Regioisomer‐Free Difluoro‐Monochloro Terminal‐based Hexa‐Halogenated Acceptor with Optimized Crystal Packing for Efficient Binary Organic Solar Cells

Abstract

AbstractHerein, we synthesized new hetero‐halogenated end groups with well‐determined fluorinated and chlorinated substitutions (o‐FCl‐IC and FClF‐IC), and synthesized regioisomer‐free small molecular acceptors (SMAs) Y‐Cl, Y‐FCl, and Y‐FClF with distinct hetero‐halogenated terminals, respectively. The single‐crystal structures and theoretical calculations indicate that Y‐FClF exhibits more compact three‐dimensional network packing and more significant π‐π electronic coupling compared to Y‐FCl. From Y‐Cl to Y‐FCl to Y‐FClF, the neat films exhibit a narrower optical band gap and gradually enhanced electron mobility and crystallinity. The PM6 : Y‐FClF blend film exhibits the strongest crystallinity with preferential face‐on molecular packing, desirable fibrous morphology with suitable phase segregation, and the highest and balanced charge mobilities among three blend films. Overall, the PM6 : Y‐FClF organic solar cells (OSCs) deliver a remarkable efficiency of 17.65 %, outperforming the PM6 : Y‐FCl and PM6 : Y‐Cl, which is the best PCE for reported hetero‐halogens‐based SMAs in binary OSCs. Our results demonstrate that difluoro‐monochloro hetero‐terminal is a superior regio‐regular unit for enhancing the intermolecular crystal packing and photovoltaic performance of hetero‐halogenated SMAs.