Upgrade to Pro — share decks privately, control downloads, hide ads and more …

Symmetry-Breaking at Defects in Perovskites

Symmetry-Breaking at Defects in Perovskites

Slides for my talk 'Symmetry-Breaking & Reconstruction at Defects in Perovskites' at MRS Spring 2023, San Francisco – discussing the issue of global optimisation for defects in solids, its particular relevance & importance for perovskites, and our work (ShakeNBreak) on tackling this issue.

YouTube video recording: https://youtu.be/yzevtGjGALI

ShakeNBreak website: https://shakenbreak.readthedocs.io/en/latest/

Our general defect calculation package doped is available here: https://github.com/SMTG-UCL/doped

See our open-access papers on defect structure-searching here:
https://www.nature.com/articles/s41524-023-00973-1
https://joss.theoj.org/papers/10.21105/joss.04817
https://www.nature.com/articles/s41567-023-02049-9

Questions welcome! For other computational photovoltaics, defects and disorder talks, have a look at my YouTube channel!
https://www.youtube.com/SeanRKavanagh
For other research articles see:
https://bit.ly/3pBMxOG

Other references:
Matter Preview of Defect Structure Searching: https://www.sciencedirect.com/science/article/pii/S2590238521002733
Metastable defects : https://doi.org/10.1039/D2FD00043A
Recombination at V_Cd in CdTe (case study): https://pubs.acs.org/doi/abs/10.1021/acsenergylett.1c00380

Seán R. Kavanagh

May 02, 2023
Tweet

More Decks by Seán R. Kavanagh

Other Decks in Research

Transcript

  1. Standard defect supercell relaxation
    Seán R. Kavanagh‡ & Irea Mosquera-Lois,‡
    Aron Walsh, David O. Scanlon
    MRS Spring 2023
    Symmetry-Breaking & Reconstruction at
    Defects in Perovskites

    View Slide

  2. Standard defect supercell relaxation
    Seán R. Kavanagh‡ & Irea Mosquera-Lois,‡
    Aron Walsh, David O. Scanlon
    MRS Spring 2023
    Symmetry-Breaking & Reconstruction at
    Defects in Perovskites

    View Slide

  3. Defect Calculation Workflow
    3
    Host primitive cell
    Goyal et al, Comp Mater Sci 2017

    View Slide

  4. Defect Calculation Workflow
    4
    Host primitive cell
    Goyal et al, Comp Mater Sci 2017

    View Slide

  5. Defect Calculation Workflow
    5

    View Slide

  6. Defect Calculation Workflow
    6

    View Slide

  7. Defect Calculation Workflow
    7

    View Slide

  8. Defect Calculation Workflow
    8

    View Slide

  9. Defect Calculation Workflow
    9

    View Slide

  10. Defect Calculation Workflow
    10

    View Slide

  11. Defect Calculation Workflow
    11
    ➡ Energy
    ➡ Concentration
    ➡ Transition Level
    ➡ Deep/Shallow
    ➡ Doping
    ➡ Carrier capture
    ➡ Diffusion
    ➡ …

    View Slide

  12. VCd
    in CdTe

    View Slide

  13. Metal-metal dimers possible for vacancies in semiconductors:
    Lany & Zunger Phys Rev Lett 2004
    Lany & Zunger Phys Rev B 2005
    VCd
    in CdTe

    View Slide

  14. Metal-metal dimers possible for vacancies in semiconductors:
    Lany & Zunger Phys Rev Lett 2004
    Lany & Zunger Phys Rev B 2005
    VCd
    in CdTe

    View Slide

  15. Metal-metal dimers possible for vacancies in semiconductors:
    Lany & Zunger Phys Rev Lett 2004
    Lany & Zunger Phys Rev B 2005
    VCd
    in CdTe

