Effects of Doping States of Polyaniline Thin Films on Their Photo-Responsive Properties

Abstract

Polyaniline (PANI) has been of great interest in development of conducting polymers because of easy bulk-scale polymerization and relatively high electrical conductivity. The physical and electrical characteristics of PANI largely depend on its protonation-induced doping states. The protonation of imine sites upon acid doping leads to the formation of a conductive polaron lattice along the backbone. The effects of acid dopants on dielectric, optoelectronic, and thermoelectric properties of PANI have recently been investigated. In this study, we investigate the effects of doping/dedoping states of PANI thin films on their photo-responses under laser irradiation in visible and near-infrared regions. The doping levels were controlled by treating as-prepared, acid-doped PANI with aqueous ammonia solutions. Spectroscopic analyses confirmed the changes in the doping states by evolution or decrease of characteristic peaks. The electrical and photo-responsive properties were significantly affected by the doping states of the PANI thin films. The photocurrent and photovoltage under irradiation of controlled wavelengths from various laser sources were measured. While the photocurrent followed the trends of electrical conductivity upon dedoping, the photovoltage was related to the absorption and photocharge generation of the PANI samples.