Effects of Humidity and Heat on the Conductivity of Poly(3-Alkylthiophenes)

The stability of the conductivity of poly(3-alkylthiophenes) has been studied in controlled environmental conditions. High humidity levels at elevated temperatures have been found to strongly influence the dedoping process. Highly FeCl 3 -doped samples lose their conductivity faster than lightly doped or undoped polymers. The conductivity of undoped poly(3-octylthiophene), however, initially increased by nearly two orders of magnitude as the relative humidity level was raised from 50% to 95% at 70 °C. The largest conductivity decay induced by humidity and heat was observed in thin samples. Measurements of the field-effect mobility reveal that the humidity-induced drop of the conductivity is caused by a decreasing number of active dopants, whereas heating the sample additionally results in a deterioration of the charge carrier mobility.