Nano-scale compositional analysis of surfaces and interfaces in earth-abundant kesterite solar cells

Abstract

Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) absorbers are considered promising alternatives to commercial thin film technologies including CdTe and Cu(In,Ga)Se2 (CIGSe) owing to the earth abundance and non-toxicity of their constituents. However, to be competitive with the existing technologies, the photovoltaic performance of CZTSSe solar cells needs to be improved beyond the current record conversion efficiency of 12.6%. In this study, nanoscale elemental mapping using Auger nanoprobe microscopy (NanoAuger) and nano secondary ion mass spectrometry (NanoSIMS) are used to provide a clear picture of the compositional variations between the grains and grain boundaries in Cu2ZnSn(S,Se)4 kesterite thin films. NanoAuger measurements revealed that the top surfaces of the grains are coated with a Zn-rich (Zn,Sn)Ox layer. While thick oxide layers were observed at the grain boundaries, their chemical compositions were found to be closer to SnOx. NanoSIMS elemental maps confirmed the presence of excess oxygen deeper within the grain boundary grooves, as a result of air annealing of the CZTSSe films.

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References

  1. 1.

    C. Candelise, M. Winskel, and R. Gross: Implications for CdTe and CIGS technologies production costs of indium and tellurium scarcity. Prog. Photovoltaics 20 (6), 816 (2012).

    Article  Google Scholar 

  2. 2.

    D.B. Mitzi, O. Gunawan, T.K. Todorov, and D.A.R. Barkhouse: Prospects and performance limitations for Cu–Zn–Sn–S–Se photovoltaic technology. Philos. Trans. R. Soc., A 371, 20110432 (2013).

    Article  Google Scholar 

  3. 3.

    X.L. Liu, Y. Feng, H.T. Cui, F.Y. Liu, X.J. Hao, G. Conibeer, D.B. Mitzi, and M. Green: The current status and future prospects of kesterite solar cells: A brief review. Prog. Photovoltaics 24 (6), 879 (2016).

    Article  Google Scholar 

  4. 4.

    W. Wang, M.T. Winkler, O. Gunawan, T. Gokmen, T.K. Todorov, Y. Zhu, and D.B. Mitzi: Device characteristics of CZTSSe thin-film solar cells with 12.6% efficiency. Adv. Energy Mater. 4 (7), 1301465 (2014).

    Article  Google Scholar 

  5. 5.

    E. Chagarov, K. Sardashti, A.C. Kummel, Y.S. Lee, R. Haight, and T.S. Gershon: Ag2ZnSn(S,Se)(4): A highly promising absorber for thin film photovoltaics. J. Chem. Phys. 144 (10), 104704 (2016).

    Article  Google Scholar 

  6. 6.

    N.A. Kattan, I.J. Griffiths, D. Cherns, and D.J. Fermin: Observation of antisite domain boundaries in Cu2ZnSnS4 by atomic-resolution transmission electron microscopy. Nanoscale 8, 14369 (2016).

    CAS  Article  Google Scholar 

  7. 7.

    T. Gokmen, O. Gunawan, T.K. Todorov, and D.B. Mitzi: Band tailing and efficiency limitation in kesterite solar cells. Appl. Phys. Lett. 103 (10), 103506 (2013).

    Article  Google Scholar 

  8. 8.

    J.J. Scragg, P.J. Dale, D. Colombara, and L.M. Peter: Thermodynamic aspects of the synthesis of thin-film materials for solar cells. ChemPhysChem 13 (12), 3035 (2012).

    CAS  Article  Google Scholar 

  9. 9.

    C.S. Jiang, M.A. Contreras, I. Repins, H.R. Moutinho, Y. Yan, M.J. Romero, L.M. Mansfield, R. Noufi, and M.M. Al-Jassim: How grain boundaries in Cu(In,Ga)Se-2 thin films are charged: Revisit. Appl. Phys. Lett. 101 (3), 033903 (2012).

    Article  Google Scholar 

  10. 10.

