New Type of Polymerized Small A-D-A Acceptors Constructed by Conjugation Extension in the Branched Direction

The current high-performance polymerized small molecular acceptors (PSMAs) are mainly polymerized through terminal groups of small molecular acceptors (SMAs), which will inevitably damage the preferred stackings of terminal groups and render an inferior photoelectric performance of all-polymer solar cells (all-PSCs). In order to liberate terminal groups for more efficient intermolecular stackings, a new pathway to construct PSMAs is explored by extending molecular conjugation in branched directions, thereby affording two PSMAs of SP-T and SP-TT with thiophene and bithiophene as linkers, respectively. Benefiting from more compact/ordered π–π stackings and superior morphology, the SP-T-based all-PSC exhibits facilitated charge generation/transport and suppressed recombination, thus yielding a greatly improved efficiency of 13.54% compared with 9.76% for the SP-TT-based one. Our work not only develops a new type of PSMA featuring much enhanced molecular packings but also demonstrates its great potential for achieving state-of-the-art all-PSCs through the delicate engineering of linkers.