Influences of Energetically Controlled Dielectric Functionality on Polymer Field-Effect Transistor Performance

Abstract

We systematically demonstrated the effects of surface modification of gate dielectrics and the thermal annealing of an ad-deposited polymer semiconducting film on the electrical performance of organic field-effect transistors in which they were incorporated. Chemically or energetically engineered dielectrics were designed by introducing various end-functional groups (CF3, CH3, NH2, Cl, and SH). Poly(dioctyl-quaterthiophene-dioctyl-bithiazole) (PDQDB), consisting of 5,5′-bithiazole and oligothiophene rings, was employed as the polymer semiconductor. We analyzed the PDQDB semiconducting films' crystalline character, which has an important effect on the FET performance and confirmed that the crystallinity of the PDQDB semiconducting films was higher in the cases (CF3 and CH3) of low surface energy than in the cases (NH2, SH, and Cl) of high surface energy, yielding μFET values as high as 0.13 and 0.12 cm2 V-1 s-1 for the CF3 and CH3 cases, respectively. Another important observation was the tendency of the μFET value to change depending on the thermal annealing temperature - increasing and decreasing in the cases of surface functionalities with low and high surface energies, respectively. These results could be interpreted on the basis of the differently competitive molecule-molecule and molecule-dielectric surface interactions, where the π-πstacking configuration of the conjugated molecular structures was enhanced on lower-energy surfaces. We also discussed the effect of permanent dipoles for the engineered self-assembled monolayer dielectrics on the threshold and turn-on voltages in the PDQDB FET devices. Copyright © 2019 American Chemical Society.