Hidden Spontaneous Polarisation in the ns2-Cation Sn2SbS2I3 Chalcohalide Photovoltaic Absorber

Slides for my SMTG Group Meeting talk on 'Hidden Spontaneous Polarisation in the ns2-Cation Sn2SbS2I3 Chalcohalide Photovoltaic Absorber' in June 2021.

Open-access Materials Horizons paper at: https://doi.org/10.1039/D1MH00764E

YouTube talk on this work here:
https://www.youtube.com/watch?v=H8cvJfZq8S8&t=1s

Questions welcome!

Also find our open-access review on perovskite-inspired materials here: https://iopscience.iop.org/article/10.1088/1361-6528/abcf6d

Transcript

1. Hidden Spontaneous Polarisation in the
   Sn2
   SbS2
   I3
   Chalcohalide Photovoltaic
   Absorber
   Seán Kavanagh, Christopher
   N. Savory, Aron Walsh,
   David O. Scanlon
   SMTG Group Meeting June 2021
   

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2. Sn2
   SbS2
   I3
   – ‘Perovskite-Inspired’
   • Novel ns2-cation chalco-halide.
   • Mixed anions (and cations) allows mixed
   ionic-covalent character.
   • Strong dielectric screening?
   • Lattice polarity?
   • Defect Tolerance?
   • Nie et al. (Group of Sang Il Seok),
   demonstrated >4% efficiency in the first
   experimental device fabrication (Nov 2020).
   1. R. Nie, K. S. Lee, M. Hu, M. J. Paik and S. I. Seok, Heteroleptic Tin-Antimony Sulfoiodide for Stable and Lead-free Solar
   Cells. 2020 Matter, S2590238520304471.
   

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3. Sn2
   SbS2
   I3
   – ‘Perovskite-Inspired’
   Project Plan:
   Quick characterisation of bulk structural
   and electronic properties.
   • Structural Relaxation
   • Dielectric Properties
   • Electronic Structure
   • Optical Absorption
   • Efficiency Potential (SLME / Blank)
   

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4. Sn2
   SbS2
   I3
   – ‘Perovskite-Inspired’
   Project Plan:
   Quick characterisation of bulk structural
   and electronic properties.
   • Structural Relaxation
   • Dielectric Properties
   • Electronic Structure
   • Optical Absorption
   • Efficiency Potential (SLME / Blank)
   

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5. Sn2
   SbS2
   I3
   – Structural Relaxation
   A. Ibanez, J.-C. Jumas, J. Olivier-Fourcade and E. Philippot, Journal of Solid State Chemistry, 1984, 55, 83–91.
   

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6. Sn2
   SbS2
   I3
   – Structural Relaxation
   Sn
   Sb
   S
   I
   Cmcm Cmc2
   1
   b
   c
   ΔE(Cmc21
   /Cmcm) =
   -35.8 meV/atom
   (RPA w/ HSE06 orbitals)
   

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7. Sn2
   SbS2
   I3
   – Structural Relaxation
   Sn
   Sb
   S
   I
   Cmcm Cmc2
   1
   b
   c
   ΔE(Cmc21
   /Cmcm) =
   -35.8 meV/atom
   (RPA w/ HSE06 orbitals)
   

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8. Sn2
   SbS2
   I3
   – Dynamic Stability
   Cmcm Cmc21
   

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9. Sn2
   SbS2
   I3
   – Structural Relaxation
   A. Ibanez, J.-C. Jumas, J. Olivier-Fourcade and E. Philippot, Journal of Solid State Chemistry, 1984, 55, 83–91.
   

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10. Sn2
    SbS2
    I3
    – Structural Relaxation
    

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11. Sn2
    SbS2
    I3
    – Structural Relaxation
    

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12. Sn2
    SbS2
    I3
    – Structural Relaxation
    

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13. Sn2
    SbS2
    I3
    – Structural Relaxation
    

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14. Sn2
    SbS2
    I3
    – Structural Relaxation
    

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15. Sn2
    SbS2
    I3
    – Structural Relaxation
    

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16. Sn2
    SbS2
    I3
    – Spontaneous Polarisation
    Cmcm ⟹ Cmc21
    ΔP(Cmc21
    /Cmcm) =
    37 μC/cm2
    (optB86b-vdW)
    c.f. BaTiO3
    (∼27 μC/cm2),
    KNbO3
    (∼30 μC/cm2),
    MAPbI3
    (4.4 μC/cm2),
    SbSI (11 μC/cm2)
    

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17. Sn2
    SbS2
    I3
    – Molecular Dynamics
    ΔP =
    37 μC/cm2
    

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18. Molecular Dynamics: T= 300K
    

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19. Molecular Dynamics: T= 500K
    

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20. Sn2
    SbS2
    I3
    – Electronic & Optical Properties
    Eg
    = 1.08 eV (HSE06 + SOC)
    

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21. Electronic & Optical Properties: Cmcm
    

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22. Electronic & Optical Properties: Cmcm
    

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23. Electronic & Optical Properties: Cmc21
    

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24. Electronic & Optical Properties: Cmc21
    

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25. Sn2
    SbS2
    I3
    – Electronic & Optical Properties
    

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26. Sn2
    SbS2
    I3
    – Potential Defect Tolerance
    Eg
    = 1.08 eV (HSE06 + SOC)
    - Small band gap
    - Anti-bonding character, high-
    energy VBM (Sn 5s2 – anion p)
    - Mixed ionic-covalent bonding:
    - Strong dielectric screening
    - Wide conduction &
    valence bands
    - Atomic-chain structure (⟹
    benign grain boundaries?)
    PL lifetime >7 ns recorded by Nie
    et al.
    R. Nie, K. S. Lee, M. Hu, M. J. Paik and S. I. Seok, Heteroleptic Tin-Antimony Sulfoiodide for Stable and Lead-free Solar Cells. 2020 Matter, S2590238520304471.
    

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27. Conclusions & Acknowledgements
    Spontaneous symmetry breaking and lattice polarization,
    hidden by macroscopic averaging, unveiled in Sn2
    SbS2
    I3
    .
    o Potential benefits for charge separation and PV efficiency.
    Promising outlook for the application in high-efficiency solution-
    processed solar cells.
    

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