Disorder Tolerance? Impact of Cation Disorder in ABZ₂ Chalcogenides

Slides from my talk 'Cation Disorder and Solar Cell Performance in ABZ₂ Chalcogenides (AgBiS₂ and NaBiS₂)' at MRS Spring 2023 in San Francisco.

YouTube video recording: https://youtu.be/h1vU2dmnJVw

Papers Discussed:
AgBiS₂: https://www.nature.com/articles/s41566-021-00950-4
NaBiS₂ (open-access): https://www.nature.com/articles/s41467-022-32669-3

Questions welcome! For other computational photovoltaics, defects and disorder talks, have a look at my YouTube channel!
https://www.youtube.com/SeanRKavanagh

If you're interested in this work, you can check out our recent review on these and other perovskite-inspired materials:
https://iopscience.iop.org/article/10.1088/1361-6528/abcf6d

For more info about me and my research articles see:
https://seankavanagh.com

Transcript

1. 1
   02/05/2023
   Cation Disorder and Solar Cell
   Performance in ABZ2
   Materials
   (NaBiS2
   & AgBiS2
   )
   Seán Kavanagh
   Profs: David O. Scanlon & Aron Walsh
   sean.kavanagh.19@ucl.ac.uk
   (University College London & Imperial College London)
   

   View Slide

2. 2
   02/05/2023
   Cation Disorder and Solar Cell
   Performance in ABZ2
   Materials
   (NaBiS2
   & AgBiS2
   )
   Seán Kavanagh
   Profs: David O. Scanlon & Aron Walsh
   sean.kavanagh.19@ucl.ac.uk
   (University College London & Imperial College London)
   

   View Slide

3. Heard about Perovskites?
   3
   Y.-T. Huang, S.R. Kavanagh, D.O. Scanlon, A. Walsh, and R.L.Z. Hoye, Nanotechnology 32, 132004 (2021)
   R.L.Z. Hoye et al. Chem Mater 29, 1964 (2017)
   ‘Perovskite-Inspired’
   Materials?
   

   View Slide

4. Perovskite-Inspired Materials
   4
   AI
   2
   BIBIIIX6
   Cation
   Substitution
   AI
   3
   B2
   IIIX9
   AI
   2
   BIVX6
   • Stable & non-toxic ✅
   • Sub-optimal bandgaps for solar cells ❌
   • Bandgap tuning via alloying & doping ✅
   • Carrier trapping & localisation due to
   reduced electronic dimensionality ❌ ❌
   Cs2
   AgBiBr6
   & Cs2
   AgSbBr6
   :
   A. H. Slavney et al. J. Am. Chem. Soc. 2016, 138, 7, 2138–2141.
   Z. Li ‡ & S. R. Kavanagh‡ et al. J. Mater. Chem. A, 2020, 8, 21780.
   Cs3
   Bi2
   Br9
   :
   B.-B. Yu et al. J. Mater. Chem. A, 2019, 7, 8818–8825.
   C. J. Krajewska, S. R. Kavanagh et al. Chem. Sci., 2021,
   12, 14686.
   Cs2
   TiX6
   & Cs2
   SnX6
   :
   M. Chen et al. Joule, 2018,
   2, 558–570.
   S. R. Kavanagh et al. J. Phys.
   Chem. Lett., 2022, 13,
   10965–10975.
   AIBIIX3
   Perovskite Structure:
   

   View Slide

5. 5
   ABZ2 – ‘Perovskite-Inspired’
   • AI,BIII = Metal cations, Z = Chalcogen (S, Se)
   • Rocksalt crystal structure (!"#
   3") with AI/BIII cation disorder
   • MX6
   octahedra -> Similar to perovskite motif
   • Close-packed and cation disorder:
   • (Pseudo-)Direct and low bandgaps
   • Lower effective masses1
   • Metal-chalcogen bonds: Stability ⬆
   • Nanocrystal solution synthesis
   AI/BIII
   Z
   1. Y.-T. Huang, S. R. Kavanagh, D. O. Scanlon, A. Walsh and R. L. Z. Hoye, Nanotechnology, 2021, 32, 132004
   

