The Structural and Electronic Properties of Pristine and Doped Polythiophene: Periodic Versus Molecular Calculations

TL;DR

This study uses density functional theory to compare the structural and electronic properties of polythiophene in periodic and molecular forms, focusing on doping effects and stacking configurations relevant for electronic device applications.

Contribution

It provides a comprehensive comparison of periodic and molecular calculations for doped polythiophene, including adsorption energies, stacking preferences, and charge transfer characteristics.

Findings

Li and Cl adsorption energies are higher in bulk/bilayer than monolayer.

Parallel stacking is energetically favored over flipped configurations.

Polarons are more stable than bipolarons for Li doping, opposite for Cl doping.

Abstract

Based on density functional theory calculations, the structural and electronic properties of polythiophene in periodic and oligomer forms have been investigated. In particular, the effects of Li or Cl adsorption onto a monolayer and Li or Cl-intercalation into bulk or bilayer polythiophene are addressed using periodic calculations. The binding energy of Li or Cl adsorbed bulk or bilayer polythiophene is significantly larger than for the monolayer. The trends in the binding energy as a function of adsorbent remain the same for both the periodic and molecular cases. The band gap or HOMO-LUMO gap and charge transfer are analysed. In addition, for the bulk or bilayer, different kinds of stacking have been considered. It is found that the parallel bulk or bilayer structure is energetically favorable compared to flipping the second layer by 180$^\circ$. This has been considered for both the periodic and oligomer forms. Moreover, for Li adsorption, polarons are found to be more stable than bipolarons, while the situation is opposite for Cl adsorption. The detailed analysis of the present study will be useful for understanding the structural properties and the tuneability of the electronic states, which is an important step to construct polythiophene based electronic devices.