The group work upon the design, synthesis and characterisation of functional materials for a range of optoelectronic applications, including field effect transistors, photovoltaic devices, light emitting diodes and sensors. Their work is highly multi-disciplinary and collaborative covering aspects of organic, polymer and materials chemistry with a central theme of establishing relationships between molecular design, synthetic methodology, processing and performance. Our research has so far led to the filing of more than 100 individual patents comprising over 40 patent families, and has led to the publication of more than 180 peer-reviewed articles in high profile journals, which have been cited more than 10,000 times to date. Current research theme ares:
Development of High Performance Air Stable Organic Transistor Materials
The development of organic polymers and small molecules exhibiting high charge carrier mobility and good ambient stability has been an area of long standing interst. By careful tuning of the backbone electronic structure and sidechains we have developed classes of polymer exhibiting excellent stability under ambient conditions, along with a tendency to self-organise into semicrystalline thin films. These guidelines have been utilised to develop classes of thiophene polymers exhibiting record performance.
- Fei, Z et al, J.Am. Chem. Soc. 2014, 15154 (ACS Editors Choice)
- Shaw, J. et al Macromolecules, 2014, 47, 8602.
- Zhang, X et al, Nature. Commun. 2013, 2238.
Ambipolar and N-type Semiconductors
The development of organic semiconductors able to transport both holes and electrons, particularly in ambient atmosphere has been an area of active research for the group. We were the first to demonstrate that selenophene inclusion is a promising strategy for ambipolar polymers, developing a series of materials with balanced transport and mobility comparable to amorphous silicon. We have also shown that oxidised DPP derivatives can be stabilised by the inclusion of four strongly electron withdrawing cyano groups. The resulting material forms highly ordered thin film and demonstrates air stable electron transport with some of the best mobilities reported to date. This work, in collaboration with Prof Thomas Anthopoulos (Dept. Physics), also demonstrated one of the first examples of an n-type transistor fabricated from a blend of the active component with an insulating polymeric binder.
- Casey, A. et al J. Mater. Chem. C 2015, 265.
- Marshall, et al J. Macromolecules 2014, 89.
- Fei, et al Z. Chem. Mater. 2013, 59
- Shahid, M. et al Chem. Sci. 2012, 3, 181. [ top 10 downloaded article 2012]
- Zhong, H. et al Adv. Mater. 2012, 3205.
- Kronemeijer et al Adv. Mater. 2012,1558.
Chalcogen Containing Organic Semiconductor
Our group has systematically investigated the effects of replacing thiophene, the ubiquitous heterocycle in organic semiconductor systems, with selenophene. This has required the development of a number of new synthetic routes to the synthesis of a number of fused selenophene containing polymers, and well as detailed device and characterisation studies. We were the first to report the synthesis of regioregular poly(3-hexyl)selenophene, the analogue to the very well-known poly(3-hexyl)thiophene, and demonstrate that the chalcogen swap can be beneficial for both solar cell and transistor performance. More recently we demonstrated that selenophene containing low band gap polymers are amongst the best ambipolar materials yet reported. We demonstrated that this high performance was due to the stabilising influence of the selenophene on the polymer LUMO.
- Al-Hashimi, M. et al Macromolecules 2011, 44, 5194.
- Shahid, M. et al J. Mater. Chem. 2012, 22, 12817.
- Tsoi, W. C. ACS Nano 2012, 6, 9646.
- Shahid, M. et al J. Mater. Chem. C 2013, 1, 6198.
- Fei, Z. et al J. Mater. Chem A, 2015, in press
Donor Polymers for Organic Photovolatic Cells.
Our group has been active in the development of donor polymers for organic solar cells for a number of years. We have extensively investigated the role of the bridging atom in fused aromatic containing polymers. We have shown that the replacement of silicon with germanium results in an significant improvement in the stability of the monomer to base, enabling polymer synthesis by the more benign Suzuki coupling rather than Stille polycondensation. The heteroatom switch also results in an increase in solar cell performance, and an increase in polymer crystallinity for a number of polymeric systems.
- Yau, C.P. et al Adv. Energy Mater. 2014, 1401228
- Kim, J. S. et al Adv. Energy Mater. 2014, 201400527
- Pang, C. Y. et al Adv. Funct. Mater. 2014, 678
- Zhong, H. et al J. Am. Chem. Soc., 2013, 135, 2040-2043.
Physical Chemistry of Polymeric Materials
In addition to developing new classes of conjugated polymers, we also strive to understand and control the complex solid state behaviour of such materials and relate this to device performance. Thus, we have been able to elucidate the relationship between polymer molecular weight, solution rheology and solar cell performance for several systems, as well as investigating the role of the polymer endgroup. By synthesising a series of well-defined oligomers, in collaboration with Prof Paul Smith (ETH Zurich), we were able to conclusively establish the packing of two crystalline polymorphs, as well as understanding the differences in growth kinetics. These fundamental studies have established important guidelines for the processing of electroactive materials.
- Himmelbert, S. et al Macromolecules 2014, 7151
- Koch, F. P.V.. et al J. Am. Chem. Soc. 2013, 135, 13699.
Synthesis of Novel Heterocycles and Development of Synthetic Methodology
A longstanding interest has been the development of new synthetic methods for the introduction of functional handles into heterocyclic systems, or to enable more facile synthesis. For example we recently reported a general synthetic methodology for the synthesis of asymmetric oligomers in practically useful quantities. A highlight has been driven by our interest in adapting flow chemistry methods to the development of highly controlled polymerisations. This led to collaboration with Prof John de Mello in the area of microdroplet reactors, which we were able to utilise to synthesise conjugated polymers for the first time.
- Al-Hashimi, M. et al Org. Lett. 2010, 12, 5478.
- Bannock, J.H. et al. Adv. Funct. Mater. 2013, 23, 2123. (Highlighted in Nature Chemistry)
- Koch, F. P.V. et al J. Am. Chem. Soc., 2013, 135, 13695.
- Bannock, J. H. et al Materials Horizons 2014, 214