, and A. Fontcuberta i Morral, “Single-nanowire solar cells beyond the Shockley–Queisser limit,” Nat. Photonics 7(4), 306–310 (2013). [CrossRef]

] and assembled [10

10. S. W. Boettcher, J. M. Spurgeon, M. C. Putnam, E. L. Warren, D. B. Turner-Evans, M. D. Kelzenberg, J. R. Maiolo, H. A. Atwater, and N. S. Lewis, “Energy-Conversion Properties of Vapor-Liquid-Solid-Grown Silicon Wire-Array Photocathodes,” Science 327(5962), 185–187 (2010). [CrossRef] [PubMed]

12

12. Z. 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,” Nat. Mater. 8(8), 648–653 (2009). [CrossRef] [PubMed]

] structures. To develop a next-generation platform for ultrathin solar cells, laterally oriented single NWs must be demonstrated in large-area arrays [25

25. S.-K. Kim, K.-D. Song, T. J. Kempa, R. W. Day, C. M. Lieber, and H.-G. Park, “Design of Nanowire Optical Cavities as Efficient Photon Absorbers,” ACS Nano140313143802002 (2014), doi:. [CrossRef]

,28

28. J. Yao, H. Yan, and C. M. Lieber, “A nanoscale combing technique for the large-scale assembly of highly aligned nanowires,” Nat. Nanotechnol. 8(5), 329–335 (2013). [CrossRef] [PubMed]

]. In this study, we investigated the light absorption properties of laterally assembled NW arrays using three-dimensional (3D) finite-difference time-domain (FDTD) simulations [29

29. A. Taflove and S. C. Hagness, Computational Electrodynamics: The Finite-Difference Time-Domain Method, 3rd ed. (Norwood, MA: Artech House, 2005).

]. First, an array comprising close-packed NWs was compared with a single NW on the basis of simulated absorption spectra and mode profiles for a number of different NW cross-sectional morphologies (various sizes and shapes). Second, examination of NW arrays with different pitches was performed to determine the optimal NW spacing, i.e., the spacing that yields the highest JSC. Finally, the absorption properties of multi-layered NW arrays were studied and compared with those of film structures with an equivalent thickness, providing insights into the feasibility of nanomaterial building blocks such as 3D ultrathin light absorbers.

2. Close-packed NW array with various cross-sectional morphologies

The absorption spectra of a single NW and a close-packed NW array were investigated with respect to their cross-sectional morphologies. Subtly changing the morphology of a NW cavity enables the tuning of its light absorption at specific wavelengths [8

8. S.-K. Kim, R. W. Day, J. F. Cahoon, T. J. Kempa, K.-D. Song, H.-G. Park, and C. M. Lieber, “Tuning Light Absorption in Core/Shell Silicon Nanowire Photovoltaic Devices through Morphological Design,” Nano Lett. 12(9), 4971–4976 (2012). [CrossRef] [PubMed]

], providing a key motivation for the continued development of NW photovoltaics. First, the cross-sectional shape of the NWs was changed from a hexagon to a circle [4

4. P. Fan, K. C. Y. Huang, L. Cao, and M. L. Brongersma, “Redesigning Photodetector Electrodes as an Optical Antenna,” Nano Lett. 13(2), 392–396 (2013). [CrossRef] [PubMed]

6

6. B. Tian, X. Zheng, T. J. Kempa, Y. Fang, N. Yu, G. Yu, J. Huang, and C. M. Lieber, “Coaxial Silicon Nanowires as Solar Cells and Nanoelectronic Power Sources,” Nature 449(7164), 885–889 (2007). [CrossRef] [PubMed]

] and then to a square [8

8. S.-K. Kim, R. W. Day, J. F. Cahoon, T. J. Kempa, K.-D. Song, H.-G. Park, and C. M. Lieber, “Tuning Light Absorption in Core/Shell Silicon Nanowire Photovoltaic Devices through Morphological Design,” Nano Lett. 12(9), 4971–4976 (2012). [CrossRef] [PubMed]

] while keeping their height fixed at 200 nm [Fig. 2(a)].
Fig. 2 (A) Absorption spectra of a single NW and a NW array with circular (top) and square (bottom) cross-sectional shape. For the square NWs, a 30-nm-thick SiO2 conformal coating was introduced. The height of each NW is 200 nm. (B) Absorption spectra of a single NW and a NW array with a height of 100 nm (top) and 300 nm (bottom). The cross section of both NW structures was hexagonal.
Note that for the square cross-sectional shape, a 30-nm-thick SiO2 conformal coating was introduced as a dielectric spacer to distinguish the rectangular NW array from a planar film structure [6