    C.S. Jiang, I.L. Repins, L.M. Mansfield, M.A. Contreras, H.R. Moutinho, K. Ramanathan, R. Noufi, and M.M. Al-Jassim: Electrical conduction channel along the grain boundaries of Cu(In,Ga)Se-2 thin films. Appl. Phys. Lett. 102 (25), 253905 (2013).

    Article  Google Scholar 

  11. 11.

    K. Sardashti, R. Haight, R. Anderson, M. Contreras, B. Fruhberger, and A.C. Kummel: Grazing incidence cross-sectioning of thin-film solar cells via cryogenic focused ion beam: A case study on CIGSe. ACS Appl. Mater. Interfaces. 8 (24), 14994 (2016).

    CAS  Article  Google Scholar 

  12. 12.

    D. Abou-Ras, S.S. Schmidt, R. Caballero, T. Unold, H.W. Schock, C.T. Koch, B. Schaffer, M. Schaffer, P.P. Choi, and O. Cojocaru-Miredin: Confined and chemically flexible grain boundaries in polycrystalline compound semiconductors. Adv. Energy Mater. 2 (8), 992 (2012).

    CAS  Article  Google Scholar 

  13. 13.

    M.E. Erkan, V. Chawla, I. Repins, and M.A. Scarpulla: Interplay between surface preparation and device performance in CZTSSe solar cells: Effects of KCN and NH4OH etching. Sol. Energy Mater. Sol. Cells 136, 78 (2015).

    CAS  Article  Google Scholar 

  14. 14.

    C.S. Jiang, I.L. Repins, C. Beall, H.R. Moutinho, K. Ramanathan, and M.M. Al-Jassim: Investigation of micro-electrical properties of Cu2ZnSnSe4 thin films using scanning probe microscopy. Sol. Energy Mater. Sol. Cells 132, 342 (2015).

    CAS  Article  Google Scholar 

  15. 15.

    H. Xin, S.M. Vorpahl, A.D. Collord, I.L. Braly, A.R. Uhl, B.W. Krueger, D.S. Ginger, and H.W. Hillhouse: Lithium-doping inverts the nanoscale electric field at the grain boundaries in Cu2ZnSn(S,Se)(4) and increases photovoltaic efficiency. Phys. Chem. Chem. Phys. 17 (37), 23859 (2015).

    CAS  Article  Google Scholar 

  16. 16.

    T. Gershon, B. Shin, N. Bojarczuk, M. Hopstaken, D.B. Mitzi, and S. Guha: The role of sodium as a surfactant and suppressor of non-radiative recombination at internal surfaces in Cu2ZnSnS4. Adv. Energy Mater. 5 (2), 1400849 (2015).

    Article  Google Scholar 

  17. 17.

    J.H. Kim, S.Y. Choi, M. Choi, T. Gershon, Y.S. Lee, W. Wang, B. Shin, and S.Y. Chung: Atomic-scale observation of oxygen substitution and its correlation with hole-transport barriers in Cu2ZnSnSe4 thin-film solar cells. Adv. Energy Mater. 6 (6), 1501902 (2016).

    Article  Google Scholar 

  18. 18.

    K. Sardashti, R. Haight, T. Gokmen, W. Wang, L.Y. Chang, D.B. Mitzi, and A.C. Kummel: Impact of nanoscale elemental distribution in high-performance kesterite solar cells. Adv. Energy Mater. 5 (10), 1402180 (2015).

    Article  Google Scholar 

  19. 19.

    R. Haight, X.Y. Shao, W. Wang, and D.B. Mitzi: Electronic and elemental properties of the Cu2ZnSn(S,Se)(4) surface and grain boundaries. Appl. Phys. Lett. 104 (3), 033902 (2014).

    Article  Google Scholar 

  20. 20.

    K. Hiepko, J. Bastek, R. Schlesiger, G. Schmitz, R. Wuerz, and N.A. Stolwijk: Diffusion and incorporation of Cd in solar-grade Cu(In,Ga)Se-2 layers. Appl. Phys. Lett. 99 (23), 234101 (2011).

