Chemically specific dynamic characterization of photovoltaic and photoconductivity effects of nanostructures by X-ray photoelectron spectroscopy

Abstract

X-Ray Photoelectron Spectroscopy is a widely used characterization method for chemical analysis of surfaces. In this thesis, We report characterization of photovoltaic and photoconductivity effects on nanostructured surfaces through light induced changes in the X-ray photoelectron spectra (XPS). The technique combines the chemical specificity of XPS and the power of surface photovoltage spectroscopy (SPV), with the addition of the ability to characterize photoconductivity under both static and dynamic optical excitation. A theoretical model that quantitatively describes the features of the observed spectra is presented. We demonstrate the applicability of the model on a multitude of sample systems, including homo- and heterojunction solar cells, CdS nanoparticles on metallic or semiconducting substrates, and carbon nanotube films on silicon substrates. A-Si/c-Si heterojunction solar cell is fabricated to characterize photovoltage generation in a nanostructured solar cell. Cadmium Sulfide (CdS) nanoparticles were synthesized by a solvothermal route. Both Multi Wall Carbon Nanotube (MWCNT) and Single Wall Carbon Nanotube (SWCNT) films were characterized with different substrates by XPS. Raman Microscopy, EDS, SEM, XRD, SAXS are used to characterize the samples and solar cells.