Direct observation of charge-inducedπ-electronic structural changes in a conjugated polymer

Abstract

Ultraviolet photoelectron spectroscopy (UPS) has been used to observe changes in the /r-band structure in poly(3-hexylthiophene) induced by doping using NOPF6. The charge-induced movement of the Fermi energy and a finite density of electronic states at the Fermi energy in the most highly doped (saturated) material are seen unambiguously with UPS for the first time in a conjugated polymer. The results imply the existence of a new, recently predicted theoretically, but hitherto unobserved, polaronlattice state of this conjugated polymer at the saturation-doping level.

Defect contributions to conductivity in poly(3‐hexylthiophene)?

“…States in the RR-P3HT HOMO-LUMO gap have certainly been suggested by other studies [4,24,25]. Short chain thiophenes [32], and short chain hexyl thiopehene segments will result in a photoemission state at about -1.7 eV binding energy as is observed here, but so could a range of other "chemical defects" [28].…”

“…From the combined photoemission and inverse photoemission spectra, we see that the chemical potential of RR-P3HT adjusts to place the Fermi level within the gap between the highest occupied molecular orbital (HOMO) and lowest molecular orbital (LUMO), with the Fermi level slightly closer to the LUMO, similar to the band offset description for undoped RR-P3HT in [24]. The experimental molecular HOMO-LUMO gap is 7.3 eV for RR-P3HT, in good agreement with our expectations from theory.…”

“…As charge mobility decreases with decreasing temperature, semiconducting regioregular RR-P3HT becomes insulating and is consistent with the polaronic conduction mechanisms proposed. As with polypyrrole [3], there are very strong indications that the temperature dependence of the conductivity is not directly related to changes in the polymer geometry with temperature, except at higher temperatures (i.e., >25 °C) where large disorder leads to a decrease in carrier mobility for RR-P3HT [24]. While reducing the temperature of these spin coated RR-P3HT fi lms leads to an increase in the polymer backbone conjugation (and resultant π band delocalization), it does not overcome the loss of phonon assisted mobile charge carriers that dominate the conductivity at room temperature.…”

Energetics at Doped Conjugated Polymer/Electrode Interfaces

“…The UPS spectra for this series are thus unlike those of highly p-doped films. [39] These observations suggest that the 3:1000 to 1:10 F4TCNQ:rr-P3HT solutions deposited onto substrates are low to intermediate doped and form films with the dopant molecules dispersed in the polymer matrix. For the 2:10 case, additional features that we attribute to F4-TCNQ appear in the frontier region ( Fig.…”

The coadsorption and interaction of molecular icosahedra with mercury

“…The evidence for metallic mercury, from the Hg 5d 5/2 core level widths does not suggest that mercury atoms may form a lattice which weakly interacts with orthocarborane lattice, or Hg may form a wetting surfactant layer and a layer between the Cu substrate and orthocarborane molecular fi lm which would easily explain a uniform shift in the molecular orbital photoemission binding energies. In this regard, Hg is very different from the more homo geneous mixtures formed with some metals and molecularly chemisorbed species [14][15][16][38][39][40][41][42][43][44][45][46][47][48][49].…”