Alkyl Side Chain Modulation of Non‐Fused Polymerized Small Molecular Acceptors for Efficient All‐Polymer Solar Cells

Abstract Optimizing the morphology within the blends of polymer donors and acceptors is crucial for enhancing the performance of all‐polymer solar cells (all‐PSCs). Therefore, the development of rational strategies to modulate the aggregation behavior of polymers, thereby driving the formation of favorable morphology, holds great significance. In this study, two non‐fused polymerized small molecular acceptors (PSMAs), PFBTz‐OD and PFBTz‐DT, featuring distinct alkyl side chains are designed and synthesized. Compared with PFBTz‐OD, PFBTz‐DT exhibits better solubility due to its longer alkyl side chains, resulting in higher molecular weight and favorable temperature‐dependent aggregation characteristics in the solution. The all‐PSC utilizing PBDB‐T:PFBTz‐DT attains a power conversion efficiency (PCE) of 9.74%, surpassing the PCE of the PBDB‐T:PFBTz‐OD device, which stands at 6.60%. The better performance is mainly attributed to the suitable compatibility between the donor and acceptor, which facilitates the formation of optimal phase separation. The proper phase separation, in turn, enhances exciton dissociation, increases the mobility of both electrons and holes and minimizes charge recombination. This study emphasizes how engineering the alkyl side chains influences the control of polymer acceptor aggregation in solution and molecular packing in the film, both of which are essential for optimizing the morphology and improving device performance.