Fundamentals of Electrochemical Doping in OECTs

Doping of organic semiconductor films enhances their conductivity for applications in organic electronics, thermoelectrics and bioelectronics. However, much remains to be learnt about the properties of the conductive charges in order to optimize the design of the materials. Electrochemical doping is not only the fundamental mechanism in organic electrochemical transistors (OECTs), used in biomedical sensors, but it also represents an ideal playground for fundamental studies. Benefits of investigating doping mechanisms via electrochemistry include controllable doping levels, reversibility and high achievable carrier densities. We introduced here a series of optoelectronic experiments, such as in-situ terahertz (THz), Raman and UV/VIS/NIR spectroscopy to directly probe the electrochemical doping processes in OECTs. This is combined with time-resolved spectro-electrochemistry and chronoamperometry. We evaluate the intrinsic short-range transport properties of the polymers (without the effects of long-range disorder, grain boundaries and contacts), while precisely tuning the doping level via the applied oxidation voltage. Results will be presented for different polymeric mixed conductors, aligned systems and covalent organic frameworks (COFs).