Double Alkyl Side Chains Functionalized Polyimide as Gate Dielectrics for Application in Organic Transistors

Compared with inorganic dielectrics, polymer-based gate dielectrics have received growing attention due to their flexibility, structural adjustability, and low cost in organic thin-film transistors (OTFTs) devices. Aromatic polyimides (APIs) stand out because of their outstanding thermal stability, structural diversity, mechanical flexibility, and large-area processability. In this work, we designed and prepared three API gate dielectrics by the low-temperature chemical imidization method. These API materials with double alkyl side chains can be easily processed into smooth, nonpinhole films with low surface energy. Simultaneously, these materials showed low leakage current densities (<10–9 A/cm2 at 2 MV/m), small dielectric loss (<0.02 at 102∼106 Hz), and good thermal stability. To inspect the potential of our modified APIs as gate dielectrics, para-sexiphenyl/vanadyl-phthalocyanine TFT devices were fabricated. As the length of alkyl side chains in the API structure increases, the field-effect mobility first rises and then drops, in line with the evolution trend of semiconductor film topography. Further, the threshold voltage shifted in a positive direction (from −3.00 to −0.01 V, which is one of the lowest values reported to date). Our results provide a strategy for the design of modified API materials as gate dielectrics to pursue high mobility and low threshold voltage OTFTs.