Two-dimensional semiconductor transition metal dichalcogenide nanosheets as charge carriers in metallophthalocyanine based solar cells

Abstract

Two-dimensional (2D) materials have received widespread attention as prime candidates for scientific research in the fields of optoelectronics and photonic applications. This thesis focuses on the use of transition metal dichalcogendes (TMDs) for solar cell application. TMDs are compounds with the general formula MX2, where M is transition metal and X is chalcogen and most of them are intrinsically n-type. These materials are arranged as layers stacked together by weak van der Waals forces. They have found application in solar cells due to their high carrier mobility, chemical stability and flexibility. Exfoliation of the bulk TMDs maintains these properties and further imparts more properties such as switching the bandgap from indirect to direct and this further increases the carrier mobility of the material. In this work we explore the use of molybdenum sulfide (MoS2) and tungsten (WS2) TMDs as electron transporting layers for solar cell application. The TMDs were successfully synthesised using the chemical exfoliation method and they were further doped with gold (Au) in order to enhance charge carrier mobility. The doped and undoped TMDs were characterised using X-ray diffraction (XRD), Raman spectroscopy, energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). These TMDs were used together with metallophthalocyanines (MPc’s) as photon absorbers. MPc’s are known to be thermally and chemically stable in addition to having a relatively high extinction coefficient in the visible range. In our study we show the photovoltaic properties of TMDs combined with a variety of MPc’s. The utilisation of these TMDs with MPc’s has led to the generation of cost-effective solar cells that can be exploited for future technological applications.