Cu2ZnSnS4 solar cells with over 10% power conversion efficiency enabled by heterojunction heat treatment

Abstract

Sulfide kesterite Cu2ZnSnS4 provides an attractive low-cost, environmentally benign and stable photovoltaic material, yet the record power conversion efficiency for such solar cells has been stagnant at around 9% for years. Severe non-radiative recombination within the heterojunction region is a major cause limiting voltage output and overall performance. Here we report a certified 11% efficiency Cu2ZnSnS4 solar cell with a high 730 mV open-circuit voltage using heat treatment to reduce heterojunction recombination. This heat treatment facilitates elemental inter-diffusion, directly inducing Cd atoms to occupy Zn or Cu lattice sites, and promotes Na accumulation accompanied by local Cu deficiency within the heterojunction region. Consequently, new phases are formed near the hetero-interface and more favourable conduction band alignment is obtained, contributing to reduced non-radiative recombination. Using this approach, we also demonstrate a certified centimetre-scale (1.11 cm2) 10% efficiency Cu2ZnSnS4 photovoltaic device; the first kesterite cell (including selenium-containing) of standard centimetre-size to exceed 10%.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: Photovoltaic device properties for the 11.0% efficient solar cell.
Fig. 2: Recombination origin analyses.
Fig. 3: Elemental inter-diffusion and high-resolution imaging.
Fig. 4: Accumulation of Na.
Fig. 5: Band alignment at the p–n junction.

References

  1. 1.

    Green, M. A. Commercial progress and challenges for photovoltaics. Nat. Energy 1, 15015 (2016).

    Article  Google Scholar 

  2. 2.

    Antunez, P. D., Bishop, D. M., Luo, Y. & Haight, R. Efficient kesterite solar cells with high open-circuit voltage for applications in powering distributed devices. Nat. Energy 2, 884–890 (2017).

    Article  Google Scholar 

  3. 3.

    Green, M. A. et al. Solar cell efficiency tables (version 51). Progress. Photovolt. Res. Appl. 26, 3–12 (2018).

    Article  Google Scholar 

  4. 4.

    Shin, D., Saparov, B. & Mitzi, D. B. Defect engineering in multinary earth-abundant chalcogenide photovoltaic materials. Adv. Energy Mater. 7, 1602366 (2017).

    Article  Google Scholar 

  5. 5.

    Shin, B. et al. Thin film solar cell with 8.4% power conversion efficiency using an earth-abundant Cu2ZnSnS4 absorber. Progress. Photovolt. Res. Appl. 21, 72–76 (2013).

    Article  Google Scholar 

  6. 6.

    Tajima, S., Umehara, M., Hasegawa, M., Mise, T. & Itoh, T. Cu2ZnSnS4 photovoltaic cell with improved efficiency fabricated by high-temperature annealing after CdS buffer-layer deposition. Progress. Photovolt. Res. Appl. 25, 14–22 (2017).

    Article  Google Scholar 

  7. 7.

    Polman, A., Knight, M., Garnett, E. C., Ehrler, B. & Sinke, W. C. Photovoltaic materials: present efficiencies and future challenges. Science 352, aad4424 (2016).

    Article  Google Scholar 

  8. 8.

    Hiroi, H., Iwata, Y., Adachi, S., Sugimoto, H. & Yamada, A. New world-record efficiency for pure-sulfide Cu(In,Ga)S2 thin-film solar cell with cd-free buffer layer via KCN-free process. IEEE J. Photovolt. 6, 760–763 (2016).

    Article  Google Scholar 

  9. 9.

    Gokmen, T., Gunawan, O., Todorov, T. K. & Mitzi, D. B. Band tailing and efficiency limitation in kesterite solar cells. Appl. Phys. Lett. 103, 103506 (2013).

    Article  Google Scholar 

  10. 10.

    Mitzi, D. B., Gunawan, O., Todorov, T. K., Wang, K. & Guha, S. The path towards a high-performance solution-processed kesterite solar cell. Sol. Energy Mater. Sol. Cells 95, 1421–1436 (2011).

