Fine patterning of glycerol-doped PEDOT:PSS on hydrophobic PVP dielectric with ink jet for source and drain electrode of OTFTs

This report describes the fabrication and the electrical characteristics of pentacene OTFTs that use the conducting PEDOT:PSS for the source and drain (S/D) electrodes. By adding a controlled amount (10–20 wt.%) of glycerol the conductivity of the PEDOT:PSS ink enhanced to 450 S/cm, and the viscosity of the ink was reduced to <20 cps in order for it to be suitable for ink jet printing. In order to create a patterned PEDOT:PSS layer for the S/D electrode on a hydrophobic polyvinylphenol (PVP) gate dielectric, oxygen plasma was applied to control the surface energy of S/D electrode area on the PVP surface. In addition, by adding a leveling agent, the pattern of PEDOT:PSS droplet was improved enough to be spread up to the corners of S/D electrode area, producing channel length of 10 μm with a fine shape. Pentacene TFTs with the PEDOT:PSS S/D electrodes exhibited a similar performance to those with Au S/D electrodes in terms of the electrode resistance, corresponding to sum of the electrode series resistance and the contact resistance, being ∼30 kΩ cm at VG = −25 V and the field effect mobility being 0.13 cm2/V s and the on/off current ratio being 5.6 × 106. However, the electrode resistance of the PEDOT:PSS needs to be further reduced for the short channels <20 μm.