Solvent-dependent electrical properties improvement of organic field-effect transistor based on disordered conjugated polymer/insulator blends

Abstract

Poly(3-hexylthiophene) (P3HT):polystyrene (PS) blends prepared from different solvents were used as the semiconducting layers in organic field-effect transistors (OFETs). The relationship between the molecular arrangement, aggregation and charge transport in P3HT:PS blends with the boil-points and solubility of different solvents were systematically analyzed. Topographic investigation by atomic force microscopy carried out on blends with various solvents revealed a lateral phase separation of the two components, which was strongly influenced by the choice of solvent. Although the blend film was highly disordered, the OFETs performed as well as that with the pristine P3HT films. Moreover, 1,2-dichlorobenzene with the high boiling temperature was found to be more desirable for achieving distinct lateral aggregation of P3HT in the blend film, which led to the superior performance of the OFET. X-ray diffraction analyses and optical absorption measurements revealed that PS matrix made the arrangement of P3HT molecules more disordered, but introduced a more efficient intermolecular coupling of P3HT molecules. This could be ascribed to that, the PS matrix made the aggregating rates of the P3HT molecules slower, inducing a uniform distribution of P3HT molecules in the blend film. This was beneficial for the efficient charge transport in the blend film, which provided a pathway between the aggregations and acted as a tie-molecule in the blend film. Consequently, the field-effect mobility of the optimized OFET (1.6 wt% P3HT) increased three times and the current on/off ratio increased two times compared to that of the pure P3HT (8 wt%). This work will fill the gap of current research about semiconductor/insulator blend transistor.