    Article  Google Scholar 

  11. 11.

    Scragg, J. J. et al. Effects of back contact instability on Cu2ZnSnS4 devices and processes. Chem. Mater. 25, 3162–3171 (2013).

    Article  Google Scholar 

  12. 12.

    Siebentritt, S. Why are kesterite solar cells not 20% efficient? Thin Solid Films 535, 1–4 (2013).

    Article  Google Scholar 

  13. 13.

    Crovetto, A. & Hansen, O. What is the band alignment of Cu2ZnSn(S,Se)4 solar cells? Sol. Energy Mater. Sol. Cells 169, 177–194 (2017).

    Article  Google Scholar 

  14. 14.

    Liu, F. et al. Beyond 8% ultrathin kesterite Cu2ZnSnS4 solar cells by interface reaction route controlling and self-organized nanopattern at the back contact. NPG Asia Mater. 9, e401 (2017).

    Article  Google Scholar 

  15. 15.

    Vermang, B. et al. Rear surface optimization of CZTS solar cells by use of a passivation layer with nanosized point openings. IEEE J. Photovolt. 6, 332–336 (2016).

    Article  Google Scholar 

  16. 16.

    Redinger, A., Berg, D. M., Dale, P. J. & Siebentritt, S. The consequences of kesterite equilibria for efficient solar cells. J. Am. Chem. Soc. 133, 3320–3323 (2011).

    Article  Google Scholar 

  17. 17.

    Chen, S., Walsh, A., Gong, X.-G. & Wei, S.-H. Classification of lattice defects in the kesterite Cu2ZnSnS4 and Cu2ZnSnSe4 earth-abundant solar cell absorbers. Adv. Mater. 25, 1522–1539 (2013).

    Article  Google Scholar 

  18. 18.

    Larramona, G. et al. Fine-tuning the Sn content in CZTSSe thin films to achieve 10.8% solar cell efficiency from spray-deposited water–ethanol-based colloidal inks. Adv. Energy Mater. 5, 1501404 (2015).

    Article  Google Scholar 

  19. 19.

    Liu, F. et al. Nanoscale microstructure and chemistry of Cu2ZnSnS4/CdS interface in kesterite Cu2ZnSnS4 solar cells. Adv. Energy Mater. 6, 1600706 (2016).

    Article  Google Scholar 

  20. 20.

    Sun, K. et al. Over 9% efficient kesterite Cu2ZnSnS4 solar cell fabricated by using Zn1–xCdxS buffer layer. Adv. Energy Mater. 6, 1600046 (2016).

    Article  Google Scholar 

  21. 21.

    Yan, C. et al. Beyond 11% efficient sulfide kesterite Cu2ZnxCd1–xSnS4 solar cell: effects of cadmium alloying. ACS Energy Lett. 2, 930–936 (2017).

  22. 22.

    Ericson, T. et al. Zinc-tin-oxide buffer layer and low temperature post annealing resulting in a 9.0% efficient Cd-Free Cu2ZnSnS4 solar cell. Sol. RRL 1, 1700001 (2017).

    Article  Google Scholar 

  23. 23.

    Shin, T., Mitsutaro, U. & Takahiro, M. Photovoltaic properties of Cu2ZnSnS4 cells fabricated using ZnSnO and ZnSnO/CdS buffer layers. Jpn J. Appl. Phys. 55, 112302 (2016).

    Article  Google Scholar 

  24. 24.

    Platzer-Björkman, C. et al. Reduced interface recombination in Cu2ZnSnS4 solar cells with atomic layer deposition Zn1−xSnxOy buffer layers. Appl. Phys. Lett. 107, 243904 (2015).

    Article  Google Scholar 

  25. 25.

    Shin, T., Tadayoshi, I., Hirofumi, H., Keiichiro, O. & Ryoji, A. Improvement of the open-circuit voltage of Cu2ZnSnS4 solar cells using a two-layer structure. Appl. Phys. Express 8, 082302 (2015).

    Article  Google Scholar 

  26. 26.

