Field-Effect Mobility of Charge Carriers in Blends of Regioregular Poly(3-alkylthiophene)s

Thin film transistors based on regioregular poly(3-hexylthiophene) (PHT) and poly(3-decylthiophene) (PDT) and their binary blends were investigated and the blend composition dependence of the charge carrier mobility was determined. The field-effect mobility of holes (μ h ) in a series of 10 binary blends of poly(3-hexylthiophene) (μ h = 0.02 cm 2 /(V s)) and poly(3-decylthiophene) (μ h = 8 × 10 -5 cm 2 /(V s)) was found to be relatively high (2 × 10 -3 cm 2 /(V s)) and constant over a broad composition range (5−80 wt % PDT). Above 80% PDT, the hole mobility decreased exponentially with composition. Atomic force microscopy of the homopolymers and blends confirmed the absence of phase separation in the blends. A similar interlayer d spacing that is intermediate between those of the homopolymers is implied by the constant hole mobility in the single-phase crystalline blends of 5−80 wt % PDT. These results demonstrate that blends of conjugated polymers are alloy semiconductors in which high and tunable charge carrier mobility can be realized.