Reversible and Irreversible Light-Induced p-Doping of P3HT by Oxygen Studied by Photoelectron Spectroscopy (XPS/UPS)

The influence of oxygen and light on the energy level alignment of poly(3-hexylthiophene) thin films (∼100 nm) is investigated quantitatively using X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS) in order to probe energetic shifts and the element distribution in the film. Upon simultaneous exposure to oxygen and light a reversible shift of the occupied states of about 0.3 eV is observed together with the presence of reversibly and irreversibly bound oxygen species. Whereas the reversibly bound species correlates with the energy shifts, the latter does not alter the electronic structure. The observations are discussed in terms of light-induced p-doping of the semiconducting material by oxygen which is completely reversible upon vacuum annealing of the polymer film above the glass transition temperature of 150 °C.