Infrared and photoelectron spectroscopy study of vapor phase deposited poly (3-hexylthiophene)

TL;DR

This study demonstrates vapor phase deposition of P3HT and uses infrared and photoelectron spectroscopy to analyze its surface chemistry and electronic structure, revealing band bending and interface properties in ultrahigh vacuum conditions.

Contribution

It introduces a vapor deposition method for P3HT and provides detailed spectroscopic analysis of its interface and electronic properties in UHV environment.

Findings

Vapor deposition produces contaminant-free P3HT films.

Band bending occurs at P3HT/Ag interface.

Valence band maximum is about 0.8 eV below Fermi level.

Abstract

Poly (3-hexylthiophene) (P3HT) was thermally evaporated and deposited in vacuum. Infrared spectroscopy was used to confirm that the thin films were indeed P3HT, and showed that in-situ thermal evaporation provides a viable route for contaminant-free surface/interface analysis of P3HT in an ultrahigh vacuum (UHV) environment. Ultraviolet photoelectron spectroscopy (UPS) as well as X-ray photoelectron spectroscopy (XPS) experiments were carried out to examine the frontier orbitals and core energy levels of P3HT thin films vapor deposited in UHV on clean polycrystalline silver (Ag) surfaces. UPS spectra enable the determination of the vacuum shift at the polymer/metal interface, the valence band maximum (VBM), and the energy of the \Pi-band of the overlayer film. The P3HT vacuum level decreased in contrast to that of the underlying Ag as the film thickness increased. XPS and UPS data confirmed the chemical integrity (stoichiometry) of the polymer at high coverage, as well as the shift of the C 1s and S 2p binding energy peaks and the secondary-electron edge with increasing film thickness, indicating that band bending is present at the P3HT/Ag interface and that the measured onset of the valence band is about 0.8 +- 0.05 eV relative to the Fermi level.