Individual and synergetic charge transport properties at the solid and electrolyte interfaces of a single ultrathin single crystal of organic semiconductors

Abstract

The chemical structures and morphologies of organic semiconductors (OSCs) and gate dielectrics have been widely investigated to improve the electrical performances of organic thin-film transistors (OTFTs) because the charge transport therein is a phenomenon at the semiconductor–dielectric interfaces. Here, solid and ionic gel gate dielectrics were adopted on the lower and upper surfaces, respectively, of a single, two molecule-thick single crystals of p-type OSCs to study the charge transport properties at individual interfaces between the morphologically compatible OSC surface and different gate dielectrics. Using the four-probe method, the solid and ionic gel interfaces were found to exhibit hole mobilities of 9.3 and 2.2 cm² V⁻¹ s⁻¹, respectively, which revealed the crucial impact of the gate dielectric materials on the interfacial charge transport. Interestingly, when gate biases are applied through both dielectrics, i.e., under the solid/ionic gel dual-gate transistor operation, the hole mobility at the solid gate interface is improved up to 14.7 cm² V⁻¹ s⁻¹, which is 1.5 times greater than that assessed without the ionic gel gate. This improvement can be attributed to the electric double layer formed at the ionic gel/uniform crystal surface, which provides a close-to-ideal charge transport interface through dramatic trap-filling. Therefore, the present dual-gate transistor technique will be promising for investigating the intrinsic charge-transport capabilities of OSCs.