The electronic structure of n- and p-doped phenyl-capped 3,4-ethylenedioxythiophene trimer

The phenyl-capped 3,4-ethylenedioxythiophene (EDOT) trimer is a well-defined oligomer of the related poly(3,4-ethylenedioxythiophene), the conjugated polymer that forms the basis of the commercialized conducting polymer "PEDOT-PSS." EDOT-based oligomers are themselves potential candidates for applications in molecular electronics, such as organic field effect transistors and organic solar cells. Well controlled chemical doping is of importance in such applications, since it enables tuning of important properties such as the electrical conductivity, the position of the Fermi-level, the optical absorption edge, and the quantum efficiency for photovoltaic devices. The effects of chemical doping, both p-type doping with iodine, and n-type doping with lithium, on the electronic structure of condensed molecular solid films of EDOT trimer have been studied using ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy. The results are discussed in terms of parameters important for device applications. © 2003 American Institute of Physics.