Abstract:
Singlet fission, the conversion of one photoexcited singlet exciton into two triplet excitons, is a promising mechanism to overcome theoretical efficiency limits in single-junction solar cells. Intramolecular singlet fission materials based on molecular dimers are a powerful platform to study singlet fission since chromophore-chromophore interactions can be fine-tuned through chemical structure. A challenge in the design of efficient intramolecular singlet fission materials is the inability to independently adjust triplet pair formation and decay rates, which have opposite dependences on chromophore coupling. This talk details several strategies to decouple these rates through molecular engineering of the bridging unit between singlet fission chromophores. We describe in detail how bridge energetics, connectivity, length, and planarity are tunable handles for controlling rates of triplet pair generation and recombination. These rates can even be modulated independent of each other, furnishing materials with fast triplet generation and long triplet lifetimes desirable for harvesting applications. This work establishes key design principles to provide greater control over triplet pair formation, dephasing, and decay in multiexcitonic materials.
