EXAFS studies of iodine-doped poly(octylthiophene)

Iodine doping of poly(octylthiophene) has been studied by EXAFS. At Tow dop ing levels, the average interatomic I-I distance is close to 2.9 Angstrom, which shows that the iodine is present mainly as triiodide. When the doping level is increased towards saturation (two I atoms per monomer), the dista nce decreases gradually to 2.73 Angstrom. This is interpreted as the presen ce of higher iodine complexes, involving I-2-like units, such as pentaiodid e. The measured coordination numbers support this interpretation. The ratio between I-3(-) and I-5(-) decreases monotonically with the total I content . In this model, the I-3(-) content saturates at a total iodine content aro und 0.5 I atoms per monomer.