High work function materials for source/drain contacts in printed polymer thin film transistors

Studies of materials for source-drain electrodes in ink-jet printed polymer-based thin film transistors (TFTs) are reported. Two systems are studied: a blend of Ag nanoparticles with poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and an ethylene glycol-doped PEDOT:PSS solution (modified-PEDOT). The semiconductor used is the polythiophene derivative poly [5,5′-bis(3-dodecyl-2-thienyl)-2,2,2′-bithiophene]. PEDOT:Ag blends and modified-PEDOT yield TFTs with mobilities around 10−2 and 10−3cm2∕Vs, respectively, subthreshold slopes around 1.6V/decade and on-to-off current ratios of 106–107. Both systems show considerable improvement over printed TFTs with Ag nanoparticle source-drain electrodes. Results on film resistivity and morphology are discussed along with device characteristic analysis.