Our research is focussed on the fundamental understanding of the charge and spin transport and thermoelectric physics of novel molecular and polymeric organic semiconductors, metal halide perovskites, two-dimensional metal-organic frameworks and related materials.
Organic semiconductors are exotic, carbon-based optoelectronic materials that owe their unique solid-state physical properties to the soft, van der Waals bonding between individual molecules. The pi-conjugated electronic states tend to be robustly delocalised across the individual covalently bonded molecular units but their shape depends strongly on the molecular geometry since the ability of the electronic wavefunctions to delocalise across molecular units is very sensitive to the intermolecular packing. Concomitantly, the molecular units are large and may contain hundreds of atoms, which implies complex structural dynamics with many different vibrational modes. Some of the intermolecular and torsional modes are very soft, resulting in large vibrational amplitudes at room temperature. This results in a strong coupling between the electronic and structural dynamics that gives rise to unique and fascinating phenomena in these molecular solids, such as a transient localisation of the electronic states.
To understand the unique fundamental physics of charge, spin and heat transport processes in these materials, we use a broad range of experimental characterisation techniques. They include measurements of transport coefficients, optical spectroscopy, spin resonance techniques, scanning probe microscopy and in-operando measurements on devices, which allow us to directly probe the key physical processes that are relevant for particular applications. We work closely with synthetic chemistry groups to investigate molecular structure-property relationships and discover materials with new functionalities and better device performance.
Our research could lead to more sustainable energy conversion, storage and information processing technologies that could make a significant contribution to a successful energy transition to a zero carbon energy economy over the next 30 years.
Key Publications
- Sirringhaus, H., Tessler, N. & Friend, R.H. Integrated optoelectronic devices based on conjugated polymers. Science 280, 1741-1744 (1998).
- Sirringhaus, H. et al. Two-dimensional charge transport in self-organized, high-mobility conjugated polymers. Nature 401, 685-688 (1999).
- Sirringhaus, H. et al. High-resolution inkjet printing of all-polymer transistor circuits. Science 290, 2123-2126 (2000).
- Chua, L.L. et al. General observation of n-type field-effect behaviour in organic semiconductors.Nature 434, 194-199 (2005).
- Zaumseil, J., Friend, R.H. & Sirringhaus, H. Spatial control of the recombination zone in an ambipolar light-emitting organic transistor. Nature Materials 5, 69-74 (2006).
- Noh, Y.Y., Zhao, N., Caironi, M. & Sirringhaus, H. Downscaling of self-aligned, all-printed polymer thin-film transistors. Nature Nanotechnology 2, 784-789 (2007).
- Banger, K.K. et al. Low-temperature, high-performance solution-processed metal oxide thin-film transistors formed by a 'sol-gel on chip' process. Nature Materials 10, 45-50 (2011).
- Eggeman, A.S., Illig, S., Troisi, A., Sirringhaus, H. & Midgley, P.A. Measurement of molecular motion in organic semiconductors by thermal diffuse electron scattering. Nature Materials 12, 1044-1048 (2013).
- Venkateshvaran, D. et al. Approaching disorder-free transport in high-mobility conjugated polymers. Nature 515, 384-388 (2014).
- Watanabe, S. et al. Polaron spin current transport in organic semiconductors. Nature Physics 10, 308-313 (2014).
- Kang, K. et al. 2D coherent charge transport in highly ordered conducting polymers doped by solid state diffusion. Nature Materials 15, 896-902 (2016).
- Broch, K. et al. Measurements of Ambipolar Seebeck Coefficients in High-Mobility Diketopyrrolopyrrole Donor-Acceptor Copolymers. Adv. Electron. Mater. 3, 1700225 (2017).
- Nikolka, M. et al. High operational and environmental stability of high-mobility conjugated polymer field-effect transistors through the use of molecular additives. Nature Materials 16, 356-362 (2017).
- Schott, S. et al. Tuning the effective spin-orbit coupling in molecular semiconductors. Nature Communications 8, 15200 (2017).
- Senanayak, S.P. et al. Understanding charge transport in lead iodide perovskite thin-film field-effect transistors. Science Advances 3 (2017).
- Statz, M. et al. On the manifestation of electron-electron interactions in the thermoelectric response of semicrystalline conjugated polymers with low energetic disorder. Commun. Phys. 1, 10 (2018).
- Kang, K. et al. Investigation of the thermoelectric response in conducting polymers doped by solid-state diffusion. Mater. Today Phys. 8, 112-122 (2019).
- Nikolka, M. et al. High-mobility, trap-free charge transport in conjugated polymer diodes. Nature Communications 10, 2122 (2019).
- Schott, S. et al. Polaron spin dynamics in high-mobility polymeric semiconductors. Nature Physics 15, 814-822 (2019).
- Wang, S.J. et al. Long spin diffusion lengths in doped conjugated polymers due to enhanced exchange coupling. Nature Electronics 2, 98-107 (2019).