Synthesis and characterization of plasma polymerized 3,4-ethylenedioxythiophene thin films

Abstract

Plasma polymerized 3,4-ethylenedioxythiophene (PPEDOT) thin films have been deposited onto glass substrates at room temperature under AC (50 Hz) and RF (13.56 MHz) power sources by using the plasma polymerization (PP) technique.3,4-ethylenedioxythiophene (EDOT) has been chosen as a monomerprecursor. The thicknesses of the films measured by Multiple-Beam Interferometer have varied with increasing deposition times. The field emission scanning electron microscopy (FESEM) images exhibit that the surface morphology of the filmsis immaculate and pinhole-free.The Fourier transform infrared spectroscopy analysis represented that the chemical compositions as depositedPPEDOT films are different from that of the EDOT monomer,indicating some structural rearrangement.The energy band gap values of the PPEDOT (AC) thin films decrease from 3.75 to 3.54 eV with the increase of film thickness. The Urbach energy, steepness parameter, extinction coefficient, refractive index, and other optical parameters are studied to indicate suitability of these films for use in various electrical and optoelectronic devices.Both TG and DSC reveal that these films are thermally stable up to 612 K temperature. DC electrical analysis exhibits that space charge limited conduction (SCLC) mechanism is active in the PPEDOT (AC) thin films. The activation energy,E, values of the PPEDOT (AC) thin films in the Ohmic region are found to be around 0.076 eV whereas, in the non-Ohmic region, Evalues are found to be around 0.119 eV.A comparative study hasalso been done on the PPEDOT thin films deposited using RF (13.56 MHz) power and observed that RF power source can produce thicker films within shorter time compared to AC power source, but no significant changes are found in the film’s quality in terms of structural, optical, and electrical properties.