“Double Lock-in” Strategy in Quasi-macromolecule Acceptors Enabling Highly Efficient Organic Solar Cells with Low Energy Disorder

To achieve superior photovoltaic characteristics, quasi-macromolecules (QMs), also known as giant molecules, require an optimal molecular configuration and packing motifs. In this work, we systematically investigate molecular planarity and π-conjugation of linear QMs through introducing dual noncovalent bonding. Compared to QM6F-OT with alkoxyl-substituted thiophene as the linker unit, the other two QMs, QM6F-T and QM6F-CT, have the same building block but differ in their substituents of the thiophene linker units, resulting in distinct backbone configurations. Consequently, an efficiency exceeding 18% was achieved in organic solar cells (OSCs) based on PM6:QM6F-OT. By integrating detailed molecular structure, morphology, device performance, and transient absorption spectroscopy analysis, a robust structure–morphology–property relationship is established. The optimization of the molecular structure via side chain engineering on the linker units with the “double lock-in” strategy benefits improved exciton diffusion length, suppressed energetic disorder and voltage losses, as well as improved charge transport in the devices. This work provides valuable design guidelines for developing a low-disordered QM acceptor and highly efficient OSCs.