The development of non-fullerene acceptors (NFAs) such as ITIC andY6 has greatly improved the efficiency of polymer solar cells. Therefore, focus shouldnow shift towards the design of donor polymers with better compatibility with theseNFAs to attempt to push efficiencies to higher levels. The indacenodithienothiophene(IDT) unit has up till now been typically incorporated into donor polymers forfullerene-based solar cells; however, the application of IDT-based polymers in NFAsolar cells is rare. In order to increase the number of donor polymer candidates, wehave synthesized two new polymers PIDT-T8BT and PIDT-T12BT conjugating IDTand perfluorinated benzothiadiazole moieties through octyl and dodecyl thiophenebridging units, respectively. These polymers were studied and revealed to becompletely amorphous without aggregates, and their glass transition temperatures weredistinct owing to the different lengths of the alkyl groups attached to the thiopheneunits. In addition, the length of the side groups greatly affects the solar cellperformance. The longer dodecyl side groups in the polymer PIDT-T12BT resulted in a lower glass transition temperature andfavorable thermal annealing conditions of the active layer blend with Y6. A promising power conversion efficiency of over 12 wasachieved for PIDT-T12BT when paired with the Y6 acceptor and thermally annealed at 170 °C, which is the highest reported valueso far for IDT-based donor polymers.
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