The singlet fission (SF) process is generally defined as the conversion of one singlet exciton (S1) into two triplet excitons (2·T1), which has the potential to overcome thermalization losses in the field of photovoltaic devices. Among the applicable compounds for SF-based photovoltaic devices, perylene bisimide (PBI) is one of the best candidates because of its electronic tunability and photostability. However, the strategy for efficient SF in PBIs remains ambiguous because of numerous competing relaxation pathways in PBI-based molecular materials. In this regard, for the first time, we observed the SF mechanism in PBI dimers by controlling the intrinsic factor (exciton coupling) and the external environment (solvent polarity and viscosity). Time-resolved spectroscopic measurements and quantum chemical simulations reveal that efficient SF occurs through the charge-transfer-assisted mechanism, entailing a large structural fluctuation. Our findings not only highlight the SF mechanism in PBI dimers but also suggest the factors responsible for an efficient SF process, which are important considerations in the design of molecular materials for photovoltaic devices.
Bibliographical noteFunding Information:
The work at Yonsei University was supported by the Strategic Research (NRF2016R1E1A1A01943379) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and an AFSOR/AOARD grant (FA2386-17-1-4086). The research at the Universität Würzburg was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the research unit FOR 1809. The work at Incheon National University was financially supported by the National Research Foundation of Korea (NRF-2019R1G1A1099961) and Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education (NRF-2017R1A6A1A06015181). This research was partially supported by the Graduate School of YONSEI University Research Scholarship Grants in 2019.
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All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry