Center for Excitonics


Exciting Metal-organic Frameworks: Electrons, Phonons, and Photons

November 28, 2017 at 4:30pm/rm: 36-428

Aron Walsh
Department of Materials, Imperial College London

Metal-organic frameworks (MOFs) are porous ordered arrays of inorganic clusters supported by organic linking units. They have attracted attention for gas storage, separation and catalysis, which rely on weak chemical bonding with an absorbate. The recent focus has shifted to physical responses, with examples of magnetic, optical, ferroelectric, and photovoltaic compounds. I will discuss progress in the understanding of how hybrid frameworks interact with charge, heat, and light.

The optical response of MOFs can be tuned by chemical modification of the organic and inorganic building blocks[1]. The control of electrical conductivity and redox activity in MOF thin-films is opening a new dimension of applications[2,3]. The combination of chemical diversity, mechanical flexibility, and electronic control in a single family of compounds could enable metal-organic frameworks to become the semiconductors of the future.

Beyond porous frameworks, I will also discuss progress in the understanding of organic-inorganic halide perovskites, such as methylammonium lead iodide, which have attracted significant attention for solar energy conversion. These compounds have been termed ‘plastic crystals’ owing to the rotational-vibrational activity of the molecular components, as well as the large anharmonic thermal displacements of the inorganic framework. We have been developing models to describe the temporal behaviour of hybrid perovskites that have been validated through a combination of quasi-elastic neutron scattering, time-resolved vibrational spectroscopy, and inelastic X-ray scattering. There remains significant challenges relating to the fundamental chemistry and physics of this growing family of hybrid compounds.

This research has been supported by the Royal Society and the European Research Council, with a wide collaboration network including simulations by Drs. Katrine Svane, Jarvist Frost, and Jonathan Skelton.

1. “Chemical principles for electroactive metal–organic frameworks” MRS Bulletin 41, 870 (2016)
2. “Metallic conductivity in a two-dimensional cobalt dithiolene metal−organic framework” J. Am. Chem. Soc. 139, 10863 (2017)
3. “Is iron unique in promoting electrical conductivity in MOFs?” Chemical Science 8, 4450 (2017)
4. “Atomistic origins of high-performance in hybrid halide perovskite solar cells” Nano Lett., 14, 2584 (2014)
5. “Direct observation of dynamic symmetry breaking above room temperature in methylammonium lead iodide perovskite” ACS Energy Lett. 1, 880 (2016)

Aron Walsh is a Royal Society University Research Fellow and Full Professor in the Department of Materials.  Aron joined Imperial College London in October 2016. He was awarded his PhD in Chemistry from Trinity College Dublin. He then worked for the US Department of Energy at the National Renewable Energy Laboratory (NREL), followed by a Marie Curie Fellowship hosted at University College London, and a European Research Council Fellowship held at the University of Bath. His research involves cutting-edge materials theory and similation applied to problems across solid state chemistry and physics, including materials for solar cells and solar fuels, information storage, batteries, thermoelectrics and solid-state lighting. He has a particular expertise in the theory of semiconductors and dielectrics, and is developing innovative solutions for materials data, informatics and design.