Dynamics of Hybrid VacancyOrdered Double Halide 

Perovskites (FA)2PtI6 and 

(GUA)2PtI6

Owen Bailey

obailey@bates.edu

Mentor: Dr. Hayden Evans
Hybrid Halide Perovskite Materials as Optoelectronics

● MAPbI3 and FAPbI3: high performance 

photovoltaic absorbers

○ MA = methylammonium (CH3NH3

+)

○ FA = formamidinium (CH(NH2)2

+)

● Why are they attractive?

○ Cheap, easy to make, easily compositionally tunable

● But...

○ Unstable (air, humidity), possible lead leaching into 

environment

https://cns.utexas.edu/news/physicists-offer-insight-into-improving-perovskite-solar-cells

https://www.cam.ac.uk/research/news/leds-made-from-wonder-materialperovskite

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Hybrid Halide Perovskite Structure

● Perovskite: ABX3

○ A site organic cation

○ BX6 octahedra

● Why hybrid? 

○ Small organic cations enable formation of the compound 

(tolerance factor)

● Organic cation is dynamic

○ Complexity of crystallography

BX6 octahedra 

A site cation

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In Search of More Stable Variants

● A2B☐I6 

○ A is an organic cation, ☐ is a vacancy

● It has been shown that though they lack 3-D connectivity, vacancy ordered 

iodides demonstrate attractive optoelectronic properties

○ Iodine-iodine interaction despite lack of 3D connected bond (valence band dispersion)

○ Much more stable, but less efficient

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Hydrogen Bonding Directs Structures at Low Temperatures

● (FA)2Pt☐I6 and (GUA)2Pt☐I6 in literature

○ GUA = guanidinium (C(NH2)3

+)

○ Organic cation/iodide hydrogen bonding controls 

structural evolution

○ Cation is static at low temperatures (NMR, X-ray 

single crystal)

● Dynamics change at higher temperatures

○ Change in dynamics, single crystal destruction, 

twinning

● How does temperature affect the 

dynamics of the organic cation, which 

controls the structure of the material?

5

Evans, H. A., Fabini, D. H., Andrews, J. L., Koerner, M., Preefer, M. B., Wu, G., ... & 

Seshadri, R. (2018). Hydrogen bonding controls the structural evolution in perovskite-related 

hybrid platinum (IV) iodides. Inorganic chemistry, 57(16), 10375-10382.
Hydrogen Bonding and Structure

● (FA)2Sn☐I6: hydrogen bonding between the organic cation and inorganic 

framework causes ferroelastic phase transition (hysteresis)

○ Directly related to the organic cation’s dynamic behavior

● Are these ferroelastic phase transitions universal in vacancy-ordered double 

hybrid halide perovskites?

○ Isostructural compound (FA)2Pt☐I6 and familial compound (GUA)2Pt☐I6

Maughan, A. E., Mozur, E. M., Candia, A. M., & Neilson, J. R. (2020). Ferroelastic Phase 6 Transition in Formamidinium Tin (IV) Iodide Driven by Organic–Inorganic Coupling. Inorganic 

Chemistry, 59(19), 14399-14406.
Approaching Our Question

● We will use X-ray diffraction and quasi-elastic 

neutron scattering (QENS) to monitor the dynamics 

of the organic cation 

○ Crystallography of a dynamic organic cation inside of a static 

inorganic cage requires a careful treatment

○ QENS allows us to look for crystallographically silent 

dynamics of the organic A site cation

■ Changes in cation dynamics impact photoconductivity 

in hybrid perovskite photovoltaic cells

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https://www.aps.anl.gov/About/Welcome

https://neutrons.ornl.gov/basis
Preparation for Incoming Data

● Crystallography bootcamp

○ Understanding of crystallographic nomenclature, multiplicity, atom 

sites, space group symbols

● Refinement practice

○ Diffraction analysis of various complex hybrid structures

■ Metal-organic-framework (MOFs)

○ Rigid bodies

○ Peak indexing and finding a structure solution

8
Solving a material’s structure

● Indexing our sample’s diffraction pattern

○ Peak location (orange ticks)

○ Match our data against hundreds of suggested 

space groups and unit cell combinations

● If ticks line up, Pawley refinement

○ Peak intensity (height)

○ Peak shape/width

○ Highest symmetry possible

● If Pawley successful, Rietveld refinement

○ Incorporates multiplicity, type, location of atoms on 

the unit cell

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Indexing process

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Indexing process

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H-Bonding Dictates Structure Through Phase Transition

● Sluggish phase transition is observed (first heating)

● High temperature phase is related to original phase

○ Original phase is metastable (never recovered)

○ Guanidinium is still hydrogen bonded and stable

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Evans, H. A., Fabini, D. H., Andrews, J. L., Koerner, M., Preefer, M. B., Wu, G., ... & Seshadri, R. (2018). Hydrogen bonding controls the structural evolution in perovskite-related hybrid platinum (IV) iodides. Inorganic chemistry, 57(16), 10375-10382.
Future Plans

● Analyze our X-ray data, receive and analyze QENS data 

○ X-ray will now inform the QENS experiment

○ QENS data by the end of August

● Eventual publication

● Add to the growing understanding of perovskite-related compounds

○ Achieve compositional control of these materials

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Acknowledgements

● SURF program directors

● NIST NCNR OU directors

● Dr. Hayden Evans, NCNR

● Dr. Geneva Laurita, Bates College

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References

● Eames, C., Frost, J., Barnes, P. et al. Ionic transport in hybrid lead iodide perovskite solar cells. Nat Commun 6, 7497 (2015). 

https://doi.org/10.1038/ncomms8497

● Maughan, A. E., Paecklar, A. A., & Neilson, J. R. (2018). Bond valences and anharmonicity in vacancy-ordered double perovskite halides. Journal of 

Materials Chemistry C, 6(44), 12095-12104.

● Maughan, A. E., Ganose, A. M., Scanlon, D. O., & Neilson, J. R. (2019). Perspectives and design principles of vacancy-ordered double perovskite halide

semiconductors. Chemistry of Materials, 31(4), 1184-1195.

● Hailegnaw, B., Kirmayer, S., Edri, E., Hodes, G., & Cahen, D. (2015). Rain on methylammonium lead iodide based perovskites: possible environmental 

effects of perovskite solar cells. The journal of physical chemistry letters, 6(9), 1543-1547.

● Nagabhushana, G. P., Shivaramaiah, R., & Navrotsky, A. (2016). Direct calorimetric verification of thermodynamic instability of lead halide hybrid 

perovskites. Proceedings of the National Academy of Sciences, 113(28), 7717-7721

● Eames, C., Frost, J. M., Barnes, P. R., O’regan, B. C., Walsh, A., & Islam, M. S. (2015). Ionic transport in hybrid lead iodide perovskite solar cells. Nature 

communications, 6(1), 1-8.

● Evans, H. A., Fabini, D. H., Andrews, J. L., Koerner, M., Preefer, M. B., Wu, G., ... & Seshadri, R. (2018). Hydrogen bonding controls the structural evolution 

in perovskite-related hybrid platinum (IV) iodides. Inorganic chemistry, 57(16), 10375-10382.

● Momma, K., & Izumi, F. (2011). VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data. Journal of applied crystallography, 

44(6), 1272-1276.

● Maughan, A. E., Mozur, E. M., Candia, A. M., & Neilson, J. R. (2020). Ferroelastic Phase Transition in Formamidinium Tin (IV) Iodide Driven by Organic–

Inorganic Coupling. Inorganic Chemistry, 59(19), 14399-14406.

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Questions?

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