Donor Engineering for High Performance n-Type OECT Materials with Exceptional Operational Stability

Donor–acceptor (D–A) conjugated polymeric mixed ionic–electronic conductors (PMIECs) have been widely used in organic electrochemical transistors (OECTs) due to their structural diversity and the tunability of their frontier molecular orbital (FMO) energy levels. However, the slower development of n-type materials compared to p-type ones limits their potential in advanced technological applications. In this study, we design and synthesize a novel thiophene-based donor building block, 2,3-di(thiophen-2-yl)fumaronitrile (DTFMCN), for D–A conjugated n-type PMIECs through donor engineering strategies. DTFMCN can be easily synthesized from commercially available starting materials via a simple one-step process. The DTFMCN-based D–A conjugated polymers, S-DTFMCN and B-DTFMCN, exhibit extremely low-lying lowest unoccupied molecular orbital (LUMO) energy levels and show typical n-type characteristics. OECT devices based on these polymers demonstrate ultra-low threshold voltages (6 and 40 mV) and high µC* values of 13.49 and 13.57 F cm⁻¹ V⁻¹ s⁻¹, respectively. More importantly, these devices exhibit exceptionally high operational stability; the current retention rate after 168 minutes of operation is 96%, making them one of the most stable n-type OECT devices reported to date. This study highlights the effectiveness of DTFMCN in improving the operational stability of n-type OECT devices, offering promising potential for applications in bioelectronics.