Phase behavior of PCBM blends with different conjugated polymers

Abstract

In this work the phase behavior of [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM) blends with different poly(phenylene vinylene) (PPV) samples is investigated by means of standard and modulated temperature differential scanning calorimetry (DSC and MTDSC) and rapid heat–cool calorimetry (RHC). The PPV conjugated polymers include poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene) (MDMO-PPV), High T_g-PPV which is a copolymer, and poly((2-methoxy-5-phenethoxy)-1,4-phenylene vinylene) (MPE-PPV). Comparisons of these PPV:PCBM blends with regioregular poly(3-hexyl thiophene) (P3HT):PCBM blends are made to see the different component miscibilities among different blends. The occurrence of liquid–liquid phase separation in the molten state of MDMO-PPV:PCBM and High T_g-PPV:PCBM blends is indicated by the coexistence of double glass transitions for blends with a PCBM weight fraction of around 80 wt%. This is in contrast to the P3HT:PCBM blends where no phase separation is observed. Due to its high cooling rate (about 2000 K min⁻¹), RHC proves to be a useful tool to investigate the phase separation in PPV:PCBM blends through the glass transition of these crystallizable blends. P3HT is found to have much higher thermal stability than the PPV samples.