Article

CdTe solar cells with open-circuit voltage breaking the 1 V barrier

  • Nature Energy 1, Article number: 16015 (2016)
  • doi:10.1038/nenergy.2016.15
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Abstract

CdTe solar cells have the potential to undercut the costs of electricity generated by other technologies, if the open-circuit voltage can be increased beyond 1 V without significant decreases in current. However, in the past decades, the open-circuit voltage has stagnated at around 800–900 mV. This is lower than in GaAs solar cells, even though GaAs has a smaller bandgap; this is because it is more difficult to achieve simultaneously high hole density and lifetime in II–VI materials than in III–V materials. Here, by doping the CdTe with a Group V element, we report lifetimes in single-crystal CdTe that are nearly radiatively limited and comparable to those in GaAs over a hole density range relevant for solar applications. Furthermore, the deposition on CdTe of nanocrystalline CdS layers that form non-ideal heterointerfaces with 10% lattice mismatch impart no damage to the CdTe surface and show excellent junction transport properties. These results enable the fabrication of CdTe solar cells with open-circuit voltage greater than 1 V.

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References

  1. 1.

    (ed.) Properties of Wide Bandgap II–VI Semiconductors (INSPEC, 1997).

  2. 2.

    , ,  & Carrier density and compensation in semiconductors with multiple dopants and multiple transition energy levels: case of Cu impurities in CdTe. Phys. Rev. B 83, 245207 (2011).

  3. 3.

     & (eds) Handbook of Photovoltaic Science and Engineering Ch. 13, 14 (Wiley, 2011).

  4. 4.

    et al. Doping of polycrystalline CdTe for high-efficiency solar cells on flexible metal foil. Nature Commun. 4, 2306 (2013).

  5. 5.

    ,  & Efficient planar heterojunction perovskite solar cells by vapour deposition. Nature 501, 395–398 (2013).

  6. 6.

    et al. High-efficiency, flexible CdTe solar cells on ultra-thin glass substrates. Appl. Phys. Lett. 106, 133501 (2015).

  7. 7.

    ,  & Polymer solar cells. Nature Photon. 6, 153–161 (2012).

  8. 8.

    et al. High-performance photovoltaic perovskite layers fabricated through intramolecular exchange. Science 348, 1234–1237 (2015).

  9. 9.

    et al. Review of progress toward 20% efficiency flexible CIGS solar cells and manufacturing issues of solar modules. IEEE J. Photovolt. 3, 572–580 (2013).

  10. 10.

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

  11. 11.

    ,  & Interface engineering of inorganic thin-film solar cells – materials-science challenges for advanced physical concepts. Adv. Mater. 21, 4196–4206 (2009).

  12. 12.

     & Physics and chemistry of CdTe/CdS thin film heterojunction photovoltaic devices: fundamental and critical aspects. Energy Environ. Sci. 7, 45–102 (2014).

  13. 13.

     & Efficiency limitations for wide-band-gap chalcopyrite solar cells. Thin Solid Films 480, 241–245 (2005).

  14. 14.

    et al. Interface engineering of highly efficient perovskite solar cells. Science 345, 542–546 (2014).

  15. 15.

    , , ,  & Reduction of Fermi level pinning and recombination at polycrystalline CdTe surfaces by laser irradiation. J. Appl. Phys. 117, 225301 (2015).

  16. 16.

    et al. Control of conduction band offset in wide-gap Cu(In,Ga)Se2 solar cells. Sol. Energy Mater. Sol. Cells 75, 121–126 (2003).

  17. 17.

    , , ,  & Fulleropyrrolidine interlayers: tailoring electrodes to raise organic solar cell efficiency. Science 346, 441–444 (2014).

  18. 18.

    CRC Handbook of Chemistry and Physics 84th edn, Section 12 (CRC, 2003).

  19. 19.

    et al. Time-resolved photoluminescence studies of CdTe solar cells. J. Appl. Phys. 94, 3549–3555 (2003).

  20. 20.

    et al. Intrinsic surface passivation of CdTe. J. Appl. Phys. 118, 155305 (2015).

  21. 21.

    et al. Analysis of bulk and interface phenomena in CdTe/CdS thin-film solar cells. Interface Sci. 12, 259–266 (2004).

  22. 22.

    , ,  & A low-cost non-toxic post-growth activation step for CdTe solar cells. Nature 511, 334–337 (2014).

  23. 23.

    et al. Impact of microstructure on local carrier lifetime in perovskite solar cells. Science 348, 683–686 (2015).

  24. 24.

    , , ,  & CdCl2 treatment, S diffusion, and recombination in polycrystalline CdTe. J. Appl. Phys. 99, 103703 (2006).

  25. 25.

    et al. Tailoring impurity distribution in polycrystalline CdTe solar cells for enhanced minority carrier lifetime. Adv. Energy Mater. 4, 1301400 (2014).

  26. 26.

    et al. Recombination by grain-boundary type in CdTe. J. Appl. Phys. 118, 025702 (2015).

  27. 27.

    et al. Dependence of carrier lifetime on Cu-contacting temperature and ZnTe:Cu thickness in CdS/CdTe thin film solar cells. Thin Solid Films 517, 2370–2373 (2009).

  28. 28.

    , , ,  & Cross-sectional mapping of hole concentrations as a function of copper treatment in CdTe photovoltaic devices. Prog. Photovolt. 23, 1466–1474 (2015).

  29. 29.

    , , ,  & Cu-related recombination in CdS/CdTe solar cells. Thin Solid Films 516, 2251–2254 (2008).

  30. 30.

    , , ,  & Solar cell efficiency tables (version 46). Prog. Photovolt. 23, 805–812 (2015).

