Molecular-weight-dependent mobilities in regioregular poly(3-hexyl-thiophene) diodes -: art. no. 122110

We have investigated the transport properties in the direction perpendicular to the substrate of regioregular poly(3-hexyl-thiophene) of different molecular weights (MW) in a diode geometry. In these devices, which exhibit space-charge-limited behavior, we find that the mobility values at room temperature increase from 1.33x10(-5) cm(2)/V s to 3.30x10(-4) cm(2)/V s as the MW is increased from 2.9 to 31.1 kg/mol. The mobility is found to be field independent for high MW films, but field dependent for the low MW films. The current-voltage characteristics of the diodes are also studied as a function of temperature from 160 K to 300 K. The activation energy for carrier transport, extracted from the Arrhenius plot, is found to decrease gradually from 143 meV to 126 meV as the MW is increased. (C) 2005 American Institute of Physics.