Organic Iono-Electronic Composite Materials Towards High-Performance Bioelectronic Devices

Organic semi-conducting materials with mixed ionic-electronic transport properties have gained a lot of attention over the past few years due to their ability to operate in close contact with the body and accurately transmit physiological signals. By mimicking the function of biological synapses, such bio-inspired conductors have shown great potential for future applications in bioelectronics and health monitoring. However, despite their better mechanical properties, biocompatibility, ease of integration into miniaturized architectures, low-cost production, low-power consumption, and chemical tunability -compared to their inorganic counterparts, organic semiconductors still suffer from a mechanical mismatch at the body-machine interface, poor charge carrier mobility, and low environmental stability. While polymer backbone and side chains engineering are promising chemistry approaches for addressing these limitations, we demonstrated that engineering organic iono-electronic composites (OIECs) further enables a fine tuning of both microstructural and electrochemical properties of conjugated polymers. OIECs were developed by blending an insulating matrix (poly(methyl methacrylate) (PMMA)) with a novel semiconducting polymer (PDPP3T-20gT), made of polar tetraethylene glycol side chains tethered to a backbone of 80% diketopyrrolopyrrole and 20% thiophene derivatives. The influence of the insulator’s tacticity (e.g., atactic, isotactic, syndiotactic) was also investigated. Structural changes across blends were characterized using high-precision atomic force microscopy, grazing-incidence wide angle X-ray scattering, and UV-vis spectroscopy. Mixed conduction properties were assessed using transducing devices (organic field-effect transistors (OFETs) and organic electrochemical transistors (OECTs)). We demonstrated that both the semiconductor/insulator ratio and the insulator’s tacticity strongly impact the nanostructure and the electrochemical properties of the semiconducting polymer. We showed that developing OIECs adds an extra layer of flexibility for engineering more mechanically compliant, low-cost, and readily processable channel materials for implementation into transducing devices. In conclusion, while engineering backbone and side chains is an efficient strategy to improve mixed ionic-electronic conduction and level up the performances of current organic bioelectronic devices, designing OIECs paves the way for the development of highly compliant materials towards prosthetics, smart electronics, and on-body computing.