   View Slide

6. Modelling Disorder – A Challenge for Theory
   Special Quasirandom Structures (SQS)
   g(r)
   supercell
   ≃ g(r)
   random
   • Snapshot of total disorder
   Structural Enumeration:
   • Generate all (440) symmetry-inequivalent cation
   arrangements within a 32-atom supercell.
   • Calculate structures, energies, optical & scattering
   properties
   • Correlate with PV performance
   6
   Total
   Disorder
   (!"#
   3"):
   Total Order (%#
   3"):
   

   View Slide

7. Cation Disorder: Optical Properties (AgBiS2
   )
   (Hybrid DFT + SOC)
   ✅
   ❌
   Y. Wang‡ & S. R. Kavanagh‡, I. Burgués-Ceballos; A. Walsh, D.O. Scanlon, G. Konstantatos Nature Photonics 2022 16, 235
   

   View Slide

8. Cation Disorder:
   Control via Annealing
   Collaborators:
   Dr. Yongjie Wang, Dr. Ignasi
   Burgués-Ceballos, Prof.
   Gerasimos Konstantatos (ICFO)
   Y. Wang‡ & S. R. Kavanagh‡, I. Burgués-Ceballos; A. Walsh, D.O. Scanlon, G. Konstantatos Nature Photonics 2022 16, 235
   

   View Slide

9. Cation Disorder:
   Control via Annealing
   Collaborators:
   Dr. Yongjie Wang, Dr. Ignasi
   Burgués-Ceballos, Prof.
   Gerasimos Konstantatos (ICFO)
   Y. Wang‡ & S. R. Kavanagh‡, I. Burgués-Ceballos; A. Walsh, D.O. Scanlon, G. Konstantatos Nature Photonics 2022 16, 235
   

   View Slide

10. XRD
    Theory:
    Expt:
    XPS
    Theory:
    Expt:
    TEM
    Theory:
    Expt:
    2θ ⬆
    2θ ⬆
    EBi 5d
    ⬇
    EBi 5d
    ⬇
    a
    AgBiS₂
    ⬇
    a
    AgBiS₂
    ⬇
    Cation Disorder: Control via Annealing Collaborators:
    Dr. Yongjie Wang, Dr. Ignasi Burgués-Ceballos,
    Prof. Gerasimos Konstantatos (ICFO)
    Y. Wang‡ & S. R. Kavanagh‡, I. Burgués-Ceballos; A. Walsh, D.O. Scanlon, G. Konstantatos Nature Photonics 2022 16, 235
    

    View Slide

11. AgBiS2
    :
    • Highest absorption coefficient ⍺ of any
    currently-studied PV material
    • Highest efficiency of any Bismuth-based
    solar material
    BiSI BiI3
    Bi2
    S3
    MA3
    Bi2
    I9
    Cs3
    Bi2
    I9
    Cs2
    AgBiBr6
    AgBi2
    I7
    Ag2
    Bi2
    I9
    AgBiS2
    0
    2
    4
    6
    8
    10
    PV Efficiency (%)
    Bi-Based PV
    • Solar cells with record-breaking efficiencies η > 9%,
    using an ultrathin 30 nm absorber (previous η = 6%)
    • Control of atomic disorder facilitates major absorption
    enhancement, allowing high-efficiency ultrathin devices
    Collaborators:
    Dr. Yongjie Wang, Dr. Ignasi
    Burgués-Ceballos, Prof.
    Gerasimos Konstantatos (ICFO)
    Y. Wang‡ & S. R. Kavanagh‡, I. Burgués-Ceballos; A. Walsh, D.O. Scanlon, G. Konstantatos Nature Photonics 2022 16, 235
    

    View Slide

12. What about NaBiS2
    ?
    AI/BIII
    Z
    Strong absorption ➡ high potential efficiency in ultrathin cells
    Y.T. Huang‡ & S. R. Kavanagh‡ et al. Nature Communications 2022 13 (1), 1-13
    Collaborators:
    Y-T. Huang, Prof. R.L.Z. Hoye
    (Oxford) I. Levine, T. Unold (HZB), L.
    M. Herz, S. M. Stranks (Cambridge)
    

