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Vibronically coherent ultrafast triplet-pair formation and subsequent thermally activated dissociation control efficient endothermic singlet fission

DOI: 10.1038/nchem.2856 DOI Help

Authors: Hannah L. Stern (University of Cambridge) , Alexandre Cheminal (University of Cambridge) , Shane R. Yost (of California, Berkeley; Lawrence Berkeley National Laboratory) , Katharina Broch (University of Cambridge) , Sam L. Bayliss (University of Cambridge) , Kai Chen (MacDiarmid Institute for Advanced Materials and Nanotechnology; Victoria University of Wellington) , Maxim Tabachnyk (University of Cambridge) , Karl Thorley (University of Kentucky) , Neil Greenham (University of Cambridge) , Justin M. Hodgkiss (MacDiarmid Institute for Advanced Materials and Nanotechnology; Victoria University of Wellington) , John Anthony (University of Kentucky) , Martin Head-gordon (University of California, Berkeley; Lawrence Berkeley National Laboratory) , Andrew J. Musser (University of Cambridge; University of Sheffield) , Akshay Rao (University of Cambridge) , Richard H. Friend
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Nature Chemistry , VOL 110

State: Published (Approved)
Published: September 2017
Diamond Proposal Number(s): 11220

Abstract: Singlet exciton fission (SF), the conversion of one spin-singlet exciton (S1) into two spin-triplet excitons (T1), could provide a means to overcome the Shockley–Queisser limit in photovoltaics. SF as measured by the decay of S1 has been shown to occur efficiently and independently of temperature, even when the energy of S1 is as much as 200 meV less than that of 2T1. Here we study films of triisopropylsilyltetracene using transient optical spectroscopy and show that the triplet pair state (TT), which has been proposed to mediate singlet fission, forms on ultrafast timescales (in 300 fs) and that its formation is mediated by the strong coupling of electronic and vibrational degrees of freedom. This is followed by a slower loss of singlet character as the excitation evolves to become only TT. We observe the TT to be thermally dissociated on 10–100 ns timescales to form free triplets. This provides a model for ‘temperature-independent’ efficient TT formation and thermally activated TT separation.

Journal Keywords: Excited states; Materials chemistry; Solar cells

Subject Areas: Chemistry, Materials, Energy

Instruments: I07-Surface & interface diffraction

Added On: 07/11/2017 14:09

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