6. B. Tian, X. Zheng, T. J. Kempa, Y. Fang, N. Yu, G. Yu, J. Huang, and C. M. Lieber, “Coaxial Silicon Nanowires as Solar Cells and Nanoelectronic Power Sources,” Nature 449(7164), 885–889 (2007). [CrossRef] [PubMed]

,7

7. T. J. Kempa, J. F. Cahoon, S.-K. Kim, R. W. Day, D. C. Bell, H.-G. Park, and C. M. Lieber, “Coaxial Multishell Nanowires with High-Quality Electronic Interfaces and Tunable Optical Cavities for Ultrathin Photovoltaics,” Proc. Natl. Acad. Sci. U.S.A. 109(5), 1407–1412 (2012). [CrossRef] [PubMed]

]. The calculation result shows that the absorption spectra of the single NW and the NW array are nearly identical for the same NW morphology. Second, the height of the hexagonal NWs was changed to 100 nm and 350 nm [Fig. 2(b)]. The larger NW exhibits an absorption spectrum that is preserved when the NW is assembled into a closed-packed NW array. In contrast, the smaller NW exhibits significantly less light absorption if it is assembled in a close-packed NW array. Although the optical antenna effect increases as nanostructures decrease in size, the diffraction effect due to the periodically assembled structures decreases [25

25. S.-K. Kim, K.-D. Song, T. J. Kempa, R. W. Day, C. M. Lieber, and H.-G. Park, “Design of Nanowire Optical Cavities as Efficient Photon Absorbers,” ACS Nano140313143802002 (2014), doi:. [CrossRef]

,26

26. G. Chen, J. Wu, Q. Lu, H. R. Gutierrez, Q. Xiong, M. E. Pellen, J. S. Petko, D. H. Werner, and P. C. Eklund, “Optical Antenna Effect in Semiconducting Nanowires,” Nano Lett. 8(5), 1341–1346 (2008). [CrossRef] [PubMed]

,32

32. Z. Yu, A. Raman, and S. Fan, “Fundamental limit of nanophotonic light trapping in solar cells,” Proc. Natl. Acad. Sci. U.S.A. 107(41), 17491–17496 (2010). [CrossRef] [PubMed]

34

34. J. Kupec and B. Witzigmann, “Dispersion, Wave Propagation and Efficiency Analysis of Nanowire Solar Cells,” Opt. Express 17(12), 10399–10410 (2009). [CrossRef] [PubMed]

]. Notably, the absorption efficiency of a NW array does not exceed unity, whereas a single NW can exhibit over-unity absorption efficiency at specific resonant wavelengths party due to the optical antenna effect [7

7. T. J. Kempa, J. F. Cahoon, S.-K. Kim, R. W. Day, D. C. Bell, H.-G. Park, and C. M. Lieber, “Coaxial Multishell Nanowires with High-Quality Electronic Interfaces and Tunable Optical Cavities for Ultrathin Photovoltaics,” Proc. Natl. Acad. Sci. U.S.A. 109(5), 1407–1412 (2012). [CrossRef] [PubMed]

,8

8. S.-K. Kim, R. W. Day, J. F. Cahoon, T. J. Kempa, K.-D. Song, H.-G. Park, and C. M. Lieber, “Tuning Light Absorption in Core/Shell Silicon Nanowire Photovoltaic Devices through Morphological Design,” Nano Lett. 12(9), 4971–4976 (2012). [CrossRef] [PubMed]

,25

25. S.-K. Kim, K.-D. Song, T. J. Kempa, R. W. Day, C. M. Lieber, and H.-G. Park, “Design of Nanowire Optical Cavities as Efficient Photon Absorbers,” ACS Nano140313143802002 (2014), doi:. [CrossRef]

]. Therefore, we conclude that the conservation of absorption efficiency and JSC from a single NW to a NW array is valid across a range of NW morphologies, as long as the NW does not exhibit a strong optical antenna effect.

