Singlet fission in polyenes

In current solar cells much of the UV and blue light absorbed is lost as heat, as the energy of the absorbed photon is much higher than the bandgap of the semiconductor material, and therefore the collected electronic energy. One mechanism for harvesting all of the absorbed photon energy is to exploit the 'singlet exciton fission' process which occurs in some organic semiconductors. Singlet fission is a process whereby the primary excited state (singlet exciton) can split into two distinct triplet excitons which can both be harvested. In this way, one absorbed photon creates two collected charges, producing a solar cell with up to 200% quantum efficiency.

Singlet fission in polyenes (linear conjugated carbon chains) occurs when there is enough space for two triplet excitons to sit near each other: either on a very long polymer chain, or on two closely spaced neighbouring molecules. Polyenes demonstrate strong photoabsorption in UV-visible region, are solution-processable and demonstrate very efficient and robust singlet fission. They are therefore excellent candidates for singlet fission solar cells.

To exploit the singlet fission mechanism and the polyene class of materials, we need better understanding of how to describe singlet fission in polyenes and how to control it through material design. In addition, we urgently need to demonstrate whether the triplet excitons created through singlet fission can be efficiently ionised to create charges. In this project, we will answer these questions using a combination of cutting-edge time-resolved spectroscopic techniques, model samples and high-level theory.

This is a 1-year project mostly dealing with fundamental physics. The short-term impacts are mainly enhancing the knowledge economy and training students/postdocs.

Scientific advances
There are gaps in the understanding of polyene (including carotenoid) excited state physics that this project will fill, for example the mechanism of singlet fission in polyenes and whether they can be used as singlet fission sensitisers for improving solar cell efficiency.

Techniques
During the project, we will complete the building of a state-of-the-art laser facility at the University of Sheffield. This will include experiments that, to the best of my knowledge, have not yet been performed with such good time resolution anywhere in the world (for example, broadband transient grating photoluminescence luminescence spectroscopy and transient absorption spectroscopy with mid-IR (2-4um) probe, both with sub-40fs resolution).

People
The PDRA employed on the grant if successful (Nick Paul) will be starting his first postdoc. He will gain supervision skills through training, mentoring and helping the PhD students. The students will benefit from the additional training provided by the PDRA and from the amazing opportunity to travel to international conferences to meet world-experts and to present their work.
This proposal will impact the PI's career significantly as this is not only her first grant, she has also just returned from two consecutive maternity leaves (two children in two years) and moved to a new institution. Following this career break, she must quickly build up her new research group starting with the postdoc named on the grant. This grant will provide the seed with which to apply for more funding to build a highly successful and productive research team.

Economy
On the longer term, it is difficult to predict the impact. It is likely to lead to new funding to research and develop singlet fission sensitised solar cells with better efficiency than today's best solar cells. This would impact the economy most likely in the form of new products in established companies such as Eight19, SolarWorld or ZNshine.