Relation between Polymer Semiconductor Morphology and the Ion-Doping Effect in Electrolyte-Gated Transistors

The behavior of ions in electrolyte-gated transistors (EGTs) is critically important in determining the device performance. For EGTs with polymer semiconductors, the ions in the gate insulator form high-capacitance electric double layers and can penetrate channel regions by the applied gate, drain, and source bias. In order to understand how the surface morphology of semiconductors influences the ion-doping effect in EGTs, a compositionally identical but structurally different polymer semiconductor utilized as a channel layer in transistors has been systematically explored. Three kinds of solvents with different boiling points were employed to prepare precursor solutions to control the surface morphology of semiconductor [poly(3-hexylthiophene), P3HT] films. Because the ions can penetrate the channel region, devices having P3HT with rough surfaces showed high specific charge density and potentiation features with pulsed gate bias. On the other hand, the ions are impermeable into smooth (dense) channel regions; thus, EGTs with smooth P3HT exhibited relatively small charge density and non-potentiation characteristics. These results emphasize that the ion-doping effect, which determines the performance of EGTs, is dependent on the surface morphology of the polymer channel region. This study could provide helpful insights into optimizing electrolyte/semiconductor interfaces in EGTs to achieve high-performance switching circuits and synaptic devices.