Length Effect of Alkyl Linkers on the Crystalline Transition in Naphthalene Diimide-Based Double-Cable Conjugated Polymers

The alkyl chains as linkers in double-cable conjugated polymers play an important role in the solubility, packing motif, morphology, and voltage loss in single-component organic solar cells (SCOSCs). In this work, we incorporate alkyl linkers with lengths from hexyl (C6H12) to hexadecyl (C16H32) into naphthalene diimide-based double-cable conjugated polymers. These polymers show a parabolictype distribution in crystallinity, in which the crystalline degree of the polymers is enhanced in sequence from P06 (C6H12 linker) to P12 (C12H24 linker) and then decreased in longer alkyl linkers. These differences bring into deviations like optical bandgaps, packing motif, charge transport, and photovoltaic performance in SCOSCs. This work demonstrates the importance of linkers' length on crystallinity and packing motif as well as provides a new viewpoint in guiding the design of new double-cable conjugated polymers.