Electrical field assisted growth of poly(3-hexylthiophene) layers employing ionic liquids: microstructure elucidated by scanning force and electron microscopy

Abstract

Layers of poly(3-hexylthiophene) (P3HT) of different thickness were made by electro-oxidative polymerization on platinum coated silicon samples employing hydrophobic ionic liquids as a medium. The P3HT films had a conductivity of >10⁻⁵ S cm⁻¹ at room temperature, high cycling life, a hole-current −7 mV cm⁻¹ at −3 V, showed p-type field effect transistors characteristics. With increasing film thickness the structure of the polymer layer transformed from a continuous film (thickness < 50 nm) to fibrils (thickness from 100 nm to 300 nm) to a highly porous structure (> 500 nm). The porosity was attributed to a three-dimensional hierarchical growth of the polymer. The porous structure produces a large interface endowing these systems with intriguing optoelectronic properties. Scanning conductive force microscopy revealed that the electrical current is uniformly distributed in both polaronic (neutral) and bipolaronic (oxidized) state. The facile fabrication process, the direct control of film thickness and the defined morphology make the films attractive for applications particularly in the field of biosensing microarrays.