Ion-Activated Greatly Enhanced Conductivity of Thin Organic Semiconducting Films in Two-Terminal Devices

摘要

The energetics of metal/organic semiconductor (OSC) and polymer electrolyte/OSC interfaces play a key role in the operation of a variety of electronic and optoelectronic devices. Despite extensive research in the field, the way such energetics impact on device properties is often poorly understood and overlooked. They can cause unusual phenomena as reported herein in the case of metal/OSC/electrolyte systems for which an increase of up to three orders of magnitude in the conductivity of thin OSC films is observed. Using coplanar electrode devices and OSC films made of regioregular poly(3-hexylthiophene) (P3HT) materials, it is shown that such a phenomenon results from synergistic effects between the metal/P3HT interface energetics, charge transport, and electrolyte conductivity. The experiments make evident the existence of a thickness-dependent electrostatic potential at the P3HT surface, which leads to ion-assisted hole accumulation at the upper edge of the P3HT film. Together with the potential of the investigated two-electrode devices for sensing applications, this study provides new insights for the development of electrolyte-gated transistors and can serve as a generic method for the extraction of parameters like the space-charge width of metal/OSC junctions.