Switching N‐Type to Ambipolar Organic Electrochemical Transistors by Donor Engineering of Polymeric Mixed Conductors Based on a Novel Electron‐Deficient BITBII Building Block

). In contrast, PBITBII-2FT exhibited only relatively weak n-type characteristics. Through theoretical calculations and film morphology analysis, the loss of ambipolarity in PBITBII-2FT is attributed to a more localized HOMO distribution, a wavy backbone leading to inferior intermolecular packing, and a rougher film morphology, all of which impede hole transport. Furthermore, a complementary inverter fabricated using PBITBII-F2T achieves a high voltage gain of up to 29.1 V/V. Cytotoxicity tests confirm the good biocompatibility of PBITBII-F2T. This work not only enriches the material library for high-performance ambipolar OECTs but also provides valuable insights into structure-property relationships governing ambipolar functionalities, offering guidance for future ambipolar molecular engineering.