Prof. Natalie Banerji, University of Bern

Charge Transfer Dynamics and Terahertz Conductivity in Electrochemically Doped Conjugated Polymers for Bioelectronic Applications


Start Date 18.04.2023 - 16:30
Event End 18.04.2023 - 17:30
Location University of Zurich, Department of Chemistry
Lecture Hall Y15-G-40

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 important for organic electrochemical transistors (OECTs) used in biomedical sensors, but 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 introduce a new technique, applying in-situ terahertz (THz) spectroscopy directly to electrochemically doped polymers in combination 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. Moreover, temperature-dependent measurements allow to extract the thermodynamic and activation parameters of the electrochemical processes. For the state-of-the-art polymer P3HT, we find that polarons and bipolarons need to co-exist in an optimal ratio to reach high THz conductivity for in aqueous KPF6 electrolyte. Moreover, the analysis of the spectro-electrochemistry data shows that those two species are generated at different rates in amorphous and crystalline regions of the film. On the other hand, in PEDOT:PSS (used for many bio-electronic applications), the conductivity continues to rise as more bipolarons are generated. The generation of those bipolarons is strongly ruled by entropic effects.