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Charge transport in thin films of semiconducting oligothiophenes

1995; American Physical Society; Volume: 52; Issue: 3 Linguagem: Inglês

10.1103/physrevb.52.1786

1095-3795

Katsunori Waragai, Hitoshi Akimichi, S. Hotta, H. Kano, H. Sakaki,

Quantum and electron transport phenomena

Electrical measurements have been carried out at various temperatures (T) and electric fields (F) on field-effect transistor (FET) devices having thin films of dimethyl-substituted oligothiophenes of tetramer to hexamer. The mobility is strongly dependent on temperature and electric field. The temperature dependence of the mobility (\ensuremath{\mu}) follows the simple Arrhenius relationship: \ensuremath{\mu} is proportional to exp(-W/kT) where W is an activation energy. The activation energy decreases with increasing electric fields as ${\mathit{F}}^{1/2}$. Electron spin resonance and x-ray studies indicate that the charged form of the oligothiophenes can be characterized as molecular polarons. Consequently, we have analyzed the charge transport results using a polaron theory. On the basis of the FET results correlated with the optical data, we show that the charge transport is described in terms of the hopping of polarons.