Mobility of holes and polarons in polyaniline films assessed by frequency-dependent impedance and charge extraction by linearly increasing voltage

Abstract

Thin films of semiconducting polyaniline hydrochloride were deposited on glass or silicon substrates. Frequency spectra of impedance measured at several voltages display regions of holes and polarons contributions and enable to evaluate their mobility 2.7×10−5cm2V−1s−1 at the electric field of 1×105Vcm−1. Good agreement of the average value 2.4×10−5cm2V−1s−1 of holes mobility was obtained by another method-charge extraction by linearly increasing voltage (CELIV). A Poole-Frenkel type of electric field dependence of mobility assessed by frequency- dependent impedance points to trapping of the charge carriers. From the value of the work function measured by the Kelvin probe and from the position of HOMO level, the hole concentration 2.9×1018cm−3 was obtained. Using this concentration together with the mobility measured by the impedance spectroscopy and the CELIV method, the conductivity 1.2×10−5Scm−1 carried by holes was estimated. Our results widen the work dealing with the mixed electron and proton conductivity of polyaniline films in aqueous solution of acids published in the literature.