title: Charge Saturation and Intrinsic Doping in Electrolyte-Gated Organic Semiconductors.
abstract: Electrolyte gating enables low voltage operation of organic thin film transistors, but little is known about the nature of the electrolyte/organic interface. Here we apply charge-modulation Fourier transform infrared spectroscopy, in conjunction with electrical measurements, on a model electrolyte gated organic semiconductor interface: single crystal rubrene/ion-gel. We provide spectroscopic signature for free-hole like carriers in the organic semiconductor and unambiguously show the presence of a high density of intrinsic doping of the free holes upon formation of the rubrene/ion-gel interface, without gate bias (Vg = 0 V). We explain this intrinsic doping as resulting from a thermodynamic driving force for the stabilization of free holes in the organic semiconductor by anions in the ion-gel. Spectroscopy also reveals the saturation of free-hole like carrier density at the rubrene/ion-gel interface at Vg < -0.5 V, which is commensurate with the negative transconductance seen in transistor measurements.
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Atallah
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Martin V
authors.initials: MV
authors.lastname: Gustafsson
authors.affiliation: Department of Chemical Engineering and Materials Science, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Elliot
authors.initials: E
authors.lastname: Schmidt
authors.affiliation: Department of Chemical Engineering and Materials Science, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: C Daniel
authors.initials: CD
authors.lastname: Frisbie
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: X-Y
authors.initials: XY
authors.lastname: Zhu
keywords: ion-gel; ionic gating; organic semiconductors; organic thin film transistor