Effect of dopants on the transparency and stability of the conductivity of plasma polymerised thiophene layers

Iodine is frequently used as dopant for plasma polymerised thiophene (PPT) layers, but suffers from several drawbacks such as the rapidly decaying conductivity upon exposure to air, and the absorption of light by iodine species that are present in the doped PPT layer (i.e., I2, I3− , and I5−). This limits the utilisation of these layers in applications that require a high transparency and a stable conductivity. Two alternative dopant systems (thiantrenium perchlorate (ThClO4) and nitrosonium hexafluorphosphate (NOPF6)) have been evaluated and with both alternatives highly transparent (>90% over the whole visible range) PPT layers were obtained of which the conductivity (10−4 S/cm) was stable during the period of evaluation (2 weeks).