Readily Accessible Benzo[d]thiazole Polymers for Nonfullerene Solar Cells with >16% Efficiency and Potential Pitfalls

摘要： Here we report facile, high-yield synthetic access to the difluoro BTA building block, 4,7-bis(5-bromo-4-(2-hexyl-decyl)-thiophen-2-yl)-5,6-difluoro-2-(pentadecan-7-yl)-benzo[d]thiazole (BTAT-2f) for use in Donor (D)-Acceptor 1(A1)-D-Acceptor 2(A2) polymers [D = bithiophene, A1 = BTA-2f, A2 = benzothiadiazole (BT) derivative] for organic solar cells (OSCs). Fine tuning of polymer optical and electronic properties is achieved by incrementally varying the A2 fluorination level. Bulk-heterojunction (BHJ) PBTATBT-4f:Y6 solar cells deliver a noteworthy power conversion (PCE) efficiency of 16.08 % (Voc =0.81 V, Jsc =27.25 mAcm-2, FF =72.70 %) without processing additives. In contrast, PBTATBT-2f:Y6 exhibits an irregular morphology and low PCE, ascribable to co-crystal formation-induced recombination, which is unprecedented for non-fullerene (NFA) OSCs. This result should be of guiding significance for future NFA design.