Fine-Tuning of Polymer Aggregation Properties via Regulating the Side Chain Arrangement for Efficient Organic Solar Cells

The active layer morphology and device performance of organic solar cells (OSCs) are highly dependent on the polymer aggregation behavior. However, controlling polymer aggregation through molecular design to influence the active layer morphology remains a challenging endeavor. In this work, we demonstrate a straightforward yet highly effective approach to modulate the aggregation behavior of the typically used temperature-dependent aggregation polymer PffBT4T(1,4) by regulating the side chain arrangement. The resulting polymer, PffBT4T(1,3), with a regionally asymmetric alkyl chain arrangement, enables efficient OSCs with power conversion efficiencies (PCEs) up to 11.2%, while the PffBT4T(1,4)-based OSC devices only obtain a relatively low PCE of 10.1%. Moreover, the OSCs were processed from a nonhalogenated solvent without using any additives. The enhanced photovoltaic performance for PffBT4T(1,3)-based devices can mainly be attributed to the increased short-circuit current and fill factor, which can be attributed to the reduced domain spacing and improved domain purity within the active layer. Our work highlights that precise control of the alkyl chain arrangement can finely tune the aggregation properties and film morphology of donor polymers, leading to the construction of high-performance OSCs.