Organic Semiconductors

Organic semiconductors can potentially be used in low-cost, disposable devices for chemical or biochemical sensing. However, operating the device in an aqueous environment raises difficulties when it comes to operational voltages or stability. One approach to reduce the gate voltage is increasing the capacitance of the gate dielectric. Several different materials, including high-k dielectrics, ultra-thin cross-linked polymers, and electrolytes have been tested for this purpose. In particular, electrolyte gates offer extraordinarily large capacitances, up to several µF/cm2 at low frequencies. The high capacitance, which is the result of the electrical double layer formation at the electrolyte – semiconductor interface, makes low-voltage operation possible without high production costs. We investigate the behavior of organic thin-film transistors with an aqueous electrolyte gate. Electrochemical impedance spectroscopy and cyclic voltammetry measurements indicate a nearly perfectly polarizable interface with negligible parasitic Faradaic currents. For gate voltages below 1 V, a conductive channel is induced at the organic semiconductor/electrolyte interface via an electrical field effect. The transistor is stable for several hours and sensitive to changes in the ionic strength (as shown in the figure on the left) or the pH of the solution. These devices have, thus, the potential of being used in disposable chemo- or bio- sensing applications.

People on the project:

Felix Buth, Deepu Kumar

Selected publications:

• Electrolyte-gated organic field-effect transistors for sensing applications
  F.Buth, D.Kumar, M.Stutzmann, J.A. Garrido
  Applied Physics Letter 98, 153302 (2011)
  Online Reference

   

• Photoresponse and morphology of pentacene thin films modified by oxidized and reduced diamond surfaces
  W. Gajewski, M. Huth, F. Buth, B. Nickel, M. Stutzmann, and J. A. Garrido
  Physical Review B 80, 235311 (2009)
  Online Reference

Funding:

Nanosystems Initiative Munich (NIM)