Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Enhanced absorption and carrier collection in Si wire arrays for photovoltaic applications

A Corrigendum to this article was published on 19 February 2010

This article has been updated


Si wire arrays are a promising architecture for solar-energy-harvesting applications, and may offer a mechanically flexible alternative to Si wafers for photovoltaics1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17. To achieve competitive conversion efficiencies, the wires must absorb sunlight over a broad range of wavelengths and incidence angles, despite occupying only a modest fraction of the array’s volume. Here, we show that arrays having less than 5% areal fraction of wires can achieve up to 96% peak absorption, and that they can absorb up to 85% of day-integrated, above-bandgap direct sunlight. In fact, these arrays show enhanced near-infrared absorption, which allows their overall sunlight absorption to exceed the ray-optics light-trapping absorption limit18 for an equivalent volume of randomly textured planar Si, over a broad range of incidence angles. We furthermore demonstrate that the light absorbed by Si wire arrays can be collected with a peak external quantum efficiency of 0.89, and that they show broadband, near-unity internal quantum efficiency for carrier collection through a radial semiconductor/liquid junction at the surface of each wire. The observed absorption enhancement and collection efficiency enable a cell geometry that not only uses 1/100th the material of traditional wafer-based devices, but also may offer increased photovoltaic efficiency owing to an effective optical concentration of up to 20 times.

This is a preview of subscription content

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Structure of Si wire arrays prepared for optical measurements.
Figure 2: Representative composition and optical properties of each wire-array tiling pattern.
Figure 3: Light-trapping techniques and figure of merit (Aavg) calculation.
Figure 4: Measured Si wire-array absorption versus theoretical absorption of an equivalently thick, planar Si absorber.
Figure 5: Photoelectrochemical characterization of Si wire arrays.

Change history

  • 19 February 2010

    In the version of this Letter originally published, the first sentence in the Acknowledgements should have been: “This work was supported by BP and in part by the Department of Energy EFRC program under grant DE-SC0001293, and made use of facilities supported by the Center for Science and Engineering of Materials, an NSF Materials Research Science and Engineering Center at Caltech.” This has been corrected in the HTML and PDF versions of this Letter.


  1. 1

    Kayes, B. M., Atwater, H. A. & Lewis, N. S. Comparison of the device physics principles of planar and radial p–n junction nanorod solar cells. J. Appl. Phys. 97, 114302–114311 (2005).

    Article  Google Scholar 

  2. 2

    Garnett, E. C. & Yang, P. Silicon nanowire radial p–n junction solar cells. J. Am. Chem. Soc. 130, 9224–9225 (2008).

    CAS  Article  Google Scholar 

  3. 3

    Kelzenberg, M. D., Putnam, M. C., Turner-Evans, D. B., Lewis, N. S. & Atwater, H. A. Proc. 34th IEEE Photovoltaic Specialists Conference 1–6 (IEEE, 2009).

    Google Scholar 

  4. 4

    Tsakalakos, L. et al. Silicon nanowire solar cells. Appl. Phys. Lett. 91, 233117 (2007).

    Article  Google Scholar 

  5. 5

    Stelzner, T. et al. Silicon nanowire-based solar cells. Nanotechnology 19, 295203 (2008).

    Article  Google Scholar 

  6. 6

    Gunawan, O. & Guha, S. Characteristics of vapor–liquid–solid grown silicon nanowire solar cells. Sol. Energy Mater. Sol. Cells 93, 1388–1393 (2009).

    CAS  Article  Google Scholar 

  7. 7

    Peng, K. et al. Aligned single-crystalline Si nanowire arrays for photovoltaic applications. Small 1, 1062–1067 (2005).

    CAS  Article  Google Scholar 

  8. 8

    Sivakov, V. et al. Silicon nanowire-based solar cells on glass: Synthesis, optical properties, and cell parameters. Nano Lett. 9, 1549–1554 (2009).

    CAS  Article  Google Scholar 

  9. 9

    Altermatt, P. P., Yang, Y., Langer, T., Schenk, A. & Brendel, R. Proc. 34th IEEE Photovoltaic Specialists Conference 1–6 (IEEE, 2009).

    Google Scholar 

  10. 10

    Hu, L. & Chen, G. Analysis of optical absorption in silicon nanowire arrays for photovoltaic applications. Nano Lett. 7, 3249–3252 (2007).

    CAS  Article  Google Scholar 

  11. 11

    Muskens, O. L., Rivas, J. G. m., Algra, R. E., Bakkers, E. P. A. M. & Lagendijk, A. Design of light scattering in nanowire materials for photovoltaic applications. Nano Lett. 8, 2638–2642 (2008).

    CAS  Article  Google Scholar 

  12. 12

    Zhu, J. et al. Optical absorption enhancement in amorphous silicon nanowire and nanocone arrays. Nano Lett. 9, 279–282 (2009).

    Article  Google Scholar 

  13. 13

    Tian, B. et al. Coaxial silicon nanowires as solar cells and nanoelectronic power sources. Nature 449, 885–889 (2007).

    CAS  Article  Google Scholar 

  14. 14

    Goodey, A. P., Eichfeld, S. M., Lew, K.-K., Redwing, J. M. & Mallouk, T. E. Silicon nanowire array photoelectrochemical cells. J. Am. Chem. Soc. 129, 12344–12345 (2007).

    CAS  Article  Google Scholar 

  15. 15

    Maiolo, J. R. I. et al. High aspect ratio silicon wire array photoelectrochemical cells. J. Am. Chem. Soc. 129, 12346–12347 (2007).

