Effect of the alkali metal content on the electronic properties of PEDOT:PSS

The effect of the sodium and cesium ion surface concentration on the electronic properties of spin-coated poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonic acid) films, known as PEDOT:PSS, has been studied by means of ultraviolet and X-ray photoelectron spectroscopy. The sodium and cesium concentration in the film has been varied by the addition of NaOH or CsOH to the PEDOT:PSS dispersion. Hydrogen ions of the acid PSSH are exchanged for sodium or cesium ions, resulting in the salt PSSNa or PSSCs without changing the oxidation state of PEDOT, i.e., without doping/dedoping the material. The work function changes from 5.1 to 4.0 eV with increasing alkali surface concentration. The ionization potential remains constant at 5.0 eV above 1 at% alkali metal content and coincides with the work function below 1 at%. Thus, the material changes from a semiconductor-like to a metal-like state.