Computational Study of P3HT/C60-Fullerene Miscibility

Abstract

Classical molecular dynamics simulations and statistical thermodynamics are used to investigate the miscibility of blends of the conjugated polymer poly(3-hexylthiophene) (P3HT) and fullerene C60 for blend ratios typically used in organic photovoltaic devices over a range of temperatures. Depending on which of two slightly different simulation force fields is used, the calculations suggest that amorphous P3HT/fullerene blends are either miscible or immisicble under typical processing conditions. The former result is consistent with recent experiments and suggests that experimentally observed nano-scale phase separation is driven by polymer or fullerene crystallisation. But the inconsistency between the different force fields indicates that these blends are close to phase coexistence between the separated and homogeneously mixed phases and suggests that care must be taken in interpreting simulation data on P3HT/fullerene blends. These findings have implications for organic photovoltaics, in which the microstructure of conjugated-polymer/fullerene blends plays a crucial role in device performance.