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.

Highly efficient Cu(In,Ga)Se2 solar cells grown on flexible polymer films


Solar cells based on polycrystalline Cu(In,Ga)Se2 absorber layers have yielded the highest conversion efficiency among all thin-film technologies1,2,3, and the use of flexible polymer films as substrates offers several advantages in lowering manufacturing costs. However, given that conversion efficiency is crucial for cost-competitiveness, it is necessary to develop devices on flexible substrates that perform as well as those obtained on rigid substrates. Such comparable performance has not previously been achieved, primarily because polymer films require much lower substrate temperatures during absorber deposition, generally resulting in much lower efficiencies4. Here we identify a strong composition gradient in the absorber layer as the main reason for inferior performance and show that, by adjusting it appropriately, very high efficiencies can be obtained. This implies that future manufacturing of highly efficient flexible solar cells could lower the cost of solar electricity and thus become a significant branch of the photovoltaic industry.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Electronic and optical structure of CIGS solar cells.
Figure 2: Deposition processes, optoelectronic properties, and composition profile analysis.
Figure 3: Temperature-dependent current–voltage measurements and simulations.
Figure 4: Illustration of the electronic barrier.


  1. 1

    Green, M. A., Emery, K., Hishikawa, Y. & Warta, W. Solar cell efficiency table (version 37). Prog. Photovolt. 19, 84–92 (2011).

    CAS  Article  Google Scholar 

  2. 2

    Repins, I. et al. 19.9%-efficient ZnO/CdS/CuInGaSe2 solar cell with 81.2% fill factor. Prog. Photovolt. 16, 235–239 (2008).

    CAS  Article  Google Scholar 

  3. 3

    Jackson, P. et al. New world record efficiency for Cu(In,Ga)Se2 thin-film solar cells beyond 20%. Prog. Photovolt. (2011).

  4. 4

    Shafarman, W. N. & Zhu, J. Effect of substrate temperature and deposition profile on evaporated Cu(InGa)Se2 films and devices. Thin Solid Films 361–362, 473–477 (2000).

    Article  Google Scholar 

  5. 5

    Chopra, K. L., Paulson, P. D. & Dutta, V. Thin film solar cells: An overview. Prog. Photovolt. 12, 69–92 (2004).

    CAS  Article  Google Scholar 

  6. 6

    Grätzel, M. Photoelectrochemical cells. Nature 414, 338–344 (2001).

    Article  Google Scholar 

  7. 7

    Bernede, J. C. Organic photovoltaic cells: History, principles and techniques. J. Chilean Chem. Soc. 53, 1549–1564 (2008).

    CAS  Article  Google Scholar 

  8. 8

    Kessler, F. & Rudmann, D. Technological aspects of flexible CIGS solar cells and modules. Sol. Energy 77, 685–695 (2004).

    CAS  Article  Google Scholar 

  9. 9

    Niki, S. et al. CIGS absorbers and processes. Prog. Photovolt. 18, 453–466 (2010).

    CAS  Article  Google Scholar 

  10. 10

    Rudmann, D., Brémaud, D. G., Zogg, H. & Tiwari, A. N. Na incorporation into Cu(In,Ga)Se2 for high-efficiency solar cells on polymer foils. J. Appl. Phys. 97, 084903 (2005).

    Article  Google Scholar 

  11. 11

    Caballero, R. et al. High efficiency low temperature grown Cu(In,Ga)Se2 thin film solar cells on flexible substrates using NaF precursor layers. Prog. Photovolt. 19, 547–551 (2011).

    CAS  Article  Google Scholar 

  12. 12

    Nakada, T. et al. Proc. 24th Eur. PV Solar Energy Conf. (EUPVSEC), 3DO.4.3 (WIP—Renewable Energies, 2010).

    Google Scholar 

  13. 13

    Bär, M. et al. Electronic level alignment at the deeply buried absorber/Mo interface in chalcopyrite-based thin film solar cells. Appl. Phys. Lett. 93, 042110 (2008).

    Article  Google Scholar 

  14. 14

    Shay, J. L., Wagner, S. & Kasper, H. M. Efficient CuInSe2/CdS solar cells. Appl. Phys. Lett. 27, 89–99 (1975).

    CAS  Article  Google Scholar 

  15. 15

    Wei, S-H., Zhang, S. B. & Zunger, A. Effects of Ga addition to CuInSe2 on its electronic, structural, and defect properties. Appl. Phys. Lett. 72, 3199–3201 (1998).

