Surface viscoelasticity of an organic interlayer affects the crystalline nanostructure of an organic semiconductor and its electrical performance

We demonstrated that the viscoelasticity of a dielectric surface affected the overlying pentacene crystalline nanostructures and the electrical performances of pentacene-based field-effect transistors (FETs). The surface viscoelasticities of the gate dielectrics were systematically controlled by varying the polymer chain lengths of polystyrene brushes (b-PSs) and the substrate temperature during pentacene deposition. The b-PSs were chosen as a model surface because the glass-liquid transition affected neither the surface energy nor the surface roughness. Moreover, the glass-liquid transition temperature increased with increasing b-PS chain length. The liquid-like b-PS chains disturbed the surface arrangement of the pentacene molecules, which reduced the organization of the crystalline structures, yielding smaller grains during the early stages of pentacene growth. The dramatic changes in the film morphology and crystalline nanostructures above the b-PS glass-liquid transition resulted in noticeable changes in the OFET performance. The systematic investigation of the dielectric surface viscoelasticity presented here provides a significant step toward optimizing the nanostructures of organic semiconductors, and thereby, the device performance, by engineering the interfaces in the OFETs.