Preparation Of Polythiophene Ultra-thin Films And Investigate Of Their Electrical And Mechanical Properties

In recent years,the preparation of intrinsically stretchable electronic devices using conjugated polymers has gradually become one of the main focuses of research in this field due to the rapidly growing demand for wearable devices and electronic skins.The properties of conjugated polymer films depend not only on their molecular structure,but are also closely related to their molecular orientation,molecular stacking,crystalline structure,film thickness and other micro-scales and mesoscopic-scales.The complex structure of conventional three-dimensional bulk phase films is not conducive to exploring the relationship between structure and electrical and mechanical properties.In contrast,two-dimensional ultra-thin films with several single molecular layer thicknesses can simplify the complex multi-level structure of bulk phase films and provide an ideal platform to explore the relationship between the structure of materials and their electrical and mechanical properties.This paper addresses the problems in the relationship between the structure and electrical and mechanical properties of conjugated polymer films.With the objectives of simplifying the structure and optimising the mechanical properties of conjugated polymer films,conjugated polymer ultra-thin films of different thicknesses were prepared using the laminating method and phase separation method,and the relationship between the microstructure and electrical and mechanical properties of ultra-thin films was investigated.Details are as follows:(1)Poly(3-hexylthiophene)(P3HT)ultra-thin films with a thickness of 2.1 nm wereprepared by transfer-etching using a vertical phase separation method,and a series of ultra-thin films with different thicknesses(2.1 nm?4.3 nm?6.5 nm)were obtained by multiple laminating.The P3HT ultra-thin film prepared by the"laminating method"has good homogeneity.(2)The relationship between the microstructure of P3HT ultra-thin films and their electrical and mechanical properties was investigated by transferring the ultra-thin films prepared by the lamination method to the surface of elastomers for tensile testing.The results show that the cracking strain of P3HT ultra-thin films decreases with increasing film thickness and the degradation of mobility with increasing strain increases.The 1-layer P3HT ultra-thin film show the best tensile resistance,with an average mobility of 6.06×10^-4cm²V^-1s^-1at 100%tensile strain,which is 25%of the initial mobility.(3)The thickness of the P3HT component in the blend films was adjusted by varying the concentration of the blending solution,and ultra-thin films of similar thickness to the laminated method(4.1 nm,6.2 nm)were directly prepared.The morphology and mobility of the P3HT ultra-thin films under tensile strain were found to follow the same trend as those of the laminated ultra-thin films,further demonstrating that thickness is an important factor affecting the electrical and tensile properties of the P3HT ultra-thin films.(4)The dichroism ratios of P3HT ultra-thin films of different thicknesses at different strains were characterised and calculated using a polarised UV-Vis spectrophotometer to investigate the reasons for the excellent tensile resistance of the ultra-thin films.The results show that the dichroism ratio of P3HT ultra-thin films at the same strain is higher as the film thickness decreases.The dichroism ratio of 2.11for a single layer of P3HT at 100%strain is much higher than the dichroism ratio of1.28 for a direct spin-coated P3HT thickness at that strain,demonstrating that the thinner the film thickness,the easier it is to orient the polymer backbone in the direction of stress,which dissipates the stress and gives the ultra-thin films excellent tensile resistance.