Photovoltaic and electrical investigation of In/WO<inf>x</inf>/CuPc/In heterojunctions with light intensity-dependent NDR behaviours

Abstract

A peripherally tetrachalcone substituted copper(II) phthalocyanine was achieved by cyclotetramerization of the phthalonitrile in the presence of anhydrous CuCl2. The modified CuPc was thermally coated on WOx thin films from which a In/WOx/CuPc/In heterojunction was obtained. The surface of the thin films was investigated using scanning electron microscopy (SEM), where energy dispersive X-ray spectra (EDX) was used to confirm chemical structure. The crystal structures of the thin films were characterized using X-ray diffractometry (XRD). To determine the photovoltaic properties of the heterojunction, I–V plots were obtained under dark and various levels of illumination. It was seen that the heterojunction was responsive to the external light. Using the I–V plots, different diode parameters such as ideality factor, barrier height, series resistance, etc., were calculated. These plots also revealed that the In/WOx/CuPc/In heterojunction exhibits negative differential resistance (NDR) characteristics. Photodiode characteristics indicate that the heterojunction exhibits self-powered photodiode behaviours. It was seen that In/WOx/CuPc/In heterojunctions are sensitive to the external light that photovoltaic characteristics alter when the light intensity alters. However, no clear relation between the light intensity and photovoltaic characteristics were evidenced.