Correlating electronic structures and performance to anisotropic conformations of molecules via the extension of local ordering and carrier densities in polymeric semiconductors

Abstract

To understand how local stacking conformations of molecules regulate the photonic properties of soft semiconductors controllable ordering and electronic structures of the soft semiconductors are a necessary platform We utilize sandwich casting nano-grooves self-assembly-monolayer (SAM) and surface energy to control intermolecular interactions of the semiconductor polymer Poly (3-hexylthiophene) (P3HT) and form unidirectional P3HT nano-fibers Varying process temperature and solvents can regulate molecular interactions and produce macroscopic order of nano-fibers with different microscopic Because higher temperature and better solvent reduce the intermolecular interactions between polymer chains and suppress aggregates then nano-grooves and SAM can be strong enough to align backbones of polymer and improve molecular order in nano-fibers In order to investigate the correlation of molecular orientation and electronic structures we design construct anisotropic quantum efficiency system by assembling integrating sphere optical parts such as dichroic mirrors and filters and automated instrumentation like stepper motors and spectrometers Adjusting laser polarization with half-wave plates rotated by stepper motor we can simultaneously measure the polarized Raman scattering spectrum and polarized fluorescent spectrum Molecular vibration of polymer films relative to full-angle polarized light is obtained from polarized Raman scattering spectrum Comparing the directional distribution of local molecular conformations with polarized fluorescent spectrum can indicate electronic structures in molecular-lever corresponding to polymorphic variation Because the electron structure of soft semiconductors is highly correlated to molecular conformations the conformation-regulated electronic structures in nano-fibers should influence the mechanical properties Varying voltage applied on P3HT films and observe how the electronic modulation results in the vibration along particular different molecular axis Through this system we can mutually analyze the conversion between photonic and mechanical properties In order to find relatively accurate luminescence efficiency we also established an optic model as well as operating principle of integrating sphere Fresnel equations Bouguer–Lambert–Beer law which deducts the absorption of silicon wafer Through this methodology we can extract real absorption of polymer film and get relatively accurate photoluminescence quantum yield

Date of Award	2020
Original language	English
Supervisor	Bang-Yu Hsu (Supervisor)