Electronic transport properties aspects and structure of polymer-fullerene based organic semiconductors for photovoltaic devices
Résumé
A series of polystyrene (PS) and fullerene (C-60) based thin films containing from 23 to 60 wt.% in fullerene were investigated. Initially, the films were characterised by Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy where the characteristic absorption bands of both the fullerene and the polystyrene were revealed. The additional characteristic absorption bands due the grafted fullerene to polystyrene were revealed as well. The relative peak intensities provided with qualitative information of the films stoichiometry in terms of the fullerene's amount that was grafted to polystyrene. The optical properties of the films were investigated by spectroscopic ellipsometry (SE). It was found that the increase of the fullerene's amount that was grafted to polystyrene results in an increase of the absorption coefficient a, refractive index n, extinction coefficient k as well as in the dielectric constant epsilon(proportional to) within the range between 2.4 and 2.8 for the lower and higher fullerene content, respectively. The films' J-V characteristics, of the space charge limited current (SCLC)) behaviour, showed increased currents with increasing the fullerene's content. The electron mobility was extracted and found to increase with increasing the fullerene amount, from 4 x 10(-9) cm(2) V/s to 2 x 10(-7) cm(2) V/s.