3. Current density of NW arrays with various pitch sizes

4. Resonance features of multi-layered NW arrays

Fig. 4 (A) Schematics of vertically aligned (top) and cross-stacked (bottom) NW arrays. (B) TE and TM polarized absorption spectra of double-stacked NW arrays: a cross-stacked NW array and a vertically aligned NW array. Each NW element has a height of 200 nm. All simulations are for a close-packed array. (C) TM absorption mode profiles of the peaks, indicated by “a,” “b,” “1,” and “2” in (B), corresponding to wavelengths of 580, 655, 690, and 715 nm, respectively. (D) Calculated current densities of vertically stacked NW arrays, cross-stacked NW arrays, and film structures as a function of the number of stacks, i.e., film thickness. (E) Calculated internal absorption per unit NW or unit volume for four-layered vertically aligned and cross-stacked NW arrays and an 800-nm-thick film structure. The inset shows a schematic of a four-layered NW array and a film structure.
We previously studied optical resonances of various NW arrays in which NW elements are assembled along the horizontal direction. As a new design for solar absorbers that outperforms conventional bulk structures, we propose multi-layered NW arrays in which each layer is parallel (vertically aligned) or orthogonal (cross-stacked) to the neighboring layers, as shown in Fig. 4(a). Such vertically-stacked NW arrays can be implemented by the multiple applications of a NW assembly technique such as a lubricant contact printing method [28

28. J. Yao, H. Yan, and C. M. Lieber, “A nanoscale combing technique for the large-scale assembly of highly aligned nanowires,” Nat. Nanotechnol. 8(5), 329–335 (2013). [CrossRef] [PubMed]

]. We calculated the polarization-resolved spectra of double-layered NW arrays with either parallel or orthogonal orientation [Fig. 4(b)]. Note that for a cross-stacked NW array, the polarization direction of incident light was defined with respect to the uppermost NW plane. Comparison of the absorption spectra between the two array structures shows that the cross-stacked NW array exhibits much greater light absorption than the vertically aligned NW array for both TE and TM polarizations. Notably, compared with horizontally and vertically aligned NW arrays, the cross-stacked NW array excites additional absorption peaks at long wavelengths (600 – 800 nm). To elucidate the additional absorption peaks, we obtained absorption mode profiles from the cross-stacked NW array [Fig. 4(c)]. The boundary of the mode profiles corresponds to the unit cell of the cross-stacked NW array. The absorption mode profiles assigned to the new peaks (indicated by “1” and “2” in Figs. 4(b) and 4(c)) indicate that the top NWs sustain normal cavity modes, whereas the bottom NWs sustain waveguide modes via a grating coupler resulting from the periodically spaced top NWs. For the waveguide modes, intensity maxima and minima appear alternately along the axis of a NW [35

35. S.-K. Kim, K.-D. Song, and H.-G. Park, “Design of input couplers for efficient silicon thin film solar absorbers,” Opt. Express 20(S6), A997–A1004 (2012). [CrossRef]

]. On the other hand, the absorption profiles assigned to the normal peaks (indicated by “a” and “b” in Figs. 4(b) and 4(c)) show that both the top and bottom NWs sustain an identical cavity mode. Note that the top and bottom images were acquired from the x-z and y-z cross sections, respectively.

Next, we compared the JSC as a function of total Si thickness for multi-stacked NW arrays with that for film structures [Fig. 4(d)]. The calculation result shows that the JSC of the cross-stacked NW arrays was significantly higher than that of the 800-nm-thick film structures. For instance, a four-layered cross-stacked NW array yields a JSC of ~14.0 mA/cm2, indicating ~60% enhancement compared with an 800-nm-thick film structure. Notably, a similar JSC (~13.5 mA/cm2) was calculated in a double-layered cross-stacked NW array with a bottom silver mirror that can be readily deposited on a transparent quartz substrate using a conventional evaporation technique [7

7. T. J. Kempa, J. F. Cahoon, S.-K. Kim, R. W. Day, D. C. Bell, H.-G. Park, and C. M. Lieber, “Coaxial Multishell Nanowires with High-Quality Electronic Interfaces and Tunable Optical Cavities for Ultrathin Photovoltaics,” Proc. Natl. Acad. Sci. U.S.A. 109(5), 1407–1412 (2012). [CrossRef] [PubMed]

]. To explain such a large enhancement in JSC for multi-layered NW arrays, we calculated the internal absorption distribution of the four-layered NW arrays and the 800-nm-thick film structures [Fig. 4(e)]. For the film structure, incident light was attenuated rapidly as it was swept from the top surface of the structure to the bottom surface. In contrast, the multi-stacked NW arrays exhibited relatively uniform light absorption across NWs, which enables each NW to sustain its localized absorption modes. Therefore, we postulate that a screening effect is mitigated in multi-stacked NW array, which accounts for its large absorption.

