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Understanding the spin-entangled triplet-pair state in organic semiconductors

  • Full or part time
  • Application Deadline
    Applications accepted all year round
  • Funded PhD Project (European/UK Students Only)
    Funded PhD Project (European/UK Students Only)

Project Description

In collaboration with theoreticians at the University of Oxford, this project involves studying the fundamental electronic behaviour of excited states in organic semiconductors (specifically ‘triplet-pair’ states) for applications in photovoltaics, displays and polaritonics. You will study model systems (either thin films, photonic devices or protein-bound semiconductors) using ultrafast spectroscopy at Sheffield’s ultrafast laser facility.

Background

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%). There has therefore been significant academic and industrial interest in developing new singlet fission sensitizers for photovoltaic or optoelectronic applications recently. Unfortunately, to-date no material has proved ideal. This is in part because of a fundamental lack of understanding of the singlet fission process and what molecular parameters control it. What is known is that singlet fission proceeds through an intermediate excited state, known as (TT): a correlated pair of triplets (spin S=1 excitations). The spins of the individual triplets may remain entangled over microseconds at room temperature, even as the triplets move apart, making it an exciting area of research with possible applications well beyond photovoltaics.

Project details

In this project you will study the magnetic-field dependent spectroscopy of organic semiconductors using ultrafast (femtosecond) pulses of light to map the electronic landscape of the singlet fission process in Sheffield’s ultrafast laser facility. The emphasis will be on developing an understanding of triplet-pair states (TT): their lifetime and energetics; how long they remain spin-coherent; how far and fast they move. The aim is to understand which molecular and film parameters govern these properties and how they can be optimized for use in a variety of optoelectronic and photonic devices.

You will be fully trained to work in the ultrafast laser facility in Sheffield as an independent scientist, you will have the opportunity to collaborate with leading theoreticians at the University of Oxford and to make photonic or optoelectronic singlet fission-based devices in Sheffield’s cleanrooms.

Person Specification

You will have a 2:1 or above (or equivalent degree) in physical chemistry, physics or material science.

If you have any questions about the project please do not hesitate to contact Jenny Clark directly.

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] Scholes, Correlated Pair States Formed by Singlet Fission and Exciton−Exciton Annihilation J. Phys. Chem. A, 119, 12699−12705 (2015);
[3] Teichen & Eaves Collective aspects of singlet fission in molecular crystals. J. Chem. Phys. 143:44118 (2015);
[4] Smith & Michl, Singlet fission. Chemical Reviews 110:6891–6936 (2010);
[5] Yong et al., The entangled triplet pair state in acene and heteroacene materials. Nature Communications 8:15953 (2017);
[6] Kollmar, Electronic structure of diradical and dicarbene intermediates in short-chain polydiacetylene oligomers, J. Chem. Phys. 98, 7210 (1993)

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