2025 Theses Doctoral

Photophysics at the mesoscale: macromolecular engineering for multiexcitonic processes

Malinowski, Daniel

As traditional solar technologies approach theoretical efficiency limits, novel approaches are necessary to continue to improve the power generation capacity of photovoltaics. Two complementary multiexcitonic processes, singlet fission (SF) and triplet-triplet annihilation upconversion (TTA-UC), show great promise in this field, allowing access to regions of the solar spectrum inefficiently harvested by silicon cells.

In designing and optimizing systems for SF and TTA-UC, macromolecular scaffolds are particularly attractive, enabling the simultaneous tuning of electronic coupling between chromophores as well as their intermolecular packing. The high modularity of these scaffolds allows for easy adjustment of component ratios or the introduction of new units to further adjust dynamics or morphology. As such, macromolecular systems have also been employed in various condensed and solid phase systems which may more readily be incorporated into photovoltaics. Herein, we expand the scope of macromolecular architectures to new domains for SF and TTA-UC.

In Chapter 1, we summarize the guiding principles for the optimization of these processes, and follow with a discussion of existing oligomeric, macromolecular, and self-assembled systems. In Chapter 2, an amphiphilic block copolymer (BCP) is introduced to explore SF in self-assembled micelles. We find that SF dynamics can be controlled by modifying BCP block ratios, as well as by co-assembly with a variety of dopants.

In Chapter 3, this amphiphilic BCP scaffold is adapted to TTA-UC, and we highlight the importance of micellar swelling in enabling this process. In Chapter 4, electron donors are incorporated into polymers alongside pendent SF chromophores to explore both intra- and intermolecular charge transfer. We observe the formation of long-lived charge separated states prompted by SF, with dynamics tunable by solvent polarity, donor strength, and mode of interaction.

And in Chapter 5, a series of hetero-oligomers are presented to explore SF at interfaces between classic acenes and the less-studied dipyrrolonaphthyridinedione. We reinforce the essential role of charge transfer states in mediating or deactivating singlet fission in a tunable fashion based on chromophore energetics. In sum, this work further demonstrates the essential role macromolecular engineering will play in the continued development of SF and TTA-UC.