Study On The Relationship Between The Solution-State Aggregation State Of Polymer And The Optoelectronic Property

Conjugated polymers have received widespread attention due to their excellent properties.Conjugated polymers have been applied in organic light-emitting diodes,organic photovoltaics,organic field effect transistors,organic thermoelectricity,biosensors and others.Studies have been proved that solid-state microstructures of conjugated polymers play an important role in their charge transport properties.In the ordered solid-state microstructures,the synergistic effect of the rigid planar polymer backbone and the strong π-π stacking facilitates the intra-and interchain transport,thereby improving the electrical properties.In recent years,research results have shown that the solid-state microstructures of conjugated polymers are not only related to the structure of conjugated molecules,but also affected by the aggregation structures of conjugated polymers in solutions.At present,a deep understanding of the self-assembly mechanism and structure of conjugated polymers in solutions are still lacking.Therefore,in-depth study of the self-assembly behavior of conjugated polymers in solution is of great significance to clarify the structure-function relationship of conjugated materials.In response to the problems,we modulated the structure of the BDOPV-based polymer backbone to control the solution-state aggregation of conjugated polymer and deeply understand the contribution of intra and inter-chain interactions to the aggregation state.This dissertation proposed an approach to adjust the solution-state aggregation structures of conjugated polymers,revealing the important influence of the complex interaction of conjugated polymer on electrical properties.In the first part,we designed and synthesized five BDOPV-based polymers with different conjugation lengths and two BDOPV-based molecules with different lengths to tune the solution-state aggregation structures of conjugated polymers through introducing conjugation-break spacers.We first tested the UV-Vis absorption spectra of polymers and model molecules in solution and films at room temperature to evaluate the effects of conjugation-break spacers on the optical and aggregation properties of these polymers.Subsequently,in order to study the aggregation behaviors of BDOPV-based molecules and polymers in dilute solution,in-situ solution temperature-dependent absorption spectra measurement was carried out.The molecular arrangement and surface morphology of these polymer films were studied by grazing-incidence wide-angle X-ray scattering(GIWAXS)and atomic force microscopy(AFM)experiments.Finally,the mobility and conductivity of these polymers were determined.The experimental results demonstrated that the aggregation state of polymers in solution was regulated by the amount of conjugation-break spacers,and further affected the charge transport characteristics and doping level of the polymers.At the same time,we have also proved that polymers with fully conjugation-break spacers would spontaneously form aggregation structures in solution.With the introduction of conjugated fragments,the length of conjugation increased,the interaction between the polymer chains increased,and the original aggregation form was replaced by π-π stacking.Our results demonstrated that introducing a small amount of conjugation-break spacers to the polymer backbones was favorable for achieving uniform mixing with the dopants and further improving the charge transport properties.Our investigation reveals the relationship between aggregation and conjugation-break spacers in solution,and provides guidance for the application of conjugation-break polymers.In the second part,we introduced the polar glycol type side chains into the polymer backbone,and changed the ratio of the alkyl side chains to the polar side chains in the backbone,achieving the purpose of improving the doping efficiency.From the current research results,the polar glycol type side chains enhances the miscibility of polymers with dopants.At present,we have synthesized a batch of BDOPV-based polymers with different proportions of side chains,and the follow-up related work is still in progress.We hope to keep both the alkyl side chains and the polar glycol type side chains on the polymer backbone,and adjust the solution-state aggregation structures of conjugated polymers by controlling the ratio of the two.In summary,this dissertation modifies the backbone structure and side chain structure of the conjugated polymer,regulates the solution-state and solid-state aggregation structures of conjugated polymer,and deeply explores the relationship between the aggregation microstructures and properties of the conjugated polymer.