Fig. 2: Bode plot of the magnitude and phase of the electrode impedance before and after electrodeposition of PEDOT:PSS. The impedance magnitude decreases significantly in the range of the seal resistance measurement between 1 Hz and 1 kHz.

The impedance decreases above 10 kHz characterized by a −90° phase arises from the stray capacitance of the printed circuit board used to interface the devices. Between 10 kHz and 100 Hz, the impedance is dominated by the spreading resistance, between 100 and 10 Hz, a transition occurs from the spreading resistance to the PEDOT:PSS capacitance with a transitory regime characterized with a −45° phase arising from the diffusion of cations through the polymer (see Supplementary Fig. 3.3 for the equivalent circuit and theoretical model). The device under test had a layer of insulating polyimide 3 µm thick, one more micron than in the rest of the study, which results in smaller stray capacitance but has no other effect on the measurements