Fig. 5 (A) TM polarized absorption spectra of a four-layered cross-stacked NW array and an 800-nm-thick) film structure. (B) TM absorption mode profiles of the four-layered cross-stacked NW array at wavelengths of 580, 620, 665, 685, 700, and 770 nm (left to right).
Finally, we calculated the absorption spectra of the four-layered cross-stacked NW array and the 800-nm-thick film structure [Fig. 5(a)]. The calculation result shows that the cross-stacked NW array exhibits more absorption peaks than the film structure. Moreover, the amplitude of the absorption peaks is enhanced by a multiple diffraction effect originating from 3D periodic structures [36

36. M. M. Hossain, G. Chen, B. Jia, X.-H. Wang, and M. Gu, “Optimization of enhanced absorption in 3D-woodpile metallic photonic crystals,” Opt. Express 18(9), 9048–9054 (2010). [CrossRef] [PubMed]

]. As discussed in Figs. 4(b) and 4(c), each absorption peak is identified as either a normal cavity mode (indicated by “a,” “b,” “c”) or a new cavity-waveguide mode (indicated by “1,” “2,” “3”) [Fig. 5(b)]. A 3D complex nanostructure based on nanowire building blocks can provide a new platform for an efficient solar absorber, surpassing conventional limits.

5. Conclusion

We studied the light absorption features of single- and multi-layered Si NW array cavities by performing FDTD simulations. Calculation results indicated that the absorption modes within each NW cavity are preserved when single NWs are combined to form NW arrays. This observation highlights an important design principle: the unique optical properties of single NWs are transferred to NW arrays, and NW arrays can thus be optimized at the single-NW level. The absorption of a NW array was significantly affected by the pitch size of the array, and it was maximized with a ~450 nm. Polarization-resolved studies revealed that the optical antenna effect along with the diffraction effect resulting from the surface modulation of NWs determines the total absorption in NW arrays. Light absorption and resultant JSC were further enhanced for multi-layered NW arrays because of new coupled modes and the mitigation of the screening effect. Designing solar absorbers based on assembled nanowire arrays is a unique strategy for realizing more efficient solar cells.

Acknowledgments

S.-K.K. acknowledges support for this work from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2013R1A1A1059423). H.-G.P. acknowledges support for this work from the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2009-0081565). T.J.K. acknowledges the support of a National Science Foundation Graduate Research Fellowship. K.-D.S acknowledges the support of a TJ Park Science Fellowship. This work was supported by a grant from the Kyung Hee University in 2013 (KHU-20130689).

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J. Tang, Z. Huo, S. Brittman, H. Gao, and P. Yang, “Solution-Processed Core-Shell Nanowires for Efficient Photovoltaic Cells,” Nat. Nanotechnol. 6(9), 568–572 (2011). [CrossRef] [PubMed]

6.

B. Tian, X. Zheng, T. J. Kempa, Y. Fang, N. Yu, G. Yu, J. Huang, and C. M. Lieber, “Coaxial Silicon Nanowires as Solar Cells and Nanoelectronic Power Sources,” Nature 449(7164), 885–889 (2007). [CrossRef] [PubMed]

7.

T. J. Kempa, J. F. Cahoon, S.-K. Kim, R. W. Day, D. C. Bell, H.-G. Park, and C. M. Lieber, “Coaxial Multishell Nanowires with High-Quality Electronic Interfaces and Tunable Optical Cavities for Ultrathin Photovoltaics,” Proc. Natl. Acad. Sci. U.S.A. 109(5), 1407–1412 (2012). [CrossRef] [PubMed]

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S.-K. Kim, R. W. Day, J. F. Cahoon, T. J. Kempa, K.-D. Song, H.-G. Park, and C. M. Lieber, “Tuning Light Absorption in Core/Shell Silicon Nanowire Photovoltaic Devices through Morphological Design,” Nano Lett. 12(9), 4971–4976 (2012). [CrossRef] [PubMed]

9.

J. D. Christesen, X. Zhang, C. W. Pinion, T. A. Celano, C. J. Flynn, and J. F. Cahoon, “Design principles for photovoltaic devices based on Si nanowires with axial or radial p-n junctions,” Nano Lett. 12(11), 6024–6029 (2012). [CrossRef] [PubMed]

10.

