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)
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)
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?
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:
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
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"):
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
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
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
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
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
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)
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
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
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
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.
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
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)