Bipolar charge transport in poly(3-hexyl thiophene)/methanofullerene blends: A ratio dependent study

We investigated the charge carrier mobility in pristine poly(3-hexyl thiophene-2,5-diyl) (P3HT):[6,6]-phenyl-${\mathrm{C}}_{61}$ butyric acid methyl ester (PCBM) blend devices by applying the time resolved photoconductivity experiment in dependence on the donor:acceptor ratio. We observe a bipolar transport in all studied samples ranging from pure polymer to polymer:fullerene with 90% PCBM content. For the ratios P3HT:PCBM 1:4 and 1:1 we observe two transit times in the electron current transients as well as hole double transients for P3HT:PCBM 1:2. We find high hole and electron mobilities in the order of ${10}^{-3}–{10}^{-2}{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ for a concentration of 90% PCBM in the blend.