S. W. Boettcher, J. M. Spurgeon, M. C. Putnam, E. L. Warren, D. B. Turner-Evans, M. D. Kelzenberg, J. R. Maiolo, H. A. Atwater, and N. S. Lewis, “Energy-Conversion Properties of Vapor-Liquid-Solid-Grown Silicon Wire-Array Photocathodes,” Science 327(5962), 185–187 (2010). [CrossRef] [PubMed]

11.

G. Mariani, P.-S. Wong, A. M. Katzenmeyer, F. Léonard, J. Shapiro, and D. L. Huffaker, “Patterned Radial GaAs Nanopillar Solar Cells,” Nano Lett. 11(6), 2490–2494 (2011). [CrossRef] [PubMed]

12.

Z. 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,” Nat. Mater. 8(8), 648–653 (2009). [CrossRef] [PubMed]

13.

P. Krogstrup, H. I. Jørgensen, M. Heiss, O. Demichel, J. V. Holm, M. Aagesen, J. Nygard, and A. Fontcuberta i Morral, “Single-nanowire solar cells beyond the Shockley–Queisser limit,” Nat. Photonics 7(4), 306–310 (2013). [CrossRef]

14.

B. Cho, J. Bareno, Y. L. Foo, S. Hong, T. Spila, I. Petrov, and J. E. Greene, “Phosphorus Incorporation during Si(001): P Gas-source Molecular Beam Epitaxy: Effects on Growth Kinetics and Surface Morphology,” J. Appl. Phys. 103(12), 123530 (2008). [CrossRef]

15.

M. C. Plante and R. R. Lapierre, “Control of GaAs nanowire morphology and crystal structure,” Nanotechnology 19(49), 495603 (2008). [CrossRef] [PubMed]

16.

T. Kuykendall, P. Ulrich, S. Aloni, and P. Yang, “Complete composition tunability of InGaN Nanowires using a combinatorial approach,” Nat. Mater. 6(12), 951–956 (2007). [CrossRef] [PubMed]

17.

L.-F. Cui, R. Ruffo, C. K. Chan, H. Peng, and Y. Cui, “Crystalline-Amorphous Core-Shell Silicon Nanowires for High Capacity and High Current Battery Electrodes,” Nano Lett. 9(1), 491–495 (2009). [CrossRef] [PubMed]

18.

M. M. Adachi, M. P. Anantram, and K. S. Karim, “Optical Properties of Crystalline-Amorphous Core-Shell Silicon Nanowires,” Nano Lett. 10(10), 4093–4098 (2010). [CrossRef] [PubMed]

19.

G. Brönstrup, N. Jahr, C. Leiterer, A. Csáki, W. Fritzsche, and S. Christiansen, “Optical Properties of Individual Silicon Nanowires for Photonic Devices,” ACS Nano 4(12), 7113–7122 (2010). [CrossRef] [PubMed]

20.

G. Brönstrup, C. Leiterer, N. Jahr, C. Gutsche, A. Lysov, I. Regolin, W. Prost, F. J. Tegude, W. Fritzsche, and S. Christiansen, “A Precise Optical Determination of Nanoscale Diameters of Semiconductor Nanowires,” Nanotechnology 22(38), 385201 (2011). [CrossRef] [PubMed]

21.

F. Qian, Y. Li, S. Gradecak, H.-G. Park, Y. Dong, Y. Ding, Z. L. Wang, and C. M. Lieber, “Multi-Quantum-Well Nanowire Heterostructures for Wavelength-Controlled Lasers,” Nat. Mater. 7(9), 701–706 (2008). [CrossRef] [PubMed]

22.

R. F. Oulton, V. J. Sorger, T. Zentgraf, R.-M. Ma, C. Gladden, L. Dai, G. Bartal, and X. Zhang, “Plasmon Lasers at Deep Subwavelength Scale,” Nature 461(7264), 629–632 (2009). [CrossRef] [PubMed]

23.

M. Khorasaninejad and S. S. Saini, “Silicon nanowire optical waveguide (SNOW),” Opt. Express 18(22), 23442–23457 (2010). [CrossRef] [PubMed]

24.

