ELECTRICAL AND PHOTOELECTRICAL PROPERTIES OF CHROMOTROPE 2R THIN FILM DEVICES, USING DIFFERENT ELECTRODES

Abstract

Electrical and photovoltaic effects observed with a thin film of Chromotrope 2R, using sandwich type Al/CHR/ITO and In/CHR/ITO devices, are explained in terms of N type semiconducting behaviour of CHR film and by the formation of a Schottky barrier with ITO with an Al or In ohmic contact. At low voltage regions (ITO positive), Ohm's law is followed, while at high voltage regions a space charge limited conduction (SCLC) was observed which is controlled by a single trap level. Various electrical parameters were determined by the analysis of J–V and C–V characteristics of the devices. Under reverse bias condition, the current is identified by a Schottky emission over the potential barrier of approximate height 0.82 eV, where the width of depletion region varies with temperature. The correlation between action spectra of the device and absorption spectra of the CHR were explained in terms of a comprehensive theoretical model suggested by Ghosh et al. for organic semiconductor solar cells. This model incorporates the generation, transportation and dissociation of excitons. An exciton diffusion length of 120 nm was determined by the analysis of action spectra, employing the same theoretical model. The typical photovoltaic parameters were evaluated from the analysis of J–V characteristics under the illumination of the devices through the ITO side and discussed in detail. © 1997 Elsevier Science Limited. All rights reserved