Emerging Organic Technologies
Electrochromic devices reversibly change color with applied potential. These devices, based on conjugated polymers, have applications as large-scale thermal windows or anti-glare rear-view mirrors in the automobile industry, for example. To bridge the research-to-production scale gap in that kind of devices, new conjugated materials and deposition methods are needed. Spray- and sheet-coating methods for depositing commonly used electroactive conjugated polymers and newly developed azomethines on large area electrodes are being examined, as is their subsequent post-deposition immobilization with a view to using these processing methods for electroactive layers in electrochromic devices.
The interplay of the conjugated polymer porosity, electrode‒electroactive conjugated polymer interfaces, and processing solvent‒polymer interface on the overall electrochromic device performance is investigated. Efforts are focusing on understanding the electrode‒electroactive layer interface of various conjugated materials (azomethines and thermally polymerizable prepared monomers) in addition to the effect of ionic liquid inclusion on device performance. The XPS, XRD, EQCM-D, and NanoIR are the principal tools for those investigations.
Organic Electrochemical Transistors (OECTs)
Flexible and stretchable OECTs are being investigated for a wide range of applications, including non-invasive electrophysiology and displays. OECTs comprise a conducting polymer film (transistor channel) in contact with an electrolyte. They may be operated in aqueous electrolytes, providing an interface between the worlds of biology and electronics. EQCM-D is used to test the ability of the OECT to incorporate/release molecules of biological interest for potential applications in drug delivery systems. Furthermore, we conduct high-resolution measurements of ionic fluxes between the polymer channel and the electrolyte via LEIS to evaluate the OECT device’s ability to deliver biologically active substances.
OECTs which use transistor channel materials with electrochromic properties facilitate the design of electrochromic transistors with tremendous potential in diverse applications, ranging from sensors to switches in optical computing. By developing the electrochromism of conducting polymers, spectroelectrochemical measurements are used to study the redox chemistry of conducting polymers processed in various ways and in the presence of different electrolytes.
A natural extension of OECTs’ is the electrolyte-gated organic light-emitting transistor (EG-OLET). In EG-OLETs, light emitting organic materials are being interfaced with ionic liquids and ion gels. This class of devices has the capacity to provide breakthroughs in brightness enhancement that is currently possible with conventional organic light-emitting diodes. The numerous available ionic liquids and ion gels represent an unprecedented opportunity to create high-performance devices and better understand organic light-emitting film/electrolyte interfaces. Mechanistic data are required to properly correlate the redox activity of the n- and p-type materials in the light-emitting layer with the ion transport and doping processes. That kind of data is being acquired by LEIS and EQCM.
Organic conducting polymers are excellent candidates in the manufacture of flexible and stretchable wearable sensors, since they conduct both ionic and electronic charge carriers. For example, flexible and stretchable OECTs based on organic conducting polymers are under investigation for applications in noninvasive electrophysiology. The inherent signal amplification of OECTs, achievable due to the presence of the gate electrode, facilitates a higher signal-to-noise ratio compared to standard electrodes. Conducting polymers offer several advantages over metals, including i) lower contact impedance, which results in higher sensitivity and stability as well as lower stimulation currents to achieve the same effect, thus resulting in longer battery life, and ii) improved mechanical interface with living tissues due to the soft nature of the polymer surface.