Singlet Fission Dynamics in the 5,12-Bis(phenylethynyl)tetracene Thin Film
Amitabha Nandi, Biswajit Manna, Rajib Ghosh
Abstract
The singlet fission (SF) process is a promising route to overcome the Shockley and Quiesser efficiency limit of organic solar cells and hence has attracted significant research interest in the recent past. Efficient SF in low-cost organic materials with broad visible absorption is desirable to potentially boost organic solar cell efficiency. Herein, we report the ultrafast and efficient SF property of a new molecular material, namely, the 5,12-bis(phenylethynyl)tetracene (BPET) thin film. Steady-state and time-resolved optical studies on the thin film of BPET revealed prompt deactivation of majority of singlet excitons with a lifetime of about 1.0 ps. Detailed analysis of transient spectral features suggests ultrafast relaxation of the singlet exciton to correlated triplet pair formation within 200 fs followed by free triplet exciton generation on the picosecond time scale. However, a slower SF component is also identified originating from the amorphous phase in the thin-film sample. Overall, high SF yield (∼90%) with long-lived triplet (∼3 ms) is estimated from spectroscopic measurements. Efficient SF in BPET as compared to parent tetracene is attributed as the influence of phenylethynyl substituents to alter the energy levels and intermolecular coupling. Wide spectral coverage of visible absorption, solution processability, and high triplet yield (∼180%) by the SF process are expected to make BPET a suitable candidate in SF-based organic solar cells.