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

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 -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.

Hybrid Carbon Nanotube Networks as Efficient Hole Extraction Layers for Organic Photovoltaics

“…The spin-orbit splitting corresponding to the S 2p 3/2 and S 2p 1/2 states expected for free rr-P3HT with an intensity ratio of 2:1 is not observed which is attributed to the high crystallinity of rr-P3HT in the nanohybrids 30 and/or interactions between S atoms in rr-P3HT with the s-SWNTs. 29 The possibility for higher crystallinity is further supported by the absence of satellite peaks on the high BE side at ~290 eV in the C 1s spectrum ( Analysis of the S 2p and C 1s of the core level XPS spectra of the nanohybrids ( Fig. 2A,B) indicates a downshift of the BE for the former (~164.5 eV in the nanohybrid compared to 164.75 eV 29 in rr-P3HT) and an up shift for the latter (~284.5 eV in the nanohybrid compared to 284.3 eV in s-SWNT).…”

Electronic Structure and Transition Energies in Polymer–Fullerene Bulk Heterojunctions

“…The exciton couples primarily to the 0.17−0.18 eV group of phonons in conjugated organic semiconductors, as several papers have reported. 8,12 These are phonon modes of the conjugated rings that comprise the polymer backbone (e.g., CC stretching modes), 13 and they dominate the phonon coupling because the conjugated rings are the origin of the π-orbitals forming the exciton and hole wave functions. Coupling to the higher energy C−H modes is not observed because these bonds do not contribute to the π-orbitals.…”

Photophysical Properties of Two New Donor-Acceptor Conjugated Copolymers and Their Model Compounds: Applications in Polymer Light Emitting Diodes (PLEDs) and Polymer Photovoltaic Cells (PPCs)

“…A large number of bands appear with very high peaks due to an induced strong dipolar moment. All characteristics of infrared bands in P3HT [125], PCz and BT vibration modes are observed.…”