Self-assembly of regioregular poly [2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene], pBTTT-C14 in solvent-mixture and study of its junction behaviour

Abstract

The molecular ordering in organic polymer chains through π-π interactions is emerged to improve semiconductor performance. In the present work, long-range ordering of poly [2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene], pBTTT-C14 fiber is optimized in mixture of good and poor solvent (chloroform+toluene) blend using the concept of solvent driven self-assembly. Here, self-assembly is introduced by ageing followed by complete dissolution at elevated temperature in solvent-mixture. UV–visible spectroscopy demonstrated that the evidence of long range pBTTT-C14 fiber when experimentation is carried out in mixture of chloroform and toluene (9:1 v/v). However, in chloroform only, aggregation is slow while in toluene, aggregation is very fast under similar conditions. The fiber growth and its size are further verified by atomic force microscopy and HRTEM exemplified that the resultant aggregation of polymer chain in nanometric (diameter∼11 nm) range. Thereafter, the change in surface potential of fiber is studied by KPFM. This fibrous polymer is further sandwiched between ITO and Al-metal in order to study its junction behaviour. Fibrous pBTTT-C14 exhibits unsymmetrical charge transport properties over its isolated analogue with ∼9 times enhancement in mobility and ∼6.5 times enhancement in forward current density under the applied potential (−1.0 V to +1.0 V). This is owing to existence of a new charge transition path along the aggregation that consists of trapped charge between π-π stacking.