Triplet Harvesting from Intramolecular Singlet Fission in Polytetracene

Singlet fission (SF), a promising mechanism of multiple exciton generation, has only recently been engineered as a fast, efficient, intramolecular process (iSF). The challenge now lies in designing and optimizing iSF materials that can be practically applied in high-performance optoelectronic devices. However, most of the reported iSF systems, such as those based on donor–acceptor polymers or pentacene, have low triplet energies, which limits their applications. Tetracene-based materials can overcome significant challenges, as the tetracene triplet state is practically useful, ≈1.2 eV. Here, the synthesis and excited state dynamics of a conjugated tetracene homopolymer are studied. This polymer undergoes ultrafast iSF in solution, generating high-energy triplets on a sub-picosecond time scale. Magnetic-field-dependent photocurrent measurements of polytetracene-based devices demonstrate the first example of iSF-generated triplet extraction in devices, exhibiting the potential of iSF materials for use in next-generation devices.

A conjugated tetracene homopolymer is synthesized, investigated spectroscopically, and employed as the active layer in photovoltaic devices. Spectroscopic measurements reveal sub-picosecond singlet fission in this material in solution or in films. Films facilitate dissociation of the resulting triplet pairs. Solution-processed devices employing polytetracene achieve singlet-fission-based photocurrent enhancement, but only when the acceptor energy levels are sufficiently low.

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