Effects of humidity on unencapsulated poly(thiophene) thin-film transistors

The effects of humidity on unencapsulated polymeric thin-film transistors (TFTs) of poly5,5’-bis(3-dodecyl-2-thienyl)-2,2’-bithiophene (PQT-12) were investigated. The field effect mobility of PQT-12 TFTs decreases and the rate of trapping of charge carriers increases under increasing humidity. The amount of water absorbed by the PQT-12 films was measured using a quartz crystal microbalance. Thin films of PQT-12 absorb comparable amounts of water to the carrier concentration in TFTs under routine operating conditions (humidity of 30% relative humidity and gate voltage of −30V); the changes in electrical characteristics under humid atmospheres are attributed to the interaction of absorbed water with the carriers in the film.