F. Qian, S. Gradecak, Y. Li, C. Y. Wen, and C. M. Lieber, “Core/Multishell Nanowire Heterostructures as Multicolor, High-Efficiency Light-Emitting Diodes,” Nano Lett. 5(11), 2287–2291 (2005). [CrossRef] [PubMed]

25.

S.-K. Kim, K.-D. Song, T. J. Kempa, R. W. Day, C. M. Lieber, and H.-G. Park, “Design of Nanowire Optical Cavities as Efficient Photon Absorbers,” ACS Nano140313143802002 (2014), doi:. [CrossRef]

26.

G. Chen, J. Wu, Q. Lu, H. R. Gutierrez, Q. Xiong, M. E. Pellen, J. S. Petko, D. H. Werner, and P. C. Eklund, “Optical Antenna Effect in Semiconducting Nanowires,” Nano Lett. 8(5), 1341–1346 (2008). [CrossRef] [PubMed]

27.

L. Cao, P. Fan, A. P. Vasudev, J. S. White, Z. Yu, W. Cai, J. A. Schuller, S. Fan, and M. L. Brongersma, “Semiconductor Nanowire Optical Antenna Solar Absorbers,” Nano Lett. 10(2), 439–445 (2010). [CrossRef] [PubMed]

28.

J. Yao, H. Yan, and C. M. Lieber, “A nanoscale combing technique for the large-scale assembly of highly aligned nanowires,” Nat. Nanotechnol. 8(5), 329–335 (2013). [CrossRef] [PubMed]

29.

A. Taflove and S. C. Hagness, Computational Electrodynamics: The Finite-Difference Time-Domain Method, 3rd ed. (Norwood, MA: Artech House, 2005).

30.

D. R. Lide, CRC Handbook of Chemistry and Physics, 88th ed. (CRC Press, 2008).

31.

K. Soderstrom, F.-J. Haug, J. Escarre, O. Cubero, and C. Ballif, “Photocurrent increase in n-i-p thin film silicon solar cells by guided mode excitation via grating coupler,” Appl. Phys. Lett. 96(21), 213508 (2010). [CrossRef]

32.

Z. Yu, A. Raman, and S. Fan, “Fundamental limit of nanophotonic light trapping in solar cells,” Proc. Natl. Acad. Sci. U.S.A. 107(41), 17491–17496 (2010). [CrossRef] [PubMed]

33.

J. Kupec, R. L. Stoop, and B. Witzigmann, “Light absorption and emission in nanowire array solar cells,” Opt. Express 18(26), 27589–27605 (2010). [CrossRef] [PubMed]

34.

J. Kupec and B. Witzigmann, “Dispersion, Wave Propagation and Efficiency Analysis of Nanowire Solar Cells,” Opt. Express 17(12), 10399–10410 (2009). [CrossRef] [PubMed]

35.

S.-K. Kim, K.-D. Song, and H.-G. Park, “Design of input couplers for efficient silicon thin film solar absorbers,” Opt. Express 20(S6), A997–A1004 (2012). [CrossRef]

36.

M. M. Hossain, G. Chen, B. Jia, X.-H. Wang, and M. Gu, “Optimization of enhanced absorption in 3D-woodpile metallic photonic crystals,” Opt. Express 18(9), 9048–9054 (2010). [CrossRef] [PubMed]

OCIS Codes
(050.0050) Diffraction and gratings : Diffraction and gratings
(140.4780) Lasers and laser optics : Optical resonators
(350.6050) Other areas of optics : Solar energy

ToC Category:
Light Trapping for Photovoltaics

History
Original Manuscript: March 17, 2014
Revised Manuscript: April 16, 2014
Manuscript Accepted: April 16, 2014
Published: April 29, 2014

Citation
Kyung-Deok Song, Thomas J. Kempa, Hong-Gyu Park, and Sun-Kyung Kim, "Laterally assembled nanowires for ultrathin broadband solar absorbers," Opt. Express 22, A992-A1000 (2014)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-S3-A992


