Dynamic Duos - Uncovering Singlet Fission Dynamics in TIPS-tetracene Crystals
Koen van den Hoven a, Vishal Bechai a, Hans Engelkamp a, Peter Christianen a
a High Field Magnet Laboratory, HFML-EMFL, Radboud University, The Netherlands
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Poster, Koen van den Hoven, 222
Publication date: 20th April 2022

In order to increase solar cell efficiencies, singlet fission materials could be of great use. In these organic semiconductors, a photoexcited singlet (spin S = 0) exciton state is converted into two triplet (spin S = 1) excitons with roughly half the initial energy. This carrier-multiplication process potentially reduces the thermalisation losses hampering solar power conversion efficiency [1].

The singlet fission process is thought to progress via intermediate triplet-pair states (total spin S = 0, 1 or 2), the properties of which are, however, still largely unknown. We identify several sharp triplet-pair peaks in the low temperature (1.4 K) photoluminescence (PL) spectrum of high-quality TIPS-tetracene (5,12-bis(triisopropylsilylethynyl)tetracene) crystals.

Using magnetic fields up to 30 T, we are able to tune the S = 1 and S = 2 triplet-pair states into resonance with the S = 0 triplet-pairs, resulting in a drastic reduction of the PL intensity at resonant magnetic fields. Surprisingly, the PL reduction can be as large as 90%, much more than the maximum of 50% anticipated before [2,3]. Lifetime measurements of the triplet-pair emission show that this is a dynamic effect, as the lifetime decreases at the resonant field strengths. Combining these findings, we construct a dynamical model where triplet dissociation can only occur via the S = 1 and S = 2 triplet-pair states. These calculations explain the >50% PL reductions and the field dependent triplet-pair PL decay times observed in our experiment.

K. van den Hoven, V.S. Bechai, H. Engelkamp, P.C.M Christianen

High Field Magnet Laboratory (HFML - EMFL), Radboud University, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands.

This work was supported by HFML-RU/NWO-I, member of the European Magnetic Field Laboratory (EMFL).

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