Hybrid Cycloalkyl‐Alkyl Chain‐Based Symmetric/Asymmetric Acceptors with Optimized Crystal Packing and Interfacial Exciton Properties for Efficient Organic Solar Cells

Abstract

Abstract Hybrid cycloalkyl‐alkyl side chains are considered a unique composite side‐chain system for the construction of novel organic semiconductor materials. However, there is a lack of fundamental understanding of the variations in the single‐crystal structures as well as the optoelectronic and energetic properties generated by the introduction of hybrid side chains in electron acceptors. Herein, symmetric/asymmetric acceptors (Y‐C10ch and A‐C10ch) bearing bilateral and unilateral 10‐cyclohexyldecyl are designed, synthesized, and compared with the symmetric acceptor 2,2′‐((2Z,2′Z)‐((12,13‐bis(2‐butyloctyl)‐3,9 bis(ethylhexyl)‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2″,3″′:4′,5′]thieno[2′,3′:4,5] pyrrolo[3,2‐g]thieno[2′,3′:4,5]thieno[3,2‐b]indole‐2,10‐ diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (L8‐BO). The stepwise introduction of 10‐cyclohexyldecyl side chains decreases the optical bandgap, deepens the energy level, and enables the acceptor molecules to pack closely in a regular manner. Crystallographic analysis demonstrates that the 10‐cyclohexyldecyl chain endows the acceptor with a more planar skeleton and enforces more compact 3D network packing, resulting in an active layer with higher domain purity. Moreover, the 10‐cyclohexyldecyl chain affects the donor/acceptor interfacial energetics and accelerates exciton dissociation, enabling a power conversion efficiency (PCE) of >18% in the 2,2′‐((2Z,2′Z)‐((12,13‐bis(2‐ethylhexyl)‐3,9‐diundecyl12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2″,3″′:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2‐g]thieno[2′,3′:4,5]thieno[3,2‐b]indole‐2,10‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (Y6) (PM6):A‐C10ch‐based organic solar cells (OSCs). Importantly, the incorporation of Y‐C10ch as the third component of the PM6:L8‐BO blend results in a higher PCE of 19.1%. The superior molecular packing behavior of the 10‐cyclohexyldecyl side chain is highlighted here for the fabrication of high‐performance OSCs.

Keywords

• asymmetric small molecule acceptors
• crystal packing
• organic solar cells
• side‐chain engineering