Mixed ionic-electronic conduction (MIEC) is a key electrochemical property underlying the operation of both organic electrochemical transistors in bioelectronic devices and energy storage in battery electrodes and supercapacitors. However, optimizing MIEC through material design is hindered by our lack of fundamental knowledge of mixed conduction. We are developing laser spectroscopy methods for probing of charge carriers in MIEC polymers in working electrochemical cells and devices to discover how to optimize their chemical and nano/mesoscale structures for improving device performance.
In electrochemical devices, doping- and swelling-induced nanostructural dynamics that occur in operando impact charge and ion conduction of MIEC polymers in unclear ways.
Ultrafast Dynamics of Photoexcited Polarons
Summary of how transient absorption (TA) spectroscopy can probe charge carrier environment and trapping in conducting polymers.
We discovered that photoexcitation of charge carriers (polarons) in conducting polymers results in spatial separation of the polaron from its counter-ion. This creates an electroabsorption signal, which can be detected in ultrafast transient absorption spectroscopy measurements, contains information about the local nanoscale environments of the charge carriers (see movie on the right or below).
Read more:
Umar, AR; Dorris, A.L.; Kotadiya, N.M.; Giebink, N.C.; Collier, G.S.; Grieco, C. Probing Polaron Environment in a Doped Polymer via the Photoinduced Stark Effect. J. Phys. Chem. C. 2023, 127, 20, 9498–9508.
We demonstrated that the decay kinetics of the transient near-infrared signals from photoexcited polarons are sensitive to their degree of trapping. We are using transient absorption spectroscopy as a method for probing charge carrier trapping in conducting polymers.