Direct Observation of Exchange-Coupled Triplet-Pair Emission in TIPS-Tetracene Crystals
Vishal Bechai a, Koen van den Hoven a, Peter Christianen a, Hans Engelkamp 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
Oral, Vishal Bechai, presentation 128
Publication date: 20th April 2022

Singlet fission (SF) in organic semiconductors is a promising concept that can be used to increase the efficiency of photovoltaic cells. Upon light absorption a singlet exciton (S = 0) is created, which via an intermediate triplet-pair (TT) state (S = 1 ⊗ S = 1) splits into two triplet excitons (S = 1). This carrier-multiplication process potentially reduces the thermalization losses hampering solar power conversion efficiency. Recently, low-temperature photoluminescence (PL) spectroscopy in magnetic fields up to 68 T has been used to study triplet-pair emission in TIPS tetracene (5,12-bis(triisopropylsilylethynyl)tetracene) [1]. Multiple triplet pairs were identified, the emission of which is quenched at resonant magnetic fields when the singlet TT-sublevel coincides with the triplet and quintet sublevels. Here, we report the direct observation of triplet-pair emission at 1.4 K and 0 T in high-quality TIPS-tetracene single crystals. From PL studies in magnetic fields up to 30 T we determine the exchange coupling constant of the emissive pair to be J = 0.44 meV. The triplet-pair emission displays a characteristic vibrational spectrum and is found to disappear above 2.4 K, which is attributed to the thermal activation of triplet-pair dissociation via the quintet states [2]. Most remarkably, we find that the 1.4 K triplet-pair PL decay time exceeds 10 microseconds, indicating that in the absence of thermal dissociation the triplet pairs can have a very long lifetime [2]. Our results pave the way for a detailed (time-resolved) study of the properties of triplet pairs and the SF process.

V.S. Bechai, K. van den Hoven, 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).

We use our own and third party cookies for analysing and measuring usage of our website to improve our services. If you continue browsing, we consider accepting its use. You can check our Cookies Policy in which you will also find how to configure your web browser for the use of cookies. More info