    CAS  Article  Google Scholar 

  16. 16

    Gabor, A. M. et al. High-efficiency CuInxGa1−xSe2 solar cells made from (Inx,Ga1−x)2Se3 precursor films. Appl. Phys. Lett. 65, 198–200 (1994).

    CAS  Article  Google Scholar 

  17. 17

    Marudachalam, M. et al. Phases, morphology, and diffusion in CuInxGa1−xSe2 thin films. J. Appl. Phys. 82, 2896–2905 (1997).

    CAS  Article  Google Scholar 

  18. 18

    Contreras, M. A. et al. Graded band-gap Cu(In,Ga)Se2 thin film solar cell absorber with enhanced open-circuit voltage. Appl. Phys. Lett. 63, 1824–1826 (1993).

    CAS  Article  Google Scholar 

  19. 19

    Seyrling, S. et al. Modification of the three-stage evaporation process for CuIn1−xGaxSe2 absorber deposition. Thin Solid Films 519, 7232–7236 (2011).

    CAS  Article  Google Scholar 

  20. 20

    Chirilă, A. et al. Influence of high growth rates on evaporated Cu(In,Ga)Se2 layers and solar cells. Prog. Photovolt. (2011).

  21. 21

    Rudmann, D. et al. Effects of NaF coevaporation on structural properties of Cu(In,Ga)Se2 thin films. Thin Solid Films 431–432, 37–40 (2003).

    Article  Google Scholar 

  22. 22

    Rudmann, D. et al. Sodium incorporation strategies for CIGS growth at different temperatures. Thin Solid Films 480–481, 55–60 (2005).

    Article  Google Scholar 

  23. 23

    Chirilă, A. et al. Proc. 35th IEEE Phot. Spec. Conf. (PVSC) 656–660 (IEEE, 2010).

    Google Scholar 

  24. 24

    Patent pending No. PCT/IB2011/000857.

  25. 25

    Bodegård, M., Lundberg, O., Lu, J. & Stolt, L. Re-crystallisation and interdiffusion in CGS/CIS bilayers. Thin Solid Films 431–432, 46–52 (2003).

    Article  Google Scholar 

  26. 26

    Lundberg, O. Band-Gap Profiling and High Speed Deposition of Cu(In,Ga) Sefor Thin Film Solar Cells. PhD thesis, Uppsala Univ. (2003).

  27. 27

    Gloeckler, M. Device Physics of Cu(In,Ga) SeThin-Film Solar Cells. PhD thesis, Colorado State Univ. (2005).

  28. 28

    Rau, U. & Schock, H. W. Electronic properties of Cu(In,Ga)Se2 heterojunction solar cells recent achievements, current understanding, and future challenges. Appl. Phys. A 69, 131–147 (1999).

    CAS  Article  Google Scholar 

  29. 29

    Burgelman, M., Nollet, P. & Degrave, S. Modelling polycrystalline semiconductor solar cells. Thin Solid Films 361–362, 527–532 (2000).

    Article  Google Scholar 

  30. 30

    Burgelman, M., Verschraegen, J., Degrave, S. & Nollet, P. Modeling thin-film PV devices. Prog. Photovolt. 12, 143–153 (2004).

    CAS  Article  Google Scholar 

  31. 31

    Jackson, P. et al. High quality baseline for high efficiency, Cu(In1−x,Gax)Se2 solar cells. Prog. Photovolt. 15, 507–519 (2007).

    CAS  Article  Google Scholar 

Download references


This work was supported by the Swiss National Science Foundation, the Swiss Federal Office of Energy, the European FP7 Project ‘hipo-CIGS’, and the Commission for Technology and Innovation, Switzerland.

Author information




A.C., S.B., F.P., P.B., S.S., S.N., Y.E.R. and A.N.T. designed the research and experiments. A.C. and P.B. fabricated the solar cells. A.C., S.B., F.P., C.G., A.R.U., C.F., L.K., J.P., R.V., G.B. and A.N.T. performed the characterization, simulation and analysis. A.C., S.B., C.G. and A.N.T. wrote the paper. All authors contributed to discussions.

Corresponding author

Correspondence to Adrian Chirilă.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Chirilă, A., Buecheler, S., Pianezzi, F. et al. Highly efficient Cu(In,Ga)Se2 solar cells grown on flexible polymer films. Nature Mater 10, 857–861 (2011).

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