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

Ambipolar organic electrochemical transistors (OECTs) are essential for the high-density integration of complementary logic circuits with reduced fabrication complexity. However, progress in this field remains limited by underdeveloped design principles, and the development of ambipolar single-component organic mixed ionic-electronic conductors (OMIECs) has lagged significantly. Herein, we design a novel electron-deficient building block BITBII, and copolymerize it with distinct electron-donating units to obtain two polymers (PBITBII-2FT, PBITBII-F2T). PBITBII-F2T-based single-component OECTs exhibited excellent ambipolar performance (p-type/n-type normalized transconductances (gm, norm): 4.7/2.92 S cm- 1; µC*: 63.37/14.58 F V- 1 cm- 1 s- 1). 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.