    View Slide

13. In-gap states impede PV performance
    Y.-T. Huang, S. R. Kavanagh, D.O. Scanlon, A. Walsh,
    R.L.Z. Hoye, Nanotechnology 32, 132004 (2021)
    Collaborators:
    Y-T. Huang, Prof. R.L.Z. Hoye
    (Oxford) I. Levine, T. Unold (HZB), L.
    M. Herz, S. M. Stranks (Cambridge)
    ➡ Calculations reveal trap levels above VBM, at Na-rich pockets
    Y.T. Huang‡ & S. R. Kavanagh‡ et al. Nature Communications 2022 13 (1), 1-13
    

    View Slide

14. What causes the localised states in NaBiS2?
    Na+ = Empty valence shell (s0), Ag+ = Filled shell (d10) -> ‘defect-tolerant’
    ➡ Spectator ion, flat non-bonding VBM ➡ Trap levels above VBM, at Na-rich pockets
    Na 3s
    Y.T. Huang‡ & S. R. Kavanagh‡ et al. Nature Communications 2022 13 (1), 1-13
    

    View Slide

15. Cation Disorder in NaBiS2
    : Electronic Properties
    ➡ Trap levels above VBM
    ➡ Ultrafast carrier trapping (% ~ ps), followed by slow decay (% ~ μs),
    confirmed by pump-probe measurements
    ➡Record efficiency η = 0.6% (c.f. η > 9% for AgBiS2)
    "
    short
    = 34 ps
    "
    long
    ~ 6 μs
    Na 3s
    Y.T. Huang‡ & S. R. Kavanagh‡ et al. Nature Communications 2022 13 (1), 1-13
    

    View Slide

16. What causes the localised states?
    Na+ = s0, Ag+ = d10s0 -> ‘defect-tolerant’
    ➡ Spectator ion, flat non-bonding VBM
    ➡ Trap levels above VBM, at Na-rich pockets
    ‘Defect tolerant’ electronic
    structure in lead halide perovskites
    Y.-T. Huang, S. R. Kavanagh, D. O. Scanlon, A. Walsh
    and R. L. Z. Hoye, Nanotechnology, 2021, 32, 132004
    R. E. Brandt et al, Chem. Mater., 2017, 29, 4667–4674.
    

    View Slide

17. BiSI BiI3
    Bi2
    S3
    MA3
    Bi2
    I9
    Cs3
    Bi2
    I9
    Cs2
    AgBiBr6
    AgBi2
    I7
    Ag2
    Bi2
    I9
    AgBiS2
    0
    2
    4
    6
    8
    10
    PV Efficiency (%)
    Bi-Based PV
    - Top performing lead halide perovskites are mixed
    triple-cation, triple-anion compositions.
    - Best performing Bi-based PV material (by far) is
    disordered AgBiS2, despite being a relative newcomer.
    - Disorder tolerance?
    Is Disorder Always Bad?
    Na 3s
    Minimal localisation with disorder in
    Sn2
    SbS2
    I3
    – potential disorder tolerance?
    A. Nicolson, S. R. Kavanagh et al. ChemRxiv
    (Under Review at J. Am. Chem. Soc)
    Localisation
    

    View Slide

18. NaBiS2: Y.T. Huang‡ & S. R. Kavanagh‡ et al. Nature Communications 2022 13 (1), 1-13
    AgBiS2: Y. Wang‡ & S. R. Kavanagh‡, I. Burgués-Ceballos; A. Walsh, D.O. Scanlon, G. Konstantatos Nature Photonics 2022 16, 235
    Key Takeaways & Acknowledgements
    Profs David O. Scanlon & Aron Walsh
    Disorder = Powerful tool for materials design
    Both the nature of the disorder and the underlying orbital
    chemistry are key considerations for disorder engineering!
    Collaborators:
    Dr. Y. Wang, Prof. G. Konstantatos
    (ICFO Barcelona, Spain)
    Y-T. Huang, Prof. R. L. Z. Hoye (Oxford), Dr.
    I. Levine, Prof. T. Unold (HZB), Prof L. Herz,
    Prof. S. M. Stranks (Cambridge)
    

    View Slide