Raman imaging of carrier distribution in the channel of an ionic liquid-gated transistor fabricated with regioregular poly(3-hexylthiophene)

Raman images of carriers (positive polarons) at the channel of an ionic liquid-gated transistor (ILGT) fabricated with regioregular poly(3-hexylthiophene) (P3HT) have been measured with excitation at 785 nm. The observed spectra indicate that carriers generated are positive polarons. The intensities of the 1415 cm(-1) band attributed to polarons in the P3HT channel were plotted as Raman images; they showed the carrier density distribution. When the source-drain voltage V-D is lower than the source-gate voltage V-G (linear region), the carrier density was uniform. When V-D is nearly equal to V-G (saturation region), a negative carrier density gradient from the source electrode towards the drain electrode was observed. This carrier density distribution is associated with the observed current-voltage characteristics, which is not consistent with the pinch-off theory of inorganic semiconductor transistors. (C) 2018 Elsevier B.V. All rights reserved.