    View Slide

  16. VCd
    in CdTe Tei
    in CdTe
    Standard Relaxation
    ShakeNBreak
    (Our Method)
    Kavanagh*, Scanlon, Walsh, Freysoldt
    Faraday Discussions 2022

    View Slide

  17. Metal-metal dimers possible for vacancies in semiconductors:
    Lany & Zunger Phys Rev Lett 2004
    Lany & Zunger Phys Rev B 2005
    Kavanagh, Walsh, Scanlon
    ACS Energy Lett 2021
    VCd
    in CdTe

    View Slide

  18. Metal-metal dimers possible for vacancies in semiconductors:
    Lany & Zunger Phys Rev Lett 2004
    Lany & Zunger Phys Rev B 2005
    Kavanagh, Walsh, Scanlon
    ACS Energy Lett 2021
    VCd
    in CdTe

    View Slide

  19. Potentially the Wrong Defect!
    Mosquera-Lois & Kavanagh* Matter 2021
    Kavanagh, Walsh, Scanlon ACS Energy Lett 2021
    Mosquera-Lois‡ & Kavanagh‡*, Walsh and Scanlon*
    npj Comput Mater 2023
    Standard defect supercell relaxation

    View Slide

  20. How Prevalent is This?
    Tested on a diverse range of materials: Si, CdTe, GaAs, Sb2
    S3
    , Sb2
    Se3
    , CeO2
    , In2
    O3
    , ZnO, anatase-TiO2
    Energy-lowering reconstructions, missed by standard relaxations, found in every material studied
    Mosquera-Lois‡ & Kavanagh‡*, Walsh and Scanlon* npj Comput Mater 2023

    View Slide

  21. Defect Calculation Workflow
    21

    View Slide

  22. How Important/Prevalent is This? Very
    Literature Examples (reconstructions found serendipitously or
    through manual searching):
    • Gallium vacancies, migration and compensation in Ga2
    O3
    1
    • Catalytic activity (divalent metal dopants in CeO2
    )2
    • CdTe solar cell performance3,4
    • Defect absorption / bandgap lowering (Sn-doped Cs3
    Bi2
    Br9
    )5
    • Persistent Photoconductivity in Si, GaAs DX centres1,6
    • Oxide polarons (in BiVO4
    )7
    • Colour centres and deep anion vacancies in II-VI compounds8
    1. Varley et al J. Phys.: Condens. Matter 2011
    2. Kehoe, Scanlon, Watson, Chem Mater 2011
    3. Kavanagh, Walsh, Scanlon ACS Energy Lett 2021
    4. Kavanagh*, Scanlon, Walsh, Freysoldt Faraday Discussions 2022
    5. Krajewska, Kavanagh et al. Chem Sci 2021
    6. Du & Zhang Phys Rev B 2005
    7. Osterbacka, Ambrosio, Wiktor J Phys Chem C 2022
    8. Lany & Zunger Phys Rev Lett 2004
    Inaccurate Structure ➡ Inaccurate Formation Energy ➡
    Inaccurate:
    ➡ Energy
    ➡ Concentration
    ➡ Transition Level
    ➡ Deep/Shallow
    ➡ Doping
    ➡ Carrier capture
    ➡ Diffusion
    ➡ …

    View Slide

  23. ShakeNBreak: Summary
    • Obtaining the correct defect structure
    is important!
    • Our current procedure for defect
    calculations is incomplete
    • Energy-lowering reconstructions
    prevalent in a wide & diverse
    range of materials/defects.
    • ShakeNBreak = easily-implemented
    method to combat this and aid the
    accuracy of defect calculations
    shakenbreak.readthedocs.io
    1. Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* npj Comp Mater 2023
    2. Mannodi-Kanakkithodi Nature Physics 2023
    3. Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* J. Open Source Software 2022
    4. Mosquera-Lois & Kavanagh*, Matter 2021
    5. Kavanagh, Walsh, Scanlon ACS Energy Lett 2021
    6. Kavanagh*, Scanlon, Walsh, Freysoldt; Faraday Discussions 2022

