Ultraviolet photoelectron spectroscopy of pristine poly (sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate) (PTEBS) and doped with perylene tetracarboxylicdiimide (PTCDI) nanobelts

Abstract

We investigated the possibility of doping poly (sodium poly[2-(3-thienyl)-ethoxy-4butylsulfonate) (PTEBS) with perylene tetracarboxylicdiimide (PTCDI) nanobelts through ultraviolet photoelectron spectroscopy (UPS) measurements. For our experiment, PTEBS was tuned to absorb maximum light in the range of 450 nm to 550 nm which corresponds to the maximum solar irradiance of the Earth's atmosphere. Nanobelts of PTCDI were synthesized by gas phase self assembly process. Doping PTEBS with PTCDI nanobelts causes a shift in the Fermi level of the composite material with respect to the vacuum level as observed in the photoemission spectrum. With increased PTCDI doping, PTCDI does not act much like an electron donor, but more like an electron acceptor. The peaks corresponding to the sigma bonds shift towards the vacuum level with higher concentrations of the dopant. Using angled resolved photoemission spectra from a 3m toroidal grating monochromator, PTEBS displays change in the highest occupied molecular orbital in respect to its Fermi level when the side groups were substituted by H + or OHgroups. The results confirm that the binding energy decreases with increase in activity of the dissolved hydrogen ions. It is evident that there is an increase in the density of states near the Fermi level and shifts to lower binding energies of the occupied molecular orbitals with pH level decrease, which is in agreement with the published optical absorption characteristics of PTEBS. Since UPS data confirm that PTCDI nanobelts dope PTEBS, along with its tunable absorption characteristics, this composite might be a promising material for optoelectronic application.