Extended Data Fig. 8: Internal channel potential profile evolution during switching of an OECT.
From: Hole-limited electrochemical doping in conjugated polymers
We measured the internal potential (with respect to the grounded source electrode) along the length of a p(g1T2-g5T2) channel (L = 3 mm, W = 0.4 mm) using inserted voltage probes (30 µm width, 0.5 mm spacing) along the channel as schematically depicted in a and b (note that the gate is not drawn to scale in a). The sample was using the same methodology described for OECT fabrication described in the methods section. Potentials were measured at each probe (V1-4) using a 4-channel oscilloscope (Keysight DSOX1204G) while a source-measure unit (Keysight B2902A) was used to apply a pulse between the Ag/AgCl gate and the gold contact. We note that the voltage probes measure the electrochemical potential of electronic charges, which includes contributions due to the local electric potential as well as shifts in the Fermi level resulting from doping. The resulting transient potential profiles c, in the hole-limited doping regime (VG from 0.4 V to −0.6 V) show a delay in the rise in potential for voltage probes further from the source electrode, closely corresponding with the turn on delay time for the OECT source-drain current (ISD). In contrast, when doped in the standard regime d, (VG from −0.3 V to −0.6 V) the potentials at each probe rise simultaneously and ISD increases immediately, indicating efficient transport of holes along the channel. The e, potential profiles along the channel during hole-limited doping additionally show that the region of largest potential drop moves from the source electrode towards the drain, comparable to the movement of the doping front observed in Fig. 4d. In contrast, when the film is initially partially doped f, the potential remains nearly linear along the channel throughout the measurement.
