CHARGE-TRANSPORT IN THIN-FILMS OF SEMICONDUCTING OLIGOTHIOPHENES

Electrical measurements have been carried out at various temperatures (T) and electric fields (F) on held-effect transistor (FET) devices ha ving thin films of dimethyl-substituted oligothiophenes of tetramer to hexamer. The mobility is strongly dependent on temperature and electr ic field. The temperature dependence of the mobility (mu) follows the simple Arrhenius relationship: mu is proportional to exp(-W/kT) where W is an activation energy. The activation energy decreases with increa sing electric fields as F-1/2. Electron spin resonance and x-ray studi es indicate that the charged form of the oligothiophenes can be charac terized as molecular polarons. Consequently, we have analyzed the char ge transport results using a polaron theory. On the basis of the FET r esults correlated with the optical data, we show that the charge trans port is described in terms of the hopping of polarons.