Ambipolar Blend-Based Organic Electrochemical Transistors and Inverters

Bioelectronic circuits translate biological to electric signals using organic electrochemical transistors (OECTs) based on organic mixed ionic-electronic conductors (OMIEC) in CMOS-like circuit architectures. Ambipolar OECTs, i.e. devices that can act as both p-type and n-type, can therefore reduce the complexity of circuit fabrication and increase device density. Ambipolarity in bioelectronics has another major advantage, the simultaneous detection of both cations and anions in one device, which further expands the prospects for diagnosis and sensing. Ambipolar OMIECs however, are scarce, limited by intricate material design and complex synthesis. We recently demonstrated that blending p-type and n-type OMIEC materials offers a simple and tunable approach for the fabrication of ambipolar OECTs and corresponding circuits. Building on the processing-morphology-performance relationships in organic solar cells, we implemented blends of polymers and small molecules where the morphology of the active layers can be controlled by materials selection blend composition and processing conditions. We will present two families of blends: n-type polymer and p-type small molecules, or p-type polymer and n-type small molecules, confirming the generality and versatility of the approach. We will also discuss how the molecular design of the materials, with respect to energy level alignment and solubility, affect device performance. Finally, we will show that the ambipolar OECTs can be used as building blocks for CMOS-like circuits, more specifically, inverters made of two identical ambipolar OECTs. These inverters show high current and voltage amplification factors and excellent stability over multiple alternating polarity cycles with ON/OFF ratios exceeding 10³ on both polarities and high gain. This work presents a simple and versatile new paradigm for the fabrication of ambipolar OMIECs and corresponding circuits with little constraints on materials design and synthesis and numerous possibilities for tunability and optimization towards higher performing bioelectronic applications.