Charge transport in intercalated and non-intercalated polymer:fullerene blends

We present charge transport properties of intercalated and non-intercalated PBTTT:fullerene based bulk heterojunctions measured with the photo-CELIV technique. The mobilities are seen to vary greatly with fullerene loading in intercalated systems whereas the mobility in non-intercalated blends is fairly constant. The transport activation energies and widths of the Gaussian density of states (DOS) indicates lower energetic disorder in intercalated blends. The highest room temperature mobility of 2 × 10−3 cm2/Vs was obtained for a blend of 1:4 weight ratio PBTTT:PCBM, which is an order of magnitude higher than the other blends studied. We attribute the high mobility to lower energetic disorder and stronger electronic coupling between the transport sites due to shorter inter-site distances in the intercalated blend.