Near-infrared double-cable conjugated polymers based on alkyl linkers with tunable length for single-component organic solar cells

The photovoltaic properties of double-cable conjugated polymers are significantly influenced by the length of the alkyl linkers that connect donor backbones and acceptor side units. In this study, a series of 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC)-based double-cable polymers with alkyl linkers ranging from C₈H₁₆ to C₁₆H₃₂ (Px, x = 8, 10, 12, 14, 16) were synthesized for single-component organic solar cells (SCOSCs). Among these, the linker length x = 12 (P12) is found to optimize the power conversion efficiencies (PCEs) in SCOSCs. Specifically, PCEs increase from P8 to P12 and then decline from P12 to P16. Detailed investigations of optical absorption, charge transport, and morphology provide insights into the underlying factors contributing to these PCE variations. The findings indicate that the exceptional photovoltaic properties observed in P12 can be attributed to three key factors: A delicate balance between enhanced charge separation facilitated by the increased spacer length and reduced crystallinity resulting from longer spacers, higher charge mobilities, and well-balanced hole/electron transport characteristics. This study highlights the critical role of linker length in determining the photovoltaic properties of double-cable conjugated polymer-based SCOSCs and offers valuable guidance for the design of novel double-cable conjugated polymers.