    Gunawan, O., Gokmen, T., Shin, B. S. & Guha, S. Device characteristics of high performance Cu2ZnSnS4 solar cell. In 38th IEEE Photovoltaic Specialists Conf. 003001–003003 (2012).

  27. 27.

    Jackson, P. et al. Effects of heavy alkali elements in Cu(In,Ga)Se2 solar cells with efficiencies up to 22.6%. Phys. Status Solidi RRL 10, 583–586 (2016).

    Article  Google Scholar 

  28. 28.

    Kannan, R., Keane, J. & Noufi, R. Properties of high-efficiency CIGS thin-film solar cells. In 31st IEEE Photovoltaic Specialists Conf. 195–198 (2005).

  29. 29.

    Green, M. A. et al. Solar cell efficiency tables (version 49). Progress. Photovolt. Res. Appl. 25, 3–13 (2017).

    Article  Google Scholar 

  30. 30.

    Tajima, S. et al. Atom-probe tomographic study of interfaces of Cu2ZnSnS4 photovoltaic cells. Appl. Phys. Lett. 105, 093901 (2014).

    Article  Google Scholar 

  31. 31.

    Sousa, M. G. et al. Optimization of post-deposition annealing in Cu2ZnSnS4 thin film solar cells and its impact on device performance. Sol. Energy Mater. Sol. Cells 170, 287–294 (2017).

    Article  Google Scholar 

  32. 32.

    Wen, X. et al. Ultrafast electron transfer in the nanocomposite of the graphene oxide-Au nanocluster with graphene oxide as a donor. J. Mater. Chem. C 2, 3826–3834 (2014).

    Article  Google Scholar 

  33. 33.

    Kunz, O., Varlamov, S. & Aberle, A. G. Modelling the effects of distributed series resistance on Suns-VOC, m-VOC and JSC-Suns curves of solar cells. In 34th IEEE Photovoltaic Specialists Conf. 000158–000163 (2009).

  34. 34.

    Sah, Ct, Noyce, R. N. & Shockley, W. Carrier generation and recombination in P-N junctions and P-N junction characteristics. Proc. IRE 45, 1228–1243 (1957).

    Article  Google Scholar 

  35. 35.

    Todorov, T. K. et al. Beyond 11% efficiency: characteristics of state-of-the-art Cu2ZnSn(S,Se)4 solar cells. Adv. Energy Mater. 3, 34–38 (2013).

    Article  Google Scholar 

  36. 36.

    Bhattacharya, R. N. et al. High efficiency thin-film CuIn1−xGaxSe2 photovoltaic cells using a Cd1−xZnxS buffer layer. Appl. Phys. Lett. 89, 253503 (2006).

    Article  Google Scholar 

  37. 37.

    Tosun, B. S., Pettit, C., Campbell, S. A. & Aydil, E. S. Structure and composition of ZnxCd1–xS films synthesized through chemical bath deposition. Acs Appl. Mater. Inter. 4, 3676–3684(2012).

    Article  Google Scholar 

  38. 38.

    Nellist, P. D. & Pennycook, S. J. Incoherent imaging using dynamically scattered coherent electrons. Ultramicroscopy 78, 111–124 (1999).

    Article  Google Scholar 

  39. 39.

    Rafferty, B., Nellist, D. & Pennycook, J. On the origin of transverse incoherence in Z-contrast STEM. J. Electron Microsc. 50, 227–233 (2001).

    Google Scholar 

  40. 40.

    Yuan, Z.-K. et al. Engineering solar cell absorbers by exploring the band alignment and defect disparity: the case of Cu- and Ag-based kesterite compounds. Adv. Funct. Mater. 25, 6733–6743 (2015).

    Article  Google Scholar 

  41. 41.

    Su, Z. et al. Cation substitution of solution-processed Cu2ZnSnS4 thin film solar cell with over 9% efficiency. Adv. Energy Mater. 5, 1500682 (2015).

    Article  Google Scholar 

  42. 42.

