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 $4\times {10}^{-8}$ and $2\times {10}^{-8}{\text{cm}}^2{\text{V}}^{-1}{\text{s}}^{-1}$ in the limit of zero field and zero carrier density with disorders of $110\pm 10$ and $100\pm 10\text{meV}$ for polymers $\text{poly}\left\{9,9\text{-dioctylfluorene-co-bis}\left[N,N^{\prime }\text{−}\left(4-\text{butylphenyl}\right)\right]\text{bis}\left(N,N^{\prime }\text{-phenyl-}1,4\text{-phenylene}\right)\text{diamine}\right\}$ and poly(9,9-dioctylfluorene-co-benzothiadiazole), respectively.

• Received 21 October 2009

DOI:https://doi.org/10.1103/PhysRevB.81.045210