2015-03-19_JarvistMooreFrost_Berlin-DPG_REDACTED

An invited talk for once! So much more content c.f. a 13 minute contributed one.

Transcript

1. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Jarvist Moore Frost, Federico Brivio, Adam Jackson, Jonathan Skelton, Aron Walsh Chris Eames, Saiful Islam (Bath) Pooya Azarhoosh, Mark van Schilfgaarde (King’s College London) Aurelien Leguy, Brian O'Regan, Piers Barnes (Imperial College London) Artem Bakulin et al. (now at Cambridge) Walsh Materials Design Group, University of Bath, UK j.m.frost@bath.ac.uk Solid state physics of hybrid halide Perovskites
2. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Perovskite (ABX 3 ) Crystal structure of the mineral CaTiO 3 A BX 3 Lev Perovski (Russia, 1839)
3. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 A - Molecular Cation B - {Pb, Sn} X 3 - Halide {I, Br, Cl*} Hybrid Perovskites (ABX 3 )
4. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 MAPI Solar Cells PbI 2 + CH 3 NH 3 .I (soln) → CH 3 NH 3 .PbI 3 ~20% efficient solar cell SQ limit Henry Snaith, University of Oxford, with a Hybrid Perovskite Film Image credit: Douglas Fry
5. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Hybrid Perovskites: The Bad News Extremely high efficiency for a solution processed solar cell technology ◆ c.f. ~10% for Dye solar cell, ~12% for organic Why? ◆ Small exciton binding energy (large ε r ~=25) ◆ Very long minority carrier diffusion lengths ◆ High ambipolar charge carrier mobility Lead (!); ◆ Tin is less stable <24 hrs lifetime Anomalous hysteresis in measurement? Snaith et al, Phys. Chem. Lett., 2014, 5 (9), pp 1511– 1515
6. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Overview MAPI: Structure & basic solid state physics Phonons & Raman Molecular Dynamics Ionic conductivity (Iodine vacancies) Classical Monte Carlo dipole simulator, STARRYNIGHT
7. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015
8. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015
9. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 N. Onoda-Yamamuro et al, J. Phys. Chem. Solids. 2, 277 (1992)
10. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Cubic? Tetragonal? Orthorhombic? Powder Neutron diffraction allows for a full solution (inc. hydrogens) ➔ 150K 1st order phase transition (Ortho-Tetra) ➔ 2nd order transition to cubic phase Weller et al. Chem. Commun., 2015, DOI: 10.1039/C4CC09944C Received 12 Dec 2014, Accepted 22 Jan 2015
11. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Methylammonium (CH 3 NH 3 +) A closed shell (18 electron) molecular cation with a large electric dipole J. M. Frost et al, Nano Letters 14, 2584 (2014) Deprotonation (pK a ~ 10): CH 3 NH 3 + → CH 3 NH 2 + H+
12. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 CH 3 NH 3 PbI 3 (MAPI for short) Configuration: PbII [5d106s26p0]; I-I [5p6] F. Brivio et al, Physical Review B 89, 155204 (2014) Relativistic QSGW theory with Mark van Schilfgaarde (KCL) Conduction Band Valence Band Dresselhaus Splitting (SOC) [Molecule breaks centrosymmetry]
13. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Absorption: Dresselhaus effect flattens the VBM bands - leading to a large density of states available for excitation. A sudden “turn-on” reminiscent of 2D band structure. Emission: Holes and electrons quickly thermalise to bottom of band (densities at 1 sun solar flux are very low); radiative recombination is strongly suppressed. → Have your cake and eat it ← Why MAPI is so great The Dresselhaus effect splits the CBM (more than VBM); the band gap becomes slightly indirect
14. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 “Natural” Valence Band Alignments K. T. Butler et al, Materials Horizons, Advance Article (2015) Similar to other thin-film PV materials Band gap engineering through A, B or X site modification
15. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 F. Brivio et al, Physical Review B 89, 155204 (2014) Bands are not parabolic, but… m h */m ~ 0.12 (light holes) m e */m ~ 0.15 (light electrons) [sampled within k B T of band edges] Optical Absorption Hole Effective Mass [110] [112] [111]
16. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 How non parabolic? Very! Implications for device models (i.e. Drift diffusion, assumptions of scattering)
17. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Free Carriers or Excitons? Exciton binding from effective mass theory: The situation is different to organic PV where the dielectric constants are small and effective masses are heavy. Semiconducting perovskites are distinct from passive dyes in sensitised cells. Carrier masses & dielectric screening favour free carrier generation J. M. Frost et al, Nano Letters 14, 2584 (2014)
18. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Overview MAPI: Structure & basic solid state physics Phonons & Raman Molecular Dynamics Ionic conductivity (Iodine vacancies) Classical Monte Carlo dipole simulator, STARRYNIGHT ( Nothing published yet, hope to have a paper on the ArXiv within two weeks. MAPI; follow up paper with MAPC, MAPBr. Raman and infrared; joint expt. and calculation )
19. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015
20. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015
21. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 a Baikie T., et al., Synthesis and crystal chemistry of the hybrid perovskite (CH 3 NH 3 ) PbI 3 for solid- state sensitised solar cell applications, J. Mater. Chem. A, 1, 5628-5641 (2013). b Stoumpos, C. C., Malliakas, C. D. & Kanatzidis, M. G. Semiconducting tin and lead iodide perovskites with organic cations: phase transitions, high mobilities, and near-infrared photoluminescent properties. Inorg. Chem. 52, 9019–9038 (2013). c Weller M. T., et al., Complete structure and cation orientation in the perovskite photovoltaic methylammonium lead iodide between 100 and 352K Chem. Comm., DOI:10.1039/c4cc09944c (2015) d Kawamura Y., Mashiyama H., Hasebe K., Structural study on cubic-tetragonal transition of CH 3 NH 3 PbI 3 , J. Phys. Soc. Japan. 71, 1694-1697 (2002). † Note: due to the manner in which orientational disorder is fitted to neutron diffraction data, this bond length represents an underestimate. To refine the orthorhombic structure, Weller et al use fixed bond lengths of 1.46Å (C-N), 1.13Å (C-H) and 1.00Å (N-H).
22. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 i.r. Raman Cubic Tetra Ortho Cation Cage
23. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Ortho. DFT, with 150 K Expt data. Cage Cation
24. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 18 Cage Modes (3 acoustic, 9 cage (3N-3), 6 rovibrational (MA))
25. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 18 MA high freq. molecular modes (3N-6)
26. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 3 mid-energy range MA hydrogen modes Most molecular modes are the same in vacuum (by DFT calculation), as in the solid state. Low-frequency molecular modes (methyl clicker) seem highly affected by environment (900 → 300 cm-1 ). Good be a useful probe of local packing / ordering.
27. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Overview MAPI: Structure & basic solid state physics Phonons & Raman Molecular Dynamics Ionic conductivity (Iodine vacancies) Classical Monte Carlo dipole simulator, STARRYNIGHT ( Initial work in APL Materials 2 (8), 081506 ; Quasi-elastic Neutron Scattering, Nature Comms (Leguy, in press) 2D infrared spectroscopy (Bakulin, in preparation))
28. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 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]
29. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Molecular Dynamics (MAPI is as soft as Jelly.) ➔ MA ion yaws ➔ ...and rolls… ➔ ...CH3 clicks ➔ so does NH3 ( 25 fs / frame 0.625 ps / s )
30. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Molecular Dynamics Challenge is getting useful science out of R{x, y,z}(t) ➔ {Static} ensemble information ➔ Dynamics ◆ Correlation (MA ion vs. Octahedra)
31. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Lead Iodine Carbon (Methylammonium)
32. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Iodine Location Need 2Nx2Nx2N supercell for tilting!
33. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Glazer Tilting - Glazer 1972
34. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Y. Kawamura et al, J. Phys. Soc. Jap. 71, 1964 (2002)
35. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Weller, 2015
36. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Rotation and tilting of octahedra Accessible ferroelectric and antiferroelectric phases A. M. Glazer, Acta. Cryst. B 28, 3384 (1972) Mike Glazer (Oxford)
37. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 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)
38. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 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
39. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 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)
40. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 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
41. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 MD: Extract methyl-ammonium alignment vectors... C-N C-N C-N
42. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 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.
43. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 FACE (X) DIAGONAL (R) EDGE (M) FACE: 42% EDGE: 31% DIAG.: 26% (weighted by MC integration of random sphere points)
44. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 (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
45. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 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.
46. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Overview MAPI: Structure & basic solid state physics Phonons & Raman Molecular Dynamics Ionic conductivity (Iodine vacancies) Classical Monte Carlo dipole simulator, STARRYNIGHT ( Out to review with Nature Comms. )
47. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 These slides removed... The figures I displayed are from our Nature Communications (currently out to review, as of 10th Feb 2015) paper, so it will hopefully be published soon: "Ionic transport in hybrid lead iodide perovskite solar cells" Christopher Eames, Jarvist M. Frost, Piers R. F. Barnes, Brian C. O’Regan, Aron Walsh and M. Saiful Islam Submitted to Nature Communications.
48. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Overview MAPI: Structure & basic solid state physics Phonons & Raman Molecular Dynamics Ionic conductivity (Iodine vacancies) Classical Monte Carlo dipole simulator, STARRYNIGHT
49. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 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)
50. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 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
51. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Ferroelectric domain Hamiltonian
52. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Display direction of Dipole by point on HSV sphere p
53. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015
54. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 STARRYNIGHT code (live 'user interface') Dipole alignment Resultant electostatic potential
55. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 → Expect anti-ferroelectric behaviour
56. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 0K 100K 300K 1000K
57. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Zero field Dipole alignment .04% aligned (noise)
58. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Zero field Dipole potential
59. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Zero field Dipole potential Zero field Dipole potential (2D FFT) Zero frequency origins
60. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 → Solar Cell at SHORT CIRCUIT (built in field)
61. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Short-circuit field Dipole alignment .5% aligned
62. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Short-circuit field Dipole potential
63. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Short-circuit field (10MV/m) Dipole potential Dipole potential (2D FFT)
64. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Zero field (open circuit) Dipole potential Short Circuit Field Dipole potential Same figures, presented side by side...
65. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Zero field (open circuit) Dipole potential (2D FFT) Short Circuit Field Dipole potential (2D FFT) Same figures, presented side by side...
66. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015
67. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 → 'strain' term from DFT calculation in 4x4x4 Cell
68. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Calculation of cage strain term...
69. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 T= 0 K (Ground State - but a bit out of eqm, due to MC) CageStrain = 0 ---> Anti-Ferroelectric (The potential at a site from the dipole on the nearest neighbour (= 1 in the internet units of Starrynight) is simply 0.165 V.)
70. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 T= 0 K (Ground State - but a bit out of eqm, due to MC) CageStrain = 2 ---> Ferroelectric (The potential at a site from the dipole on the nearest neighbour (= 1 in the internet units of Starrynight) is simply 0.165 V.)
71. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Anti Ferroelectric --- increase in temperature sees a slow broadening of density of states T
72. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Ferroelectric --- increase in temperature sees a large broadening in density of states T
73. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Quantifying order: Where is the Physics? Landau Order parameter, gives metric when you have long range order - but doesn't describe partial ordering. Alexey A. Sokol
74. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 R→ infinity value is the same as the Landau order Define a radially-dependent autocorrelation function of the dipoles Ziman - Models of Disorder, 1979
75. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Cagestrain=0 → Antiferroelectric (AFE) ground state. No easy definition of AFE order parameter? ??? 0K
76. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Cagestrain=1 → Ferroelectric ground state; Intermediate long range order (dynamic) at finite T 0K 128K 64K 256K 384K
77. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Cagestrain=1 → Ferroelectric ground state; Intermediate long range order (dynamic) at finite T 0K 128K 64K 256K 384K
78. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Evidence from numerics... ➔ 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
79. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Why is MAPI great? ➔ Dresselhaus Flattened VBM → sharp, strong, absorption ➔ Split conduction band → reduced radiative recombination (lost in k-space) All the benefits for PV of a direct AND indirect gap ➔ Dipole domains lead to charge segregation in valleys / ridges of potential ?
80. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Defects Why is MAPI so electrically benign? Schottky analysis suggests 0.4 % defects! Ionic disorder is favoured - lattice defects are low energy to form & so they compensate. High dielectric constants screen effects; clustering of defects neutralises them. Self-Regulation Mechanism for Charged Point Defects in Hybrid Halide Perovskites† Prof. Aron Walsh, Dr. David O. Scanlon, Prof. Shiyou Chen, Prof. X. G. Gong and Dr. Su-Huai Wei Article first published online: 11 DEC 2014 DOI: 10.1002/ange.201409740
81. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Hysterisis ➔ Ionic (iodine, vacancy mediated) conductivity is theoretically justified, with an activation energy that agrees with expt. ➔ Extremely rich ferroelectric + anti- ferroelectric and mixed phase behaviour expected ➔ My suspicion is that both effects are present; experiment is needed to differentiate
82. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Acknowledgments:- Barnes - Imperial College London, Bakulin - Cambridge, Schilfgaarde - King's College London, Islam - Bath Piers Barnes Aurelien Leguy Pooya Azarhoosh Mark van Schilfgaarde Aron Walsh Federico Brivio
83. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 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 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
84. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 Ziman's "Models of Disorder" 1979
85. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 BUT - not the complete story; need higher order distribution functions → compactness / smoothness
86. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 T= 128 K (Ground State - but a bit out of eqm, due to MC) CageStrain = 0 ---> Anti-Ferroelectric (The potential at a site from the dipole on the nearest neighbour (= 1 in the internet units of Starrynight) is simply 0.165 V.)
87. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 T= 128 K (Ground State - but a bit out of eqm, due to MC) CageStrain = 1 ---> Partial ferroelectric (The potential at a site from the dipole on the nearest neighbour (= 1 in the internet units of Starrynight) is simply 0.165 V.)
88. Jarvist Moore Frost (University of Bath, UK) DPG Berlin - Solid state physics of hybrid Perovskites 19th March 2015 T= 128 K (Ground State - but a bit out of eqm, due to MC) CageStrain = 2 ---> Ferroelectric (The potential at a site from the dipole on the nearest neighbour (= 1 in the internet units of Starrynight) is simply 0.165 V.)