    Hironiwa, D. et al. Impact of annealing treatment before buffer layer deposition on Cu2ZnSn(S,Se)4 solar cells. Thin Solid Films 582, 151–153 (2015).

    Article  Google Scholar 

  43. 43.

    Xie, H. et al. Impact of Na dynamics at the Cu2ZnSn(S,Se)4/CdS interface during post low temperature treatment of absorbers. Acs Appl. Mater. Inter. 8, 5017–5024 (2016).

    Article  Google Scholar 

  44. 44.

    Li, J. V., Kuciauskas, D., Young, M. R. & Repins, I. L. Effects of sodium incorporation in Co-evaporated Cu2ZnSnSe4 thin-film solar cells. Appl. Phys. Lett. 102, 163905 (2013).

    Article  Google Scholar 

  45. 45.

    Liu, C.-Y. et al. Sodium passivation of the grain boundaries in CuInSe2 and Cu2ZnSnS4 for high-efficiency solar cells. Adv. Energy Mater. 7, 1601457 (2017).

    Article  Google Scholar 

  46. 46.

    Chirilă, A. et al. Potassium-induced surface modification of Cu(In,Ga)Se2 thin films for high-efficiency solar cells. Nat. Mater. 12, 1107–1111 (2013).

    Article  Google Scholar 

  47. 47.

    Santoni, A. et al. Valence band offset at the CdS/Cu2ZnSnS4 interface probed by x-ray photoelectron spectroscopy. J. Phys. D 46, 175101 (2013).

    Article  Google Scholar 

  48. 48.

    Minemoto, T. et al. Theoretical analysis of the effect of conduction band offset of window/CIS layers on performance of CIS solar cells using device simulation. Sol. Energy Mater. Sol. Cells 67, 83–88 (2001).

    Article  Google Scholar 

Download references

Acknowledgements

This contribution has been financially supported by the Australian Government through the Australian Renewable Energy Agency (ARENA) (grant no. 1-USO028 and 1-SRI001) and the Australian Research Council (ARC) and Baosteel (grant no. LP150100911). The authors thank C. Kong and K. Levick for technical assistance and use of facilities at the Electron Microscope Unit at University of New South Wales. The authors acknowledge the facilities, and the scientific and technical assistance, of the Australian Microscopy and Microanalysis Research Facility at the Australian Centre for Microscopy and Microanalysis at the University of Sydney. The authors appreciate the use of facilities and the assistance of D. Mitchell and G. Casillas Garcia at the University of Wollongong Electron Microscopy Centre. We thank R. Liu at the Western Sydney University SIMS Facility. C.Y. would like to acknowledge the insightful discussions with Z. Su, H. Sugimoto, H. Hiroi and A. Crovetto.

Author information

Affiliations

Authors

Contributions

M.A.G. and X.H. supervised the whole project. C.Y., F.L. and X.H conceived the idea and designed the experiments. C.Y. and Y.Z. fabricated the solar cell devices. J.H. prepared TEM specimens and performed HAADF characterizations. K.S. assisted TRPL characterizations. S.J. conducted temperature-dependent measurements. L.Y. and K.E. prepared APT samples and conducted APT measurements, respectively. C.Y., J.H., K.S., A.P., S.J., K.E., J.M.C., N.J.E.-D., S.C., Z.H. and H.S. analysed the data. Z.H., F.L. and M.H. helped with characterizations, J.A.S., F.L., H.S. and M.H. assisted the experiments. C.Y., J.H., X.H. and M.A.G. wrote the paper. All authors commented on the manuscript.

Corresponding authors

Correspondence to Fangyang Liu or Xiaojing Hao.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figures 1–19, Supplementary Tables 1–9, Supplementary Notes 1–4, Supplementary References

Reporting Summary

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Yan, C., Huang, J., Sun, K. et al. Cu2ZnSnS4 solar cells with over 10% power conversion efficiency enabled by heterojunction heat treatment. Nat Energy 3, 764–772 (2018). https://doi.org/10.1038/s41560-018-0206-0

Download citation

Further reading

Search

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