  31. 31.

    ,  & CdTe solar cells at the threshold to 20% efficiency. IEEE J. Photovolt. 3, 1389–1393 (2013).

  32. 32.

    , , ,  & Copper inclusion and migration from the back contact in CdTe solar cells. Sol. Energy Mater. Sol. Cells 82, 481–489 (2004).

  33. 33.

    Accelerated stress testing and diagnostic analysis of degradation in CdTe solar cells. In Proc. SPIE 7048, Reliability of Photovoltaic Cells, Modules, Components, and Systems (ed. Dhere, N. G.) 70480N (SPIE, 2008).

  34. 34.

    et al. Optical enhancement of the open-circuit voltage in high quality GaAs solar cells. J. Appl. Phys. 113, 123109 (2013).

  35. 35.

    ,  & Electronic properties of A centers in CdTe: a comparison with experiment. Phys. Rev. B 48, 11726–11731 (1993).

  36. 36.

    , ,  & How polycrystalline devices can outperform single-crystal ones: thin film CdTe/CdS solar cells. Adv. Mater. 16, 879–883 (2004).

  37. 37.

    et al. Physics of grain boundaries in polycrystalline photovoltaic semiconductors. J. Appl. Phys. 117, 112807 (2015).

  38. 38.

    et al. Grain-boundary-enhanced carrier collection in CdTe solar cells. Phys. Rev. Lett. 112, 156103 (2014).

  39. 39.

    et al. Direct imaging of Cl- and Cu-induced short-circuit efficiency changes in CdTe solar cells. Adv. Energy Mater. 4, 1400454 (2014).

  40. 40.

     & The impact of charged grain boundaries on thin-film solar cells and characterization. J. Appl. Phys. 98, 063701 (2005).

  41. 41.

    et al. Dependence of the minority-carrier lifetime on the stoichiometry of CdTe using time-resolved photoluminescence and first-principles calculations. Phys. Rev. Lett. 111, 067402 (2013).

  42. 42.

    et al. Enhanced p-type dopability of P and As in CdTe using non-equilibrium thermal processing. J. Appl. Phys. 118, 025102 (2015).

  43. 43.

    et al. Tuning the Fermi level beyond the equilibrium doping limit through quenching: the case of CdTe. Phys. Rev. B 90, 245202 (2014).

  44. 44.

     & Time-Correlated Single Photon Counting (Academic, 1984).

  45. 45.

    et al. Radiative and interfacial recombination in CdTe heterostructures. Appl. Phys. Lett. 105, 222107 (2014).

  46. 46.

     & Concentration-dependent absorption and spontaneous emission of heavily doped GaAs. J. Appl. Phys. 47, 631–643 (1976).

  47. 47.

    et al. Direct evidence of a buried homojunction in Cu(In,Ga)Se2 solar cells. Appl. Phys. Lett. 82, 127–129 (2003).

  48. 48.

    et al. Development of thin-film Cu(In,Ga)Se2 and CdTe solar cells. Prog. Photovolt. Res. Appl. 12, 93–111 (2004).

  49. 49.

    , , ,  & Optical properties of indium doped CdS thin films. Sol. Energy Mater. 17, 55–64 (1988).

  50. 50.

    ,  & Morphology and electrical properties of In doped CdS thin films. J. Vac. Sci. Technol. A 5, 1956–1959 (1987).

  51. 51.

    , ,  & Characterizing recombination in CdTe solar cells with time-resolved photoluminescence. In Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion Vol. 1, 372–375 (IEEE, 2006).

  52. 52.

    ,  & Numerical modeling of CIGS and CdTe solar cells: setting the baseline. In Proc. 3rd World Conference on Photovoltaic Energy Conversion, 2003 Vol. 1, 491–494 (IEEE, 2003).

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Acknowledgements

The work at NREL and Washington State University is supported by the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, under Contract No. DE-AC36-08GO28308. This research was supported, in part, by Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences, where part of the TEM work was performed, which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, DOE, in collaboration with R. R. Unocic. Other parts of the TEM work were performed at the LeRoy Eyring Center for Solid State Science at Arizona State University in collaboration with T. Aoki. The X-ray diffraction experiments were performed at the University of Tennessee, Knoxville, using instruments procured through the general infrastructure grant of the DOE-Nuclear Energy University Program (DE-NE0000693).

Author information

Affiliations

  1. National Renewable Energy Laboratory, Golden, Colorado 80401, USA

    • J. M. Burst
    • , J. N. Duenow
    • , D. S. Albin
    • , E. Colegrove
    • , M. O. Reese
    • , J. A. Aguiar
    • , C.-S. Jiang
    • , M. M. Al-Jassim
    • , D. Kuciauskas
    •  & W. K. Metzger
  2. Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA

    • M. K. Patel
  3. Center for Materials Research, Washington State University, Pullman, Washington 99164, USA

    • S. Swain
    • , T. Ablekim
    •  & K. G. Lynn

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Contributions

J.M.B., J.N.D., E.C. and D.S.A. established anion doping and fabricated devices. M.O.R. developed surface cleaning and passivation methods. J.A.A., M.K.P., C.-S.J. and M.M.A.-J. directed and executed aberration-corrected STEM, HAADF, EELS, AFM, SKPM, SEM and EDS. D.K. performed two-photon excitation time-correlated single-photon counting. S.S., T.A. and K.G.L. made crystals. W.K.M., J.N.D., D.S.A. and J.M.B. directed research. All authors discussed the results and contributed to the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to W. K. Metzger.

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    Supplementary Information

    Supplementary Figures 1–2, Supplementary Tables 1–2.