Temperature-dependent electron and hole transport in disordered semiconducting polymers: Analysis of energetic disorder

We have used space-charge limited current measurements to study the mobility of holes and electrons in two fluorene-based copolymers for temperatures from 100 to 300 K. Interpreting the results using the standard analytical model produced an Arrhenius-type temperature dependence for a limited temperature range only and mobility was found to be apparently dependent on the thickness of the polymer film. To improve on this, we have interpreted our data using a numerical model that takes into account the effects of the carrier concentration and energetic disorder on transport. This accounted for the thickness dependence and gave a more consistent temperature dependence across the full range of temperatures, giving support to the ex-tended Gaussian disorder model for transport in disordered polymers. Furthermore, we find that the same model adequately describes both electron and hole transport without the need to explicitly include a distribution of electron traps. Room-temperature mobilities were found to be in the region of 4×10^-8 and 2×10^-8 cm² V^-1 s^-1 in the limit of zero field and zero carrier density with disorders of 110±10 and 100±10 meV for polymers $poly{9,9-dioctylfluorene-co-bis[N,{N}^{{'}}{{-}}(4{-}butylphenyl)]bis(N,{N}^{{'}}-phenyl-1,4-phenylene)diamine}$ and poly(9,9-dioctylfluorene-co-benzothiadiazole), respectively.