    CAS  Article  Google Scholar 

  16. 16

    Plass, K. E. et al. Flexible polymer-embedded Si wire arrays. Adv. Mater. 21, 325–328 (2009).

    CAS  Article  Google Scholar 

  17. 17

    Spurgeon, J. M. et al. Repeated epitaxial growth and transfer of arrays of patterned, vertically aligned, crystalline Si wires from a single Si(111) substrate. Appl. Phys. Lett. 93, 032112–032113 (2008).

    Article  Google Scholar 

  18. 18

    Tiedje, T., Yablonovitch, E., Cody, G. D. & Brooks, B. G. Limiting efficiency of silicon solar-cells. IEEE Trans. Electron Devices 31, 711–716 (1984).

    Article  Google Scholar 

  19. 19

    Wagner, R. S. & Ellis, W. C. Vapor–liquid–solid mechanism of single crystal growth. Appl. Phys. Lett. 4, 89–90 (1964).

    CAS  Article  Google Scholar 

  20. 20

    Putnam, M. C. et al. 10 μm minority-carrier diffusion lengths in Si wires synthesized by Cu-catalyzed vapor–liquid–solid growth. Appl. Phys. Lett. 95, 163116 (2009).

    Article  Google Scholar 

  21. 21

    Kelzenberg, M. D. et al. Photovoltaic measurements in single-nanowire silicon solar cells. Nano Lett. 8, 710–714 (2008).

    CAS  Article  Google Scholar 

  22. 22

    Kelzenberg, M. D. et al. Proc. 33rd IEEE Photovoltaic Specialists Conference 1–6 (IEEE, 2008).

    Google Scholar 

  23. 23

    Kayes, B. M. et al. Growth of vertically aligned Si wire arrays over large areas (>1 cm2) with Au and Cu catalysts. Appl. Phys. Lett. 91, 103110–103113 (2007).

    Article  Google Scholar 

  24. 24

    Marion, B. et al. Validation of a photovoltaic module energy ratings procedure at NREL. Report No. NREL/TP-520-26909 (1999).

  25. 25

    Aspnes, D. E. in Properties of Crystalline Silicon (ed. Robert, H.) 683–690 (INSPEC, IEE, 1999).

    Google Scholar 

  26. 26

    Yablonovitch, E. Statistical ray optics. J. Opt. Soc. Am. 72, 899–907 (1982).

    Article  Google Scholar 

  27. 27

    Boettcher, S. W. et al. Energy-conversion properties of vapor–liquid–solid-grown silicon wire-array photocathodes. Science 327, 185–187 (2010).

    CAS  Article  Google Scholar 

  28. 28

    Tsakalakos, L. et al. Strong broadband optical absorption in silicon nanowire films. J. Nanophoton. 1, 013552 (2007).

    Article  Google Scholar 

  29. 29

    Campbell, P. & Green, M. A. The limiting efficiency of silicon solar cells under concentrated sunlight. IEEE Trans. Electron Devices 33, 234–239 (1986).

    Article  Google Scholar 

  30. 30

    Kupec, J. & Witzigmann, B. Dispersion, wave propagation and efficiency analysis of nanowire solar cells. Opt. Express 17, 10399–10410 (2009).

    CAS  Article  Google Scholar 

  31. 31

    Yoon, J. et al. Ultrathin silicon solar microcells for semitransparent, mechanically flexible and microconcentrator module designs. Nature Mater. 7, 907–915 (2008).

    CAS  Article  Google Scholar 

  32. 32

    Fan, Z. et al. Three-dimensional nanopillar-array photovoltaics on low-cost and flexible substrates. Nature Mater. 8, 648–653 (2009).

    CAS  Article  Google Scholar 

  33. 33

    Putnam, M. C. et al. Secondary ion mass spectrometry of vapor–liquid–solid grown, Au-catalyzed, Si wires. Nano Lett. 8, 3109–3113 (2008).

    CAS  Article  Google Scholar 

Download references


This work was supported by BP and in part by the Department of Energy EFRC program under grant DE-SC0001293, and made use of facilities supported by the Center for Science and Engineering of Materials, an NSF Materials Research Science and Engineering Center at Caltech. S.W.B. acknowledges the Kavli Nanoscience Institute for fellowship support. The authors acknowledge D. Pacifici for useful discussions and assistance in generating the quasi-periodic hole-array patterns, B. Kayes and M. Filler for their contributions at the outset of this project and M. Roy and S. Olson for their advice and skill in machining the components of the experimental apparatus.

Author information




M.D.K. participated in the design and execution of the experiments, analysed the results and prepared the manuscript under the advisement of H.A.A. and the guidance of N.S.L. and S.W.B. J.A.P. contributed to the design and fabrication of the array template photomasks, the integrating-sphere apparatus and the image processing software. S.W.B., J.M.S., J.A.P., M.C.P. and D.B.T-E. assisted in the fabrication of the wire arrays and R.M.B. carried out the deposition and characterization of the SiNx antireflective coating. S.W.B., E.L.W. and J.M.S. assisted with the photoelectrochemical measurements and fabricated the electrodes. All authors discussed the results and commented on the manuscript.

Corresponding author

Correspondence to Harry A. Atwater.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary Information (PDF 1831 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Kelzenberg, M., Boettcher, S., Petykiewicz, J. et al. Enhanced absorption and carrier collection in Si wire arrays for photovoltaic applications. Nature Mater 9, 239–244 (2010).

Download citation

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing