High performance amorphous polymeric thin-film transistors based on poly[(1,2-bis-(2 '-thienyl)vinyl-5 ',5 ''-diyl)-alt-(9,9-dioctylfluorene-2,7-diyl] semiconductors

Abstract

We have synthesized a new p-type polymer, poly [(1,2-bis-(2'-thienyl)vinyl-5',5 ''-diyl)-alt-(9,9-dioctyldecylfluorene-2,7-diyl] (PTVTF), via a Suzuki coupling reaction. PTVTF was found with UV - vis absorption spectroscopy, GIXD, AFM, and NEXAFS to be an 'annealing-free' amorphous polymer. Despite its amorphous nature, our time-of-flight measurements demonstrate that PTVTF is a good hole transport material with an intrinsic hole mobility of 2 x 10(-4) cm(2)/Vs, which is comparable to those of crystalline polymers such as P3HT. A solution-processed PTVTF FET with a bottom gate/top contact geometry was found to exhibit good device performance with superior reproducibility. The field-effect mobility of holes was found to be 2 x 10(-2) cm(2)/Vs with a good subthreshold swing of 1.7 Vdecade(-1). The output characteristics indicate that good saturation and ohmic contact are present. The amorphous nature of PTVTF makes it a very promising candidate for commercial OTFTs since its properties are independent of fabrication conditions. From the temperature dependence of the mobility of amorphous PTVTF, we found that increases in the hydrophobicity of the dielectric substrate improve the mobility of PTVTF by reducing the trap density of the semiconductor layer.