A Blend Strategy to Achieve High Gain and Long-Term Stability in Complementary Inverters via Vertical Organic Electrochemical Transistors

While complementary inverters form the foundation of modern digital electronics, the performance of flexible and wearable counterparts is still limited. Organic electrochemical transistors (OECTs) offer a new route to address this challenge. They can leverage their unique intrinsic ion-to-electron transduction mechanism and high intrinsic transconductance to increase the gain of inverters. Furthermore, the ionic modulation observed in OECTs enables new functionalities, in particular neuromorphic behavior. In this work, complementary inverters based on vertical OECTs (vOECTs) are successfully fabricated, employing poly(benzimidazobenzophenanthroline) (BBL) as the n-type semiconductor, while poly(3-hexylthiophene-2,5-diyl) (P3HT), poly(3-2-(2-methoxyethoxy)ethoxyethylthiophene-2,5-diyl) (P3MEEET), or a blend of both polymers is used as p-type counterparts. These devices achieve high voltage gain and fast transient response depending on the employed p-type material system. A maximum voltage gain of 200 V/V is obtained using P3HT-based devices with reduced solution concentration, while P3MEEET-based inverters exhibit faster switching kinetics, with transient response times down to 1 ms. Furthermore, P3HT-based inverters provide superior operational stability when compared with P3MEEET-based devices. By blending both polymers, a balanced device response is achieved, combining the fast transient characteristics of P3MEEET with the stability of P3HT. The resulting blend-based inverters maintain stable operation for over 18,000 cycles at 10 Hz, demonstrating a versatile vOECT platform and an effective materials-engineering approach to simultaneously achieve high speed, high gain, and robust long-term stability in organic electronics.