Influence of Fullerene Grafting Density on Structure, Dynamics, and Charge Transport in P3HT-<i>b</i>-PPC₆₁BM Block Copolymers

A series of tailor-made poly(3-hexylthiophene)-block-PPCBM (P3HT-b-PPCBM) block copolymers incorporating P3HT as donor and a polystyrene with pendant fullerenes (PC61BM) as acceptor block (PPCBM) is presented. The grafting density of PC61BM was varied between 26 and 60 wt %. This has high impact on structure formation, molecular dynamics, and charge transport. It causes considerable increase in glass transition temperature (Tg from 150 to 200 °C). The Tg of the amorphous PPCBM block restricts the dynamics of structure evolution of the block copolymer resulting in an incomplete microphase separation, although structural studies revealed a donor–acceptor nanostructure of 30–40 nm in bulk and thin films. All block copolymers exhibit ambipolar charge transport in organic field-effect transistors. Further, the most densely grafted system showed 2 orders of magnitude higher electron mobility. Thus, the fullerene grafting density turned out as a key parameter in designing P3HT-b-PPCBM systems for tuning phase separation and charge transport.