Fig. 2: A change in ion diffusion rate causes the kink.

a Schematic showing organic electrochemical transistors (OECTs) used in this article. Channel width (W) is fixed at 500 µm, and length (L) is varied from L = 30 µm, 50 µm, 80 µm, 150 µm, 200 µm, and 250 µm. OECTs are in bottom-contact bottom-gate configuration, with a polymer coated gold electrode as the gate electrode. b Ionic charge injection (Q_injected) as a function of gate voltage (V_G) for the smaller channels: L = 30 µm, 50 µm, and 80 µm. c Q_injected as a function of V_G for the larger channels: L = 150 µm, 200 µm, and 250 µm. The sweep rate is 11 mV/s for all data. d Square root of the drain current (√I_D) measured at drain voltage (V_D) = –0.9 V for L = 250 µm. e Q_injected for L = 250 µm measured at sweep rate 11 mV/s, with a dashed line to indicate that the kink in √I_D directly corresponds with the change in rate of injected ionic charges. f √I_D measured at V_D = – 0.9 V for L = 30 µm. g Q_injected for L = 30 µm measured at sweep rate 20 mV/s, where the difference in scan rate does not impact overall conclusion and funding (see Fig. S11). Again, the dashed line indicates that the kink in √I_D directly corresponds with the change in rate of injected ionic charges. All measurements are all carried out under vacuum with pT2gTT as the active channel material and BMIMPF₆^– as the electrolyte.