2014-09-NanoGe-Oxford

Perovskite work presented at the NanoGe conference in Oxford in September 2014.

Transcript

1. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Jarvist Moore Frost, Federico Brivio, Christopher Hendon, Keith Butler, Aron Walsh Walsh Materials Design Group, University of Bath, UK j.m.frost@bath.ac.uk Hybrid halide perovskites: Modelling crystal dynamics and devices
2. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Molecular Dynamics on MAPI (PBESol, Γ-point, VASP) Soft crystal; large distortions of octahedra Repercussions for grain boundaries? (fortuitous?) Accuracy of electronic structure calculations on 'perfect' 'equilibrated' crystals? Would fluctuations lead to polaron localisation? [2x2x2 Pseudo cubic relaxed supercell, lattice parameters held constant during MD (NVT simulation). PBESol Functional at the Gamma point (forces + energies should converge well). dt=0.5fs, T=300K]
3. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Molecular Dynamics Video (hopefully...) • MA ion yaws • ...and rolls… • ...CH3 clicks • so does NH3 ( 25 fs / frame 0.625 ps / s )
4. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Molecular Dynamics Challenge is getting useful science out of R{x, y,z}(t) • {Static} ensemble information • Dynamics ◦ Correlation (MA ion vs. Octahedra)
5. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Purple - Iodine Green - Lead Orange - Carbon (methylammonium) Disordered & soft! Tilting octahedra
6. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Lead Iodine Carbon (Methylammonium)
7. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Iodine Location
8. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Glazer Tilting - Glazer 1972
9. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014
10. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014
11. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Perovskite Distortions • DISTORTIONS of the octahedra • DISPLACEMENTS of cations (i.e. BaTiO3) • TILTING of the Octahedra Distortion & displacement driven by electronic instabilities of A-cation (Here, Pb) Tilting retains same 1st coordination sphere (octahedra), while cation-anion distance changes (After Woodward, 1997)
12. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 MAPI: Tilts, Distorts & Displaces • This is a problem; how to deconvolve? "Gauge kinematics of deformable bodies" Shapere, Wilczek Am. J. Phys. 57, 514 (1989); DOI: 10.1119/1.15986
13. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Previously: POTATO Given Glazer notation & tilt angles, generates corner-sharing Octahedra 2x2x2 supercell. Acta Cryst. (1997). B53, 32-43 [ doi:10.1107/S0108768196010713 ] Octahedral Tilting in Perovskites. I. Geometrical Considerations P. M. Woodward
14. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Here: SMASH • Framework of ab-initio perovskite analysis codes • Written in julia ◦ Easier to extend analysis to further parameters • Work in progress! © National Cancer Institute, Renee Comet (photographer)
15. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Deformation potential Large scale movement of ions considerably varies Hamiltonian used to calculate the electronic structure Disorder of movement means there is no longer a perfect lattice - Bloch states feel a disordered potential Consequence for band transport? (i.e. polaron localisation) For absorption? (losing dimensionality of bands increases absorption coefficient, i.e. as amorphous silicon vs. X'taline)
16. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Band Gap variation (Gamma, PBESol) during MD Qualitative only. Gamma point PBESol occ->unocc energy only! No fermi golden rule / overlap consideration Need a quasi-particle theory for proper absorption
17. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 MD: Extract methyl-ammonium alignment vectors... C-N C-N C-N
18. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 A total of 58 ps (2319 frames) of data was used for analysis, after an equilibration run of 5 ps. This generated 18547 unique MA alignment vectors.
19. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Octahedral symmetry... Pseudo cubic, therefore Oh symmetry… But how to apply the reductions? (Brews ohare, Wikimedia Commons) (Tom Ruen, Wikimedia Commons)
20. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014
21. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Reduce to first octant… abs(r), r=[x,y,z]
22. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Apply reflection symmetry… sorted(abs(r)) , r={x,y,z} = 48 fold increase in SNR (Tom Ruen, Wikimedia Commons)
23. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 FACE (X) DIAGONAL (R) EDGE (M)
24. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 FACE (X) DIAGONAL (R) EDGE (M) FACE: 42% EDGE: 31% DIAG.: 26% (weighted by MC integration of random sphere points)
25. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 (1 frame = 25 fs) Sampling both residence time (long tail) & time taken to move (short time peak) ~2.5 ps for average (mean) dynamics ~1.25 ps for first peak (fast) dynamics
26. 2D photon echo anisotropy measurements • monoexponential decay ~2 ps reorientation time • This is the fastest estimate as energy transfer may be involved Pump 1470 cm-1 Probe 1445 cm-1 Experiment & Data Analysis by Artem Bakulin et al.
27. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 What effect do these rotating cations have? There are a lot of dynamic processes here... Monopoles moving (i.e. ions) will dominate dielectric response, dipole rotation will add an additional smaller contribution Now we build a model for electrostatic interacting dipole domains
28. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Ferroelectric domain Hamiltonian
29. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 STARRYNIGHT code; live user interface Dipole alignment Resultant potential
30. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Electrostatic potential projected onto electron density isosurface (iso value = 0.02) 0.6 0.375 0.3 Electrostatic Potential Vacuum calculation CCSD/cc-pVTZ on b3lyp/6-31g* geom. Gaussian09 2.2 Debye Φ E 18 electrons,closed shell = happy quantum chemical days Hartrees (x 27.211 V)
31. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Same data, volume slice projection 0.6 0.0 Hartrees (x 27.211 V)
32. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Interaction Energy Vacuum dielectric (effect through empty cage gap) On-lattice dipoles, spacing of 6.29Å. Point dipole approximation * = 25 meV * MA Dipole moment massively dominates in polarisation tensor, point approximation possibly not valid r=6.29Å 2.2 Debye
33. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Display direction of Dipole by point on HSV sphere p
34. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 0K 100K 300K 1000K
35. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Zero field Dipole alignment .04% aligned (noise)
36. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Zero field Dipole potential
37. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Zero field Dipole potential Zero field Dipole potential (2D FFT) Zero frequency origins
38. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Short-circuit field Dipole alignment .5% aligned
39. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Short-circuit field Dipole potential
40. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Short-circuit field (10MV/m) Dipole potential Dipole potential (2D FFT)
41. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Zero field (open circuit) Dipole potential Short Circuit Field Dipole potential Same figures, presented side by side...
42. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Zero field (open circuit) Dipole potential (2D FFT) Short Circuit Field Dipole potential (2D FFT) Same figures, presented side by side...
43. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Conclusions • MAPI is soft. Distorting / Tilting @ 300K • MA is highly rotationally mobile… ◦ … with a large static dipole along it ◦ Cage:Cage dipole interaction ~25meV • Very rich phase behaviour of 'Potts' style classical model • Dipole domains form regions of electro static potential which may be relevant for charge carrier mobility & recombination
44. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 WMD Group (Bath) Piers Barnes, Aurelien Leguy (Imperial - quasi-inelastic neutron scattering data & device operation & hysteresis / effect of built in fields) Hugo Bronstein, Robert Palgrave (UCL - discussing hybrid perovskites & the potential for alternative cations) Artem Bakulin (direct time constant measurements; following discussion at EMRS) Piers Aurelien Hugo Artem Acknowledgments
45. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Papers & codes Atomistic Origins of High-Performance in Hybrid Halide Perovskite Solar Cells Jarvist M. Frost, Keith T. Butler, Federico Brivio, Christopher H. Hendon, Mark van Schilfgaarde, and Aron Walsh Nano Letters 2014 14 (5), 2584-2590 DOI: 10.1021/nl500390f Molecular ferroelectric contributions to anomalous hysteresis in hybrid perovskite solar cells Jarvist M. Frost, Keith T. Butler, and Aron Walsh APL Mat. 2, 081506 (2014); DOI: 10.1063/1.4890246 Barnes, Leguy et al. - quasi-inelastic neutron scattering - in production MD Videos - on YouTube: https://t.co/5z81WfUZhw https://github.com/WMD-Bath/StarryNight - Starrynight code (classical dipoles 2D MC code) https://github.com/jarvist/MAPI-MD-analysis - Analysis codes for MD (Python) https://github.com/WMD-Bath/Hybrid-perovskites - Hybrid perovskite DFT structures
46. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Dipole angle distributions Increasing (applied) electric field E=1 kBT (NB: Enormous applied electric fields!) E=2 kBT E=10 kBT
47. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Red: Zero Field Green: Applied Field
48. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Classic dipole model MAPI perovskite has competing interactions giving rise to geometric frustration i.e. similar to a spin glass, but with various electrostatic and cage distortion interactions rather than ferromagnetic and anti-ferromagnetic. Potts model (Potts, 1952), n-dimensional, generalisation of Ising (Ising, 1925) model. Simple 'dipole like' dot-product interaction energy:- See: F. Y. Wu, The Potts model Rev. Mod. Phys. 54, 235 – Published 1 January 1982
49. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014
50. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Directly animated live in the terminal...
51. Jarvist Moore Frost (University of Bath, UK) Hybrid halide perovskites: Modelling crystal dynamics 12th September 2014 Piet Mondrian, 'Broadway Boogie-Woogie', 1942