Controlling ambipolar OECT threshold voltage through acceptor unit engineering of conjugated polymers

Abstract

Single-component ambipolar conjugated polymers are crucial in developing organic electrochemical transistors (OECTs) and complementary logic circuits, primarily because they simplify the fabrication process. However, ambipolar OECTs face significant challenges in achieving precise control over the threshold voltage (V_Th). This study demonstrates that V_Th can be effectively regulated by modifying the electron-withdrawing acceptor units in the conjugated polymer backbone. By comparing two ambipolar polymers, PThDPP-BTz and PThDPP-BBTz, we find that the stronger electron-withdrawing BBTz unit lowers the energy levels, enhances electrochemical doping efficiency, and significantly reduces V_Th. Specifically, the n-type V_Th shifts from 0.7 V to 0.02 V, and the p-type V_Th adjusts from −0.68 V to −0.61 V. Consequently, the inverter using ambipolar PThDPP-BBTz OECTs achieves a voltage gain of 93 V/V at V_in = 0.1 V, while the inverter based on ambipolar PThDPP-BTz OECTs shows an apparent voltage gain when V_in exceeds 0.6 V. This study clarifies the critical factors influencing the threshold voltage of OECT devices and introduces a methodology for precise V_Th regulation.