Modulation and evaluation of the charge carrier mobility in a polymer alloy of polythiophene and an insulating matrix with an electron accepting molecule

Abstract

The modification of the backbone conformation and aggregation behaviour of conjugated polymers is of great importance for aiding the design of efficient organic semiconductors. We report the optical and electronic properties of polymer alloys comprising regioregular poly(3-hexylthiophene) (P3HT) and an insulating matrix of polystyrene (PS) or poly(methyl methacrylate) (PMMA). The charge carrier mobilities in the polymer alloys were evaluated by flash-photolysis time-resolved microwave conductivity (FP-TRMC) and transient absorption spectroscopy (TAS). The mobility was found to vary with the matrix and blend ratio. Photoabsorption and fluorescence spectroscopies provide a rationale for the conformation and aggregation of P3HT. Phase separations in the blend films were investigated by atomic force microscopy to support the FP-TRMC results. Moreover, we design a styrene–perylene-diimide (PDI) copolymer (St–PDI) and a methyl methacrylate–PDI copolymer (MMA–PDI), which simultaneously allow the dispersion of electron-accepting PDI removing the contribution of electron mobility, a spectroscopic probe of the PDI radical anion, and modulation of the electronic features of P3HT. A hole mobility of 0.07 cm² V⁻¹ s⁻¹ was determined for P3HT : St–PDI by FP-TRMC and TAS. The proposed polymer alloy approach is useful and applicable for a wide range of p-type polymers to investigate the matrix-induced changes in the charge transport properties.