    View Slide

  24. Indicators of Defect Reconstructions &
    Metastability
    • Multinary composition
    • Reduced crystal symmetry
    • Space to distort / ‘open’ crystal structures
    • Mixed ionic/covalent bonding
    • Dynamic structure
    (i.e. more complex PES)

    View Slide

  25. Case Study: Double Perovskites (A2
    BIBIIIX6
    )
    Cs2
    AgBiBr6
    Large energy lowering of ΔE: -0.1 – -2.75 eV for many antisite defects
    e.g.

    View Slide

  26. Case Study: Double Perovskites (A2
    BIBIIIX6
    )
    • AgCs
    0, AgCs
    +1 (all AgCs
    charge states)
    • BiCs
    0, BiCs
    +1, BiCs
    +2 (all BiCs
    charge states)
    • BrCs
    0
    • CsAg
    -1, CsAg
    0, CsAg
    +1 (all CsAg
    charge states)
    • BiAg
    0, BiAg
    +1
    • BiAg
    -2, BiAg
    -1, BrAg
    0 (all BrAg
    charge states)
    • AgBi
    -2
    • BrBi
    0, BrBi
    -1, BrBi
    -2, BrBi
    -3, BrBi
    -4 (all BrBi
    charge
    states)
    • AgBr
    0, AgBr
    +1, AgBr
    +2 (all AgBr
    charge states)
    • BiBr
    0, BiBr
    +1, BiBr
    +2, BiBr
    +3, BiBr
    +4, BiBr
    +5 (all BiBr
    charge states)
    • CsBr
    0, CsBr
    +1, CsBr
    +2 (all CsBr
    charge states)
    Cs2
    AgBiBr6
    Large energy lowering of ΔE: -0.1 – -2.75 eV for many antisite defects

    View Slide

  27. BiCs
    0 – Neutral Bismuth-on-Caesium
    Unperturbed; 2 Bi-Br bonds, slightly distorted
    octahedra
    ShakeNBreak: tetra-coordinated Bi-Br, off-centred Ag
    -> ΔE = -1.25 eV

    View Slide

  28. BiCs
    0 – Neutral Bismuth-on-Caesium
    Unperturbed; 2 Bi-Br bonds, slightly distorted
    octahedra
    ShakeNBreak: tetra-coordinated Bi-Br, off-centred Ag
    -> ΔE = -1.25 eV

    View Slide

  29. BiCs
    0 – Neutral Bismuth-on-Caesium
    Unperturbed; 2 Bi-Br bonds, slightly distorted
    octahedra
    ShakeNBreak (metastable): similar tetra-coordinated
    Bi-Br (square planar), off-centred Ag -> ΔE = -1.1 eV

    View Slide

  30. BrAg
    -2 – Fully-ionised Bromine-on-Silver
    Unperturbed; 2 elongated Br-Br bonds,
    undistorted octahedra
    ShakeNBreak: BrAg
    displaces from octahedron centre, gives
    7-fold coordinated Bi and off-centred Ag -> ΔE = -1.5 eV

    View Slide

  31. BiAg
    0 – Neutral Bismuth-on-Silver
    Unperturbed; Bi-Br octahedron replacing
    Ag-Br, minimal distortion
    ShakeNBreak: Tetragonal elongation of BiAg
    octahedron ->
    square-planar coordination, displaced Ag -> ΔE = -0.35 eV

