Operando structure determination of mixed conducting polymers

Polar conjugated polymer based organic mixed ionic-electronic conductors (OMIECs) are exciting class of materials for electrochromic, charge storage, biological sensor, neuromorphic, and electrochemical transistor applications, amongst others. In these electrolyte swollen applications the structure of OMIECs are not constant, rendering static ex situ characterization inadequate. Here, we report the grazing incidence x-ray scattering of the prototypical polythiophene/polyelectrolyte blend, PEDOT:PSS, and the glycolated polythiophene, p(g2T-TT), under operating conditions (i.e. exposed to electrolyte, at controlled electrochemical potential). This has required the development of new in situ/operando cells that overcome electrolyte absorption/scattering to preserve the scattered x-ray intensity from the OMIEC film. Steady-state and time-resolved measurements reveal the profound effect of electrolyte on crystallite lattice spacings and quantify the structural kinetics that accompany electronic charging and discharging, respectively. Coupled with optical and X-ray spectroscopy, we correlate these results with doping composition, charge carrier dynamics, and charge trapping, which gives insight into electronic transport in these materials.