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References

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  2. C. Hahn, Z. Zhang, A. Fu, C. H. Wu, Y. J. Hwang, D. J. Gargas, and P. Yang, “Epitaxial Growth of InGaN Nanowire Arrays for Light Emitting Diodes,” ACS Nano5(5), 3970–3976 (2011). [CrossRef] [PubMed]
  3. Y.-S. No, J. H. Choi, H.-S. Ee, M.-S. Hwang, K.-Y. Jeong, E.-K. Lee, M.-K. Seo, S.-H. Kwon, and H.-G. Park, “A Double-Strip Plasmonic Waveguide Coupled to an Electrically Driven Nanowire LED,” Nano Lett.13(2), 772–776 (2013). [CrossRef] [PubMed]
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  7. T. J. Kempa, J. F. Cahoon, S.-K. Kim, R. W. Day, D. C. Bell, H.-G. Park, and C. M. Lieber, “Coaxial Multishell Nanowires with High-Quality Electronic Interfaces and Tunable Optical Cavities for Ultrathin Photovoltaics,” Proc. Natl. Acad. Sci. U.S.A.109(5), 1407–1412 (2012). [CrossRef] [PubMed]
  8. S.-K. Kim, R. W. Day, J. F. Cahoon, T. J. Kempa, K.-D. Song, H.-G. Park, and C. M. Lieber, “Tuning Light Absorption in Core/Shell Silicon Nanowire Photovoltaic Devices through Morphological Design,” Nano Lett.12(9), 4971–4976 (2012). [CrossRef] [PubMed]
  9. J. D. Christesen, X. Zhang, C. W. Pinion, T. A. Celano, C. J. Flynn, and J. F. Cahoon, “Design principles for photovoltaic devices based on Si nanowires with axial or radial p-n junctions,” Nano Lett.12(11), 6024–6029 (2012). [CrossRef] [PubMed]
  10. S. W. Boettcher, J. M. Spurgeon, M. C. Putnam, E. L. Warren, D. B. Turner-Evans, M. D. Kelzenberg, J. R. Maiolo, H. A. Atwater, and N. S. Lewis, “Energy-Conversion Properties of Vapor-Liquid-Solid-Grown Silicon Wire-Array Photocathodes,” Science327(5962), 185–187 (2010). [CrossRef] [PubMed]
  11. G. Mariani, P.-S. Wong, A. M. Katzenmeyer, F. Léonard, J. Shapiro, and D. L. Huffaker, “Patterned Radial GaAs Nanopillar Solar Cells,” Nano Lett.11(6), 2490–2494 (2011). [CrossRef] [PubMed]
  12. Z. 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,” Nat. Mater.8(8), 648–653 (2009). [CrossRef] [PubMed]
  13. P. Krogstrup, H. I. Jørgensen, M. Heiss, O. Demichel, J. V. Holm, M. Aagesen, J. Nygard, and A. Fontcuberta i Morral, “Single-nanowire solar cells beyond the Shockley–Queisser limit,” Nat. Photonics7(4), 306–310 (2013). [CrossRef]
  14. B. Cho, J. Bareno, Y. L. Foo, S. Hong, T. Spila, I. Petrov, and J. E. Greene, “Phosphorus Incorporation during Si(001): P Gas-source Molecular Beam Epitaxy: Effects on Growth Kinetics and Surface Morphology,” J. Appl. Phys.103(12), 123530 (2008). [CrossRef]
  15. M. C. Plante and R. R. Lapierre, “Control of GaAs nanowire morphology and crystal structure,” Nanotechnology19(49), 495603 (2008). [CrossRef] [PubMed]
  16. T. Kuykendall, P. Ulrich, S. Aloni, and P. Yang, “Complete composition tunability of InGaN Nanowires using a combinatorial approach,” Nat. Mater.6(12), 951–956 (2007). [CrossRef] [PubMed]
  17. L.-F. Cui, R. Ruffo, C. K. Chan, H. Peng, and Y. Cui, “Crystalline-Amorphous Core-Shell Silicon Nanowires for High Capacity and High Current Battery Electrodes,” Nano Lett.9(1), 491–495 (2009). [CrossRef] [PubMed]
  18. M. M. Adachi, M. P. Anantram, and K. S. Karim, “Optical Properties of Crystalline-Amorphous Core-Shell Silicon Nanowires,” Nano Lett.10(10), 4093–4098 (2010). [CrossRef] [PubMed]
  19. G. Brönstrup, N. Jahr, C. Leiterer, A. Csáki, W. Fritzsche, and S. Christiansen, “Optical Properties of Individual Silicon Nanowires for Photonic Devices,” ACS Nano4(12), 7113–7122 (2010). [CrossRef] [PubMed]
