Effect of Hydroxyl Group of Polymer Gate Insulators on Characteristics of Dihexylsexithiophene Organic Field-Effect Transistors Using Poly(p-silsesquioxane) Derivatives

The characteristics of p-type organic field-effect transistors (OFETs) based on α,ω-dihexylsexithiophene (DH-6T) and fabricated using poly(p-silsequioxane) (PSQ) derivatives, which contained various ratios of a phenol group with a hydroxyl group bonded to a phenyl ring in the side chain of their molecular structures, were investigated. An OFET with a PSQ derivative that contained part of a hydroxyl group in the side chain had a maximum carrier mobility of 0.14 cm2 V-1 s-1. The carrier mobility of OFET with a PSQ derivative that had no hydroxyl group but only a methoxy group in all the side chains, is lower than that with other polymer insulators that had a hydroxyl group in the side chain, owing to the different growth modes of DH-6T grains. The threshold voltage shifted from the + side to the - side as the ratio of the hydroxyl group decreased. The current on/off ratio of OFET increased with decreasing ratio of the hydroxyl group when gate voltage was scanned from 0 to -30 V. We demonstrated that the threshold voltage is dependent on the ratio of the hydroxyl group in the polymer gate insulator.