    View Slide

  32. Case Study: Vacancy-Ordered Perovskites (A2
    BIVX6
    )
    AI
    2
    MIVX6
    ≋ A(00/MIV)X3
    Kavanagh et al. ‘Frenkel Excitons in Vacancy-
    Ordered Titanium Halide Perovskites (Cs2
    TiX6
    )’
    J. Phys. Chem. Lett. 2022, 13, 10965–10975
    Kavanagh‡ & Liga‡ et al. In Submission
    Cs2
    TiI6
    Large energy lowering of ΔE: -0.4 – -2.5 eV for many native defects:
    • VTi
    0, VTi
    -1, VTi
    -2, VTi
    -3, VTi
    -4 (all VTi
    charge states)
    • Ii
    0, Ii
    -1 (all Ii
    charge states)
    • Csi
    +1
    • ICs
    0, ICs
    -1, ICs
    -2 (all ICs
    charge states)
    • TiCs
    0, TiCs
    +1, TiCs
    +2, TiCs
    +3 (all TiCs
    charge states)
    • ITi
    0, ITi
    -1
    • TiI
    +2, TiI
    +5

    View Slide

  33. VTi
    -4 – Fully-ionised Titanium Vacancy
    Unperturbed; Slightly contracted octahedron ShakeNBreak: Iodine trimer; ΔE = -0.8 eV

    View Slide

  34. VTi
    -1
    Unperturbed; distorted contracted octahedron ShakeNBreak: double Iodine trimer; ΔE = -1.1 eV

    View Slide

  35. VTi
    -1
    Unperturbed; distorted contracted octahedron ShakeNBreak: double Iodine trimer; ΔE = -1.1 eV

    View Slide

  36. VTi
    0 – Neutral Titanium Vacancy
    Unperturbed; distorted contracted octahedron ShakeNBreak: effective ITi
    + VI
    complex -> ΔE = -1.6 eV

    View Slide

  37. TiCs
    +3 – Fully-ionised Titanium-on-Caesium
    Unperturbed; Ti-Ti bond within
    Iodine octahedron
    ShakeNBreak: Ti split, one goes to vacant octahedral
    site near missing caesium -> ΔE = -2.5 eV

    View Slide

  38. TiI
    +5 – Fully-ionised Titanium-on-Iodine
    Unperturbed; Ti-Ti bond, distorted
    octahedron
    ShakeNBreak: off-centred Ti to vacant octahedral site
    -> ΔE = -2 eV

    View Slide

  39. TiI
    +5 – Fully-ionised Titanium-on-Iodine
    Unperturbed; Ti-Ti bond, distorted octahedron ShakeNBreak: off-centred Ti to vacant octahedral site
    -> ΔE = -2 eV

    View Slide

  40. TiI
    +5 – Fully-ionised Titanium-on-Iodine
    Unperturbed; Ti-Ti bond, distorted octahedron ShakeNBreak: off-centred Ti to vacant octahedral site
    -> ΔE = -2 eV

    View Slide

  41. What about polarons / self-trapped excitons?
    A4
    MIIX6
    :
    ➡ High thermal sensitivity of PL lifetimes
    ➡ Ultra-high spatial and thermal resolution
    devices (for remote thermography)
    MII = Pb, Sn
    1. Yakunin, S. et al. Nature Materials 2019
    2. B. Kang & K. Biswas J. Phys. Chem. Lett. 2018

    View Slide

  42. Previous calculations (unperturbed relaxations) predict tetragonal contracted
    octahedron for self-trapped exciton structure.
    Unperturbed; Tetragonally-Contracted Octahedron ShakeNBreak; Tetragonally-Expanded Octahedron
    ΔE ~ -0.4 (MII = Pb, Sn)

    View Slide

  43. Does it matter?
    Thanks to Dr. Youngkwang Jung @ Cambridge for the figure!
    Initial octahedron structure

    View Slide

  44. Energy-lowering reconstructions prevalent in
    a wide & diverse range of materials/defects.
    44
    Importance of Defect Structure
    Searching!
    shakenbreak.readthedocs.io
    1. Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* npj Comp Mater 2023
    2. Mannodi-Kanakkithodi Nature Physics 2023
    3. Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* J. Open Source Software 2022
    4. Mosquera-Lois & Kavanagh*, Matter 2021
    5. Kavanagh, Walsh, Scanlon ACS Energy Lett 2021
    6. Kavanagh*, Scanlon, Walsh, Freysoldt; Faraday Discussions 2022
    Particularly strong for perovskites, due to:
    • Multinary composition
    • Reduced crystal symmetry
    • Space to distort / ‘open’ crystal structures
    • Presence of ionic & covalent bonding
    • Dynamic crystal structure