    Article  Google Scholar 

  21. 21.

    T. Nakada and A. Kunioka: Direct evidence of Cd diffusion into Cu(In,Ga)Se-2 thin films during chemical-bath deposition process of CdS films. Appl. Phys. Lett. 74 (17), 2444 (1999).

    CAS  Article  Google Scholar 

  22. 22.

    D.A.R. Barkhouse, O. Gunawan, T. Gokmen, T.K. Todorov, and D.B. Mitzi: Device characteristics of a 10.1% hydrazine-processed Cu2ZnSn(Se,S)4 solar cell. Prog. Photovoltaics 20 (1), 6 (2012).

    CAS  Article  Google Scholar 

  23. 23.

    T.K. Todorov, K.B. Reuter, and D.B. Mitzi: High-efficiency solar cell with earth-abundant liquid-processed absorber. Adv. Mater. 22 (20), E156 (2010).

    CAS  Article  Google Scholar 

  24. 24.

    T.K. Todorov, J. Tang, S. Bag, O. Gunawan, T. Gokmen, Y. Zhu, and D.B. Mitzi: Beyond 11% efficiency: Characteristics of state-of-the-art Cu2ZnSn(S,Se)(4) solar cells. Adv. Energy Mater. 3 (1), 34 (2013).

    CAS  Article  Google Scholar 

  25. 25.

    A. Jablonski and C.J. Powell: Information depth and the mean escape depth in Auger electron spectroscopy and X-ray photoelectron spectroscopy. J. Vac. Sci. Technol., A 21 (1), 274 (2003).

    CAS  Article  Google Scholar 

  26. 26.

    A. Jablonski and C.J. Powell: Practical expressions for the mean escape depth, the information depth, and the effective attenuation length in Auger-electron spectroscopy and x-ray photoelectron spectroscopy. J. Vac. Sci. Technol., A 27 (2), 253 (2009).

    CAS  Article  Google Scholar 

  27. 27.

    L.C. Lynn and R.L. Opila: Chemical-shifts in the MNN Auger-spectra of Cd, in, Sn, Sb and Te. Surf. Interface Anal. 15 (2), 180 (1990).

    CAS  Article  Google Scholar 

  28. 28.

    I. Milosev, T.K. Mikic, and M. Gaberscek: The effect of Cu-rich sub-layer on the increased corrosion resistance of Cu–x Zn alloys in chloride containing borate buffer. Electrochim. Acta 52 (2), 415 (2006).

    CAS  Article  Google Scholar 

  29. 29.

    M. Bar, B.A. Schubert, B. Marsen, S. Krause, S. Pookpanratana, T. Unold, L. Weinhardt, C. Heske, and H.W. Schock: Native oxidation and Cu-poor surface structure of thin film Cu2ZnSnS4 solar cell absorbers. Appl. Phys. Lett. 99 (11), 112103 (2011).

    Article  Google Scholar 

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ACKNOWLEDGMENTS

The information, data, or work presented herein was funded in part by the U.S. Department of Energy, Energy Efficiency and Renewable Energy Program, under Award Number DE-EE0006334. The information, data, or work presented herein was funded in part by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof; see the Supporting Information section of this article for more information. Part of this work was performed at the Stanford NanoShared Facility (SNSF). The CAMECA nanoSIMS 50L was supported by the National Science Foundation under award # 0922648. Special thanks to Liang-Yi Chang for supplying the CZTSSe films used in these investigations. Funding for the technique development was also provided by National Science Foundation Grant DMR 1207213.

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Correspondence to Andrew C. Kummel.

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Sardashti, K., Paul, D., Hitzman, C. et al. Nano-scale compositional analysis of surfaces and interfaces in earth-abundant kesterite solar cells. Journal of Materials Research 31, 3473–3481 (2016). https://doi.org/10.1557/jmr.2016.389

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