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Spin-orbit coupling in synthetic semiconductor-protein complexes for solar energy harvesting


Project Description

Singlet fission is a process whereby one photon creates two excited states. This two-for-one mechanism could dramatically increase solar cell efficiency (from 33% to >40%). Recently, there has been much academic and industrial interest in developing new singlet fission sensitizers, but to-date no material has proved ideal [1].

The biggest hurdle for using singlet fission sensitizers for solar harvesting is that of transferring the triplet excitons to the photovoltaic. Previous work suggests direct energy- or charge-transfer of the triplets into silicon is extremely inefficient [1]. Instead radiative transfer (i.e. photon emission then reabsorption into silicon) has been suggested [1]. Unfortunately, triplet excitons are non-emissive! They could transfer to an efficient emitter as suggested in Ref. [2], but we suggest an alternative approach: protein-induced triplet emission, i.e. phosphorescence.

We have recently created a new range of synthetic ‘maquette’ proteins that bind organic semiconductors (non biological pigments) in a specific dimer configuration. You will use these proteins to induce triplet emission (phosphorescence) in the organic semiconductors.

Room temperature phosphorescence has been known to occur in proteins since the 1970s [4,5]. We aim to design proteins that exploit this behaviour, hindering non-radiative deactivation and enabling pigment phosphorescence. To increase the phosphorescence efficiency further, we will use external spin-orbit coupling, as demonstrated in molecular crystals [6]. Compared with molecular crystals, our synthetic proteins offer a much more fine-tuned approach to achieving phosphorescence: we can place heavy elements at specific locations within the protein core. Achievement of this would constitute a major breakthrough.

In this project, you will work closely with biologists to develop and characterize semiconductor-proteins capable of efficient triplet emission. To achieve this aim, you will use time-resolved optical spectroscopy to track the singlet fission process in absorption and emission as a function of protein structure at the recently opened ‘Lord Porter Laser Facility’ in Sheffield.


Science Graduate School:
As a PhD student in one of the science departments at the University of Sheffield, you’ll be part of the Science Graduate School – a community of postgraduate researchers working across biology, chemistry, physics, mathematics and psychology. You’ll get access to training opportunities designed to support your career development by helping you gain professional skills that are essential in all areas of science. You’ll be able to learn how to recognise good research and research behaviour, improve your communication abilities and experience technologies that are used in academia, industry and many related careers. Visit http://www.sheffield.ac.uk/sgs to learn more.

Funding Notes

If you submit your application after the 31 March 2019, you will be considered for any remaining funding, but please note all of our funding may be allocated in the first round.

References

[1] Rao & Friend, Harnessing singlet exciton fission to break the Shockley–Queisser limit Nature Reviews, 2, 17063 (2017)
[2] Davis et al. Singlet Fission and Triplet Transfer to PbS Quantum Dots in TIPS-Tetracene Carboxylic Acid Ligands. Journal of Physical Chemistry Letters 9:1454–1460 (2018)
[3] Yang et al., The influence of the molecular packing on the room temperature phosphorescence of purely organic luminogens Nature Commun. 9:840 (2018)
[4] Vanderkooi, et, al. On the Prevalence of Room-Temperature Protein Phosphorescence Science 236:568 (1987)
[5] Saviotti et al., Room Temperature Phosphorescence and the Dynamic Aspects of Protein Structure Proc. Nat. Acad. Sci. 71, 4154-4158, (1974)
[6] Xiao et al., Highly Efficient Room-Temperature Phosphorescence from Halogen-Bonding-Assisted Doped Organic Crystals J. Phys. Chem. A, 121, 8652-8658 (2017)

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