    View Slide

  45. Studies using ShakeNBreak (and finding lower energy defect structures):
    • X. Wang, S. R. Kavanagh, D. O. Scanlon, A. Walsh; Under Review at Phys Rev Lett (arXiv: 2302.04901)
    • C. Krajewska, S. R. Kavanagh et al. Chem Sci 2021
    • S. R. Kavanagh*, D. O. Scanlon, A. Walsh, C. Freysoldt Faraday Discussions 2022
    • J. Cen et al; J. Mater. Chem. A (Accepted) 2023
    • J. Willis, Q. Zhou et al. In preparation.
    • Y. T. Huang & S. R. Kavanagh et al. Nature Communications 2022
    • A. Nicolson et al; Under Review at J. Am. Chem. Soc. (ChemRxiv: 10.26434/chemrxiv-2023-7454p)
    • Y. Kumagai et al; In submission
    • A. Samli et al;. In preparation
    Acknowledgements
    Profs David Scanlon & Aron Walsh
    Irea Mosquera-Lois
    @Kavanagh_Sean_

    View Slide

  46. View Slide

  47. Standard Relaxation
    (Metastable)
    Example: Vacancies in Sb2
    Se3
    /Sb2
    S3
    Reveals rare 4-electron negative-U behavior and ultra-
    strong self-compensation in Sb2
    S3
    & Sb2
    Se3
    Difference in predicted VSb
    concentration = 1021
    Our Method
    (Ground-state)
    Wang, Kavanagh, Scanlon, Walsh;
    ‘Four-electron Negative-U Vacancy Defects in Antimony Selenide’
    Under Review (arXiv: 2302.04901)
    Do we expect this behaviour in perovskites?

    View Slide

  48. Key Takeaways
    • Obtaining the correct defect structure
    is important!
    • Our current procedure for defect
    calculations is incomplete
    • Energy-lowering reconstructions
    prevalent in a wide & diverse
    range of materials/defects.
    • ShakeNBreak = easily-implemented
    method to combat this and ensure the
    accuracy of defect calculations
    @Kavanagh_Sean_ [email protected]
    1. Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* npj Comp Mater 2023
    2. Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* J. Open Source Software 2022
    3. Mosquera-Lois & Kavanagh*, Matter 2021
    4. Kavanagh, Walsh, Scanlon ACS Energy Lett 2021
    5. Kavanagh*, Scanlon, Walsh, Freysoldt; Faraday Discussions 2022

    View Slide

  49. How Important is This? Very
    VCd
    -1
    VCd
    0
    h+ e-
    Our Method
    (Ground-state)
    Standard Relaxation
    (Metastable)
    h+ capture
    e– capture
    h+ capture
    e– capture
    Kavanagh, Walsh, Scanlon
    ACS Energy Lett 2021
    Inaccurate Structure ➡ Inaccurate Formation Energy ➡
    Inaccurate:
    ➡ Energy
    ➡ Concentration
    ➡ Transition Level
    ➡ Deep/Shallow
    ➡ Doping
    ➡ Carrier capture
    ➡ Diffusion
    ➡ …

    View Slide

  50. Why isn’t this an issue for bulk structure prediction?
    Good initial guesses from experimental databases, starting us close to the global minimum
    For unknown crystal structure prediction,
    this is a huge avenue of research
    Ø PES exploration
    But defects are unknown structures!
    No database of known defect structures
    Ø Efficient structure-searching techniques
    required

    View Slide

  51. View Slide