Mixed Ionic‐Electronic Transport in A Series of New Cyano‐Functionalized N‐Type Conjugated Ladder Copolymers

N‐type conjugated ladder polymers without side chains, such as BBL, have been shown to exhibit record‐high mixed ionic‐electronic transport properties, which have enabled diverse device applications. This study reports herein the design and synthesis of a series of dicyano‐functionalized n‐type conjugated ladder copolymers, BBL‐ x 2CN, as new organic mixed ionic‐electronic conductors (OMIECs). By combining the cyanation and random copolymerization design motifs, this study demonstrates that the electronic band structure (LUMO/HOMO energy levels) can be effectively tuned as a function of the copolymer composition of the dicyano functional group without compromising the unique planar polymer backbone intrinsic to BBL‐type ladder polymers. Optimal mixed ionic‐electronic transport properties probed via organic electrochemical transistors (OECTs) are found in BBL‐202CN (20 mol%) devices that feature a high transconductance (≈3 mS), a good µ C * value (≈2.8 FV −1 cm −1 s −1 ), and a fast transient response ( τ on / τ off = 40 ms/12 ms), which are substantially enhanced compared to those of the parent BBL of comparable molecular weight. The better OECT device performance found in BBL‐202CN copolymer, compared to other copolymers, can be explained by a combination of improved crystallinity, delocalization length, and suppressed conformational disorder. These results provide new structure‐property relationships with implications for the molecular engineering of high‐performance n‐type OMIECs.