  20. G. Brönstrup, C. Leiterer, N. Jahr, C. Gutsche, A. Lysov, I. Regolin, W. Prost, F. J. Tegude, W. Fritzsche, and S. Christiansen, “A Precise Optical Determination of Nanoscale Diameters of Semiconductor Nanowires,” Nanotechnology22(38), 385201 (2011). [CrossRef] [PubMed]
  21. F. Qian, Y. Li, S. Gradecak, H.-G. Park, Y. Dong, Y. Ding, Z. L. Wang, and C. M. Lieber, “Multi-Quantum-Well Nanowire Heterostructures for Wavelength-Controlled Lasers,” Nat. Mater.7(9), 701–706 (2008). [CrossRef] [PubMed]
  22. R. F. Oulton, V. J. Sorger, T. Zentgraf, R.-M. Ma, C. Gladden, L. Dai, G. Bartal, and X. Zhang, “Plasmon Lasers at Deep Subwavelength Scale,” Nature461(7264), 629–632 (2009). [CrossRef] [PubMed]
  23. M. Khorasaninejad and S. S. Saini, “Silicon nanowire optical waveguide (SNOW),” Opt. Express18(22), 23442–23457 (2010). [CrossRef] [PubMed]
  24. F. Qian, S. Gradecak, Y. Li, C. Y. Wen, and C. M. Lieber, “Core/Multishell Nanowire Heterostructures as Multicolor, High-Efficiency Light-Emitting Diodes,” Nano Lett.5(11), 2287–2291 (2005). [CrossRef] [PubMed]
  25. S.-K. Kim, K.-D. Song, T. J. Kempa, R. W. Day, C. M. Lieber, and H.-G. Park, “Design of Nanowire Optical Cavities as Efficient Photon Absorbers,” ACS Nano140313143802002 (2014), doi:. [CrossRef]
  26. G. Chen, J. Wu, Q. Lu, H. R. Gutierrez, Q. Xiong, M. E. Pellen, J. S. Petko, D. H. Werner, and P. C. Eklund, “Optical Antenna Effect in Semiconducting Nanowires,” Nano Lett.8(5), 1341–1346 (2008). [CrossRef] [PubMed]
  27. L. Cao, P. Fan, A. P. Vasudev, J. S. White, Z. Yu, W. Cai, J. A. Schuller, S. Fan, and M. L. Brongersma, “Semiconductor Nanowire Optical Antenna Solar Absorbers,” Nano Lett.10(2), 439–445 (2010). [CrossRef] [PubMed]
  28. J. Yao, H. Yan, and C. M. Lieber, “A nanoscale combing technique for the large-scale assembly of highly aligned nanowires,” Nat. Nanotechnol.8(5), 329–335 (2013). [CrossRef] [PubMed]
  29. A. Taflove and S. C. Hagness, Computational Electrodynamics: The Finite-Difference Time-Domain Method, 3rd ed. (Norwood, MA: Artech House, 2005).
  30. D. R. Lide, CRC Handbook of Chemistry and Physics, 88th ed. (CRC Press, 2008).
  31. K. Soderstrom, F.-J. Haug, J. Escarre, O. Cubero, and C. Ballif, “Photocurrent increase in n-i-p thin film silicon solar cells by guided mode excitation via grating coupler,” Appl. Phys. Lett.96(21), 213508 (2010). [CrossRef]
  32. Z. Yu, A. Raman, and S. Fan, “Fundamental limit of nanophotonic light trapping in solar cells,” Proc. Natl. Acad. Sci. U.S.A.107(41), 17491–17496 (2010). [CrossRef] [PubMed]
  33. J. Kupec, R. L. Stoop, and B. Witzigmann, “Light absorption and emission in nanowire array solar cells,” Opt. Express18(26), 27589–27605 (2010). [CrossRef] [PubMed]
  34. J. Kupec and B. Witzigmann, “Dispersion, Wave Propagation and Efficiency Analysis of Nanowire Solar Cells,” Opt. Express17(12), 10399–10410 (2009). [CrossRef] [PubMed]
  35. S.-K. Kim, K.-D. Song, and H.-G. Park, “Design of input couplers for efficient silicon thin film solar absorbers,” Opt. Express20(S6), A997–A1004 (2012). [CrossRef]
  36. M. M. Hossain, G. Chen, B. Jia, X.-H. Wang, and M. Gu, “Optimization of enhanced absorption in 3D-woodpile metallic photonic crystals,” Opt. Express18(9), 9048–9054 (2010). [CrossRef] [PubMed]

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